AWWA MTC64621

A model was developed, based on computational fluid dynamics (CFD) for the description ofthe complete flow field inside a membrane capillary, driven in inside-out mode. Particle orfloc transport and deposition can be described by superimposing the calculation of forcesand torques equilibria on the previously modelled fluid flow field. The model is used to givean overview of deposition behavior of flocs of certain size depending on operation condition,i. e. dead-end or slow cross-flow. The results can be used to derive appropriate operationand cleaning procedures. It is shown that the choice of dead-end or cross-flow operation ismore significant if small particles or floc aggregates have to be filtered by the membrane.Small particles will be deposited more or less homogeneously along the membrane wall aftersome significant distance to the capillary inlet, letting the first membrane area, hereapproximately 30% unused for floc deposition. A slow cross-flow could be used to transportsmall flocs out of the capillary which entered the capillary cross section area in theneighborhood of the axis. Larger flocs will be "collected" in one resulting equilibriumtrajectory and are transported to the rear end of the capillary, independent of their startingradial position at the inlet and operation condition. It can be further assumed that floc growthoccurs during transport along this equilibrium trajectory. This will lead to transport of largerflocs out of the capillary lumen in cross-flow operation, avoiding excessive floc depositionand clogging of the membrane. Includes 24 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

03/01/2007

Number of Pages:

10

File Size:

1 file , 660 KB