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A representative pressure–volume diagram for a refrigeration cycle. Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), [1] in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles.
A two stage Peltier cooler can achieve around -30°C, -75°C with three stages, -85°C with four stages, -100°C with six stages, and -123°C with seven stages. Refrigeration power and efficiency are low but Peltier coolers can be small, for small cooling loads resulting in overall low power consumption for a Peltier cooler with three stages.
Common absorption refrigerators use a refrigerant with a very low boiling point (less than −18 °C (0 °F)) just like compressor refrigerators.Compression refrigerators typically use an HCFC or HFC, while absorption refrigerators typically use ammonia or water and need at least a second fluid able to absorb the coolant, the absorbent, respectively water (for ammonia) or brine (for water).
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. [1] A heat pump is a mechanical system that transmits heat from one location (the "source") at a certain temperature to another location (the "sink" or "heat sink") at a higher temperature. [2]
This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.
Class 1: This class includes refrigerants that cool by phase change (typically boiling), using the refrigerant's latent heat. Class 2: These refrigerants cool by temperature change or 'sensible heat', the quantity of heat being the specific heat capacity x the temperature change. They are air, calcium chloride brine, sodium chloride brine ...
Leaving the freezer door open too long is probably the most common. A worn or damaged gasket (the door seal) will allow warm air in and cold air to escape, contributing to freezer frost.
The material is placed in thermal contact with the environment to be refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q). Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle can restart.