Various kinds of two-phase cold plates are currently under development for thermal management systems of future spacecraft (1). Their evaporative heat transfer modes are basically classified into two categories according to the state of liquid-vapor interfaces, that is, evaporation from liquid films held on wicking structures and forced convective boiling. The evaporation mode is the most important factor determining the loop characteristics and its control technology. With respect to liquid film evaporation, the operation in a zero gravity environment is clarified theoretically and is proven by many flight experiences of heat pipes.
According to such a consideration, we have chosen an arterial heat pipe as an evaporator for two-phase cold plates and have developed a heat pipe of grooved double pipe type. The design concept was verified as a loop heat pipe through tests previously made(2). Next, it was integrated as a pump assisted heat pipe system and was operated successfully(3). From the tests, the feasibility of a pump-driven two-phase fluid loop system using liquid film evaporation has been confirmed and our research is in a new stage where development effort will be focused on a loop control technology (4).
This paper describes the test results of a two-phase cold plate consisting of many parallel evaporator pipes including uneven heat load tests and parallel operation tests. Also given are discussions on the heat transfer characteristics and the hydrodynamic behaviors from the viewpoint of loop control technology.