A model for sieving of dilute paarticles in an ultrafiltration process is presented with specific application to the design of filters for virus removal from biological rpoducts. The model considers a membrane of known pore diameter distributions, F(a), with N~D defects of diameter a~D through which virus-containing fluid is flowing in accordance with some flow rate function, Q(a), and for which the downstream particle concentration is given by some hindrance function, S(a). The model provides a framework for assessing the effects of filtration area, pore diameter distribution, and defect diameter and density on virus reduction. Using a gamma pore diameter distribution, Poiseuille pore flow, and the hindrance model of Bunjay and Brenner (1973), results demonstrate the profound effect of the population of large pores and of surprisingly feo defects. demonstrate the profound effect of the population of larger pores and of surprisingly few defects. This model is further coupled with a model for simulation of a nitrogen diffusion integrity test for filter transport characterization. The analysis, which considers parallel diffusive flow through wetted pores and convective flow through opened pores and defects, demonstrates the power of this simple physical test in discriminating among filters of varying virus reduction capability.
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