Abstract:
2D transient multi-mode film boiling simulation of water near critical pressure (p = 0.99p = 21.9 M Pa) on a heated horizontal surface is carried out using an in-house Level Set (LS) method based semi-explicit finite volume method code. The influence of initial vapor film thickness (y(0)) on the dominant instability mode is evaluated by carrying out simulations on domain having width greater than most dangerous Taylor wavelength i.e. L(X) = 4 lambda(d) with y(0)= 0.0425 lambda(d) and 0.125 lambda(d) at low wall superheat (Delta T = 2K). For lower initial film thickness, the viscous force dominated Rayleigh-Taylor instability is captured and the average bubble spacing is found close to the prediction made using lubrication theory i.e. lambda(p) = root 2 lambda(c) = 0.816 lambda(d). However, for higher initial film thickness, the inertia force dominated TaylorHelmholtz mode of instability is found with the average bubble spacing close to lambda(d). Simulations are carried out to check the existence of Rayleigh-Taylor instability on various domain width Lx = 2 lambda(d), 3 lambda(d), 4 lambda(d) and ad at y(o)= 0.0425 lambda(d) and Delta T = 2K. The average bubble spacing for all domain widths is found to be less than root 2 lambda(c) indicating that the Rayleigh-Taylor instability is dominant.