Macroscopic fluid flow conditions in plate-and-frame elements

To fully evaluate the potential of RO and facilitate scale-up procedures, t he modelling of the process is an important tool. The concentrate-side of t he membrane (which is also the feed side) plays the hey-role. The determina tion of the flow regime and hydrodynamics in the concentrate-channel can be carried out through the measurements of the residence time distribution (R TD), which is used in our research. Results obtained stress its applicabili tly to this specific geometrical layout and demonstrate that the experiment al average residence time of the concentrate channel is smaller than the th eoretically calculated residence time, with differences between both values gradually decreasing with increasing liquid flow rate. This observation po ints toward the presence of dead volumes, which reduce the veal average res idence time. The flow regime can be defined in terms of several model appro aches. Application of a laminar flow pattern with a parabolic velocity grad ient gives a reasonable fit of experimental RTD-curves. Experimental RTD cu rves can also be fitted using the Plug Flow with Dispersion model. Model pa rameters are determined from comparison of calculated and experimental RTD curves. The definition of this flow profile in the concentrate channel is i mportant in the use of transport models to characterise the membrane perfor mance, since mass transfer and pressure drop are a function of the flow reg ime.