The investigation of Daum focused attention on the problem of condensation in hypersonic wind tunnels. In such tunnels there is often a conflict between the desire to obtain the maximum Reynolds number and the necessity of operating with a sufficiently high stagnation temperature to avoid liquefaction of the working gas. The hypersonic gun tunnel, in which the present tests were made, is capable of running at relatively high Reynolds numbers and to define the operating limits of the RARDE gun tunnel, Bowman made measurements similar to those of Daum, but using nitrogen as the working gas. It will be recalled that Daum made measurements of static and pitot pressures at varying temperatures. He deduced from these measurements that below a certain working section pressure significant degrees of supersaturation could be tolerated before breakdown to the condensed state. Thus three regions can be defined; in order of increasing temperature these are:

(i) condensing flow;

(ii) supersaturated uncondensed flow; and

(iii)unsaturated flow (see Fig. 1).