[AR] Re: Estimating Coefficient of Discharge (Cd)
- From: "Graham Sortino" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "gnsortino@xxxxxxxxx" for DMARC)
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sat, 13 Sep 2014 13:30:48 -0700
Apologies... yes that was a typo. The orifice diameters are 0.023 and 0.035
respectively.
On Saturday, September 13, 2014 4:18 PM, David Weinshenker
<daze39@xxxxxxxxxxxxx> wrote:
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
Other related posts:
