[AR] Re: Estimating Coefficient of Discharge (Cd)
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sat, 13 Sep 2014 15:54:59 -0500
Cd is sensitive to the L/D of the orifice, a wider orifice through the same
plate can have a lower Cd because of that, if it's in a certain range.
As David said, Cd is very sensitive to inlet geometry.
There's a good NASA SP on orifice geometry, definitely worth looking up.
On Saturday, September 13, 2014, Redacted sender gnsortino@xxxxxxxxx for
DMARC <dmarc-noreply@xxxxxxxxxxxxx> wrote:
> 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.
>
>
>
> I have 3 theories about what could possibly cause this difference:
>
> (1) Cd is sensitive to the orifice diameter (eg. The larger the diameter
> the lower the Cd)
>
> (2) Cd is sensitive to the upstream pressure or pressure drop
>
> (3) A combination of 1 and 2
>
>
>
> 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.
>
>
>
> 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?
>
>
>
> *http://www.valvias.com/flow-equations-discharge-coefficient-c.php*
> <http://www.valvias.com/flow-equations-discharge-coefficient-c.php>
>
> *http://en.wikipedia.org/wiki/Discharge_coefficient*
> <http://en.wikipedia.org/wiki/Discharge_coefficient>
>
>
Other related posts:
