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Lithium-ion batteries are widely used in electric vehicles because of their high capacity and voltage. However, some drawbacks to the battery stability exist. The aim of our research was to determine the optimum width and number of channels of a cold plate. To estimate the temperature distribution and heat transfer rate, the MSMD (multi-scale multi-dimensional) - Newman P2D model in ANSYS Fluent was used. Prior to comparing the heat transfer rates of the various battery surfaces using different cold plates, the surface temperature of the battery (LiFePO4) at discharge rates of 2C, 3C, and 4C was calculated to determine the battery characteristics. Subsequently, two cold plates were attached to both sides (front and back) of the batteries and the heat transfer rate of the battery surface in contact with the cold plate, and the pressure drop between the inlet and outlet of the channels during the discharge process were estimated. In addition, the j and f factors, which are used to estimate the cooling performance of the cold plates, were calculated. In determining the most efficient cold plate options, the trade-off between the heat transfer coefficient and the pressure drop is also important for the relationship between the two factors (j and f factors). [ABSTRACT FROM AUTHOR]

• Vertical downward condensation plate heat exchanger. • Electrochemical etching generates microscale roughness. • Enhance thermal-hydraulic performance of plate heat exchanger. • Analyze effect of heat flux, mass flux, vapor quality and surface roughness on heat transfer. • Multi-objective generic algorithm optimized designed roughness. • Pareto front solutions for maximizing performance. This research employed electrochemical etching to generate microscale roughness on a plate heat exchanger (PHE) thereby enhancing condensation heat transfer in a vertical downward flow. The effects of the mass flux, vapor quality, heat flux, saturation temperature and microscale surface roughness on the condensation heat transfer coefficient (HTC) and frictional pressure drop (FPD) of R-513a flowing through a PHE was experimentally investigated. Experimental measurements were made under various heat fluxes of 5–15 kW/m2, mass fluxes of 60–80 kg/m2s, saturation temperatures of 40–50 °C, and mean vapor qualities of 0.1–0.7. HTC increased by up to 28, 26, 74, and 32.5 % as the heat flux, mass flux, average quality, and microscale surface roughness were respectively increased, but decreased by 19 % with the saturation temperature. FPD increased as the mass flux and average vapor quality increased, whereas it was reduced as the refrigerant saturation temperature increased. In contrast, the heat flux had little to no influence on FPD. Correlations for predicting the Nusselt number and friction factor were postulated by considering influential dimensionless numbers during heat transfer. Maximizing the Nusselt number and thermal performance factor was ultimately resolved using a multi-objective genetic algorithm to find a Pareto front solution. Consequently, the optimal surface roughness was found to be 9.94 μm. [ABSTRACT FROM AUTHOR]

A hydrophobic surface promotes bubble nucleation due to hydrophobicity. Thus, a hydrophobic surface has a higher boiling heat transfer coefficient (BHTC) than a hydrophilic surface. In contrast, a hydrophilic surface supplies liquid to a heating surface. This mechanism enhances the critical heat flux (CHF). In this respect, there is a trade-off between a hydrophobic and a hydrophilic surface. In this study, we examined the effect of heterogeneous wetting surfaces on flow boiling performance. We designed four types of hydrophobic stripes; there are two directions, parallel and crossed to the flow, and the width (the pitch) of the hydrophobic stripes in each direction is 3 or 1 mm. In the macro-channel, the flow boiling performance on the surfaces depended on the patterns. The parallel striped surfaces had higher CHFs than the crossed striped surfaces. In addition, the narrow patterns in each direction had higher CHFs than the wide patterns. The difference in BHTC among the parallel striped surfaces was not large, but the difference in BHTC among the crossed striped surfaces was considerable. A visualization technique revealed that the merging and confinement of bubbles were key factors in explaining the boiling characteristics. Considering the drag coefficient and bubble breakup, we suggest appropriate designs of the hydrophobic pattern for the improvement of BHTC and CHF in the flow boiling performance. [ABSTRACT FROM AUTHOR]