Contact Photothermal Techniques for Thermal Characterization of Liquids

Abstract

Two contact photothermal (PT) techniques, the well-known photopyroelectric (PPE) calorimetry, and a recently introduced photothermoelectric (PTE) one, are proposed for thermal inspection of some liquid samples. The paper contains a summary of the recent results and a comparison of the investigations performed with the previously mentioned techniques for the measurement of the dynamic thermal parameters (thermal diffusivity and effusivity) of some liquids of interest: magnetic nanofluids with transformer oil as carrier liquid and various concentrations of magnetite (Fe₃O₄) nanoparticles. For both techniques, the same detection configurations have been used: (i) the front detection configuration, together with the thermal-wave resonator cavity (TWRC) method as scanning procedure, was used to measure the value of thermal effusivity; (ii) the back configuration, together with the same TWRC technique, leads to the direct measurement of thermal diffusivity. The main theoretical aspects of the particular detection cases for both techniques are described and the performances (advantages and limitations) of the methods are analyzed. Concerning the nanofluid under investigation, small increases of thermal diffusivity (9.33 m²s^-1 – 10.33 m²s^-1) and effusivity (450 Ws^1/2 m^-2K^-1 – 530 Ws^1/2 m^-2K^-1) with increasing nanoparticles' concentration (0.156 mg(Fe₃O₄)/ml fluid - 0.623 mg(Fe₃O₄)/ml fluid) are observed.