how the refrigerator works?

Table of Contents

    Summary

    How the refrigerator works?

    In order to cool the fruits and vegetables in the refrigerator, its heat must be transferred to the room environment. Moreover heat always flows from a high temperature body to a low temperature body.

    Therefore, to cool these foods below room temperature, the refrigerator should make it possible to transfer the heat from a low temperature food to a high temperature environment.

    In Refrigerator, it is possible to cool the stuff below the room temperature because of the application of the 2nd law of thermodynamics in it.

    It states that heat can be transferred from a low temperature to a high temperature through a system if the work is added to that system.

    Refrigerators work on the vapour compression cycle to cool the stuff below the room temperature by using Compressor, Condenser, Evaporator, expansion valve and refrigerant.

    To know more about How the refrigerator works according to the vapour compression cycle by the application of 2nd law of thermodynamics in it, read this article.

    Introduction

    You might have wondered how the stuff inside the refrigerator gets cooled? What is the science behind it? How the refrigerator works? Right? To know the answer for it, first you should know the concept of heat flow during cooling as well as heating.

    Concept of heat flow

    Let’s consider 2 different cases

    Figure explaining direction of heat flow

    In case 1, Room temperature (Tr) =28 degree Celsius and the temperature of the object is (To)=50 degree Celsius

    When you keep that object inside the room, it will start to cool instead of heating till the temperature of the object becomes equal to the room temperature.

    Note Here that heat is transferred from the high temperature object to the low temperature environment

    In case 2, the temperature of the object is (To)=10 degree Celsius and the temperature of the room is (Tr)= 28 degree Celsius.

    When you keep this object inside the room, it will get heated up instead of cooling till the temperature becomes equal to the room temperature i.e. 28 degree Celsius.

    In this case, heat is transferred from the high temperature room to a low temperature object.

    Conclusion

    If you observe in the both the above cases, we can conclude that

    1.Heat flows from the high temperature body/environment to a low temperature environment/body

    2. When the temperature of both the room and the object becomes equals then heat transfer between room and object ends (Case 3).

    That means temperature difference is required to transfer the heat between the bodies.

    3. Heat never flows from low temperature body/environment to a high temperature environment/body by itself! (Case4).

    Figure explaining conditions where heat transfer is not possible

    Science Behind the working of a refrigeration system

    In order to cool the object below a room temperature, heat must flow from a low temperature body to a high temperature room. But it is not possible because heat always flows from high temperature to a lower temperature side.

    If so, then how does the stuff inside the fridge gets cooled to below room temperature?

    Cooling of the stuff inside the refrigerator is possible according to the second law of thermodynamics!

    2nd Law of thermodynamics states that heat can move from a cold body to a hot body through a ‘system’ if a ‘work’ is added to the ‘system’.

    How the refrigerator works according to the 2nd law of thermodynamics?

    Schematic diagram explaining 2nd law of thermodynamics

    In the case of a refrigerator, ‘system’ is a refrigerator and ‘work’ is added to this system through a compressor.

    Hence, it is possible to transfer the heat from the stuff inside the refrigerator, to room environment(which is at high temperature) in order to cool the stuff.

    Parts of a household Refrigerator

    Main parts of a refrigerator are 1. compressor 2. condenser 3. evaporator and 4. expansion valve

           Refrigerant is a fluid through which the heat is transferred from the stuff inside the fridge to an environment using compressor, condenser, evaporator and expansion valve

    Figure showing main parts of a refrigerator

    Compressor and condenser is placed at behind the refrigerator, where as evaporator is located at inside the freezer and the capillary tube or expansion valve is kept in between the evaporator and the condenser line.

    Vapour compression cycle

          In the household refrigeration system, usually vapour compression cycle is utilized to achieve the cooling

    Vapour compression cycle consists of a four process viz 1. Evaporation, 2. compression, 3. condensation and 4. expansion Process

    Let’s briefly discuss each process to know how exactly it is practically possible to transfer heat from a body at low temperature, to an environment at higher temperature, in order to cool the body further

    Evaporation

    Schematic diagram of an evaporator

    During this process, cold liquid refrigerant which is flowing inside the evaporator tube of the refrigerator will absorbs the heat of the stuff inside the refrigerator and thereby refrigerant gets vaporized.

    Compression

    Schematic diagram a Compressor

    In this process, the compressor sucks the vapour refrigerant from the evaporator and compresses it to a high pressure and temperature (above the room temperature), thus it becomes a superheated vapour refrigerant and is delivered to the condenser!

    Compressor is the reason for the circulation of refrigerant in the refrigeration system, just like our heart which circulates blood throughout the body

    Condensation

    Schematic diagram of a condenser

    Here, Superheated Vapour refrigerant from the compressor gives off heat (which is absorbed from the stuff inside the refrigerator) to an environment and the refrigerant starts to condensate (transforming into liquid) in the condenser tube.

    Expansion

    Schematic diagram of an Expansion valve

    Here saturated liquid refrigerant with high pressure and temperature from the condenser is expanded by using the expansion valve and due to this refrigerant gets cooled up and become low pressure cold liquid refrigerant. Here cycle completes

    Now again this cold liquid refrigerant is ready to take up the heat from the stuff inside the refrigerator further and the cycle repeats!

    Schematic diagram of a Vapour Compression Cycle

    How the refrigerator works In general?

    The Real magic happens at the compressor and in the expansion valve to cool the stuff inside the refrigerator according to the second law of thermodynamics.

    In the expansion valve, refrigerant is cooled to a temperature below the temperature of the stuff which is kept inside the refrigerator and makes it possible for refrigerant to absorb the heat from the stuff inside the refrigerator using evaporator.

    Whereas compressor increases the temperature of the refrigerant above the room temperature to help in discharging the heat(which is absorbed by the refrigerant form the food inside the refrigerator) to the environment using condenser!

    References

    1. Thermal Science & Engineering by M.L. Mathur, F.S. Mehta
    2. Refrigeration and Air Conditioning by C.P Arora
    3. work | Definition, Formula, & Units | Britannica
    4. Thermodynamic system – Wikipedia
    5. The Physics Classroom Tutorial

    Did you find this article helpful in finding the answer about your curiosity on the refrigeration system? If you have any query, opinion, or any suggestions then comment here.

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