Claude on Question 7, Oct 2

A refrigerator works by moving heat from inside the insulated cabinet to the room outside, which it accomplishes by exploiting the way a fluid absorbs and releases energy when it changes between liquid and gas. The fluid, called a refrigerant, circulates continuously through a closed loop of tubing driven by a compressor, which is the humming motor usually tucked into the back or bottom of the appliance.

The cycle begins with the compressor squeezing low-pressure refrigerant vapor into a much smaller volume, which raises both its pressure and its temperature so that the gas becomes hotter than the surrounding kitchen air. This hot gas then travels through the condenser coils, the black grille of tubing on the rear or underside of the unit, where it gives up heat to the room and cools enough to condense into a warm, high-pressure liquid. Some models use a fan to blow air across these coils to speed the process along, and this is why the space behind a refrigerator feels warm.

The liquid refrigerant next passes through a narrow constriction, typically a long thin capillary tube or an expansion valve, which throttles its flow and causes a sudden drop in pressure on the other side. Because the boiling point of a fluid falls as pressure falls, the refrigerant now finds itself able to evaporate at a very low temperature, and as it boils inside the evaporator coils within the freezer compartment it draws in the latent heat it needs from its surroundings. That stolen heat is what chills the air, the walls of the compartment, and ultimately the food. A fan often circulates this cold air through ducts into the fresh food section below, and a thermostat compares the resulting temperature to the setting you have chosen, switching the compressor on and off to maintain it.

Having absorbed heat and returned to a cool, low-pressure vapor, the refrigerant arrives back at the compressor and the whole sequence repeats. Insulation in the walls and gaskets around the doors slow the inevitable leakage of warmth back in, reducing how often the compressor must run. A further detail is that moisture from the air and from food freezes onto the evaporator coils, so most modern units periodically warm those coils with a small electric heater, and the resulting meltwater drips into a shallow pan near the condenser where the waste heat evaporates it away. Nothing in this process creates cold as such; the appliance simply relocates heat, which is why leaving the door open cools the food but warms the kitchen overall.