Separated liquid-vapor pathways: a hybrid cooling strategy with selective surface modification and jet impingement in open microchannels for enhanced heat transfer

With the rapid development of chip technology and the ever-increasing power density of high performance devices, the demand for efficient thermal management solutions has become increasingly critical. This study demonstrates that, in flow boiling, the “separated liquid-vapor pathway” strategy can be realized far more effectively than in pool boiling. We propose an integrated cooling scheme combining jet impingement, open microchannels, and selective surface modification to regulate bubble dynamics. By enforcing a controlled cycle of bubble generation, migration, growth, and departure, the design maintains effective liquid replenishment and prevents dry-out, thereby sustaining a well-wetted channel wall across the nucleate boiling regime. As a result, a high critical heat flux (CHF) of 615 W/cm 2 is achieved under combined channel and jet flows (each at 75 mL/min), even with minimal heat transfer area augment of fin-top modification. The underlying mechanism of the pathway-separation strategy is clarified, showing that its efficacy is substantially enhanced in flow boiling through the synergistic combination of channel flow, jet impingement, and selective modification. High-speed flow visualization captures the complete bubble motion cycle: bubbles nucleated at the channel bottom first condense and break up under the jet, then migrate to the fin tops via bubble-induced macro convection, where they grow further before departing under channel-flow inertia. A predictive model is developed to quantitatively analyze the CHF triggering mechanism, providing further insight into the performance enhancement achieved by this integrated approach.