APPLICATION OF THE TRANSIENT GRATING METHOD TO THE MEASUREMENT OF TRANSPORT-PROPERTIES FOR HIGH-PRESSURE FLUIDS

We have applied the transient grating method to the measurement of the transport properties for high pressure fluids, such as carbon dioxide and trifluoromethane from the gaseous- to the liquid-density regions for the first lime. Using nitrobenzene and methyl red as probe moolecules, we have made the transient grating in a high pressure fluid by a nanosecond-pulsed laser. By the analysis of the time profile of the transient grating signal in sub-microsecond to sub-millisecond range, we have succeeded in measuring the density and the temperature dependences of various transport properties such as the thermal diffusion constant, the sound velocity, the sound absorption, and the mass diffusion constant under the same experimental condition. The thermal diffusion constant of our measurement is identical with 4% error to the value reported in literature, irrespective of probe molecules. We have determined the sound velocity within 0.5% error in a high frequency region around hundreds of MHz. The mass diffusion constant of methyl red is determined within 5% error in trifluoromethane at high densities. We have also demonstrated that the thermal diffusion obeys the critical exponent near the critical point.