Local heat transfer of saturated flow boiling in vertical narrow microchannel

Abstract

In this experimental study, saturated flow boiling in a one-side-heating vertical narrow rectangular microchannel is conducted with deionized water as the working fluid, the mass flux is in the range of 120 kg/m2s – 360 kg/m2s, the wall heat flux varies from 6 W/cm2 to 24 W/cm2 and the inlet vapor quality is 0.03 or 0.1. The bottom surface of the microchannel is constructed of two different material, one is the untreated hydrophilic silicon wafer with a contact angle of 65° ± 3°, the other is the super-hydrophilic silicon wafer deposited with a thin film of 100-nm-thickness silicon dioxide through PECVD with a contact angle less than 5°. The flow patterns in almost all experimental conditions are the annular flow and the heat transfer mechanism is dominated by convective evaporation, the heat flux transfers through the conduction and convection in the thin liquid film and evaporation at the interface between the vapor and liquid. The thinner the liquid film, the greater the heat transfer coefficient. The local dryout phenomenon is observed on the untreated hydrophilic surface while the super-hydrophilic surface can keep the liquid film uniform and restrict the occurrence of local dryout phenomenon. Through the evaluation of the correlations of heat transfer coefficient, this study proposes the modified Li and Wu [18] correlation as a formula for calculating the heat transfer coefficient of saturated flow boiling in a vertical narrow one-sided heating microchannel.