Multiphase systems drag force

The drag force depends upon the particle Reynolds number. Different Co-Re relationships have been used in the past. Further, several investigators have attempted fluid-mechanical description of multiphase systems. It was thought desirable to analyze all these attempts in view of the discussion given earlier. Such an analysis is summarized in Table II. Some additional points are given next. 

Summarizing the forces introduced above, tests carried out in different multiphase systems have shown that the order of importance of the different forces involved typically ranks buoyancy and drag in the first positions and then lift and virtual-mass forces for fluid-solid systems and virtual-mass and lift forces for fluid-fluid systems (see, for example, the studies on non-drag forces by Diaz et al (2008) and Barton (1995)), whereas the most common values for the corresponding constants are Cl = 0.25 and Cv = 0.5 both for fluid-fluid and for fluid-solid systems. Naturally, since it is straightforward to implement all the forces in a computational code (Vikas et al, 201 lb), it is best to include them all for the sake of generality. 

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