Numerical study on the activation of nucleation sites and bubble interactions in twin-bubble nucleate boiling

The present study aims to investigate the interplay between the activation behavior of neighboring nucleation sites and the corresponding bubble dynamics in twin-bubble nucleate boiling. For this purpose, boiling of water on a copper heater with two nucleation sites is simulated by using a thermal-hydrodynamic coupling method. This method treats active nucleation sites as vapor sources, and the vapor generation rates from the nucleation sites are incorporated into the two-phase flow simulation as the inlet boundary conditions at the corresponding sites, which are computed via a dynamic model of microlayer evaporation. Various sizes and arrays of cavities are considered to investigate the activation timing of the nucleation sites, temperature fluctuations of the heated surface, and dynamics of the two bubbles. The simulated results show that the hydrodynamic interaction between the adjacent bubbles can cause the alternative activation of the nucleation sites and lead to irregular fluctuations to the temperature of the heated surface. The difference of the critical activation superheats between the neighboring nucleation sites can induce intermittent activation of the nucleation sites accompanied with a waiting time of the activation for the smaller-size cavity. The smaller the cavity is, the longer the waiting time of the activation becomes. The two bubbles growing from different nucleation sites are observed to approach each other, which stem from the wake flow left by the neighboring rising bubbles.