Mesoscopic study on effect of electric field and heater characteristics on saturated pool boiling heat transfer

Abstract

The phase change lattice Boltzmann (LB) model combined with the electric field model is employed to investigate the heat transfer performance of saturated pool boiling. Particular attention is paid to the influence of heater surface wettability and heater length on bubble behaviors, including generation, merging, and fracture during boiling in a uniform electric field. Moreover, the effects of the bubble behavior on heat transfer performance are also investigated. The study results indicate that the enhancement of boiling heat transfer by the electric field is dependent on both the heater length and the wettability. In the case of a hydrophilic surface, when the heater length <inline-formula><tex-math id="M5">\begin{document}$L_H^*\leqslant 6.25$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M5.png"/></alternatives></inline-formula>, the bubble interaction force generated on the heater surface during boiling is weak due to the small size of the heater. Thus the effect of a uniform electric field on the bubble dynamic behaviors is mainly manifested by reducing the bubble size. As a result, the whole boiling phase is suppressed in this case. In the case of <inline-formula><tex-math id="M6">\begin{document}$6.25 < L_H^*\leqslant9.375$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M6.png"/></alternatives></inline-formula>, the uniform electric field enhances the critical heat flux (CHF), and the enhancement degree increases with electric field strength increasing. This can be attributed to the longer heater providing sufficient space for bubble generation, resulting in increased bubble nucleation sites and stronger interaction forces between bubbles. On the other hand, the distance between adjacent bubbles increases with the heater length increasing,thus further contributing to the improved CHF percentage. When <inline-formula><tex-math id="M7">\begin{document}$L_H^*>9.375$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20230341_M7.png"/></alternatives></inline-formula>, the rewetting resistance increases with heater length increasing. So the vapor generated in the boiling process is prone to be closely adhered to the heating surface under the action of electric field force, forming a thin layer of vapor on the heater surface. The vapor not only increases the heat transfer thermal resistance between the solid and the fluid but also creates no vortex near the bubble. This is not conducive to the movement of the bubble to the middle of the heater, thereby slowing down the heat mass exchange between the hot fluid on the heating surface and the colder fluid on both sides. As a result, the improved percentage of CHF decreases gradually with the increase in the heater length. In the case of hydrophobic surfaces, the increased percentage of CHF initially increases with heater length increasing and then decreases. However, comparing with the hydrophilic surface, the increase of the heater source length corresponds to the beginning of the decrease of critical heat flux.