One needs the heat capacitance of the fluid

power/flow/(specific heat) in SI units gives the temperature difference.

There is still an art in making a good set-up: the designer needs electronic skills and thermal at the same time. One should get between 1 and 20°C, if needed, one can adapt the power. NTC resistors change 4.5%/K, Take care that NTC sensors feel 50% of their temperature by their wires. Heat paste to the pipe, insulation around. On has to think thermally. No power should give the same temperature, no flow also. That is why the pipe needs to be horizontal. I used the principle first with air, afterwards for cyclopentane. Calorimeters with air are described in "inductors and transformers for power electronics". I did never publish the  fluid one. If you want a paper could be published together (if the principle is what you need...)

Alex

Adel,

I cannot think of many.

A piezoelectric vane might deflect in a flow field - generating a voltage.

A flexible paddle might deflect and in doing so permit an light beam to progress towards a sensor (intensity: as in power per square area?)

Most such schemes will rely on an assumed density of the fluid.

Do you happen to have more details about the work (flow speed, fluid type, working temperature, steady flow versus pulsed flow, etc.)?

Dear James, 

Yes thanks.

I 'am agree with you. The questions posed actually include several parts: the voltage interval in volt, the correlation that connects the voltage to the measured physical variable.

greetings

At low flow I did make calorimetric ones:  By preference a horizontal pipe, measure temperature left and right, with NTC resistances, heat with a given power in the middle, insulate well thermally. In set-ups it can work well.

Dear Alex,

Thank you for the informations. Do you have the correlation which gives the temperature as a function of resistance.

Regards

One needs the heat capacitance of the fluid

power/flow/(specific heat) in SI units gives the temperature difference.

There is still an art in making a good set-up: the designer needs electronic skills and thermal at the same time. One should get between 1 and 20°C, if needed, one can adapt the power. NTC resistors change 4.5%/K, Take care that NTC sensors feel 50% of their temperature by their wires. Heat paste to the pipe, insulation around. On has to think thermally. No power should give the same temperature, no flow also. That is why the pipe needs to be horizontal. I used the principle first with air, afterwards for cyclopentane. Calorimeters with air are described in "inductors and transformers for power electronics". I did never publish the  fluid one. If you want a paper could be published together (if the principle is what you need...)

Alex

Adel,

If sensors that do not directly generate a voltage or an 'intensity' are appropriate for you then I heartily recommend the hot-wire anenometer approach advocated by Alex.

There are a number of firms that manufacture such devices, and circuit diagrams for the ingenious inventor are readily available on the web.

I have used these sensors from IST for airflow measurement with success:

https://www.ist-ag.com/sites/default/files/DFMFS02_DFMFS02_on_PCB_E.pdf

Hello James, it was not a hot wire!

Hot wire measures the local speed, where usually you need the average speed for flow. Using a hot wire is a good check if there is flow or not, but could be influenced by dirt, turbulence and so on.

Alex,

Ah, I was thrown by this line, 

" heat with a given power in the middle,"

...that sounded a lot like adding heat to the centre of the flow.

I understand my confusion - yours is an interesting variant - and although the heat capacity of the pipe would dampen the responsivity, for constant flows this is an interesting variant.

Well worth investigating from an Intellectual Property perspective! Mind, a calibration run is needed to 'null' the conduction path along the pipe wall.

Things can be calculated, but calorimetric things are not  IP any more, but there is still an art to do it: how to inject power, how to fix NTC's. in one or  two minutes it stabilises. Parasitic thermal resistance between left and right. But a thin stainless steel pipe does not conduct so much.

Air flow calorimeters need rather 10-30 minutes time constant. I used them for lamp converters, 50Hz in 4 wires out for CFL.

Hello all.

Though not my area of expertise, from books I woud say that a coriolis effect flowmeter could do the trick, the output of commercial ones normally give an industrial standard output (4-20 mA for example).

Attached is a link to a video from Siemens, it's in Spanish but the idea is clear.

Best wishes.

https://www.youtube.com/watch?v=T89G4Ht09Jw

Dear colleague, 

Ok, thank you. It"s a good answer.

best regards