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Originally Posted by Rick360
Dave,
Interesting post, as are some of your other posts.
When you refer to a "sharp edged" orifcice are you really referring to a "square edged" orifice? To be a sharp edged orifice shouldn't the inside edge of the orifice be machined at an angle down to a "sharp" point?
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Yes I'm referrring to a square edged orifice plate that has been correctly made so there is absolutely no rounding of the edges. With mine you can drag them across the back of a fingernail and slice material away.
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Do your calculations for "flow" convert to ACFM or SCFM?
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Not sure what you mean here but I'll guess the A and S are intended to mean Actual and Standard CFM. My computer program works out all of them. Actual CFM at actual test conditions, Actual CFM at standard (15c, 1013.25mb) conditions and nominal flow at standard pressure drop of say 10", 25" or anything else I enter. I say 'nominal' because the generally accepted square root law to convert from one pressure drop to another doesn't actually work but that's a topic for another time.
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When you measure your accuracy and indicate they are less than 1% you are using a testing method that also has a measurement error of 1%. It is my understanding that you can never be better than 1% when using an orifice. After they are calibrated to some much better standard (such as LFE or nozzle in a lab environment) and placed into service, you are never certain it is better than +/- 1%.
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Yes, as I said the margin of uncertainty in compressible flow tests is 1%. It just happens that my bench comes out with exactly the numbers that the flow equations predict for each test plate.
Dave