Heat transfer efficiency of annular-type heat pipes is investigated experimentally and theoretically, for the evaporating section and condensation section respectively. The heat transfer coefficients of evaporating liquid film are obtained under several conditions of the annular gap, charged volume rate of the working fluid, wall superheating and rotational speed. It is shown that the results of theoretical analysis for condensation heat flux agree well with experimental results, and also that the taper angle of the condensation wall greatly influences on the heat transfer efficiency.
