Optical device for thermal effusivity estimation of liquids

Abstract

We determined the thermal effusivity of liquids using an optical sensor based on the laser beam deflection technique, without directly heat the samples and thus minimally altering them. Applying a heat pulse in a thermo-optical slab we generate a unidimensional temperature distribution. This temperature distribution modifies the refractive index in the slab that finally causes the deflection of a laser beam that propagates perpendicularly to the direction of the heat propagation. The deflection of the laser beam depends on the interaction of the thermal energy with the sample at the slab interface. The exchange of thermal energy between the thermo-optical slab and the sample depends, on the thermal properties of both of them, being the thermal effusivity of our particular interest. Utilizing a theoretical model, we estimate the thermal effusivity of liquids using tridistilled-water and glycerine as reference.
We present a simplified version of a past sensor proposal as well as the theoretical analysis of the sensor response. We obtain the thermal effusivity of tridistilled water and glycerine samples with a maximum error of 3%. Finally, we estimate the thermal effusivity of dissolutions of NaCl in tridistilled-water with maximum error of 7.3%.