Tractorsport Flowbench Forum Archive

Posted: **Mon Dec 20, 2004 10:06 am**

I made an excel file for calculating flow CFM. Now I'd like to compare my theoretical results with somebodys real life results. Could anybody give me his test results (ID of pipe where annubar is, velocity pressure[inH2o] and the calculated CFM)
Is it normal (on annubar bench) that to get 200CFM with 2" tube the velocity pressure on inclined manometer has to be ~8"H2O vertically measured!?

Posted: **Sat Jan 08, 2005 1:02 am**

I asked this same question before I started working on my annubar bench. It's not done but I did get it put together enough to run a test to see if I had any major problems. I saw 13.5" of water column on my inclined manometer with the 2" flow tube, or about 331 cfm @ 28" depression. My inclined is designed for a maximum of 15". This was with five of the six motors running. Flow tube is 42" long with the annubar placed 2/3 of the distance from the inlet end. The length was picked to allow the 3" flow tube to be interchanged with the 3" flow tube butted tight to the 3" adapter stubs on each end for a total length of 48" of 3". One single static pickup is placed 1/2" in front of the annubar and 90* from the annubar axis. The 1.5" and 2" flow tubes are chamfered to a knife edge at the inlet end to match the rubber Fernco coupling reducer angle for a smooth transistion. The readings are dead stable using Marvel Mystery oil (.83 sp. gravity) for the manometer. The maximum reading obtained with six motors running @ 28" depression was 630 cfm through the 3" tube @ 9" w/c on the inclined. The readings will need to be verified as it seems a little high, but it was quick and dirty test.

Posted: **Sat Jan 08, 2005 1:08 am**

Gaz,
It would be cool if you could post your excel file, I know I'd like to see it

Scott

Posted: **Sat Jan 08, 2005 4:11 pm**

thanks for the feedback.
RRBD you can download my "masterpeace" . and ofcourse I'm waiting for suggestions and questions because I dont say that its 100% correct.

Posted: **Sat Jan 08, 2005 4:14 pm**

sorry the previous link doesnt work.

Posted: **Sat Jan 08, 2005 10:07 pm**

Marvel Mystery oil (.83 sp. gravity) for the manometer.so if i use this in my flowbench it shoulds not freeze right . also what do i need to change thes to 28 inchs of water when using this oil jim

Posted: **Sun Jan 09, 2005 12:34 am**

Posted: **Mon Jan 10, 2005 11:27 am**

2seater: I did some calculations with your given results (13,5 inH2O inclined and 2" tube with ID~1.81") and I got only about 264 cfm?! I wonder what others have to say about that.
Do you recalculate the reading of your inclined manometer to get the vertical pressure difference (vpd).
vpd=L*sin(a) ,where L-is the reading on inclined manom. and a-is the degree of inclination of the manometer.

p.s. I found some mistakes on my excel sheet and repaired them.

Posted: **Mon Jan 10, 2005 10:24 pm**

Posted: **Tue Jan 11, 2005 4:53 am**

Thanks 2seater the ID of the 2" PVC tube in Europe and in America seem to be different. I did my calculations according to "euro PVC" with ID ~1.81 inch. With 2.05 inch ID my result came 336 cfm in normal conditions (air temp 70K and airpressure 29.9inHg). Now I now my excel sheet could produce results that are OK.

Posted: **Tue Jan 11, 2005 10:16 pm**

Yah, that's a pretty substantial difference in diameter. If I plug in the same 29.9"hg and 70*F. I get 337.84 cfm using .02292 sg.ft. for the 2.05" id pipe. Not a big difference, but I'm trying to learn too.

Posted: **Sun Jan 16, 2005 12:28 am**

Dont forget to take off the area of the annubar from the inside area of the test pipe. ???

Posted: **Sun Jan 16, 2005 12:00 pm**

Interesting thought, if the velocity profile in the pipe impacts the front of the annubar does the area behind the impact point need to be accounted for in CFM calculations?

Posted: **Sun Jan 16, 2005 11:48 pm**

That is an interesting conjecture? I would like to know that answer myself. My logic says it shouldn't matter, since the air flow velocity is measured on the incoming side, just slightly ahead of the restriction caused by the annubar. The annubar itself is a small restriction, but it should just reduce the total flow capability, through the whole system. Does anyone know for sure?

Posted: **Fri Feb 04, 2005 8:23 am**

[color=#000000]To gaz
That