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Heat Exchanger Wetted Surface Area Relief

relief sizing

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#1 Xenolithian

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Posted 22 September 2023 - 10:15 AM

Hello,

I am searching for guidance on best practice for considering the wetted surface area for the tube side of a shell and tube heat exchanger. I have read in some engineering manuals that if the shellside material bubble point at relieving temperature is higher than the tubeside, then the shell surface area should be considered in the tube side wetted surface area because heat will transfer through the shell fluid into the material in the tubes and tube side and contribute heat through that. 
 

My question is what is the best practice to consider for if the material in the shell and tube side is the same? I think the conservative answer is to include both the shell and tube area in the interest of increased safety. I also think that the shell side relief will open and if sized properly will be able to handle the heat input from the shell side fire exposure. And logically I think the tube side will see some increased heat input albeit likely less than the full heat input to the shell as vaporizing liquid removes heat input from the shell. I have internal resources I can consult for this question but I am validating an old contingency that used only the tube side head area in the exchanger in question with the same material on both sides. Any guidance is appreciated even if you are able to direct me to resources to read (I have read and can consult further API520/521 if I am misremembering a section that deals with this question in particular, etc)

I can provide more information if necessary about the exchanger in question but I'm more interested in a general guidance on what surface area to consider for a shell and tube heat exchanger with the same material on both sides. 

Thank you for your time.



#2 Pilesar

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Posted 22 September 2023 - 05:02 PM

I have read in some engineering manuals that if the shellside material bubble point at relieving temperature is higher than the tubeside, then the shell surface area should be considered in the tube side wetted surface area because heat will transfer through the shell fluid into the material in the tubes and tube side and contribute heat through that. 

I've never heard of that consideration! The tubeside heads would be the only surface area I would use. I am interested if this is true so I don't do wrong calcs.



#3 Xenolithian

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Posted 26 September 2023 - 08:05 AM

Hello, thank you for your reply.

This guidance came from an old (90's) copy of a Jacob's relief sizing book. I think the reasoning behind it made sense to me as far as making a conservative estimate though heat transfer from the shell to the tubeside may have a reduced rate of heat transfer, if the shell side fluid boils at a higher temperature the shell fluid would provide some additional heat input to the tubeside than what is provided by the heads alone. That is my thought. I am trying to open conversation about if it is the same fluid on both sides but I am unsure if I am being overly conservative by considering the shell side area for the tube side relief due to baked in conservative assumptions within the heat input estimate equations etc based on some of the reasoning of my initial post.

 

Thanks



#4 fallah

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Posted 28 September 2023 - 02:02 AM

Hello,

I am searching for guidance on best practice for considering the wetted surface area for the tube side of a shell and tube heat exchanger. I have read in some engineering manuals that if the shellside material bubble point at relieving temperature is higher than the tubeside, then the shell surface area should be considered in the tube side wetted surface area because heat will transfer through the shell fluid into the material in the tubes and tube side and contribute heat through that. 
 

My question is what is the best practice to consider for if the material in the shell and tube side is the same? I think the conservative answer is to include both the shell and tube area in the interest of increased safety. I also think that the shell side relief will open and if sized properly will be able to handle the heat input from the shell side fire exposure. And logically I think the tube side will see some increased heat input albeit likely less than the full heat input to the shell as vaporizing liquid removes heat input from the shell. I have internal resources I can consult for this question but I am validating an old contingency that used only the tube side head area in the exchanger in question with the same material on both sides. Any guidance is appreciated even if you are able to direct me to resources to read (I have read and can consult further API520/521 if I am misremembering a section that deals with this question in particular, etc)

I can provide more information if necessary about the exchanger in question but I'm more interested in a general guidance on what surface area to consider for a shell and tube heat exchanger with the same material on both sides. 

Thank you for your time.

 

Hi,

 

Fire case heat rate into tube side fluid, through the shell, should be considered when the bubble point of the tube side fluid at relevant MAWP is less than the bubble point of the shell side fluid at relieving pressure.



#5 fallah

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Posted 28 September 2023 - 02:16 AM

Hi,

 

Then, generally in any case, the tube side relief rate would be as follows:

Tube Side Relief Rate = (Qchannels, gained directly from fire through the front and rear heads+Qhead, gained indirectly from fire through the shell) / latent heat



#6 Xenolithian

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Posted 28 September 2023 - 07:17 AM

Thank you for your response.

For the same fluid on both sides (bubble point equal) then the wetted surface area of the tubes does not include the shell side area?

Appreciate the help.



#7 fallah

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Posted 28 September 2023 - 08:00 AM

Thank you for your response.

For the same fluid on both sides (bubble point equal) then the wetted surface area of the tubes does not include the shell side area?

Appreciate the help.

 

Hi,

 

At a glance, in such case during fire scenario appears the heat gain from shell side material by tube side might not be considerable...

 

Anyway, the heat transfer from the shell material to the tube side material should be estimated and if not so negligible is to be considered in total heat gained by tube side material to calculate the relief load of the tube side in fire case. 



#8 Xenolithian

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Posted 22 November 2023 - 03:53 PM

Thank you for your response and time.






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