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KOZHEVNIKOV, Igor; BOLOGA, Mircea; GROSU, Fiodor; MOTORIN, Oleg. Stability of characteristics of a multistage electrohydrodynamic converter. In: Materials Science and Condensed Matter Physics. Ediția a 9-a, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, p. 255.
|Materials Science and Condensed Matter Physics
Ediția a 9-a, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
Chișinău, Moldova, 25-28 septembrie 2018
The operation of electrohydrodynamic converters (EHDC) is based on the phenomenon of electroconvection that takes place in a dielectric liquid under the influence of an electric field. EHDC are usually used for pumping dielectric liquids, gaseous media, mono- and two-phase coolants in various heat exchangers. As a rule, single-stage converters consist of an emitter and a collector. Ideally, the medium acquires the charge near the emitter, moves under the Coulomb forces to the collector where its charge is neutralized and the medium is ejected from the interelectrode space (IES). Similar processes take place near the collector, where the medium acquires an electric charge of polarity of the collector. In this case backward flows may arise that result in reduction of the pumping efficiency. Thus, in order to increase the pumping efficiency it is necessary to increase the intensity of fluid charging at the emitter and to reduce that on the collector. The latter is achieved by the proper selection of the electrodes geometry (in particular, sharply asymmetric), dielectric coatings, and electrophysical properties of the working agent. In addition to controlling the electrification of liquids on electrodes, it is necessary to organize EHD flows in IES, in order to suppress backward flows that reduce EHDC efficiency. Converters of various designs and sizes, ranging from micro to conventional [1, 2] have been developed. A review of the literature shows that there is a lack of information regarding the converters characteristics stability. We have investigated changes in the output characteristics of the eight-stage EHDC in the process of its long-term operation. The electrodes of each stage are made in the form of wire mesh spaced at a circular metal rim parallel to each other with a certain pitch. The emitter wires have a perforated insulation coating. The working liquid (silicone oil) was pumped through a loop channel. The dynamic pressure generated by the EHDC, the rate of pumping of the working medium, and the leakage current from the collectors were recorded over time. A periodic change in the dynamic pressure and a synchronous change in the leakage current from the collectors have been found. After 2200 hours, a drop in head (corresponding to the leakage current) was recorded. After increasing the voltage on the electrodes up to 25 kV and operating the converter in this mode for 4 hours, a gradual increase in the pressure in the channel is observed. Later, up to 5,260 hours, there was no such deterioration in EHDC performance. The pressure (at 5260 h) was 90% of the initial value. On all collectors and exposed surfaces of emitters, a plaque with a large ohmic resistance is detected, preventing charge-exchange at the electrode-liquid interface. Also, the dielectric coating reduces the electric field in the IES, and an increase in the voltage promotes the appearance of new centers of charge exchange. Thus, the main reason for the reduction in the generated pressure, or EHDC efficiency, is the formation of a high-resistance coating on the electrodes. The use of low voltage on the electrodes and liquids with ≥ 10-10 S/m, the proper operating mode EHDC (breaks of certain duration) can considerably suppress this undesirable process. If there is a drop in performance, it is necessary to restore the surface of the electrodes and promote the formation of new ionization centers by increasing the electric field intensity between the electrodes.