Self-rewetting heat transfer fluids and nano-brines for space heat pipes

This paper summarizes the main activities in preparation of microgravity experiments dedicated to performances characterization of innovative heat pipes systems based on ‘‘self-rewetting fluids’’, i.e. fluid mixtures with a non-linear dependence of the surface tension with temperature. In preparation of the flight experiments, laboratory researches have been carried out to identify potential heat transfer fluids. The activities include measurements of surface tensions, contact angles and thermal conductivities for a number of multicomponent solutions, including self-rewetting alcohol solutions, brines and nanofluids. A non-linear surface tension dependence with temperature was found not only in binary mixtures but also in brines and nanofluids with small concentrations of butanol or heptanol. A number of figures of merit are introduced and evaluated on the basis of several fluid properties, including surface tension, contact angle, viscosity, freezing point, thermal conductivity. The paper discusses the results of these investigations and laboratory characterization tests of different heat pipes, including reference ordinary heat pipes and innovative pipes filled with self-rewetting fluids, brines and nanofluids.