Specific charge measurements in electrostatic air sprays

An experimental study of the effects of nozzle parameters and fluid properties on specific charge and ratio of ion to drop current for electrostatic air sprays is reported. The specific gun used and the parameter ranges investigated are characteristic of many industrial painting processes. A simple collector system that discriminates between drop and ion currents was used to measure ensemble-averaged specific charge for the drops and the ratio of ion to drop current. The data exhibit a coupled dependence on applied potential, liquid flow rate, atomizing air flow rate, and fluid properties. The trends are consistent with contact charging of the liquid and ion generation during breakup of the bulk liquid into drops. Specific charges range from 0 to 9 μC/g and the ratios of ion to drop currents range from 0 to 6. Analysis of the current ratios indicates that under many conditions the ion charge density near the substrate is small in comparison to the drop charge density. Consequently, the ion charge density may be neglected and only the drop charge density must be considered in simulating the electrostatic fields