The Structure and Concentration Decay of High Pressure Jets of Natural Gas

Abstract

The concentration field in compressible sonic jets of natural gas over the pressure range from 2 to 70 bar has been studied using gas chromatography. At these pressures the jet expands immediately downstream of the nozzle in order to equilibriate with ambient conditions. The behaviour of such underexpanded jets is shown to be similar to classical free jets provided that an appropriate scaling factor is employed to describe the effective size of the jet source. This notional source is referred to as the pseudo-diameter and a theroretical analysis for its derivation is presented. The experimental data support this approach, and the decay constants for the jet concentration field agree with previous measurements in incompressible jets. Comparison with results obtained from a high pressure jet of ethylene at 8 bar indicate that the effect of jet fluid density in concentration decay is the same as in classical free jets.