Patent Application
20050262720
The present invention relates to novel energy efficient sorption processes and systems for cooling, dehumidifying and heating using multistage liquid desiccant regenerators, or hybrid cooling systems or adsorption cooling systems involving appropriate combinations of rotating contacting devise, adsorption module with heat transfer passages in thermal contact with the adsorption module wall and switchable heat pipes. The sorption processes of this invention lead to flexible designing of compact cooling, dehumidifing, heating systems easy operability.
Equipment often employed for regeneration process of LD are packed bed regenerators, spray towers with finned tube heat exchangers, solar regenerator, simple boiler and multiple effect boiler. Processes requiring mass transfer between two contacting fluids often employ equipment such as spray towers, packed towers and tray towers. In spray towers and spray chambers the liquid is generally sprayed into a gas stream by some means to disperse the liquid into fine spray of drops. The flow may be counter current and co-current as in vertical towers, or parallel as in horizontal spray chambers. These devices have the advantage of low-pressure drop of the gas but may suffer from relatively high pumping cost for the liquid in spray. The tendency for carry over of liquid by the air/gas is considerable in the spray towers and mist eliminators will almost always be necessary leading to increase the air/gas side pressure drop. In conventional vapour compression refrigeration, system (VCRS) air is cooled below its dew point to reduce the moisture content, followed by reheating of the air to the desired temperatures prior to its introduction in the conditioned space. As the evaporator operates at lower temperature, the COP of the conventional VCRS is low.
Certain substances have the property of adsorbing some fluids at low temperatures and desorbing them at high temperatures. Adsorption Module is an apparatus, which facilitates the containment of the adsorbent and adsorbate and the process of its heating and cooling. These substances are selective in nature, i.e. they adsorb only specific fluids. This phenomenon can be used for separation of fluids. Alternatively, in sorption cooling applications these are used to adsorb refrigerants at low temperatures and pressure, and desorb them at high temperature and pressure.
The key problem in adsorption systems is low conductivity of the adsorbents and that of the adsorption bed, which in turn effects the cycle time of the system. An important aspect in the design of adsorption modules is to achieve higher heat transfer rates to and from the adsorption beds that results in low cycle time. To make the system compact number of cycles per unit time need to be increased resulting in reduced requirement of adsorbant and adsorbate. We now review the prior art relevant to the invention.
Packed tower is used for regeneration process of LD (Martin, V. and Goswamy D. Y., Heat and Mass Transfer in Packed Bed Liquid Desiccant Regenerators—An Experimental Investigation, Journal of Solar Energy Engineering, Transactions of the ASME, Vol 121, pp 163-169, USA, 1999). In this case the desiccant is distributed over the packing by spray heads and the process air was blown through the packing for regeneration of LD. The process air picks up the water from the LD because of the partial pressure difference of water in the process air and LD. The main problem associated in this regeneration process is carryover of LD along with air stream. Requirement of minimum irrigation rate and limitations of flooding in packed towers complicates the design or reduces the efficacy of the regeneration process. Also large power is required to circulate air/gas through packed bed.
Spray chamber with finned tube heat exchanger is the practical equipment for regeneration process of LD (Peng, C. S. P. and Howell R. J., The Performance of Various Types of Regenerators for Liquid Desiccants, Journal of Solar Energy Engineering, Transactions of the ASME, Vol 106, pp 133-141, USA, 1984). Finned tube heat exchangers are stacked horizontally with a column with hot water flowing in the tube side. LD was sprayed on the heat exchanger and drips down. A blower was used to circulate process air through the regenerator counter current to the falling LD. The advantage of the system is lower pressure drop for the air/gas side. However, there is a relatively high pumping cost for spraying the LD. The tendency for carry over of liquid by the air/gas is considerable in the spray towers and mist eliminators will almost always be necessary leading to increase the air/gas side pressure drop. Even with mist eliminators 100% elimination of carryover is not ensured.
Regeneration of LD can be done using solar energy. Solar regenerator comprises inclined surface with transparent glazing as a covering where weak LD that is to be regenerated flows down the sloping surface as a falling film and is heated by the absorbed solar radiation (Peng, C. S. P. and Howell R. J., The Performance of Various Types of Regenerators for Liquid Desiccants, Journal of Solar Energy Engineering, Transactions of the ASME, Vol 106, pp 133-141, USA, 1984). The water vapour that is evaporated from the solution surface is removed by blowing air through the slot formed between the glazing and the film surface. The disadvantage of the regeneration process is that the system is not operative during non-solar hours. There must be backup heat source for the regeneration of LD during non-solar hours.
The regeneration process of LD in a simple boiler can be achieved by heating the LD to boiling temperature (Lowenstein, A. I. and Dean, M. H., The Effect of Regenerator Performance on A Liquid Desiccant Air-Conditioner, ASHRAE Transactions: Symposia, Vol. 98, No. 1, pp 704-711, USA, 1992). This regeneration process increases the energy required to preheat the weak desiccant that enters the regenerator. The higher the regeneration temperature higher is the regenerator corrosion rate. The regeneration process in a simple boiler is not energy efficient since the latent heat of the vapour generated is not recycled. Regeneration at sub atmospheric pressure can reduce the higher temperature of the simple desiccant boiler. Adding a vapour condenser to the boiler can do this. A non-condensable pump is required to maintain the vacuum in the regenerator. This increases the electrical power consumption.
In a double effect boiler, vapour from high-pressure boiler has a saturation temperature that is sufficient to provide required thermal input to lower pressure boiler. Low-pressure boiler is operating under vacuum. A non-condensable pump is required to maintain vacuum (Lowenstein, A. I. and Dean, M. H., The Effect of Regenerator Performance on A Liquid Desiccant Air-Conditioner, ASHRAE Transactions: Symposia, Vol. 98, No. 1, pp 704-711, USA, 1992). Latent heat of vapour from high-pressure boiler is utilised in low-pressure boiler. However, maintaining vacuum in low-pressure boiler increases the electrical power consumption. Costly components are required for high-pressure boilers and an issue of safety becomes more complex.
U.S. Pat. No. 5,213,154, “Liquid Desiccant Regeneration System”, discloses a single stage regeneration system for use in air conditioning system. The system comprises of a direct-fired natural circulation boiler for regenerating LD. A falling film heat exchanger is used for transferring heat from concentrated desiccant to dilute desiccant. It is single stage regeneration process, the latent heat from the vapour leaving from the boiler is not recycled/reutilised. The single stage regeneration process is exergetically less efficient.
U.S. Pat. No. 4,939,906, “Multi-Stage Boiler/Regenerator for Liquid Desiccant Dehumidifier”, describe a regeneration process with a gas fired desiccant boiler and a combined desiccant regenerator/interchange heat exchanger for use in air-conditioning system. The regeneration process accomplished by diverting portion of LD flowing through a desiccant conditioner and heating the desiccant in an interchange heat exchanger, an air desiccant regenerator, a second interchange heat exchanger and a boiler. The latent heat of vapour generated in the boiler is delivered to the air in a heat exchanger. The weak desiccant is preheated in another heat exchanger using heated air, before entering the boiler. Two heat exchangers are used to deliver the latent heat of vapour to pre heat the LD, which is not energy efficient.
U.S. Pat. No. 5,097,668,“Energy Reuse Regenerator for Liquid Desiccant Air Conditioners”, discloses the regeneration process of LD in air-conditioners, which uses LD for dehumidification of air. The regeneration of LD is achieved in a desiccant boiler and a desiccant evaporator/condenser in combination with heat exchangers. The evaporator/condenser receive the vapour produced by the boiler to provide a reuse of heat for regeneration. Certain quantity of LD from air-conditioner is flowing to evaporator /condenser, where it is sprayed over the surface through which vapour from boiler is flowing. Certain quantity of LD from air-conditioner is directly flowing to boiler for regeneration. As the LD is sprayed in presence of air in the evaporator/condenser carryover of LD with the air stream is inevitable. Additional electrical power is required for spraying LD in the evaporator/ condenser.
U.S. Pat. No. 4,189,848 “Energy Efficient Regenerative Liquid Desiccant Drying Process”, discloses a method and apparatus for the drying of harvested crops by utilising desiccants with a closed loop drying loop and open drying loop. In the closed drying loop cycle the drying air brought in to contact with a desiccant in a packed tower after it exits from a crop-drying bin. During the open loop drying cycle the used desiccant is heated and regenerated at high temperature driving water vapour from the desiccant. The water vapour condensed was used to pre heat the dilute desiccant before heat is added from the external source in the regenerator. As the regeneration and absorption processes are taking place in the packed towers the carryover of LD in to the air stream is inevitable. Large electrical power is required to circulate the air through packed towers.
U.S. Pat. No. 4,941,324, “Hybrid Vapour Compression/Liquid Desiccant Air Conditioner”, discloses a hybrid air-conditioning system consisting of a compressor, evaporator, condenser and refrigerant. LD and refrigerant are simultaneously circulated between evaporator and condenser for cooling and dehumidifying air forced therein. The regeneration of the LD is achieved by spraying the LD on the condenser of vapour compression refrigeration system. A blower is provided to circulate the outdoor air to regenerate the LD. The main problem with such arrangement is corrosion of the condenser coil. Moreover as the LD is sprayed, carryover and loss of LD to indoor and out door air streams is inevitable.
U.S. Pat. No. 4,180,985, “Air-conditioning System with Regeneratable Desiccant Bed” discloses the regeneration process using a desiccant pad material such as fibreglass pads, wire screens and packed steel shavings. The desiccant pad is disposed and supported within the feed duct. Condenser coil of vapour compression refrigeration system is disposed within the regenerator duct. The air is directed across the condenser coil by mean a fan. Liquid desiccant is sprayed in presence of hot air stream across the desiccant pad, which provides large surface area between desiccant and air. In this process carryover of LD to air stream is inevitable. In spite of use of mist eliminators carryover of LD is inevitable.
U.S. Pat. No. 4,259,849, “Chemical Dehumidification System Which Utilises A Refrigeration Unit for Supplying Energy to the System”, discloses a sorbent type air-conditioning system which employs refrigeration unit, including a compressor, evaporator, condenser and refrigerant. The regeneration of LD is achieved in a packed tower with spray nozzles. Corrugated sheet material impregnated with a thermosetting resin is the packing material, through which LD trickles by gravity. Large pressure drops across the packing material. Carryover of LD with air stream is not addressed.
Packing in packed towers provide large interfacial surface between liquid and air/gas. The key requirements of the packing are large surface area per unit volume and must permit large volume flow of fluids through small tower cross section with lower pressure drop for the air/gas. Packings in the form of Ranching rings, Lessing ring, Partition ring, Berl saddle and Pall rings are commonly used in packed columns (Robert, E. Treybal, Mass—Transfer Operations, pp 187-191, Mcgraw-Hill Book Company, 1981). Random packings offer large specific surface but suffer from larger air/gas side pressure drop. Regular or stacked packings like Ranching rings, Double spiral ring, Wood grids offer lower pressure drop than random packings for the air/gas side. Generally absorbers with regular packings are designed for air/gas side pressure drop of 200 to 400 Pa per m of packed depth (Robert, E. Treybal, Mass—Transfer Operations, pp 187-191, Mcgraw-Hill Book Company, 1981). Regular packings are costlier than random packings. polypropylene Rauschert Hiflow rings of size 2.54 cm offer a surface density of about 210 m2/m3 (Oberg, V. and Goswamy D. Y., Experimental study of the heat and mass transfer in a packed bed liquid desiccant air dehumidifier, Journal of Solar Energy Engineering, Transactions of the ASME, Vol 120, pp 289-297, USA, 1998). Such equipments need well-designed tower shells, packing supports, liquid distributors, packing restrainers, entrainment eliminators etc., which make them fairly expensive. Minimum irrigation rate and flooding in packed towers complicates the design or reduces the efficacy of the process. Large power is required to circulate air/gas through packed bed.
The long felt need in this field has been to innovate contacting devices that are techno-economically viable and provide for the essential functional features so as to:
U.S. Pat. No. 4,333,894, loses mass transfer column consisting of one or more contact zones. The contact zones are exclusively provided with packings placed in prearranged locations. In the contact zones, optimal operating conditions for the packing are created over the entire height of the contact zones in order to achieve a minimal pressure loss at a concomitant high separating efficiency. This is done by a suitable gradated adaptability of the packing to vapour and liquid loads varying over the height of the contact zones. It was claimed uniform flow of liquid through the bed. However, this patent does not address the issue of carry over of liquid along with air/gas.
U.S. Pat. No. 5,679,290, describes an improved packed tower for effecting the adsorption of a gas into a liquid, comprising a cylindrical tower wall defining a packing zone; a plurality of packing pieces contained within a packing zone; a liquid distributor above the packing zone for distributing liquid on to the packing pieces; a gas feeding inlet below the packing pieces for feeding gas through the packing zone. The improvement claimed in this patent is in the plurality of packing pieces and the packing of different sizes in two zones. First packing zone is an annulus adjacent at an upper part of the tower wall. Rest of the tower acts as the second zone. First packing pieces are smaller than the second plurality of packing pieces. Surface area of the packing is 119 m2/m3 with 2×2×4 inch ceramic saddles in the first zone. In the second zone the packing is also ceramic saddled of size 3×3×6 inch which were giving a surface area of 93 m2/m3. In this patent too the carryover of liquid along with air/gas stream is not addressed.
In U.S. Pat. Nos. 5,882,772 and 6,007,915, packing materials to increase the surface area, in packed bed towers are reported but do not comprehensively resolve all the issues as required.
Contacting discs have been used in evaporatively cooled condenser for vapour compression refrigeration system (Yunho, Hwang, Reinhard Radermacher and William Kopko, “An Experimetal Evaluation of A Residential Sized Evaporatively Cooled Condenser”, International Journal of Refrigeration, 24, pp 238-249, 2001). Plastic discs of 2 feet diameter are used as contacting device between ambient air and water used for condensing the refrigerant. However, the prior art does not teach any of the aspects of the wetting of the discs by water, their optimal sizes, etc.
In the development of vapour absorption heat pump, contacting discs have also been used in mixed alkali hydroxides to absorb water vapour (Shallow, F. E. and Smith, I. E., “Vapour Absorption Into Liquid Film on Rotating Discs” Proceeding of the Work Shop on Absorption Heat Pumps, London, pp 373-381, 1988). Copper discs of 110 mm diameter were rotated at the speed of 200 rpm in vacuum chamber. There is no specific teaching about spacing between the discs and wetting of the surface of the discs with liquid.
The rotary evaporative cooler with rotary vertical wheel shaped saturating pads 127 mm thick and 660 mm to 1370 mm diameter, composed of spirally wound layers of alternatively flat or crimped bronze screen wires have been losed in the article by (John, R. Watt, Evaporative Air Conditioning hand Book, pp 115-161, Chapman and Hall, New York, 1986). This device does address the issue of proper wetting of the pad without splashing or blowing, at rotating speeds of around 2 rpm, but the cost of the rotor is high.
Desiccants are a subset of a group of materials called sorbents. Desiccants in particular have high affinity for water and their absorption capacity varies with the structural characteristics of the material. For example, nylon can absorb up to 6 percent of its weight of water, wood can absorb 23 percent of its weight, whereas a commercially available desiccant can hold about 1100 percent of its weight of water. Some examples of such desiccants are Lithium chloride, Lithium bromide, etc. (ASHRAE, “Fundamentals Handbook”, American Society for Heating Refrigeration and Air-conditioning Engineers, pp 21.1-21.5, Atlanta, USA, 1997).
The desiccant affinity to absorb the moisture can be regenerated repeatedly by applying heat to the desiccant material to drive off collected moisture. Low-grade heat can be obtained from a variety of sources such as solar collector, radiator hot water, engine exhaust, condenser heat recovery from refrigeration machines, burning bio mass, etc. The temperature for this process is generally in the range of 50° C. to 260° C. depending on the material.
Desiccant cooling systems (DCS) are energy efficient and environmentally safe. In recent years, DCS have received considerable attention due to their inherent ability to use low-grade thermal energy and reduce the latent cooling load significantly. Desiccant dehumidification can reduce total electricity demand by as much as 25% in humid regions. These systems provide a drier, more comfortable and cleaner indoor environment with lower consumption of electric power.
In liquid desiccant (LD) dehumidification systems air is dehumidified when exposed to hygroscopic solutions. At a given temperature the desiccant has a lower vapour pressure than pure water, and hence moisture transfer takes place from air to solution. Several desiccants such as Triethylene glycol, Lithium chloride, Lithium bromide, Calcium chloride etc. are extensively in use. Some desiccants also have the ability of simultaneously controlling microbiological contaminants from air streams to improve the quality of air (ASHRAE, “Fundamentals Handbook”, American Society for Heating Refrigeration and Air-conditioning Engineers, pp 21.1-21.5, Atlanta, USA, 1997). It may also be noted that as the process air is not allowed to reach the saturation condition at any point in the desiccant cycle it prohibits the growth of moulds, fungi, or other microbial organisms in air conditioners (Lowenstein, A. I. and Dean, M. H., “The Effect of Regenerator Performance on A Liquid Desiccant Air-Conditioner”, ASHRAE Transactions: Symposia, Vol. 98, No. 1, pp 704-711, USA. 1992).
Similar to conventional DCS, most of HCS have two air streams, one is the processed air delivered to conditioned space, the other stream is used to regenerate liquid desiccant. Howell and Peterson, 1986 have studied a hybrid system combining liquid desiccant dehumidification with VCRS (Howell, J. R. and Peterson, J. C., “Preliminary Performance Evaluation of A Hybrid Vapour Compression/Liquid Desiccant Air-Conditioning System”, ASME, paper 86- WA/sol.9, Anaheim, Calif., USA., December 1986). It was found that the hybrid system reduces area of evaporation and condensation by 34%, and power consumption by 25%, compared with VCRS alone. Study on a gas fired air conditioning system combining vapour compression machine with solid desiccant dehumidifier, it is reported that cooling capacity of hybrid system increased by 50% and the COP increased by 40%. However, the initial cost increased to US$ 140 per kW cooling capacity (Parson, B. K., Pesaran, A. A., Bharathan, D. and Shelpuk, B. “Improving Gas Fired Heat Pump Capacity and Performance by Adding A Desiccant Dehumidification Subsystem”, ASHRAE Transactions, Vol 95, pp 835-844, USA. 1989).
Hybrid vapour compression/liquid desiccant air conditioner has been described in U.S. Pat. No. 4,941,324. In this approach, the LD is sprayed on the evaporator of the vapour compression refrigeration system for cooling and dehumidification of air. The regeneration of the LD is achieved by spraying the LD on the condenser of vapour compression refrigeration system. Two blowers were provided to circulate the indoor air over the cooling coil and out door air to regenerate the LD. An adiabatic humidifier is provided in the cycle. The main problem with such arrangement is corrosion of the condenser and evaporator coils. Moreover as the LD is sprayed, carryover of LD to indoor and out door air streams is inevitable.
U.S. Pat. No. 5,022,241 discloses a residential type hybrid air conditioning system, having a conventional absorption refrigeration subsystem to handle the sensible heat loads and a LD subsystem to handle the system latent load. This system incorporates an evaporative cooler for cooling and re-humidification of the process air. In this case too the carry over of LD with the process air is unavoidable as the desiccant is sprayed in the system.
U.S. Pat. No. 4,180,985 discloses an air-conditioning system with a regeneratable desiccant bed. This arrangement employs a desiccant pad of any suitable material that can be disposed and supported within the feed duct to allow the moist feed air to flow through the pad and contact the LD material. Materials such as fiber glass pads, wire screens, packed steel shavings have been used. In this patent problems due to the carryover of LD with air stream are not addressed
U.S. Pat. No. 4,887,438 describes a desiccant assisted air conditioning system with silica gel. Regeneration temperature was around 98° C. It is reported that energy saving can be 10 to 15% and reheating after refrigeration is eliminated. As the regeneration temperature is high, the coefficient of performance (COP) of this VCRS is low.
Applicants recognised that it desirable to have adsorption modules that exhibit the following characteristics:
Past, attempts to achieve the above objectives have been any of the following four approaches:
U.S. Pat. No. 6,102,107 relates to a sorption cooling module employing a uniform adsorbent coating on a fin plate surface which does not build up on heat transfer medium tubes passing through the fin plates even in a dense plate configuration. The large number of small diameter tubes complicates the fabrication of such a system. The increased number of tubes and the joints enhances the possibility of leakage.
U.S. Pat. No. 5,518,977 relates to sorption cooling device, which employ adsorbent-coated surfaces to obtain a high cooling coefficient of performance. Thermal mass of the surface which is coated adds to the thermal mass, which leads to reduced COP. Also, with time the adsorbent coating might get dislodge due to cycling and/or thermal shocks.
In a review paper titled “Solar adsorption technologies for ice-making and air-conditioning purposes and recent developments in solar technology” by Wang and Dieng (“Literature review on solar adsorption technologies for ice-making and air-conditioning purposes and recent developments in solar technology”, Renewable & Sustainable Energy Reviews, Vol. 5, pp. 313-342, 2001) conclude that some crucial points in the development of sorption systems still exists especially those related to problems of low specific cooling power of the machine and high investment costs. It also mentions that thermosyphons and heat pipes are one of the most convenient heat transfer devices for the solid and liquid sorption machines due to their flexibility, high thermal efficiency, cost-effectiveness and reliability.
However the thermosyphones and heat pipes disclosed in the prior art suffer from low heat transfer rates when used without fins and increase in thermal mass when used with fins. Heat pipes are defined as systems employing closed evaporating-condensing cycles for transporting heat from a location of heat generation to a location of heat reception capable of transporting large amount of heat with small temperature gradient. They are configured in various shapes and geometry and may optionally use a capillary structure or wick to facilitate return of the condensate. A heat pipe may be represented by a tube with both ends sealed and partially filled with liquid, one end of which is capable of acting as an evaporator and the other end acting as the condenser. Such heat pipes can continuously transfer heat from the hot end to cold end. A heat pipe capable of controlling the heat transfer is known as switchable heat pipe.
Switchable heat pipes as effective heat transport devices have been developed for a variety of applications in space technology, refrigeration, air-conditioning, electronic cooling, etc. Prior art is based on two approaches:
In these patents, the switching mechanisms are implemented as follows:
An ideal switchable heat pipe should be compact, simple to operate with minimum number of components, should have low thermal mass and internal voids. The prior art on switchable heat pipes listed above do not satisfy all these criteria and hence the long felt need to design heat pipes that would meet such requirements.
Heat driven sorption refrigeration cycles have existed in literature since 1909, and refrigerators are commercially available since 1920's. Environment friendly solid sorption systems with non-polluting refrigerants can efficiently use natural gas or solar energy as primary energy. Further this provides a system with no moving parts making it silent and maintenance free. Adsorption heating and cooling is therefore a good alternative to classical vapor compression systems. Adsorption cooling units are attractive as they can be operated at temperatures in which liquid absorption systems cannot work. The desirable features are high coefficient of performance (COP), high specific cooling power (SCP) and the thermodynamic efficiency, which is the ratio between the COP and the Carnot COP.
The thermodynamic efficiency of the adsorption heat pumps is much lower than that of the conventionally employed compression heat pumps. Adsorption heat pumps are generally suitable for waste heat and solar energy based operation.
U.S. Pat. No. 4,183,227 disclose an adsorption based heat pump providing semi-continuous or substantially continuous refrigeration and/or heating. The limitations of such systems are intermittency in supply of useful cooling or heating effects and varying heat delivery temperatures.
Continuous delivery of output with small temperature variation is achieved through ‘regenerative cycles’ in which at least two reactors operate out of phase with internal heat recovery. U.S. Pat. No. 5,347,815, U.S. Pat. No. 5,046, 319 of Jones, and U.S. Pat. No. 4,694,659, U.S. Pat. No. 4,610,148 of Shelton disclose various ways of implementing separate heat transfer fluid loop passing through the bed for regeneration. Heat transfer fluid loop in the regenerative cycle helps increase COP. However, in such systems pumps are required to circulate the heat transfer fluids through the beds, valves and their control systems are needed to regulate and divert the flow in various loops. This results in operational complexity and increased capital cost due to requirements of pumps valves and their controls. Such systems are not suitable for very small capacities (e.g. 50 to 500 W).
U.S. Pat. No. 5,847,507 discloses an efficient adsorption based thermal compressor which used heat recycling. The system uses a thermal storage device for storing the heat released during adsorption which is used in next cycle during generation. Technology for heat transfer fluid loops is disclosed in U.S. Pat. No. 5,847,507. Its cost is high and requires thermal storage, pumps and associated controls. These systems are also not suitable for very small capacities (e.g. 50 to 500 W).
U.S. Pat. No. 4,765,395 and U.S. Pat. No. 5,079,928 disclose a scheme of cascading reactors, each using a solid adsorbent and refrigerant. Heat released during adsorption in one module is used for generation in the subsequent module. COP is increased by exchanging heat between the reactors. But, this arrangement is not appropriate for small refrigeration systems.
U.S. Pat. No. 5,477,705 discloses an adsorption system in which the reactor has separate compartments. It has means for circulation of heat transfer fluid through hot and cold reactors in such a fashion that a solid sorbent temperature front successively passes through the first compartment to the last and vice versa. This allows the efficient recycling of heat. However this requirement of several valves and controls complicates the system and increases the capital cost. Literature review by Wang and Dieng (“Literature review on solar adsorption technologies for ice-making and air-conditioning purposes and recent developments in solar technology”, Renewable & Sustainable Energy Reviews, Vol. 5, pp. 313-342, 2001) on solar adsorption systems indicates that to produce simple and cost effective devices more attention is needed to reduce the number of valves.
U.S. Pat. No. 4,594,856 describes a single stage pressure equalization technique, which increases the COP, but the complexity of the system makes this system inappropriate for small capacities.
Cycle time plays an important role in determining the compactness of the system. Cycle time can be decreased in adsorption refrigerators and heat pumps by improving heat and mass transfer rates. But, increasing heat transfer area to increase heat transfer rates leads to increase in thermal mass which increases thermal cycling losses and leads to reduction in COP.
Applicants recognized that the desirable features of the adsorption refrigeration system are:
Applicants found the following problems with the conventional refrigeration systems.
The LD regeneration process/system ideally should exhibit the following attributes:
In the field of regeneration of LD, the challenges have been to make the process techno-economically viable by designing features to meet the needs of regeneration and achieve with significant reduction in the consumption of electrical power. It is desirable to increase the specific water removal rate from the LD. The specific water removal rate is the water removed from the LD in kg/kWh of heat input. It is desirable to increase this value in order to make the regeneration process efficient.
In the field of hybrid cooling systems the challenges have been to make them techno-economically viable by designing features to meet the needs of dehumidification, decrease in temperature, eliminating carryover of LD in to air streams and operate with significant reduction in electrical power consumption.
The main object of the present invention is to provide a novel energy efficient multi-stage regeneration process, for regenerating liquid desiccant (LD), with application of rotating contacting disks to provide intimate contact between LD and vapour/gas to enhance the interfacial area between them for increased heat and/or mass transfer, without problems of carryover of liquid in to the vapour/gas stream or flooding having the provision to heat/cool the liquid based on the application. Further it is an object of the invention to explore applications in Hybrid Cooling Systems (HCS), in which air temperature and humidity are simultaneously controlled using a contacting device, which meets the needs of dehumidification, decrease in temperature and significant reduction in electrical power consumption with increase in cooling and/or dehumidification capacity for a given refrigeration compressor.
One of the objects of the invention is to regenerate the LD with higher specific water removal rates.
Another object of the invention is to develop HTR with no carryover of LD in to the steam, in which water rich LD boil to remove water in the form of steam, while performing the operation of regeneration of LD.
Another object of the invention is to develop HTR, which operates at atmospheric pressure.
Another object of the invention is to pass the partially regenerated LD from HTR to LTR for further regeneration or pass the partially regenerated LD from LTR to HTR for further regeneration or split the flow of LD into two streams and pass them to HTR and LTR
Another object of the invention is to provide intimate contact between LD and air to enhance the interfacial area between the vapour/gas stream and LD using large heat and mass transfer area, which ensures no carryover of LD in to the outdoor air stream, while, regenerating LD.
Another object of the present invention is to develop regenerator that has no limit on liquid throughput leading to high efficacy of the process (by reducing recirculation losses at lower liquid throughputs).
Another object of the invention is to provide a contacting device that operates with low power consumption.
Yet another object of the invention is to deliver the latent heat of the vapour generated in HTR to LD in LTR for regeneration.
Yet another object of the invention is to use alternate materials to reduce the weight and cost, while eliminating corrosion problems.
Yet another object of the invention is to develop a multi-stage regenerator comprising of Intermediate Temperature Regenerator/s (ITRs) to operate in conjunction with the HTR and LTR.
Another object of the invention is to provide a contacting device that incorporates surface density in the rage of 450 to 600 m2/m3, which is far superior to conventional polypropylene Rauschert Hiflow rings of size 2.54 cm having surface density of 210 m2/m3.
Yet another object of the invention is to provide a contacting device that does not have any carryover of liquid with the vapour/gas stream.
Yet another object of the invention is to provide a contacting device to operate with pressure drop across the contacting device as low as 5 Pa.
Another object of the present invention is to provide a contact device that has no limit on liquid throughput leading to high efficacy of the selective applications.
Another object of the invention is to provide a contacting device that operates with low power consumption.
Another object of the invention is to provide an easy to assemble contact device and yet providing sufficient rigidity to the contacting surface.
Yet another object of the invention is to provide a contacting device having the provision to heat/cool the liquid, vapour/gas, based on the application.
Another object of the invention is to provide design for HCS with significantly higher cooling capacity, than that of the VCRS using similar compressor.
Yet another object of the invention is to provide design for a HCS with significantly lower compressor displacement requirement as compared to that of a VCRS for a required cooling capacity
Yet another object of the invention is to develop an ICD a non-adiabatic or adiabatic absorber that ensures no carryover of LD to the indoor air stream, while performing operations of dehumidification and/or cooling of the indoor air stream.
Yet another object of the present invention is to develop an regenerator/outdoor contacting device (OCD), a non-adiabatic or an adiabatic regenerator, that ensures no carryover of LD in to the outdoor air stream, while, performing the operation of regeneration of LD.
Yet another object of the invention is to use alternate materials to reduce the weight and cost, while eliminating corrosion problems.
Yet another object of the invention is to use the liquid-liquid heat exchanger to increase the cooling capacity and COP of the HCS.
The main object of the invention is to provide system based on adsorption cycle having high coefficient of performance (COP), high specific cooling power (SCP) with easy operability and lower cycle times using novel adsorption modules which are easy to fabricate and overcome the problems of low thermal conductivity of adsorbents, without increasing the thermal mass of the system. It also relates to refrigeration cum heating system that can be heated by various heat sources like solar energy, direct fuel fired systems and waste heat fired systems using said adsorption module. Further, it relates to switchable heat pipes with a system to actuate or isolate hot end from the cold end to transfer heat intermittently as per the requirement.
One of the objects of the present invention is to provide design for adsorption modules that make it possible to develop compact adsorption systems by overcoming the problems of low thermal conductivity of adsorbents without increasing the thermal mass of the adsorption modules, thereby increasing heat transfer rates and reducing cycle time while maintaining high efficacy of the cycles and processes in which they are used.
The other object of the invention is to achieve the low thermal mass using a set of passages to and from the containment vessels thereafter termed “passages”.
It is another object of the invention to provide designs of “passages” that function as heat pipes that are in thermal contact with the wall of the containment vessels in diverse configurations.
It is yet another object of the invention to provide design of a system of “passages” preferably constructed of the high conductivity material.
It is yet another object of the invention to provide design of a system of “passages” that preferably enable the use of the containment vessel wall itself as the fin thereby eliminating the need for separate fins.
It is yet another object of the invention to provide design of a system of “passages” that preferably enable the use of the containment vessel wall and partitions as the fins thereby eliminating the need for separate fins.
Another object of the invention is to provide design of a system of “passages” with the option of increasing or decreasing number of the “passages” per containment vessel based on the desired cycle time.
Another object of the invention is to provide design of a system of “passages” in a manner to reduce the effective thermal mass at the same time achieving high COP and high SCP.
Another object of the invention is to provide design of a system of shared “passages” between multiple containment vessels in a manner to reduce the effective thermal mass at the same time achieving high COP and high SCP.
Yet another object of the invention is to provide design of a system of “passages” in a manner that is simple to fabricate, easy to operate and provide options for a wide range of application involving heat transfer.
Another object of the invention is to provide low cost and compact refrigeration cum heating system, based on adsorption refrigeration cycle that can be heated by various sources like solar energy, direct fuel firing and waste heat.
Another object of the invention is to provide a system comprising of a plurality of adsorption modules operating out of phase, to give continuous refrigeration and/or heating.
Yet another object of the invention is to increase the COP of the system without a separate loop circulating the heat transfer fluid.
Another object of the invention is to provide regeneration using multi stage pressure equalization process.
Yet another object of the invention is to reduce cycle time without affecting COP.
Yet another object of the invention is to reduce life cycle cost of the adsorption system.
Another object of the invention is to use waste heat as heat source
Yet another object of the invention is to provide a means for simple control of the system
Another aspect of this invention relates to switchable heat pipes using a system for actuating or isolating the evaporator or condenser capable of transferring heat intermittently when desired, based on parameters of the system for applications where a common evaporator is connected to multiple condensers and enabling operating selective set of condenser where plurality of evaporators are connected to a single condenser
Another object of the invention is to provide a method for isolation of heat pipes as per need and application in a system of multiple heat pipes in the case of adsorption refrigeration module, which is to be periodically heated and cooled. For example, in the case of a tailored switchable heat pipe as in this invention, during the adsorption phase when the module needs to be cooled, the cooling heat pipe with its evaporator integrated with the module would be operative, while the heating heat pipe whose evaporator is integrated with the module would be switched off.
Another object of the invention is to provide means for the isolation of heat pipes as per need and application in a system of multiple heat pipes in the case where, heat transfer rate is to be varied while exchanging heat between to fix temperature source and sink. Heat transfer rate can be varied, in such a situation, by varying the number of active heat pipes.
Another object of the invention is to provide a cost effective means of isolating heat pipes as per need and application in a system of multiple heat pipes in a system of multiple heat pipes in case of application where several heat pipes are to be switched on and off as per a desired sequence. It is also possible to pinch multiple squeezable tubes fixed on a large number of heat pipes using a single low cost drive mechanism.
Yet another object of the invention is to provide for a simple, easily implementable and maintainable means for the isolation of heat pipes as per the need and application.
Thus in accordance with the invention for example a single stage regeneration process comprises of:
Further in accordance with the invention the single stage regeneration process may be extended to a two-stage regeneration process in a system comprising:
Further in accordance with the invention the two-stage regeneration process may be extended to a multi-stage regeneration process in a system comprising:
The number of stages in regeneration process may be increased by appropriately adding ITRs, liquid-liquid heat exchangers and pressure reducing devices between HTR and LTR.
The contacting device providing intimate contact between fluids to enhance the interfacial area between them comprises of:
The Hybrid Cooling System (HCS) in accordance with the invention comprises:
Other features and advantages of this invention will become apparent in the following detailed description of the preferred embodiments of this invention with reference to the accompanying drawings, in which:
a is a contacting mesh
b a single stage low temperature regenerator with fan and chimney
a is a a series flow two-stage regenerator with weak LD entering HTR
b is a series flow two-stage regenerator with weak LD entering LTR
c is a parallel flow two-stage regenerator
a is a series flow three-stage regenerator with weak LD entering HTR
b is a series flow three-stage regenerator with weak LD entering LTR
c is a parallel flow three-stage regenerator
a shows the contacting mesh for the mass transfer. Dimples, 114 are provided to give the required gap between the discs, when they are assembled on the shaft. Dimples on the mesh are providing the self-spacing between the discs. This leads to reduction in time required to assemble the discs on the shaft. The depth and diameter of the dimple can be varied. The spacers of required thickness on the shaft can provide spacing between the discs. This eliminates the dimples on the circumference of the disc A lip, 115 on the circumference of the contacting disc provides enough rigidity to the contacting surface. Inner surface of the disc is 116. A square hole at the centre is 117. The discs can be thermally bonded with the shaft. Thermally bonded discs can be acting as fins and help in heat transfer between fluid in the trough and fluid flowing through the shaft.
b shows a single stage Low Temperature Regenerator. The disc, 1 provides the contacting surface between the LD and air. The contacting surface is the mesh, or roughened surface, which holds the liquid on the surface for mass transfer. The disc, in plurality are mounted on a square hallow or solid shaft 2. A trough, 3 contains the LD. Material of construction of the trough can be a metallic, non-metallic or any other suitable, which is compatible with the LD and vapour/gas. The LD to be regenerated flows in to the trough 3 through inlet conduit 6. The regenerated LD flows out from the trough 3 through outlet conduit 7. Passages, 9 in plurality are in thermal contact with the trough. They can be inside/outside or integrated with the wall of the trough and be used for heat transfer to the LD in the trough. The passages can be metallic or non metallic or any other suitable material, which is compatible with fluid flowing through it. A hood, 14 is provided to ensure to vapour/gas passes in closed contact with contacting discs 1. Optionally a chimney 15 or a fan 16 is provided to circulate the air/gas through the contacting device. The heat transfer fluid is supplied through conduit 10 to the passages 9 wherein it exchanges heat with the LD in the trough and leaves through conduit 12. A device 5 is provided to rotate the contacting disc assembly and is supported on support 4.
The surface of the contacting disc can hold large quantity of the liquid. Rotating contacting surface partially dipped in a liquid eliminates the need for a pump to irrigate the contacting device. Thereby making the irrigation mechanism simpler. Carryover is eliminated if low vapour/gas velocities are maintained.
Fluid flowing through the passages, which are in thermal contact with the trough, can be a hot or cold fluid. The hot fluid can be steam, compressed air, exhaust gases from the engine or any hot fluids from suitable hot source. The cold fluid can be a cold refrigerant from heat pump, water from the cooling tower.
There are several variants of the contacting that may be designed as per the application.
In one of the embodiments the contacting disc may be a mesh, plain, roughened surface, and porous material.
Another embodiments the contacting device is preferably circular.
In other embodiments the contacting disc may be octagonal, hexagonal or any other shape based on the application. In a specific embodiment the contacting device is of metal.
In other embodiments, the contacting may non-metallic or of any suitable material that is compatible with the fluids.
In one embodiment, the central hole in the contacting device preferably a non-circular cross section to ensure that the discs move along with the shaft. In yet another embodiment the hole in the contacting can be circular.
In one of the embodiments, the contacting disc may optionally have dimples/projections on the circumference to provide self-spacing when the discs are assembled on a shaft. In other embodiments, the contacting discs do not have dimples, but spacing between the discs is provided with spacers.
In the other embodiments the spacers may be metallic or non metallic or any other suitable, which is compatible with liquid and vapour/gas.
One of the preferred embodiments is a square shaft that could be passed through the square hole in the contacting disc.
In an embodiment of the contacting disc assembly the shaft may be a hollow or solid as per the application.
In an embodiment of the contacting disc assembly the shaft is metallic.
In other embodiments, the shaft may be non-metallic or any other suitable material, which is compatible with the fluids.
In one of the embodiments, the trough holding the liquid may have the discs that are partially submerged.
In the other embodiments, material of construction of the trough may be a metallic, non-metallic or of any suitable material, which is compatible with the fluids.
In one of the embodiments, the heat exchanging passages on the trough is a coil, or multiplicity of tubes of any material in thermal contact with the inner or outer surface of the trough or integrated into the trough.
In other embodiments, the material of the passages may be metallic, non-metallic, or any other suitable material, which is compatible with the fluid flowing through it.
In one of the embodiments, a cover with chimney is provided to circulate the vapour/gas through the device.
In the other embodiments, the material of construction of enclosure to guide the flow of vapour/gas may be metallic or non metallic which is compatible with the fluids. In one of the embodiments, a low speed drive may be used to rotate the contacting disc assembly.
a shows a series flow two-stage regenerator with weak LD entering HTR. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21, through conduit 29 and where it is heated, further it passes through conduit 30 and gets heated in High Temperature Regenerator Heat exchanger (HTRHE) 41 further and then through conduit 33 it is introduced in to HTR 32. Vapour is generated from the LD at high temperature and pressure due to the addition of heat 39. This vapour passes through conduit 36 and gets sensibly cooled in HTRHE 41, further it passes through conduit 10 and flows through the passages of LTR 18 and gets condensed completely in passages of LTR. This condensate then passes through conduit 12 and further passes through Low Temperature Regenerator Heat Exchanger (LTRHE) 21 where it gets sub cooled further. This condensate is collected from the outlet conduit 73.
Partially regenerated LD from HTR 32 exits through conduit 34 and then passes through HTRHE 41 where it gets sub cooled and passes to LTR 18 through conduit 6. After complete regeneration of LD in LTR it exits through conduit 7 and then passes through LTRHE 21 where it gets sub-cooled and the regenerated LD leaves through conduit 24.
The vapour generated in HTR flows to HTRHE, 41 through conduit 36 and gets desuperheated and the desuper heated vapour flows to the LTR 18 through conduit 10 and is condensed in passages thermally in contact with LTR 18 and the condensate from LTR flows to LTRHE 21 through conduit 12 and then subcooled in LTRHE and comes out through conduit 73.
b shows a series flow two-stage regenerator with weak LD entering LTR. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21, through conduit 29 and where it is heated, further it passes to LTR through conduit 6 then it is partially regenerated in LTR. Partially regenerated LD from LTR flows through the conduit 7 to the suction of the pump 64 and pumped through HTRHE 41 where it is preheated and then flows to HTR 32 through conduit 34. The LD level in the HTR is 37 and the insulation to HTR is 38. In the HTR the LD is fully regenerated by absorbing heat from the heat source 39. The fully regenerated LD from HTR flows to HTRHE 41 through conduit 33 and then subcooled in HTRHE and flows to LTRHE 21 through conduit 43, where it is subcooled further before being returned to the source through conduit 24.
The vapour generated in HTR flows to HTRHE, 41 through conduit 36 and gets desuperheated and the desuper heated vapour flows to the LTR 18 through conduit 10 and is condensed in passages thermally in contact with LTR 18 and the condensate from LTR flows to LTRHE 21 through conduit 12 and then subcooled in LTRHE and comes out through conduit 73.
c shows a parallel flow two-stage regenerator. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21, through conduit 29 and where it is heated and passes through conduit 30, and part of the LD flow is throttled into the LTR in throttling device 25 and fully regenerated and the other part of the LD flow is preheated through HTRHE, 41 on its way to HTR. The LD level in the HTR is 37 and the insulation to HTR is 38. In the HTR the LD is fully regenerated by absorbing heat from the heat source 39. After regeneration the LD flows to the HTRHE, 41 through conduit 34 where it is subcoled and then further it passes through conduit 43 before being combined with the fully regenerated LD stream from LTR 18 and then flows through conduit 23 and further passes through LTRHE 21 where it is subcooled before being returned to the source through condut 24.
The vapour generated in HTR flows to HTRHE 41 through conduit 36 and gets desuperheated and the desuperheated vapour flows to the LTR 18 through conduit 10 and is condensed in passages thermally in contact with LTR 18 and the condensate from LTR flows to LTRHE 21 through conduit 12 and then subcooled in LTRHE and comes out through conduit 73.
a shows a series flow three-stage regenerator with three pumps and two throttle valves. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21, through conduit 29 and then is heated, further it passes through conduit 30 and gets heated in Intermediate Temperature Regenerator Heat exchanger (ITRHE) 61, further it passes through conduit 42 which leads it High Temperature Regenerator Heat exchanger (HTRHE) 41 where it gets heated further and then through conduit 33 it is introduced into HTR 32. Vapour is generated from the solution at high temperature and pressure due to the addition of heat 39. This vapour passes through conduit 36 and gets sensibly cooled in HTRHE 41, further it passes through conduit 45 and condenses in heat exchanger 60 and further condensate passes through ITRHE 61 where it gets subcooled and it passes through throttle valve 66 and is led through conduit 10 after mixing with vapour coming from ITR 51 through conduit 67. This condensate vapour mixture condenses completely in passages of LTR 18 and then passes through conduit 12 and further passes through Low Temperature Regenerator Heat Exchanger (LTRHE) 21 where it gets sub cooled further. This low-pressure condensate stream is then pumped using pump 72 to atmospheric pressure. The condensate is collected from the outlet conduit 73.
Partially regenerated LD from HTR 32 is led through conduit 34 into HTRHE 41 where it gets sub cooled before it is throttled in throttling device 46 and led through conduit 52 into ITR 51. Vapour is generated in ITR 51 at intermediate temperature and pressure due to heat delivered through heat exchanger 60. This vapour passes through conduit 55 which is desuperheated in ITRHE 61 and further it passes through conduit 67 leading to conduit 10. Partially regenerated LD from ITR 51 which operates under vacuum passes through conduit 54 which leads into LD pump 64 which increases the pressure of the LD from ITR to atmospheric pressure which is then led in to trough of LTR 18.
After complete regeneration of LD in LTR it is led through conduit 7 to LTRHE 21 where it gets sub-cooled further. The regenerated LD flows out through outlet conduit 24.
b shows a series flow three-stage regenerator with weak LD entering LTR. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21, through conduit 29 and then is heated and further passes to LTR 18 through conduit 6 and partially regenerated in the LTR then pumped to ITRHE 61 with pump 64, through conduit 7, where it is preheated before it is regenerated further in ITR 51. The partially regenerated LD is pumped to HTR 32 with pump 64 through the HTRHE 41 where it is preheated through HTRHE and passes to HTR through conduit 33 and regenerated further in HTR thereafter the fully regenerated LD flows to HTRHE wherein it is subcooled, and passes to ITRHE through conduit 43 and further flows to LTRHE 21 through conduit 23 and then pumped back to the source through conduit 24
The vapour generated in HTR flows to HTRHE 41 through conduit 36 and gets desuperheated and the desuperheated vapour flows to the ITR 51 and gets condensed and further subcooled in ITRHE 61 and throttled in throttling device 66 and mix with the vapour generated in ITR. This liquid vapour stream is then condensed in “passages” thermally in contact with LTR, 18 and the condensate from LTR passes to LTRHE 21 through conduit 12 and subcooled in LTRHE before being pumped out through conduit 73.
c shows the parallel flow three stage regenerator. The weak LD from the source passes to the pump 75 through inlet conduit 74 and is pumped to LTRHE 21 through conduit 29 and then it is heated and a portion of the LD further passes to LTR 18 through conduit 6 through throttling device 25 and conduit 6. Another portion of weak LD passes through conduit 30 to ITRHE 61. This stream of LD passes from ITRHE 61 to ITR 51 through conduit 68 and portion of this stream is taken into ITR 51 through throttling device 49 and conduit 52. The remaining portion of this stream flows through throttle valve 48 and conduit 42 to HTRHE 41 and flows through conduit 33 to HTR. The partially regenerated LD from LTR 18 passes through pump 64 through conduit 63 to ITRHE 61 and flows to HTR 32 through HTRHE.
The vapour generated in HTR flows to HTRHE 41 through conduit 36 and gets desuperheated and the desuperheated vapour flows to the ITR 51 through conduit 45 and gets condensed in the heat exchanger 60 in ITR and flows to the ITRHE through conduit 57 and further subcooled in ITRHE 61 and throttled in throttling device 66 and mix with the vapour generated in ITR. This liquid vapour stream is then condensed in “passages” thermally in contact with LTR, 18 and the condensate from LTR passes to LTRHE 21 through conduit 12 and subcooled in LTRHE before being pumped out through conduit 73.
The number of stages in regeneration process may be increased by adding ITRs, liquid-liquid heat exchangers and pressure reducing devices between HTR and LTR.
In one of the embodiments, the heat source to the HTR is electric heater, solar collector, burning of biomass or biogas.
In the other embodiment, the heat source to the HTR may be waste heat source from the engine exhaust or any other waste heat source.
In one of the embodiments, the HTR may be a metallic or non-metallic, which is compatible with LD.
In the other embodiment, the shape of the HTR may be a cylindrical, rectangular, square or any other suitable shape for integration with the heat source.
In the other embodiment the HTR may be placed horizontally, vertically or any position suitable for integration with the heat source.
In one of the embodiments the HTR is covered with insulating material to avoid heat transfer between LD and ambient.
In one of the embodiments, a solution heat exchanger is incorporated to preheat the weak LD flowing to HTR, using heat from high temperature LD flowing from HTR.
In one of the embodiment, additional solution heat exchangers may be incorporated to internally recycle heat from hot to cold LD.
In the other embodiment, the material of construction of heat exchanger may be a plastic or any other suitable material compatible with LD.
In one of the embodiments entire flow of the LD, after regeneration in HTR is flowing through LTR. In this case, HTR and LTR are operating in series.
In the other embodiment certain flow of LD after regeneration in HTR may be bypassed. In this case HTR and LTR are operating in parallel.
In another embodiment partially regenerated LD passes from the HTR to LTR for further regeneration or the partially regenerated LD may pass from LTR to HTR for further regeneration or the flow of LD is split into two streams and then passed to HTR and LTR
In another embodiment, the LTR incorporates rotating disks as the contacting media between LD and vapour/gas.
In one of the embodiments, the condensation of vapour takes place in the passages, which are in thermal contact with the LTR.
In a specific embodiment the passages, through which vapour condenses may be in thermal contact while being inside or outside or integrated with LTR.
In one of the embodiments an arrangement such as a hood with chimney is provided to aid the ambient air through the LTR over the contacting media, which is wet with LD.
In one of the embodiments, the HTR is at a higher elevation than the LTR, and one LD pump is used to pump the weak LD to HTR.
In another embodiment, two pumps are used, one pump to LTR and the other to HTR.
In the other embodiment, one pump to pump LD to LTR and LD from LTR flows due to gravity.
In another embodiment, the heat source to the ITR may be the vapour generated in HTR.
In other embodiments, the ITR may be a metallic or non-metallic, which is compatible with LD.
In the other embodiment the shape of the ITR may be a cylindrical, rectangular, square or any other suitable shape for integration with the heat source from ITR/HTR operating at next higher pressure level.
Yet other variants of this invention with more than two-stages of regeneration, which incorporates additional components such as, ITRs, liquid-liquid heat exchangers and pressure reducing devices.
Refrigerant exits from the absorber/ICD through conduit 312 and moves to the compressor 320. Refrigerant after compression passes through conduit 10 to the passages 9 of regenerator/OCD, 18 which are in thermal contact with the outer lower surface or inner surface or integrated with the trough wall of the regenerator/OCD. The weak LD from absorber/ICD after liquid-liquid heat exchanger flows to the regenerator/OCD. The weak LD enters the regenerator/OCD through conduit 6. The heat required for the regeneration is supplied by the refrigerant condensing in the passages 9. After condensation of the refrigerant in regenerator/OCD, it moves through conduit 12 which led to throttling device 321.
The regenerated, strong LD flows out from the regenerator/OCD through conduit 7 and pumped with LD pump 332 to the absorber/ ICD through the liquid-liquid heat exchanger, 331. A hood 14 is provided to guide the outdoor air through the regenerator/OCD. A fan 16 is provided to circulate the outdoor air through the regenerator/OCD. The contacting disc assembly is partially submerged in the LD in the regenerator/OCD. The ambient air pickups the moisture from the hot desiccant, in the trough of regenerator/OCD. The disc assembly is rotated by a motor at low rpm in the LD, preferably at around 3 to 5 rpm or oscillated to an angle greater than 30° in either direction.
In one of the embodiments, an absorber/ICD is coupled with an evaporator of conventional VCRS.
In another embodiment, the absorber/ICD is an adiabatic contacting device with a separate heat exchanger to cool the LD.
In one of the embodiments, the evaporation of the refrigerant takes place in the passages, which are in thermal contact with the trough containing the LD.
In a specific embodiment, the passages may be in thermal contact by being placed inside or outside the trough or integral with trough.
In one of the embodiments an absorber/ICD and/or regenerator/OCD incorporates large surface density rotating contacting disc assembly as the contacting media between air and LD.
In another embodiment, the rotating contact disc assembly in the absorber/ICD and/or regenerator/OCD is a mesh, plain /roughened surface or porous material and their like constructed of materials such as a plastic or any other suitable material, which is compatible with LD and air.
In one of the embodiments the contacting disc assembly absorber/ICD and regenerator/OCD is rotated at low rpm in the LD, preferably at around 3 to 5 rpm or oscillated to an angle greater than 30° in either direction.
In another embodiment the contacting disc assembly in the absorber/ICD and/or regenerator/OCD is mounted in a trough or any suitable container constructed of non conducting material with wall thickness of <0.2 mm and to withstand the pressure of the heat transfer fluid.
In one of the embodiments the absorber/ICD and/or regenerator/OCD, optionally incorporates Spiral Contacting Device (SCD) as the contacting media between the LD and air.
In another embodiment SCD in the absorber/ICD and/or regenerator/OCD is rotated at low rpm in the LD, preferably at around 3 to 5 rpm or oscillated to an angle greater than 30° in either direction.
In one of the embodiments, SCD in the absorber/ICD and/or regenerator/OCD is mounted in a trough or any suitable container without passages.
In the other embodiment the trough to mount the SCD is constructed of conducting /non conducting material without limitation of wall thickness In one of the embodiments, a liquid-liquid heat exchanger selected from any suitable material compatible with the LD may be incorporated in the system to recycle heat from the hot regenerated strong LD coming from the regenerator/OCD into the weak LD coming out of the absorber/ICD.
In one of the embodiments, a regenerator/OCD is coupled with a condenser of conventional VCRS.
In another embodiment, the regenerator/OCD is an adiabatic contacting device with a separate heat exchanger to heat the LD.
In one of the embodiments the condensation of the refrigerant takes place in the passages, which are in thermal contact with the inner or outer or integrated into the trough of regenerator/OCD.
In one of the embodiments the evaporation of the refrigerant takes place in the passages, which are in thermal contact with the inner or outer or integrated into the trough of absorber/ICD.
In the specific embodiment, where the elevation difference between the regenerator/OCD and the absorber/ICD is not sufficient, two LD pumps are used to pump the LD, one from the absorber/ICD to regenerator/OCD and the other from the absorber/ICD to regenerator/OCD.
In an embodiment the regenerator/OCD may be placed at higher elevation than the absorber/ICD in which case the LD flows by gravity from the regenerator/OCD to absorber/ICD
In the specific embodiment, where the regenerator/OCD is at a higher elevation than the absorber/ICD, one LD pump is used to pump the LD from the absorber/ICD to regenerator/OCD.
In one of the embodiments, absorber/ICD may be placed at higher elevation than the regenerator/OCD in which case the LD flows by gravity from the absorber/ICD to regenerator/OCD.
In the specific embodiment, where the absorber/ICD is at a higher elevation than the regenerator/OCD, one LD pump is used to pump the LD from the regenerator/OCD to absorber/ICD
In another set of embodiments the said VCRS is replaced by Vapour Absorption/Adsorption System.
This invention provides a compact refrigeration cum heating system as described in
The adsorption module comprises (
The switchable heat pipes as described in
One of the heat pipes 504, 531 acts as the means of transferring the heat to the module 500 and other acts as the means to remove the heat from the module. At any given time, only one of the two heat pipes 504, 531 is active. These heat pipes 504, 531 are in thermal contact with the containment vessel 550 that is achieved by either being in thermal contact with the wall of the containment vessel 550 or any internal partition of the containment vessel 551. As per this the containment vessel wall 550/partition 551 acts as fin leading to increase of the containment vessel surface area that is in contact with the adsorbent. This eliminates the need for separate metal fins, thereby reducing the overall thermal mass of the system. Lower thermal mass is a desirable property in case of applications pertaining to adsorption refrigeration or heat pumps. The design described herein achieves the objective of obtaining high rate of heat transfer along with low thermal mass.
Cross sectional area (CSA) of the containment vessel 550 is determined on the basis of amount of adsorbent to be packed in each module 500. As the “CSA” of the module 500 is increased, the fin effectiveness of the containment vessel wall 550 decreases, which in turn decreases the efficiency of heat transfer from the heat pipes 504, 531 to the adsorption module 500 and vice versa. An optimized “CSA” of the module 500 has to be selected based on the desired cycle time and compactness of the system. An optimum “CSA” needs to be arrived at based on the desired adsorption system compactness and COP. Increasing the number of passages 504, 531 for heat transfer can further increase fin effectivness of the containment vessel wall 550. All “passages” 504 used for supplying heat to the module 500 should preferably be equidistant from each other. Same should be done in case of cooling “passages” 531. Fabrication and type of the heat pipes 504, 531 to be used, is based on the desired capacity of heat transfer.
During operation, working fluid at the hot end takes heat from the surroundings to produce vapour, which is then transported to the cold end. At cold end this vapour is condensed on the walls and the liquid drains back to the lower hot end. Liquid drains back by the help of gravity, in case of gravity assisted heat pipes 504, 531, or through a wick due to capillary action. To facilitate the draining back of the liquid, groves or wick may be provided on the inner side of the heat pipe wall. The two side tubes of smaller diameters function as heat pipes 504, 531 that are used to transfer heat to the adsorption module 500 and remove the heat from the module 500. At any given point of time only one of the two heat pipes 504, 531 is operational. The module wall 550 that is preferably made of high conducting material performs the function of fin attached to the heat pipes 504, 531.
The module design disclosed in this invention may be used in a wide range of applications including purification of gases, separation of gases, removal of contaminants from a gas stream, pressure wing adsorption, catalytic reactions, and removal or supply of heat during the reactions, etc.
In other embodiments, the CSA of the containment vessel 550 may be circular, square, rectangular, elliptical or any shape based on space constraints or the need to increase the surface area of the wall in contact with the adsorbate.
In another embodiment, the “CSA” of the “passages” 504, 531 may be circular, square rectangular, elliptical or any shape governed by the space constraints or the method of fabrication being adopted. The containment vessel 550 along with the “passages” 504, 531 may be extruded with “passages” 504, 531 integrated with the containment vessel wall 550 or partition 551. It would improve the fin effectiveness of the containment vessel walls 550.
In other embodiments, the number of “passages” 504, 531 for supplying and removing heat from the module 500 may be varied depending on the desired heat transfer rate. Increasing the number of “passages” 504, 531 increases the fin effectiveness of the module wall 550, resulting in reduction of time required to transfer the requisite amount of heat to and from the module 500.
In another embodiment, the “passages” 504 for supplying the heat to the module 500 is not necessary as in the case of applications where the module 500 is placed directly at the eye of a solar collector. Under such circumstances heat is supplied to the module 500 directly through radiation and the “passages” 531 are required to ensure removal of the heat from the module 500.
In another embodiment, the “passages” 531 for removal of heat from the module 500 is not necessary as in the case of applications where the module 500 is placed directly in cooling fluid stream. Under such circumstances heat is removed from the module 500 directly through the containment vessel wall 550 and the “passages” 504 are required to supply heat to the module 500.
In one of the embodiments, the “passages” 504, 531 run along the partial complete length of the module 500.
In yet other embodiments, the “passages” 504, 531 may be thermally in contact with the inner side of the containment vessel wall 550.
In one of the embodiments, the “passages” 504, 531 are constructed as “heat pipes”. In another embodiment, electric heater may be thermally in contact with the containment vessel wall 550 or partition 551.
In another embodiments, the “passages” 504, 531 may be press fitted inside/outside the containment vessel wall 550 or partition 551.
One of the heat pipes 504, 531 acts as the means of transferring the heat to the module 500 and other acts as the means to remove the heat from the module. At any given time, only one of the two heat pipes 504, 531 is active. These heat pipes 504, 531 are in thermal contact with the containment vessel 550 that is achieved by either being in thermal contact with the wall of the containment vessel 550 or any internal partition of the containment vessel 551. As per this the containment vessel wall 550/partition 551 acts as fin leading to increase of the containment vessel surface area that is in contact with the adsorbent. This eliminates the need for separate metal fins, thereby reducing the overall thermal mass of the system. Lower thermal mass is a desirable property in case of applications pertaining to adsorption refrigeration or heat pumps. The design described herein achieves the objective of obtaining high rate of heat transfer along with low thermal mass.
Cross sectional area (CSA) of the containment vessel 550 is determined on the basis of amount of adsorbent to be packed in each module 500. As the “CSA” of the module 500 is increased, the fin effectiveness of the containment vessel wall 550 decreases, which in turn decreases the efficiency of heat transfer from the heat pipes 504, 531 to the adsorption module 500 and vice versa. An optimized “CSA” of the module 500 has to be selected based on the desired cycle time and compactness of the system. An optimum “CSA” needs to be arrived at based on the desired adsorption system compactness and COP. Increasing the number of passages 504, 531 for heat transfer can further increase fin effectivness of the containment vessel wall 550. All “passages 38504 used for supplying heat to the module 500 should preferably be equidistant from each other. Same should be done in case of cooling “passages” 531. Fabrication and type of the heat pipes 504, 531 to be used, is based on the desired capacity of heat transfer.
During operation, working fluid at the hot end takes heat from the surroundings to produce vapour, which is then transported to the cold end. At cold end this vapour is condensed on the walls and the liquid drains back to the lower hot end. Liquid drains back by the help of gravity, in case of gravity assisted heat pipes 504, 531, or through a wick due to capillary action. To facilitate the draining back of the liquid, groves or wick may be provided on the inner side of the heat pipe wall. The two side tubes of smaller diameters function as heat pipes 504, 531 that are used to transfer heat to the adsorption module 500 and remove the heat from the module 500. At any given point of time only one of the two heat pipes 504, 531 is operational. The module wall 550 that is preferably made of high conducting material performs the function of fin attached to the heat pipes 504, 531.
The module design disclosed in this invention may be used in a wide range of applications including purification of gases, separation of gases, removal of contaminants from a gas stream, pressure wing adsorption, catalytic reactions, and removal or supply of heat during the reactions, etc.
In other embodiments, the CSA of the containment vessel 550 may be circular, square, rectangular, elliptical or any shape based on space constraints or the need to increase the surface area of the wall in contact with the adsorbate.
In another embodiment, the “CSA” of the “passages” 504, 531 may be circular, square rectangular, elliptical or any shape governed by the space constraints or the method of fabrication being adopted. The containment vessel 550 along with the “passages” 504, 531 may be extruded with “passages” 504, 531 integrated with the containment vessel wall 550 or partition 551. It would improve the fin effectiveness of the containment vessel walls 550.
In other embodiments, the number of “passages” 504, 531 for supplying and removing heat from the module 500 may be varied depending on the desired heat transfer rate. Increasing the number of “passages” 504, 531 increases the fin effectiveness of the module wall 550, resulting in reduction of time required to transfer the requisite amount of heat to and from the module 500.
In another embodiment, the “passages” 504 for supplying the heat to the module 500 is not necessary as in the case of applications where the module 500 is placed directly at the eye of a solar collector. Under such circumstances heat is supplied to the module 500 directly through radiation and the “passages” 531 are required to ensure removal of the heat from the module 500.
In another embodiment, the “passages” 531 for removal of heat from the module 500 is not necessary as in the case of applications where the module 500 is placed directly in cooling fluid stream. Under such circumstances heat is removed from the module 500 directly through the containment vessel wall 550 and the “passages” 504 are required to supply heat to the module 500.
In one of the embodiments, the “passages” 504, 531 run along the partial complete length of the module 500.
In yet other embodiments, the “passages” 504, 531 may be thermally in contact with the inner side of the containment vessel wall 550.
In one of the embodiments, the “passages” 504, 531 are constructed as “heat pipes”.
In another embodiment, electric heater may be thermally in contact with the containment vessel wall 550 or partition 551.
In another embodiments, the “passages” 504, 531 may be press fitted inside/outside the containment vessel wall 550 or partition 551.
Two adsorption modules 500, 600 are connected through valve 711 to allow pressure equalization between the two adsorption modules 500, 600, at end of generation and/or adsorption phases. The refrigeration sub-system operates on an adsorption refrigeration cycle with pressure equalization for heat recovery. The two-module operate out of phase, i.e. one module is being heated while the other is being cooled. During pressure equalization between two modules or two sets of modules, refrigerant from a module or a set of module at high pressure is allowed to flow to a module or a set of modules at relatively lower pressure. This method of regeneration between two modules or sets of modules reduces the requirement of heat input from the external heat source in the generation phase and thus increases COP.
Pressure equalization between two sets of modules is single stage pressure equalization. Multi-stage pressure equalization is achieved if pressure equalization is effected sequentially between three or more modules or sets of modules. Vapour and heat regeneration efficacy increases with increase in number of stages of regeneration. Multi-stage regeneration eliminates the need for heat transfer fluid loops and the associated complex valve arrangements and controls otherwise needed for regeneration. Vapour equalisation technique enhances COP of the system and also reduces cycle time. Cycle time is reduced because the time required to equalize pressure is a fraction of the time required to regenerate the heat using heat transfer fluid loops. Also the auxiliary power required to pump the heat transfer fluids is eliminated.
Adsorption modules 500, 600 used in refrigeration cum heating system, are shown in
The module design may be further modified based on the application requirements. Shape of module and the heat pipes may be varied on the basis of the ease of fabrication or other application constraints. Diameters of the module and heat pipe are governed by the desired capacities. Number of heat pipes of each type can be varied to increase or decrease the heat transfer rate. In some cases, the heat pipes either for heating or cooling are not required. Due to some constraints, it might not be possible to make the heat pipe run along the complete length of the module. Heat pipes may be thermally affixed on the inner side of the module wall, or they may be co-extruded along with the main pipe or affixed by any other means. But the basic idea of using the heat pipes for supplying and removing the heat from the adsorption modules, and integrating the same with the walls of the module to avoid the need of separate fins to facilitate heat transfer within the adsorbent bed still holds. In this design the wall of the module acts as a fin to facilitate heat transfer thereby reducing the overall thermal mass of the system, leading to lower cycle times and higher COP.
Hot/cold ends 501, 534, 504, 531, 604, 631 of switchable heat pipes, used in refrigeration cum heating system, use a system to isolate hot end from cold end or vice versa.
This novel construction and arrangement gives this heat the flexibility to use it in diverse ways. Heat pipe cross-section used may be of any shape (such as circular, elliptical, rectangular, etc.). Cross-sectional area of the heat pipe is decided on the basis of the desired capacity of heat transfer. The flexible tube used to connect the heat receiving section and the heat giving section can be made of any material as long as it can be pinched/squeezed to isolate the two sections as long as the material of the flexible tubing is compatible with the fluid used in the heat pipe. A wick may be provided on the inner wall of the heat receiving section, heat giving section and flexible tubing to facilitate the draining back of the fluid. There is no restriction on the type of wick that should be used, except that in the flexible tube section the wick should be also flexible. A sealant has to be applied to seal the flexible tube and metal tube joints. Sealant should be able to withstand pressures at which heat pipe is supposed to operate. Any material may be used for making the heat receiving or condenser sections 501, 504 of the heat pipe as long as it is compatible with the working fluid. Any pinching mechanism may be used to pinch the flexible tube 502 depending on the application.
In refrigeration cum heating system, as shown in
The system described in this invention may also function without pressure equalisation. In such cases the COPs obtained will be low, as compared to the system operating with heat regeneration as described above.
This novel construction and arrangement provides flexibility to use it with diverse systems as listed below:
The invention is now illustrated with non-limiting examples.
A preferred embodiment of the Energy efficient regeneration process is illustrated with a non-limiting example.
A two-stage regenerator device was fabricated and tested for regeneration of calcium chloride LD. It comprises a HTR made of aluminium rectangular channel in which electrical heaters are incorporated as heat source. LTR incorporates the aluminium disks are of 150 mm diameter, with circumferential lip and dimples as the contacting device between LD and ambient air. The disks are mounted on an aluminium shaft of diameter 9.5 mm. The disks are placed in a semi hexagonal aluminium trough 500 mm (length)×200 mm (width)×210 mm (height). It incorporates 337 m2/m3 surface density, when maintaining 5 mm gap between the disks using plastic spacers. Contacting device is covered with a hood and a chimney of diameter 100 mm, length 1.5 m. Airflow through the contacting device is due to natural convection induced by the chimney effect. The disks are made to rotate at 5 rpm using an electric motor. Inlet and out let of LD to the trough is through 9.5 mm diameter aluminium tubes. The experimental result in Table 1, shows that the regenerator is capable of removing 2.6 kg/kW-h water from calcium chloride LD. It is observed that there is no carry over of LD with air stream and along the condensate collected from LTR.
Q Electric heat input
DBT Dry bulb temperature,
RH Relative humidity
mfw Total water removed from LD
WBT Wet bulb temperature
V Velocity of air at exit
The other associated advantages of this two stage/multistage regeneration process are, no corrosion, no orifices or nozzles to wear or clog, modular system that can be installed with flexibility, silent operation without splashing or spraying sounds and low electrical power consumption.
The invention is now illustrated with a non-limiting example.
The contacting device was fabricated and tested for humidification of ambient air. It comprises discs made of aluminium mesh. The discs are of 150 mm diameter, with circumferential lip and dimples. The discs are mounted on an aluminium shaft of diameter 9.5 mm. The discs are placed in a semi hexagonal aluminium trough 500 mm (length)×200 mm (width)×210 mm (height). It incorporates 337 m2/m3 surface density, when maintaining 5 mm gap between the discs using plastic spacers. Contacting device is covered with a hood and a chimney of diameter 100 mm, length 1.5 m. Airflow through the contacting device is due to natural convection induced by the chimney effect. The discs are made to rotate at 5 rpm using an electric motor. Inlet and out let of water to the trough is through 9.5 mm diameter aluminium tubes. The experimental result in Table 2 shows that the contacting device efficiency for humidification of air is as high as 98% for the ambient conditions are 26.8° C. and 48% relative humidity. It is observed that there is no carry over of liquid with air stream.
DBT Dry bulb temperature,
WBT Wet bulb temperature
RH Relative humidity
The other associated advantages of this contacting device are, no corrosion, no pumps, no tubes, no orifices or nozzles to wear or clog, modular system that can be installed with flexibility, silent operation without splashing or spraying sounds and low electrical power consumption.
A hybrid cooling system is designed with the following specification:
The salient features of the model are as follows:
h. The relevant simulated results are given in Table 3.
The main advantages of the system are the significantly improved energy efficiency, zero carryover of LD into process air streams, increase in cooling capacity for a given compressor in comparison to the conventional HCS using “packed” or “spray type-contacting devices”. This is possible with the appropriately designing of the absorber, regenerator, liquid-liquid heat exchanger and other components of HCS. Significant reduction in weight and cost is achieved with the use of alternate materials such as plastics and eliminates any problems due to corrosion of the absorber/regenerator as in conventional systems. The contacting media disclosed in this invention offers high surface densities as high as 600 m2/m3, which is about 185% greater than conventional packing. The system is compact, lower weight and techno-economically viable for air-conditioning.
In order to establish the performance of the adsorption module, its performance has been evaluated for example in a model adsorption refrigeration system.
Some of the important parameters that are considered fixed for the model system are as follows:
The findings are:
The system disclosed in the invention clearly brings out the advantages over the prior art in terms of the following:
The results of an adsorption refrigeration cum heating system, using adsorption cycle with pressure equalisation for heat regeneration, with activated carbon/ ammonia as working adsorbent—adsorbate pair are given to serve as a non-limiting example of the present invention.
Table 4 presents the simulation results for a system using solar collector as the heat source. Some of the important parameters that are considered fixed for the system in this example for simulation are as follows:
Though this system can operate with various heat sources, one of the very common applications of the adsorption systems is solar refrigeration. Solar refrigeration is an important use of solar energy because the supply of solar energy and the demand for cooling are greatest during the same season. It has the potential to improve the quality of life of people who live in areas where the supply of electricity is far from sufficient. The success of solar cooling is dependent on the availability of low cost and high performance of solar collectors. In the disclosed refrigeration cum heating system if solar energy is used as the input, solar collector contribute to more then 80% of the system cost. Still the costs have been brought down significantly by reducing the solar collector area required per kg of ice produced per day and the cost of adsorption modules. This has been made possible in the present invention due to high COP of the system with low cycle time. After optimizing the system to minimize the system cost the overall system is expected to cost one-third of the currently commercially available solar refrigeration system. In addition to that system is very compact and gives hot water as an additional utility.
| Number | Date | Country | Kind |
|---|---|---|---|
| 151/MUM/2002 | Feb 2002 | IN | national |
| 152/MUM/2002 | Feb 2002 | IN | national |
| 153/MUM/2002 | Feb 2002 | IN | national |
| 154/MUM/2002 | Feb 2002 | IN | national |
| 155/MUM/2002 | Feb 2002 | IN | national |
| 767/MUM/2002 | Aug 2002 | IN | national |
This application claim priority from Indian Provisional Application Ser. Nos. (1) “Contacting Device,” 153/MUM/2002 filed on 19 Feb. 2002; (2) “Hybrid Cooling Systems,” 154/MUM/2002 filed on 19 Feb. 2002; (3) “Energy Efficient Regeneration,” 767/MUM/2002 filed on 23 Aug. 2002; (4) “Refrigeration cum Water Heating System,” 151/MUM/2002 filed on 19 Feb. 2002; (5) “Switchable Heat Pipe,” 152/MUM/2002 filed on 19 Feb. 2002; and (6) “Adsorption Module” 155/MUM/2002 filed on 19 Feb. 2002, the entire disclosures of which are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10367982 | Feb 2003 | US |
| Child | 11180650 | Jul 2005 | US |
