Influence Of Near Wall Bubble Dynamics On The Heat Transfer During Nucleate Pool Boiling

Due to the significant heat transfer rates nucleate boiling has been widely applied in both traditional and high-tech processes and has become a very active research topic in the heat transfer field. This dissertation analysis the bubble growth process theoretically and experimentally. Bubble interactions are also experimentally observed using a high speed camera.The simulation of bubble growth process included the wall temperature variations and the evaporation heat flux from the liquid microlayer. The results show that the liquid subcooling and wall superheat significantly influence the bubble growth rates. Large contact angles also lead to a large bubble growth rates but the total heat transfer has a peak at 60 degrees. In addition, the wall material influence bubble growth rates through thermal diffusivity.Visual observations of the bubble growth during nucleate boiling show that the bubble remains spherical for small subcooling conditions while bubble interface oscillates for big subcoolings. Ethanol bubbles are more likely to move around on the surface during subcooled nucleate boiling and keep growing until departing from the wall. When the distance between two bubbles is less than twice the bubble departure diameter, the hydrodynamic interactions between two bubbles and the thermal interactions between two nucleation sites both affect the bubble dynamics. For saturated nucleate boiling, bubbles growing from the same site vertically coalescence two and even three times. Sometimes, bubbles growing from two adjacent sites could first coalescence in the horizontal direction and then coalesce with the previously departed bubble in the vertical direction. Sweeping ethanol bubbles can collide with each other when moving around on the surface.