Heat Pipes

It’s like a little steam engine converting solar radiation into hot water! The heat pipe is a hollow tube that is evacuated to form a vacuum inside it, in much the same way as the evacuated tube. The reason for evacuating the heat pipe, however, is not insulation but to promote a change of state of the liquid it contains. Inside the heat pipe is a small quantity of purified water. The vacuum enables the liquid to turn from liquid to vapor at a much lower temperature than it would at normal atmospheric pressure.

When solar radiation falls on the surface of the absorber, the liquid within the heat tube quickly turns to hot vapor and rises to the top of the pipe into the condenser. The copper heat pipe conducts from within the evacuated tube to its tip (condenser), which is plugged into the header pipe contained in the manifold. The condenser is made of copper and is nickel-plated this to ensure that the heat pipe can be removed for service or replacement (if the heat exchanger and the heat pipe are both made from copper the molecules can fuse over time). Water, or glycol, flows through a manifold and picks up the heat, while the fluid in the heat pipe condenses and flows back down the tube for the process to be repeated.

 

 

Advantages

The pipes must be angled at a specific degree above horizontal so that the process of vaporizing and condensing functions. Evacuated tubes offer the advantage that they work efficiently with high absorber temperatures and with low radiation. Higher temperatures also may be obtained for applications such as hot water heating, steam production, and air conditioning. An advantage of heat pipes over direct-flow evacuated-tubes is the "dry" connection between the absorber and the header, which makes installation easier and also means that individual tubes can be exchanged without emptying the entire system of its fluid.