Experimental Investigation on Pool Boiling Performance of Expanding-Microchanneled Surface at Sub-Atmospheric Pressure Environment

Abstract

In the present work, visualization experiments on the saturation boiling of deionized water were conducted at sub-atmospheric pressure using microchanneled surfaces. Pool boiling characteristics, including pool boiling curves, heat transfer coefficients (HTC), and bubble departure diameters on straight- and expanding-microchanneled surfaces (SCS and ECS), were compared with a plate surface (PS) under various saturated pressures PS (8.80 kPa, 13.0 kPa, 18.0 kPa, 26.0 kPa, 38.5 kPa). The experimental results revealed that under 8.80 kPa conditions, the HTC of the ECS was improved by 296% compared to PS. Besides, bubble departure diameters on the microchanneled surfaces remained smaller than those on the plate surface under all sub-atmospheric pressure conditions. Consequently, more and smaller bubbles on ECS enhanced the perturbation of the thermal boundary layer, leading to the reduced wall superheat. The pool boiling heat transfer performance of ECS was found to be less sensitive to saturated pressure than SCS, attributed to asymmetric evaporative momentum force. Additionally, based on bubble force analysis, empirical models are established to relate the bubble detachment diameter, boiling curve and HTC on the microchanneled surface.

Keywords: Pool boiling enhancement, Sub-atmospheric pressure condition, Asymmetric evaporative momentum force, Bubble dynamics, Visualization experiment