POOL BOILING IN THE PRESENCE OF AN ELECTRIC FIELD AND IN A VARIABLE GRAVITY FIELD: RESULTS OF EXPERIMENTS IN PARABOLIC FLIGHT

The electric field has an influence on boiling heat transfer, as evidenced many years ago, and can act as a replacement of buoyancy in the absence of gravity. An experimental facility was set up to investigate pool boiling on a Pt heated wire of 0.2 mm diameter in the presence of an electric field and in microgravity. The working fluid was R-113 (C2Cl3F3). On-earth experiment revealed that the critical heat flux undergoes a three-fold increase or more by applying a high voltage cylindrical electrostatic field around the wire: this effect was suitably scaled by means of an electric influence number. Nucleate boiling performance is on the contrary slightly affected in the present configuration. The facility was then operated in parabolic flight at an acceleration level of 0.03 g. The results indicates that, notwithstanding the dramatic alteration of bubble size, the nucleate boiling performance is weakly affected by gravity acceleration both in the presence of the electric field or less. The critical heat flux is decreased in microgravity with respect to ground values, but the electric field substantially improves it also in this condition. The analysis of the data on the basis of the available scaling groups indicates that the scaling based on Bond number seems to be effective, while a more thorough analysis is needed to test the validity of the electrical influence number.