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Terminal fall velocity of particles of irregular shapes as affected by surface area




Alger, George R., author
Simons, D. B., advisor
Albertson, Maurice L., committee member
Karaki, Susumu, committee member
Fead, John W. N., committee member
Johnson, Roberta F., committee member

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The objective of this research is to study the effect of surface area on terminal fall velocity of particles and objects of irregular shapes. An auxiliary study was also made in a qualitative manner on the effect of various concentrations of neutrally buoyant fine material on the fall velocity of spheres. The results of this auxiliary study are given in Appendix (B). It is expected that these investigations will lead to further research in areas related to these topics. Various shapes of gravel-sized particles were studied. The terminal fall velocities were obtained by repeatedly dropping the same particles in fluids with different viscosities. A photographic technique was used to determine these terminal velocities. A new shape parameter was developed and the variation of drag coefficient with Reynolds number using this new parameter is given. This Cd versus Re relation leads to the possibility of a model law for the irregular shapes with the new shape parameter as the third variable. A limited verification is given for several selected machined shapes and for ordinary concrete test cylinders. The model verification was accomplished by dropping larger scale particles in water and measuring terminal fall velocity using a specially constructed large scale speedometer. Plastic (Vestyron) particles were used to form a neutrally buoyant suspension in salt water. A small plastic sphere was dropped through various concentrations of this suspension and the fall velocity was determined with a stop watch. The results indicate the nee d to study the electrochemical properties of the suspended fine material as they appear to affect the fall velocity of the larger particle. The writer believes from the results obtained that the consideration of the Zeta potential of the fine material would ultimately lead to a better description of the apparent viscosity effects when used in conjunction with existing theories.


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Particle size determination


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