heat pipes

[schnell]

anyone ever play with making their own heat pipes?

in school i met the nephew of the inventor, who had several demonstration versions he inherited through the family. they were small simple and amazing in their capacity to move heat from one end to the other.

i was thinking a home built heat pipe might be the solution for a project i've got where i want to move heat from outside to inside the building.

this would also be great for the folks who use wood, or coal, as i've recently read to fire a boiler.

any thoughts?

[defcon4]

From what little I know about heat pipes. I remember reading that they work best as a closed tube with 25% of the inside volume filled with anything that boils/evaporates at a low temperature. Pure ammonia would be great, if not, you could use alcohol (95% ABV) I think.

[nanosleep]

Actually you can use any liquid which has a reasonable boiling point. For water you'd have to draw a vacuum so the water will boil at your operating temperature (unless you want to operate at 100C then you'd have water near one atmosphere pressure). If you operate above 100C you need to be sure the tube can safely contain the pressure. You'd probably be better off finding another working fluid with a higher boiling point (lower vapor pressure).

An important point to remember for homebuilt heat pipes is you will need to remove the air from the pipe before sealing it. If you don't the air will form a "blockage" which won't let the vapor reach the cold end of the tube. If the vapor doesn't reach the cold end of the tube, it doesn't condense and no heat is transfered. The obvious way to do this is with a vacuum pump. The non-obvious way is to fill your tube with a little extra liquid. Heat the liquid to boiling and let the vapor push the air out of the tube. You have to then quickly seal the tube after the air is purged but before you loose too much vapor.

[schnell]

i could do both. heat it and vacuum it.

i was thinking i could cap a tube on one end, add a tee to the other, which would have a valve on the side and a blind end leading to a cap.

this way i could volatize the working solution and then seal the valve. it might leak, but could be refilled/recharged through the valve.

i tried to imagine boiling a tube of alcohol and soldering on the other end. my imagination was vivid, so i though the valve thing might be a good safe alternative.

without a capillary insert you'd have to tilt the thing for gravity return.

need to make some time to try this out. if someone beats me to it, let me know how you like it.

Aaron

[nanosleep]

Water is almost a perfect substance for this. It's nonflammable. It requires a large amount of heat to boil (ie. it transfers a lot of heat without moving a lot of water). It's easy to find and practically free.

The downside to water is there's a lower limit on temperature due to freezing. For low temperatures you might have to use something like propane, butane, freon or something similar. Each of these has a higher vapor pressure at typical temps (something like 300psi for propane IIRC). The higher pressures in combination with the flamability requires more caution.

[runwild]

Years ago I designed a wood hot water boiler to heat my 2000 sq. foot home and 1600 sq. foot. shop. This is a closed loop system with heat exchangers at house and shop. 300 ft. round trip to house and 200 ft. to shop. 1” pipe 3’ under ground With cutting the wood myself. Gas for saw , truck and electric fore two pumps and fans the total cost is under 500 $ fore six months. 35 to 40 cords of wood a year. I can keep the temperature of the water at 175 to 190 degrees with the use of a Aqua stat this sends a 24 volt signal to a blower the blower turns on at 175 and turns it off at 190 degrees It also opens and closes a damper between the boiler and the blower making it 98 percent air tight. Heats 40 gal. water. Most pop offs go off at 30 psi. A must with this kind of heat. Live in northern Mich. Wind chill 30 below tonight 70 degrees in here.

runwild