Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Flow Elements - Differential Pressure

flow meters- fuel gas

This topic has been archived. This means that you cannot reply to this topic.
15 replies to this topic
Share this topic:
| More

#1 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 25 April 2016 - 07:28 AM

Hi,

 

Which is the difference between following concepts when calculating Flow Rates across Orifice Plate-Standard. (Fuel Gas).

 

Diff. Pressure

Pressure Loss

Static Pressure

 

I´m checking a very old vendor datasheet and I do not see the difference between those concepts and which ones I have to use for recalculating the flowrate.

 

e.g.: (P1-P2)= Diff. Pressure or Pressure Loss???

 

Sizong criteria is according to ISO 5167-2003.

 

Thanks a lot.



#2 breizh

breizh

    Gold Member

  • Admin
  • 6,292 posts

Posted 25 April 2016 - 08:09 AM

Hi ,

Check in the document attached , you will get your answer .

 

Breizh



#3 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,930 posts

Posted 25 April 2016 - 09:40 AM

 

I´m checking a very old vendor datasheet and I do not see the difference between those concepts and which ones I have to use for recalculating the flowrate.

 

e.g.: (P1-P2)= Diff. Pressure or Pressure Loss???

 

Sizong criteria is according to ISO 5167-2003.

 

 

AOC,

 

Actually, you should use the terms have been applied in sizing criteria included in ISO 5167-2003.
 



#4 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 25 April 2016 - 09:55 AM

Hi and thanks,

 

The thing is that I am recalculating the Differential Pressure that I have in the datasheet by using the rest of info, but I do not get the same value as the vendor had.

 

Anyway, as I understood from the attachement, correct me if I'm wrong:

 

 

Diff. Pressure:  P1-P2

Pressure Loss: P3: Pressure downstream orifice and vena contracta.

Static Pressure (Potential Energy): P0: P/Density

 

Is it right?



#5 shantanuk100

shantanuk100

    Gold Member

  • Members
  • 104 posts

Posted 26 April 2016 - 12:15 AM

Hi AOC,

 

1. The Differential pressure across the orifice is the pressure drop across the orifice that you require. This is the deciding parameter to size the orifice.

 

2.Even though there is a differential pressure, there is some amount of pressure energy that is lost in the entrance, exit of the orifice as heat, sound energy. This is what is called the pressure loss. It can be found in Crane Fluid Flow Technical Paper TP-410.

 

3. The Static Pressure at a point is nothing but the pressure measured at that point using devices like the pitot tube.

There are two components to pressure.

-- One is by the bulk fluid at rest, called the static pressure.

-- The other is by virtue of the force exerted by the same fluid if it is in motion, called dynamic pressure

 

The sum of the these pressures is called the Stagnation pressure.

 

4. So, the static pressure in your case would be the pressures measured at the tappings of the orifice in question.

 

Regards,

Shantanu


Edited by shantanuk100, 27 April 2016 - 12:19 AM.


#6 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 26 April 2016 - 02:58 AM

Hi,

 

Thanks a lot!

 

The terms are now clear for me.

 

Now the problem is that when I´m trying to reproduce the vendor datasheet with the values I have in the Maximum Flow Case I´m not getting exactly same results as vendor.

 

I use the diff. pressure, which is 2500 mm-H2O but I do not get same flow rate as result. Vendor flow rate is 361,381 kg/h (750 Nm3/h that I converted as follow: 750*10,8/22,414 where 10.8 is Mol. Weight) and the flow rate calculated by me is 370..44 kg7h.

 

 

If I do the opposite and I try to calculate the Diff. Pressure, then I get 2379,20 mm-H2O instead of 2500 mm-H2O

 

I´m getting crazy!!!



#7 breizh

breizh

    Gold Member

  • Admin
  • 6,292 posts

Posted 26 April 2016 - 03:15 AM

AOC ,

What about compressibility factor Z in your density calculation ? 

 

My 2 cents

 

Breizh



#8 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 26 April 2016 - 03:58 AM

Hi,

 

I´m using the density calculated by vendor.

 

According to Density= M*P/zRT

 

Which pressure should I use? P1 or P2?

 

Regards,



#9 shantanuk100

shantanuk100

    Gold Member

  • Members
  • 104 posts

Posted 27 April 2016 - 12:42 AM

Hi AOC,

 

You should always use the inlet conditions, so it will be P1.

 

And please find attached below, a spreadsheet I made based on Crane Fluid Flow Technical Paper TP410, 2009 Edition.

It is for preliminary restriction Orifice (Not Orifice plate) Liquid flow sizing, but the principles remain the same for gas flow too.

Just take care of velocity and compressibility calculations if you wish to calculate for gases.

 

Note : Please note, the spreadsheet is for preliminary Restriction Orifice calculations, and not Orifice plate, but the principles remain the same. Please refer to specific formulae in case of Orifice plates.

 

Regards,

Shantanu

Attached Files


Edited by shantanuk100, 01 May 2016 - 05:39 PM.


#10 breizh

breizh

    Gold Member

  • Admin
  • 6,292 posts

Posted 27 April 2016 - 06:05 PM

AOC ,

another excelsheet to support your work , for both liquid and gas .

 

Hope this helps.

Good luck

 

Breizh



#11 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 28 April 2016 - 03:42 AM

Thanks a lot!

 

I will tell you how it is going!



#12 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 28 April 2016 - 08:30 AM

Your excelsheet are amazing!

 

The only thing is that as far as I have checked them, the calculation is not in accordance to ISO 5167. So I´m not getting the same results as per vendor datasheet.

 

 

The problem is that when I´m trying to close a balance, two flowmeters are not reading properly and the reason is because two of them were calculated with wrong Mol. Weight and the density in the base case is wrong.

 

Crazy!



#13 shantanuk100

shantanuk100

    Gold Member

  • Members
  • 104 posts

Posted 29 April 2016 - 04:49 AM

Hi AOC,

 

Which spreadsheets are you talking about. 

The one Breizh attached or the one I did ?

Because mine is not applicable to Orifice Plate, and is only applicable to preliminary sizing of Restriction Orifices so don't use it in your case of orifice plates.

It  is just to illustrate the calculations that are similar in both cases.


Edited by shantanuk100, 01 May 2016 - 05:31 PM.


#14 katmar

katmar

    Gold Member

  • ChE Plus Subscriber
  • 663 posts

Posted 29 April 2016 - 05:24 AM

Shantanuk, is your spreadsheet for a restriction orifice, or for a flow element? Your heading and Design Background notes refer to restriction orifices, but in cells D42 to D44 you refer to the pressure differential between the corner tappings which is usual for a flow element. I cannot find the permanent pressure drop that the designer of a restriction orifice would be interested in.

Being a bit pedantic - you should not refer to a differential pressure as absolute (or gauge).

In Cell D65 the Beta Ratio (i.e. Cell D62) is squared, but the formula in Cell H51 refers to the fourth power of this ratio.



#15 shantanuk100

shantanuk100

    Gold Member

  • Members
  • 104 posts

Posted 01 May 2016 - 05:23 PM

Hi Katmar,

 

The spreadsheet is only for preliminary RO sizing, not orifice plates, that's why I have considered ideal pressure differential without loss.
I have mentioned in that post to AOC, that the spreadsheet is only to illustrate the principle and way of calculations for Orifice calcs, and have written it is for RO sizing, but since it is prone to be used for plates as well, as you have noted, I have put in a specific note now mentioning it is not for Orifice Plates but only RO.

 

As for the tappings, I had included all three types of tappings. Corner, Flange, D D/2. The cell is not restricted to Corner tappings since it is a dropdown box, so the other types and their L1, L2 values are included as well and freely selectable.

https://en.wikipedia...essure_tappings

 

Regarding the pressure differential; it's true, it shouldn't be mentioned as absolute or gauge, but I've put it in absolute to be precise, so that people don't consider gauge in their calculations. And regarding the Beta ratio, I've noted it and uploaded the revised version in the original post itself.

 

Thanks and Regards,

Shantanu


Edited by shantanuk100, 01 May 2016 - 05:44 PM.


#16 AOC

AOC

    Brand New Member

  • Members
  • 7 posts

Posted 06 May 2016 - 06:43 AM

Hi guys!

 

Thanks for helping so much.

 

It was very nice to get your support.

 

The excelsheets, both of them were realy useful for learning all the concepts and understand the inputs I need for sizing plates.

 

Finally I used a couple of programs that I found. One of them is Swedish and the other one belongs to a big company.

 

The problema is solved.

 

I will recalculate the differential pressure according to new values of temperatura, pressure and density that we are facing right now. The new data will be loaded to each instrument with the aim of reducing the error in the material balances.

 

Thanks  a lot!!

 

Regards,






Similar Topics