14 replies to this topic

[Sherif Morsi]

Hi,

 

I am currently calculating the pressure losses and the NPSH for a new pump that will be installed downstream an existing tank.

 

How should I account for the pressure drop in the nozzle?

 

Thanks,

Sherif

[fallah]

Sherif,

 

For a sharp edge nozzle entrance getting 0.5 V2/2g is a good estimation for head loss in the tank outlet nozzle...

[Sherif Morsi]

Thanks for the reply.

 

Regarding the calculation of NPSH using API 14E (Page 20), if the tank is atmospheric, how would you account for the absolute pressure head in feet? Is it Rho x g x h?

[fallah]

 

Regarding the calculation of NPSH using API 14E (Page 20), if the tank is atmospheric, how would you account for the absolute pressure head in feet? Is it Rho x g x h?

 

Sherif,

 

It is as follows:

 

NPSHA= Available Static Head (Tank Low Low Level-Center Line Level of pump Suction Line)+ Corresponding Head of local Absolute Atmospheric pressure-Head Loss due to entrance and friction-Vapor Pressure of the Fluid at Operating Temperature

 

Absolute pressure Head in Feet=Absolute pressure (psi)*2.31/SG (Specific Gravity)
 

[proinwv]

Sherif,

 

I would add that you should consider purchasing Crane Technical Paper 410, Flow of Fluids.

 

It is an excellent reference for calculating fluid flows, losses etc. I believe that most of the engineers on this forum use this reference.

[Sherif Morsi]

Thanks alot for your feedback....

[Sherif Morsi]

proinwv,

 

A copy has been ordered already Appreciate your advice

[proinwv]

I believe that you will get many years use of this. Enjoy!

[Sherif Morsi]

Hi,

 

I got Crane 410. I am currently working some numbers and things are critical given the low NPSHA due to space limitations.

 

For the pressure drop across the 8" nozzle located at the bottom of the tank (2.7 x 2.7 x 1.4), I am calculating the pressure drop across it using Eq 2-23 page 2-14.

For the factor C, I am referring to the graph on page A-20 (appendix A).

 

Is that a correct approach? If so, in estimating the ration B=d1/d2, I considered it the ratio between the nozzle size and the tank width, i.e. 0.2032m (8") divided by 2.7m. If not, please advise.

 

Fallah, just confirming your equation. Is it 0.5 v^2/2g or v^2/2g?

 

Thanks,

Sherif

[PingPong]

For the tank nozzle, use Crane page A-29 PIPE ENTRANCE

 

For a sharp-edged entrance (r/d = 0.00) you see that K = 0.5

In other words: the head loss of a sharp-edged pipe entrance (tank exit) nozzle is 0.5 velocity heads,

or as fallah put it: 0.5 * (v²/2g)

Edited by PingPong, 30 July 2015 - 10:02 AM.

[Sherif Morsi]

Thanks for the feedback.

 

But why can't I use Euqation 2-23 (Page 2-14)? It's under the title "Flow through Nozzles and Orifices".

[PingPong]

Because that is not about tank nozzles.

 

The definition of nozzle there is that of a restriction in a line, for example to measure (meter) flow. It is then a low pressure alternative to an orifice plate. See first figure on page A-20.

And read first line on page 2-14: Orifices and nozzles are used principally to meter rate of flow.

[Kiran T]

Hi,

 

I am currently calculating the pressure losses and the NPSH for a new pump that will be installed downstream an existing tank.

 

How should I account for the pressure drop in the nozzle?

 

Thanks,

Sherif

You can also refer coulson & Rechardson Volume 6

Attached Files

•  R C Volume 6.doc   52KB   41 downloads

Edited by Kiran T, 01 August 2015 - 06:11 AM.

[Sherif Morsi]

Hi Kiran,

 

What's the source of that table?

 

Regards,

Sherif

[PingPong]

As Kiran indicated, it is from:

 

Coulson & Richardson's Chemical Engineering Series, Volume 6 (Chemical Engineering Design)

 

Note that, like Crane, it also indicates a pressure loss of 0.5 velocity heads for a Sharp reduction (tank outlet),

and you can find that well known fact in many other books.