Twisted tapes as turbulence promoters in the microfiltration of milk

This study is concerned with the application of a twisted tape, as low pressure loss turbulence promoter, in the microfiltration of milk. By application of twisted tapes both reversible and irreversible fouling are reduced and the permeate fluxes are remarkably increased. The flux improvement increases with decrease of an aspect ratio of twisted tape. The highest flux improvements (relative to the conventional operation) were obtained by application of the tightest twisted tape of aspect ratio 1.0, 400–600% for the same cross-flow rate and 25–82% at the same hydraulic dissipated power. Considerable energy savings can be obtained by application of twisted tapes as compared to the conventional operation and to the operation with some other promoters such is KM Kenics™ mixer. The high efficiency of twisted tapes as turbulence promoters is contributed to the intensive promotion of turbulence and low pressure loss compared to some other turbulence promoters. Alternation of streamline path from straight to helically shaped proved to be more efficient in disruption of the fouling layer than just an increased axial cross-flow velocity. In the membrane fitted with twisted tape turbulence is the most intensive at the membrane wall were the helically shaped streamline path is the longest. This contributes to the intensive disruption of boundary layer and scouring of fouling forming material.

► Twisted tapes remarkably increase permeate flux. ► Both the reversible and irreversible fouling are reduced. ► To the fouling reduction mostly contributes alternation of streamline path from straight to helically shaped. ► Specific energy consumption is reduced due to the high fluxes obtained by application of twisted tapes.