A numerical study of saturated pool film boiling over a sphere

Abstract

A detailed numerical investigation of saturated pool film boiling over a sphere is presented in this work. The CLSVOF method was used for capturing the dynamic interface. Computations were performed to study the effect of dimensionless sphere diameter (D/λ0), the dimensionless wall superheat (Jav) and the external gravity field on the interface evolution and the associated heat transfer characteristics. The simulations were performed for D/λ0 varying in the range of 0.5-5.0, while Jav varies in the range of 6.36-19.07 for both normal and reduced gravity field. Under the normal gravity conditions, a periodic vapour bubble ebullition cycle is observed for D/λ0=0.5 and 1.0, whereas a stable vapour column is observed to develop for D/λ0=5.0. The vapour film thickness decreases as the D/λ0 increases for a constant Jav under normal gravity conditions. Furthermore, under the normal gravity conditions, vapour generation is observed to be asymmetrical in the thin vapour film for D/λ0=5.0. For D/λ0=0.5 and 1.0, vapour bubbles are released further downstream of the heated sphere as the dimensionless wall superheat increases under normal gravity. When compared to the normal gravity conditions, the interface evolution pattern changes significantly at low gravity. The space–time averaged Nusselt number is used to quantify the heat transfer in the present work. A Fast Fourier Transform (FFT) analysis of the temporal evolution of the space averaged Nusselt number reveals a complex interplay between different forces for saturated pool film boiling over a sphere for various flow and geometrical conditions.