Measuring Thermal Diffusivity of Dilute Nanofluids Using Interferometry-Based Inverse Heat Transfer Approach

Measurement of thermophysical properties of nanofluids is essential to understand the heat transfer performance of nanoparticles suspended in base fluids. In this direction, as a definite advancement over the conventional methods, laser interferometry has been employed to study the dependence of thermal diffusivity of dilute nanofluids on increasing volume concentration of nanoparticles using the principles of inverse heat transfer. Two types of nanofluids, namely, SiO2 and Al2O3 with de-ionized water as the base fluid, have been considered for this analysis. The experimental configuration consists of a layer of working fluid (water or nanofluid) contained between two differentially heated horizontal walls of a rectangular cavity. Temperature potential is applied to the fluid layer by raising the temperature of the upper horizontal wall of the cavity with respective to the lower one. Transient evolution of the thermal diffusion field (from top plate to the lower horizontal wall) has been recorded in the form of interferograms at various time instants. As the forward model, the transient form of heat diffusion equation has been analytically solved for a guessed value of thermal diffusivity. Finally, the experimentally determined temperature field has been compared with the analytical solution, and following the principles of inverse heat transfer, the thermal diffusivity of the working fluid has been calculated. The methodology developed has first been benchmarked by determining the thermal diffusivity of the base fluid, that is, water, and thereafter it has been employed to determine the corresponding thermophysical properties of the dilute nanofluids. Results showed an increase in the thermal diffusivity of dilute nanofluids as a function of increasing volume concentration of the nanofluids.