Characterization of liquid entrainment in a counter flowing gas using Phase Doppler Interferometry

An 8 inch ID spray column was used to characterize the entrainment of water droplets into counter flowing air. The ability of Phase Doppler Interferometry (PDI) to measure the size and velocity distributions of entrained droplets resulting from a single full cone Bete® nozzle was proven, and the total volume of liquid entrained was gravimetrically quantified. The experimental setup consisted of a variable speed pump and air blower which allowed for droplet measurements over a range of gas and liquid rates. This work illustrates the effect of nozzle supply pressure and air rate on the entrainment rates and PDI measured droplet size distributions. The magnitude of the droplet size distribution, as well as the rate of entrainment, increased with the liquid spray rate, but the unimodal distribution peak diameter remained consistent. The same conclusion was true at an increased gas rate, in addition to an overall decrease in entrained droplet Sauter mean diameter and an increase in the total liquid entrained. The use of a theoretical entrainment model with PDI measured droplet diameters was explored. Applying the measured PDI diameters was found to significantly decrease the estimated entrainment from the theoretical entrainment based on a droplet buoyancy concept. This effect was further explored by comparing the sizing of a de-entrainment mesh pad for both cases.