In this paper, the growth processes of a single bubble on a fixed single site in different gravity are numerically investigated for saturated water at 0.1 MPa. The departure diameter decreases with the decrease of the wall superheat, while the growth period increases. Both the growth period and departure diameter decrease with the decrease of the contact angle, but increase with the decrease of gravity. The numerical results of single bubble boiling indicate that the heat transfer through the micro-wedge region has a very important contribution to the whole heat transfer in boiling.The area-averaged heat fluxes in different gravity are approximately proportional to the 1.5th power of the wall superheat when the number density of active nucleation sites fixes, which is consistent with empirical correlation based on experiments in normal gravity.
A space experiment on bubble behavior and heat transfer in subcooled pool boiling phenomenon has been performed utilizing the temperature-controlled pool boiling (TCPB) device both in normal gravity in the laboratory and in microgravity aboard the 22 nd Chinese recoverable satellite. The fluid is Rl13 at 0.1MPa and subcooled by 26~ nominally. A thin platinum wire of 60#m in diameter and 30mm in length is simultaneously used as heater and thermometer. Only the lateral motion and the departure of discrete vapor bubbles in nucleate pool boiling are reported and analyzed in the present paper. A scale analysis on the Marangoni convection surrounding a bubble in the process of subcooled nucleate pool boiling leads to formulas of the characteristic velocity of the lateral motion and its observability. The predictions consist with the experimental observations. Considering the Marangoni effect, a new qualitative model is proposed to reveal the mechanism underlying the bubble departure processes and a quantitative agreement can also be acquired.
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