Did You Know?

If you're at sea level, you'll see that the temperature of water will begin to boil at 212 degrees Fahrenheit (100 degrees Celsius), but if you live in the mountains, where the air pressure is lower than it is at sea level, the boiling point will be a bit lower, say 190 to 200 degrees Fahrenheit (87 to 93 degrees Celsius). This is why many foods have special high-altitude cooking directions printed on the box.

Understanding Refrigeration

To understand what's happening inside a refrigerator, let's learn a little more about how refrigerants work. You will need:

  • An oven-safe glass bowl filled with water
  • A thermometer that can measure up to at least 450 degrees Fahrenheit (232.2 degrees Celsius)

Add the thermometer to the water filled bowl and place both in the oven. Set the oven to 400 degrees Fahrenheit (204.4 degrees Celsius).

As the oven heats up, the temperature of the water will rise until it hits 212 Fahrenheit (100 degrees Celsius) and it starts boiling. The water temperature will stay at 212 degrees Fahrenheit (100 degrees Celsius) even though it's completely surrounded by the 400 degrees Fahrenheit environment inside the oven. If you let all the water boil away, the temperature on the thermometer will shoot up to 400 degrees Fahrenheit (232.2 degrees Celsius).

Let's look at this experiment another way: Imagine the existence of an exotic creature able to live happily in an oven at 400 degrees Fahrenheit. Let's call him Max. If Max is hanging out in a 400 degree Fahrenheit oven next to a bowl of water boiling away at 212 degrees Fahrenheit (100 degrees Celsius), how is he going to feel about that water? He's going to think the boiling water is really cold. After all, the boiling water is 188 degrees colder than the 400 degrees Fahrenheit that he thinks is comfortable. That's a big temperature difference!

This is exactly what happens when humans deal with liquid nitrogen. We feel comfortable at 70 degrees Fahrenheit (21.1 degrees Celsius), but liquid nitrogen boils at -320 degrees Fahrenheit (-195.5 degrees Celsius). If you had a pot of liquid nitrogen sitting on the kitchen table, its temperature would be boiling away at -320 degrees Fahrenheit (-195.5 degrees Celsius) -- to you, of course, it would feel incredibly cold (so cold it would burn you!).

Modern refrigerators use a regenerating cycle to reuse the same refrigerant over and over again. You can get an idea of how this works by remembering Max and his bowl of water. He could easily create a regenerating cycle by taking the following steps:

  1. The bowl of water in the oven example boils away, remaining at 212 degrees Fahrenheit (100 degrees Celsius) but producing lots of 400 degree Fahrenheit steam. Let's say Max collects this steam in a big bag.
  2. Once all the water boils off, Max pressurizes the steam into a steel container, where the temperature rises to 800 degrees Fahrenheit (426.6 degrees Celsius) as the pressure increases. Now, Max thinks the steel container feels really "hot" because it contains 800 degree Fahrenheit (426.6 degrees Celsius) steam instead of 400 degree Fahrenheit steam.
  3. The steel container releases or dissipates its excess heat to the air in the oven, and it eventually drops to the oven's temperature of 400 degrees Fahrenheit. In the process, the high-pressure steam in the container condenses into pressurized water.
  4. At this point, Max releases the water from the steel pressurized container into a pot, and it immediately begins to boil, its temperature dropping to 212 degrees Fahrenheit.

By repeating these four steps, Max can reuse the same water over and over again to provide refrigeration.