Experimental observation

shreesha87 · January 30, 2014, 15:58

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

m.vegad · January 31, 2014, 03:09

Dose the system have nozzle?

shreesha87 · January 31, 2014, 10:57

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.

lovecraft22 · February 1, 2014, 04:05

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.

shreesha87 · February 3, 2014, 02:01

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?

lovecraft22 · February 3, 2014, 02:40

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.

shreesha87 · February 3, 2014, 18:38

But what is the physical reason for the graph to become steeper at higher pressures? I am still not clear.

January 30, 2014, 15:58	Experimental observation	#1
shreesha87 New Member Join Date: Oct 2013 Posts: 13 Rep Power: 12	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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January 31, 2014, 03:09		#2
m.vegad New Member Mitesh Vegad Join Date: Apr 2013 Posts: 18 Rep Power: 13	Dose the system have nozzle?

February 1, 2014, 04:05		#4
lovecraft22 Senior Member lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18	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.

February 3, 2014, 02:01		#5
shreesha87 New Member Join Date: Oct 2013 Posts: 13 Rep Power: 12	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?

February 3, 2014, 02:40		#6
lovecraft22 Senior Member lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18	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.

February 3, 2014, 18:38		#7
shreesha87 New Member Join Date: Oct 2013 Posts: 13 Rep Power: 12	But what is the physical reason for the graph to become steeper at higher pressures? I am still not clear.