Effect of Non-Uniform Nanofluid Concentration on Interferometric Heat Transfer Measurements

Abstract

The effect of non-uniform nanofluid concentration on the accuracy of interferometric heat transfer measurements has been investigated using a Mach-Zehnder interferometer. Because the refractive index is a function of concentration as well as temperature, concentration variations within the nanofluid can produce unwanted interference fringes, leading to temperature measurement errors. Measurement errors in the temperature gradient are demonstrated for conduction within a cavity heated from top to bottom, filled with an Al2O3-water nanofluid (0.16 wt.%) produced using a standard two-step method. The measurement problem is delineated, and several approaches to mitigate this source of measurement error are outlined. The technical trade-offs associated with designing interferometric heat transfer experiments to reduce the sensitivity to concentration differences are discussed. An isothermal stability test is recommended to detect nanofluid concentration gradients prior to temperature-based interferometry experiments.

Keywords: Nanofluid stability, Non-uniform nanofluid, Interferometry, Heat transfer measurement, Measurement error