Interferometry-based whole field investigation of heat transfer characteristics of dilute nanofluids

The present work is concerned with understanding the heat transfer characteristics of dilute nanofluids using laser-based non-intrusive measurement techniques. Experiments have been conducted on a vertical heated flat plate immersed in nanofluids of varying concentrations, with water as the base fluid. Natural convection regime of the heat transfer between the flat plate and the ambient fluid medium is considered. Aluminium oxide (Al2O3) nanoparticles with volume concentrations in the range 0.005-0.02% are dispersed in the basefluid to prepare nanofluids of dilute concentrations. The phenomenon of convective heat transfer between the flat plate and the ambient fluid medium has been mapped using laser interferometry. Real time evolution of thermal boundary layers as a function of concentration of nanofluids has been recorded in order to understand the plausible role of nano particles in the heat transfer enhancement. Recorded interferograms have then been quantitatively analyzed to retrieve the two-dimensional temperature fields in each case and local distributions of heat transfer coefficients have been estimated. Results have been presented in the form of interferometric images of convective field in the vicinity of the flat plate, contours of whole field temperature distribution and local variation of heat transfer coefficient as a function of nanofluid concentration. The thermal boundary layer profiles as recorded using interferometry clearly reveal the effects of varying nanofluid concentration. In quantitative terms, an enhancement of about 21% in the heat transfer coefficient was observed for 0.02% concentration of nanofluid as compared to the base fluid whereas the Nusselt number was seen to deteriorate with increasing concentration of nanofluids.