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Abstract

Micropipes, with their sizeable surface-area-to-volume ratio, result in an elevated heat transfer rate, making them excellent tools for compact heat exchangers, offering the advantage of higher heat removal capacities. Discrepancies exist between classical macro-pipe flows and micro-pipe flows in the literature, and one of the reasons is the assumption of constant thermo-physical properties. Analyzing microchannel flows with water as the fluid at a constant wall temperature with varying properties is paramount in understanding the fundamentals of heat transfer. This work performs numerical simulations for single-phase, steady-state, incompressible water flow through a two-dimensional axisymmetric micro-pipe under laminar conditions. The entrance effect problem is studied simultaneously for hydrodynamic and thermally developing flow with isothermal wall boundary conditions. The water properties–-namely viscosity, thermal conductivity, and specific heat–-are evaluated as temperature-dependent. The variation of density with temperature is also considered. The influence of the temperature dependence of these properties on hydrodynamic and heat transfer behavior is studied. The investigation also analyzes the changes in the Nusselt number and surface pressure losses against varying diameters and inlet velocities. The solution obtained with variable-property flow is compared to baseline results of constant-property and classical theory. From the results analysis, it was found that the diameter of the microchannel has a strong influence on the Nusselt number. The variable-property computed predictions are always greater than the results obtained with constant properties.

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172

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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