Brownian diffusion Darcy-Forchheimer theory Darcy–Forchheimer model Maxwell nanofluid PCR Poiseuille flow aspect ratio boundary condition carbon nanotubes chemical reaction conjugate interface convective conditions deionized water droplet coalescence flow distributions fluid network forced convection friction factor heat enhancement heat transfer heat transfer enhancement heat transfer experiment inertial migration lattice Boltzmann method liquid metal loop heat pipe magnetohydrodynamics measurement mesh model microchannel