Charge Injection Electrostatic Atomizer Modeling

Abstract

The charge injection electrostatic atomizer is rooted in the theoretical, and now experimentally verified, observation that spray mean droplet size, if larger than about one micron, is solely dependent on charge density level. The SPRAY TRIODE^R atomizer represents the first, and the simplest, example of this spray technique. By submerging a field emission electron gun in the spray liquid, it is possible to spray low conductivity fluids, at high volumetric flow rates, using compact devices. Extensive testing of devices involving an electron gun formed by an emitter cathode centrally positioned immediately upstream from an orifice anode, has permitted the formulation of a simplified description of overall operating behavior.

Tests show that output charge density is completely describable in terms of the electrohydrodynamics of the anode, independent of the details of the cathode, electrode position, internal fluid mechanics, orifice shape, materials of construction, or spray fluid properties. Within narrow limits, the operation of all cold-cathode field emission atomizers, can be described in terms of a minimum electron density criterion (Thompson's theorem).

A one-parameter, two-flow regime model based on this criterion is shown to be capable of correlating all spray fluid, breakdown-limited atomizer operation. In addition, the model verifies the existence of a minimum spray droplet size, and predicts mean droplet sizes that are consistent with observation. A more sophisticated model, capable of providing quantitative spray plume droplet size distributions, will form the topic of subsequent papers.