A heat pipe is an evaporator-condenser system in which the liquid is returned to the evaporator by capillary action. In the simplest form it consists of a wire-mesh region that serves to act as a wick. Heat pipes can be used in many applications, although the original application was for space vehicles, since in space gravity effects are weak, and hence surface tension was used as the motive force for liquid transport. The applications include solar thermal devices, pipelines over permafrost, etc. A heat pipe also provides an interesting multi-faceted example of application of models for convective heat transfer. A phenomenologically based modeling approach for heat pipes is discussed in the book by Mills (1993). The book by Faghri (1995) is another important reference on this field. Analyze the models for prediction of the performance of heat pipe.