Air velocity sensor for air with particles

Join Date
Dec 2010
Location
Somewhere, Ohio
Posts
53
I am looking for an air velocity sensor that, along with measuring air velocity, can withstand being impacted by flour, corn meal, etc at 5000 fpm. There are plenty of thermal-based sensors out there that are designed for clean air, but I am looking for something that can survive and not clog in dirty air. Extreme precision is not needed for this application.
 
Imagine 5000 fpm of cornmeal! Now that is really "slinging the hash"!

With that impact problem, you may have to use some type of indirect measurement. Could you use a pressure gage to compute velocity from the air pressure?
 
Still, that Sensocon device has the RTD surrounded by a horseshoe-shaped heating element. I would guess that high-speed particles would eventually clog the gap and cause errors.

Have you looked at magnetic sensors and magnetic meters (magmeters)? Their sensor elements are non-clogging, and go up to at least a 12" pipe diameter. However, you would have to find out if they are capable of measuring air velocity in the cornmeal airstream. Magmeters are normally used for conductive liquids, so may not be suitable. However they are also used for slurries and sludges. Whether a magmeter would measure airflow will depend on the conductivity of the airstream.

Is this device permanently mounted, or hand-held? If not permanent, then you could simply wipe it off when it gets clogged. If permanent, and under PLC control, you might build some type of cleaning device to periodically blow, wash, or wipe off the cornmeal. If this is a large duct, you could mount a funnel drain right under a thermal-type flow sensor, and a spray nozzle above it, and periodically hit it with a short blast of water to clear the clogs.
 
Last edited:
some ways are:
like an airplane with a pitottube Put a small valve in the line to clean the hose.
with a differential airpressuresensor in bottom and top of line you will see some difference from resistance.
Use a valve as pressuredropper.
same like in liquid is used in heating systems.
it is 50mph not too much.
and you can measure how much air is going in and out after the filter so it will not clog at all.
 
I've used an Endress and Hauser which worked in a similar way to the sensor you found. I am not at work so can't give you the model number but the fan duct it was on was 18,000 m3/hr on a 160kw drive!!
 
One question about using a heated RTD type would be is there any danger of triggering an explosion in flour-laden air? I know that flour-in-air mixture is very explosive.
 
Do it the old school way.
Use a venturi and a DP transmitter. You have to do the calculation (or get someone to do that for you). Have your tapping points on upper side of the venturi and mount your DP transmitter higher still then any solid or liquid contaminants will not be a problem.
 
Thanks for all the help. Markie, I cannot find any such partnumber on E & H's website. RDS, FCI's flowmeters can beused in a commbustible gas environment, but I don't know if they would hold up to being bombarded by basic food ingredients at 5000 fpm. Markie, installing a venturi is out of the question for this project.

This is one of those projects where someone decided to save money and use various elements from different manufacturers rather than using a tried and true solution. I have doubts about the design of the system, but it is my job to make it work.

The part of the system I'm talking about involves combustible dust going into a filter followed by the exhaust blower, which is followed by the exhaust blower ventilation piping. Rather than measure the intake velocity, I am contemplating measuring the exhaust velocity. This puts the flowmeter in a much less harsh environment - one where insertion type thermal flow sensors are going to have a better environment. Furthermore, I do get a 4-20ma signal from the baghouse controller that let's me know the pressure drop across the filters. Perhaps the baghouse manufacturer might be able to give me some data on flow vs the pressure drop across the filter.

Again, thanks for all the input and more help is always welcome.
 
Let me clarify my previous post. I will essentially be using the pressure drop across the filters as a poor man's venturi or orifice plate. I'm thinking flow should be proportional to the square root of the pressure drop.

The "fun" part of this project is that I will not be regulating motor speed to regulate air velocity, but rather control several valves on the intakeside of the system.
 
I'm thinking flow should be proportional to the square root of the pressure drop.
System velocity should be proportional to exhaust velocity (which you can measure) X some factor proportional to differential pressure across filter.
 

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