Interferometric study of nanofluid-based heat transfer phenomena in compact channels

The present work is concerned with the interferometric measurements of dilute nanofluid-based heat transfer enhancement in compact rectangular channels. The heat transfer experiments have been conducted in forced convection regime for a range of Reynolds number. Simultaneously developing flow regimes have been considered. Al2O3-based dilute nanofluids with volume concentrations of 0.01% and 0.05% have been employed with deionized water as the base fluid. A Mach-Zehnder interferometer has been used to record the line-of-sight images of the convective fields inside the channel. Interferometry experiments have been performed in infinite as well as wedge fringe-setting mode of the interferometer. The images recorded in infinite fringe setting mode have been qualitatively interpreted to understand the effect of increasing volume concentration of nanofluids on phenomena like disruption of thermal boundary layer, temperature gradients etc. The interferograms corresponding to the wedge fringe-setting mode have been quantitatively analyzed to retrieve the whole field temperature distribution inside the compact channel, local variation of heat transfer coefficient for the range of volume concentration of nanofluids and Reynolds numbers studied in the present work. Results have been presented in the form of interferometric images, the contours of two-dimensional temperature distribution, local variation of thermal boundary layer thicknesses and heat transfer coefficients along the length of the channel and percentage enhancement in heat transfer rates due to increasing volume concentration of nanofluids for each Reynolds number. The experimental study clearly reveals a reduction in the thickness of the thermal boundary layer with increasing volume concentration of nanofluids and hence the increasing strength of the thermal gradients. An overall enhancement of heat transfer coefficient by a factor of about 1.7-2 in the case of nanofluid is observed in comparison with that obtained with the base fluid.