Visualization study on temporal regime transition of multicomponent subcooled flow in microchannel

Abstract

Researching the regime transition of the subcooled flow is essential for designing high-performance heat exchangers. A high-speed camera platform is built to study the bubble behavior of the subcooled boiling of a water-ethanol mixture in a microchannel. Simultaneous synchronisation of thermodynamic transient characterisation and high speed flow visualisation. The flow in the microchannel can be divided into single-phase convection, isolated bubble, bubbly flow, and slug flow regions. The combination of micro-channel and multi-component coolant along with keeping the subcooled boiling within the bubbly flow region can improve the heat transfer performance. The wall effect in the microchannel will enhance the bubble-induced heat transfer and result in a reduced heat transfer performance under higher inlet velocity conditions. Compared with lower velocity of 0.05 m/s, the bubble departure frequency for higher velocity of 0.15 m/s decreased by a maximum of 2 times in the bubbly flow region. The heat transfer coefficient for the bubbly flow regime is found to be universally proportional to the void fraction for all conditions analysed in this paper. Hence, the manners that are beneficial for void fraction improvement can be utilized to regulate the heat transfer coefficient of the microchannel within the bubbly flow regime.