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# Multi port diffusers

Hello colleges,

I am working on WWTP with outfall inside the sea water with multi port diffusers. I need to know the design criteria and formulas for these diffusers and how to model in WaterCAD?

• Hello Abdullah,

You could model the diffuser either as reservoir which will have fixed elevation which you can set to water surface in this case  the flow through them will be controlled by the headloss through the diffuser pipes. Or you can use minor loss coefficients on pressure pipes and model the diffusers as emitter coefficients.

Let us know if this helps or not.

Regards,

Sushma Choure

Bentley Technical Suppport

• The link that Sushma posted has some good tips. It depends on what problem you're solving and what you know now. Do you know the upstream HGL or flow? Are you trying to size the orifices? With multiple outlets, are you trying to determine how many or how big?

The problem with using an emitter coefficient is that there isn't much literature on how to determine the emitter coefficient.

My suggestion is to model each outlet as a short pipe with the diameter equal to that of the orifice and a minor loss equal to the 90 degree bend the water must take. Place a reservoir at the downstream end of each small pipe with the HGL equal to the elevation of the receiving water surface. This will enable you to experiment with different sizes and spacing of outlets.

If you want to get an even distribution of flow, the outlets should be small relative to the diameter of the pipeline.

Is the source going to be gravity flow from a tank or pumped?

If it is pumped, you trade off pump size vs. size of pipeline and size and number of orifices.

If it's gravity flow, you can

a. Set the desired flow and see if the HGL is adequate. If not, increase/decrease size and number of outlets.

b. Set the desired HGL and see if the flow is adequate. If not, increase/decrease size and number of outlets.

• There have been a few other discussions on this topic in the past, which are accumulated in this article: Modeling a wastewater effluent diffuser

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows