This thesis presents an analytical and experimental study of the effects of a superimposed forced vortex on the flow characteristics of a circular sedimentation tank. In the analytical section, a theoretical flow through curve for a circular sedimentation tank was derived as a result of considering the flow through the tank on a diffusion basis. The theoretically derived equation was then compared with the N-formula. A new parameter for measuring the tank hydraulic efficiency was introduced, and the manner the diffusion coefficient; D of the tank affects its short-circuiting behaviour studied. With the help of Reynolds stresses and turbulent energy equations ti the effects of a superimposed forced vortex on the tank diffusion coefficient was investigated. An analysis of the problem dimensionally revealed that the tank characteristic number N was a function of Froude number and a dimensionless term wr/rg where w, v, r and g are the angular speed, kinematic viscosity, radius of the paddles and the acceleration due to gravity respectively. The experimental investigation was conducted with a model circular sedimentation tank, covering a suitable range of speeds of the paddles, and flow rates through the tank. N was found to have a relationship with Froude number and We as predicted by the dimensional analysis. The effects of the forced vortex on N and D were found to be in accordance less term where a.), 9, r and g are the angular speed, kinematic with the analytical considerations. As a result of the experimental study, the existence of critical flow rates. the optimum flow rates and the critical speeds of the paddles were revealed. The setting up of secondary currents by the forced vortex which has both beneficial and harmful effects was also studied. The present investigation have established analytically and experimentally that the effects of a forced vortex on a circular sedimentation tank are, up to a limit, to inhibit the short-circuiting of flow through the tank and to increase the tank hydraulic efficiency. Experimental results obtained with three types of inlets showed that the uniform flow inlet with baffles which was specially designed for this investigation was definitely superior to other inlets having slotted cylinder or cylindrical submerged weir diffuser. Some tracing techniques were modified and improved, especially those concerning the injection of dye and the dye concentration measurement.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:602133 |
| Date | January 1962 |
| Creators | Tonsiengsom, Surintra |
| Contributors | Bruce, F. E. |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/13581 |
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