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Restriction orifice

Allgemeine Diskussion » Restriction orifice Posted: 27. Juni 2023 - 20:19

Hello,

 

I have a few questions on CONVAL 11 restriction orifice program. 

 

1) I tried to size multi-stage orifice plate for a pump recirculation line to the storage tank. I selected 2 stages because 1 stage will give incipient cavitation. However, result shows throttle orifice d = 2.19 in. Is this means that the two stages will be same orifice diameter? Please see attached screen shot (Q1)/sites/default/files/users/u39816/Q1.jpg

 

2) If I selected two stage orifice, what should be the distance between the two orifice in the pipe? What should be minimum straight pipe length upstream of the first orifice?

 

3) Below I am doing a single stage orifice calculation. I get an warning on the incipient cavitation. Is this a significant error? Please see attached screen shot. (Q2)/sites/default/files/users/u39816/Q2.jpg

 

 

Kommentare

Dirk Hackländer

Bild des Benutzers Dirk Hackländer

Hello Bin Zhang,

Posted: 28.06.2023 - 11:48

Hello Bin Zhang,

Below are some comments on your questions:

  1. The throttle orifice specified here is that of the last plate. To display the data of the individual stages, please click on [Restistance table].


     

  2. We recommend a distance of at least one tube diameter (1 D). Our calculation model is based on constructions measured with these distances. However, particularly reliable rules for calculating the distances are difficult to find. This can also be understood from the image a CFD calculation below.

     

    For very large distances (from approx. 8-10 D), the theoretical approach is to calculate the orifices individually again. Of course, this must be done depending on the process conditions.

  3. Partial cavitation by itself is not necessarily a reliability issue for the device. Only in combination with high pressure differences, high flow rates and sound levels potential damage results. Here is an excerpt from the CONVAL Help:

    Cavitation damage caused by initial pressure > 25 bar:

    Providing non-corrosive, clean fluids are used, even relatively severe cavitation up to p1 = 10 bar is not normally sufficient to damage the surface structure of steel.

    Tests with differential pressures > 25 bar reveal first signs of destruction in the microstructure of metallic surfaces.

    Since cavitation generally causes wet vapor to reach sound velocity in the throttling range, increased metal removal - which can drastically shorten the service life - occurs with corrosive media such as acids. Cavitation should be avoided.

    If the grain boundaries of metal surfaces have previously suffered damage from corrosion or abrasion, cavitation will accelerate the destruction process and should preferably be avoided completely.