Experimental apparatus for measuring the thermal diffusivity of pure fluids at high temperatures

Dynamic light scattering represents a suitable method for measuring the thermal diffusivity of optically transparent fluids. The classic application of the method is the immediate vicinity around the critical point due to its dependence upon the intensity of scattered light and its high sensitivity to undesired light scattering. By means of subsequent modifications of the experimental setup, we have been able to expand this region of applicability over the last 12 years and could systematically investigate numerous substances and their binary mixtures within a temperature range of 280 K<T<350 K. Our planned investigation of fluids suitable for ORC-HP-technology necessitates performing measurements at higher temperatures and pressures. The experimental apparatus newly designed for this purpose is capable of sustaining a relatively high temperature constance at temperatures up to 700 K. Factors restricting the measurable range of state and their influence on the design of the sample cell are discussed.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.