Is supercritical flow acceptable in open channel flows? My question is focused on water and wastewater treatment plants. What problem could supercritical flow possibly give?
What would be the factors to be considered?
Velocity? Material of conduit? Length of conduit?
What if the velocity is below the erosion velocity?
The only thing I see is excessive head loss because of the increased slope. But what if the slope and channel dimensions area fixed?
In what part of the wastewater treatment plant do you see a supercritical flow regime? Specify.
The supply canal is dimensioned under the assumption of a subcritical flow. The Froude number is less than 1. In all other parts of the station, the same thing : bar screens, grit chamber, comminutors, pre-aeration tank, primary settling tank, aeration tank, secondary settling tank, biological filters, sludge handler etc. In all these parts, it is necessary that there be no turbulence. Otherwise, it will not work for the removal of suspended solids.
A supercritical flow regime is never considered.
Regards
water temperature may have an effect on viscosity and hence the flow velocity?
In free surface flows, it is the Froude number which determines the subcritical, supercritical or critical state of the flow regime. It is independent of the viscosity in contrast to the Reynolds number which governs the flow under pressure. In the latter case, the kinematic viscosity has a great influence on the laminar or turbulent flow character of the flow.
Regards
@Devansh Sharma Supercritical flows are acceptable in open channels for certain treatment units in water treatment plants. Supercritical flow through cascades could result to the occurrence of hydraulic jumps, thereby enhancing air entrainment. The air entrainment would enable increase in dissolved oxygen, removal of fowl odour etc. There are other instances where the occurrence of hydraulic jumps enhance the mixing of chemicals required for the treatment of water in water treatment plants.
On the other hand, if quiescent conditions are required, then supercritical flow would constitute a nuisance in such scenarios. A typical example is during sedimentation especially when quiescent conditions are desired.
Thanks all for pitching in.
Bachir Achour, N. M. Ogarekpe , sure we always try to design it for subcritical flows, even for Fr
Its apt @Devansh Sharma, has collated a summation and following guidelines on Fr values, flow gradient and parameters on velocity and voumes Etc.
Most process at influent stage have an equalising chamber to cushion shock loading and no trapped volumes are present.
Wishing well to evolve a safe - design.
Since supercritical flow is a flow that occurs above the ambient temperature and pressure, the effect on this kind of flow depending on the constriction that is involved will affect the ambient states of the water to be treated.
Nyakno jimmy George I think you confused supercritical flow regime with supercritical states. I am simply taking about supercritical flow related to Froude's number.
Devansh Sharma what is paramount here is the flow velocity that is larger than the wave velocity and the flow whose depth of the channel is less than critical depth. When the above accurs the velocity of flow is bigger than critical velocity and gradient of the channel is also higher than the critical gradient. With these conditions, the ambient parameters such as temperature/viscosity and pressure will be changed and this also affects the water to be treated. What characterises the various flow regimes in an open channel flow is the Froude's number, which gives the idea of what happens when the propagating speed of water is less than the speed of the flowing water (supercritical flow). This actually changes the temperature/viscosity and pressure of the treated water.
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