Thermal Characteristics of Refrigerant Flow Boiling in Two Mini-Channel Heat Sinks of Different Aspect Ratios for Battery Thermal Management

The two-phase refrigerant cooling system has excellent thermal management performance, which can provide good temperature control of lithium-ion batteries. In this paper, the thermal performance of mini-channel heat sinks with different aspect ratios was investigated for a battery system with a small-scale vapor compression refrigeration system. Two mini-channel heat sinks (MiCHS), one with a square channel cross section of 3mm×3mm (MiCHS1) and the other with a narrow channel cross section of 2mm×4.5mm (MiCHS2), were fabricated with a visualization window and connected in parallel in the system. The experiments were run at different openings of expansion valve (OEV) and heating power. Under the same OEV condition, the heat transfer coefficient and average temperature of MiCHS increase with the increase of heating power for both MiCHSs. With the increase of OEV, the refrigerant in mini-channels gradually experiences different flow patterns of annular flow, slug flow and small bubble flow. The BTMS can achieve the best cooling performance in slug flow, corresponding to a moderate OEV. Compared with the narrow channels with a large aspect ratio, the flow boiling in wide channel of MiCHS2 can achieve a better cooling performance due to the well-confined bubbly flow