Two-phase analysis of heat transfer and entropy generation of water-based magnetite nanofluid flow in a circular microtube with twisted porous blocks under a uniform magnetic field

Abstract

In the present numerical analysis, the forced convection of nanofluid flow is investigated in a microtube with twisted porous blocks while existing a uniform magnetic field based on the first and second laws of thermodynamics with various geometries. Using the finite volume technique and SIMPLE algorithm, the governing equations are discretized and solved. The governing equations are solved using a two-phase mixture model and second-order upwind technique. With the heat flux of 5000 W.m−2, the effects of Hartmann number, Reynolds number, the volume fraction of nanoparticles, as well as porosity percentage of twisted porous blocks are investigated on pressure drop, heat transfer rate, and flow fields. The values of the Hartmann and Reynolds numbers are different within the range of Ha = 0 to Ha = 20 and Re = 250 to Re = 1000, respectively, and the volume fraction of nanoparticles is different within φ = 0 to 2%. The findings indicate that placing the porous blocks in the microtube leads to protrusions in the local diagrams, moreover, by increasing the number of twisted porous block layers, the vertices value of these protrusions increments. By incrementing the Reynolds number, the pressure drop and convective heat transfer coefficient are increased, and the friction factor is decreased. Incrementing φ and the thermal conductivity of the fluid increase the heat transfer rate. Moreover, by increasing the Hartmann number, the local friction factor and the Nusselt number are increased. According to the results, by increasing the number of twisted porous block layers in the highest φ, the average pressure drop becomes 38.171 Pa. The performance evaluation criterion in Ha = 20 and microchannel with three twisted block layers possess the highest value of 1.717.