Vapor compression system and method

In a method of operating a vapor compression refrigeration system wherein a medium having a given relative humidity is withdrawn from a refrigerated compartment, circulated through an evaporator in heat exchange relation with an evaporator coil, and returned to said compartment, said evaporating coil including an inlet which is in flow communication with a refrigerant expansion device and an outlet which is in flow communication with a compressor, the improvement comprising, supplying a mixture of refrigerant vapor and liquid to the evaporator coil inlet, said mixture including a substantial vapor portion, substantially all of said liquid being converted to vapor as said mixture passes through said evaporator coil, said mixture being supplied to the evaporator coil at a given linear velocity, measured at the evaporator inlet, and the relative amounts of liquid and vapor present in said mixture at said evaporator coil inlet being sufficient to provide efficient heat transfer between said mixture and said air medium along substantially the entire length of said coil, the differential temperature between said coil and said air medium adjacent at least the inlet to said evaporator during at least a portion of a refrigeration cycle being sufficient to substantially maintain said given relative humidity in said medium and thereby substantially eliminate the build-up of frost along substantially the entire length of said evaporator coil.

A vapor compression refrigeration system comprising:

• a compressor for increasing the pressure and temperature of a refrigerant vapor, said compressor having an inlet and an outlet;
• a condenser having an inlet in flow communication with the outlet of said compressor for liquefying pressurized refrigerant vapor received from said compressor;
• an expansion device having a first inlet which, during a cooling mode of operation of said refrigeration system, is in flow communication with an outlet of said condenser for receiving liquid refrigerant from said condenser and vaporizing a substantial portion of the same;
• an evaporator including an evaporating coil having an inlet and an outlet, said evaporating coil being in heat exchange relation with an air medium along substantially the entire length of said coil;
• an evaporator feed line providing flow communication of said expansion device with said evaporating coil inlet;
• a suction line providing flow communication of said evaporating coil outlet with said compressor inlet;
• said expansion device and said evaporator feed line, during a cooling mode of operation of said vapor compression refrigeration system, being sized to provide said evaporating coil inlet with a refrigerant liquid and vapor mixture that includes a substantial vapor portion,
• said evaporating coil being sized to provide said refrigerant liquid and vapor mixture with a linear velocity sufficient to provide efficient heat transfer along substantially the entire length of said coil;
• and,
• a sensor in said suction line operatively associated with said expansion device for regulating the flow of refrigerant from the inlet of said expansion device to the inlet of said evaporating chamber.

A vapor compression refrigeration system comprising:

• a compressor for increasing the pressure and temperature of a refrigerant vapor, said compressor having an inlet and an outlet;
• a condenser having an inlet in flow communication with the outlet of said compressor for liquefying pressurized refrigerant vapor received from said compressor;
• an expansion device which, during a cooling mode of operation of said refrigeration system, is in flow communication with an outlet of said condenser for receiving liquid refrigerant from said condenser and vaporizing a substantial portion of the same, said expansion device including a thermostatic expansion valve having an inlet and an outlet, the outlet of said thermostatic expansion valve being in series flow communication with an inlet to a multifunctional valve which includes an expansion chamber whereby liquid refrigerant supplied to said expansion device undergoes a two-stage expansion;
• an evaporator including an evaporating coil having an inlet and an outlet, said evaporating coil being in a heat exchange relation with an air medium along substantially the entire length of said coil;
• an evaporator feed line providing flow communication of said expansion device with said evaporating coil inlet;
• a suction line providing flow communication of said evaporating coil outlet with said compressor inlet;
• said expansion device and said evaporator feed line, during a cooling mode of operation of said vapor compression refrigeration system, being sized to provide said evaporating coil inlet with a refrigerant liquid and vapor mixture that includes a substantial vapor portion,
• said evaporating coil being sized to provide said refrigerant liquid and vapor mixture with a linear velocity sufficient to provide efficient heat transfer along substantially the entire length of said coil;
• and,
• a sensor in said suction line operatively associated with said expansion device for regulating the flow of refrigerant from the inlet of said expansion device to the inlet of said evaporating chamber.

In a method of operating a vapor compression refrigeration system wherein an evaporator removes heat from a air medium which is passing through said evaporator in heat exchange relation with an evaporator coil in said evaporator, said coil including an inlet which is in flow communication with an expansion device, said evaporator coil also having an outlet which is in flow communication with a compressor, the improvement comprising:

• providing said expansion device with an expansion valve having an outlet which communicates with an inlet to a multi-functional valve which includes an expansion chamber;
• supplying a liquid refrigerant to said expansion device where it undergoes a two-stage series expansion to produce a mixture of refrigerant vapor and liquid which is supplied at a given mass flow rate and at a given linear velocity to the evaporator coil inlet, said mixture including a substantial vapor portion, substantially all of said liquid being converted to vapor as said mixture passes through said evaporator coil, said given linear velocity and the relative amounts of vapor and liquid present in said mixture at said evaporator coil inlet being sufficient to provide efficient heat transfer between said mixture and said medium along substantially the entire length of said coil, whereby the build-up of frost on said evaporator coil is substantially reduced enabling said vapor compression refrigeration system to be operated without requiring a defrosting cycle over a substantially increased number of refrigeration cycles as compared to a conventional vapor compression refrigeration system operating at the same cooling load and evaporating temperature conditions.