I am troubleshooting a water treatment skid.
This forum was very useful for confirming the Froude number design guide and source. Thank you very much for previous contributions.
Briefly, the skid discharges 15-30m3/h water into a 100mm pipe at 8m elevation. There is no vent in the line. The discharge pipe runs down 4m, across 15m, down 3m, across 2.5m, back up 1m, then across, down etc. (there are about 20 elbows) into an underground tank sump (open to atm). Discharge in the tank is a dip pipe 2.5m below grade, submerged and no holes are drilled into dip pipe. Total pipe length approx. 60m.
The U in the pipe (about 1 meter) is for analysers which have to maintain wet.
Yes, the discharge point (inlet of pipe), runs at vacuum (no surprise).
Client needs to acquire a water sample and cannot.
I have two questions below:
Hill paper suggests Froude number has to be less than 0.3. Chart suggests an 8 inch pipe for free flow.
I have a 170mm ope in the floor. A 6 inch sched 10 has OD 168mm, ID 162mm yielding Fr 0.32-odd. There is equipment below, adjacent pipes in the floor ope and it is preferable not to have to re-core the floor.
Q1 - how strict is the Froude criterion - will exceeding it by a small margin (even if only for the 0.3meters thickness of the slab + 100mm above and below) make a large difference?
My thought is to replace only the pipe section before the analysers with a larger pipe.
The Hill paper and advice on this forum in previous threads suggest that such a tortuous path can be problematic to achieve free draining.
Q2 - Will the below pipe route option 1 work or should I use the alternate route option 2?
Route option 1 - horizontal discharge (pipe) drops vertically 2.5m through an ope in first floor, runs horizontal, changes direction 3 times (one 90, two 45 elbows), drops vertically 0.5m, runs horiz again changing direction 3 times (90 deg elbows) and then drops down vertically 3m to the analysers.
The pipe is PVC - I am not sure if standard elbow bend radius r/D is adequate (Hill suggested 5). I can make the 90 degree elbows 2 x 45 degree to control bend. I can also slope the horizontal sections (but that will require extra turns).
My route option 2 is to run across at the high level immediately after discharging from the skid before dropping down 'close to' the analysers. Admittedly, this second option also makes the first question moot as a new ope in the floor can be made for 8 inch (it's just money). All the same, I'd be interested in the answer to Q 1.
I have no other route options due to clashes, access ways etc. I need the cheapest workable solution, not the best solution. Option 1 is cheaper.
Cheers