4000 Open Channel Mixers
Westfall Model 4000 Leading Tab Low Head Mixer Excels in Open Channel Applications
Download the Alden Lab’s test results.
Download the Model 4000 Channel Mixer Headloss Chart downloadable Excel spreadsheet. Enter the pipe interior diameter to calculate headloss for the Westfall model 4000 open channel mixer.
Download the Japanese 3050 and 4000 Low Headloss Mixer Catalog.
Alden Labs Simulations
Alden Research Laboratory Inc. tested the performance of the three-stage Westfall 4000 mixer for use in open channel applications, to determine the mixer’s effectiveness in achieving low CoV (coefficient of variation) — optimal mixing, with as little pressure loss as possible. Two configurations were tested: one with inlet and diffuser cones and one without.
Alden reported that the mixer “will work very well as an open channel mixer in either configuration tested. The low pressure loss characteristics are very desirable for pressure limited operation, and the raked angles prevent fouling.” In addition, “the mixer tabs break up any swirling flow, which at high velocities or low submergence depths could cause air-entraining vortices to form, which would reduce flow rate.”
In settings where the best possible mixing is required, the mixer without inlet and diffuser cones has the most effective mixing.
Reducing Pressure Loss
For situations where reducing pressure loss is most important, the inlet and diffuser cones are recommended. Mixing is still excellent, though marginally less efficient than the mixer without the cones. Pressure loss is optimally reduced.
Balancing Mixing and Pressure Loss
Where a balance of mixing efficiency and reduced pressure loss is desired, the mixer with inlet cone but without the diffuser is recommended.
Save Money and Operate “Green”
Because the mixer requires no electric connections, you will save significantly on the installation, operation and maintenance. And of course, the energy savings are good for the environment as well as your budget.
If Reducing Pressure Loss is Paramount, Use Inlet and Diffuser Cones
The inlet and diffuser cones reduced mixer pressure loss by 32% at a given flow rate, or increased flow rate by 18% at a given head loss. 52% of the decrease in pressure loss is attributable to the inlet cone, and 48% to the diffuser. According to Alden, “The diffuser reduces energy loss of the flow through the mixer by limiting the turbulent momentum transfer with the bulk fluid as it slows and expands the flow.” This “reduces the energy available for mixing once the flow exits the diffuser.” Without the inlet cone, pressure loss is greater as there is a large separated flow region at the walls in the first stage of the mixer; whereas with the inlet cone, the flow remains attached to the mixer walls throughout. The K value using inlet and diffuser cones is 2.0.
To Balance Mixing and Pressure Loss, Use Only the Inlet Cone
Testing indicated a mixer with an inlet cone but without a diffuser cone would have mixing performance similar to the configuration that uses the mixer alone, offering the best of both parameters. The K value with an inlet cone is 2.5.
If Mixing is More Important than Reducing Pressure Loss, Skip the Cones
Both mixers offer excellent mixing performance, with very low CoV values ten mixer diameters downstream of the bulkhead (30-ft). However, the mixer without inlet and diffuser has a CoV = 0.008, better than the mixer with the inlet and diffuser which has a CoV = 0.018. The K value without the cones is 2.95.
What to Do with Changeable Water Surface Elevation
If your system has water surface elevation that changes significantly with flow rate, installation needs to ensure that “the downstream end of the mixer will be submerged under all operating conditions, and the mixers should have the capacity to pass the maximum required flow at the available head without overtopping the channel,” according to Alden.
Alden recommends that to satisfy both low and high flow requirements, the mixer centerline should be located approximately 1.5 diameters above the channel floor. If the channel is wide enough, “installing 4 X 18” mixers rather than 1 X 36” mixer would lower the minimum operable water level by approximately 3-ft, while maintaining the same maximum cross sectional mixer area, the same pressure loss, and the same maximum flow rate.”
Bonus: Flow Rate Measurement
Alden suggests another benefit of using the mixer: “Since the pressure loss coefficient of the mixer is known, the mixer could also be used for flow rate indication by measuring the water surface elevation difference across the mixer, assuming the bulkhead is sealed adequately to the channel walls.”
- Open Channel Water Treatment for Wastewater or Potable Water
- No Power Consumption
- Excellent Mixing
- Accommodates Changing Water Levels and Flow Rates
- Low Permanent Pressure Loss
- Resists Fouling
- Suitable for Remote Locations
- Short Laying Length
- Minimal Maintenance Needed
- Long Service Life