Orifice Plate in a tube flow device - discussion on anything pertaining 2 this

[106-1194218389]

Bjorn (SWR) - I flowed my Dart Iron Eagle 180cc intake port head - stock no porting with 2.050" intake valve. My tube is 4" id and has 2 feet of tube on both sides of the orifice plate. My flow source is 2 shop vacs by Craftsman, one a 6hp and one a 4 hp. I flowed at an actual 6" h2o depression (test pressure). I used both the Performance Trends Black Box feeding into Port Flow Analyzer 3.5 by PT and also my new inclined manometer that is 36" long with a 12" WC calibrated using Ed's spreadsheet. Now keep in mind my inclined is not perfectly calibrated yet and the orifice is glued into the flow tube and I cannot change it and it is a square edged 1.670" diameter 1/16" thick and has a cd of .633 so at 12" is 134 cfm. You will note that below the 50% range the accuracy drops off but at 50% and up is pretty good showing we need to flow at at least 50% of the orifice capacity. Results are below:
all results are CFM converted to 28" h2o test pressure.
PT black box inclined manometer
.050" 23.5 .050" no results
.100" 59.7 .100" 43.4 15%
.150" 92.6 .150" 78.2 27%
.200" 121.8 .200" 108.5 37.5%
.250" 150.1 .250" 141.8 49%
.300" 178.4 .300" 172.2 59.5%
.350" 201.5 .350" 197.7 68.3%
.400" 220.8 .400" 213.6 73.8%
.450" 231.8 .450" 225.2 77.75%
.500" 236.0 .500" 230.1 79.5%
.550" 235.3 .550" 230.1 79.5%
.600" 229.7 .600" 230.1 79.5%
.650" 225.5 .650" 227.2 78.5%
.700" 224.3 .700" 225.8 78%
.750" 222.6 .750" 224.3 77.5%

The flow with the PT black box is very close to my FLowQuik and a couple of other flow benches. The low lift flow below .350" with the PT black box is a little lower than the others which I attribute to the one size orifice. I should be closer once I get my inclined calibrated and my 6" tube built with changeable orifices. I feel you can make an orifice in a tube work.

[SWR]

So,the difference isn't that bad with a 1.67" orifice / 4" tube and low test pressure... I'm curious to see if you get the same problems I tend to have if you make bigger orifices and pull at 28" through the test piece. I used a 5" tube,but with exchangeable orifices at 10cfm / 45cfm / 60cfm / 80cfm / 105 cfm / 145 cfm / 200 cfm and a 2.65" SEO (300 cfm @ 10") as the biggest. And going from the 145 to the 200,and then from the 200 to the 300 always makes a "step" in the flow curve...

But one thing that puzzles me then is that I can't flow my 200-orifice using the 300 in the bench... then it shows 206,3. And I'm positive that it's accurate,it's sharp as a razor (drawn blood some times) and machined to 1/100 of a mm. That's 0.0003937" to you guys. If I put in the 145 one,which is just as accurately machined and pull with it,and calc it to the same depression,it shows 195.6... ???

[106-1194218389]

When I first started playing with the orifice in a tube it was aimed at low buck using a shop vac. So it will be low test pressure. Also I have always notice if you get too close to the same size as the tube then it gets weird. The first tube we tried was 1.5" with a 1" orifice and it was basically not functional. Then I tried a 2" tube and was pretty good until I got above about 1.250" orifice. Now the 4" tube acts much better, but still if the orifice gets too big it acts a little weird. I think it was about 2" orifice in a 4" tube that was not real good and a 1.75" orifice was ok but the 1.670" one worked best for both upper and lower flows. I think once I get the 6" tube done it will be better, but I don't know how it will act with more test pressure. Flow straighteners really help though.

[SWR]

[Tony]

This is to be expected. A one inch orifice in a twelve inch pipe is really like having a big round settling chamber up stream of the orifice.

As the orifice becomes larger, and/or the pipe smaller it all starts to go terribly wrong fairly quickly. There is no ideal ratio of pipe to orifice, the larger the ratio of size difference, the closer to ideal it becomes.

Natural flow into an orifice plate is mostly radial. Flow along a pipe is axial.

By placing an orifice in a pipe you are forcing it to do something unnatural, and the flow coefficient is changed in an unpredictable way.

[larrycavan]

[thomasvaught-1]

When you ran your first test with the 1.0" orifice in the 1.5" pipe your beta ratio was .816

The 1.25" orifice in the 2.0" pipe was .719

The 2.0" orifice in the 4" pipe was .707

The 1.75" Orifice in the 4.0" pipe was .661

Your best results were with the 1.67" orifice in
the 4.0" pipe. A .646 beta ratio.

The magic Number is a Beta ratio of .612 in my mind:

1.5" orifice in a 4" pipe
2.25" orifice in a 6" pipe
3.0" orifice in a 8" pipe
3.75" orifice in a 10" pipe
and finally a 4.50" orifice in a 12" pipe

All of the above relationships will have a .612 beta ratio and will work great. If you want to
trim the air flow further to hit a certain flow vs test pressure you can reduce the orifice diameter vs pipe relationship further and
move into the .5XX range.

I try to never go over a .612 beta ratio on any flow testing with a orifice in a pipe. JMO

Tom V.

[106-1194218389]

Whoa Thomas, you just saved me about a month of testing! :laugh: I owe you. If we ever have a flow bench forum get together I'll buy you dinner. I think the 2.25" orifice is all I would need and then I could of course use smaller ones to get the lower ranges. My main goal is to build a regular flow bench with 8 motors, but I love to tinker and I love playing with this tube. It is a challenge and I really like that.

John

[106-1194218389]

[Tony]

If two identical orifices offer identical pressure drops when one is installed flat over the test hole, and the other in the measurement location within the bench, you have achieved a perfect result. No improvement is possible.

If your orifice in a pipe reads different to the same identical orifice supplied from open up stream air, then you have a big problem.

Do it properly and a one inch, two inch, and a four inch orifice will read EXACT flow numbers in the ratios of 1:4:16 CFM.

Put these same four orifices in a pipe and the numbers will be badly skewed between ranges.

You will have a crazy bench that has a series of odd sized orifices with odd unpredictable flow readings in every range, and you will never know where you are.

It is really nice to be able to switch between ranges and get the exact same consistent reading. It is also nice to have a series of orifice plates that go up evenly in exact size to get that result.

In my bench orifices go up in the following diameter sequence:
1.000
1.414
2.000
2.828 and so on.

Each flows twice the CFM of the previous smaller size.

[larrycavan]

This got rather interesting. I found regarding flow through an orifice inside a pipe.

A ratio of the orifice being not greate than 30% of the diameter of the pipe is their suggested "ideal" ratio. If the [orifice size / pipe diameter] ratio is increased, flow increases [same orifice in smaller diameter pipe] flow increases & a correction factor gets applied.

Using this method, the [orifice / pipe diameters] in Tom's calculations are too large. I'm not assuming either to be correct or incorrect. Just pointing out that they are not equal.

This type of bench is out of the "norm" so to speak. We have proven builds of both pitot and orifice that work well. The orifice in a pipe concept is a bit of a hybrid derived from the 2 proven designs.

One question that just begs answering is this. If you're going to use pipes, why not just build a pitot bench and be done with it?

Larry C:;):

[SWR]

[SWR]

[thomasvaught-1]

I think there is some confusion on the internet on the true definition of Beta Ratio.

Most say it is simple the ratio of the orifice diameter divided by the pipe diameter.

This is not true. The correct definition is the
"Square root of the orifice Area divided by the pipe Area"

If you look at this spread sheet posted by Bruce (which is on our board's web site) you will see the calculator and formula which was used in my post.



Orifice flow in a pipe, thanks to Greenlight for this spreadsheet. It is a rather large file (almost 2 megs)

Orifice flow in a pipe

You will see on the right of the document the Beta Ratio Calculator and the Formula

By the way the 30% rule would have a .74 Beta ratio. Plus in a 4" pipe and a 2.19" (30% orifice)
and you will get a .74 Beta ratio.

Tom V.

[thomasvaught-1]

Quote:

I am confused by your post:

"I flowed at an actual 6" h2o depression (test pressure). I used both the Performance Trends Black Box feeding into Port Flow Analyzer 3.5 by PT and also my new inclined manometer that is 36" long with a 12" WC calibrated using Ed's spreadsheet. Now keep in mind my inclined is not perfectly calibrated yet and the orifice is glued into the flow tube and I cannot change it and it is a square edged 1.670" diameter 1/16" thick and has a cd of .633 so at 12" is 134 cfm."

If I am reading it correctly you are trying to use a 12" inclined manometer (with a 1.670" orifice in a 5" pipe, right?)

The test pressure was 6 inches across the test piece.

Tom V.