The role of Tesla valves in microchannel flow boiling

Tesla valves is one century-old design with excellent single-phase flow diodicity. Tesla valves have been extensively investigated to control the single-phase and two-phase flows. It is of great interest to comprehensively investigate the effects of Tesla valves in enhancing microchannel flow boiling. Normally, unwanted vapor backflow is a common phenomenon in conventional microchannel flow boiling due to the confinement effect, accompanying with severe two-phase flow instabilities. These two factors seriously deteriorate the flow boiling performances. Achievement of directional two-phase flows by rectifying vapor backflow is highly desired for flow boiling. Herein, copper Tesla microchannel consisted of periodic well-designed Tesla valve structures was proposed and a heat sink was fabricated to completely inhibit the vapor backflow. Characteristics of flow boiling including HTC, CHF and fluctuations of pressure and wall temperature were systematically studied. Experimental results indicate that this as-designed Tesla microchannel is able to significantly enhance flow boiling performances by successfully suppressing reverse two-phase flow. Comprehensive comparison was conducted to elucidate the enhanced mechanisms by comparing with other three configurations, including plain-wall microchannel, saw-tooth microchannel and Tesla-type microchannel. The CHF of Tesla microchannel is significantly increased by 128 % at a flow rate of 5.4 kgh^-1, reaching to about 310 Wcm^-2. The Tesla microchannel completely outperform the other microchannel configurations with functionality of suppressing vapor backflow at some extent. The wall temperature and pressure oscillations are decreased significantly. The two-phase pressure diodicity is also examined, which is up to 1.8.