Applicability Assessment of Subcritical Flux Operation in Crossflow Microfiltration with a Concentration Polarization Model

In the process of crossflow microfiltration, a deposit of cake layer tends to form on the membrane, which usually controls the performance of filtration. However it is found that there exists a condition under which no deposit of cake layer is made. This condition is called the subcritical flux condition and the maximum flux in the condition here is called the critical flux. Which means, it is a flux below which a decline of flux with time due to the deposit of cake layer does not occur. This study develops a concentration polarization model to predict the critical flux condition and to study about its characteristics. The model is verified with experimental results. For the model, the concept of effective particle diameter is introduced to find a representative size of various particles in relation to diffusive properties of particles. The modeling and the experimental results include that the critical flux condition can be determined by the use of effective particle diameter and the ratio of initial permeate flux to crossflow velocity. This study also finds that the (sub)critical flux operation is limited for the real world application because of the limitation to increasing crossflow velocity and its sensitivity to the change of feed composition.