A spin extractor can remove more water in two minutes than a dryer in twenty
Hospital laundries often put wet sheets through a centrifuge before any heat touches them. Spinning far faster than a washing machine, these extractors can shed as much water in a couple of minutes as a heated tumbler removes in twenty, saving a large amount of time and energy.
A conventional tumble dryer draws in room air, heats it with a gas flame or an electric element, and blows it through a rotating drum that keeps the laundry loose. The hot, damp air is then vented outdoors. Gas models exhaust combustion products such as carbon dioxide along with the moisture, while electric models use nichrome wire or semiconductor heaters. Tumbling can shrink clothes or strip away soft short fibres, which is why delicate items sometimes go into a stationary drying cabinet instead.
Condenser dryers skip the vent. They pass the moist air over a heat exchanger cooled by room air, condensing the water into a tank or drain, then recirculate the drier air, using about 2 kilowatt-hours per average load. The trade-offs are a warmer room and longer drying times, since the recycled air never gets as dry as fresh outdoor air. They suit homes where venting would need long, complicated ducting.
Heat pump dryers go further. The cold side of a heat pump condenses the moisture and the hot side reheats the air, keeping most of the heat inside the machine. They use under half the energy of a condenser model, around 1 kilowatt-hour per load, and because the air is already hot they may even finish faster than a standard dryer. Still in development, mechanical steam compression dryers heat the drum to 100 degrees Celsius, drive out the air with steam from the clothes, then compress and superheat that steam and inject it back; they match heat pumps on efficiency but take roughly half as long.
At the simple end sit convectant dryers: a heater at the bottom of a vertical chamber, relying on warm air rising through hanging clothes. They are slow but cheap, and they beat line drying clearly in cold, humid weather, though barely at all in hot, dry conditions.
Source: Clothes dryer
