How the refrigerator works

how the refrigerator works?

Summary

How the refrigerator works? or how does 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 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 the 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 1 explaining direction of heat flow

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

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

Conclusion

If you observe in 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 a temperature difference is required to transfer the heat between the bodies.

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

Figure 2 explaining conditions where heat transfer is not possible

Science Behind the working of a refrigeration system

In order to cool the object below room temperature, heat must flow from a low-temperature body to a high-temperature room (refer to case 4). But it is not possible because heat always flows from a 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?

Fig 3 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 the room environment(which is at high temperature) in order to cool the stuff.

Parts of a household Refrigerator

The 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 a compressor, condenser, evaporator and expansion valve

main parts of a refrigerator
Fig. 4 Main parts of a refrigerator

Compressor and condenser are placed behind the refrigerator, whereas evaporator is located 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

The 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 a low temperature, to an environment at a higher temperature, in order to cool the body further

Evaporation

Fig 5 Schematic diagram of an evaporator

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

Compression

Fig 6 Schematic diagram of a Compressor

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

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

Condensation

Fig 7 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

Fig 8 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!

Fig 9 Schematic diagram of a Vapour Compression Cycle

How the refrigerator works In general?

In the refrigerator, 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 an 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 from the food inside the refrigerator) to the environment using condenser!

Meaning and definition of some of the terms used in this article

Energy

It is the capacity to do work. Energy can’t be seen and doesn’t have substance. The presence of energy is indicated through the properties of matter such as its pressure, temperature etc.

Heat

It is energy in transition, which means it is one of the modes of energy transfer

Work

This is also an energy in transition, which means it is one of the modes of energy transfer.

Temperature

It is the measure of hotness or coldness of a body

System

The system is any prescribed and identifiable collection of matter whose behaviour is being investigated.

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 to your curiosity about the refrigeration system? If you have any queries, opinions, or suggestions then comment here.

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