Flow boiling heat transfer characteristics of de-ionized water in superhydrophobic microchannels under electrowetting actuation

Surface wettability is a critical factor influencing microchannel boiling phase-change heat transfer. Most current methods produce surfaces with unitary hydrophilic or hydrophobic properties, which cannot dynamically adjust wall wettability in response to boiling characteristics. The electrowetting effect offers the advantage of real-time surface wettability modulation. This study experimentally investigates the impact of the electrowetting effect on flow boiling in superhydrophobic microchannels, exhibiting a static contact angle of 153.4° ± 1.5°. Experimental results reveal that the electrowetting exerts a greater influence on wall temperature when large bubbles dominate the flow boiling process compared to scenarios with smaller bubbles. In the voltage range of 60–100 Vrms, higher voltages intensify vapor–liquid interface oscillations and promote rewetting of dry-out regions, leading to enhanced wall cooling. However, as the heating power increases, the cooling effect exhibits a non-monotonic trend due to competing interfacial forces: evaporation momentum forces generated during bubble nucleation and growth progressively surpass electrowetting-induced liquid film movement, diminishing interfacial modulation. At flow rates of 0.3–0.8 ml/min, higher flow rates reduce bubble nucleation sites while accelerating bubble detachment, limiting both the spatial extent and temporal duration of electrowetting-induced interfacial interactions, consequently reducing wall cooling performance. At a low flow rate of 0.3 ml/min and a low heating power of 4.77 W, applying a high voltage of 100 Vrms reduces the local wall temperature up to 13 °C and increases the local and average heat transfer coefficients by 180.9% and 31.0%, respectively. This study provides significant insights for advancing applied research on electrowetting-enhanced boiling heat transfer in microchannels.