Half a croissant, on a plate, with a sign in front of it saying '50c'
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Vacuum Reducer 2

Vacuum engine to dehydrate
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After seeing the Vacuum Reducer idea [see link], I realised that the same thing could be done faster, and with less energy, using a similar principle to my vacuum clothesdryer idea.

In this case, you would have an airtight potlid with a rubber seal on the bottom to make a seal with any pot or pan (as in the Vacuum Reducer idea), but instead of a vacuum pump run by an electric motor, it would have a vacuum pump run by a pneumatic motor.

Air would enter through a flexible tube, which stays in whatever shape it's bent, which is directed to suck air from the flame below the pot/pan. It would then pass through a pneumatic motor, into the area between the lid and the liquid. It would then pass through a small radiator (either cooled by the air, or by an ice cube or two), and then into the vacuum pump, and out into the room.

The machine would need to be manually started, but once going, the engine should continue to run as long as heat is provided.

goldbb, Feb 26 2009

Original Vacuum Reducer Vacuum_20Reducer
[goldbb, Feb 26 2009]


       If I'm reading this right you have a constant flow of hot air over the liquid which should collect a fair amount of moisture... where does the "vacuum" come in ?
FlyingToaster, Feb 26 2009

       The vacuum is produced by an air pump, which is constantly sucking out the moist air. But it's only doing it after that moist air has passed through the radiator (which is probably cooled by an ice cube, to make the machine more efficient), so it's merely lukewarm (or perhaps even cool) moist air, with droplets of water in it, rather than hot moist air.   

       As long as the total volume of air/water being removed by the pump is no greater than the volume of really hot air passing in through the pneumatic motor, the system maintains a vacuum, and the machine keeps running.   

       The reason for wanting to maintain a vacuum, is of course to encourage evaporation, to reduce the sauce or soup.
goldbb, Feb 27 2009

       we've been over this.....
WcW, Feb 27 2009

       You had me at what I anno'd before... passing very high temeperature air through the the pot will collect a load of moisture; if you run it through a condensing coil to a bucket on the floor you'd have a siphon thing happening without needing external power.   

       But I still don't get what you're powering the vacuum pump with... or how you're going to "maintain a vacuum" when you've got flue-gas coming in one side... oh wait you've got 2 pumps ? a "pneumatic" one based on rising hot air and a vacuum one... driven by the pneumatic one ? err. your bootstraps are broken.
FlyingToaster, Feb 27 2009

       The flue gas isn't passing through a pump, it's passing through a motor.   

       This motor takes hot air at one pressure and expands it to a region of lower pressure, extracting mechanical energy.   

       The mechanical energy produced by this motor is used to drive the vacuum pump.
goldbb, Mar 01 2009

       I think [boldBB] is wanting to run a heat engine of some kind off the heat of the stove, which will provide the power for the vacuum pump. Unfortunately, I think the theory of operation of heat engines has been lost along the way somewhere.
Skrewloose, Mar 02 2009

       What am I missing?   

       To operate a heat engine that doesn't have a phase change, you start with air at a high pressure, heat it, pass it through a device which expands it to a low pressure and extracts mechanical energy, then cool the low pressure air, then compress it back to high pressure.   

       Since the inside of the pot is at low pressure, the atmosphere can be considered high pressure (relative to the inside of the pot).   

       The air is heated at this "high" pressure by the fire.   

       The air passes through a motor, generating torque and rotation (i.e., mechanical energy).   

       The air, now at low pressure, but still warm, passes through an icewater cooled heat exchanger.   

       The cool low pressure air passes through a compressor, and moves back to "high" pressure (atmospheric pressure).   

       All very straightforward.   

       The prescence of the water does complicated things slightly, but the engine should still work.   

       I'll also admit that it's not the most energy efficient engine, since the thermal efficiency of any heat engine depends in large part on the pressure difference between the low pressure side and the high pressure side... The highest the pressure difference can possibly be is 15 PSI, which isn't very much.   

       (by the way, I'm posting a new version of the vacuum reducer, which eliminates all of the problems of this one).
goldbb, Mar 03 2009


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