When the air pressure is lower, the rate of evaporation of water increases; this could be used to dry clothes, or maybe even to dehydrate foods.

Oh, and to make it more energy efficient, use a heat pump instead of gas or electrical resistance.

To start, take fresh air in through the intake, and pass it through the refrigerant condenser, heating up the air.

Then, pass the now warm air through a pneumatic motor, reducing it's pressure.

Then put the air through the tumbler full of clothes.

Pass the air through the refrigerant evaporator, chilling the air.

Then compress the air back to atmospheric pressure and send it out the exhaust.

Another advantage of this system is that if we pick the right pressure and temperature, the temp of the air inside the dryer is the same as that of the room, eliminatating the need for insulation.
-- goldbb, Jan 04 2009

pumping the water out of the clothes is going to be very energy intensive. Since dryers are already comical energy wasters reducing their efficiency even further is silly.
-- WcW, Feb 04 2009


WcW, what aspect of my design do you percieve as consuming more energy than a normal clothesdryer?

A normal clothesdryer needs to tumble the clothes; my machine uses the same amount of energy to do this.

A normal clothesdryer needs to move fresh air in, and stale are out. In a normal clothesdryer, this is done using a fan. A fan, of course, consumes energy. In my design, more energy is *generated* expanding (heated) air from the atmosphere into the low pressure interior, than is consumed compressing (chilled) air out of the machine. So my machine doesn't merely use *less* energy for air circulation, it *generates* energy from air circulation.

A normal clothesdryer consumes energy heating the air coming in. If it's an electric clothesdryer, this is done using a resistor. Producing heat from resistance is 100% efficient. My design uses a an air source heat pump. Air source heat pumps, for heating homes or domestic hot water, are generally quoted as being 150% to 300% efficient. I don't know how efficient the heat pump in my system would be, but I can guarantee that it would be more efficient than electrical resistance.

If you're comparing my design to a gas clothesdryer, consider that an efficient gas heat exchanger typically works with about 95% efficiency -- I still come out ahead, energywise.
-- goldbb, Feb 06 2009


[+] The only problem I see is that the air will be delivering less heat per cubic-inch because of the lower pressure. I like the exhaust/inflow heatpump idea; should be a standard on all dryers regardless. Ya know I don't think it would dry things much faster, but using a lower pressure drum would allow you to keep the temperature down so it would be safe for more fabrics. Either way at the end of the day you still have to pump in enough energy to evaporate all the water that is in the clothes when you put them in... probably.
-- FlyingToaster, Feb 06 2009


Had a similar idea about 15 years back, but it went like this:

maintain a constant vacuum pressure on the slowly tumbling clothes. zap periodically with microwave energy through a microwave-transparent tumbler.

if enough of a vacuum is created, the evaporating water will begin pulling heat from the surrounding air, saving a little power.

problems: microwave-safe clothes, and freezing.
-- TIB, Feb 06 2009


TIB, if you add heat inside the partial vacuum, then you need to move a larger volume of air out of the vacuum than is moved in. (I assume that you would be constantly letting dry air in to replace the damp air that's being sucked out).

Consequently, it would take more work to move that air out of your machine than could be extracted from the movement of air into your machine.

That's why I heat the air *before* it's expanded... so that I have a larger volume of air to expand (and thus I can extract more work), and why I cool the air before compressing it out the exhaust (so that I have a smaller volume of ait to remove, and thust less work to do).

Hmm... good point about the freezing. But since heat is always being added to the fresh air going in, (in my design) or directly to the clothes via microwave (in your design) I doubt that it would be a real problem.
-- goldbb, Feb 24 2009



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