Bottom Clearance Research Articles

Mixing and power characteristics of drag board device in shallow pool

Mixing and stirring of a 20-m(2) shallow pool by means of a drag board device has been investigated. The board closes the pool cross section except for a slit of a few centimeters above the bottom, and it is slowly moved back and forth, forcing the water to run through the slit and thereby creating a turbulent backwhirl. Power drawn and the drag on the board has been measured together with the velocities of the water at different locations in the wake of the board. Power number N(p) has been correlated with the Reynolds N(Re) and the bottom clearance numbers N(c) by the expressions \documentclass{article}\pagestyle{empty}\begin{document}$$ N_p = 13,465N_{\rm Re};{-0.774} N_c;{0.1016} N_{\rm Re} < 80.000\\N_p = 5.4N_{\rm Re};{-0.0863} N_c;{0.104} N_{\rm Re} > 80.000 $$\end{document} Power and Reynolds numbers are defined as usual with the square root of the board-immersed-area as the characteristic length. The bottom clearance number is defined as the ratio of the water depth in the pool to the difference between water depth and the board width immersed in water. Flow pattern behind the board consists of large vortex loops causing the fluid to circulate from bottom to top and producing a thorough mixing effect. The drag board seems to have several advantages over conventional paddle wheels for the mixing and stirring of algal cultures in shallow ponds.

The sound radiated from gears. On the existence of aerodynamic sound.

The behaviour of tooth mesh frequency sound radiated from a tooth mesh point of a spur gear pair was investigated to see how it is generated. after examining the effect of bottom clearance, torque and material (steel or nylon) upon the radiation, the sound proved to be an aerodynamic sound; i.e., the sound is born from the pumping action of the clearance between meshing teeth, under high speed conditions. Especially towards the exit side of meshing, the radiation is prominent, with a level trough feature, which occurs due to the existence of two sorts of sounds having a phase difference of 180° near the meshing point. It has also become clear that this aerodynamic sound can not necessarily be reduced by increasing the clearance, after a consideration based on an analogy to the fluctuation of the flow rate of a gear pump.

The sound radiated from gears. 2nd, report On the existence of aerodynamic sound.

The behaviour of tooth mesh frequency sound radiated from a tooth mesh point of a spur gear pair was investigated to see how it is generated. After examining the effect of bottom clearance, torque and material (steel or nylon) upon the radiation, the sound proved to be an aerodynamic sound ; i.e., the sound is born from the pumping action of the clearance between meshing teeth, under high speed conditions. Especially in the direction of the exit side of meshing, the radiation is prominent, with a feature of level trough, which occurs due to the existence of two sorts of sounds having the phase difference of 180° nearby the meshing point. It has become also clear that the aerodynamic sound can not necessary be reduced by increasing clearance, after an analogical consideration on the fluctuation of the flow rate of a gear pump.

Performance of a large-cone-angle hydrocyclone—II: Separation properties

The separation properties of large-cone-angle hydrocyclones of two different sizes have been determined at different cyclone configurations and input variables. Experiments have been carried out with a mixture of sand and a low fraction of magnetite of almost equal free-fall velocities. Also residence time distributions of magnetite have been determined. Analysis of the experimental results shows that for each volume flow of solids through the cyclone there will be a specific apex opening at which a maximum separation efficiency is reached. If a high separation efficiency is wanted at a high throughput of solids and a low energy consumption, the cyclone should operate with a high vortex finder bottom clearance.

Efficiency of Pumping from Small Circular Sumps

Efficiency and minimum safe submergence of a 4-in. vertical turbine tail-water recovery pump in a circular pump are affected by side clearance and inflow velocity, but not by bottom clearance. Highest pump efficiency was attained in laboratory tests with a bottom clearance of either 0.5 D, D, or 2 D; a side clearance of 2 D or greater; and an inflow velocity of 1 fps. Minimum safe submergence of approximately 9 D is required to avoid vortex formation; however, lowest values of minimum safe submergence were observed at small side clearances. Reductions in normal pump efficiency as a result of reduced side clearance or increase inflow velocity were most pronounced at the low rate at which peak efficiency is normally attained. Such reductions averaged approximately 2%, with a maximum loss in efficiency of 4.6%.