Air speed and Differential pressure

[Chestermiller]

Good Afternoon,

I'm a little bit disappointed by my calculation, sure I made a mistake, but where?
By experimentation k is not constant ; from 0,16 @ 0,52 m/s to 0,07 @ 6,88 m/s and with calculation k is 1,3e5... something is wrong.
Please see my (bad) calculation in this upload file :

Please show some data on Δp vs v. Please give the units of Δp. Also please make a graph of Δp vs v. What does it look like?

(Giving values of the parameters without their units is useless.)

Chet

 

[MARECHAL]

Chet,

Thank's for your reply, sincerely.
Yes sorry, Δp is in Pa, I found a mistake in my data since I wrote my reply, the value of L is 13 mm ; I must reviewing all calculation, it is not the only one error : the results I gave are not k but 1/k .
Since I am on PF, I do any mistake, I'm not very proud of that in comparison to all posts of all engineer there are here...
in "up load" an excel file of the experiment results hoping it could help you and me :

 

[Chestermiller]

Chet,

Thank's for your reply, sincerely.
Yes sorry, Δp is in Pa, I found a mistake in my data since I wrote my reply, the value of L is 13 mm ; I must reviewing all calculation, it is not the only one error : the results I gave are not k but 1/k .
Since I am on PF, I do any mistake, I'm not very proud of that in comparison to all posts of all engineer there are here...
in "up load" an excel file of the experiment results hoping it could help you and me :

Your graph seems to have a sharp break at the 6th point. When I plot the data, it doesn't show that sharp break.

Later, I'm going to try to calculate the permeability from your data to see how it matches up with the theoretical result. After I do some calculations, I'll get back to you about the curvature of the plot.

Chet

 

[Chestermiller]

I calculated the permeability of the combined two honeycombs from your data, and it came out to 0.004 - 0.0097 cm^2. The theoretical value I calculated from the equation I presented in post #24 was 0.0045 cm^2. So the data are in the same ballpark as the theoretical value. However, it isn't clear why the permeability seems to be decreasing with increasing flow rate. I checked, and I don't think that the flow in the honeycomb is turbulent.

Chet

 

[MARECHAL]

However, it isn't clear why the permeability seems to be decreasing with increasing flow rate. I checked, and I don't think that the flow in the honeycomb is turbulent.

Probably due to the placement of the two points of measurement of pressure, I put them inside the tube but at the periphery of the internal section, so I take measure of pressure at the points where the speed is low instead of at the center of the tube where the speed is more important.
With the anemometer I measure air velocity at each point of the internal section of the tube, a kind of integral of air speed.
Even if the honeycomb played their part in the laminar function of the speed, I'm not sure it is the same for pressure upstream or downstream of the honeycomb, and I have not enough knowledge base in this kind of physique. It is only presumption of what I observe with instrument.

I calculated the permeability of the combined two honeycombs from your data, and it came out to 0.004 - 0.0097 cm^2. The theoretical value I calculated from the equation I presented in post #24 was 0.0045 cm^2. So the data are in the same ballpark as the theoretical value

I really don't understand how you calculate to obtain these results, but it is not the matter, what is important is the results, and your analysis and what I found by experimentation is coherent with you found.