Mathematical Investigation into Nanofluids Flow and Heat Transfer in Microchannels Filled with Porous Media

Abstract

In the contemporary world, the demand for electronic devices that are smaller in size and owning fast performing capability is increasing at a tremendous pace. However, under oper ating conditions the lessening of size accompanied with high heat flux generation and hence sometimes these devices fail and damage due to overheating. As a consequence, numer ous efforts have been undertaken by the thermofluidic industries in establishing the thermal management systems. Therefore, nowadays the demand for novel technologies concerning cooling mechanisms for thermal management in several electronic industries is increasing. Among such novel technological revolutions, microchannels are the most essential one to transport fluids in the miniaturization systems. Despite of their high heat transfer capa bilities, microchannel flows require a greater pumping power and hence nanofluids were invented to overcome such a challenging problem in microchannels. Nanofluids flow and heat transfer in microchannels have a wide range of attributes in industrial process as well as engineering and biomedical applications. Further augmentation of heat transfer rates in microchannels as well as in heat exchangers can be achieved by the syndication of nanoflu ids with porous media. Due to the aforementioned reasons, the hydrodynamic and thermal behaviours of nanofluids flow in microchannels filled with porous media were studied in this dissertation. Flows induced due to the pressure gradient, suction/injection and buoyancy forces were given attention and the Darcy-Forchheimer model was considered to examine the nanofluds and porous media interaction. Specific problems were mathematically mod eled and studied under various scenarios including variable transport properties, thermal radiation, chemical reaction, no slip and convective boundary conditions. Therefore, mixed convection flows of variable transport properties nanofluids without as well as with thermal radiation and chemical reaction were investigated. The Buongiorno nanofluids flow model was used to analyze the effects of the Brownian diffusion and thermophoresis of nanoparti cles. Moreover, the hydrodynamic and thermal behaviors of ferrofluid (Fe3O4 −H2O) using the Tiwari and Das nanofluids flow model was examined. Hence, the highly non-linear partial differential equations that govern the flow problems were formulated, transformed into ordinary differential equations using the semi-discretization finite difference method and solved numerically via the fourth order Runge-Kutta integration scheme. Consequently, the wall heat transfer rate for the variable viscosity nanofluid indicated an increasing pat tern with increasing values of the pressure gradient parameter, variable viscosity parameter, thermal Grashof number, Schmidt number and Prandtl number. Similarly, the heat transfer rate for the ferrofluid revealed a rising behaviour with rising values of variable viscosity parameter, Darcy number, Eckert number and Prandtl number. Furthermore, the radiation parameter indicated a retarding effect on the temperature profiles of the radiating and react ing nanofluid and hence, radiation quite effectively controls the microchannel temperature distribution and flow transport which plays a significant role in cooling the system. The results were also compared with that of the existing related literature where a very sound agreement has been attained. Finally, summary and conclusions as well as recommendation and suggestions for future research were given based on the findings.