Turbulent natural convection along a vertical electrode
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INTRODUCTION
NUMEROUS ~-8 studies have been carried out on the natural convection along the surface of a plane vertical electrode installed in an unstirred electrolyte. However, most of the previous studies used tiny electrodes, and the efforts have been concentrated mainly on the analysis of laminar natural convection. In this sense, these studies on the natural convection are thought not to be closely related to the industrial electrolytic processes. 9 In the present paper, the development of turbulent natural convection is studied on a vertical electrode of industrial size installed in an unstirred electrolyte: the turbulent natural convection is visualized by the Schtieren technique under the experimental conditions similar to the industrial electrolytic refining of copper. Then, the time-averaged velocity profile of the turbulent natural convection is measured by a tracer technique on the surface of a plane vertical cathode placed at a horizontal distance of 20 cm from the anode surface. Based on the obtained experimental results, the analogy between the phenomena of momentum transfer associated with the present turbulent natural convection and induced by the heat transfer along a heated vertical plate is discussed.
II.
20 cm (for velocity profile measurement). A free space of 30 cm height was provided at the bottom of the electrolytic cell. Each electrode was placed o n a n insulated metal hook shown in Figure 1. An aqueous 0.6 M CUSO4-1.85 M H2SO4 solution was used, and the current density was varied from 20 to 200 A / m 2. Electrolysis was carried out at 293 K. Under the electrolytic conditions shown in Table I which are similar to the industrial practice of copper electrolytic refining except for the temperature and current density, the time variation of Schlieren pattern of the electrolyte between both electrodes was taken with a cinecamera. The optical arrangement is shown in Figure 2. The displacement of colophonium particles (about 20/xm in diameter) suspended in the electrolyte was filmed on 16 mm cinefilm. It was analyzed with NAC film motion analyzer (PH 160B), and the time-averaged velocity profile of turbulent natural convection was obtained. The optical
EXPERIMENTAL PROCEDURES
In order to visualize the natural convection developing along the electrode, a thin electrolytic cell shown in Figure 1 was used. The inner dimensions of the plexiglass cell were 3.5 cm (thickness), 30 cm (width), and 140 cm (height). The size of both copper electrodes was 0.5 cm x 2 cm x 110 cm, and they were insulated with PVC resin except for the working surface of 2 cm x 100 cm between the vertical distance of 0 and 100 cm from the lower edge. Each electrode was vertically installed in the electrolytic cell at a horizontal distance of 3.5 cm (for flow visualization) or
K. DENPO, Graduate Student, Y. FUKUNAKA, Research Associate, Department of Metallut;gy, and Y. KONDO, Professor, Departmertt o f Metallurgy, are all at Kyoto University, Kyoto 606, Japan. S. TERUTA, former Graduate Student at Kyoto University, i
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