CO2 in solar collectors??

[Solar Mike]

Originally Posted by AC_Hacker

Mike, do you have more info on this? The amount of heat isn't such a big surprise, but the distance (10 meters or about 30 feet) is big news to me.

-AC_Hacker

I have made several longish heat pipes, one was 6m long made from 6mm (1/4") copper tubing, heating one end, the other was hot within seconds.
Similarly a heat pipe made from 15mm copper tube 5m length behaved the same. The length of the pipe between hot and condensing ends has to be insulated.
The speed of heat transfer is determined by the vapor velocity of the gas, obviously the whole pipe gets hot when heating at one end, so provided the whole thing is well insulated no heat is lost. The amount of heat that can be moved is determined by the dia of the pipe, the vapor velocity and the latent heat of vaporization of the media.

The 10m length whilst I have not made one this long, should work as successfully at the shorter versions.

I was experimenting making a heat transfer device for plugging in to the waste heat going up the flue from my pellet wood burner. My intention was to place a preheat water tank up in the roof space directly above the hot water cylinder, when the fire was going, the heat pipe would capture some of the heat going up the chimney and conduct it to the water tank approx 10 meters away. This would be less complex than putting a wetback in the fire, the heated end of the heat pipe could get up to the same temp of the exiting gases from the fire, which is a good thing as the pipe wouldn't get carboned up the same way one filled with water.

I have tried several media inside the pipe, Butane, water, R22. Butane didn't work that well, we cannot get pure propane here so couldn't try that. Water worked but is very difficult to evacuate the tube to < 100 microns, then put some water in it, R22 worked best as standard refrigeration techniques can be used to evacuate and inject the liquid gas.

This DIY method of construction only conducts heat upwards, as upon condensing, the media in the pipe has to drain back to the heated end. Commercial devices can have a wick that by capillary action draws the condensed liquid to the heated end, so these would work at any angle.

Mike