Model solving and size optimization of dryout threshold for vertical micropillar evaporators

The existing dryout threshold model was optimized by adding gravity and combining with capillary force and permeability solution methods, so as to obtain the best combined model (Darcy_avg(S)+SE) for characterizing the heat transfer performance of a vertical micropillar evaporator with an average error of about 7%. The effect of micropillar geometry was investigated using this model. Model predictions indicated that the maximum heat transfer capacity of the evaporator was balanced between permeability and capillary pressure; those geometries close to the optimal pitch ratio (d/l≈0.35) and higher micropillars correspond to greater heat dissipation capacity; and that micropillar arrays with smaller receding contact angles correspond to greater dryout thresholds. The increase of the dryout length under gravity led to a significant decrease of the dryout threshold, and the genetic algorithm can be effectively used to solve for the optimal size at different dryout lengths. The arrangement method affected the dryout threshold, the forked-row arrangement of the micropillar arrays increased the heat transfer capacity by nearly 13% compared with the smooth-row arrangement at optimal spacing ratio.