measure low flow rate under low pressure 1

[simplemath]

Is there an easy and effective way to measure low flow rate fo air(6-10gal/hour) under low pressure (1psi)?

This is calc of orifice size.

Thanks

It boils down to simple math.

 

[BigInch]

Make the orifice size small enough to get a pressure drop you can measure with a water column differrential pressure gage.

You might also be able to calibrate a hot wire to air flow. The wire will cool faster in higher flows, so you can measure the current it takes to keep the wire at a given temperature and correlate that to air flow past the wire.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[moltenmetal]

Is the flow into or out of the thing in question?

Do you need a continuous measurement of the flow? How accurate? And does the output need to be electronic, and trended, or is a periodic observation OK? And do you need flowrate rather than (totalized) flow quantity?

If the flow is out of a system and can be collected at a single point, a wet test meter (positive displacement flowmeter) will do the job most accurately, with a stopwatch if you want average flowrate. Want it electronioc? Put an encoder on it.

Or you can do it by simple downward displacement of water.

If the flow is into a system through a single point, what's feasible depends on what you mean by low pressure. Is the system pressure low AND the air supply pressure low?

No need to make your own hotwire anemometer- there are plenty on the market. Better still for low flows, there are thermal mass flowmeters and controllers- if your upstream pressure is high enough for them. See Brooks, Porter, Aalborg, Bronkhorst etc.

 

[BigInch]

Of course no need to DIY, somebody is always ready to sell you something, but very easy to do this, if you want to try.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[BigInch]

Do please be careful with the hotwire natural gas meters though.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[dcasto]

PD meters or rotary work well here.

 

[simplemath]

Thanks for all comments.

Biginch:
The tubing outside is 3/8" and I could just feel a little flow by hand. The flow rate is needed for environmental analysis and do not have to be very accurate.
I thought of the same thing and tried to use a differential pressure gauge to catch the flow rate. But I do not know how to make the orifice.

moltenmetal:

I wish I can find something inline and plug&play. Thanks.




It boils down to simple math.

 

[unclesyd]

The old reliable and inexpensive gas bubble meter for measuring low and lower flows.

http://www.bubble-o-meter.com/

 

[BigInch]

Maybe you otta' buy one then, or try

unclesyd,
great idea.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[sailoday28]

You might want to investigate the following:

http://www.flowmeterdirectory.com/flowmeter_artc/flowmeter_artc_02111201.html