Terrestrial and microgravity applications of self-rewetting fluids

Dilute aqueous solutions of high-carbon alcohols (number of C≥4) show an increase in the surface tension with increasing temperature in a particular temperature region. Liquid/vapor phase change in these aqueous solutions induces a very strong liquid flow in the vicinity of the interface due to both thermocapillary flow and the Marangoni flow caused by the preferential evaporation of alcohol-rich composition. Since such a spontaneous local liquid flow directs toward dry patch or hotter area, the expression of “self-rewetting” has been employed for these liquids. The present author focused his attention to this particular surface tension behavior, and has been studying both terrestrial and microgravity applications utilizing self-rewetting fluids as a working fluid in heat transfer devices. This article briefly introduces some of the recent research subjects related to self-rewetting fluids conducted by the present author and co-workers. First, the improvement in the thermal performance of wicked heat pipes with using self-rewetting fluids is emphasized based on detailed experimental evaluations. The experimental results on ultra-light weight wickless heat pipes, fabricated with 25µm thick polyimide film, in low gravity condition are then given.