Question

Consider two identical rooms, one with a refrigerator in it and the other without one. If all the doors and windows are closed, will the room that contains the refrigerator be cooler or warmer than the other room? Why?

Short answer

Explain the reason behind your answer. Answer: The room containing a refrigerator will be warmer than the room without one. This is because the refrigerator's function is to remove heat from its interior and release it into the room, increasing the room temperature. The heat exchange between the refrigerator and the room air makes the room with the refrigerator warmer than the one without it.

Step-by-step solution

Understand the working principle of a refrigerator

A refrigerator works by moving heat from its inside to the room in which it is placed. The refrigerator's compressor compresses a refrigerant gas, raising its temperature and pressure. This hot gas then moves through the condenser coils, which are located outside the refrigerator. Here, the refrigerant gas releases heat to the room as it cools down and condenses into a liquid. The cold liquid refrigerant then moves through the evaporator coils, where it absorbs heat from the inside of the refrigerator. This process keeps the inside of the refrigerator cool.

Heat exchange in the room

The refrigerator's function is to remove heat from its interior, not to cool the room. It exchanges heat between its inside and the room. When the room's air comes into contact with the condenser coils, it gains heat from the warm coils. This heat transfer increases the room temperature.

Compare the room temperatures

Since the refrigerator transfers heat from its interior to the room, the room with the refrigerator will be warmer than the other room without one. The room without a refrigerator will not have any additional heat source, while the room with the refrigerator has the heat transferred from the refrigerator, making it warmer.

Conclusion

The room that contains the refrigerator will be warmer than the other room because of the heat exchange between the refrigerator and the room air. The refrigerator removes heat from its interior and releases it into the room, increasing the room temperature.

Key concepts

Thermodynamics

Understanding thermodynamics is essential to explain why a refrigerator heats a room instead of cooling it. Thermodynamics, in its simplest terms, is the study of energy, its forms, and its transformation from one form to another. In the context of a refrigerator, thermodynamics dictates that energy cannot be created or destroyed, a concept known as the first law of energy conservation. As such, the refrigerator cannot simply eliminate the heat from its interior; it must move it elsewhere, which in this case, is the surrounding room.

When the refrigerator's compressor works, it converts electrical energy into mechanical energy to compress the refrigerant gas, raising its temperature. This high-temperature, high-pressure gas then releases its heat into the room as it condenses back into a liquid. The continuous cycle of absorbing heat from the fridge and releasing it into the room complies with the second law of thermodynamics, which states that heat naturally flows from an area of high temperature to an area of lower temperature until equilibrium (equal temperature) is reached.

Refrigeration Cycle

The refrigeration cycle is a closed-loop process that employs the principles of thermodynamics to cool down a designated space, like the interior of a refrigerator. It consists of four main components: the compressor, the condenser, the expansion valve, and the evaporator. Together, these elements use a refrigerant substance to transport heat energy from inside the refrigerator to the outside environment.

Initially, the compressor pressurizes the refrigerant, increasing its temperature due to the compression heat. The hot pressurized gas then travels to the condenser where it dissipates heat to the surroundings and condenses into a high-pressure liquid. Following that, the liquid refrigerant, now at a lower temperature but still at high pressure, passes through an expansion valve, where it experiences a drop in pressure and temperature. Lastly, the cold refrigerant flows through the evaporator coils inside the fridge, absorbing heat and cooling the interior. This cycle repeats continuously to maintain a cool environment within the refrigerator.

Heat Exchange

Heat exchange is the process by which heat is transferred from one body or system to another. In a household refrigerator, this is achieved via the condenser coils and evaporator coils. The condenser coils, usually located at the back or bottom of the fridge, act like a radiator, dispersing the heat into the surrounding air. By contrast, the evaporator coils inside the fridge absorb heat from the food and air within. This entire process is a practical example of how heat exchange can be controlled and harnessed to create cold spaces.

It's important to note that while the refrigerator interior becomes cooler, the by-product of this heat exchange is that the expelled heat actually warms up the room environment slightly. This is why the room with the refrigerator ends up warmer than a room without one.

Energy Conservation

Energy conservation in the context of thermodynamics refers to the principle that the total amount of energy in a closed system remains constant despite the internal changes that occur. In a refrigerator, the electrical energy used to power the compressor is not lost but is rather converted into other forms of energy, such as the thermal energy that heats the condenser coils. The refrigerator exemplifies energy conservation by demonstrating how work (energy in the form of electrical power supplied to the compressor) is transformed into thermal energy, which is then dissipated into the room.

With this understanding, it becomes quite clear why the room with a working refrigerator cannot be cooler than one without it. The energy used to remove heat from inside the refrigerator is ultimately added to the room, consistent with the law of energy conservation. Even though the interior of the fridge is kept cool, the ambient temperature of the room increases as the heat is rejected into it.