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

- - - - -

Rho.v2 Criteria For Heat Exchanger Nozzles.

heat exchanger nozzles momentum

This topic has been archived.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

#1 CSNK

CSNK

    Gold Member

  • Members
  • 73 posts

Posted 23 April 2014 - 12:27 AM

Dear experts,

 

Can anyone please help me to know what is the rho.v2 criteria followed for checking heat exchanger nozzles.


Edited by chiks, 23 April 2014 - 12:28 AM.


#2 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,684 posts

Posted 23 April 2014 - 01:09 AM

 

Can anyone please help me to know what is the rho.v2 criteria followed for checking heat exchanger nozzles.

 

chiks,

 

In general, when shell entrance line's rho v2 exceeds a prespecified value for each fluid type, an impingement plate is required for tube bundle protection against impinging fluid...



#3 CSNK

CSNK

    Gold Member

  • Members
  • 73 posts

Posted 23 April 2014 - 01:25 AM

Dear fallah,

 

Thanks for prompt response,

 

What you said is true, but even if impingement plate is provided, than what is the maximum allowable rho.v2.

You said it depends on fluid type:

"when shell entrance line's rho v2 exceeds a prespecified value for each fluid type"

From where i can get this information prespecified value for different fluid type.

 

As per TEMA:-

It says, in any case (with impingement plate), shell entrance rho.v2 should not be higher than 5953 kg/m.s2 - should i consider it as shell side nozzle criteria ?

and for tube side (axial inlet nozzle), rho.v2 should not be higher than 8928 kg/m.s2 - should i consider it as tube side nozzle criteria?

 

TEMA doesn't clearly mentions criteria for the nozzles with different fluid types.

 

 

Thanks.



#4 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,684 posts

Posted 23 April 2014 - 02:25 AM

 

TEMA doesn't clearly mentions criteria for the nozzles with different fluid types.

 

 

chiks,

 

Please see the attached from TEMA. It is included different values for various fluids...

Attached Files



#5 Pilesar

Pilesar

    Gold Member

  • Members
  • 574 posts

Posted 23 April 2014 - 06:24 AM

   For nozzle sizing, use the same criteria you would use for other piping or vessel nozzles. As a general rule, make your exchanger nozzles at least line size. Consider making them larger than line size where it makes sense -- the region near the nozzles is the most vulnerable to erosion of exchanger components. TEMA does NOT address nozzle sizes except for the criteria for impingement protection to prevent tube erosion.

   There is nothing in TEMA about the maximum criteria for "shell entrance line's rho v2" to use in nozzle sizing. Read the TEMA excerpt fallah provided carefully as it can be confusing. The definition of "shell or bundle entrance and exit areas" is DIFFERENT from "shell inlet or outlet nozzle area." The same TEMA page excerpt gives several explanations of the flow area to use for momentum calculations for the bundle and shell with and without impingement protection. The focus of this section of TEMA is on erosion of tube components only. 



#6 xavio

xavio

    Gold Member

  • Members
  • 102 posts

Posted 24 April 2014 - 02:46 AM

chiks,

 

What do you mean by different fluid types? like water vs. methanol vs. ammonia?

Their rhos are different, so you can calculate different rho.v2 for different fluids.

 

TEMA does mention about the maximum criteria for "shell entrance line's rho v2" to use in inlet nozzle sizing, you can see in fallah's excerpt.

It is 2232 kg/m.s2 for single phase vapor/gas, 500 for liquid.

 

shell entrance rho.v2 should not be higher than 5953 kg/m.s2 --> it is for shell entrance/exit area, not nozzle

 

For tube entrance line (nozzle) it is 8968 kg/m.s2 (liquid).

 

If you use a simulator, it will give you warning when any of the limit is exceeded.

 

Maximum rho.v2 is the same with our without impingement baffle.

 

Thanks.

 

xavio



#7 CSNK

CSNK

    Gold Member

  • Members
  • 73 posts

Posted 24 April 2014 - 04:43 AM

Dear fallah, - Thanks for the attachment, from this it is not clear about exchanger nozzle criteria.

 

Dear Pilesar, - Thanks for the input.

But one specific query for avoiding tube erosions, isn't the momentum criteria should be applied to nozzles too (instead of applying momentum criteria of vessels nozzles).?

 

Dear xavio - thanks for reply,

shell entrance is from nozzle only, hence shouldn't we use the same momentum criteria for nozzles too?

 

 

Basically my perception is that we should use the same momentum criteria as specified by TEMA for the nozzle check of heat exchanger also. Even though it does not specifically says for nozzles but indirectly it can be related to nozzles.

 

Thanks



#8 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,684 posts

Posted 24 April 2014 - 11:42 AM   Best Answer

 

Basically my perception is that we should use the same momentum criteria as specified by TEMA for the nozzle check of heat exchanger also. Even though it does not specifically says for nozzles but indirectly it can be related to nozzles.

 

 

chiks,

 

Agreed, in fact when i refered to a page of TEMA that i attached, i did think so i.e. the entrance line shall go through the inlet nozzle; therefore that criteria can be applied for the nozzle sizing/checking eventhough isn't directly mentioned in TEMA...
 


Edited by fallah, 24 April 2014 - 11:42 AM.


#9 aroon

aroon

    Gold Member

  • Members
  • 86 posts

Posted 24 April 2014 - 08:23 PM

To support Fallah's interpretation. Please find the attached extract on nozzle sizing from one of reputed book on Heat Exchanger Design.

Attached Thumbnails

  • ST-HE-Nozzle Sizing Criteria.png


#10 Pilesar

Pilesar

    Gold Member

  • Members
  • 574 posts

Posted 24 April 2014 - 10:20 PM

TEMA gives no guidelines on sizing nozzles. None. As I warned, you must read TEMA carefully as it is confusing. Where TEMA discusses the entrance area, it is not referring to the cross-sectional area of the inlet nozzle. Even the "extract on nozzle sizing" posted by aroon does not give any guidelines on sizing exchanger nozzles! Read aroon's extract sentence by sentence. It discusses whether an impingement device is needed and then gives guidelines on rhoV2 for the entrance and then explains that the entrance area is not the same thing as the inlet nozzle.



#11 CSNK

CSNK

    Gold Member

  • Members
  • 73 posts

Posted 24 April 2014 - 10:40 PM

Dear pilesar,

 

You are absolutely right that there is no explicit note in TEMA, but entrance area will be higher than nozzle area and there is no specific guideline on how to calculate entrance area momentum and hence infact that criteria if followed for nozzle will be indirectly applicable to entrance area too.

Hence i agree with fallah and the same criteria can be followed for nozzles too.

 

Regards



#12 CSNK

CSNK

    Gold Member

  • Members
  • 73 posts

Posted 05 August 2014 - 06:51 AM

Dear all,

 

This was very nice and interesting topic.

One doubt i have is that what is the criteria for nozzles of air-cooler or condensers.

Can anyone throw some light on it.

 

Thanks 



#13 srfish

srfish

    Gold Member

  • ChE Plus Subscriber
  • 408 posts

Posted 05 August 2014 - 01:49 PM

For air coolers there is no limit on rhoV2 except for erosion considerations. At Gulley & Associates, the nozzle size is based on a percentage of the allowable tube-side pressure drop. If the allowable is  .GT. 4 psi, then a starting rhoV2 of 3200.lb/(ft-sec2) is used. After the final air cooler is sized, the nozzles can be re-sized to use any remaining allowable pressure drop that is not being used. 

 

The above does not apply if the tube-side nozzles are in-line with the tube ends. Then tube fluid distribution has to be considered.






Similar Topics