How does a Fridge Work?

Refrigerators are machines that allow us to store the food we put in it for a long time, thanks to cooling systems. It has become used in any environments in our lives, from houses to offices and even automobiles. Although of different sizes, they all have the same principle of operation. Thanks to heat transfer, hot air from the cabin is released outside. Cooling in refrigerators is carried out using thermodynamics, which is one of the basic laws of physics.

When an object is placed in the refrigerator, the object cools down because its temperature is higher than the environment. The temperature on it is mixed with the cold air in the refrigerator. This heat exchange forms the basis of the principle of operation of refrigerators. We encounter resistance to open the refrigerator. One of the reasons for this is that the pressure in the refrigerator, which is cold inside, is lower than the pressure outside. This creates resistance. In addition, the magnets inside the rubber band next to the covers that provide insulation make it easier to close the lids.

 

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2.How Refrigerators Work

  • There is a special fluid (such as hydrofluorocarbons) that moves through the refrigerator’s circulatory system. This substance is constantly rotated in the system with the help of a compressor. This fluid substance is present in gas or liquid form depending on the temperature of the environment. It has the ability to transfer heat. Meanwhile, it takes the heat from inside the refrigerator and transfers it into the air outside. Thus, the air inside loses heat and cools until it drops to the set temperature.
  • The compressor (usually located in the lower back of the refrigerators) compresses the refrigerant into the condenser with pressure. In other words, the refrigerant is transmitted to the rotating pipes located behind the refrigerators.
  • This substance, which has high pressure and temperature, gives heat to the outside when passing through the rotating pipes. It is recommended not to put your refrigerator against the wall for easier heat transfer. When the heat is transferred out, the coolant cools and enters the small tube, which travels inward from the back of the refrigerator.
  • When entering the evaporator, the tube expands. The temperature drops as more space are opened up, and less friction occurs between molecules.
  • Evaporator provides evaporation work. An evaporator is a tube that surrounds the freezer section. Fluid matter evaporates here, taking heat from the environment. Thus, the surface and circumference of the evaporator cool down. The cooling air descends to the lower parts thanks to the pipes surrounding the refrigerator, and the hot air rises up. The temperature of the air going up again warms the fluid substance. There’s such a cycle in itself.
  • Finally, the refrigerant that receives the heat again turns into a gas and passes to the compressor. Thus, a loop is formed that allows the refrigerator to cool down. The thermostat that provides the heating scheme allows us to adjust the temperature of the refrigerator. When the refrigerator is sufficiently cold, the electrical connection is disconnected, and the circulation provided by the compressor is stopped.

In short, a refrigerator is a machine that throws out the heat and cools the inside, thanks to the fluid that circulates systematically in the cabin. It keeps our food fresh and our drinks cold.

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Steam Compression Cooling Cycle

3.1.Ideal Steam Compression Cooling Cycle

The cycle that can be performed under the best conditions. (You can right-click to enlarge the pictures and open them in the new tab.)

1-2; Isentropic compression in the compressor

2-3; Heat loss in the constant heat in the condenser

3-4; Dimming in the expansion valve

4-1; Heat intake at constant pressure in the evaporator

COP: Coefficient of Performance== QL/Wnet,in

The evaluation of a cooling machine is carried out with a performance coefficient. We can also write this down:

COP= the work to be obtained/ the work spent

Must be greater than 1. It should not be confused with thermal yield, which should be less than 1.

3.2. Cooling Cycle in reality

In ideal conditions, heat losses and pressure play between transitions are not seen. In constant entropy, events such as compression, loss of heat at a constant temperature or heat intake occur.

However, such an environment has not yet been achieved. As with many systems, energy losses are seen in refrigerators. The value shown by 2′ is the location of the refrigerant in the graph after the work that the compressor can actually transmit to the system. In other words, an image in 2 cannot be obtained by transmitting all the power of the compressor directly to the system. During this transmission, some of them are lost.

Source

  • How It Works – Art Kids
  • How Does It Work – Discovery
  • Thermodynamic Notebook Note – Prof.Dr. Mecit Sivrioglu
  • Thermodynamics 5th Edition – Prof.Dr. Yunus Ali Çengel
  • Cooling Technology Lecture Notes – Dr Volkan Şahin
  • Termadinamic Course Notes – Prof.Dr. Bulent Yeşilata

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