Orifice in tube

[Tony]

One of the things which always surprises me is the effort people make to improve port flow is seldom seen in flowbench internal flow.

That is very true, but where the port in your cylinder head may be (say) two inches in diameter, the internal flow path inside the flow bench may have four inch, or even larger diameter minimum flow areas.

But, how big does your orifice box have to be to absorb an incoming jet? Imagine you're standing in front of someone with an electric leafblower. He turns it on, you hold your palm in front of the jet and back up until you no longer feel it.

The answer to that, is that the sensitivity of any sharp edge orifice to up stream turbulence depends on the pressure drop across the orifice.
If the air flowing through the orifice is like a gentle summer breeze, with hardly any pressure drop at all, even the slightest up stream disturbance is going to upset things considerably.
But with a relatively high orifice pressure drop, the relative fury and violence at the orifice is so great, that it becomes far more tolerant of up stream air conditions.
Taking that to the ultimate, if an orifice goes into total sonic choke, nothing including a massive increase of up stream air pressure will make it flow any more.

So the tip is, keep all the internal flow areas at least as large as the test hole.
Fit as large a settling volume as convenient immediately up stream of the orifice.
And use as high a design orifice pressure drop as you have blower pressure/horsepower to support.

[maineSS]

I hope Bruce isn't thinking I'm attacking his work- quite the opposite. Over the years, he's likely done more than anyone to demystify flowtesting and make it more affordable, which can only advance cylinder head development. However, vigorous discussion is the best way to uncover new ideas, hopefully followed by experimentation.

I tried seeing how far an air jet could be felt by setting a 6.5 Hp shop vac with a 2" nozzle on "blow" and aiming it parallel with floor. I had to back up 18 ft before it couldn't be felt on the skin. Next, I covered the nozzle with duct tape and cut out a rough port shape (1 1/4" wide). I thought this might cut down the range, but I ended up backing out to 27 ft!

I'm quite sure you'd see results on a manometer if you aimed this jet at an orifice that was pulling from an undisturbed source. It looks like any confined orifice, even in a very large box, will need some sort of "Beta Ratio" correction compared to one that's pulling from quiet air. So it seems the question is the .60 sharp edge coefficient- is it dimensionless, or is it meant for a specific test condition?

[Brucepts]

No attack taken, we are simply pointing out it needs not be complicated to build an accurate and repeatable flowbench

[1960FL]

Main,

You are correct except when you DO THE MATH you will see that when the Beta ratio falls below .25 the effect on the correction is negligible. As noted in the formulae

For values of less than 0.25, approaches 0 and the last bracketed term in the above equation approaches 1.

So in doing the math for the worst case in a PTS bench if I remember correctly the affect of Beta Ratio was less than 1/10 of a CFM. And that is counting on the two closest sides of the chamber. But then again if you look at a big blue this number gets much worse.


Rick

[budman]

I am a retired Analytical Chemist with a solid background in instrumental analysis. Back about 13 years ago, I decided that I wanted to build a flow bench. I researched all of the scientific and engineering sources that I could find. I found that the majority of the information was regarding flow through an orifice in a pipe. This was the method of choice for measuring fluid flows in industrial applications until fairly recently. It seemed too complicated for my use, so I designed and built my own. (As it turns out, it is quite similar to the PTS bench). When I found out about the PTS digital manometer, I decided to give it a try. I adapted it to my bench and found that it not only replaced my liquid manometers, but I did not have to use my computer to correct for compressibilty and other factors that screw up flow calculations. I was so impressed that I got a second manometer and a set of PTS plans and helped a friend build his own bench which he needed for his business. The PTS bench is now finished, calibrated and in service. At present, it calibrated to 600 cfm and will duplicate, number for number, the results of the most expensive blue bench at a small fraction of the price. MY hat is off to Bruce and the crew that made this possible.

[Tony]

I hope Bruce isn't thinking I'm attacking his work- quite the opposite. Over the years, he's likely done more than anyone to demystify flowtesting and make it more affordable, which can only advance cylinder head development. However, vigorous discussion is the best way to uncover new ideas, hopefully followed by experimentation.

You are quite right about that.
Questioning and vigorous discussion is a very healthy way to raise the bar of knowledge.
And this is where the Forum comes in.
What has been achieved has been the result of a great deal of thinking, discussion, and experimentation over many years by some very clever and determined people.
No single person could ever have come as far as we all have come as a mutually supportive group.
I think the final results far surpass anything any of us believed was even possible.

[Brucepts]

No single person could ever have come as far as we all have come as a mutually supportive group.
I think the final results far surpass anything any of us believed was even possible.

I'll second that!

I was simply the guy whom years ago decided this forum might be a good thing to get started since I was looking for info and could not find anything (late 90's) so, figured if I was looking so were others, and you know what I was right

[maineSS]

One of the interesting features of the Audie design is the flow straightener immediately upstream of the orifice. Also, the orifice dia seems to be about 1/2 the tubing ID, based on "photo analysis" of the pic in Vizard's book. I doubt the flow straightener location was accidental on Audie's part, as it's generally used with flexible tubing, which has awful flow chracteristics, especially the corrugated type. From what I've heard, the Flow Quick corelates well to the Industry Standard, so maybe the straightener is doing something positive for Beta Ratio.

About 20 years ago, professional head porter friend and I constructed a bench with a flow straightener close to the orifice. After making up a number of orifices, we calibrated the bench on a Superflow and never observed any strange effects following that and subsequent checks. We were using 4" ID PVC pipe, and the orifice plates were inserted into a 4" PVC slidevalve housing. Max orifice size was about 2". We had more problems finding leaks than with the calibration. I'm really pushed for time, so I have to run, but I'll go into more detail Sat.

[Brucepts]

From what I've heard, the Flow Quick corelates well to the Industry Standard, so maybe the straightener is doing something positive for Beta Ratio.

Industry Standard??? Is there an "Industry Standard"? Or is it an "Accepted Standard" because nobody else came along and proved different?

Might want to take the time to do some reading in this post:

http://www.flowbenchtech.com/forum/view ... ?f=5&t=458

We have no agreed upon "Industry Standard". The one that is out there now is getting pretty many holes shot in it to be the Defacto Standard

You are not some much addressing designing a project as you are discussing other products on the market already? Is there some underlying agenda maybe? Just curious if you want to discuss designing something or just name dropping for web exposure?

My mind goes hummmmm ............. ????

[Tony]

Anyone can make a plastic flow measuring product and "calibrate" it.
Even correct for some really crazy measurement characteristics with a lookup table.
The auto manufacturers do this all the time with mass airflow meters.
If you don't believe this, try replacing your MAF with one taken from a totally different vehicle.

What we here at the Forum are trying to do is come up with something that anyone can build themselves, in any part of the world, and that will be simple to make, low cost, repeatable, and accurate.

And the WORST possible way to start going about doing that would be with an orifice in a tube, simply because of it's unpredictability.