Design and Test Results of Reversible Loop Heat Pipe 1999-01-2053

In typical loop heat pipe (LHP) applications, the LHP design calls for a dedicated evaporator and a dedicated condenser. Applications exist for reversible loop heat pipes (LHPs), which can transport heat in either direction. In the reversible LHP design, two evaporator pumps are plumbed together, one which acts as an evaporator while the other acts as a condenser. The two pumps can reverse roles, simply by reversing the temperature gradient across the loop. Thus, either pump can be used as an evaporator or a condenser, depending upon the environment. Reversible LHPs can be used to share heat between components, or to cross-strap opposing spacecraft radiators.

A reversible LHP was built and tested to demonstrate feasibility and to characterize its performance capabilities and attributes. The device was tested by either alternately heating each evaporator electrically or by inducing a temperature difference between the two ends of the device. The reversible LHP exhibited reliable start-up behavior, and excellent thermal performance in both operating scenarios. The device demonstrated its ability to reliably start and automatically reverse flow direction as heating was alternated from one evaporator to the other or as end-to-end temperature gradients were reversed. Tests were performed in various orientations to demonstrate the loop’s insensitivity to the relative orientation of the evaporating and condensing pumps in one-g. This paper describes the design of the reversible loop and the test program implemented to quantify its performance, and provides a summary of the test results.