Filter filtration curves

When CMP was first emerging as an important process, microporous membranes were tested in a tangential flow filtration (TFF) mode. In typical CMP slurries, TFF was found to be unacceptable due to the high solids content. Also, there was insufficient control of the retentate build-up on the membrane face, called concentration polarization. TFF works best with applications that have lower solids and a greater spread between retained and passed species. The excessive polarization we observed with high solids silica slurries prevented useful fractionation. TFF may be useful for the newer slurries with low solids content. Three critical questions to any filter design in slurry applications are (i) how sharp can the filtration curve be to enable clean fractionation, (ii) how is retained material handled to control filter life, and (iii) how does media selection affect the above two points. 

The above conditions aUow 90% recovery of the input ceUs, and differences in filterability of cells among different lines appear both in filtration time and filtration kinetics. AU the filtration curves exhibit steep slopes in the beginning and then decrease, so that 50%... 

Data from precoat tests, however, generally produce filtrate curves with much steeper slopes. The precoat bed has a greater resistance than most filter fabrics, and the particles which are separated on a continuous precoat usually form a cake which has a relatively low resistance when compared to that of the precoat bed. Once the thickness of the deposited solids becomes significant, their resistance increases. Thus, at very short form times, the slope of the filtrate curve may be close to 1.0, but as form time increases, the slope of the curve will decrease and will approach -tO.5 (Fig. 18-113). 

The functional form of the static filtration curve (Figure 33) may be readily derived if it is assumed that the flow of the filtrate through the filter cake is governed by Darcy s law (126). The flow rate of the filtrate dVfe/df is given by Darcy s equation... 

The anticipated filtration curve for microemboli-laden blood is described as follows The rate of obstruction of the filter pores by rigid particles would be... 

Laboratory Exercise Filtration Curves Using a Filter Press... 

Figure 14.3 Commercial pressure filtration apparatus and data acquisition unit to assess the full filtration curve following the VDI Richtlinie 2762. The media holder allows the testing of a large variety of filter media.

The filtration curve can be assessed by using a filtration apparatus as, for example, described in the VDI Richtlinie 2762. The filtered volume is determined as a function of time, allowing the calculation of both the resistance of the filter cake and the filtration media using Equation 14.3. The apparatus allows the testing of a variety of filter media (Figure 14.3). 

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

Program FILTWASH models the dimensionless filtration wash curves for the above case of a filter cake with constant porosity, axial dispersion in the liquid flow and desorption of solute from the solid particles of the filter bed (Boyd, 1993). 

Figure 1.4 shows a typical curve demonstrating the dependence of concentrations of copper, lead, and cadmium in the filtrate on the volume of seawater sampled. Metal levels become constant after 1-1.51 of sample have been filtered, and it can be concluded that at this point, contamination of the sample by the filtration equipment is negligible. 

These large groups of particles are not desirable in CMP slurry. They will cause scratches and show an additional peak on the particle size distribution curve (see Fig. 6). To fix these problems, milling and/or slurry filters can be used. Milling is used at the point of slurry manufacture, and filtration is used at the point of use (filtration can also be used to fix the long tail problems mentioned in Fig. 2b), as discussed in the following. 

Figure 3.8. Experimental curves of heat output during polyurethane curing. 1 - true curve (as a result of filtration) 2 - no filtering (2).

The use of a filter determined by Eq. (3.15) allows the true form of the signal to be restored (Fig. 3.8, curve 1). In this case, both the magnitudes of the quantities measured and the qualitative shape of the experimental curve change. The use of this filtration method has enabled us to broaden the frequency range of the instrument by about an order of magnitude and to reduce the effective time constant of the calorimeter from 4 min to 30 sec. 

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