[AR] Re: Estimating Coefficient of Discharge (Cd)
- From: "Monroe L. King Jr." <monroe@xxxxxxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 13 Sep 2014 14:06:51 -0700
Without the typo orifice geometry is the only answer.
Monroe
> -------- Original Message --------
> Subject: [AR] Re: Estimating Coefficient of Discharge (Cd)
> From: David Weinshenker <daze39@xxxxxxxxxxxxx>
> Date: Sat, September 13, 2014 1:16 pm
> To: arocket@xxxxxxxxxxxxx
>
>
> gnsortino@xxxxxxxxx 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,
>
> Is there a typo in one of those diameter figures? The second looks
> much smaller than the first (0.23 in. vs. 0.035 in.), but your
> description below suggests that the second was larger - was it
> actually 0.35 in., or was the first one 0.023 in. or something?
>
> > 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
>
> Couple more factors (perhaps in combination)?
>
> (4) uncertainty in the measurement of
> actual (vs. nominal) orifice diameter
>
> (5) differences in the finish of the bore
> or the edges of the different size orifices.
>
> -dave w
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