Large particle retention

Large-particle retention, flow rate, and Ap from filtration tests using tighter graded-density depth media samples show dramatically different behavior in the silica, alumina, and ceria abrasive slurries, indicating that new CMP slurries filter optimization still remains empirical in nature. 

The retention efficiency of membranes is dependent on particle size and concentration, pore size and length, porosity, and flow rate. Large particles that are smaller than the pore size have sufficient inertial mass to be captured by inertial impaction. In liquids the same mechanisms are at work. Increased velocity, however, diminishes the effects of inertial impaction and diffusion. With interception being the primary retention mechanism, conditions are more favorable for fractionating particles in liquid suspension. 

Because of greater mechanical damage catalyst particles at high fluid velocities, and because of the poor retentivity of fines produced by attrition in beds of large particles, the use of small-diameter catalyst particles in fluidized beds is more usual (Gunn, 1968). In many applications of fluidization, the particles are in the range 30 -300 pm (Smith, 1981 ... 

The total volume of solvent in the column can be divided into two categories Vv is the volume of solvent in the voids between the gel particles, and Vp is the volume of solvent in the pores. Not all of the pore volume is accessible to particles in a given molecular weight class. We define K,VP as the pore volume into which molecules from the ith class can permeate. Thus, K, describes what fraction of a pore is accessible to molecules in class i. The fraction K, is zero for very large particles and unity for very small particles and varies over this range for particles of intermediate size. The retention volume for molecules in class i is given by... 

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