Settling velocity of a porous object
Ngew, Thomas Tze Hao
Date of Issue2017
School of Civil and Environmental Engineering
Terminal settling velocities of objects are usually determined by the usage of Stokes’ Law. This may be valid if the objects are of regular shapes, such as spheres, and have no pores and only at low Reynolds number. With porosity, Stokes’ Law is no longer adequate for calculating the terminal settling velocities of objects even with low Reynolds number. Lim (2014) and Khalil (2015) experimentally determined the settling velocities of porous spheres constructed with various materials, sizes and porosities. The settling experiments were conducted using different fluid viscosities and a curve of Reynolds number and drag coefficient is obtained. By comparing this curve with that of the solid smooth spheres, the effect of porosity would be obvious. However, as the porosity decreases, it is doubtful that the fluid may even penetrate the sphere at all, rendering it to be equivalent to a solid sphere with a “lower” density. Therefore, experiments of permeability were also tested on the spheres used and a curve of permeability and porosity is obtained in this study. As a continuation of Khalil’s works, the spheres that were previously used in his experiments were used to investigate the effects on permeability and settling velocity. The results obtained for the CD vs Re curve is similar to that plotted by Lim and Khalil and thus confirms the reproducibility of their results. An empirical equation is obtained to calculate the terminal velocity of porous spheres based on the properties of the spheres.
Final Year Project (FYP)
Nanyang Technological University