Numerical study on vapor–liquid phase change in an enclosed narrow space

Abstract

Based on the multiphase lattice Boltzmann method, a transient model of vapor–liquid phase change in an enclosed narrow space during startup operation is developed and numerically analyzed to investigate the two-phase dynamics and heat transfer behaviors in the confined flat two-phase thermosiphon. The transient temperature distribution, vapor–liquid interface evolution and thermal performance are investigated over a wide range of heat load and liquid filling ratio. The results indicate that, as heat load increases, the intermittent nucleation boiling, fully developed nucleation boiling and film boiling sequentially takes place at the evaporator section of the confined flat two-phase thermosiphon. Correspondingly, the transient temperature evolution shows the periodic large-amplitude fluctuation, the random medium-amplitude fluctuation, and gentle small-amplitude fluctuation. The fully developed boiling is desirable for the heat transfer enhancement on the evaporator surface due to smaller temperature fluctuation and lower thermal resistance. The moderate liquid filling ratio ensures the desired interaction between the evaporator and condenser, resulting in superior thermal performance. To optimize the thermal performance, the optimal liquid filling ratio is about 40%.