Flow boiling behavior of R1233zd(E) in embedded silicon microchannel heat sinks: Flow visualization, heat transfer and pressure drop

To meet the increasing thermal management demands of high-power electronic devices, two-phase flow boiling in embedded microchannel heat sinks has attracted considerable attention because of its high heat transfer capability and compact structure. However, a systematic investigation combining flow visualization, infrared thermography, and local heat transfer analysis for R1233zd(E) under different operating conditions is still lacking. In this study, flow boiling experiments are conducted using R1233zd(E) in four silicon microchannel heat sinks with channel widths of 100, 150, 200, and 300 µm and a constant channel depth of 100 µm. Infrared thermography is employed to measure the wall temperature distribution, while high-speed visualization is used to investigate the evolution of boiling flow regimes. Furthermore, local heat transfer coefficients are calculated by combining infrared temperature measurements with fluid pressure and temperature measurements, enabling a detailed analysis of the local boiling heat transfer behavior. The effects of channel width, mass flux, and heat flux on average heat transfer performance, pressure drop, wall temperature distribution, local heat transfer behavior, and flow regime evolution are systematically investigated. Bubbly, slug, and annular flow regimes are identified under different operating conditions. Increasing heat flux promotes an earlier onset of nucleate boiling (ONB), enlarges the boiling region, and accelerates the transition of flow regimes. In contrast, increasing mass flux delays boiling inception and shifts the boiling region downstream because of the enhanced liquid convection. Pressure-driven flashing is observed under high mass flux conditions and gradually weakens with increasing heat flux and is replaced by nucleate boiling. The results show that mass flux and channel width have only a minor influence on the average heat transfer coefficient under two phase conditions, whereas the pressure drop increases significantly with increasing mass flux and channel width. Local heat transfer analysis reveals that the local heat transfer coefficient highly depends on heat flux, while mass flux and channel width mainly influence the ONB location and the local heat transfer distribution. The present study provides a comprehensive understanding of the coupling between flow regime evolution, wall temperature distribution, and local heat transfer behavior during flow boiling of R1233zd(E), providing valuable experimental guidance for the design and optimization of microchannel heat sinks for two-phase electronics cooling.