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A method and apparatus for maintaining a relatively constant temperature of a working fluid in an evaporator of a refrigeration system by providing a constant volumetric displacement compressor and a heat exchanger for exchanging heat between the high pressure and low pressure portions of a refriger

A method and apparatus for maintaining a relatively constant temperature of a working fluid in an evaporator of a refrigeration system by providing a constant volumetric displacement compressor and a heat exchanger for exchanging heat between the high pressure and low pressure portions of a refrigeration circuit to superheat, and hold substantially constant, the temperature of the refrigerant entering the compressor. In doing this, the pressure of the refrigerant in the low pressure portion of the circuit, including the evaporator, and the mass flow rate of the refrigerant remain substantially constant. As a result, the temperature of the saturated refrigerant in the evaporator remains substantially constant.

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What is claimed is: 1. A refrigeration system comprising: a compressor including an inlet and an outlet; a working fluid present throughout the system, the working fluid capable of being in a mixed liquid/gaseous state; a condenser including an inlet and an outlet, said condenser inlet in fluid com

What is claimed is: 1. A refrigeration system comprising: a compressor including an inlet and an outlet; a working fluid present throughout the system, the working fluid capable of being in a mixed liquid/gaseous state; a condenser including an inlet and an outlet, said condenser inlet in fluid communication with said compressor outlet; a sub-cooler, said sub-cooler having first and second fluid passages, said first passage having an inlet and an outlet, said second passage having an inlet and an outlet, said first passage inlet in fluid communication with said condenser outlet, said first passage and said second passage in a heat exchange relationship; an expansion device having an inlet and an outlet, said expansion device inlet in fluid communication with said sub-cooler first passage outlet; and an evaporator having an inlet and an outlet, said evaporator inlet in fluid communication with said expansion device outlet; said sub-cooler second passage inlet in fluid communication with said evaporator outlet, said second passage outlet in fluid communication with said compressor inlet, the temperature of the working fluid at said second passage outlet being substantially constant and substantially equal to the temperature of the working fluid at said sub-cooler first passage inlet, wherein the mass flow rate of the working fluid is substantially constant and the pressure of the working fluid at said sub-cooler second passage outlet is substantially constant, whereby the pressure and temperature of the working fluid in said evaporator are substantially constant; said sub-cooler further including: a working fluid bypass flow passage, said bypass flow passage having a different length than said second passage, said bypass flow passage in fluid communication with said second passage inlet and outlet; and an apportioning valve fluidly connected to said sub-cooler second passage inlet, said apportioning valve further fluidly responsive to the liquid content of the working fluid connected to said second passage and said bypass flow passage. 2. The refrigeration system of claim 1, wherein the working fluid at said sub-cooler second passage outlet is in a superheated thermodynamic state. 3. The refrigeration system of claim 1, wherein ambient air cools said condenser, and wherein the temperature of the working fluid at said sub-cooler second passage outlet substantially equals the temperature of the ambient air cooling said condenser. 4. The refrigeration system of claim 1, wherein the working fluid in said evaporator is in a two-phase thermodynamic state. 5. The refrigeration system of claim 1, wherein said working fluid comprises a first refrigerant having a boiling point and a second refrigerant having a boiling point, said first refrigerant boiling point different than said second refrigerant boiling point, said first refrigerant being in a substantially liquid state while said second refrigerant is in a two-phase state. 6. The refrigeration system of claim 1, wherein the working fluid at said sub-cooler first passage outlet is in a sub-cooled thermodynamic state. 7. A refrigeration system comprising: a compressor including an inlet and an outlet; a working fluid present throughout the system, the working fluid capable of being in a mixed liquid/gaseous state; a condenser including an inlet and an outlet, said condenser inlet in fluid communication with said compressor outlet; a sub-cooler, said sub-cooler having first and second fluid passages, said first passage having an inlet and an outlet, said second passage having an inlet and an outlet, said first passage inlet in fluid communication with said condenser outlet, said first passage and said second passage in a heat exchange relationship; an expansion device having an inlet and an outlet, said expansion device inlet in fluid communication with said sub-cooler first passage outlet; and an evaporator having an inlet and an outlet, said evaporator inlet in fluid communication with said expansion device outlet; said sub-cooler second passage inlet in fluid communication with said evaporator outlet, said second passage outlet in fluid communication with said compressor inlet, the temperature of the working fluid exiting said second passage outlet being substantially constant and substantially equal to the temperature of the working fluid entering said sub-cooler first passage inlet, wherein the mass flow rate of the working fluid is substantially constant and the pressure of the working fluid exiting said sub-cooler second passage outlet is substantially constant, whereby the pressure and temperature of the working fluid in said evaporator are substantially constant, said sub-cooler further including: a working fluid bypass flow passage, said bypass flow passage longer than said second passage, said bypass flow passage in fluid communication with said second passage inlet and outlet; and a liquid-responsive valve apportioning the flow of working fluid through said second passage and said bypass flow passage in response to the liquid content of the working fluid, said liquid-responsive valve fluidly connected to said sub-cooler second passage inlet and to said second passage and said bypass passage. 8. The refrigeration system of claim 7, said second passage including porous media, said porous media expandable when exposed to a liquid portion of said working fluid, said second passage substantially obstructed by said expanded porous media, wherein substantially all of said working fluid passes through said bypass flow passage when said second passage is substantially obstructed. 9. The refrigeration system of claim 1, wherein said compressor is a constant volumetric displacement compressor. 10. The refrigeration system of claim 1, wherein said compressor is a variable displacement compressor. 11. A method of operating a refrigeration cycle comprising the steps of: compressing a working fluid to a high-pressure working fluid with a compressor, said working fluid capable of being in a mixed liquid/gaseous state; cooling said high-pressure working fluid in a condenser; transferring said high-pressure working fluid from said condenser to an expansion device through a first passage in a heat exchanger; decompressing said high-pressure working fluid to low-pressure working fluid using said expansion device; heating said low-pressure working fluid in an evaporator; transferring said low-pressure working fluid from said evaporator to said compressor through a second passage in said heat exchanger while transferring heat between said high-pressure working fluid and said low-pressure working fluid in said heat exchanger; maintaining the temperature and mass flow rate of said low-pressure working fluid exiting said heat exchanger substantially constant, thereby maintaining the pressure and temperature of said low-pressure working fluid in said evaporator substantially constant, and further including the step of diverting at least a portion of the working fluid entering said second passage into a bypass passage as a function of whether the working fluid is in a liquid state, a gaseous state or a liquid/gaseous state, to thereby transfer more heat to said working fluid in said bypass passage than would be transferred to said working fluid in said second passage. 12. A heat exchanger, comprising: a housing, including: an inlet; an outlet; a first flow path in fluid communication with said inlet and said outlet; a second flow path in fluid communication with said inlet and said outlet; and porous media in fluid communication with said inlet, said porous media expandable when exposed to a working fluid, said working fluid substantially impeded from flowing through said first flow path when said media has expanded, whereby substantially all of said working fluid will flow through said second flow path to said outlet when said working fluid is substantially impeded from flowing through said first flow path. 13. The heat exchanger of claim 12, said porous media expandable when exposed to a working fluid in liquid form. 14. The heat exchanger of claim 12, said first flow path including a chamber, said porous media contained within said chamber, said porous media expandable to substantially fill said chamber. 15. The heat exchanger of claim 12, said second flow path including a conduit, the length of said conduit selected to control the thermodynamic properties of said working fluid exiting said heat exchanger through said outlet. 16. The heat exchanger of claim 12, said heat exchanger further including a heat transfer fluid in said housing, said heat transfer fluid and said working fluid in a heat transfer relationship. 17. A valve, comprising: a housing including: at least one inlet, at least one outlet, a primary flow path in fluid communication with said at least one inlet and said at least one outlet; a bypass flow path in fluid communication with said at least one inlet and said at least one outlet; and porous media, whereby liquid portions of a working fluid entering said housing through said at least one inlet is trapped by said porous media, said porous media expanded by said liquid portions, said primary flow path substantially obstructed by said porous media when said porous media expands, whereby said fluid will flow substantially through said bypass to said at least one outlet. 18. The valve of claim 17, said primary flow path including a chamber, said porous media contained within said chamber, said porous media expandable to substantially fill said chamber. 19. The valve of claim 17, wherein said bypass flow path includes a conduit, said conduit extending into a heat exchanger, wherein working fluid passing through said conduit is in a heat exchange relationship with said heat exchanger. 20. The heat exchanger of claim 19, wherein the length of said conduit is selected to control the thermodynamic properties of said working fluid exiting through said at least one outlet.