Imagine a large piston engine. Single cylinder. Now invert it. At the bottom, we have the intake valves, above that a wire mesh which suspends wet laundry in the "combustion chamber" of the device. The piston is above that. When we start the device the piston moves up, pulling a partial vacuum. The vacuum should get the pressure down to about 1/5th of atmospheric. This will encourage some of the water in the laundry into the air as the boiling point is now around 40-50C.

When the piston reaches bottom dead center (BDC, which is now at the top, because of the whole inverted thing) the intake valves open. Behind those, in the intake manifold some pre-warmed air now rushes upward toward the clothes, hopefully lofting them into the air for a bit of a tumble... maybe that happens a bit later when they're less heavy.... anyhow. Shortly after the intake valve opens, the exhaust valves open. These are in the piston itself, and behind them is another modest vacuum. Think vacuum cleaner level. Just as the piston starts to move down again, the exhaust valves remain open. The scavanged exhaust will remove the water laden air and help remove the air displaced by the descending piston to ensure no compression. The exhaust valves close when the piston reaches the bottom (which is the inverted TDC, stay with me...).

Then the whole thing starts again. Lovely. Should be needlessly expensive and complex, but a touch more efficient.
-- bs0u0155, Jul 18 2016

Dew point https://en.wikipedia.org/wiki/Dew_point
Highly relevant [8th of 7, Jul 18 2016]

When the intake valves open, the water vapour will condense instantaneously into fog.

No need for vacuum on the exhaust; better just to maintain positive pressure on the inlet as the piston moves down.
-- 8th of 7, Jul 18 2016


//When the intake valves open, the water vapour will condense instantaneously into fog.//

But the intake air is hotter than the boiling point by a fair way... well, sort of, and I want to whoosh that fog out of the exhaust anyhow.

//No need for vacuum on the exhaust; better just to maintain positive pressure on the inlet as the piston moves down.//

My thinking is that the exhaust vacuum would pre- depressurize the cylinder a little. Adding to the decompression ratio. Or subtracting from the compression ratio. Which is a minus number. It gets confusing.
-- bs0u0155, Jul 18 2016


The thermodynamics are easier if you just invert the signs on everything.
-- 8th of 7, Jul 18 2016


[+] Interesting. In order to actually //save energy// though, the piston would have to be allowed to spring back on its own. Water would evaporate from the clothes on the upstroke then, mostly above the clothing, condense in the chamber on the freewheeling downstroke, after which some air could be blown through to clear the mist (which is where you'd lose piston momentum).
-- FlyingToaster, Jul 18 2016


Vacuum drying, if carefully designed, tends to be more thermodynamically efficient than simply heating things above ambient.
-- 8th of 7, Jul 18 2016



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