A CFD image of pressure distribution illustrates the concept of upflow pressure, where the expansion and fluidization of the filter bed is not constrained by pressure acting on the top surface of the media.
Click here to enlarge imagePitt’s original design featured weep holes to allow the water to drain out of the filter media between storm events to prevent bacteria growth. But Hydro engineers were concerned that unfiltered water would drain out of the weep holes during storm events. They designed a series of small weep holes covered with filter fabric. The flow through the weep holes is restricted by the small size of the holes and low porosity of the filter fabric. This allows the filter to drain while ensuring against the release of unfiltered water.
An important part of the design process was simulating the flow through the filter using computational fluid dynamics (CFD). CFD can evaluate the performance of a computational based prototype in much less time than would be required to build and test a physical prototype. CFD also provides more information on the design than physical testing. For example, it can predict flow velocity and direction throughout the analytical domain and can also trace the path of particles of different sizes as they flow through the system.
In this case, CFD showed that in the original design, there was substantial variation in the flow velocity over the media cross-section. This would have reduced the efficiency of the filter because certain areas of the media would have been working at far below their capacity. Hydro engineers solved the problem by adding a layer of flow distributing media just below the filtration media.
The resulting Up-FloTM Filter is the first high-rate, modular upflow filtration system designed to meet the needs of the stormwater market. Its small footprint and high flow rate per unit of filter media distinguish it from conventional downflow and radial flow stormwater filtration devices. The resulting reduction in the size of the concrete filter chamber means the complete installed cost of the new filter is approximately half as much as conventional stormwater filters for the same flow rate. Additional savings can be achieved in many cases because the new filter can be positioned at hot spots to reduce flow rate requirements.
Maintenance costs are also substantially reduced because the new modular filter media is divided into components, the heaviest of which weighs 45 pounds. No heavy lifting equipment is required to replace.
The unique design was recognized by the Environmental Business Journal which awarded the product one of its 2005 Business Achievement Awards. It is now being marketed in the North American and European stormwater treatment markets.