Combined effect of electric field, subcooling and microgravity on critical heat flux on a wire in pool boiling

An experimental facility was set up to investigate pool boiling on a heated wire in the presence of an electric field and in reduced gravity. The arrangement allowed achieving various pressure and subcooling combinations, independently of the environmental conditions. The test section was an electrically heated platinum wire with diameter of 0.2 mm. The working fluid was R113 (C2Cl3F3). A cylindrical electric field was generated imposing 0 to 10 kV d.c. to a 60 mm diameter "squirrel cage" mounted coaxially to the heater. Ground experiments were mainly devoted to assessing the combined influence of subcooling and electric field on critical heat flux at different pressures. The two factors seem to act independently of each other in the tested range, and the pressure has no influence. Experiments in reduced gravity were run in a parabolic night campaign, covering mostly the nucleate boiling and critical heat flux (CHF) region at a pressure of 1 bar and with slightly subcooled liquid. An improvement in CHF due to electric field is evident both in normal gravity (as well known) and in micro-g. However, the relative enhancement of the critical heat flux, with respect to the zero-field one, is the same both in normal and in reduced gravity. No further improvement at lower electric field, as predicted by a theory based on scaling groups, seems to take place in reduced gravity with respect to normal gravity.