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Join Date: Apr 2017
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Flow Rate and Pressure in Parallel Pipe System

04/07/2017 4:24 PM

Dear All,

I need some help in understanding as to how do i go about fixing a glitch in my project where I am stuck.

Background - I am designing a Water Flow Meter using an Arduino and a water flow sensor who limits are - (60Litres/Min and Pressure <1.7Mpa). The entire project is ready but while testing at the facility I have encountered a problem.

Problem - The water pump which feeds the water into the pipe ( between which my system will be put in) at 300 Litres per Minute. The diameter of the pipe is 1.5Inches.

Advice needed - I was thinking and please correct me or point me in the right direction, that if i create a small thin branch of pipe parallel to the main 300 lites/min pipe and attach my system, maybe the flow rate will decrease to be less than 60 litres per min and then I can extrapolate the total flow basis the reading i get in that thin pipe.

1. Is my understanding correct or totally flawed?

2. If it is correct can you point me or tell me the setup I should put like what should be the diameter of my thin pipe so as to make sure the flow rate and pressure of the arduino sensor are not overloaded.?

Thank you very much.

Cheers RJ

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#1

Re: Flow Rate and Pressure in Parallel Pipe System

04/07/2017 5:01 PM
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#2

Re: Flow Rate and Pressure in Parallel Pipe System

04/07/2017 5:02 PM
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#3

Re: Flow Rate and Pressure in Parallel Pipe System

04/07/2017 5:24 PM

Surely it would be cheaper to get a sensor with a higher max limit?

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#4
In reply to #3

Re: Flow Rate and Pressure in Parallel Pipe System

04/07/2017 7:14 PM

Yeah, plumbers don't come cheap...

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#7
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Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 2:30 PM

Exactly. It sounds as though the design, as it stands, is inadequate.

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#5

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 12:00 PM

Nope, that's a bias data gathering.

Try another scheme of sensing that should not even influence the flow. What type of transducer are you using?

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#6

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 2:23 PM

It's flawed. Pressure drop down pipes is not a linear function of diameter when the Reynolds Number is above 2100 or so, and yours is above that. Plus, although the top rating is stated, no one here knows what the maximum pressure is that your pump is capable of producing.

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#8

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 4:01 PM

Thank u all for the inputs and answers.

1. As per theoretical calculations, the 1.5hp pump will generate around 300+ litres/ min at 75% efficiency.

2. In long term can order a higher limit sensor but at the moment it shows 3-4 weeks to deliver to my region from China and i cant find it locally. The project demo is in 12 days time so cannot take the risk, hence the work around with the split pipe mechanism.

3. Fortunately the plumber is free as my partner's dad owns a real estate company and have plumbers available.

4.@gutmonarch - not using transducers but rather this sensor with higher limit.

http://www.electroschematics.com/12145/working-with-water-flow-sensors-arduino/

I am going to try the setuo advised by you guys and update the findings.

Thanks RJ

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#12
In reply to #8

Re: Flow Rate and Pressure in Parallel Pipe System

04/09/2017 1:57 PM

Oh, thats a positve displacement type flow meter. I just dont know exactly whats your set up. It is a big no to measurements if you make it to represent the whole flow with that parallel pipe configuration. Except if it pass the criterion basing on reliability and precision with some stat tools.

Anything that converts process variables to other communication signal to a processing module is a tranducer.

You better be posting your set up. Picture paints thousand words.

Why not make a semi- flexible bend and attach a strain gauge then analyse signal using Adruino. That's best non-invasive solution.

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#9

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 5:08 PM

For a given pressure drop per length of pipe, the flow capacity of a pipe varies as the 2.5 power of its i.d. (Darcy-Weisbach). Not just simply as the area. To handle this example, one needs to know the pipe schedule(s) involved so that the i.d.'s can be accurately known. In this network:

|
|____YF S201___1/2" pipe____
|.................................................|
|____main line 1-1/2" pipe____|____

the 300 L/m flow would divide something like 20/280 between the two lines. (The dots don't mean anything except to space out the vertical bar at the right.)

With a stopwatch and a barrel, you can get a decent measurement and simply adjust a constant in the program to match the actual result.

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#10
In reply to #9

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 5:37 PM

Thanks Tornado for the reply. This is exactly how I am trying out the test setup. Will update you on the results shortly.

I might have a question of the Darcy Friction Factor and as to how to calculate it accurately. Can you shed some thoughts on that?

Thanks RJ

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#11
In reply to #10

Re: Flow Rate and Pressure in Parallel Pipe System

04/08/2017 6:05 PM

Darcy-Weisbach calcs are usually done in conjunction with a Moody chart. A pipe design text or Wiki articles will do better justice to this than I can do. (Unless I just copy stuff....)

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#13

Re: Flow Rate and Pressure in Parallel Pipe System

04/10/2017 9:03 AM

Why don't you go with an industrial water flow meter that is relatively cheap (Signet, or other brand), and use the 4-20 mA output as analog input over a pull-up resistor as analog voltage in? These sensors (and their associated transmitters) allow programming the K value of the sensor associated with the correct pipe diameter in the first place, and are available down to fairly small pipe diameters, of at least as small as 12 mm. You have also the option of making the local pipe large at the sensor such as 30-50 mm, and programming in the K value for that pipe.

It is not rocket science or every industrial plant (including the ones I work at) would have to hire NASA every time we installed a new flow meter.

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#14

Re: Flow Rate and Pressure in Parallel Pipe System

04/10/2017 11:42 AM

Do you have a method to calibrate the flowmeter, specifically, can you collect the system throughput and measure the flowrate directly. If so, you can set up whatever branch path you prefer with your existing flowmeter in it and set up a calibration curve for total flow vs flowmeter reading and do the math in the arduino to directly output the actual flow. As long as you don't change the system geometry or working fluid, you will get a mathematically adjusted total reading based on the flowmeter output.

I did something similar years ago for an ultrasonic flowmeter, great big tank and weighing scale for the great big tank. We took flowmeter readings while filling and weighing the tank to establish and confirm a calibration curve.

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#15
In reply to #14

Re: Flow Rate and Pressure in Parallel Pipe System

04/10/2017 11:54 AM

I agree that this ad hoc calibration might be best for him in the long run, since he has already most of the equipment for that.

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