Experimental and analytical investigation of flow boiling maldistribution in parallel mini/micro-channel heat sinks under non-uniform heating conditions

Abstract

This study elucidates the mechanism of flow boiling maldistribution in parallel mini/micro-channel heat sinks under non-uniform heat flux conditions, with particular emphasis on key instability phenomena. The relative dominance of forward and backward forces in individual channels critically influences the intensity of flow maldistribution, and a modified instability parameter, R *, was introduced to quantify this dominance. A strong correlation is established between R * and the degree of flow non-uniformity, with the most severe maldistribution observed near R * ≈ 1.58. The analysis reveals that flow resistance in individual channels—governed by both thermal and hydrodynamic factors—is the dominant factor affecting flow distribution. Unlike single-phase flow, where resistance depends solely on hydrodynamics, two-phase flow boiling is highly sensitive to heat flux, inlet subcooling, and vapor backflow. The study further identifies a coupling mechanism between pressure-coupled instability (PCI) and vapor backflow, where vapor propagation into the inlet plenum elevates the local temperature, alters the flow inertia, and reshapes the distribution among channels. These findings highlight the critical role of thermal characteristics in the inlet plenum and the importance of dynamic instabilities and thermal non-equilibrium in predicting and controlling flow maldistribution in high-heat-flux thermal management systems. © 2025 Elsevier Ltd.