The next time you indulge in an ice cold drink on a hot day, you have your refrigerator (and onboard freezer) to thank for the refreshingly chilled beverage. It wasn't so long ago that you'd have to be very rich or well connected to score a chilled drink with a few ice cubes floating inside. Today, we take refrigeration for granted, but once upon a time, fortunes were made shipping large blocks of ice around the world in insulated holds to sell to the rich.
Before refrigeration, preserving food was a big job. You could salt foods, and in winter, you could bury food in a snow drift and hope the critters didn't find it. To stay stocked with the essentials, though, you had to work at it -- or be rolling in money. Refrigeration is one invention that changed the way we conduct our daily lives. We can preserve food more easily nowadays, so we have much less to worry about when it comes to food-borne illnesses. The food supply is more stable, too. That gallon of milk can last a couple of weeks in the fridge as opposed to a couple of hours on your countertop. That's huge. It means you don't need to keep a cow in your backyard if you want a regular supply of milk.
The fundamentals of refrigeration are also at work in another important household appliance: the air conditioner. It's estimated that around 5 percent of all the electrical energy used in the U.S. is expended to keep our homes cool. That's pretty amazing, especially when you consider the fact that the principle behind most refrigeration is simple. Here it is in one sentence: When a liquid evaporates, it absorbs heat in the process. If you want to get rid of heat, you need to coax a liquid to convert to its gaseous state.
The Purpose of Refrigeration
The fundamental reason for having a refrigerator is to keep food cold. Cold temperatures help food stay fresh longer. The basic idea behind refrigeration is to slow down the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the food.
For example, bacteria will spoil milk in two or three hours if the milk is left out on the kitchen counter at room temperature. However, by reducing the temperature of the milk, it will stay fresh for a week or two -- the cold temperature inside the refrigerator decreases the activity of the bacteria that much. By freezing the milk you can stop the bacteria altogether, and the milk can last for months (until effects like freezer burn begin to spoil the milk in non-bacterial ways).
Refrigeration and freezing are two of the most common forms of food preservation used today. For more information on other ways to preserve food.
Parts of a Refrigerator
If you pour a little rubbing alcohol on your skin, it'll feel cold -- really cold. It isn't refrigerated, so how does this happen? Well, alcohol evaporates at room temperature the way water evaporates at a low temperature in an oven. As it evaporates, it absorbs the heat on the surface of your skin, making your skin cooler. A special coolant called a refrigerant functions in a refrigerator the way alcohol works on your skin, except in a refrigerator, the coolant is trapped inside a series of coils. As it makes a circuit through them, it changes back and forth from a liquid to a gas.
To pull off this frosty feat, a refrigerator uses five major components:
- Heat-exchanging pipes (serpentine or coiled set of pipes outside the unit)
- Expansion valve
- Heat-exchanging pipes (serpentine or coiled set of pipes inside the unit)
- Refrigerant (liquid that evaporates inside the refrigerator to create the cold temperatures)