Mixing Mechanisms in a Pair of Impinging Jets

Abstract

An experimental investigation of mixing in impinging jet atomizers is conducted. Both miscible and immiscible liquid jets are tested. In the miscible liquid jet experiments, two water jets are impacted on each other. One of the jets is colored and traced across the spray. The liquid is sampled at different locations in the spray using a linear patternator. The volume fraction of each jet in the sampled volume is determined through the measurement of the color intensity. In the immiscible liquid jet experiments, a water ‐kerosene combination is used. The local volume fractions are determined by direct measurement of the volume of each component in the sampled volume. The volumefractionproe lesareusedtocharacterizethemixingprocessesanddeterminethequality (orextent)ofmixing in such atomizers. Results show that two distinct processes control mixing: 1 ) the ability of the two jets to redirect each other on impact and before atomization (preatomization process ) and2) the turbulent dispersion in the spray region(postatomizationprocess ).Thepreatomizationprocesscan resultin two typesofatomizations:ree ectiveand transmitive atomization. In the ree ective atomization, the jets basically bounce off of each other, causing the e uid ofeach jetto remain on thesamesideof thejet. Inthetransmitiveatomization,thedirection of themomentum does not changecompletely, and the e uid ofeach jet e owsto the side of theotherjet. Theresultsshow thatin thistype of atomization, the higher the jet momentum in the plane of jet centerlines, the higher the degree of stream crossing and, therefore, the lower the extent of mixing. The directional momentum increases by increasing jet velocity and diameter and the impingement angle. On the other hand, the turbulent dispersion in the postatomization region improves the mixing. Consequently, the extent of mixing increases downstream of the impingement point.