Liquid restriction orifice sizing 1

[MariusChE]

Here is a quick and dirty to size a restriction orifice:
Q = flow in m3/hr
SG = SG dimensionless
C = constant = 195,78
Cd = discharge coefficient = 0,61 (See Crane) dimensionless
dP = diff. pressure in kPa
A = orifice area in mm2
d = orifice diameter in mm

Calculation calculates A:
A = C*Q/Cd*sqrt(SG/dP)
and hence d = 2*sqrt(A/PI)

The calculation does not account for approach velocity and I would not use it for very sensitive applications. However, I have used it to restrict flow to centrifuges and it was within 5%.

 

[H20RO]

Hello,
Is the equation for area = C*(Q/Cd)*sqrt(SG/dP)
or
CQ/(Cd*sqrt(SG/dP))?

Thank you

 

[TD2K]

H2ORO,

area = C*(Q/Cd)*sqrt(SG/dP)

I took a look at Crane's technical paper 410 and by manipulating their equation (which is the same format as the one Marius posted) I convinced myself this is the correct order of operations.

 

[H20RO]

To TDK,
Thank you, you have restored my faith in the joy of asking, I guess, stupid questions. If I may ask, in my ignorance, is the Crane 410 paper kind of the holy grail of orifice design? I have seen several references to it. I had already run some calc’s on ‘knowns' and so deduced the correct order but it is great to have it backed up.

Best regards,
H20RO

 

[TD2K]

They are on page 3-5 in Crane under "flow through nozzles and orifices".

There are many forms given, the one I used was:

Q = 236*di^2*C*(dP/rho)^0.5

 

[TD2K]

It depends on what type of orifice sizing you are talking about.

For a restriction orifice, I typically use Crane. If it's an orifice for metering, use a orifice meter sizing program as the dPs for an orifice meter are not the same as the dPs Crane uses. DPs for meter sizing are a combination of permanent and temporary pressure losses (the relative amounts vary depending on the type of taps you have). The dPs Crane uses are permanent pressure losses.

There's also been a lot of discussion on the site about whether gases really choke in most thin orifices and how thick of an orifice you need before choking actually occurs. The method in Crane assumes the orifices will choke so if they don't, flow rates through them will be higher than if they did. A keyword search should turn up additional threads to look at.

 

[H20RO]

Thank you for your help and excellent information. The actual problem involves trying to model the pressure drops, bypass and process flows through ultra-filtration elements in a dairy process. These elements are actually 40 “ long so are far from being a “sharp edged” hole. The shear effects over this length are probably more important than the orifice effect but we crawl before we walk when modeling these systems. Interesting problem though.

My degree is actually in biochemistry but we all end up where we have the most fun and can buy the beans. Went through Naval Nuclear Power School and had Bernoulli up the Kazoo but it’s been awhile.

Again, thank you and have a good holiday.

 

[sibelius]

Hi
I am trying to find a correlation of Reynolds number against 2.5D-8D tappings as per your note, plotted at different beta ratios. The one in Crane is for D-0.5D which is no good for sizing restriction orifices
Can you help please
Thanks
John