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Text 9. The Coolest Sound
In just a few years, refrigerators and air conditioners could be humming a differenttune, keeping us cool by applying a recently discovered thermodynamic principle. Called thermoacoustic refrigeration, the process uses only environmentally friendly gases and sound.
The technique uses an unusual relationship between temperature and sound. Classblowers have known for centuries that a globe of hot glass at the end of a long metal rod frequently “sings” as it cools. But 10 years ago a group of physicists at Los Alamos National Laboratory discovered that the process by which sound is produced from cooling could be reversed so that cooling could be produced from sound. The group since has been awarded several basic patents for thermoacoustic refrigeration, and several other teams are developing systems.
At the heart of every thermoacoustic cooling device is a loudspeaker mounted on the end of a metal tube - prototype units range from the size of an aspirin bottle to 40-feet long - filled with a mixture of stable inert gases such as helium and argon. When a tone of just the right frequency is played, a standing sound wave is created inside the tube so that the wave’s crests form at each end and its trough lies in the middle.
Because sound is a pressure wave, the crests correspond to regions of highest pressure and the trough to that of lowest pressure. But while the pressure regions remain stationary, the gases in the tube are in constant motion as they are buffeted back and forth between the two high-pressure ends of the tube. When the volume is turned up to levels as high as 180 decibels - an intensity 100,000 times louder than a rock concert and one at which the pounding gases would destroy living tissue - the gases resonate forcefully back and forth.
Gases moving toward high pressure heat up as they are compressed, while those moving toward low pressure cool off as they expand. To capture the cold, most designs call for a simple heat exchanger, usually a strip of plastic rolled up like a jelly roll with an air space where the jelly should go. The coil is placed inside the tube - with its flat sides facing the flow of gases - about halfway between the high-pressure crest at the speaker end of the tube and the low-pressure trough, so gases can travel through the air space in both directions.
That way, as gas molecules rush toward the high-pressure region and heat up, they blast through the coil, bumping into its walls and transferring heat to the plastic. An instant later, they reverse direction and dance through the coil toward the low-pressure trough, cooling down and transferring cold to the plastic walls. Each time the molecules oscillate, they move a tiny bit of heat in one direction, a tiny bit of cold in the other direction. With millions of molecules shifting back and forth, a significant temperature differential builds up at the two sides of the coil.
Steven Garrett, a physicist at the Naval Postgraduate School in Monterey, Calif., was one of the first to pursue practical uses for thermoacoustic cooling, serving as a consultant to the Los Alamos group. Garrett explains that for spot cooling in uses such as electronic circuit boards, the cold can simply be conducted toward the desired object with a piece of metal called a heat pipe. For large-scale applications such as home refrigeration and air-conditioning, in which refrigeration would have to be delivered over greater distances, any environmentally safe heat-exchange fluid, even water, could be used to transfer coldness.
Thermoacoustic systems have two other potential advantages, Garrett maintains. The first is that thermoacoustic systems are quiet. Although the sounds inside can reach dangerous levels, the pressure vessel is so rigid that it does not vibrate at the same frequency as the gas inside.
The second advantage is control: “In an ordinary refrigerator, you have binary control: the system stays on and cools until it’s too cold, then it shuts off until it’s too warm”, says Garrett. Conventional refrigerators therefore waste energy by overcooling. But a thermoacoustic device could avoid overcooling, he says, because it could be set to continuously maintain an exact temperature.
Wade Roush. Technology Review, 1994
Vocabulary and Comprehension Exercises
I. Translate these into your own language:
• the coolest sound
• thermodynamic principle
• thermoacoustic refrigeration
• environmentally friendly
• mixture of stable inert gases
• just the right frequency
• to remain stationary
• to resonate back and forth
• a strip of plastic
• the flow of gases
• the high-pressure crest
• the low-pressure trough
• a significant temperature differential
• spot cooling
• a heat pipe
• to waste energy by overcooling
II. Find the synonyms in A column and antonyms in B column:
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A | |
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to destroy |
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to lose |
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exact |
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stationary |
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oscillate |
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to ruin |
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to stable |
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precise |
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to waste |
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to vibrate |
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B | |
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compress |
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forth |
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heat |
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outside |
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inside |
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low |
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back |
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cold |
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high |
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to expand |
III. Give the situations from the text in which the following words and
expressions are used:
at the heart of
just the right frequency the wave’s crests
the wave’s trough
to resonate back and forth the coil
to move a tiny bit of cold/heat
a significant temperature differential
IV. Arrange the items of the plan in a logical order according to the text.
• Garrett’s explanations about the applications of thermoacoustic refrigeration.
• The coil as a simple heat exchanger.
• The structure (construction) of every thermoacoustic cooling device.
• The discovery of thermodynamic principle.
• The advantages of thermoacoustic systems.
• The behaviour of gases inside the tube after creating a sound wave.
V. Agree or disagree with the following statements:
• Recently the scientists discovered thermodynamic principle which we can apply for keeping us cool.
• Thermoacoustic refrigeration uses not only environmentally friendly gases.
• This technique uses quite usual relationship between temperature and sound discovered many years ago.
• There is a metal tube filled with a mixture of stable inert gases inside any thermoacoustic cooling device.
• A standing sound wave is created inside the tube only in case a tone of just the right frequency is played.
• The wave’s crests correspond to regions of lowest pressure and it’s trough to that of highest pressure.
• Gases moving toward high pressure cool off as they are compressed, while those moving toward low pressure heat up as they expand.
• To capture the cold, the scientists use the coil.
• The coil is placed inside the tube near the high-pressure crest, so gases can travel through the air space only in one direction.
• Gases don’t reverse their direction while passing through the coil.
• A significant temperature differential is made up by millions of molecules shifting back and forth.
• Conventional refrigeration has more significant advantages over thermoacoustic systems.
VI. Answer the questions:
• What did the scientists discover recently?
• What is the technique called thermoacoustic refrigeration based on?
• Could cooling be produced from sound? When was it found?
• What constitutes the heart of every thermoacoustic cooling device?
• When is a standing sound wave created inside the tube?
• What do the wave’s crests correspond to?
• What corresponds to regions of lowest pressure?
• When do gases resonate forcefully back and forth?
• What do most designs call for to capture the cold?
• Where is the coil placed?
• What happens with gases while passing through the coil?
• How does a significant temperature differential build up at the two sides of the coil?
VII. Write a summary in English (or in your own language).
• Give each paragraph a suitable title in English (or in your own language).
• Develop the titles of the paragraphs into topic sentences. Join the topic sentences together.
• Re-read your summary and make sure that the sentences are presented in a logical order.