Experimental investigation of flow boiling in a 4.0 mm tube at different gravity conditions: 0g, 1g, and 2g

Convective boiling in reduced diameter channels has been presented as an efficient way of cooling high heat fluxes generated by electronic components. In this context, a large number of authors have dedicated their efforts to study this heat transfer mechanism in normal gravity conditions. However, in space applications under microgravity conditions, and in aircrafts, which have variations in a range of acceleration in that fluid is undergoing, the number of studies is reduced. It is well known that bubble nucleation process and flow behavior are affected by the gravitational acceleration which fluid is subjected. Therefore, this paper aims to evaluate experimentally convective boiling in a small diameter channel under micro and hyper gravity conditions and compare them with results obtained on the ground. Tests were conducted with Perfluorohexane in a horizontal 4.0 mm I.D. circular channel with a heated length of 155 mm for mass velocities of 115 kg/(m2 s), 215 kg/(m2 s) and 323 kg/(m2 s) and a broad range of heat fluxes and vapor qualities. Gravity tests were performed during parabolic flights, managed by NOVESPACE. Experiments show the influence of gravity on flow pattern characteristics and transitions. Moreover, the highest heat transfer coefficients were observed under microgravity conditions. However, this behavior becomes less evident with increasing the mass velocity.