Helix-academic-study

In this study, both the fluid flow and particle behavior of a single Pentair X-Flow Compact Helix membrane were simulated. Although there has been a lot of research and experiments with regard to helical ridges inside membranes, the study at Ghent University is the first model-based approach to deliver detailed insights into the hydrodynamics taking place near the membrane wall. The outcomes offer new opportunities for model-based design of membranes with helical inserts, and also for optimizing the operating conditions.

Fouling is an ongoing concern in membrane filtration installations, and not only because of suspended solids in the feed stream in MF or UF processes. Dissolved substances can also cause fouling problems in NF or RO processes, even if we then call it scaling caused by concentration polarization. Both phenomena hinder the efficiency of the separation process, and will increase energy demand to keep up performance.

Membrane operators and developers have come up with several answers to fouling issues. 

One proven effective way to reduce fouling does not rely on removing the accumulated dirt at set intervals, but on designing the hydrodynamic conditions inside the membrane to prevent or minimize accumulation in the first place. During the earlier stages of development in membrane technology, rotating or vibrating units have been tried, as well as membranes with pulsating feed flows. All of these designs increased energy demand. That is why a new approach was adopted, involving helical structures to alter the fluid flow. Early results were promising and included a reported flux increase of up to 69 percent.

Pentair successfully introduced its Helix technology to optimize productivity and long-term membrane performance. The flux-enhancing technology reduces fouling and saves energy. It does so by preventing the buildup of foulants into a cake layer, which would otherwise quickly reduce the hydraulic permeability of membranes. 

The optimum configuration remained elusive for years. Reported flux improvements varied widely, likely as a result of the many variables in membrane materials, pore sizes, feedwaters, and operating conditions. As even very small differences in shape can greatly impact the hydrodynamics and flux increase, it is reasonable to assume that more experimental work needs to be complemented by a more theoretical approach to gain knowledge on the working principles.

Pentair X-Flow applied a new design for the helical ridge on the tubular membrane wall in the Compact Helix membranes. The introduction of helically wound ridges delivers enhanced mixing and high turbulence at a low additional energy consumption, so that these membranes can yield a productivity increase of up to 100 percent or reduce energy costs by 50 percent (by using lower cross-flow velocities), depending on the feed characteristics.

The researchers conclude that the study results can be the start of a model-based design of the optimum tubular membrane with helical ridges. Increasing the average wall shear stress while minimizing the shadow zone can be the goal of an optimization study.