Numerical Study of Entropy Generation in a Flowing Nanofluid Used in Micro- and Minichannels


This article mainly concerns theoretical research on entropy generation influences due to heat transfer and flow in nanofluid suspensions. A conventional nanofluid of alumina-water (Al 2 O 3-H 2 O) was considered as the fluid model. Due to the sensitivity of entropy to duct diameter, mini-and microchannels with diameters of 3 mm and 0.05 mm were considered, and a laminar flow regime was assumed. The conductivity and viscosity of two different nanofluid models were examined with the help of theoretical and experimentally determined parameter values. It was shown that order of the magnitude analysis can be used for estimating entropy generation characteristics of nanofluids in mini-and microchannels. It was found that using highly viscous alumina-water nanofluid under laminar flow regime in microchannels was not desirable. Thus, there is a need for the development of low viscosity alumina-water (Al 2 O 3-H 2 O) nanofluids for use in microchannels under laminar flow condition. On the other hand, Al 2 O 3-H 2 O nanofluid was a superior coolant under laminar flow regime in minichannels. The presented results also indicate that flow friction and thermal irreversibility are, respectively, more significant at lower and higher tube diameters. Nomenclature Ф volume fraction C Specific heat J/KG. k ƒ friction factor K thermal conductivity D diameter of tube, m N shape constant Nu Nusselt Number Ρ density Reynolds Number ṁ mass flow rate Be Bejan Number µ Viscosity Ṡ entropy generation per unit length, W/m.k Subscript " heat flux per unit length, W/m BF base fluid C µ viscosity coefficient NF nanofluid C k thermal conductivity coefficient P nanoparticles

DOI: 10.3390/e15010144

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