Salt solutions in supercritical water. Some preliminary studies on the influence of gravity

Abstract

Among the peculiarities reportedly exhibited by salt solutions near to the critical point of water is a tendency to stratification. In order to eliminate and help understand this complication, studies under microgravity conditions have been proposed. Two preliminary experiments conducted on sounding rockets are described, as are experiments undertaken in preparation for them. Conductance techniques were employed on dilute supercritical NaCl solutions mostly within ±4 °C of the critical point of water and between 0.92 and 1.38 of its critical density. The ground-based experiments showed evidence for either a strongly sedimented state or, more likely, an actual phase change at least 2.5 ± 0.5 above the expected critical temperature of the solution. The simplest explanation is that the gravitational field of the earth increases the apparent critical temperature above its true, zero-g, value. The results of the first sounding-rocket experiment were complicated by the unexpected presence at launch of temporarily precipitated sodium chloride. The very interesting complications are discussed. The results of the second experiment showed that destratification was by no means complete in the 6 min of weightlessness which was available.