Laser-based thermal pulse measurement of liquid thermophysical properties

In this work, a laser-based thermal pulse technique is presented that simultaneously measures thermal conductivity and thermal diffusivity for liquids, from which the volumetric specific heat can be determined as well. The measurement is based on photothermal deflection of a HeNe laser beam that passes through the test liquid next to a thin heating wire. Liquid thermophysical properties are determined by fitting a numerical simulation of the heat conduction and probe beam deflection to the measured time-dependent probe beam deflection. Results are presented for five liquids: glycerol, 1-propanol, 2-propanol, methanol, and ethanol, and are found to be in very good agreement with values reported in the literature. The experimental setup is small, inexpensive and reliable. The temperature dependence of the liquid refractive index is also determined during the measurement process, and the same experimental technique is capable of measuring the thermal conductivity and thermal diffusivity of thin conducting wires.