Understanding Refrigeration

To understand what is happening inside your refrigerator, it is helpful to understand refrigerants a little better. Here are two experiments that help you see what is happening.

Experiments
 These experiments can help you understand the properties of gases and their role in refrigeration.

Experiment 1
You will need:

Put the pot of water on the stove, stick the thermometer in it and turn on the burner. You will see (if you are at sea level) that the temperature of the water rises until it hits 212 F. At that point, it will start boiling, but will remain at 212 F -- this is the boiling point of water at sea level. If you live in the mountains, where the air pressure is lower than it is at sea level, the boiling point will be lower -- perhaps between 190 and 200 F. This is why many foods have "high-altitude cooking directions" printed on the box. You have to cook foods longer at high altitudes.

Experiment 2
You will need:

  • An oven-safe glass bowl
  • A thermometer that can measure up to at least 450 F
  • An oven
Put the thermometer in your container of water, put the container in the oven and turn it to 400 F.

As the oven heats up, the temperature of the water will again rise until it hits 212 F, and then start boiling. The water's temperature will stay at 212 F even though it is completely surrounded by an environment that is at 400 F. If you let all of the water boil away (and if the thermometer has the range to handle it), as soon as the water is gone the temperature of the thermometer will shoot up to 400 F.


The second experiment is extremely interesting if you think about it in the following way: Imagine some creature that is able to live happily in an oven at 400 degrees Fahrenheit. This creature thinks 400 F is just great -- the perfect temperature (just like humans think that 70 F is just great). If the creature is hanging out in an oven at 400 F, and there is a cup of water in the oven boiling away at 212 F, how is the creature going to feel about that water? It is going to think that the boiling water is REALLY cold. After all, the boiling water is 188 degrees colder than the 400 F that this creature thinks is comfortable. That's a big temperature difference!

(This is exactly what is happening when we humans deal with liquid nitrogen. We feel comfortable at 70 F. Liquid nitrogen boils at -320 F. So if you had a pot of liquid nitrogen sitting on the kitchen table, its temperature would be -320 F, and it would be boiling away -- to you, of course, it would feel incredibly cold.)

Butane Lighters
If you go to the local store and buy a disposable butane lighter with a clear case (so that you can see the liquid butane inside), what you are seeing is liquid butane stored in a high-pressure container. Butane boils at 31 degrees F at normal atmospheric pressure (14.7 PSI). By keeping butane pressurized in a container, it remains liquid at room temperature. If you took a cup of butane and put it on your kitchen counter, it would boil, and the temperature of the boiling liquid would be 31 F.

The boiling point of butane, by the way, also explains why butane lighters don't work very well on cold winter days. If it is 10 degrees Fahrenheit outside, the butane is well below its boiling point, so it cannot vaporize. Keeping the lighter warm in your pocket is what allows it to work in the winter.

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 again imagining our oven creature and his cup of water. He could create a regenerating cycle by taking the following four steps:

  1. The air temperature in the oven is 400 degrees F. The water in the cup boils away, remaining at 212 F but producing a lot of 400 F steam. Let's say the creature collects this steam in a big bag.

  2. Once all the water boils away, he pressurizes the steam into a steel container. In the process of pressurizing it, its temperature rises to 800 F and it remains steam. So now the steel container is "hot" to the creature because it contains 800 F steam.

  3. The steel container dissipates its excess heat to the air in the oven, and it eventually falls back to 400 F. In the process, the high-pressure steam in the container condenses into pressurized water (just like the butane in a lighter -- see sidebar).

  4. At this point, the creature releases the water from the steel pressurized container into a pot, and it immediately begins to boil, its temperature dropping to 212 F.
By repeating these four steps, the creature now has a way of reusing the same water over and over again to provide refrigeration.

Now let's take a look at how these four steps apply to your refrigerator.

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