Hi All,
We are dealing with a proposed pipeline on a steep slope (10-20%) and need to allow for air entrainment in the pipe in line with the local authority requirements.
Is there any way to allow for bulking of flow without actually manually changing the volumes in each pipe? possibly a table that allows for bulking factors correlating to the slope of the pipe?
Stormwater - Air Entrainment
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Matthew John Smith
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Stormwater - Air Entrainment
Matthew Smith
Civil Engineer
Cameron Gibson & Wells Ltd
Civil Engineer
Cameron Gibson & Wells Ltd
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Owen Thornton
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We do not currently support air-bulking factors for aerated stormwater flow.
Depending on the particular arrangement you are proposing, you might be able to synthesize it by increasing Ku factors at one or both ends. I suppose it depends on what your local authority means by "allow for air entrainment".
Depending on the particular arrangement you are proposing, you might be able to synthesize it by increasing Ku factors at one or both ends. I suppose it depends on what your local authority means by "allow for air entrainment".
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Matthew Smith
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- Joined: Mon Jul 09, 2012 1:42 pm
Sorry Owen, back again as im doing another Air Entrainment calc for a design pipeline.
I Suppose its more of an issue here due to steep natural contours in residential areas, which i assume is not an issue in Australia.
Slopes of up to 1 in 5 are very common for pipelines here (Nelson, NZ)in residential areas on hill sides.
The local authority requires Air Entrainment calculations on all pipes over 10% and can result in a significant decrease in pipe capacity.
We have previously manually calculated the bulking factor using the Hydraulics output file to excell and then added and removed the flow in each section of pipe.
So for a section of 675 pipe, the flow might be 1000l/s and capacity is 1200 l/s. Air entrainment calculations give a bulking factor of 0.35 resulting in a bulked flow of 1350 "l/s", and hence the pipe is now under capacity.
The problem is that this process is quite time consuming, as increasing the pipe changes the bulking factor (changed V and HRad) and the calcs have to be re run again.
Is there any future plans to support air-bulking (or my other bugbear is Benching in Pits reducing K factors)?
Thanks again.
I Suppose its more of an issue here due to steep natural contours in residential areas, which i assume is not an issue in Australia.
Slopes of up to 1 in 5 are very common for pipelines here (Nelson, NZ)in residential areas on hill sides.
The local authority requires Air Entrainment calculations on all pipes over 10% and can result in a significant decrease in pipe capacity.
We have previously manually calculated the bulking factor using the Hydraulics output file to excell and then added and removed the flow in each section of pipe.
So for a section of 675 pipe, the flow might be 1000l/s and capacity is 1200 l/s. Air entrainment calculations give a bulking factor of 0.35 resulting in a bulked flow of 1350 "l/s", and hence the pipe is now under capacity.
The problem is that this process is quite time consuming, as increasing the pipe changes the bulking factor (changed V and HRad) and the calcs have to be re run again.
Is there any future plans to support air-bulking (or my other bugbear is Benching in Pits reducing K factors)?
Thanks again.
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Owen Thornton
- Posts: 5711
- Joined: Tue Oct 04, 2005 12:50 pm
- Location: Brisbane
- Contact:
What are the empirical methods you currently use to achieve these two requirements? If you can detail the methods, we can begin to look.
I admit that I have no clear understanding of how air entrainment could increase the design flow rate. I would have thought that it either reduces the flow rate or increases the water levels (depending on the hydraulic model). It might also reduce the Mannings capacity. But how the flow rate compares with the Mannings capacity is not typically used as a criterion for sizing the pipes. Perhaps I am not understanding your design method.
The difficulty with reducing Ku/Kw factors for benched pits, is that the method we currently use to calculate Ku/Kw factors does not consider them and critically, the method depends on the water level in the pit (S/Do ratio). Yes, we could apply some blanket reduction after the fact, but it would be entirely ad hoc and not in keeping with the existing method. Of course, we allow you to set Ku/Kw factors manually, where required.
Feel free to email me directly about this stuff, using the button within this post.
I admit that I have no clear understanding of how air entrainment could increase the design flow rate. I would have thought that it either reduces the flow rate or increases the water levels (depending on the hydraulic model). It might also reduce the Mannings capacity. But how the flow rate compares with the Mannings capacity is not typically used as a criterion for sizing the pipes. Perhaps I am not understanding your design method.
The difficulty with reducing Ku/Kw factors for benched pits, is that the method we currently use to calculate Ku/Kw factors does not consider them and critically, the method depends on the water level in the pit (S/Do ratio). Yes, we could apply some blanket reduction after the fact, but it would be entirely ad hoc and not in keeping with the existing method. Of course, we allow you to set Ku/Kw factors manually, where required.
Feel free to email me directly about this stuff, using the button within this post.