Testing the Thermal Resistance and Power Capacity of Production Heat Pipes

In recent years heat pipes have become widely use in high performance air-cooled heat sinks for cooling electronics equipment. Such heat sinks rely on the heat pipes to collect heat from small high heat flux sources, transport it over some distance, and spread the heat efficiently to a volume of fins where the heat is transferred to an air flow stream by convection. When used effectively, heat pipes enable heat sinks that have low thermal resistance and low mass. For the heat sink to be successful, the heat pipes must also have sufficient heat transport capacity. To deliver their design thermal resistance and heat transport capacity, heat pipes need to be manufactured with well-controlled wick characteristics, working fluid fill volume and minimal residual non-condensable gases. It is standard procedure for heat pipe manufacturing companies to test 100 percent of the heat pipes they manufacture. The most commonly used production test is designed to rapidly show whether or not a heat pipe functions as a heat pipe. On a sampling basis, manufacturers also test the heat transport capacity of their heat pipes. There is no rapid test that can verify that any specific heat pipe will achieve the desired operational life — this is achieved by validation of the manufacturing process and adequate manufacturing process controls. In this paper we describe a test method and apparatus that can be used to rapidly test whether a heat pipe has the required thermal resistance at the specified heat transport capacity. The apparatus is capable of testing heat pipes over a wide range of diameters and lengths in their end use configuration (with bends and flattened regions). The key design criteria for the test apparatus is described and test data for several application specific heat pipes is presented.