# Flow through Convergent-Divergent Duct

#### neostalker

Guys, i would like to ask some opinion from u all. About the convergent-divergent duct, it is horizontal flow and the water is incompressible.

So, based on Bernoulli's equations, elevation and density is the same. Because of the frictional losses, the actual total pressure head, H is less than then the Ideal Pressure Head.
Any disagreement from you guys, or any other opinion.

If the convergent-divergent duct is inclined upward, what will happen???

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#### Relena

If the duct was inclined upwards the pressure head will increase at the upstream due to difference in height , but the total head loss will stay constant .
The flow will continue until the pressure head at upstream equals the elevation head at downstream thus velocity head will be zero and the fluid comes to rest.

#### johntyroger

Guys,

Following the quesrtion by neostalker, I would like to know what would happen if the flow is with compressible fluids ? What will be pressure loss in this case ?

#### johntyroger

Given the generality of your question, here is a good point to start reading:

http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html

CS

It was a very good start for me. In the case of the pressure relief valves, usually the convergent and divergent sections of the nozzle are perpendicular to each other. Is this angle between going to affect the behaviour of CD nozzle ?

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#### stewartcs

It was a very good start for me. In the case of the pressure relief valves, usually the convergent and divergent sections of the nozzle are perpendicular to each other. Is this angle between going to affect the behaviour of CD nozzle ?
With relief valves you'll have a coefficient of discharge from the manufacturer to account for the flow through the valve. The rule of thumb is 0.975 if I recall correctly (per ASME and API). However, the manufacturer should provide it to you. A good reference is API 520 and ASME BPV Code.

CS

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