Discovery Express
  • Welcome!
  • Blog
  • Ask Dr. E!
  • Check out our store!
  • 9 Apples Math Game
  • Your questions answered!
  • Events and Announcements
  • About/Contact

Keeping Your Cool: How Refrigerators Work

7/18/2014

7 Comments

 
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:

Picture
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:
Picture
Picture
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. 
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!

7 Comments
Infrared Thermometer link
1/18/2018 02:53:10 am

thanks

Reply
AIMAL KHAN marwat
10/7/2018 09:33:45 am

Good amazing

Reply
Amy Winters link
6/24/2019 08:30:22 pm

Thank you for pointing out how refrigeration systems work. I had no idea that they are cooled through the evaporation of a volatile liquid. It's incredible to see how the things we use daily work.

Reply
gasNtools link
8/19/2019 01:55:16 am

The post explains well about the working of refrigerators. It is pretty interesting post I have read in recent days.

Reply
Randy Chorvack link
8/28/2019 02:01:18 pm

I really like how you said that the evaporation of liquid actually cools a lot of things. This makes a lot of sense because we sweat when we feel hot. It must be so that the sweat evaporates and cools us down in the process! Thank you for putting this in terms that I could understand.

Reply
OKOK
5/10/2020 08:10:18 pm

THANKssss!!!!

Reply
Maryam
6/11/2020 09:20:18 am

Really amazing explanation with explanation n pics. Helped me alot for my Physics assignment. Thankyou!

Reply

Your comment will be posted after it is approved.


Leave a Reply.

    Follow us on Pinterest!
    Picture
    Check out our new game for math education, grades 1-7!

    Archives

    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    January 2014

      Tell us what interests you most, and we'll send you a free PDF of a lesson in that subject!

    Submit

    Categories

    All
    Age 10 12
    Age 12 14
    Age 14 16
    Age 16+
    Age 8 10
    Anatomy/Physiology
    Biology
    Chemistry
    Engineering
    Food Science
    Geology/Earth Science
    Health Science
    Math
    Microbiology
    Physics
    Plant Science
    Psychology
    Weather Science

Proudly powered by Weebly