Numerical investigation of power-law hybrid nanofluid in a wavy micro-tube with the hydrophobic wall and porous disks under a magnetic field

Abstract

In the current study, the second law of thermodynamics and heat transfer of a power-law hybrid nanofluid in a micro-tube with a variable heat flux on the hot wall, the attendance of two porous disks and the hydrophobic wall under a magnetic field with Finite Volume Method (FVM) has been studied. The non-Newtonian nanofluid has contained water/Al2O3-TiO2 in the volume concentrations of 1.5% and 2% nano-particles. The present study has been investigated in four parts in the range of the Reynolds number (10−100) and the nanoparticles volume concentrations (1.5–2%). The first part has examined the influence of using porous disks in the Darcy number (5 × 10−4–5 × 10−6) on nano-fluid flow, cooling and entropy generation. The results showed that the porous medium improves the mean Nusselt number and decreases and increases thermal entropy generation and frictional entropy generation, respectively. In the second part, the impacts of the thermal conductivity ratio (1–16) of the porous disks were studied. Increasing this parameter caused a slight improvement in the mean Nusselt number in almost all cases and enhancing the thermal entropy generation. In the third part, the influences of the Hartmann number (0−30), which shows the strength of the magnetic field, were investigated. Increasing the magnetic force led to improvements in the mean Nusselt number. It also decremented the thermal entropy generation but increased the generation of frictional entropy and added the term's magnetic entropy. In the fourth part, the effects of the hydrophobic wall in first-order and second-order models, and the slip coefficient (0–0.1) were examined. The results determined that the hydrophobicity of the surfaces and the development of the slip factor in both models improves the mean Nusselt number and decreases in all the parameters of the thermodynamics second law, which were seen more changes in the first-order model.