A nice cool drink on a hot day is something most of us take for granted. We also seldom think too much about the ice cream in our freezer or the well preserved food in our refrigerator. While refrigeration to keep things cool is common today, it was not always. The first patent for a refrigeration system similar to those we know today was filed in 1856 by James Harrison, an English journalist living in Australia. Before this, food was preserved with lots of salt, covered in snow during the winter, or simply kept alive on farms and harvested when you needed to eat!
So how does refrigeration work?
In general, refrigerators are cooled through the evaporation of a volatile liquid—that is, they use a liquid that evaporates very easily, and this evaporation creates the cooling effect. They then compress the gas into a liquid again, and the whole process starts over.
Let’s look at this in more detail; refrigerators have basically five parts:
So how does refrigeration work?
In general, refrigerators are cooled through the evaporation of a volatile liquid—that is, they use a liquid that evaporates very easily, and this evaporation creates the cooling effect. They then compress the gas into a liquid again, and the whole process starts over.
Let’s look at this in more detail; refrigerators have basically five parts:
1. A cooling box, where you put your food
2. Coils full of liquid
3. A compressor
4. Coils full of gas
5. A valve that separates the liquid-containing coils from the gas-containing coils
The liquid inside many household refrigerators is called HCFC (hydro chloro floro carbon). This type of liquid has replaced the traditional CFC (chloro floro carbon), which is bad for the environment (www.epa.gov). The HCFC refrigerant is the liquid (or gas) contained in the coils in the refrigerator, and is what actually cools the box where you store your food. The refrigerator cycles this HCFC from liquid to gas and back to liquid in the following steps:
2. Coils full of liquid
3. A compressor
4. Coils full of gas
5. A valve that separates the liquid-containing coils from the gas-containing coils
The liquid inside many household refrigerators is called HCFC (hydro chloro floro carbon). This type of liquid has replaced the traditional CFC (chloro floro carbon), which is bad for the environment (www.epa.gov). The HCFC refrigerant is the liquid (or gas) contained in the coils in the refrigerator, and is what actually cools the box where you store your food. The refrigerator cycles this HCFC from liquid to gas and back to liquid in the following steps:
1. Liquid HCFC is contained in the coils on the outside of the refrigerator—the ones that are usually hot. The liquid inside these coils is at about room temperature.
2. This room temperature liquid flows from the liquid-containing coils through a valve into the gas-containing coils. Here the liquid HCFC is allowed to evaporate, which it does very easily since HCFC boils (turns from liquid to gas) at -41.3°F.
3. The compressor now pulls in the HCFC gas, and compresses it until it turns back into a liquid. This makes it hot!
4. The hot HCFC proceeds back into the liquid containing coils, which allow the heat in the HCFC liquid to dissipate into the surrounding air (which is why the coils feel hot). Now the HCFC is liquid at room temperature again, and the whole cycle repeats.
The part of this cycle which cools the refrigerator box (and therefore your food) is step #2, the part where the HCFC evaporates. In fact, the evaporation of liquid is responsible for cooling many things, including you!
Evaporating liquid is a very efficient way of cooling something. It’s used in refrigerators, air conditioners, and humans—when you sweat, the water is evaporating off your skin, thus keeping you cool! What makes this work is something called the enthalpy of vaporization or heat of vaporization, which is the amount of heat a certain liquid needs to go from the liquid phase to the gas phase.
Picture it like this: you have a pot of water on the stove, and you want to bring it to a boil. When water boils, it turns from a liquid to a gas (i.e. steam). To make water boil you need to increase the amount of heat in the water, so you turn up the burner under the pot. As the water absorbs more and more heat, it gets hotter and hotter until it reaches 212°F, at which point it becomes steam. At the point when the water becomes steam, it takes a lot of that heat energy with it into the air and away from the remaining water. Since the steam removes the heat energy, it cools the water left behind.
2. This room temperature liquid flows from the liquid-containing coils through a valve into the gas-containing coils. Here the liquid HCFC is allowed to evaporate, which it does very easily since HCFC boils (turns from liquid to gas) at -41.3°F.
3. The compressor now pulls in the HCFC gas, and compresses it until it turns back into a liquid. This makes it hot!
4. The hot HCFC proceeds back into the liquid containing coils, which allow the heat in the HCFC liquid to dissipate into the surrounding air (which is why the coils feel hot). Now the HCFC is liquid at room temperature again, and the whole cycle repeats.
The part of this cycle which cools the refrigerator box (and therefore your food) is step #2, the part where the HCFC evaporates. In fact, the evaporation of liquid is responsible for cooling many things, including you!
Evaporating liquid is a very efficient way of cooling something. It’s used in refrigerators, air conditioners, and humans—when you sweat, the water is evaporating off your skin, thus keeping you cool! What makes this work is something called the enthalpy of vaporization or heat of vaporization, which is the amount of heat a certain liquid needs to go from the liquid phase to the gas phase.
Picture it like this: you have a pot of water on the stove, and you want to bring it to a boil. When water boils, it turns from a liquid to a gas (i.e. steam). To make water boil you need to increase the amount of heat in the water, so you turn up the burner under the pot. As the water absorbs more and more heat, it gets hotter and hotter until it reaches 212°F, at which point it becomes steam. At the point when the water becomes steam, it takes a lot of that heat energy with it into the air and away from the remaining water. Since the steam removes the heat energy, it cools the water left behind.
Your body does the same thing when you sweat. The water in the sweat goes from liquid (sweat) to gas (steam), and as it does so it takes heat energy with it, cooling your body.
The HCFC is like the water in the pot, or like the sweat on your skin, except that it boils (turns to gas) at -41.3°F instead of 212°F. This means as soon as it enters the coils inside the refrigerator box, it immediately evaporates, taking heat energy away from the box, cooling the air inside and keeping your food fresh!
TRY AN EXPERIMENT WITH DIFFERENT EVAPORATING LIQUIDS!
Here’s what you’ll need:
1. Two small saucepans, they should be the same size
2. Two cups plus one tablespoon water
3. One tablespoon isopropyl alcohol (available at grocery and drug stores)
4. A stovetop
5. A non-contact infrared thermometer (this is the kind you can point a laser beam at an object, and it measures the temperature)
6. Cotton balls (optional)
Here’s what you need to do:
It is pretty simple to demonstrate how evaporation of liquids can cool something. If you have extra isopropyl alcohol (the kind sold at most drug stores) , soak one cotton ball in water, and another in alcohol. Rub the water on the back of your left hand, and the alcohol on the back of your right hand. Your right hand should feel cooler—this is because the alcohol boils at a lower temperature (181°F) than the water (212°F). This means that the alcohol will evaporate from your skin faster, carrying heat energy with it as it evaporates, making your right hand feel cooler than your left hand (for more information about thermal energy, see our blog about energy transfer).
To see how evaporation of liquids affects temperature, try this:
1. Pour one cup of water into each of your small saucepans. Bring them both to a boil, and let them sit at a boil for at least 1 minute.
2. Remove the pans from the heat, and pour out the water (be careful not to burn yourself with the water or the escaping steam!)
3. Add one tablespoon of water to one pan, and one tablespoon of alcohol to the other pan. Swirl the water and alcohol in the pans for 15 seconds, and pour the liquids out again.
4. Measure the temperature of the bottom of each pan with your infrared thermometer, and write down what you find.
What was the temperature of the saucepan with the tablespoon of water? What about the saucepan with the tablespoon of alcohol? Why should these be different? Be sure to write down all your observations!
The HCFC is like the water in the pot, or like the sweat on your skin, except that it boils (turns to gas) at -41.3°F instead of 212°F. This means as soon as it enters the coils inside the refrigerator box, it immediately evaporates, taking heat energy away from the box, cooling the air inside and keeping your food fresh!
TRY AN EXPERIMENT WITH DIFFERENT EVAPORATING LIQUIDS!
Here’s what you’ll need:
1. Two small saucepans, they should be the same size
2. Two cups plus one tablespoon water
3. One tablespoon isopropyl alcohol (available at grocery and drug stores)
4. A stovetop
5. A non-contact infrared thermometer (this is the kind you can point a laser beam at an object, and it measures the temperature)
6. Cotton balls (optional)
Here’s what you need to do:
It is pretty simple to demonstrate how evaporation of liquids can cool something. If you have extra isopropyl alcohol (the kind sold at most drug stores) , soak one cotton ball in water, and another in alcohol. Rub the water on the back of your left hand, and the alcohol on the back of your right hand. Your right hand should feel cooler—this is because the alcohol boils at a lower temperature (181°F) than the water (212°F). This means that the alcohol will evaporate from your skin faster, carrying heat energy with it as it evaporates, making your right hand feel cooler than your left hand (for more information about thermal energy, see our blog about energy transfer).
To see how evaporation of liquids affects temperature, try this:
1. Pour one cup of water into each of your small saucepans. Bring them both to a boil, and let them sit at a boil for at least 1 minute.
2. Remove the pans from the heat, and pour out the water (be careful not to burn yourself with the water or the escaping steam!)
3. Add one tablespoon of water to one pan, and one tablespoon of alcohol to the other pan. Swirl the water and alcohol in the pans for 15 seconds, and pour the liquids out again.
4. Measure the temperature of the bottom of each pan with your infrared thermometer, and write down what you find.
What was the temperature of the saucepan with the tablespoon of water? What about the saucepan with the tablespoon of alcohol? Why should these be different? Be sure to write down all your observations!
