NUMERICAL SIMULATION OF BUBBLE SHAPE AND DEPARTURE IN NUCLEATE POOL BOILING AT HIGH SUPERHEAT

In this work, the authors reported the dynamics of bubble shape and departure in nucleate pool boiling at the heated surface at a high superheats of 34 K. The numerical results of bubble shape and departure have also been compared with the CFD-results in literature and with our experimental results. The shape of the bubble is influenced by superheats and Bond number Bo. We have improved our numerical model by including the effect of radial variation of film pressure on microlayer evaporation to accurately compute the bubble shape, bubble diameter and growth time. We see that the approximate analytical solution works much better than the direct numerical integration of Young-Laplace equation for non-spherical bubble at high superheat. The Young-Laplace equation seems to include the growth force for capturing the shape of non-spherical bubbles. Interestingly, we find a train of small bubbles at a low Bo, which coalesce to form a big bubble on increasing Bo. While analysing the forces acting on the bubble surface, we also see that the growth force imparting the liquid inertia becomes important for the hemispherical bubbles.