How to beat stadium shivers.
But thanks to a new line of microwavable earmuffs, scarfs, pocket warmers, and seat cushions, you can cheer (or sneer) for the home team without catching the big chill. After just two minutes in the microwave, these products will keep you warm for hours and hours. The weirdest part: They do it by freezing!
To find out how, we talked to chemist Ival Salyer of the University of Dayton in Ohio, who invented the hot new technology.
JUST A PHASE
Instead of merely trapping your own body heat--the way most jackets, sweaters and other insulating clothes do--these new products actual give off heat to keep you warm, Salyer says The secret: Each item has a removable "heat pack" filled with a phase-change material (PCM).
As the name implies, phase-change materials change phases, or states of matter, for example, from solid to liquid or back (see diagram, p. 10). When matter changes its phase, Salyer explains, "heat energy is either absorbed [stored] or emitted [released]." The trick is to find materials that store and release heat energy when you want them to.
For Salyer's earmuffs and other cold-weather items, the perfect PCM is a type of paraffin wax. When you pop a paraffin-filled heat pack in the microwave for about two minutes, Salyer explains, the heat generated by the microwave energy melts the wax--turning it from solid to liquid.
But the heat energy used to melt the wax doesn't disappear. It gets stored in the liquid wax molecules, making them move faster and flow more than they did in their solid phase. (That's one reason you can pour liquids.)
The wax doesn't really feel melted because a powder in the heat pack soaks it up, Salyer says. That helps prevent a leaky mess if the pack tears open.
But the heat pack does feel warm. When you slip it back in the earmuffs, the melted wax molecules gradually "chill out." As their temperature sinks below 60'C 140[degrees]F--paraffin's melting point), the wax molecules begin to resolidify, or freeze. (That's because the freezing point and melting point for a given substance are the same. See "Deep-freeze meltdown," p. 11.) As this freezing phase change occurs, the stored-up heat energy that kept the liquid molecules moving is released onto your ears. Ahhh!
"The earmuffs will keep your ears warm for longer than two hours," Salyer says. The seat cushions, he adds, work the same way, but stay warm for eight hours. That's long enough for a Super Bowl to go into overtime--and then some.
"They really work," says Cathy Miller, a Kansas department-store salesclerk who sold out her entire supply of "Heat Seat" cushions last football season. She owns some of these Microcore products, which are distributed under the Dearfoams brand name, and says, "They're great!"
But what if you don't have a microwave to heat up your clothes? You might want to try another new type of phase-change fabric: one that uses your own body heat to make matter change phases.
This fabric is coated with millions of microscopic paraffin-filled capsules, says Bernard Perry, whose company, Gateway Technologies Inc., developed the Outlast fabric. But this paraffin melts at a "cool" 29[degrees]C (85[degrees]F). Since that's below normal body temperature, Perry says, your body heat can melt the solid paraffin inside each capsule.
The material actually makes your body feel cool for an instant as heat flows from your body to melt the wax, Perry says. But once the wax is melted, it won't resolidify (freeze) as long as it's near your warm body. And the layer of warm liquid-wax-filled capsules keeps your body heat from escaping to the cold outside.
Hats made of the Outlast fabric are due in ski shops this winter. Maybe the Chicago Bear's Chris Zorich, our "cool" cover athlete, should think about getting one so he can keep his head from steaming!
THE NEXT STEP
Can you think of other uses for these hot new products? How about ways to use phase-change materials to keep you cool on hot days?
RELATED ARTICLE: Hot food on the go
Ever wish for a hot meal when there's no cafeteria or microwave in sight? Never fear, HeaterMeals are here!
These "meals with a stove inside" are just that: non-refrigerated entrees that come with a "flameless food heater" and a utensil pack. Just squirt the provided packet of water onto the flameless food-heater tray; set the entree tub on top; and slide it all back into the carton. After 10 to 15 minutes, you pull out a piping hot meal.
Where's the heat coming from? Quick-rusting metal. The heater tray contains a magnesium-iron metal plus salt. Adding water makes salt water, which corrodes, or rusts, the metal. That chemical reaction gives off a burst of heat--enough to heat your meal.
The technology was created to give soldiers a way to heat up meal packets during the 1991 Persian Gulf war. Civilians can now enjoy six different HeaterMeals entrees sold in truck stops and sporting-goods stores across the country.
And the taste? Not bad, actually. But then I never minded school lunches, either!
RELATED ARTICLE: DEEP-FREEZE MELTDOWN
Do materials like the paraffin pellets in microwavable earmuffs really freeze and melt at the same temperature? Experiment with water to find out.
WHAT YOU NEED:
laboratory thermometer * clean, empty 6-oz frozen juice can with cardboard sides and metal bottom * water at room temperature * aluminum foil * rubber band * freezer
WHAT TO DO: PART I: THE DEEP FREEZE
1. Place thermometer, bulb-side down, in juice can.
2. Add enough water to just cover thermometer bulb.
3. Punch a hole in a small square of aluminum foil to make a cover that holds the thermometer straight in the center of the can. Secure foil around can with rubber band, if necessary.
4. Record the starting temperature.
5. Place entire setup in freezer.
6. Take temperature readings at 5- or 10-minute intervals until ice is completely frozen. Record each reading with the time.
7. Make a line graph with temperature on the vertical axis and time on the horizontal axis to show your results.
PART II: THE MELTDOWN
1. Remove frozen juice container and thermometer setup from freezer and place in a warm room.
2. Record starting temperature.
3. Take temperature readings at 5- or 10-minute intervals until ice is completely melted and water has reached room temperature. Record each reading with the time.
4. Make a graph with temperature on the vertical axis and time on the horizontal axis to show your results.
What is the freezing point of water? What is the melting point of water? Does your graph have any "flat" areas? Is the ice/water losing or gaining energy during these parts of the experiment? Explain.
DON'T STOP NOW!
Would you want to use water as a phase-change material to keep you warm in winter? Why or why not? What could you use water's phase-change properties for?
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|Title Annotation:||cold weather clothes like earmuffs and hats have heat packs: includes an experiment on freezing and melting wax|
|Author:||Carson, Mary Kay|
|Article Type:||Cover Story|
|Date:||Dec 8, 1995|
|Previous Article:||Move over, T. rex!|
|Next Article:||Teens talk genes.|
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