Reynolds drag force, liquid-solid

The settling rate of a solid in a liquid is determined by its drag, a force defined by many parameters, including the shape-dependent drag coefficient. The motion of particle settling is described by the particle Reynolds number, as seen in... 

A drop rises or falls through a liquid as the result of buoyancy or gravity forces opposed by frictional resistance to motion. The latter is characterized by a drag coefficient, the knowledge of which makes it possible to calculate drop velocity and hence the residence time of the drop in the column. Although the variation of drag coefficients with Reynolds number is well known for solid spheres, this is not the case for liquid drops, as shown by the bottom line of Fig. 2. 

Kariyasaki [61] studied bubbles, drops, and solid particles in linear shear flow experimentally, and showed that the lift force on a deformable particle is opposite to that on a rigid sphere. For particle Reynolds numbers between 10 and 8 the drag coefficient could be estimated by Stokes law. The terminal velocity was determined to be equal to that of a particle moving in a quiescent liquid. The fluid particles would deform into airfoil shapes when submitted to shear flow. Kariyasaki proposed to calculate the lift force Ifom a balance of buoyancy, gravity, drag and lift, hence ... 

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