Exploring flow boiling characteristics on surfaces with various micro-pillars using the lattice Boltzmann method

Abstract

In this study, the lattice Boltzmann method is utilized to simulate flow boiling within a microchannel featuring a micro-pillar surface. This investigation aims to explore the impacts of micro-pillar shape and quantity on the flow boiling characteristics across various superheats and Reynolds numbers (Re). A systematic examination is conducted on three types of micro-pillars, five quantities of micro-pillars, four Re values, and 18 superheat levels. The mechanisms contributing to enhanced heat transfer in flow boiling are elucidated through a comprehensive analysis of bubble dynamics, temperature and velocity fields, local and transient heat fluxes, and boiling curves. Moreover, the critical heat fluxes (CHF) of all surfaces are evaluated to identify the superior micro-pillar configurations. The findings revealed that microchannels with micro-pillar surfaces induce more vortices compared to those with smooth surfaces, attributable to the combined effects of bubble dynamics and micro-pillars. Bubble patterns and boiling curves demonstrated the significant impact of micro-pillar geometrical shapes on the boiling regime and heat transfer performance. As flow boiling progressed, an increase in micro-pillar quantity and Re can mitigate the fluctuation and decline rate in transient heat flux, respectively. Among the three types of micro-pillar surfaces, the circular shape exhibited the highest flow boiling performance, followed by the triangular and rectangular shapes. For all surfaces, the CHF increased with Re, and each micro-pillar type displayed an optimal quantity for achieving maximum CHF, with the highest increase reaching 45.2%. These findings are crucial for optimizing microchannel designs to enhance flow boiling heat transfer efficiency.