A defrost system is disclosed that includes a cooling device disposed in a freezer, a heat exchanger pipe leading into a casing, a drain receiver unit; a refrigerating device for cooling and liquefying CO.sub.2 refrigerant; a refrigerant circuit for permitting the CO.sub.2 refrigerant to circulate to the heat exchanger pipe; a defrost circuit branched from the heat exchanger pipe forming a CO.sub.2 circulation path with the heat exchanger pipe; an on-off valve so that the CO.sub.2 circulation path becomes a closed circuit; a pressure adjusting unit for adjusting the pressure of the CO.sub.2 refrigerant; and a first heat exchanger unit for heating the CO.sub.2 refrigerant circulating with brine, disposed below the cooling device to which the defrost circuit and a first brine circuit in which brine, a first heating medium, circulates, are led, in which the CO.sub.2 refrigerant naturally circulates in the closed circuit when defrosting by a thermosiphon effect.

Surged vapor compression heat transfer systems, devices, and methods are disclosed having refrigerant phase separators that generate at least one surge of vapor phase refrigerant into the inlet of an evaporator after the initial cool-down of an on cycle of the compressor. This surge of vapor phase refrigerant, having a higher temperature than the liquid phase refrigerant, increases the temperature of the evaporator inlet, thus reducing frost build up in relation to conventional refrigeration systems lacking a surged input of vapor phase refrigerant to the evaporator.

A method of defrosting a transcritical vapor compression system having a compressor for compressing a refrigerant, a first heat exchanger for cooling the refrigerant during a cooling mode, an expansion valve for decreasing the pressure of the refrigerant, and a second heat exchanger for cooling a space during the cooling mode. The method includes attaining a superheated refrigerant condition in a defrost mode of the transcritical vapor compression system and defrosting the second heat exchanger in the defrost mode by directing the superheated refrigerant to the second heat exchanger without bypassing the first heat exchanger.

A sublimation defrost system for a refrigeration apparatus including: a cooling device in a freezer, and includes a casing containing a heat exchanger pipe; a refrigerating device for cooling and liquefying a CO.sub.2 refrigerant; and a refrigerant circuit connected to the heat exchanger pipe permitting the cooled and liquefied CO.sub.2 refrigerant to circulate. The defrost system includes: a dehumidifier device; a CO.sub.2 circulation path in the heat exchanger pipe, an on-off valve in the heat exchanger; a circulating unit for the CO.sub.2 refrigerant; a first heat exchanger part exchanging heat between a brine as a first heating medium and the circulating CO.sub.2 refrigerant; and a pressure adjusting unit for the circulating CO.sub.2 refrigerant during defrosting so that a condensing temperature of the CO.sub.2 refrigerant becomes equal to or lower than a freezing point of a water vapor in the freezer inner air without a drain receiving unit.

Refrigeration systems and refrigerator appliances are provided. A refrigeration system includes a compressor for compressing a refrigerant, a first evaporator, and a second evaporator. The refrigeration system further includes a conduit for flowing the refrigerant through one of the first evaporator or the second evaporator, the conduit configured around the other of the first evaporator or the second evaporator such that heat exchange occurs between the refrigerant flowing through the conduit and the other of the first evaporator or the second evaporator.

Disclosed are a refrigerator cooling system and a method for defrosting a refrigerator. The refrigerator cooling system includes a refrigerant circulation flow path provided with a compressor, a condenser, a throttling device and an evaporator. The throttling device has a throttling working mode for cooling and a defrosting working mode not used for cooling. The throttling working mode and the defrosting working mode are switched with each other. The condenser has a first heat release mode corresponding to the throttling working mode and a second heat release mode corresponding to the defrosting working mode, and a heat release amount of a refrigerant flowing through the condenser in the second heat release mode is lower than a heat release amount of the refrigerant flowing through the condenser in the first heat release mode.