Pulse-Testing Method for Measuring Thermal Properties of Solids

Abstract

Abstract This paper describes a new technique, thermal pulse testing, for the measurement of thermal conductivity, volumetric heat capacity, and thermal diffusivity of solids. Thermal pulse testing is a transient technique which is pulse testing is a transient technique which is analogous to the present technique of pressure pulse testing, a method of obtaining fluid flow pulse testing, a method of obtaining fluid flow properties between two or more wells. properties between two or more wells. Thermal pulse testing is superior in two major ways to other methods of obtaining thermal conductivities, heat capacities and thermal diffusivities. First, several simultaneous measurements of all three properties of a sample are obtained with one test. Secondly, an appropriate method of analysis eliminates any effect of linear temperature changes in the system during the measurement period, and it tends to reduce any nonlinear trends. One such method is described. Also, a measure of precision is obtained from tests made under precision is obtained from tests made under essentially identical conditions. The method uses a small heater along the axis of a cylindrical sample and an accurate temperature sensor on the midplane of the cylinder at a known radial distance between the heater and outer boundary. Power is input, at a constant rate, to the heater with an alternating on/off pulse, while the resulting temperature response out in the sample is detected with the temperature sensor. The thermal properties are then determined from interpretation charts based on the exponential integral (Ei) solution of the diffusion equation, which assumes that the system is homogeneous with infinite outer boundaries and zero inner radius. Data from nonradial or finite-acting systems can be interpreted with other analytic solutions of the diffusion equation or by numerical regression techniques. Experiments have been conducted to test the thermal pulse-test technique. The effects of changing pulse length and distance to the temperature probe were considered. Results obtained from a thermal pulse test of a known sample were compared with published values and with results obtained from the same sample by the thermal conductivity probe technique. The results obtained from this new technique compared well with both the published values and the probe technique. The work described in this paper has shown that thermal pulse testing as a method of obtaining thermal properties is useful and practical.