An hydrodynamic investigation of microfiltration and ultrafiltration in a vibrating membrane module

The performance of a vibratory shear-enhanced processing (VSEP) vibrating laboratory module was investigated in microfiltration (MF) of yeast suspensions and in ultrafiltration (UF) of bovine albumin solutions. The membrane displacement (d) was measured as a function of radius and vibration frequency with an accelerometer and its maximum amplitude was found to be 30 mm at the resonant frequency of 60.75 Hz. The shear rate at the membrane γw was calculated as a function of frequency, displacement and fluid viscosity in the limit of large Reynolds numbers. When the frequency is lowered, d drops rapidly to 5.7 mm at 59 Hz (81%), while the permeate flux dropped by 46% in the case of yeast MF and by 48% in the case of albumin UF. The variation of permeate flux with shear rate was investigated by varying the frequency. In the case of yeast MF the permeate flux was found to be proportional to γw0.19 at a frequency below 59.7 Hz and to γw0.50 at higher frequency. In UF of albumin, the permeate flux was proportional to γw0.426 at all frequencies. The radial distribution of permeate flux was determined in the case of yeast MF using modified annular membranes. The local flux was found to be constant when the radius r was less than 7.5 cm and increased as r2.4 at larger radii. In concentration tests the device was able to reach a yeast concentration of 330 g l−1. In UF of albumin, the permeate flux varied linearly with the logarithm of concentration, predicting a gel concentration of 300 g l−1 in accordance with the literature.