Performance Characteristics of a Concentric Annular Heat Pipe: Part I—Experimental Prediction and Analysis of the Capillary Limit

This paper describes the design, testing, and theoretical capillary limit prediction of a new heat pipe configuration, which is the concentric annular heat pipe. The concentric annular heat pipe is made of two concentric pipes of unequal diameters that create an annular vapor space. With this arrangement, capillary wicks can be placed on both the inside of the outer pipe and the outside of the inner pipe. This design significantly increases the heat capacity per unit length compared to conventional heat pipes, since the cross-sectional area of the wick as well as the surface area for heating and cooling are increased. The heat pipe was tested for the temperature distribution in the three sections of the heat pipe under various tilt angles and heating loads through the inner and outer pipes in the evaporator section. A simple analysis for the prediction of the capillary limitation of the concentric annular heat pipe is presented.