Simultaneous measurements of thermal expansion and thermal conductivity of FRPs by employing a hybrid measuring head on a GM refrigerator

Abstract

This paper describes a setup for the simultaneous measurements of thermal expansion and thermal conductivity at temperatures down to 20 K. The sample holder is an integrated compartment of two cells––one for the measurement of thermal expansion coefficient and another for that of thermal conductivity. The sample holder is thermally isolated from all modes of heat inleak using 130 μPa vacuum and sufficient number of aluminized mylar layer. Linear thermal expansion coefficient and thermal conductivity are measured by 3-terminal capacitance technique and double-specimen guarded-hot-plate method respectively. Experiments are carried out under steady state condition with a set of stability criteria. The effect of addendum, stray capacitance and frequencies, non-uniformity of electric flux on the measurement of capacitance, the effects on heat inleak by gaseous conduction, radiation, copper lead wires and contact resistance on this measurement are made to minimum. The setup is calibrated with standard teflon as sample. The experimental values of teflon show the deviation of about −9% for thermal expansion and about −8% for thermal conductivity from the published values.