The determination of the pore distribution and the consideration of methods leading to the prediction of retention characteristics of membrane filters

The new method described in this paper for the determination of the pore size distribution of a membrane microfilter is based upon the solution of the integral flow equation for the pore distribution function. A computer program evaluates the flow test data and calculates the numerical pore distribution, water-flow distribution, air-flow distribution and capillary area distribution, as a function of the pore size.;The gas flow laws, in the range of Knudsen and Reynolds numbers encountered in this testing, were examined and verified by flow testing over the entire range of flow rates. A general equation of gas flow for low Reynolds numbers was written which was found accurate over the entire range of Knudsen numbers. An excellent correlation between the gas flow theory and the measured responses was found.;The reflectivity factor was found to remain constant over the range of Knudsen numbers tested. By analysis of the flow versus average pressure, a value of the hydrodynamic pore size and effective capillary length could be obtained. Applying this capillary length to the distribution analysis offers a method of scaling the numbers of pores found so that a direct comparison between membranes under test is possible.;The retention mechanism of the membrane filter was evaluated using E. coli and styrene latexes. No appreciable adsorption could be demonstrated with these particles. By testing the membranes well beyond the point of bacterial passage, (the retention being measured by the titer reduction) a linear response between the logarithm of the titer reduction and the number of particles challenging the filter was observed. A similar response was found when one layer of membrane was analyzed for sieve retention.;A model of a membrane filter was proposed as a collection of sieves in series, all having the same pore distribution. The mechanism of retention is purely mechanical with adsorption having no significant role. Using the distribution of the pores, and the flow distribution, a method of predicting the retention of the membrane was suggested.