3 replies to this topic

[Leonie]

Hi everyone, thank you for taking time to read this message. I am trying to look for a flow meter with +/- 0.5% accuracy for the following application:

- Process fluid: methanol
- Flow: continous at 0.011 - 0.064 m3/h
- Pressure: op 1042 kPag max 1379 kPag
- Temp: 10 deg C
- Line size: 1/2" tubing

Vendor suggested a Coriolis meter. I understand Coriolis provide good accuracy at low flow rates but it is also quite expensive. I've narrowed down to couple other flow meter options: 

- Flow nozzle
- Segmental wedge
- Rotary piston (+ve displacement)

Does anyone have experience in using these flowmeters for similar application? If so, what range of accuracy, pressure drop, calibrated range and flow velocities am I looking at? Feel free to suggest other flow meter types. Thanks! 

[shan]

Usually, metering pumps with suction calibration tubes or Skoflo valves are used to control the flow rates for the chemical injection services without any flow meter installation.

[JMW]

Some form of peristaltic pump perhaps. That might be within budget if you can find one with the necessary control.

Otherwise there are ultrasonic meters for pharmaceutical applications..... which handle low flows such as that by Flow Technology Inc. though looking at the specs it doesn't seem to give the needed accuracy... http://www.ftimeters...ters/slf100.htm

 

PD meters is a possibility but methanol is non-lubricating. Rotary piston is only semi-positive displacement and for low flows you may need to think about a true PD meter. Perhaps oval gear or for really low flows the reciprocating piston meters from Max http://www.maxmachin...w-meter....... or the external (two meshing gears) gear meter .....https://www.youtube.com/watch?v=pplr5hSQ-34

 

..........no idea of the prices for any of them I'm afraid but these handle low flows with good accuracy.

[Leonie]

Thank you Shan and JMW for your inputs. 

 

I am afraid using a pump with better control is not an option. The pump has already been purchased separately. 

 

If the measurement accuracy can be loosen up to +/- 2%, would differential pressure flow meters be able to satisfy my needs? Based on my calculations, Reynolds number over the operating range goes between 2300 - 7950. From what I read on the internet, a lot of the DP flowmeters don't seem to give good confidence in measurement accuracy at low Re range. Is that true? What about a positive displacement meter, does it work well for low Re range?

 

A few other questions:

 

If flow rate is low, does it imply using meters with large pressure drop would induce large error in flow measurement? 

 

Is there a pipe size requirement for different type of flow meters? For example, I doubt a flow nozzle/ vortex can be fitted into a 1/2" tubing but I can't find relevant pipe size limit online.

 

Apologies for raising so many questions. I am pretty new to this, I don't seem to find good explanation on the internet but I really want to understand better. I think the best way is to seek for help here!

 

Cheers.

 

Leonie