Man's physical universe

xanabras

230 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

pressures in

boilers as does water at the high temperatures necessary

for high efficiency in power generation, and thus replaces the boiler

water in some power plants.

A liquid suitable for use in refrigeration must be readily liquefied by

pressure at ordinary temperatures; i.e., its critical temperature must

be above room temperature. Water should meet the requirements

of a good refrigeration liquid because it is easily condensed and has a

high heat of vaporization, but inasmuch as its boiling-point is 80" C.

above ordinary room temperatures, it does not vaporize rapidly enough

at ordinary pressures to be effective.

Air is often cooled by the vaporization

of water, however. A simple house air-cooler, shown in the

Fig. 72.

A very simple type of air-conditioning unit.

the long wet wicks.

The fan blows air over

illustration,

depends upon increasing the. cooling by evaporation by

directing a current of air against a wet cloth by a fan.

Desert water bags are kept cool by the evaporation of the moisture

which seeps through the canvas bags. Refrigerators covered with

moistened cloth are sometimes used for camping trips.

Nearly everyone has experienced the cooling of the body when

standing in a wind when clothed with wet garments.

Inasmuch as the liquid in a refrigeration system must be condensed

as rapidly as it vaporizes, some provision must be made for this process.

In the majority of refrigeration systems, small or large, the vapors are

condensed by power-driven compressors.

The gas-operated refrigerator originated as an invention of two

Swedish students, Carl Munters and Baltzar van Platen, who made

their brilliant discovery while still undergraduates at the Royal Institute

of Technology at Stockholm. The process represents an ingenious

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