Bubble formation and pressure drop characteristics during evaporation in a lattice-shaped microchannel

This study investigates bubble formation, pressure drop (flow rate), and wall temperature variation during fluid heating in a lattice-shaped microchannel under constant heat flux conditions. The microchannel was designed with periodically arranged pillars to trap bubbles in specific regions, enabling simplified and controlled observation of bubble behavior and its influence on neighboring bubble formation. Imaging and infrared thermography were used to visualize bubble dynamics and measure wall temperature distributions. The fluid was supplied under constant driving pressure, and the flow rate during bubble formation was recorded. To complement the experiments, a numerical simulation was performed by coupling two-dimensional flow analysis with a probabilistic element-filling model. Two bubble formation models were considered: a random model, in which bubbles form independently, and a neighbor-driven model, in which the filling probability increases near already filled regions, mimicking bubble propagation. The neighbor-driven model produced clustered bubble patterns and wider flow passages, resulting in lower pressure drops compared to the random case. An analytical model for pressure drop was developed based on the simulation results, incorporating both random and propagative bubble formation mechanisms. This model was applied to the experimental data and showed good agreement with the measured relationship between unfilled ratio and flow rate. Temperature measurement showed that the effect of heat transfer to the bubble propagation was relatively small in this study. The findings underscore the importance of accounting for both stochastic and deterministic effects in bubble formation within microchannels.