Abstract:
Performance evaluation of two types of nanofluids in influencing the heat transfer phenomena in the context of compact channels has been presented. Experiments have been conducted in forced convection regime for a range of Reynolds numbers. Three different types of coolant fluids i.e. de-ionized water (base fluid), Al2O3 and SiO2-based dilute nanofluids with volumetric concentrations of 0.005%, 0.01% and 0.02% have been employed. A Mach-Zehnder interferometer has been used for recording the real time projection data of the convective field. The interferometer has been operated in infinite as well as wedge fringe setting mode. The infinite fringe setting images have been employed for discussing the effect of nanoparticles on phenomena like thermal boundary layer profiles, changes in the thickness of thermal boundary layers, etc. The wedge interferograms have been employed for quantitative analysis. A direct comparison of heat transfer characteristics of Al2O3 and SiO2 nanoparticles has been presented on the basis of their relative influence on the thickness of thermal boundary layers, temperature gradients and the resultant heat transfer rates. The results of the study clearly reveal the effectiveness and higher heat transfer characteristics of Al2O3 nanoparticles than that of SiO2. It is seen that the Al2O3 nanoparticles have greater ability in disrupting the thermal boundary layer profiles and lead to higher percentage reduction in the thickness of thermal boundary layers. The resultant heat transfer coefficients with Al2O3-based dilute nanofluids have been found to be significantly higher than the base fluid and the SiO2-based nanofluids for any given volumetric concentration. It is experimentally demonstrated that the phenomena like increased thermal conductivity, boundary layer disruptions and advection effects primarily control the heat transfer rates in the lower range of Reynolds numbers (Re < 500) while at higher Reynolds numbers, it is mainly the advection effects that influence the heat transfer coefficients in the range of volume concentrations of dilute nanofluids employed in the experiments. (C) 2015 Elsevier Ltd. All rights reserved.