flow rate measurement

[ren_]

I have 110mm pipe that is receiving outlet wastewater from a treatment system. the flow is continuous but can be zero at times but mostly continuous, It varies constantly diurnal mainly and is very low. I am looking for an alternative way to measure the flow rate of water from the pipe without the use of a flow metre.

 

[EmmanuelTop]

Measure the flow without flow measurement? That is an interesting concept.

Is there a way to measure any other variable that is dependent on flow - e.g. the time required to fill/empty certain volume etc.?



Dejan IVANOVIC
Process Engineer, MSChE

 

[ren_]

Yes I was looking for a device maybe that can give me volume per specific time. is the use of the following feasible for a low flow rate pitot tube, vortex meter, pygmy meter, flume?

 

[EmmanuelTop]

But these are flow meters (pitot, vortex etc.). Pitot has low rangeability, vortex may be a good choice.

Dejan IVANOVIC
Process Engineer, MSChE

 

[ren_]

Oooo did not know, thank you how about venture flume is it applicable to low flow rates? I had also thought of using a positive displacement pump to measure volume per time

 

[EmmanuelTop]

Flumes are used for open channel (surface) flow, if I remember well. If that fits the description of your application, you might as well use V-notch or weir, which has 100:1 turndown.

Dejan IVANOVIC
Process Engineer, MSChE

 

[ren_]

No it does not fit well. I'm measuring flow rate from an waste treatment outlet

 

[bimr]

For low flow metering, the Trapezoidal Flume is the best option. The throat of a Parshall flume will be too small.

http://www.plasti-fab.com/portfolio-items/trapezoidal-flumes/

 

[SandCounter]

Use ballistics to calculate velocity from the length and slope of the outlet stream. Multiply the velocity by the outlet pipe internal area for flow.

 

[LittleInch]

ren,

The permutations and ideal systems are endless, but give us a bit more data here please:

What is your max / normal flowrate / velocity?
Is the pipe always full or sometimes / mostly partially full? - makes a huge difference in what works or doesn't work
Pressure?
lengt of pipe
Is pipe flat or sloping down?
Room to fit any device?

simple way is just a three way valve into a known volume and time how long it takes to fill said known volume or time it and then measure contents - then revert back to normal flow and drain volume back into the line.

Or just put a bucket under the end?

You tell us how sophisticated you want this be.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pennpiper]

ren,
You might want to look into an external "Ultrasonic Flow meter".

https://www.google.com/#q=external+flow+meter

Sometimes its possible to do all the right things and still get bad results

 

[ren_]

Thank you all for responses

The pipe is never full maybe a quarter way full, it is on a flat surface, a bucket cannot be used since the depth between the pipe and water surface is low as shown in the diagram. the flow rate is approximately 0.47m3/hour, worse case 0m/hour, minimum 0.06m3/hour highest 1.03m3/hour.

 

[ren_]

Penpipper, A flow meter was used before and it did not work well, so I'm tring to run away from a flow meter

 

[ren_]

bimr, would trapezium flumes fit with the pipe diameter i have and where exactly would i insert them?

sandcounter,i know ballistics for a projectile are they any for flow in a pipe? and since the height in the pipe is always varying would they work?

 

[LittleInch]

In your chamber you probably need to create a weir and be able to measure depth of water over the weir.

Do a search on this site on "open channel flow measurement" and things like this crop up -

http://www.eng-tips.com/viewthread.cfm?qid=400406

Try looking up V notch flow meters.

Look like they could be the right sort of thing, but again you will need a fairly accurate height measurement.

Something like this maybe?

http://soil.co.uk/products/water-monitors-piezometers-meters/v-notch-weir-monitor/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ren_]

LittleInch, thank you let me look into that

 

[hydtools]

Ren, if this is for you float siphon, you know the volume of discharge water when it reaches draw down height. Measure the discharge time to deliver that volume of water. The result will be average flow rate.

The manufacturer publishes flow rates for various configurations.

Ted

 

[ren_]

hydtool, as it is I have the average flow coming in as 2.1m3/hour but it is the outflow rate I am concerned about. Please note picture attached

 

[bimr]

ren_

The Trapezoidal Flume would not fit in a pipe, but would replace a pipe segment. It is similar to the parshall flume but more compact.

http://openchannelflow.com/blog/trapezoidal-flumes-for-industrial-pretreatment-discharges

The Trapezoidal Flume works well with lower flows, has little head loss, and is compact.

http://openchannelflow.com/blog/trapezoidal-flumes-for-industrial-pretreatment-discharges

 

[LittleInch]

Really cheap and cheerful - Drop a couple of weighted buckets into your chamber. Lift water out until you get just below the outlet pipe. Then lift even more out quickly - measure the water you've now removed and then time how long it takes from when you start for the water to start flowing back down the outlet pipe again... Simples

For something online you would need some instruments like we-ve all just been discussing. You could build a small weir / V notch meter in that pit.

Bimr - that's a nice looking piece of kit. I'll have to remember that one.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.