A Transient Method of Measuring Thermal Contact Conductance Between Metal-Plastic Surfaces

Abstract

The thesis describes a method developed to measure thermal contact conductance between metal-plastics surfaces by transient experiments. Published literature contains no comparable transient experimental technique and no conductance values for metal-plastics surfaces. Thermal transients set up by a radiant heat flux in two aluminium alloy rods which sandwich between them a thin sheet of plastic material are used to evaluate the contact conductance. Crank-Nicolson's finite difference scheme is used to evaluate the time-temperature history in a three body composite system with contact resistance at two interfaces. The details of the experimental equipment designed and constructed for this work is presented. Dimensionless groups obtained from the heat conduction equation, initial and boundary conditions predict the contact conductance from experimental data and the limits to the accuracy of the measurements of contact conductance. Optimisation techniques are used to find the minimum of the sum of squares function formed by the theoretically predicted and experimentally measured temperature values. The thermal conductivity of the plastic material is also evaluated from these measurements. The thermal contact conductance values obtained by this method at various applied pressures lie in the range of 40 BTU/hr ft² ºF (227.2 W/m² ºK) to 200 BTU/hr ft² ºF (1136 W/m² ºK) and the thermal conductivity of the plastic material was 0.1042 BTU/hr ft ºF (0.1803 W/m ºK). This conductivity value agrees with that given in the literature. The effects of applied pressure and ambient pressure on contact conductance are investigated.