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Old   January 30, 2014, 16:58
Default Experimental observation
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Hi All

I have a question regarding general fluid mechanics. I did an experiment with a off-the-shelf air amplifier which takes certain amount of compressed
air and then entrains air from the surroundings and multiplies the flow rate. I connected it to a compressed air supply.

I hooked up a pressure guage and flow meter to the tube on the way to the air amplifier to measure the inlet pressure and flow rate conditions. What I recorded was
that initially as I increased the pressure, the flow rate was also increasing. Then, as the pressure went past 50 PSI, the increase in the flow rate was minimal.

Can anyone tell me why this was happening?

Shree
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Old   January 31, 2014, 04:09
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Dose the system have nozzle?
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Old   January 31, 2014, 11:57
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The system (air amplifier) has a threaded opening through which air enters and then leaves through an orifice. Kindly see the picture attached for your reference.
Attached Images
File Type: png Air_Amplifier.PNG (47.3 KB, 12 views)
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Old   February 1, 2014, 05:05
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If you look here, you can see that the performance curve of the air amplifier at some point becomes steeper, meaning with an increase in pressure you get a smaller increase in massflow.

http://www.eputec.de/en-exair-airamp...-amplifier.php

I would say that the reason for that is that the relationship of your pressure drop (deltaP) in the orifice and the massflow (q) going through it is:

q=sqrt(deltaP/A) where A is a constant. This curve has the same shape of the picture in the link above. So, at some point, by increasing your reservoir pressure, you get a smaller increase of the massflow going through your orifice with a smaller massflow going through your air mover.

All of this in theory, in a real case you also have blockage effects and separations which play an important role.
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Old   February 3, 2014, 03:01
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Hi Lovecraft22

You equation basically tells me that as deltaP increases, q increases.

Doesn't this contradict what you are saying? You told that as the inlet/supply pressure increases, the pressure drop across the orifice increases and the flow reduces right?
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Old   February 3, 2014, 03:40
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Hi Shreesha,
You are right, my answer wasn't clear, sorry about that.

What I wanted to say is that if you have a look at the plot, at some point, at high pressure values, an increase in pressure doesn't give you the same mass flow increase given by the same pressure rise occurring at lower values of pressure.
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Old   February 3, 2014, 19:38
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But what is the physical reason for the graph to become steeper at higher pressures? I am still not clear.
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