Influence of energy exchange between air and liquid streams on spray characteristics and atomization efficiency of water–air impinging jets

The paper evaluates the interaction between atomization quality and atomization efficiency, of a twin water impinging jets atomizer. Liquid jet breakup length, liquid jets separation distance at the breakup region and spray angles were measured with high speed photography and spatial distributions of mean droplet velocities and diameters and normalized liquid volume flux with phase Doppler particle analyzer (PDPA). The results show that the breakup length decreased and the separation distance of the interacting liquid jets at the geometrical’impingement’ region increased rapidly as air-to-liquid momentum ratio (ALMR) increased and then remained constant for ALMR > 9. Spray angles were different on different planes through the spray and generally decreased with increasing ALMR and were insensitive to liquid jets impingement angle. The spatially-averaged Sauter mean diameter (SMD) of the sprays quantified uniquely the atomization quality and showed, for the first time, that it did not depend on liquid jets impingement angle. The atomization efficiency was quantified from the spatially-averaged SMD, for the first time, according to formalisms of Lefebvre (Lefebvre, A.H., Energy Considerations in Twin-Fluid Atomization, J. Eng. Gas Turbines Power, vol. 114, no. 1, pp. 89–96, 1992) and Pizziol et al. (Pizziol, B., Costa, M., Panao, M.O., and Silva, A., Multiple Impinging Jet Air-Assisted Atomization, Exp. Therm. Fluid Sci., vol. 96, pp. 303–310, 2018). The values of the atomization efficiency of Lefebvre’s formalism were around 0.7% of the supplied air kinetic energy, in agreement with the measured energy exchange between the air and liquid streams up to liquid breakup, while the values of Pizziol et al. (2018) were larger.