Study of micro-heater shape and wettability effects on inception of boiling phenomenon using a multiphase lattice Boltzmann method

Abstract

In the present paper, the inception of boiling phenomenon and the resulting bubble dynamics are investigated using a multiphase lattice Boltzmann method (LBM). Two equations of state (EoS), namely the Peng-Robinson (P-R) and the Redlich-Kwong-Soave (R-K-S), are employed and their capability for the prediction of the bubble nucleation, growth, and departure is evaluated against the available data in the literature. The effect of the micro-heater surface wettability and shape, namely the grooved and cavity, are studied on the separation time and velocity of the detached bubble at different flow conditions. Based on the present results, the boiling phenomenon nucleates from sharp-angled edges of the groove and cavity that are the region with higher temperature gradients. For the hydrophilic heated surface, the growth of the bubble continues on the sharp edges with the minimum dry spot on the surface. However, the hydrophobic heated surface tends to attract the forming bubble in the inception process, so that the boiling bubble is flattened on the heated surface after formation and tends to stick to the micro-heater. It is found that the bubble separation time from the micro-heater surface is longer, and the departure velocity is lower for the hydrophobic heated surface in comparison with the hydrophilic wetting condition. Also, the present study shows that the bubble separation from the grooved micro-heater occurs faster and with a higher velocity in comparison with the cavity micro-heater at a certain contact angle that demonstrates the significant effect of the surface shape on the boiling phenomenon. Hence, the grooved micro-heater is incorporated with two triangular pillars. The results demonstrate that using pillars provides more time for the bubble to grow before departure from the surface due to the blockage of the liquid flow coming from the lateral sides to the bubble formation site.