Performance of Electrohydrodynamic Gas Pumps and Heat Transfer Enhancement in Circular Tubes
| Autor: | YILMA TADESSE BIRHANE |
|---|---|
| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 Flow characteristics of electrohydrodynamic induced gas pumps in circular tubes has been experimentally evaluated in this work. The gas pumps use eight evenly spaced emitting electrodes which are flush mounted on the tube wall. Two tube diameters (61.8 mm and 127.8 mm) and two electrode gap distances (25 mm and 50 mm) have been considered for both single-stage and two-stage EHD pumps. For two-stage cases electrodes aligned and offset orientations are investigated. Additionally, the effect of ascending or descending order of applied voltages on the two-stage EHD gas pump at flow dominant areas is examined. Experiments are conducted using positive corona discharge with voltage varying from 17.5 kV to 30 kV depending on required parameters. As a result, flows induced by the pumps have an inverted parabolic profile with a higher velocity near the wall and a lower velocity at the tube center. The results also show that the volume flow rate increases with the applied voltage but approaches an asymptotic value before sparkover takes place. Several important implications from the present results for practical engineering applications are presented. Heat transfer analysis of a targeted thermal management (thermal cooling) for special designed circular heater is investigated to evaluate the EHD pump effectiveness in enhancing the heat transfer. The convective heat transfer coefficient for different constant-heat fluxes at various applied voltages of EHD gas pump is studied. And it is shown that the Nusselt number is the reciprocal of the non-dimensional surface temperature of the heater tube. Also the EHD gas pump induced forced convection effectively enhances the heat transfer aided by the natural convection. The variation of vertical height of the circular tube heater and non-dimensional Nusselt number is evaluated and it shows that the Nusselt ratio decreases with the height of the heater tube which in fact signifies heat transfer enhancement. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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