On the Mach Number Invariance of Gas Jets Expanding Into Hot or Cold Environments

Abstract

Gas jet flows expanding into a space containing the same medium but at a significant temperature difference are of concern in many fields of engineering. One such example is the expansion of supersonic oxygen jets in the basic oxygen furnace (BOF) steelmaking process. While studying the characteristics of such gas jets, an interesting invariance of the local Mach number with the change in the surrounding temperature was found. The velocity and temperature of the jet at any given location increased with the increasing ambient temperature. However, the local Mach number remained the same for all ambient temperatures. This interesting result was further studied since there is no mention of it in any published literature. The reasons for these characteristics of the jet are analyzed in this paper. It is stressed that this finding is of practical importance and can be used in experimental studies of submerged gas jets expanding into environments with different ambient temperatures.