Electrohydrodynamic flow in air produced by electric corona discharge (numerical and experimental studies of the EHD phenomena in the electrostatic levitation unit and the industrial electrostatic precipitators).

摘要

This thesis presents the numerical and experimental studies of the secondary electrohydrodynamic (EHD) flow in air produced by electrical corona discharge. A hybrid algorithm for numerical simulation of the EHD flow, in both steady and transient states, is described in detail. The Boundary Element Method, the Finite Element Method and the Method of Characteristics were used for the corona simulation, and the CFD commercial software FLUENT was employed for the calculation of the flow field. The fully coupled corona model, in which the EHD body force and the gas velocity are transferred between the corona discharge model and the CFD model in FLUENT using the User-Defined-Functions, is discussed and has been applied throughout the entire thesis. All essential parameters of both the electric and flow fields can be predicted. The reliability of this model has been verified by comparison of the simulation and the experimental results for air velocity in the needle-grid configuration. These results proved that at normal pressure the EHD flow has a negligible influence on the corona characteristics, while the effect of the external gas flow on the corona may be significant depending on the flow properties and system configurations. The effect of the EHD flow on the electric corona discharge in compressed gases is also addressed: the corona discharge current is not proportional to the ion mobility because of the stronger ion convection effect under higher pressures; the ion drift region is also much narrower. The idea of an electrostatic levitation unit has been proved experimentally and the EHD flow has been analyzed in order to explain the thrust force generation. The numerical predictions have been verified by the comparison with the experimental results for the thrust force. Guidelines for the optimum design of the lifter are suggested. The EHD flow modification in a wire-plate electrostatic precipitator has been investigated and an entire flow regime map for a large variety of the Reynolds and Electrohydrodynamic numbers has been created.; Keywords. electrohydrodynamic flow, electric corona discharge, numerical simulation, electrostatic levitation, electrostatic precipitation.