Patent Grant
11719449
The present disclosure relates generally to vapor compression systems such as refrigeration systems and air-conditioning systems and, more particularly to, vapor compression systems capable of utilizing water as a refrigerant.
In conventional refrigeration systems, particularly vapor compression refrigeration systems, synthetic refrigerants, such as but not limited to, chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC) are employed for ease of availability and favorable thermal properties for refrigeration. Consequently, the resultant refrigeration systems are characterized with improved energy efficiency and thermal performance However, the use of synthetic refrigerants, discharge into atmosphere that are harmful to the earth's ozone layer, leading to ozone layer depletion and global warming, which is catastrophic.
To overcome the aforementioned limitation, technology has paved way for use of refrigerants such as ammonia (R717), water (R718) and the like, which are configured with a lower potential to damage the ozone layer and global warming. Among these refrigerants, R718 is chemically stable, non-flammable, physiologically harmless and abundantly available for access. However, due to the physical properties of R718 in its refrigeration temperature range (i.e. 0° C. to 10° C.), utilization of R718 as the refrigerant poses unique challenges. One of the physical properties which is the vapor pressure, that is required to be maintained for use as the refrigerant is 12 mbar for 10° C., which is less than two thousandths with that of ammonia at the same temperature. Moreover, the volumetric flow rate of the water that is to be compensated with its working pressure is much higher (for e.g., 230-fold larger at 10° C.) than ammonia for the same refrigeration capacity. To comply with these requirements an evaporator, an intermediate cooler, a condenser and two-stage turbo compressors inside a vacuum tight enclosure is required to be installed. Such requirement is technologically demanding, and their bulky dimensions can at most serve large refrigeration facilities. Beyond these challenges, the complete processes of evaporation, compression, transportation and condensation of water vapors should be carried out under a good vacuum. Consequently, additional roots and oil-less screw vacuum pumps should be installed to maintain this working condition. These indispensable vacuum devices are costly and deteriorate the performance of prior art water chillers.
Therefore, there is a need for techniques which can overcome one or more limitations stated above in addition to providing other technical advantages.
Various embodiments of the present disclosure provide a refrigeration system. The system including an evaporator unit including a housing configured to receive water and including an air inlet port configured to route air into the housing. A compressor unit is fluidically coupled with the housing and is configured to maintain a vacuum condition or induce an evacuation action within the housing. The evacuation action enables air to enter the housing from the ambient surroundings via the air inlet port. A porous material is disposed within the housing for defining a first compartment and a second compartment within the housing. The first compartment is configured to receive the water and the second compartment configured to receive the air through the air inlet port. The porous material is positioned above the air inlet port for allowing the air into the housing through the porous material. The air routed through the porous material disperses within the housing to form air bubbles. The air bubbles induce turbulent mixing between phase boundaries of water molecules and air molecules within the housing, wherein interfacial areas of the air bubbles and the turbulent mixing enhance evaporation rate of the water thereby converting a portion of the water into water vapors. The water vapors on discharging from the housing cools the portion of the water via evaporative cooling to form a cooled water. A heat exchanger unit is fluidically coupled to the housing and to an enclosure. The heat exchanger unit is configured to refrigerate the enclosure. The pump also ensures that mixture of the air and the water vapors is expelled from the housing to the ambient environment or to a condenser, suitably.
In another embodiment, the present disclosure also provides an air conditioning system. The system including an evaporator unit including the housing configured to receive water and including the air inlet port configured to route air into the housing. The porous material is disposed within the housing for defining the first compartment and the second compartment within the housing. The first compartment is configured to receive the water and the second compartment configured to receive the air through the air inlet port. The porous material is positioned above the air inlet port for allowing the air into the housing through the porous material. The air routed through the porous material disperses within the housing to form air bubbles. The air bubbles induces turbulent mixing between phase boundaries of water molecules and air molecules within the housing, wherein interfacial areas of the air bubbles and the turbulent mixing enhance evaporation rate of the water thereby converting a portion of the water into water vapors. The water vapors on discharging from the housing cools the portion of the water via evaporative cooling to form a cooled water. The heat exchanger unit is fluidically coupled to the housing and to an enclosure. The heat exchanger unit is configured to air-condition the enclosure.
The following detailed description of illustrative embodiments is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to a specific device or a tool and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers:
The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearance of the phrase “in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not for other embodiments.
Moreover, although the following description contains many specifics for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to said details are within the scope of the present disclosure. Similarly, although many of the features of the present disclosure are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the present disclosure is set forth without any loss of generality to, and without imposing limitations upon, the present disclosure.
Overview
Various embodiments of the present disclosure provide a refrigeration system. The refrigeration system is capable of utilizing water as a refrigerant, without a need for cumbersome equipment required for maintaining working condition within the system for using water as the refrigerant. The system is therefore cost-effective in operation and maintenance while improving the overall coefficient of performance (COP) or energy efficiency ratio (EER).
The system includes an evaporator unit having a housing configured to receive water. The housing may be fluidically connected to a reservoir for receiving water. The housing includes an air inlet port, preferably positioned at a bottom portion of the housing, configured to route air into the housing. A compressor unit is fluidically coupled with the housing and is configured to maintain a vacuum condition or induce an evacuation action within the housing. The evacuation action enables air to enter the housing from the ambient surroundings via the air inlet port. A porous material is disposed within the housing, for defining a first compartment and a second compartment. The first compartment is configured to receive the water, as such, the first compartment may be fluidically connected with the reservoir for receiving the water. The second compartment is configured to receive the air routed via the air inlet port, due to the evacuation action of the pump. The porous material is positioned above the air inlet port for allowing the air into the housing through the porous material. The air routed through the porous material disperses within the housing to form air bubbles. The air bubbles induces turbulent mixing between phase boundaries of water molecules and air molecules within the housing, wherein interfacial areas of the air bubbles and the turbulent mixing enhance evaporation rate of the water, thereby converting a portion of the water into water vapors. The water vapors when discharged from the housing via the compressor unit or the pump, cools the remaining portion of the water via evaporative cooling to form cooled water. The cooled water settles on the porous material. A heat exchanger unit is coupled to the housing and to an enclosure, which may be a fluid container unit, a food storage compartment or an indoor space, via a conduit or a pipe. The conduit includes water, which is circulated between the evaporator and the enclosure for heat transfer therebetween for refrigeration.
The system may also include a condenser unit, fluidically coupled to the housing for receiving the water vapors. The condenser unit is configured to receive a mixture of the air and the water vapors from the housing via the compressor unit. The compressor unit maintains a vacuum condition in the housing, for ensuring routing of the water vapors from the housing to the condenser unit. In one configuration, the compressor unit may maintain or induce sufficient pressure difference between the condenser unit and the housing for ensuring routing of the water vapors from the housing to the condenser unit. The condenser unit is configured to condense the water vapors to the water for recirculation within the system. This configuration ensures recirculation of the water, thereby mitigating the need for fresh water in each cycle of operation of the system. Thus, if the water source is from municipal tap, the water can be recirculated in the system based on the above configuration.
The present disclosure also provides an air-conditioning system for air-conditioning the enclosure or the indoor space. The air-conditioning system may be controlled by a control unit, to ensure selective increase and decrease in the temperature of the indoor space.
Various embodiments of a refrigeration system are explained below in a detailed manner, herein with reference to
The evaporator unit 102 includes a housing 108 configured to receive water. The housing 108 may be fluidically coupled to a reservoir 110 for receiving the water. The reservoir 110 may be a tank containing the water body, a pond, a sea or an ocean as per requirement. The housing 108 may be fluidically coupled to the reservoir 110 via a conduit 112 for receiving the water. The conduit 112 is fluidically coupled to an evaporator inlet port 114 for supplying the water from the reservoir 110. A valve 116 may also be incorporated in the conduit 112 for controlling the flow of the water into the housing 108. The valve 116 may be communicably coupled or associated with a control unit (not shown in Figures). The control unit may operate the valve 116 for supplying the water into the housing 108 as per requirement. In one implementation, the control unit operates the valve 116 based on the level of the water within the housing 108. That is, if the level of the water in the housing 108 is lower than a pre-set limit, the valve 116 is operated to an open position (not shown in Figures) for supplying the water. A fluid level sensor 118 may be mounted to the housing 108 for determining the level of the water therein. In one configuration, the valve 116 may be one of a directional control valve or shut-off valve or any other valve as per design feasibility and requirement. In another configuration, the reservoir 110 may be integrated within the housing 108 (not shown in Figures).
A compressor unit or a pump 130 is fluidically coupled with the housing 108 and is configured to maintain a vacuum condition or induce an evacuation action within the housing 108. The evacuation action enables air to enter the housing 108 from the ambient surroundings via an air inlet port 122. Further, the evaporator unit 102 includes a porous material 120 disposed within the housing 108, particularly towards a bottom portion 108c of the housing 108. The porous material 120 is configured to divide or split the housing 108 into a first compartment 108a and a second compartment 108b. The first compartment 108a is configured to receive the water, while the second compartment 108b is configured to receive air through the air inlet port 122 configured in the housing 108. In one implementation, as the porous material 120 is mounted towards the bottom portion 108c of the housing 108, the first compartment 108a is configured with a larger volume than the second compartment 108b. In another implementation, the volume of the first compartment 108a and the second compartment 108b may be selected based on the required volume of the water, the type of the evaporator unit 102, a required cooling rate or any other suitable parameter as per feasibility and requirement. The porous material 120 may be a sheet-like structure including a plurality of pores (not shown in Figures). The porous material 120 is mounted above the air inlet port 122 so that the air when routed into the housing 108 passes through the porous material 120 and thereafter fills within the housing 108. The air, when routed to the housing 108 filled with the water, disperses as air bubbles upon passing through the porous material 120. The air bubbles induce turbulent motion or turbulent mixing of water molecules with the air molecules, within the housing 108, wherein interfacial areas of the air bubbles and the turbulent mixing enhance evaporation of the water, thereby converting a portion of the water into water vapors. The water vapors when discharged from the housing 108 via the compressor unit 130 cool the remainder portion of the water to a cooled water, due to evaporative cooling. Further, the air bubbles being characterized by a larger interfacial area, aid in generation of the water vapors. The mechanism employed in the evaporator unit 102 for air bubble enhanced evaporation is further explained in this description.
In one embodiment, the mechanism for air bubble enhanced evaporation of ‘water’ in the evaporator unit 102 is described herein. According to the thermodynamic properties of water, liquid H2O molecules or water molecules evaporate spontaneously under reduced pressure. Meanwhile, the evaporated H2O molecules that escape from the surface carry away the internal energy of the liquid (heat of vaporization, ΔH=40.6 kJ/mol). Thus, the evaporation of water, e.g., at 25° C., cools the remaining liquid into a state of lower temperature under reduced external pressure. Further, the equilibrium vapor pressure of H2O at 10° C. is determined to be 12 mbar. As such, water can be cooled to 10° C. eventually when the external pressure is maintained by a suitable device (a vacuum pump or a compressor) at this pressure. Also, due to the low vapor pressure of water in the refrigeration temperature range, a colossal volumetric flow rate of water vapor is generated. Thus, a matching pressure difference is required to be maintained in order to evacuate the water vapors, leaving behind cold water (cooled refrigerant) for maintaining the required refrigeration. In one implementation, for a vapor compression water chiller at 10° C. with a refrigeration capacity of 10 kW, the chiller is required to evacuate water vapor out of the evaporator at a rate of 25.7 m3/min for maintaining the refrigeration capacity.
Further, the rate of evaporation is typically controlled kinetically. According to the kinetic theory of liquid vaporization, the rate of evaporation dN/dt is given by Eq. 1, as mentioned below.
where:
Further, the heat of vaporization is a thermodynamic bulk property of the liquid, it is anticipated that escaping molecules from the surface only experience the attractive potential from the domain of the liquid phase. Thus, the activation energy Eact in Eq. (1) can be estimated to be half the value of ΔH and is given by 20 kJ/mol for water. Additionally, from Eq. (1), the evaporation rate of water at 300 K under vacuum is calculated to be 3.6×10−2 mol/min, where the liquid-vacuum interface area is chosen to be 200 cm2 and Eact is 20 kJ/mol. Also, since a vapor compression water chiller or refrigeration system with a refrigeration capacity at 1 ton is thermally equivalent to a 5 mol/min evaporation rate of water, a direct pumping scheme on a limited interfacial area cannot be utilized in a practical device. As such, the interfacial area ‘A’ between the liquid and air phases is the only parameter which can be manipulated in Eq. (1). Further, in order to lift the constraints imposed on limited phase boundary areas, air flow is purposely introduced into the housing 108 through the porous material 120. In one implementation, 0.02 mol/s of air is introduced within the housing 108 such that the air mass is dispersed by the porous material 120 into air bubbles. In one implementation, if these bubbles flow through water within is and their diameter is 1 um, the interface area between air bubbles and liquid water is estimated to be 1.2×105 cm2 at any instant.
Further, according to Eq. (1), the air bubbles expand larger under the lower pressure. Thus, lower the pressure maintained in the evaporator unit 102, greater is the size of the air bubble. Moreover, even for moisture-saturated air, the partial pressure of water vapor inside the inflated bubbles will be diminished to one-tenth of its original magnitude. Since the partial pressure of water in this scenario is lower than that in the equilibrated state at 0° C., ΔP in Eq. (1) is a positive definite value at 0° C. This fact implies that air can be directly drawn from the environment without dehumidification and be employed to cool down water all the way to 0° C., as long as the compressor unit 130 maintains the pressure ratio to raise the water pressure from 4.6 mbar to above 1 bar. The compressed air can thus be expelled to the outside world directly. Additionally, the pressure difference across the porous material 216 due to the pumping action on the air phase above the bulk water or the cooled water generates air bubbles spontaneously. The upward flowing of inflated air bubbles and their mutual interactions in the evaporator causes a turbulent motion of the water mass. The turbulence results in efficient mixing of phase boundary between air bubbles and liquid water. The turbulent motion induces a better probability for the high energy molecules inside the liquid phase to reside on the phase boundary surface. This efficient mixing process of air bubbles with liquid mass, which agitates high energy H2O molecules to the interfacial area, is essential to the cooling efficiency of the system 100. The bulk water or the cooled water, left subsequent to the evaporation process and evacuation of the water vapors, is circulated for refrigeration and/or air-conditioning of the enclosure 106.
In an embodiment, the air bubble enhanced evaporation process of the water corresponds to higher air flow pressures within the evaporator unit 102 (for e.g. as illustrated in
The housing 108 further includes an evaporator outlet port 124 mounted to a top portion 108d of the housing 108, for discharging the mixture of the air and the water vapours to ambient environment or surroundings. The evaporator outlet port 124 is preferably positioned on the top portion 108d, as the mixture of the air and the water vapors occupy the top portion 108d. This eases the process of discharge of the mixture of the air and the water vapors from the housing 108. Referring to
Referring back to
In one configuration, the enclosure 106 may be one of a water container unit, a food storage compartment and an indoor space. In one implementation, the system 100 with the enclosure 106 of the water container unit type, corresponds to a water chiller unit, which may be configured with a water storage tank including tap water to be chilled or refrigerated. In another implementation, the system 100 with the enclosure 106 of the food storage compartment type corresponds to a refrigeration unit, which is required to be refrigerated for preserving food products stored therein. In yet another implementation, the system 100 with the enclosure 106 of the indoor space type is an air-conditioning system, which requires the indoor space to be conditioned.
The casing 204 also includes a sparger plate 212 disposed towards the bottom portion 204b of the casing 204, so that the mixture of the air and the water vapors pass through the sparger plate 212 prior to filling the casing 204. The sparger plate 212, similar to the porous material 120, further disperses the mixture of the air and the water molecules. The dispersion generates air bubbles with trapped water molecules inside. The air bubbles along with the water molecules rise up within the casing 204. Further, due to the lower temperature of the casing 204, the water vapors in the air bubbles condense to form liquid water, which settles down on the sparger plate 212 or on the bottom portion 204b. Thus, the water are recycled back to utilize as the refrigerant. For enhancing the condensation process in the condenser unit 202, a heat exchanger (not shown in Figures) may be mounted within the casing 204. In an embodiment, the casing 204 may be filled with a coolant for enhancing the rate of condensation of the water molecules within the casing 204.
A first condenser outlet 218 is positioned on the top portion 204a of the casing 204 for ease of discharging the air to the surroundings, as the air being less dense, floats in the top portion 204a of the casing 204. The casing 204 further includes a second condenser outlet 220 mounted to the casing 204, preferably to the bottom portion 204a of the housing 204. The second condenser outlet 220 is configured to discharge the condensed water from the casing 204 into the evaporator unit 102. The second condenser outlet 220 is coupled to an inlet port 138 of the evaporator unit 102 via a tube 222, which may include a valve (not referenced in Figures), for ensuring recirculation of the water in the system 200. The valve may be communicatively coupled to the control unit. The control unit is configured to operate the valve suitably, for controlling the rate of discharge of the water from the condenser unit 202 to the evaporator unit 102. In one configuration, the tube 222 may extend and connect to the reservoir 110, for recirculating the condensed water into the reservoir 110 (not shown in Figures).
In one configuration, the size and configuration of the conduits or tubes employed in the system 100/200 (for e.g. conduits 112, 132 and 222) are selected based on the flow rate or the desired discharge rate. In an embodiment, the conduits 112, 132 and 222 may be selected as a single joint configuration, to prevent possible loss of flow associated with multiple joints.
In an embodiment, the housing 202, the casing 204, the baffle plates 126 and the porous material 120 are made of stainless-steel material, due to its inherent anti-corrosive properties, thermal conductivity and high strength to weight ratio. Alternatively, the evaporator unit 102, the condenser unit 202, the baffle plates 126 and the porous material 120 can be made of other materials as per feasibility and requirement. In an embodiment, the porous material 120 is porous disk made of stainless-steel grade material.
Thus, various embodiments of the present disclosure provide systems 100/200 for employing water as the refrigerant, without the use of cumbersome equipment, required for maintaining working conditions to use water as the refrigerant.
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| Number | Date | Country |
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| Entry |
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| Partial English Machine Translation: WO2015068874A1. Accessed Oct. 2021. |
| Number | Date | Country | |
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| 20210080134 A1 | Mar 2021 | US |
