Evaporator/boiler design for thermosyphons utilizing segregated hydrofluoroether working fluids

Abstract

In this work, a new micro porous metallic coating method is used to produce two compact boiler assemblies that are practical for use in thermosyphons in electronics systems. These assemblies were tested using a segregated hydrofluoroether (HFE) working fluid C3F7 OCH3 on 1.0, 4.0 and 13.7 cm2 heat sources at atmospheric pressure. The best of these yielded sink-to-fluid resistances, Rsf, at 230W of 0.092, 0.047 and 0.024degC/W, respectively. This boiler assembly was incorporated into a thermosyphon with a remote 100times100times2.2mm finned-tube condenser that produced a condensation resistance, Rfa, of ~0.1degC/W with a 7.6W 92times3 8mm fan. That thermosyphon was tested on the aforementioned heat sources yielding much improved Rsf values of 0.083, 0.026 and 0.014degC/W at 150W. Data gathered with larger condensers or more powerful fans suggest that it is quite practical to produce a compact thermosyphon that can cool a 20mm device generating 250W with Rsa<0.10C/W, a performance level competitive with forced water systems