Household refrigerators and most refrigeration appliances operate using a vapor-compression refrigeration cycle that consists of main components: (1) compressor, (2) condenser, (3) expansion valve, and (4) evaporator. This closed-loop cycle continuously circulates the refrigerant, transferring heat from the inside of the refrigerator to the outside.
Additional components may be present depending on the refrigerator design and refrigerant used, such as filters, oil separator, valves and control circuits operated mechanically or electronically by a number of thermostats and heat sensors.
The Basic Principle of Refrigeration:
When we add heat to a liquid under constant pressure, it reaches a certain temperature where it begins to transform into a gas. This temperature is the evaporation temperature. Similarly, when we remove heat from this gas, it reaches a certain temperature, and begins to transform back into a liquid at this temperature, which is the condensation temperature, and this also occurs under a constant pressure.
A simple everyday example is water. Water changes from a liquid to vapor when we add heat, gradually reaching its evaporation temperature. When we remove heat from the vapor, it starts to condense back into a liquid at its condensation temperature. This occurs under constant pressure, which is atmospheric pressure.
The refrigeration cycle applies this principle using a refrigerant, which absorbs heat from inside the refrigerator, evaporating into a gas. The compressor pressurizes the refrigerant gas, increasing its temperature. Then, the hot, high-pressure refrigerant gas releases heat to the surrounding air in the condenser, condensing into a liquid. Afterward, the liquid refrigerant passes through the expansion valve, decreasing its pressure and temperature. The cold, low-pressure refrigerant liquid absorbs heat from the inside of the refrigerator, evaporating back into a gas.
By manipulating the pressures applied to the refrigerant, we can achieve the desired evaporation and condensation temperatures, effectively cooling the refrigerator.
What is a Refrigerant?
Refrigerants are substances used in the compression refrigeration cycle in refrigeration and air conditioning systems to absorb heat and transfer it to another location. Refrigerants are essential for creating and maintaining temperatures below or above freezing, depending on the desired application.
The world of refrigerants is vast and diverse, encompassing a wide range of substances with varying properties. These refrigerants differ in their ability to absorb and release heat, their operating pressures, their physical and chemical characteristics, their interaction with metals, their toxicity, and their environmental impact. A crucial factor in selecting the appropriate refrigerant is its evaporation and condensation temperatures. These temperatures determine the refrigerant’s effectiveness and efficiency in absorbing and releasing heat, thereby influencing its overall cooling performance.
How the Compression Refrigeration Cycle Works
- The compressor pressurizes the refrigerant gas to the appropriate evaporation pressure.
- The high-pressure refrigerant gas flows through the pipes of the cycle to the condenser.
- At the condenser, the refrigerant starts to condense and changes from a gas to a liquid.
- This occurs by dissipating or releasing heat to the outside through a large heat exchange surface exposed to the outside air or a smaller surface that transfers heat using a fan.
- This liquid passes through the pipes to the expansion valve or capillary tube.
- At the end of this valve, the refrigerant liquid drops in pressure to the appropriate evaporation pressure. It then enters the evaporator inside the refrigeration chamber.
- Inside the refrigeration chamber, heat is drawn from the inside through the cooling surface to the refrigerant liquid.
- The refrigerant liquid gradually turns into vapor at the same pressure. It carries this heat towards the compressor to complete the cycle.
- This cycle continues to work, transferring heat out of the refrigeration chamber until the desired temperature is reached.
- This temperature is sensed by a thermostat that sends a signal to the control circuit which shuts off the compressor when the air reaches the desired temperature.
- The compression refrigeration cycle continues to work again when the temperature is rises above the required limit.
Conclusion
Refrigerators, cooler and air conditioners differ in their design and shape based on the cooling method, temperature desired, cooling efficiency, control method, and displays. However, the principle of refrigeration using the compression refrigeration cycle is the same.