[AR] Re: Estimating_Coefficient_of_Discharge_(Cd)
- From: "Monroe L. King Jr." <monroe@xxxxxxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 13 Sep 2014 13:29:36 -0700
Cavitation a hissing sound find it with a screwdriver to your ear.
Another thing you can do is manually regulate with a valve for a test.
Increase the upstream pressure may also work.
Monroe
> -------- Original Message --------
> Subject: [AR] Estimating_Coefficient_of_Discharge_(Cd)
> From: "" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender
> "gnsortino@xxxxxxxxx" for DMARC)
> Date: Sat, September 13, 2014 1:03 pm
> To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
>
>
> I was just performing some flow tests of my injector with water and I noticed
> that the Coefficient of Discharge (Cd) surprisingly changed from 0.65 to 0.47
> when the orifice diameter was also changed from 0.23 in to 0.035 in. In both
> of these cases the downstream pressure was ambient, however, for the first
> test the upstream pressure was about 412psi although for the second it was
> closer to 380 psi. Presumably the pressure difference is due to my regulator
> unable to keep up with higher flow-rates.
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> I have 3 theories about what could possibly cause this difference:
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> (1) Cd is sensitive to the orifice diameter (eg. The larger the diameter the
> lower the Cd)
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> (2) Cd is sensitive to the upstream pressure or pressure drop
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> (3) A combination of 1 and 2
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> My suspicion is that most of the difference is due to higher pressure drop.
> Unfortunately, I don’t have an easy way of proving this without buying a new
> regulator.
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> Does this this theory somewhat make sense? I also found 2 links to formulas
> online (both formulas are fairly similar) that estimate Cd. Is this a viable
> approach to do at least a first approximation of correct Cd values?
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> http://www.valvias.com/flow-equations-discharge-coefficient-c.php
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> http://en.wikipedia.org/wiki/Discharge_coefficient
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