A cold drink poured out from a container in your Washington D.C. refrigerator is done without thought today, but eighty years ago was a miracle of modern convenience affordable only to the very rich. Large blocks of ice were once delivered and stored in a box to keep food cool, making the name “ice box” linger as a term for refrigerators long afterwards.
Without refrigeration, our eating habits would be very different because many foods in our diet would go bad within a day.
Bacteria spoils food. The fundamental idea behind a refrigerator is to keep food cool so that the natural process of bacterial damage is slowed. By freezing food, you can stop the bacteria altogether.
When a liquid evaporates into gas, it absorbs heat in the process. If you want to get rid of heat, you need to coax that liquid to convert back into its gaseous state. Refrigerators and freezers are designed to condition the air in a confined space to much cooler temperatures to slow or stop the process of bacterial decay and preserve food longer.
A refrigerator uses five components to manufacture the cooler temperatures:
- a compressor
- heat-exchanger pipes outside the unit
- heat-exchanging pipes inside the unit
- an expansion valve
- and a refrigerant, a liquid that evaporates rapidly
Ammonia, in its pure state, boils at a brisk minus 27 degrees Fahrenheit and turns to gas. The compressor forces this ammonia gas into a pressurized state that creates heat. Flowing through the coils of outside piping, the heat is allowed to dissipate which condenses the gas back into its liquid state.
In this pressurized state, the liquid travels through the expansion valve where low pressure on the other side allows the liquid to cool back to its boiling point. At that low temperature, the ammonia cools the air inside the piping and within the refrigerator as well.
A Better world
Since pure ammonia is very toxic to human health, a substitute known as CFCs (clorofluorolcarbons) was used until it was discovered that they were harmful to the environment. Today, all refrigerators and air conditioners use refrigerants that do not destroy the ozone.