This paper aims to numerically investigate the effects of adding nanoparticles on the entropy generation of water-Al2O3 nanofluid flows through a circular pipe under constant wall temperature also constant heat flux thermal boundary conditions in laminar regime. Approved formulations of mixtures are used for density and specific heat of the nanofluids. Nanofluid model proposed by Koo and Kleinstreuer [1] based on experimental data of Das et al. [2] is employed for conductivity of the nanofluids and an experimental correlation presented by Rea et al. [3] is used to model the viscosity of the nanofluid. The problem has been simulated numerically using a CFD finite-volume code and results are validated with the available experimental data. It is found that for the case of constant heat flux boundary condition, adding nanoparticles decreases the entropy generation and improves the thermal performance of water-Al2O3 flow. Moreover optimum Reynolds number to minimize the ratio of nanofluid entropy generation number to water is obtained for this case. For the case of wall constant temperature boundary condition, adding nanoparticles to water leads to heat flux increase, therefore the entropy generation number remains approximately constant.

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