DESIGN OF ELECTRONIC CIRCUITRY FOR SHORT TIME EASUREMENTS OF THERMAL PROPERTIES OF SOLIDS USING THE TRANSIENT HOT STRIP METHOD

Abstract

A non steady state ' TRANSIENT HOT STRIP'method has been used' for measuring the thermal conductivi ty and thermal diffusivity of non conducting solids. The techniaue uses a metal film deposited on a substrate sample . The dimensions of strip aresuch as to realize an infinitely long continuous plane heat source of negligible thickness and finite width . Power supplied to the strip is electrical the heat conducti on equation for the strip being solved in ter ms of the voltage devel oped across it. This voltage is time varying because resistance of strip increases as temperature increases with time . From the volta~e variation we can get the thermal properties of substrate. Whereas the THS method has been used before~ ,in this work the technique was improvised for milli- second time range . Short time measurements required fast switching with rather small voltage variation . This necessiated use of electronic instrumentation . Various sophisticated circuits were desi~n ed and tesl ed . Finally a Bridge Circuit was made r. ich was simpl e and a c cur ate . Short time THS method was used for measur eme n t s on pure fused quartz , an isotropic mate - r ial • It is p o s s ible to use the THS for anisotropic samples ; a solut ion of the heat conduction equation for . , such a situation has been attempted . The results for 34 fused quartz are consistent with those obtained by others