Multiscale Modelling of Nanofluid Heat Transfer for Advanced Cooling of Nigerian Power Electronic Systems

Power electronic systems including inverters, rectifiers, and motor drives used in Nigeria's industrial and renewable energy sectors generate substantial heat loads that demand advanced thermal management solutions. Nanofluids, prepared by dispersing nano-sized particles in conventional heat transfer fluids, offer enhanced thermal conductivity and heat transfer coefficients that can significantly reduce cooling system size and energy consumption. This study develops a multiscale modelling framework for nanofluid heat transfer in mini-channel heat sinks applicable to cooling of power electronic systems deployed in Nigeria's solar inverter and industrial drive industry. The multiscale framework integrates molecular dynamics simulation of nanoparticle-fluid interfacial thermal resistance, mesoscale lattice Boltzmann simulation of nanofluid flow and heat transfer in idealised pore geometries, and macroscale Navier-Stokes simulation of the full mini-channel heat sink with effective medium nanofluid properties derived from the lower scales. Alumina and copper oxide nanofluids prepared with water-ethylene glycol base fluid are experimentally characterised for viscosity, thermal conductivity, and convective heat transfer coefficient and used for model validation. Results show a 28 percent enhancement in effective thermal conductivity for 4 percent volume fraction Al2O3 nanofluid, agreeing with molecular dynamics predictions within 6 percent. The macroscale heat sink model predicts junction temperatures 18 degrees Celsius lower than baseline water cooling under identical pumping power constraints. Keywords: nanofluid, heat transfer, multiscale modelling, power electronics, thermal management