214 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 93 NR 2/2017 Janusz PODLIŃSKI 1 , Katarzyna GARASZ 1 , Artur BERENDT 1 , Jerzy MIZERACZYK 2 The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-231 Gdańsk, Poland (1) Department of Marine Electronics, Gdynia Maritime University, Morska 81-87, 81-225 Gdynia, Poland (2) doi:10.15199/48.2017.02.47 Electrohydrodynamic Flow Evolution in a Narrow Wire-Plate Electrostatic Precipitator Abstract. In this study, the temporal and spatial evolution of the electrohydrodynamic (EHD) flow for a high voltage positive pulse in a wire-plate electrostatic precipitator (ESP) is investigated, using the Time-Resolved Particle Image Velocimetry (PIV) method. The ESP consisted of a single wire electrode supplied by a positive high voltage and a two grounded plate electrodes. The images recorded just after applying the high voltage as well as velocity field maps of the EHD flow of the dust particles suspended in the air are presented. The results illustrate the temporal and spatial evolution of the EHD flow for different applied voltages and for cases without and with externally forced flow. Streszczenie. W niniejszym artykule przedstawiono wyniki badań rozwoju przepływu elektrohydrodynamicznego (EHD) w elektrofiltrze z jedną drutową elektrodą wyładowczą zasilaną dodatnimi impulsami napięciowymi oraz z dwiema uziemionymi elektrodami płytowymi. Do badań wykorzystano czasowo-rozdzielczą metodę anemometrii obrazowej. Zaprezentowane wyniki ukazują rozwój przepływu EHD dla różnych napięć oraz dla przypadków bez i z wymuszonym przepływem (Rozwój przepływu elektrohydrodynamicznego w wąskim elektrofiltrze typu drut-płyty). Keywords: Electrostatic Precipitator, Electrohydrodynamic Flow, Temporal Flow Evolution, Time Resolved Particle Image Velocimetry. Słowa kluczowe: Elektrofiltr, przepływ elektrohydrodynamiczny, rozwój przepływu w czasie, czasowo rozdzielcza metoda PIV. Introduction In the presence of the electric discharge, e.g. corona discharge or dielectric barrier discharge (DBD), the so-called ionic wind appears between the high voltage and grounded electrodes. The ionic wind sets the gas molecules and dust particles in motion and, as a consequence, an electrohydrodynamic (EHD) flow is formed. The interest of EHD flows has been rising, mostly due to its influence on the electrostatic precipitators (ESPs) performance [1-3] and the EHD flow potential to control the airflow around aerodynamic elements (e.g. airfoils) [4-7]. The subject of EHD flows behaviour in ESPs in the steady state (or time- averaged mode) has been undertaken and widely described by theoretical [e.g. 8-10] and experimental [e.g. 11-15] researchers. However, there is still a lack of knowledge in the area of the evolution of EHD flow in ESPs. It is not yet explained, how the ionic wind and EHD flow behave at the early stages, just after applying the high voltage to the discharge electrode or for the pulsed high voltage, which is increasingly used. Some initial research on the time development of ionic wind and EHD flow in the wire-plate ESP was presented [16]. An interesting experimental results on the EHD flow evolution in a needle-to-plate corona discharge were also obtained [17, 18]. The results presented in [16-18] showed that during the unstable state of the discharge the EHD flow dramatically changes. One of the proposals to improve the collection efficiency of particles in ESPs is to use a new kind of power supply with combined DC and pulsed voltage. In such case electric field and corona discharge affected by the voltage pulses cause strong changes in the generated EHD flow, and, as one can suppose, the mechanism of dust particle collection is different than the one at the steady state (for DC high voltage). It is presently not clear, how this changes affect the overall collection efficiency of ESPs. We believe that temporal investigations of the EHD flow generated by the time-varying corona discharge with different parameters, could reveal some processes which are difficult to observe in other cases. Therefore, the study can be found very useful in providing a wider knowledge of the EHD phenomena occurring in devices, such as ESPs. In this paper the images and flow velocity fields of the EHD flow evolution in a narrow ESP are presented. Narrow ESPs have become a subject of interest [19-22] because of their possible application for the cleaning of the exhaust gases emitted by diesel engines. In this work the ESP with a one discharge wire electrode and a two grounded plate electrodes was investigated. The EHD flow evolution was studied for three different values of the positive high voltage pulse applied to the wire electrode. The measurements were carried out without and with an externally forced flow. Experimental setup During the experiment, the temporal and spatial EHD flow structures generated by a corona discharge in the narrow wire-plate ESP were investigated. The flow images and vector velocity fields were registered using 2 Dimensional Time-Resolved Particle Image Velocimetry (2D TR PIV) method. The experimental setup (Fig. 1) consisted of the narrow wire-plate ESP, a high voltage power supply, a digital oscilloscope with a high-voltage probe and an ammeter, and a 2D TR PIV equipment. The ESP electrode arrangement consisted of a three electrodes closed in a 500 mm x 120 mm x 50 mm acrylic box. The 0.9 mm in diameter stainless steel wire electrode was placed in the middle between the two plate electrodes, parallel to them, at 25 mm distance from each. The plate electrodes (500 mm long and 120 mm wide) were made of stainless steel. The positive high voltage was applied to the wire electrode through a 3.3 MΩ resistor. The plate electrodes were grounded. High voltage applied to the wire electrode was measured with the oscilloscope Tektronics DPO 3034 and the discharge current was measured with the ammeter Brymen BM859CF. The current-voltage characteristics of the investigated wire-plate ESP for the DC positive voltage (at a steady state of voltage) are presented in Fig. 2. The measured corona onset voltage was about 14.5 kV. The time-resolved measurements of the EHD flow evolution were taken for the early stage of the EHD flow occurring just after applying the DC high voltage to the discharge electrode. The measurements were carried out for a three different values of the DC voltage, i.e. amplitudes of a positive voltage pulse applied to the wire electrode: 16 kV, 18 kV and 20 kV. The time of appearing and pulse amplitude were remotely controlled by the digital function generator (Tektronix, AFG 3052C). The positive voltage pulse was generated by a high-voltage amplifier (TREK, 40/15). The rise time of the voltage pulse (from zero to the set value) was about 200 s.