Dilute Particle Suspension Effects
The liquid preparations utilized in this study were suspensions more dilute than are customarily employed. The investigations disclose insights not apparent from the experimental results garnered from more concentrated suspensions. Dilute suspensions represent worst-case situations, those least encouraging to particle retentions.
In more concentrated suspensions it is conceivable that so large a number of smaller particles may simultaneously arrive at a pore/fiber matrix as to give the appearance of its immediate blockage by a larger particle. This would result in a more rapid reduction in the number of larger pores, reducing over time the opportunities for smaller particles to penetrate them. It is a matter of the rate at which a sufficient mass of smaller particles reaches the larger pores to block them, and of the number of individual smaller particles that escape capture during the period of time leading up to the blockage.
The period during which the larger pores are available for penetration by the separate smaller particles of dilute suspensions is foreshortened in the case of concentrated dispositions, where more sudden pore blockages take place. Thus, the same total number of particles impacting a membrane over different durations can yield different throughputs. In essence, the diluter suspension represents the worst-case condition in that it makes more likely the escape of the smaller individual particles through still-unclogged larger pores.
As a result of the above discussion, it is posited that the coincidence of pores and particles can perhaps better be perceived when investigated in suspensions of dilute concentrations.
American Society for Testing and Materials (ASTM), ASTM Standard F-316-03 -2003. “Pore-Size Characteristics of Membrane Filters for Use with Aerospace Fluids,” ASTM, West Conshohocken, PA.
Emory S.F., Koga, Y., Azuma, N., Matsumoto, K. (1993). The Effects of Surfactant Type and Latex-Particle Feed Concentration on Membrane Retention, Ultrapure Water 10(2): 41–44.
Grant, D.C. and Zahka, J.G. (1990). Sieving Capture of Particles by Microporous Membrane Filters from Clean Liquids. Swiss Contamination Control 3(4a): 160–164.
Lee J.K., Liu B.Y.H., Rubow K.L. (1993-a). Latex Sphere Retention by Microporous Membranes in Liquid Filtration. J. Inst. Environ. Sci. 36(1): 26–36. (Jan./Feb).
Lee J., Liu B.Y.H., Rubow K.L. (1993-b) Latex Sphere Retention by Microporous Membranes in Liquid Filtration. J. Inst. Environ. Sci. 36(1): 26–36.
Lee, K. W., and Liu, B. Y. H. (1980). On the Minimum Efficiency and the Most Penetrating Particle Size for Fibrous Filters. Air Poll. Control Assoc. J. 30, 377–381.
Lee, J.K., Liu. B.Y.H., Rubow, K.L., and Zahka, J.G. (1990). Pore Size Characteristics of Microporous Membranes and Filters by Airflow Porosimetry and Particulate Loading Studies. Swiss Contamination Control. 3: 160–164.
Zahke, J.G. and Grant, D.C.(December 1991). Predicting the Performance Efficiency of Membrane Filters in Process Liquids Based on Their Pore-Size Ratings. Microcontaminants. pp. 23–29.
Zeman, L.J. (1996). Characterization of MF/UF Membranes. Chapter 4, pages 180–291 in Microfiltration and Ultrafiltration: Principles and Applications, Eds L.J. Zeman and A.L. Zydney, Marcel Dekker, New York, NY.