Heat Pipe
Heat Pipe
The heat pipe is hollow with the space inside evacuated, much the same as the solar tube. In this case insulation is not the goal, but rather to alter the state of the liquid inside. Inside the heat pipe is a small quantity of purified water and some special additives. At sea level water boils at 100oC (212oF), but if you climb to the top of a mountain the boiling temperature will be less that 100oC (212oF). This is due to the difference in air pressure.