Coalescence and counterflow of droplets on needle electrode with negative corona discharge

The coalescence of droplets on the discharge electrode surface in high humidity environments has rarely been studied, which may affect discharge characteristics. Meanwhile, directional transport of droplets is of great significance for many applications ranging from fluidic processing to thermal management. Here, corona discharge in needle-plate electrode is adopted to explore the coalescence rule of droplets attached on the discharge electrode surface in high-humidity environment, and realize the counterflow of droplets. The experimental results show that the amount of coalesced droplets on the needle electrode surface reaches the maximum under -7.5 kV at relative humidity ~ 94% and ambient temperature ~ 20 ℃. When the applied voltage increases from -6 kV to -11 kV, the droplet moves up 2.76 mm in 5 s. The size of attached droplet depends on the balance of coalescence and evaporation. The coalescence is mainly attributed to the dielectrophoretic force caused by the high electric field gradient. The evaporation is related with the ionic wind generated by the corona discharge. As for the counterflow phenomenon of droplet, we speculate that the high concentration gradient of positive ions near the needle electrode provides a driving force for the negatively charged droplets. Meanwhile, the electrons and negative ions below the needle tip offer a repulsive force to the droplet. The shape and moving direction of the droplet attached on the needle surface can be manipulated by changing the voltage applied to the needle electrode, which shows the potential application value in realizing self-cleaning of electrode, liquid lens and so on.

Experimental Study of the Performance of a Laboratory-Scale ESP with Biomass Combustion: Discharge Electrode Disposition, Dynamic Control Unit and Aging Effect

The increasing use of biomass combustion systems as household appliances for heat generation is causing concern about local air quality. Areas with high concentrations of particulate matter (PM) emissions are linked to health risks. There is a need for a removal device that collects the particles before they reach the atmosphere. Electrostatic precipitators (ESPs) are the most suitable option. In this study, a laboratory-scale prototype ESP was tested with a pellet boiler. Retention efficiencies above 90% were obtained with three different discharge electrode dispositions. The continuous operation of the ESP was achieved with a dynamic control system despite fluctuations in emissions, gas conditions, etc. The accumulation of particles on inner ESP surfaces over the operation time reduced the effectiveness of the electric field, and thus retention efficiency. In this study, the retention efficiency fell from 90% to 31% in 34 h.

Effect of the Sound Source Position Error on Distribution Characteristics of Underwater Shock Wave Bunching Sound Field

Curved reflection bunching technique of underwater plasma sound source (UPSS) uses the geometric characteristics of the curved reflector to reflect and bunching intense sound shock wave, so the center position error of the sound source is one of the important factors affecting the bunching performance of the shock wave. In this paper, the cause of the sound source position error is analyzed in detail, and nonlinear finite element software ANSYS/LS-DYNA (dynamic analysis software developed by LSTC) is used to establish the model of the shock wave bunching sound field. Through numerical simulations, the shock wave bunching sound field distribution characteristics under the influence of different position errors are comprehensively simulated, and the bunching performance of the shock wave and its influence law are deeply analyzed according to the simulation results. It provides guidance for reasonably controlling the machining error and installation error of the reflector and discharge electrode, estimating the effective discharge times of the discharge electrode, and formulating the design process.