Hot-spot self-cooling effects on two-phase flow of R245fa in 85µm-wide multi-microchannels

Two-phase refrigerant flow boiling was shown to be effective in handling hot-spots. The footprint heat transfer coefficients followed the local heat flux and formed a self-compensating cooling mechanism by increasing the local heat transfer coefficient at the hot-spot. Data reduction using one-dimensional heat conduction overestimated the heat transfer coefficient at the hot-spots and underestimated it around its location. Heat spreading effects should be taken into account for more precise calculations (work in progress). Existing two-phase heat transfer prediction methods for micro-channels are accurate and can be applied to nonuniform heat flux conditions, independently of the data reduction method. The three-zone model of Thome et al. was found to be the most accurate, placing 53.3% of the predicted data within ±30% of the experimental values. If the hot-spot is placed toward the outlet, the resulting pressure drop will be smaller and the base temperature lower. The thermal resistance of two-phase flow cooling decreased with increasing heat flux and became smaller than that of the composite wall at high heat fluxes.