Refrigeration is the transfer of heat from a lower temperature region to a higher temperature region. The most common refrigeration cycle-used in home refrigerators-is the vapor-compression refrigeration cycle. This cycle has four components, as seen in Figure 1: 

• Compressor
• Condenser Coil
• Expansion Valve
• Evaporator Coil

Figure 1: Basic Refrigeration Cycle

The beginning of the refrigeration cycle starts at Point 1, as seen lower right in Figure 1. At this step, the refrigerant in the system is saturated-or a superheated vapor-and has a low pressure. This low-pressure refrigerant in the suction line is then driven through the compressor to Point 2, upper right on the diagram.

The compressor, shown in Figure 1, compresses the saturated vapor, increasing the pressure and temperature, turning it into a superheated vapor.

Next, the superheated vapor flows through the condenser coil. There, two processes occur: 1) the refrigerant is condensed, or changes from a vapor to a liquid, and 2) the refrigerant is subcooled from its superheated state. The cooler refrigerant is now present as 100% liquid in the liquid line at Point 3, upper left in Figure 1.

After the refrigerant passes through the expansion valve, it takes the form of a mixture - consisting of 75% liquid and 25% vapor. This mixture now has a temperature lower than the refrigerated space. The expansion valve controls the flow of the refrigerant to the evaporator coil.

Finally, the liquid/vapor mixture enters the evaporator coil, as seen at Point 4, lower left in Figure 1. Here the mixture completely evaporates-changing from a liquid to a gas-by absorbing heat from the refrigerated space. The refrigerant then exits the evaporator coil as a saturated vapor and reenters the compressor, completing the cycle. In a home refrigerator, this process keeps food cold.

CONCLUSION:
One of the many industries using brazing is the refrigeration industry. This article describing the basic refrigeration cycle is Part 1 of our two-part series on brazing for the refrigeration industry. Join us for Part 2 as we highlight proper brazing methods and correct brazing alloys for refrigeration.

Questions about brazing? Contact us for further assistance. For more information on HVAC/R brazing, see our blogs and website. For detailed questions regarding specific applications, please call Lucas Milhaupt's Technical Department at 800.558.3856.

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