Electrical charging of liquid sprays in high pressure gas flows for electro-fluiddynamic processes

In the electrofluiddynamic (EFD) generator process the kinetic energy of a gas flow is directly transformed into electrical energy. This process is similar to Magnetohydrodynamics except that unipolar charges are employed, and the working fluid is highly nonconductive. In EFD generator processes, a particular problem exists in generating low mobility unipolar charges in subsonic flow since expansion processes providing consideration around ions in subsonic flow is not possible. Thus experimental effort was imitiated on generation of charged aerosols by electrohydrodynamic spraying. This process however is also applicable in supersonic flow. Various liquids were sprayed through a metal capillary at very high electric field strengths into high pressure (up to 40 atms) gas flows to simulate conditions in an EFD generator. The current produced as the charged spray ruptures is a function of local electric field strength, the liquid properties, and the velocity of the working fluid. Of these parameters the effects of liquid properties, such as surface tension, electrical conductivity, density, and mass flow rate are investigated. The experiments show that the current generated increases with the surface tension, electrical conductivity, mass flow rate of the liquid, and the velocity of the working fluid. The current output decreases at the same time with an increase of the density of the liquid. A semi-empirical relation of the current output with the indicated variables is obtained using dimensional analysis, and good agreement is shown with the experimental values.