Numerical simulation of gravity effect on heat transfer in single bubble pool boiling

The bubble dynamics and heat transfer in single bubble pool boiling of saturated FC-72 at different gravity levels are studied numerically, having transient thermal response of the heated SiO₂ wall with a thickness of 5 mm. A constant and uniform temperature corresponding to a superheat of 10 K is prescribed at the bottom surface of the solid wall. Multi-cycle simulations are conducted and quasi-steady state of boiling process is achieved. It is observed that the bubble departure diameter, inversely proportional to the square root of gravity, is consistent with the Fritz model, and the bubble frequency is proportional to the gravity. There are two regions with obvious differences in terms of heat transfer, namely a gravity-dependent region and a gravity-independent region. The corresponding transition or critical value of the gravity is about 0.03g₀. The heat flux has a power law relation with the gravity at constant superheat if the gravity is larger than the critical value, while this trend will break down when gravity is less than the critical value. The boundary between these two regions is located in the range of dimensionless heater length based on the Laplace length from 2 to 3, which is close to 2.1 proposed by Raj-Kim-McQuillen model. In the gravity related region, the exponent of the power law relation increases monotonously with the superheat, but its value is obviously larger than the prediction of Raj-Kim-McQuillen model. It is also found that the transient thermal response of the solid wall has a more obvious effect on the heat transfer performance in SDB region than in BDB region.