THE INTERACTION OF WELL-CHARACTERIZED, LONGITUDINAL ACOUSTIC-WAVES WITH A NONREACTING SPRAY

The effect of a variable acoustic field olt the evaporation characteri stics of a nonreacting ethanol spray has been investigated in a long, vertical tube using a phase Doppler particle analyzer. The parametric effect of the first, second, and third acoustic modes,were studied for a constant sound pressure level, using the steady flow condition as a reference, Axial and radial profiles of Sauter mean and arithmetic me an droplet diameters, and time-resolved droplet velocities, were measu red and compared for the four experimental conditions while holding th e spray location fixed inside the tube. Spectral analysis of the dropl et axial velocity component revealed dominant frequencies equal to the frequencies of the acoustic waves in the tube. Average droplet veloci ties under all four experimental conditions remained the same. Droplet diameters decreased between 13% and 31%, 15% on average, ill the pres ence of the first and third modes, compared to steady values. The seco nd mode had little effect on the droplet diameters because the locatio n of the nozzle corresponded to a velocity node of the stationary acou stic field for the second harmonic. A simple mathematical model descri bing the evaporation of a droplet in a pulsating flow field yielded re sults that agreed qualitatively well with the experimental results obt ained.