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Saving Ozone Shield Through Sound

By G V Joshi
THERE ts renewed pressure on governments of most countries, envt ronmcnlallsls and scientists to tackle ozone depiction in the atmosphere due to man-made chlorofluorocarbons.
it is now well established that when released into the air. choforofluorocarbons rise over a period of years Into the stratosphere (atmosphere above 20 km and below 50 km from the earth's surface), where ultraviolet (UV) radiation breaks them down into their components — carbon, chlorine, bromine and flourinc.
Chlorine In CFCs destroys ozone, a minor but very important part of the stratosphere, which shields the Earth from much of the sun's harmful UV rays.
Today the family of CFCs includes many hundreds of compounds. But only five of them arc considered as most damaging to the ozone layer. They arc CFC-11 CFC-12. which are used in refrigerators; CFC-113 used mainly as a cleaning agent, and CFC-114 and CFC-115, which have a variety of uses.
The first three constitute more than 90 per cent of the CFCs. Teflon, the non-reactive polymer used In non-stick frying pans and Halon used in fire extinguishers are also among them.
The main ozone-destroying refrigerant CFC-12 (Freon) could be replaced by another CFC- 134a. CFC-12 is very easy to manufacture, but CFC-134a is much more difficult to make commercially. It is also likely to cost three times as much as CFC-12 and may not last as long. It can not be used In present-day refrigerators working on CFC-12 because It is highly corrosive.
The proposed replacement for CFC-11. used to make plas tic foam and in central air conditioning systems,, is a compound HCFC-22. This is a CFC already In use in domestic air conditioners and is much more expensive than CFC-11. Its potential applications are limited, however, by its inferior characteristics.
HCFC-22 to not as good a heat insulator as CFC-11 and It Is therefore unsuitable as a foaming agent for insulating plastic foams. In addition HCFC-22 to also a CFC and has to be replaced ultimately by 2010 AD., as per the Montreal Protocol.
A Washington-based environmental research Institute has Issued a report that HCFC-22 Is a very harmful chemical and should be banned along with CFCs immediately and not allowed to be used until 2010 AD
Several groups of scientists and engineers are working on development of new refrtgera Bon technologies that do not depend upon CFCs at all and many even be more efficient than conventional cooling sys terns. Attempts are also being made to revive old technologies with present-day superior engineering materials.
One of these uses sound energy blasted into a kid of organ pipe to achieve cooling. Deve lopers of sou nd-driven refrigeration say that such thermoaccoustic devices could chill nitrogen to Its liquefaction temperature of — 195.5
degrees Celsius or cool the air in a room or an automobile by only a few degrees. One of them was tested aboard the Space Shuttle mission in January this year.
Another of the new refrigeration technologies subjects liquids rather than gases in present-day refrigerators of cycles of compression and expansion to move heat away from the objects being cooled.
Some experts suggest a return to refrigerants like ammonia and sulphur dioxide used during the 1930s before the invention of CFCs. But sulphur dioxide is very toxic and
ammonia Irritates the lungs. Many easily liquified gases like butane and octane that might serve as refrigerants are undesirable because they pose fire and explosion hazards if released accidently.
Many other easily liquified gases that might otherwise serve as refrigerants are unde sirable because they cause rapid corrosion of metal parts and seals, destroying the compressors. and valves essential in conventional refrigerators.
The Invention of CFCs was regarded as a breakthrough because they are non-toxic, non-flammable, noncorrosive and practically indestructible tn normal use.
Thermoaccoustic refrigerators have no moving parts, aside from the diaphragm of its loud speaker and can use environment-friendly working gases. Although the design Is complex and subtle, the underlying principle is simple.
A loudspeaker at the end of a tube erpits an extremely loud note that resonates inside the gasfilled tube to form what ts called an accoustic "standing wave' in which individual molecules of gas are tn rapid oscillating motion while the wave as a whole docs not nvrrc at all. Organ pipes and other wind Instruments set up similar standing wave resonances. The gas molecules move back and forth at the same frequency as thal of the loudspeaker at the end of the pipe, and as they move they act as microscopic workers In a bucket brigade, carrying heat away from the thinner regions of the standing wave toward Its thickest bulge. Ils antinode.
If a metal plate Is placed within this antinode, the plate absorbs heat from the gas molecules and can conduct it away from the refrigerator, leaving cooled gas in Its place. The cool gas in turn can draw heat away from refrigerators or air conditioners.
The sound note played by the thermoaccoustic loudspeakers is so loud that it would destroy living tissue exposed to it, but the sound it almost confined in the resonating tube. The noise the user will hear outside is less than the noise of an electric Ian.
One thermoaccoustic refrigerator built was tested aboard a space shuttle flight in January 1992, where it reduced the temperature of an object under study by 118 degrees Celsius. By modifying the design, the device could be made to move much more, heat over a smaller temperature range as required in a household size refrigerator or airconditioner. Such a unit could chill beer as well as preserve vegetables and meat.
Another group of scientists is working on an entirely different refrigeration system in which liquids rather than gases are compressed under enormous pressure and used to pump heat away from the interior of refrigerators or even rooms, as a matter of fact many liquids like water can be compressed under high pressure and can be even more efficient than compressed gases In moving heat from one place to another as in domestic refrigerators.
In one model, scientists used liquid carbon dioxide, an environmentally friendly' gas at one time, at a pressure of 141 kg per square centimeter. However, tt must be much more robust to confine this enormous pressure.
The principle of working Is the same as tn conventional refrigerators. A carbon dioxide refrigerator will be much heavier and bulkier and would be most useful as an industrial plant unit for chilling waler which may be used to cool entire buildings.
The ozone depletion problem has finally forced scientists to take a fresh look at the refrigerators and a working so hition may come out sooner than expected However, one thing is clear A housewife will have to spend more money while- buying a new refrigerator and the unit is going to be bigger and bulkier for the same interior capacity