Laminar forced convection in a tube with a nano-encapsulated phase change materials: Minimizing exergy losses and maximizing the heat transfer rate

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The present work investigates the potential of NEPCM mixtures via analyses of convective heat transfer and exergy losses, and trade-offs between them inside a tube with a constant wall temperature. Experimental data for viscosity and thermal conductivity of the mixture was used within numerical simulations over a broad range of dimensionless parameters, including Reynolds number, mass fraction, melting strength, phase change zone thickness, and location of phase change zone. The effect of these parameters on the melting process, convective heat transfer and exergy loss is evaluated. The findings indicate that, although employing a NEPCM can boost the Nusselt number and heat transfer rate by 9.3 % and 16.1 %, as compared to the water, the exergy losses were enhanced up to 17 %. Additionally, in some circumstances, the Nusselt number and heat transfer rate both increased by 5.9 % and 2.5 %, respectively, whereas the exergy losses were zero. An optimal value of ω=0.02 was found to provide reasonable improvement in heat transfer rate increase with no exergy losses. Importantly, the present study shows that although higher NEPCM mass fractions can continue to increase the heat transfer performance, their benefit is rapidly offset above ω=0.02 due to heat transfer related exergy losses. Additionally, it was concluded that, in comparison to other parameters, the location of the phase change and the mass concentration of NEPCMS substantially affected the percentage of molten NEPCM and the latent heat efficacy.