..Math..

[Bootlegger]

  What is the formula for figuring venturi size when the spray bar is .159, or what ever size and goes thru the venturi ?

  Thanks for your help...

[Akihiro Danjo]

Math professor is here 

Aki

http://www.nclra.org/Programs/Venturi.php

[Gordon Tarbell]

Venturi sizes are best compared by way of square area. This is how I do it.  Measure the dia. of the venturi at smallest point , called the vena contracta if I remember my 7th and 8th grade latin,(this should also be where the spray bar goes through). Let say it measures .250" , plug it into this formula  .250X .250 X .7854 = .0490875  this is the area of the venturi , now multiply the dia. of the spray bar .159 by the dia. of the venturi .200 (.159X.200 = .0318 , this is the square area of the spray bar.  Subtract the square area of the spray bar from the square area of the venturi and this give the effective area of the venturi.    .0490875 - .0318= .0172875 area in square inches. this gives the effective dia. of .1485 for the venturi. if there was no spray bar going through it.  It can be calculated more accurately to allow for the radiused ends of the spray bar but for what we are doing it is close enough. I am not good at typing math so I hope you get the drift. Find the area of the venturi then subtract the area of the spray bar to get the effective area of the venturi/spraybar combo. Then you can conver the square are back to effective dia. to compare to a set up that does not use a through the venturi spray bar setup.

[BillLee]

Venturi sizes are best compared by way of square area. This is how I do it.  Measure the dia. of the venturi at smallest point , called the vena contracta if I remember my 7th and 8th grade latin,(this should also be where the spray bar goes through). Let say it measures .250" , plug it into this formula  .250X .250 X .7854 = .0490875  this is the area of the venturi , now multiply the dia. of the spray bar .159 by the dia. of the venturi .200 (.159X.200 = .0318 , this is the square area of the spray bar.  Subtract the square area of the spray bar from the square area of the venturi and this give the effective area of the venturi.    .0490875 - .0318= .0172875 area in square inches. this gives the effective dia. of .1485 for the venturi. if there was no spray bar going through it.  It can be calculated more accurately to allow for the radiused ends of the spray bar but for what we are doing it is close enough. I am not good at typing math so I hope you get the drift. Find the area of the venturi then subtract the area of the spray bar to get the effective area of the venturi/spraybar combo. Then you can conver the square are back to effective dia. to compare to a set up that does not use a through the venturi spray bar setup.

Or do what was suggested earlier:  http://www.nclra.org/Programs/Venturi.php

Example for a .312" venturi and a .159" spraybar:

[Bootlegger]

  Thanks a lot fellows...

[Tim Wescott]

Gordon's example contains an error: he starts with a diameter of 0.25", then jumps to 0.20".  So the "real" answer using his method is:

total area: (0.25")²(pi/4) = 0.04909 sq in

blocked area: (0.25")(0.159") = 0.03975 sq in

total un-blocked area: 0.04909 - 0.03975 = 0.00934 sq in

Bill's example is more accurate, but oh, the math:

ventarea = 0.25^2 * pi/4 = 0.04909 sq in
Y = sqrt(0.25^2 - 0.159^2) = 0.19292"
alpha = atan(0.159 / Y) = 39.50 degrees
arcArea = ventarea * 4 * alpha / 360 = 0.02154 sq in
triangleArea = Y * 0.159" / 2 = 0.01534 sq in
blocked area = triangleArea + arcArea = 0.03688 sq in
unblocked area = 0.04909 - 0.03688 = 0.01221 sq in

[john e. holliday]

Now I know why I almost failed Algebra I.   If I had said I was going for Algebra II, it would have flunkville for me.

[Tim Wescott]

Math professor is here 

Aki

http://www.nclra.org/Programs/Venturi.php

If you enter ".25" for the venturi diameter instead of "0.25" it thinks the diameter is 2.5", and messes up the calculations.  It seems to be fine with ".159" for the spraybar diameter, though.

[BillLee]

If you enter ".25" for the venturi diameter instead of "0.25" it thinks the diameter is 2.5", and messes up the calculations.  It seems to be fine with ".159" for the spraybar diameter, though.

That's not a bug, that's a FEATURE!  

The code builds the image that is returned and saves it in a file on the server. If someone comes in later and asks for the same parameters, the code just serves up the previously created image instead of re-creating it. The image for the combination of .25x.159 was wrong, and hence it gave a wrong answer.

Fixed now. Correct answer is given.

[Gordon Tarbell]

Ok Ok I was typing too fast. but the formula and method is valid. and No I did not Fail Algebra! and as stated it does not allow for the arc at the end of the spray bar. But it is close enough for what we do.