Heat and mass transfer and thermodynamic analysis of power-law fluid flow in a porous microchannel
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Heat and mass transfer and thermodynamic analysis of power‑law fluid flow in a porous microchannel Mahnaz Javidi Sarafan1 · Rasool Alizadeh1 · Abolfazl Fattahi2 · Mostafa Valizadeh Ardalan3 · Nader Karimi4 Received: 25 March 2020 / Accepted: 7 April 2020 © The Author(s) 2020
Abstract Transfer of heat and mass and thermodynamic irreversibilities are investigated in a porous, parallel-plate microreactor in which the working fluid is non-Newtonian. The investigated microreactor features thick flat walls with uneven thicknesses, which can be subject to different thermal loads. The dimensionless governing equations of the resultant asymmetric problem are first derived theoretically and then solved numerically by using a finite volume technique. This results in two-dimensional solutions for the velocity, temperature and concentration fields as well as the distributions of Nusselt number and local and total entropy generations. The results clearly demonstrate the significance of the numerical value of the power-law index and departure from Newtonian behavior of the fluid. In particular, it is shown that by increasing the value of power-law index the Nusselt number on the wall decreases. This leads to the intensification of the temperature gradients in the system and therefore magnifies the local and total entropy generations. Also, it is shown that the wall thickness and thermal asymmetry can majorly affect the heat transfer process and thermodynamic irreversibility of the microreactor. It is noted that the current work is the first comprehensive study of heat transfer and entropy generation in porous micro-chemical reactor with non-Newtonian, power-law fluid. Keywords Porous microchannel · Microreactor · Non-equilibrium thermodynamics · Entropy generation · Power-law fluid · Forced convection List of symbols asf Interfacial area per unit volume of porous media (m−1) Bi Biot number C Mass species concentration (kg m−3) C0 Inlet concentration (kg m−3) Cp Specific heat capacity (J K−1 kg−1) D Mass diffusion coefficient (m−2 s−1) Da Darcy number DT Coefficient of thermal mass diffusion, (m (K kg s)−1) * Nader Karimi [email protected] 1
Department of Mechanical Engineering, Quchan Branch, Islamic Azad University, Quchan, Iran
2
Department of Mechanical Engineering, University of Kashan, Kashan, Iran
3
Department of Mechanical Engineering, Shahroud University of Technology, Shahroud, Iran
4
School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK
h1 Half-thickness of the microchannel (m) h2 Half-height of microchannel (m) hsf Interstitial heat transfer coefficient (W K−1 m−2) Hw Wall heat transfer coefficient (W K−1 m−2) k Effective thermal conductivity ratio of the fluid and the porous solid k1 Thermal conductivity of wall 1 (W K−1 m−2) k2 Thermal conductivity of wall 2 (W K−1 m−2) ke1 Ratio of thermal conductivity of wall 1 and thermal conductivity of the porous solid ke2 Ratio of thermal conductivity of wall 2 and thermal conductivity of the porous solid kef Effectiv
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