A Method for Measuring Thermal Conductivity of Fluids by Using a Small Bead Thermistor

Abstract

This paper describes a method for measuring the thermal conductivity of gases and liquids by using a small bead thermistor. The method is based on the theoretically established heat transfer characteristics for steady free convection from an isothermal small sp. here. Various effects caused by the difference in shape between the thermistor and an ideal sphere, nonuniform temperature distribution due to heterogenious heat generation in the thermistor and heat loss from lead wires are accurately estimated by introducing an effective diameter of the thermistor and three apparatus constants. These values have been determined so that the difference between the measured values for air, water and ethanol and their nominal values is within two percent in thermal conductivity when the other physical properties are known. When a smaller thermistor in comparison with its lead wire diameter is used, the inaccuracy becomes a little more. Measured values of methanol, refrigerant Rll3 and toluene, under atmospheric pressure and near room temperature, are also p. resented.