Constant‐Rate and Constant‐Pressure Filtration Look Similar—But Are They?

Abstract

Work on correlating constant‐rate and constant‐pressure filtration has been inconclusive. The author shows that correlation is not possible with current technology and explains why.

Using mechatronics technology to assess pressure filtration

“…In Figure 9 with the higher compressibility talc system significant differences between theoretical predictions and experimental data are typically seen. Several researchers [15][16][17], including the author [18], have questioned the philosophy of combining filtration data obtained over different pressure/flow regimes as there are inherent differences between cakes formed under conditions of constant and variable pressure. When compressibility is present in a forming cake, the rate of change in the pressure gradient across the cake affects the manner in which the particles in the cake are arranged, and this in turn influences both cake resistance and cake porosity.…”

“…Here, it is perhaps more normal to transport suspensions into filter chambers using either positive displacement or centrifugal pumps and perform filtrations according to the pressure and flow characteristics of the pumping device. A few researchers have suggested that data obtained at constant pressure may not correctly predict filtrations over other pressure regimes and some have attempted difficult laboratory experiments in order to assess performance at constant flow/variable pressure or variable pressure/variable flow [12][13][14][15][16][17]. Due to experimental constraints only limited progress has previously been possible and it is difficult to resolve the inherent problems of more conventional apparatus/methods, such as particle breakage and surface modification by pumps, with confidence.…”