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How a Refrigerator Moves Heat

8th grade nonfiction passage about heat and machines: 258 words, eight questions, an answer key and vocabulary.

8th grade nonfiction heat and machines 258 words

How a Refrigerator Moves Heat

A refrigerator does not make cold. Cold is simply the absence of heat. What a refrigerator does is move heat from the inside of the box to the outside, so that the inside gets cooler. The trick is a special fluid called a refrigerant, which circulates through a sealed loop of tubes.

The loop has four main parts. The cycle begins at the compressor, a pump that squeezes the refrigerant gas. Squeezing a gas makes it hot, so the gas leaves the compressor under high pressure and at a high temperature.

Next, the hot gas flows through the condenser, the coils on the back or the bottom of the refrigerator. The air in the room is cooler than the gas, so heat flows from the gas into the air. As the gas loses heat, it condenses into a liquid. If you touch the coils, you can often feel the warmth.

The liquid then passes through a narrow opening called the expansion valve. When the pressure drops, the liquid expands and becomes very cold, and some of it turns into a gas.

Finally, the cold refrigerant flows through the evaporator, the coils inside the refrigerator. The inside of the refrigerator is warmer than the refrigerant, so heat flows from the food and the air into the coils. The heat makes the liquid evaporate completely into a gas, and the gas returns to the compressor, where the cycle starts again. As long as the compressor keeps running, heat keeps moving out of the box, and the food inside stays cool.

Questions

  1. What does a refrigerator really do? in the text

  2. What is a refrigerant? in the text

  3. What does the compressor do to the refrigerant? in the text

  4. What happens in the condenser? in the text

  5. What happens at the expansion valve? in the text

  6. What happens in the evaporator? in the text

  7. Why are the coils on the back of a refrigerator often warm? think about it

  8. Would leaving the refrigerator door open cool a room, and what in the passage tells you? think about it

Words to know

refrigerant
the special fluid that carries heat around a refrigerator's tubes
compressor
a pump that squeezes a gas into a smaller space
condenser
the coils where a hot gas gives off heat and turns into a liquid
expansion valve
a narrow opening where a liquid's pressure drops so it becomes very cold
evaporator
the coils where a cold liquid takes in heat and turns into a gas

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put refrigerant, compressor, condenser, expansion valve and evaporator on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 3 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 7 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "How a Refrigerator Moves Heat"?

It was written for 8th grade. It has 258 words and works out to a Flesch-Kincaid grade level of about 7.0. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are eight. 6 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 3 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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