The performance of methanol and water heat pipes for electronics cooling applications in spacecraft instrumentation

Increases in the power density of electronics and the corresponding decreases in packaging space have driven the development and enhancement of numerous electronics cooling strategies. The design of cooling systems for electronics are particularly challenging in spacecraft environments where there exists the additional requirements of minimal mass and volume, high reliability, reduced complexity and number of moving parts, and ability to operate in a reduced or gravity-free environment. One cooling technique that has proven to satisfy these demanding and integrated requirements for spacecraft electronics cooling applications, involves the use of heat pipes. The heat pipe is a passive heat transport device that requires no moving parts, is highly compact and reliable, and is an efficient mover of thermal energy in reduced gravity environments. Despite all of these positive features, heat pipes do have limitations and functional characteristics that designers must be keenly aware of when incorporating them into the development of electronic cooling systems. These include, in part, limits on the heat transport capacity and operational temperature, as well as performance variations between seemingly identical heat pipes due to contamination or manufacturing flaws. This paper discusses thermal analyses and performance testing of commercial copper heat pipes that utilize a sintered copper wick with either methanol or water as the working fluid. First, the electronic cooling application, thermal operating requirements, and commercial heat pipe designs are introduced. Next, the models and analyses used to predict the heat transport limits for the heat pipes are discussed. Following this, the experimental apparatus and procedures used to characterize the thermal performance of the heat pipes are presented. Finally, with the aid of empirical data, assessments of the thermal performance of each heat pipe, the range of performance variation between heat pipes, as well as the applicability and accuracy of the analytical performance models are provided.