FIELD OF THE INVENTION
The invention relates to system and method of mechanical compression refrigeration. In particular, the present invention discloses the use of a two-phase ejector to improve efficiency and stability of mechanical compression refrigeration system.
BACKGROUND OF THE INVENTION
In recent years, technological advancements in the field of equipment optimization and controls have substantially reduced energy consumption. At the same time, the demand for increased comfort (for example, heating and air-conditioning) or production of goods (for example, Agro-food industry), however, undermines these achievements by giving rise to demands for additional energy consumption. As a result, the overall costs relating to energy consumption increase.
Estimations by research carried out by Natural Resources Canada indicate that ten percent of total energy consumption in commercial, institutional and industrial activities relates to refrigeration. Refrigeration, or more generally, air conditioning, are no longer an option but a requirement for daily consumptions, given the increasing demand from consumers.
Currently, one of the solutions most investigated in improving energy efficiency in refrigeration involves the use of an ejector which may be integrated into conventional refrigeration systems as internal components in order to form hybrid cycles and improve performance. A number of these options are being considered in the current research (for example, cascades, hybrids, subcooling agents, ejecto-compression or ejecto-absorption).
Some of these options, such as cascade and hybrid configurations, have a good potential for performance improvement and have been studied theoretically and experimentally at CanmetENERGY. They are typically suitable for low temperatures and medium to large capacities.
The refrigeration systems most currently used are based on mechanical compression. Electrically driven compressors are the main components in such systems. Decent performance is generally obtained in such systems, which explains the popularity of this technology. However, low temperature refrigeration or heat pumping in cold conditions or air conditioning in a hot environment imposes a heavy load on the electrical grid so that innovative ways of increasing efficiency and decreasing energy consumption are sought.
Other than ejectors, other technologies based on heat activation (i.e. absorption, adsorption and chemical heat pumps) may also be available. However, they are complex, bulky and are not suitable alternatives to mechanical compression.
Mechanical based compression refrigeration becomes increasingly complex and consumes increasingly more electricity (noble energy) at high and/or low temperature working conditions.
Therefore, there is the need for an efficient mechanical compression refrigeration system.
SUMMARY OF THE INVENTION
The objective of the present invention is to enhance the efficiency of the existing refrigeration cycles by assisting the compressor in a refrigeration system with a two-phase ejector activated by potential energy and available internal heat recovery.
According to one aspect of the invention, there is provided a refrigeration system, comprising:
- a metering device for controlling flow of a refrigerant,
- an evaporator,
- means for supplying the refrigerant from the metering device into the evaporator wherein the refrigerant evaporates into vapor,
- a two-phase ejector comprising means defining a liquid chamber having a liquid inlet, means defining a vapor chamber having a vapor inlet, and an outlet discharging a two-phase vapor-liquid refrigerant stream,
- means for supplying the vapor from the evaporator into the vapor inlet of the two-phase ejector,
- a flash tank compound separator,
- means for supplying the refrigerant from the two-phase ejector into the flash tank compound separator wherein the refrigerant separates into two phases,
- a compressor,
- means for supplying the refrigerant from the flash tank compound separator into the compressor wherein the refrigerant compresses,
- a condenser,
- means for supplying the refrigerant from the compressor into the condenser wherein the refrigerant condenses,
- a receiver,
- means for supplying the refrigerant from the condenser to the receiver,
- means for supplying the refrigerant from the receiver to the liquid inlet of the two-phase ejector,
- means for supplying the refrigerant from the receiver to the metering device and then into the evaporator to start another cycle through the system,
- means for supplying the refrigerant from the flash tank compound separator into a pump where the pressure of the refrigerant is regulated,
- means for supplying the refrigerant from the pump into the receiver,
- wherein the two-phase ejector then draws vapor from the evaporator lifting its pressure to an intermediate level when activated a mixture of condensate from the condenser and subcooled refrigerant fed by the pump, and
- wherein the pressure of the liquid inlet of the two-phase ejector is controlled by the pump in accordance with the operating conditions of the compressor.
According to another aspect of the invention, there is provided a refrigeration system, comprising:
- a metering device for controlling flow of a refrigerant,
- an evaporator,
- means for supplying the refrigerant from the metering device into the evaporator wherein the refrigerant evaporates into vapor,
- a two-phase ejector comprising means defining a liquid chamber having a liquid inlet, means defining a vapor chamber having a vapor inlet, and an outlet discharging a two-phase vapor-liquid refrigerant stream,
- means for supplying the vapor from the evaporator into the vapor inlet of the two-phase ejector,
- a flash tank compound separator,
- means for supplying the refrigerant from the two-phase ejector into the flash tank compound separator wherein the refrigerant separates into two phases,
- a compressor,
- means for supplying the refrigerant from the flash tank compound separator into the compressor wherein the refrigerant compresses,
- a condenser,
- means for supplying the refrigerant from the compressor into the condenser wherein the refrigerant condenses,
- a heat exchanger,
- means for supplying the refrigerant from the condenser to the heat exchanger,
- means for supplying the refrigerant from the heat exchanger to the liquid inlet of the two-phase ejector,
- means for supplying the refrigerant from the heat exchanger to the metering device where the pressure and temperature of the refrigerant decrease and then into the evaporator to start another cycle through the system,
- wherein the heat exchanger simultaneously increases condensate subcooling at the inlet of metering device and decreases motive liquid subcooling at the liquid inlet of two-phase ejector,
- means for supplying the refrigerant from the flash tank compound separator into a pump where the pressure of the refrigerant is regulated,
- means for supplying the refrigerant from the pump into the heat exchanger,
- wherein the two-phase ejector then draws vapor from the evaporator lifting its pressure to an intermediate level when activated a mixture of condensate from the condenser and subcooled refrigerant fed by the pump, and
- wherein the pressure of the liquid inlet of the two-phase ejector is controlled by the pump in accordance with the operating conditions of the compressor.
According to a further aspect of the invention, there is provided a refrigeration system, comprising:
- a metering device for controlling flow of a refrigerant,
- an evaporator,
- means for supplying the refrigerant from the metering device into the evaporator wherein the refrigerant evaporates into vapor,
- a two-phase ejector comprising means defining a liquid chamber having a liquid inlet, means defining a vapor chamber having a vapor inlet, and an outlet discharging a two-phase vapor-liquid refrigerant stream,
- means for supplying the vapor from the evaporator into the vapor inlet of the two-phase ejector,
- a flash tank compound separator, means for supplying the refrigerant from the two-phase ejector into the flash tank compound separator wherein the refrigerant separates into two phases,
- a compressor,
- means for supplying the refrigerant from the flash tank compound separator into the compressor wherein the refrigerant compresses,
- a condenser,
- means for supplying the refrigerant from the compressor into the condenser wherein the refrigerant condenses,
- a mixing junction,
- means for supplying the refrigerant from the condenser to the mixing junction,
- means for supplying the refrigerant from the mixing junction to the liquid inlet of the two-phase ejector,
- means for supplying the refrigerant from the flash tank compound separator to the metering device where the pressure and temperature of the refrigerant decrease and then into the evaporator to start another cycle through the system,
- means for supplying the refrigerant from the flash tank compound separator into a pump,
- means for supplying the refrigerant from the pump into the mixing junction,
- wherein the two-phase ejector then draws vapor from the evaporator lifting its pressure to an intermediate level when activated a mixture of condensate from the condenser and subcooled refrigerant fed by the pump, and
- wherein the pressure of the liquid inlet of the two-phase ejector is controlled by the pump in accordance with the operating conditions of the compressor.
According to one aspect of the invention, there is provided a refrigeration system, comprising:
- a metering device for controlling flow of a refrigerant,
- an evaporator,
- means for supplying the refrigerant from the metering device into the evaporator wherein the refrigerant evaporates into vapor,
- a two-phase ejector comprising means defining a liquid chamber having a liquid inlet, means defining a vapor chamber having a vapor inlet, and an outlet discharging a two-phase vapor-liquid refrigerant stream,
- means for supplying the vapor from the evaporator into the vapor inlet of the two-phase ejector,
- a flash tank compound separator,
- means for supplying the refrigerant from the two-phase ejector into the flash tank compound separator wherein the refrigerant separates into two phases,
- a compressor,
- means for supplying the refrigerant from the flash tank compound separator into the compressor wherein the refrigerant compresses,
- a condenser,
- means for supplying the refrigerant from the compressor into the condenser wherein the refrigerant condenses,
- a heat exchanger,
- means for supplying the refrigerant from the condenser to the heat exchanger,
- means for supplying the refrigerant from the compressor to the heat exchanger,
- a first valve for controlling the supply of the refrigerant from the compressor to the condenser and a second valve for controlling the supply of the refrigerant from the compressor to the heat exchanger;
- wherein by controlling and adjusting the first and/or the second valve, the heat exchanger transfers part of condensation heat of the compressed vapor to subcooled compressed liquid circulated by pump to the two-phase ejector,
- means for supplying the refrigerant from the heat exchanger to the liquid inlet of the two-phase ejector,
- means for supplying the refrigerant from the heat exchanger to the metering device where the pressure and temperature of the refrigerant decrease and then into the evaporator to start another cycle through the system,
- wherein the heat exchanger simultaneously increases condensate subcooling at the inlet of metering device and decreases motive liquid subcooling at the liquid inlet of two-phase ejector,
- means for supplying the refrigerant from the flash tank compound separator into a pump where the pressure of the refrigerant is regulated,
- means for supplying the refrigerant from the pump into the heat exchanger,
- wherein the two-phase ejector then draws vapor from the evaporator lifting its pressure to an intermediate level when activated a mixture of condensate from the condenser and subcooled refrigerant fed by the pump, and
- wherein the pressure of the liquid inlet of the two-phase ejector is controlled by the pump in accordance with the operating conditions of the compressor.
According to one aspect of the invention, there is provided a refrigeration system, comprising:
- a metering device for controlling flow of a refrigerant,
- an evaporator,
- means for supplying the refrigerant from the metering device into the evaporator wherein the refrigerant evaporates into vapor,
- a two-phase ejector comprising means defining a liquid chamber having a liquid inlet, means defining a vapor chamber having a vapor inlet, and an outlet discharging a two-phase vapor-liquid refrigerant stream,
- means for supplying the vapor from the evaporator into the vapor inlet of the two-phase ejector,
- a flash tank compound separator,
- means for supplying the refrigerant from the two-phase ejector into the flash tank compound separator wherein the refrigerant separates into two phases,
- a compressor,
- means for supplying the refrigerant from the flash tank compound separator into the compressor wherein the refrigerant compresses,
- a condenser,
- means for supplying the refrigerant from the compressor into the condenser wherein the refrigerant condenses,
- a direct contact condenser,
- means for supplying the refrigerant from the condenser to the direct contact condenser,
- means for supplying the refrigerant from the compressor to the direct contact condenser,
- a first valve for controlling the supply of the refrigerant from the compressor to the condenser and a second valve for controlling the supply of the refrigerant from the compressor to the direct contact condenser;
- wherein by controlling and adjusting the first and/or the second valve, the direct contact condenser transfers part of condensation heat of the compressed vapor to subcooled compressed liquid circulated by pump to the two-phase ejector,
- means for supplying the refrigerant from the direct contact condenser to the liquid inlet of the two-phase ejector,
- means for supplying the refrigerant from the flash tank compound separator to the metering device where the pressure and temperature of the refrigerant decrease and then into the evaporator to start another cycle through the system,
- means for supplying the refrigerant from the flash tank compound separator into a pump where the pressure of the refrigerant is regulated,
- means for supplying the refrigerant from the pump into the direct contact condenser,
- wherein the two-phase ejector then draws vapor from the evaporator lifting its pressure to an intermediate level when activated a mixture of condensate from the condenser and subcooled refrigerant fed by the pump, and
- wherein the pressure of the liquid inlet of the two-phase ejector is controlled by the pump in accordance with the operating conditions of the compressor.
Preferably, the metering device is a thermal expansion valve, or a capillary tube.
Preferably, refrigerant used in the refrigeration system is carbon dioxide.
Other features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
By way of example only, preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic representation of an embodiment of a conventional refrigeration cycle (prior art);
FIG. 2 is a schematic representation of an embodiment of a two-phase ejector assisted mechanical refrigeration cycle according to the present invention;
FIG. 3 is a schematic representation of a second embodiment of a two-phase ejector assisted mechanical refrigeration cycle according to the present invention;
FIG. 4 is a schematic representation of a third embodiment of a two-phase ejector assisted mechanical refrigeration cycle according to the present invention;
FIG. 5 is a schematic representation of a fourth embodiment of a two-phase ejector assisted mechanical refrigeration cycle according to the present invention; and
FIG. 6 is a schematic representation of a fifth embodiment of a two-phase ejector assisted mechanical refrigeration cycle according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Mechanical refrigeration is the utilization of mechanical components arranged in a “refrigeration system” for the purpose of transferring heat. The refrigeration cycle is based on the well-known physical principle that a liquid evaporating into a gas extracts heat from the surrounding area. The refrigeration cycle is to remove unwanted heat from one place and discharge it into another. To accomplish this, the refrigerant is pumped through a closed refrigeration system.
Refrigerants are chemical compounds that are alternately compressed and condensed into a liquid and then permitted to expand and to evaporate into a vapor or gas as they are pumped through the mechanical refrigeration system to cycle. Refrigerants evaporate at much lower temperatures than water, which permits them to extract heat at lower temperature than water.
Two different pressures exist in the cycle—the evaporating or low pressure in the “low side,” and the condensing, or high pressure, in the “high side.” These pressure areas are separated by two dividing points: one is the metering device where the refrigerant flow is controlled, and the other is at the compressor, where vapor is compressed.
Referring to FIG. 1, a schematic representation of an embodiment of an existing conventional refrigeration cycle system 1, a metering device 5 may be a thermal expansion valve, a capillary tube, or any other device to control the flow of refrigerant into an evaporator 6, or cooling coil, as a low-pressure, low-temperature refrigerant. The expanding refrigerant evaporates as it goes through evaporator 6, where it removes the heat from the substance or space in which evaporator 6 is located. Heat travels from the warmer substance to evaporator 6 cooled by the evaporation of the refrigerant within the system, causing the refrigerant to evaporate to a vapor. This low-pressure, low-temperature vapor is then drawn to a compressor 7 where the low-temperature vapor is compressed into a high-temperature, high-pressure vapor. Compressor 7 then discharges the high-temperature, high-pressure vapor to a condenser 8. The high-temperature, high-pressure refrigerant vapor is at a higher temperature than the air or water passing across the condenser, therefore heat is transferred to the cooler air or water. As heat is removed from the vapor, the vapor is condensed into a liquid, at a high-pressure. The liquid refrigerant travels to metering device 5 where it passes through a small opening or orifice where a drop in pressure and temperature occurs, and then it enters into evaporator 6. As the refrigerant makes its way into the large opening of the evaporator tubing or coil, it vaporizes, ready to start another cycle through the system.
An ejector is a device in which two streams flow in intimate contact at relatively high velocity such that the driving stream transfers momentum to the driven stream, thereby increasing the stagnation pressure of the driven stream. The two streams are accelerated in separate nozzles to approximately the same pressure before being brought together in a mixing section and the mixed stream is decelerated in a diffuser. An ejector can be used to generate isentropic condition in the throttling process. Because the phase of the working fluid in the diffuser is a two phase, an ejector is usually named as two-phase ejector.
In the present invention, two-phase ejector(s) activated by pressurized refrigerant are used and strategically located in the cycle of the refrigeration system so as to provide part of the compression effect required for the refrigeration load, thereby relieving the conventional mechanical compressor from part of its duty, hence increasing the overall cycle efficiency of the refrigeration system.
The two-phase ejectors are pressure-activated. In a mechanical refrigeration cycle, the two-phase ejectors can recover internal energy otherwise wasted, in order to produce a modest compression effect, a pseudo-isentropic expansion and an appreciable refrigerant circulatory effect. The two-phase ejectors can be integrated therefore in a mechanical compression system to produce improved cooling or refrigeration of the conventional cycle.
Unlike conventional mechanical compressors, the two-phase ejectors are static mechanical components; they are compact, flexible, simple and low cost.
In its function, the two-phase ejector contributes to the overall compression so that conventional mechanical compressor's work is reduced, and its efficiency improved, resulting in overall improved cycle performance.
Because two-phase ejectors are static and compact components, modification to the conventional refrigeration cycle to incorporate the two-phase ejectors introduces no major and/or costly changes but results in substantial performance gains.
According to the present invention, the two-phase ejector does not completely replace the conventional mechanical compressor but serves to build a new cycle arrangement in which the conventional mechanical compressor and the two-phase ejector can fulfill their respective duties of fluid circulation and compression without or with minimal interference.
According to the present invention, the two-phase ejector is placed in series with the conventional mechanical compressor to the suction of which it feeds refrigerant drawn from the evaporator, but it is activated independently from the conventional mechanical compressor.
The two-phase ejector and conventional mechanical compressor assembly forms a hybrid system which uses a common refrigerant to both components.
In existing prior art refrigeration systems, either:
- (1) the two-phase ejector completely replaces the conventional mechanical compressor which is then replaced by a pump; or
- (2) the two-phase ejector and the conventional mechanical compressor are arranged in series in such a way that the ejector is activated by the conventional mechanical compressor via the condensate and in turn the two-phase ejector feeds the conventional mechanical compressor in vapor via the evaporator.
In these types of existing setups, it is obvious that both the two-phase ejector and the conventional mechanical compressor are strongly coupled, therefore preventing their stable operation.
In contrast, the refrigeration cycle options described in the present invention hybrid the two-phase ejector and conventional mechanical compressor configurations. Their main features are summarized below.
In FIG. 2, an embodiment of a two-phase ejector assisted mechanical refrigeration system 10 consists of a cycle in which a two-phase ejector 11 and a flash tank compound separator (or a second reservoir) 12 are positioned sequentially between a receiver (or the first fluid distribution reservoir) 9 and a compressor 7. Part of the liquid in receiver 9 is expanded through metering device 5 to the conditions of evaporator 6. The two-phase ejector 11 draws vapor from evaporator 6 lifting its pressure to an intermediate level when activated a mixture of condensate and subcooled refrigerant fed by a pressure pump 13. Therefore, adequate subcooling of the two-phase ejector feed and the evaporator can be adjusted for optimal operation. This combination minimizes the detrimental coupling of two-phase ejector 11 and compressor 7 and results in improved cycle stability and performance. The two-phase ejector 11 and compressor 7 are in series and are always both in operation. The system uses one refrigerant and is suitable for a wide range of applications and capacities.
FIG. 3 depicts another embodiment of a two-phase ejector assisted mechanical refrigeration system 20, which is a variant of system 10 as described in FIG. 2.
In FIG. 3, receiver (or the first fluid distribution reservoir) 9 in FIG. 2 is replaced by a compact heat exchanger 21, which allows for more operational flexibility. This measure simultaneously increases condensate subcooling at the inlet of metering device (expansion valve) 5 and decreases motive liquid subcooling at the primary inlet of two-phase ejector 11, which improve the overall cycle performance. In addition, the primary inlet pressure of two-phase ejector 11 is controlled by pump 13 independently of the pressure of condenser 8.
FIG. 4 depicts another embodiment of a two-phase ejector assisted mechanical refrigeration system 30, which is a variant of system 10 and 20 as depicted in FIGS. 2 and 3, respectively.
In FIG. 4, evaporator 6 is fed by the refrigerant from flash tank compound separator (or a second reservoir) 12 at intermediate pressure; and receiver (or the first fluid distribution reservoir) 9 in FIG. 2 is replaced by a mixing junction 31. This configuration simplifies the cycle of the refrigeration system further by the removal of a vessel, therefore reducing expansion losses in evaporator 6.
FIG. 5 represents an additional embodiment of a two-phase ejector assisted mechanical refrigeration system 40 wherein the condenser 8 is partially replaced by a heat exchanger 21, achieved by controlling valves 42 (valve 42a for controlling the supply of the refrigerant from compressor 7 to condenser 8 and/or valve 42b for controlling the supply of the refrigerant from compressor 7 to heat exchanger 21) and depend on the expansion extent and quality in the nozzle of two-phase ejector 11; the other components remaining unchanged.
In this case, heat exchanger 21 transfers a variable part of the condensation heat of the compressed vapor to the highly subcooled compressed liquid circulated by pump 13 to two-phase ejector 11. This process has, inter alia, the following advantages:
- By condensing part of the compression vapor, the size of condenser 8 will be substantially reduced;
- The two-phase ejector 11 subcooled inlet conditions can be adjusted to maximize its efficiency;
- The level of heat rejection can be varied to maximize the efficiency of compressor 7 and maximize overall performance of the system, particularly when condenser 8 is less needed; and
- Where condenser 8 is fully used, two-stage compressor and multi-circuit heat exchanger may be contemplated to divert only minimal stream to condenser 8 in order for the compressor 7 to operate with minimal consumption.
FIG. 6 depicts another embodiment of a two-phase ejector assisted mechanical refrigeration system 50, which is a variant of system 40 as described in FIG. 5.
In FIG. 6, the heat exchanger 21 in FIG. 5 is replaced by a more efficient and direct contact condenser 55 and an evaporator feed from intermediate pressure flash tank compound separator (or a second reservoir) 12 to further reduce expansion losses.
Any of the configurations as described above may use any of the refrigerants currently available.
Preferably, carbon dioxide (CO2) is more suitable for the intended two-phase ejector refrigeration/heat pump operation.
Preferably, the metering device is a thermal expansion valve, or a capillary tube.
Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments and modifications are possible. Therefore, the scope should not be limited by the preferred embodiments set forth in the afore-mentioned illustrative examples but should be given the broadest interpretation consistent with the description as a whole.
Patent Application
20220026114
