Holographic interferometry near gas/liquid critical points: Ground-based study of a D1 experiment

Ground-based investigations for a Spacelab Holographic Optics Laboratory study of density distribution in three cells filled with SF6 at different near-critical densities cycled through the critical temperature are described. Results show that cooling is so fast that gravity-induced free convection can develop in the sample. As a result, temperature gradients are formed which, via thermal expansion coefficient, cause density gradients, like gravity via compressibility. At the critical point, thermal expansion coefficient and compressibility are singular; the density gradients caused by temperature gradients and gravity are large. For small cooling rates and gravitational effects, density distribution is greatly affected by temperature gradients produced from outside or by temperature gradients produced as a result of adiabatic mass rearrangements inside the sample.