Water-copper nanofluid application in an open loop pulsating heat pipe

Several investigations have pointed the operational behavior of passive thermal control devices such as loop heat pipes (LHPs) and pulsating heat pipes (PHPs) in the past, which have cleared many points related to their design. However, an interesting aspect related to passive thermal control devices that operate by means of capillary forces to pump the working fluid have gained attention during the last years, is in regard to the use of nanofluids on such devices. Nanofluids are known as regular fluids with addition of solid nanoparticles with sizes (diameter) below 40 nm, which are used to enhance the working fluid’s thermal performance by enhancing its thermal conductivity. Previous works have demonstrated that the liquid’s thermal conductivity can be enhanced by 20% if nanoparticles are added on a concentration of 5% by mass. PHPs operate by the dynamics of slug/plug formation, removing heat from a high temperature source and dissipating in a low temperature sink, and are highly influenced by the bubble critical diameter related to a specific working fluid. Thus, an experimental open loop PHP (OLPHP) was tested with water-copper nanofluid, with an addition of 5% by mass of copper nanoparticles. Improvements on the overall device’s operation have been observed when using the nanofluid with lower temperatures, as well as a direct influence on the thermal conductances throughout the PHP.