Effect of heat load on pneumatic temperature control characteristics of a pressure-controlled loop heat pipe

Abstract

The effect of the supplied heat load on the operating characteristics of the pneumatic temperature control technique was systematically investigated. A pressure-controlled loop heat pipe employing water as a working fluid was designed and constructed to provide a unique thermohydraulic linkage between temperature and pressure. The temperature of the high-speed vapor was precisely controlled by using helium (control gas) to actively control the compensation chamber pressure; the stability of the pneumatically controlled temperature was approximately 0.01 °C regardless of the heat load. Stable stepwise temperature increase was attained below a critical pressure step that rose with increasing heat load. This behavior implied that a stable range of pneumatic temperature control became larger with increasing heat load. In addition, the maximum pressurization rate for rapid, stable, and unlimited temperature rise increased with increasing heat load. The uniformity of the controlled temperature field was less than approximately 0.2 °C over 25 cm; effects of the heat load were insignificant at all tested conditions. Overall, pneumatic temperature control over extended pressure and temperature ranges was attained at higher heat loads with insignificant effects of the heat load on stability and uniformity.