Hi all!
I need to detect the water flow in an enclosed pipe, ie, should now cut open the pipe. I wanted to place a sensor above the pipe and check the water flow. No need to measure anything like flow rate. The task is to detect only the flow. I wanted to know different approaches to this. Please help me!

 

... making an assumption or two, here is one possibility:
https://en.m.wikipedia.org/wiki/Rotameter

... available as :
https://www.instrumart.com/products/10153/king-instrument-7520-7530-series-rotameter

... did your post intend to read 'not' cut open the pipe?

 

... If in fact you are not willing or able to cut open the pipe, then one option is the device here:
https://www.bergeng.com/product/PT9...LbV7AW6bav_rZqot92sRyjZMdep8Z4-waAuY6EALw_wcB

... at a somewhat higher price category.

 

But I need to do it as a project with low cost, is there any ways to detect the flow in a pipe?
I don't want to measure the flow rate or usage, just simply to detect the flow.
for example: by attaching the thermistor to the pipe with Arduino and calculate the temperature change and detect the flow.

 

... If the anticipated flow rate is great enough, and the pipe material has some degree of elasticity, such as plastic PVC, there is a resistance based sensor called a strain gauge, which produces a signal that changes with the minute expansion and contraction of the outside of the pipe, as the pressure inside the pipe varies, according to whether the fluid inside is flowing or static. The strain gauge is applied with adhesive to the external surface of the pipe. An amplifier is used to magnify the sensor output to a readable level. ... not up to date on the costs involved, but may be feasible.

 

... another plan
Obtain a laser pointer and a magnifier Lens of some type or other. See if you can focus the laser pointer into a small dot or point. Next, find a small mirror, and use super glue or something similar to fasten the mirror to the pipe exterior ... it might need to be cleaned or prepped in some manner. Then aim the focused laser pointer beam at the mirror surface so that the beam hits the mirror at an angle and is reflected. Get a white piece of paper and prop it so that the reflected pointer beam intersects it. Use a marker to locate the reflected pointer beam on the paper. Try to determine if the reflected pointer beam dot on the paper changes as the fluid in the pipe is moving or static.
... Some experimentation will be necessary ... not absolutely sure that the pipe dilation will be sufficient to produce the desired result. However, if this scheme does work, it may be possible to replace the paper target with a low cost photo-diode and connect to an arduino.

 

hi,
What is the pipe diameter and material/thickness.?
How is the pipe enclosed and what is the minimum flow that you need to detect.?
E

 

Is this a school/college project?

 

hi,
What is the pipe diameter and material/thickness.?
How is the pipe enclosed and what is the minimum flow that you need to detect.?
E

pipe diameter can be anything also with the thickness

 

Is this a school/college project?

it is a college project

 

hi 11,
Is this a a college assignment.?
E

 

pipe diameter can be anything also with the thickness

You are setting up something that will prove to be basically impossible since now you have to have a system that can detect flow in anything from a 1/4" vinyl tube to the Alaskan Pipeline.

Techniques that will work in one situation will not work in another. You need to significantly narrow your specifications. Ask WHY you need to detect flow (and also what is the minimum flow that you need to be able to detect) as a starting point.

Probably the most reliable method for many situations would be to detect the vibration of the pipe when fluid is flowing.

If the material and fluid is suitable, an ultrasonic sensor could be used to look for Doppler signals.

Temperature is a possibility if the fluid is at a significantly different temperature when flowing than when not (such as in the hot water lines in a house), but there can be a considerable time-delay and you have to be able to set a reliable threshold temperature.

 

But I need to do it as a project with low cost, is there any ways to detect the flow in a pipe?
I don't want to measure the flow rate or usage, just simply to detect the flow.
for example: by attaching the thermistor to the pipe with Arduino and calculate the temperature change and detect the flow.

Great project, I hope you have a lot of fun with the build. While this is not a typical homework problem, the project does sound like an assignment and nobody will want to do it for you and you are not asking for that. Also, if this is due Friday and you have not done anything, I imagine we will not hear from you.

You have already been given some advice and I agree with that, especially your lack of specifying the problem and what you hope to accomplish – that is more than a detail.

That being said, I have a couple of suggestions. First, I would suggest that you go to Digikey and search on flow detectors and sort them by price, low to high https://www.digikey.com/products/en...low+sensors&pageSize=25&pkeyword=flow+sensors. Then start browsing the data sheets to get a handle on how they work. This will take you less than 30 minutes since you just need to get an idea of the methodology (usually appears in the first pph) and not necessarily direct suitability for your project.

Second, I would advise you to set up your testing platform (that will be part of your project) without delay.

Now consider your idea of an Arduino and a thermistor taped to the outside of the pipe. Do you see any flow meters that work on a thermal principle? How about those thermal mass transfer sensors? Look further and you will find, not a flow detector, but a non-intrusive method to detect the temperature of a liquid inside the pipe. Check out this presentation https://www.digikey.com/en/ptm/a/am...ine-flow-through-temperature-sensors/tutorial While you wondered about attaching a thermistor to the pipe and they have a customized, but still non-intrusive method, it looks like the same technique. So, I wondered about this as well and tried a little 3 minute experiment using one of these that I have handy https://www.banggood.com/BENETECH-G...s=detail-left-hotproducts__4&cur_warehouse=CN I simply pointed at the base of the disposal mounted under my kitchen sink. First, I took a reading with the faucet off. Then I turned on the cold water and took a reading. Then I turned on the hot water and took a reading. This gave me some encouraging results for your project, but it certainly revealed some limitations – what if the water temperature was the same or close to the ambient temperature?

Putting that method aside for the moment, what other methods are seen in the product list? How about ultrasonic? Yeah, they have those, like this one http://www.audiowell-international.com/flow-sensors.html In fact, this product looks pretty darn good except for that pesky $1700 price tag https://shopclamponflow.com/product...MIupvS6-zg3wIVSwOGCh25cw36EAYYASABEgIyUPD_BwE

But could you do something more limited with ultrasonics in your project? Look around at what others have tried – like this teaser

measuring air flow with a those cheap ultrasonic distance devices. What effect would water have on the transmission of the ultrasonic wave? Could that be useful?

Time is wasting and I am counting on folks like you to keep social security viable, so please get busy.

 

I think the commercial go-to these days is ultrasonic. You would have learned this in a 2-minute google search.

An alternative method is thermal.
https://en.wikipedia.org/wiki/Thermal_mass_flow_meter

I haven't studied either in detail but it's my hunch that you could execute the thermal approach much cheaper than the ultrasonic approach, especially since you don't need accuracy.

 

How about sticking a microphone on to the pipe and detect the sound?

 

I think the commercial go-to these days is ultrasonic. You would have learned this in a 2-minute google search.

An alternative method is thermal.
https://en.wikipedia.org/wiki/Thermal_mass_flow_meter

I haven't studied either in detail but it's my hunch that you could execute the thermal approach much cheaper than the ultrasonic approach, especially since you don't need accuracy.

After skimming that wiki, I'd also recommend the thermal method as a first candidate. But you still need to drastically narrow your application specs down first.

 

I second (or third) that thermal technique.

Edit: on second thoughts, this is a great idea. I would use multiple sensors on both sides of the heater. I bet you can measure the flow rate with proper calibration.

This is an excellent college project.