Transient conjugate heat transfer problem of laminar flow for nanofluids in microchannels

The transient regime problem for the effect of nanofluids on thermal performance in a microchannel of laminar flow has been considered within the scope of the current thesis study. The situations where Al2O3, CuO and TiO2 nanoparticles added separately to water as base fluid at different volumetric concentration values ( = 1%, 4% and 7%) have been compared in terms of heat transfer characteristics such as interfacial heat flux, interfacial temperature, bulk temperature and radial temperature. In this manner, two different thermophysical property models of open literature have been contrasted for each nanoparticle. Accordingly, the effects of Peclet number (Pe = 1, 5, 20 and 50), wall thickness ratio (d' = 0.02, 0.1, 0.2, 0.3, 0.6, 1 and 1.4), thermal diffusivity ratio (αw-nf = 0.1, 1 and 10), thermal conductivity ratio (kw-nf = 0.1, 1 and 10) and Brinkman number (Br = -0.2, -0.1, 0, 0.1 and 0.2) on the numerical solution have been evaluated. It has been observed that axial conduction is more effective at low Peclet numbers, and for Pe ≥ 20, this value does not significantly affect heat transfer. It has been seen that the increase in the wall thickness ratio and the decrease in the thermal conductivity ratio have a decreasing effect on heat transfer. The change for the thermal diffusivity ratio was quite ineffective parametrically. At values where the Brinkman number, showing the effect of viscous dissipation, is not equal to zero, the direction of heat transfer has been significantly changed. As the values of these parameters increased, the required time for steady state has tended to decrease. The conditions stated for the base fluid water are also valid for those of nanofluids. Heat transfer have also been enhanced by increasing the volumetric concentration for the nanofluid. In terms of nanoparticle effect, more thermal performance has been obtained at constant volumetric concentration via CuO, Al2O3 and TiO2, respectively. According to the thermophysical models compared for each nanoparticle, the models for nanoparticle of Al2O3 have presented the closest results to each other. However, it has been observed that one model for other nanoparticles is inadequate in this manner.