Effects of gas density on the structure of liquid jets in still gases

A theoretical and experimental study of the near jet-exit region of nonevaporatin g round liquid jets in still gases is described, emphasizing effects of ambient gas density in the atomization breakup regime where liquid breakup begins right at the jet exit. Mean liquid volume fraction distributions were measured for 9.5-mm-diam water jets in still air at pressures of 1-8 atm. Mixing was strongly affected by the gas/liquid density ratio and the degree of flow development at the jet exit, with the largest gas/liquid density ratio and fully developed turbulent pipe flow yielding the fastest mixing rates. Flow properties were predicted using the locally homogeneous flow approximation, where relative velocities between the phases are assumed to be small in comparison to mean flow velocities. Predictions were in good agreement with measurements, including representation of effects of gas/liquid density ratio and flow development at the jet exit, but only at relatively high mixture fractions. In contrast, separated flow effects caused predictions to overestimate rates of flow development at low mixture fractions.