How Everything Works
How Everything Works How Everything Works

Question 755

How does a refrigerator work? - SK
A refrigerator uses a material called a "working fluid" to transfer heat from the food inside the refrigerator to the air around the refrigerator. This working fluid moves through the refrigerator's three main components—the compressor, the condenser, and the evaporator—over and over again, in a continuous cycle. I'll begin as the fluid enters the refrigerator's compressor, which is usually located on the bottom of the refrigerator where it's exposed to the room air. The working fluid enters the compressor as a low-pressure gas at roughly room temperature. The compressor squeezes the molecules of that gas closer together, increasing the gas's density and pressure. Since squeezing a gas involves physical work (a force exerted on an object as that object moves in the direction of the force), the compressor transfers energy to the working fluid and that fluid becomes hotter as a result.. The working fluid leaves the compressor as a high-pressure gas that's well above room temperature. The working fluid then enters the condenser, which is typically a snake-like pipe on the back of the refrigerator. Since the fluid is hotter than the room air, heat flows out of the fluid and into the room air. The fluid then begins to condense into a liquid and it gives up additional thermal energy as it condenses. This additional thermal energy also flows as heat into the room air.

The working fluid leaves the condenser as a high-pressure liquid at roughly room temperature. It then flows into the refrigerator, then through a narrowing in the pipe, and then into the evaporator, which is another snake-like pipe that's wrapped around the freezing compartment (in a non-frostfree refrigerator) or hidden in the back of the food compartment (in a frostfree refrigerator). When the fluid goes through the narrowing in the pipe, it's pressure drops and it enters the evaporator as a low-pressure liquid at roughly room temperature. It immediately begins to evaporate and expands into a gas. In doing so, it uses its thermal energy to separate its molecules from one another and it becomes very cold. Heat flows from the food to this cold gas. The working fluid leaves the evaporator as a low-pressure gas a little below room temperature and heads off toward the compressor to begin the cycle again. Overall, heat has been extracted from the food and delivered to the room air. The compressor consumed electric energy during this process and that energy has become thermal energy in the room air.


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