Drop-charge correlations for polydisperse electrostatically atomized liquid sprays

In many applications liquid sprays are atomized using electrostatic methods, and typically these spray plumes containing drops that have a range of diameters. To understand and predict the dynamics of polydisperse electrically charged spray plumes, knowledge of how the electrical charge is distributed amongst the drops is required. This has been achieved by post-processing phase Doppler anemometry data for two electrostatically atomized liquid sprays and fitting the drop diameter-charge correlation to an assumed relationship of form q=ADⁿ, Here q and D are drop charge and diameter and n and A are empirical constants that describe the correlation. Values of n and A were calculated to be 2.1 to 2.9 and 5.8 ×10^-5 for a spray of specific charge 1.8 C/m³ and 2.1 to 3.2 and its value of A is 2.5×10^-4for a spray of specific charge 1.2 C/m⁶. It was found that the mean drop charge, for all drop diameters, for both data-sets, was almost always less than the drop Rayleigh limit. This latter fact gives confidence in the procedure used since no restriction was placed on this parameter during the processing. We also estimate the distribution of drop charge about the mean value and as a function of diameter and suggest that small drops possess higher rms charge levels.