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Shell And Tube Exchanger Overall U

overal heat transfer abnormal heat releief calc

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#1 Shirley2012

Shirley2012

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Posted 29 May 2014 - 06:31 PM

Can anyone help me to understand how the overal heat transfer coefficient changes in an existing shell & tube exchanger if the hot side flowrate increases?

 

In order to calculate the maximum relief rate through PSVs on the shell side of an existing exchanger, I need to assume that the TCV on the tube (hot) side fails open - hence more heat is provided to the shell (cold) side.  Looking at very long and complicated formulas scares me and I'm looking for some practical shortcuts. Please bear in mind that both shell/tube outlet temperatures will also change and are not fixed.  Both sides are liquid.

 

Sorry, maybe a bit hard to explain in limited words, but appreciate your advices.



#2 xavio

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Posted 29 May 2014 - 09:44 PM

Shirley2012,

 

U value increases with increasing velocity.

The change is more pronounced with single phase fluid where heat transfer is done through convection.

 

You mention that your hot fluid (liquid) flows in tube side, correlations for your condition are well developed.

You should find that convective heat transfer coefficient is proportional to Reynolds number.

Reynolds number, in turn, is proportional to velocity.

 

Good luck.

 

xavio



#3 breizh

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Posted 30 May 2014 - 02:48 AM

Shirley2012,

 

Consider reading this paper , it should help .

Good luck.

 

Breizh



#4 Padmakar Katre

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Posted 18 August 2014 - 12:33 AM

Can anyone help me to understand how the overal heat transfer coefficient changes in an existing shell & tube exchanger if the hot side flowrate increases?

 

In order to calculate the maximum relief rate through PSVs on the shell side of an existing exchanger, I need to assume that the TCV on the tube (hot) side fails open - hence more heat is provided to the shell (cold) side.  Looking at very long and complicated formulas scares me and I'm looking for some practical shortcuts. Please bear in mind that both shell/tube outlet temperatures will also change and are not fixed.  Both sides are liquid.

 

Sorry, maybe a bit hard to explain in limited words, but appreciate your advices.

 

Hello,

Could be please brief the scenario for having PSV on shell side. Increase in hot side flow will surely lead to increase duty which may result in cold side outlet temperature higher than current or hot fluid temperature higher than current based on delta T (EMTD). Please specify the system details such as fluid conditions (phase), T, P at inlet and outlet of both side (shell and tube side as well). Need of PSV is not well understood to me; do you consider shell side outlet blocked hence no shell side flow. Please provide system details which will help users to asses the problem and comment accordingly.






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