Experimental investigation of spray from two-fluid nozzles: Universality of size distributions, dispersion of ethanol-water mixtures, and spray evaporation*

Within the scope of investigations on spray flame pyrolysis, the spray of different commercial two-fluid nozzles is investigated with phase doppler anemometry. The investigations cover a wide range of operating conditions where sprays with mean Sauter diameters in the order of 10 micrometres are produced from water-ethanol mixtures atomised with compressed air (Webber number > 10^3).

The investigation shows that the size distribution of the spray under the different conditions collapses very well into a single distribution when scaled appropriately. This is the case when the relative contribution to the surface area of the spray is considered in the distribution. The universal distribution found is well approximated by a gamma distribution. A deviation from this universal property is observed when water-ethanol mixtures are dispersed under certain conditions. In such cases, the distributions tend to develop a heavy tail at larger sizes. This observation could be related to the tendency of ethanol to accumulate at the surface of the mixture, causing similar behaviour in the ultrasonic dispersion of such mixtures. The measurement of evaporating spray further shows how the substance properties of the mixtures are related to the evaporation rates of the spray.