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Exchanger Design In Cryogenic Process


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#1 Syed saqib ahmed

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Posted 03 January 2018 - 12:57 PM

this is my final year project to design NRU,

MY QUESTION is how can i design aluminium plate fin multi pass exchanger?(design calculation).

any book or referance?such as we use kern for shell & tube and double pipe.



#2 Bobby Strain

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Posted 03 January 2018 - 01:59 PM

Nobody designs such equipment except the supplier. And a student should never be required to undertake such a task.

 

Bobby



#3 srfish

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Posted 03 January 2018 - 05:56 PM

One text is Process Heat Transfer by Hewitt, Shires and Bott



#4 Padmakar Katre

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Posted 03 January 2018 - 11:33 PM

this is my final year project to design NRU,

MY QUESTION is how can i design aluminium plate fin multi pass exchanger?(design calculation).

any book or referance?such as we use kern for shell & tube and double pipe.

 

Hi,

These are specialty exchanger type and designs are generally supplied by vendors. The major application of the core exchangers (plate-fin exchangers or brazed aluminum plate heat exchangers) are in cryogenic applications like LNG, Olefins etc.

 

You may get some literature from vendors like Kobe, Fives Cryo, Chart etc. You may also like to go thru guidelines by ALPEMA.

 

Aspen EDR and HTRI has capabilities of designing / rating the core exchangers with great accuracy.   



#5 Saml

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Posted 04 January 2018 - 08:05 PM

I agree with a previous poster that you should not design such an exchanger in your professional life (unless you are working for a plate fin supplier). However, if it is clear that this is just an academic excercise,  and this helps you understand what these exchangers are capable of, then I think that it is not a bad idea to do it. Ideally you should have an actual example to compare how off you are with the published calculation methods.

 

Check the following publication. It is protected by Copyright so  cannot post it here. But probably you can get it from your college library

It is a good one.

 

"M. Picón-Núñez, G.T. Polley, M. Medina-Flores, Thermal design of multi-stream heat exchangers, In Applied Thermal Engineering, Volume 22, Issue 14, 2002, Pages 1643-1660, ISSN 1359-4311, https://doi.org/10.1...4311(02)00074-1.
(http://www.sciencedi...359431102000741)"



#6 Pilesar

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Posted 05 January 2018 - 10:01 AM

There is more than one type of 'design calculation'. I've designed these exchangers many times without getting into the details of mechanical design. Process design is required to understand the exchanger heat and material balance in order to predict the exchanger performance. The basic questions are 'what are the outlet conditions for my streams?, what are the duties for each process stream? What exchanger area can I expect?' These calculations are not trivial, but do not require expert knowledge of fin design or layer stacking arrangement. For mechanical design background, first review the ALPEMA standards to get an idea of what these exchangers look like. AspenPlus has some tools for rigorous design of these exchangers. But I suggest you ignore the mechanical design details in the end as they are highly specialized. 

   Key to getting a reasonable process design for these exchangers is thermodynamics. These exchangers are designed with very tight internal temperature approaches. The heat curves for the process streams all are non-linear and it is just these bends (even slight bends without phase change) that can cause problems in heat transfer. With accurate heating curves, you could design these exchangers by hand, but it is much easier with a steady-state process simulator like Pro/II or AspenPlus that include a multistream heat exchanger unit. When modelling, you leave one of the outlet streams unspecified and adjust the flow rates and inlet conditions until you get the best result. To keep the hot and cold temperatures from crossing inside the exchanger, you should specify a Minimum Internal Temperature Approach (MITA) and 10 or more internal zones. Enough zones are critical because the non-linearity of the heat curves means you cannot rely on the overall inlet and outlet temperatures to identify a temperature cross. The MITA for a well-designed exchanger will probably be around 2 to 3 F.

   You likely will not get a good MITA without much trial and error. Note that this exchanger design is very integrated with the rest of the nitrogen rejection unit (NRU) so your steady-state model should be of the whole NRU for your final design. The steady-state simulator suppliers offer example models which can be invaluable for getting started.






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