Drag force on particles

Rusche, H. and Issa, R. I., The Effects of voidage on the drag force on particles, droplets and bubbles in dispersed two-phase flow. Proceedings of the 2nd Japanese-European Two-Phase Flow Group Meeting, Tsukuba, Japan, 2000. 

Whenever relative motion exists between a particle and a surrounding fluid, the fluid will exert a drag upon the particle. In steady flow, the drag force on the particle is... 

Entrainment from fluidized beds is also affected by temperature and pressure. Increasing system pressure increases the amount of solids carried over with the exit gas because the drag force on the particles increases at higher gas densities. May and Russell (1953) and Chan and Knowlton (1984) both found that pressure increased the entrainment rate from bubbling fluidized beds significantly. The data of Chan and Knowlton are shown in Fig. 13. 

For dense gas-solid two-phase flows, a four-way coupling is required however, the coupling between particles is managed in a natural way in DPMs. The task is, therefore, only to find a two-way coupling between the gas and the solid phases, which satisfies Newton s third law. Basically, the gas phase exerts two forces on particle a a drag force Vda due the fluid-solid friction at the surface of the spheres, and a force Vpa = -Va Vp due to the pressure gradient Vp in the gas phase. We will next describe these forces in more detail, along with the procedure to calculate void fraction, which is an essential quantity in the equations for the gas-solid interaction. 

It is seen therefore that, in the absence of any entirely satisfactory theoretical approach or reliable experimental data, it is necessary to adopt a highly pragmatic approach to the estimation of the drag force on a particle in a non-Newtonian fluid. 

Richardson, J. F. and Meikle, R. A. Trans. Inst. Chem. Eng. 39 (1961) 357. Sedimentation and fluidisation. Part IV. Drag force on individual particles in an assemblage. 

In a concentrated suspension, the drag force on a particle will be a function of its velocity up relative to the liquid and will be influenced by the concentration of particles that is, it will be a function of the voidage e of the suspension. 

Thus, for any voidage the drag force on a sedimenting particle can be calculated, and the corresponding velocity required to produce this force on a particle at the same voidage in the model is obtained from the experimental results. All the experiments were carried out at particle Reynolds number greater than 500, and under these conditions the observed sedimentation velocity is given by equations 5.76 and 5.84 as ... 

If segment S were coupled to the central molecule only, its segments would simply drift as a particle cloud towards the junction and the drag force on the central chain would be approximately... 

I drag force on a particle due to passing air g acceleration due to gravity... 

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