Is there a way to make a heat pipe that can transfer heat downward? Is there a way to make a heat pipe that can transfer heat downward? As in a 10 to 20 ft vertical pipe with 100°f at the top and 50°f at the bottom.
 A: You can circulate chilled water through the pipe which should distribute the temperature. Rate of circulation, along with the thermal properties of the pipe and embed media will control the precise temperature gradient - if thats even important for your application. 
Lastly, the problem of steady state temperature distribution in a metal rod is well understood and doesn't depend on the pipe orientation (up, down, left, right).
You can enter your specific numbers on this website:
http://demonstrations.wolfram.com/TemperaturePropagationInAThinSteelRod/
A: Use heat pipes. They work in large lengths far better than anything else. They can transfer far more heat than anything else. It is a pipe with some sort of porous wick coating the inner surface of the pipe that transports the liquid back to the hot end. At the hot end the liquid evaporates and travels down the center of the pipe and condenses at the cold end. The pipe itself is iso-thermal but allows for you to maintain ideal gradients on each end of the pipe. It is like a thermosyphon only because of the wick works in any orientation.
A: Yes, large OHP's can accomplish this. Also, I've seen experiments with tesla type valves within phase change heat pipes that force fluid flow in one direction against gravity.
