A heat pipe for long-distance downward heat transfer

(The text and drawing below are from Steve Baer's book, Sunspots, an exploration of solar energy through fact and fiction,  1979, Cloudburst Press, ISBN 0-88930-061-5, p. 30. Excerpt published here by permission of Steve Baer.)

Start of excerpt:

A New Kind of Heat Pipe

Heat pipes conduct heat by using the evaporation and condensation of a liquid inside a closed tube. Normally such a cycle can only work if the heat is introduced at a lower level than where it is taken out. The low liquid boils; the vapor rushes to the cold end where it condenses; and the liquid condensate drips back to boil once more. The heat pipe ignores this requirement of gravity by using a wick. Even if the heat is applied at the top end of a heat pipe the cycle of evaporation and condensation will continue. The wick within the tube pumps the cold condensate back up to the hot end to be boiled away again cycle after cycle. If the wick were not there, the top end of the pipe would stay hot and the cold end cold, and there would be no evaporation or condensation and thus very little heat transport. (Conduction down the tube would continue at its relatively slow rate, as would radiant transfer within the tube.) The heat pipe is a wonderful invention, but it has great limitations. Wicks cannot lift the liquids more than a few inches. We can never put the heat in very much higher than where we take it out.

One day while looking at a diagram of a semipermeable membrane in Enrico Fermi's Thermodynamics I realized that heat pipes could be built with enormous differences in elevation using a semipermeable membrane to return the liquid from the low cold end to the high hot end.

Impurities--such as a salt--must be added to the solution so that there will exist a concentration gradient across the membrane. The pure distilled condensate collecting at the low end will then be driven through the semipermeable membrane to re-enter the solution.

Although I obtained a patent on this heat transport device (United States Patent No. 3,561,525), I am ashamed to say I never once tried out the idea.

End of excerpt.

Click here to see US patent 3,561,525.  (PDF, 250KB)

Note unrelated to heat pipes:  Steve Baer's company, Zomeworks, specializes in passive solar energy products. See Zomeworks Double Play Systems for passive heating and cooling of buildings: http://www.zomeworks.com/tech/doubleplay/index.html.  The principles of Double Play Systems should, for the first time, make thermal components needed for 100% passive solar houses profitable for manufacturers, and perhaps create an entirely new market.