Robert Runcewitch, age l3, of Somerset, N.J., for his question:
How does a refrigerator work?
The old fashioned ice box was cooled by a melting chunk of ice and its dripping water was a problem. modern refrigeration is a closed system that cools by letting a liquid boil to vapor. It solves the drip problem by making it a useful part of the system.
A refrigerator has a built in circuit for both heating and cooling. The substance that flows through the system is the refrigerant, and the boiling point at which it changes to vapor must be very low. The cooling system also has a compressor to squeeze and heat the vapor and a condenser to cool it into its liquid form. The refrigerant is sealed in a closed circuit and changed back and forth from its gaseous form to its liquid form. This simple trick keeps the air inside the refrigerator at a constantly cool temperature.
It works because of the changes that occur when a liquid substance becomes a gas. It absorbs heat energy from the substances around it. In a smaller way the same thing happens when a chunk of ice melts to a liquid. In the old fashioned ice box, the melting ice stole heat from the air inside and kept its store of food cool. Modern refrigerants absorb much more heat and change to vapor far below the melting point of ice. What's more, they create no mess of dripping liquid.
The storage compartment of a refrigerator is a double walled box and the refrigerant circulates through pipes between the walls. On this part of the trip around; it is a liquid, boiling into a bubbly gas and absorbing heat from the walls. Heat is a great traveler, always moving from warmer to cooler substances. The foods give up their heat to the cooled air and walls.
The circulating refrigerant boils and bubbles on its way to the compressor which is a motor driven piston and cylinder. The gas, bearing a load of heat absorbed from inside the refrigerator, is compressed and made still hotter. This must be done because the vaporized refrigerant is cooler than the room and heat will not flow from cooler to warmer objects. The compressed gas must be hot enough to cool off at room temperature..
A condenser, somewhat like a radiator, is waiting for the hot vapor. As it circulates through these pipes, the gaseous refrigerant gives up its heat and chills back into a liquid. The closed circuit then pipes the liquid on another trip around the walls where it boils and absorbs another load of heat from inside the refrigerator.
The same principle is used in kitchen refrigerators and air cooling units, in refrigerated trucks and freight cars. A refrigerant having a very low boiling point is sealed and circulated in a closed system. Motor units are used to compress the heat ladened gas and keep it circulating. The liquid refrigerant changes itself to vapor at ordinary temperatures. It cools the inside of the refrigerator because when a liquid evaporates into a vapor it absorbs heat from the substances around it