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I am 3rd yr Chem Eng Student. Working on a design project - waste treatment plant. I have to specify and provide a design for a spiral heat exchanger. Can find lots of examples of finished products but am having difficulty getting info on how to approach designing the item

[Art Montemayor]

Ned:

I don’t know what university you are studying at, but if you have accurately communicated the scope and definition of your engineering assignment, then something is definitely wrong with your assignment, your professor, or the course you are taking.

In my experienced opinion, there is no way you, your professor, and all the rest of your engineering class can design a credible and workable spiral heat exchanger under specific basic data requirements. And I mean <u>all of you</u> working together as a combined team!

You can certainly specify (fill in a Specification Sheet) a spiral heat exchanger. But no professional engineer in his right mind is going to place any faith on your calculations or results for the total transfer area, the predicted pressure drop, and the inlet and exit temperatures. Spiral heat exchanger are designed and fabricated under tightly held proprietary information and methods. This information is not passed on to academia (or anyone else) because of common sense: why would Alfa Laval give away its trade secrets and information to world-wide competitors? The answer is: they don’t (& probably never will).

What is conventionally done is that process engineers fill in a specification sheet (very much like the ones I attach here) and submit it to likely, acceptable vendors. The designer/fabricator calculates what needs to be fabricated in order to comply with the specifications and proposes the required spiral exchanger – while warranting the results. The fabricator furnishes the identification of the required heat transfer area and the configuration required to effect the desired result. You, as the end user don’t do that. There have been some articles published on spiral exchanger design (in magazines such as Chemical Engineering, Chemical Engineering Progress) but never have I seen a published, recognized, and used algorithm (complete with equations) for the successful design of a spiral heat exchanger. The HTRI (Heat Transfer Research Institute), to my knowledge, has steered clear of this subject because it is too specific and specialized in industry. The HTRI has published articles on the subject, but always pointing out the specific and very un-researched portions of the fluid flow and heat transfer involved. I have designed and built numerous spiral tube exchangers in the past (& I suspect others have also), but have relied almost entirely on empirical experience and factors. I would not expect all engineers to have compiled extensive field experience in this area. You can continue with your research on finding an acceptable algorithm and related equations, but I highly suspect you will not find an answer to what you have stated.

I recommend you go to your professor and discuss this application with him/her, obtaining their recommendations on how to successfully search and get the acceptable algorithms and equations for this very specialized piece of equipment. The same recommendation would apply to very low vacuum process condensers and plate and frame type of exchangers. These are all very, very specialized equipment that are fabricated under highly guarded proprietary designs – stuff that is not revealed to text book writers, professors, and much less students.

Someday – perhaps – the design of such units may be mundane and an every-day occurrence (much like the design of shell & tube exchangers. But for now, that information is not available to the public. I'm sorry for the negative nature of this response, but I hope it has helped to put the subject in the correct perspective and that this helps you out to better define what you have to do to meet your assignment.

Attached Files

•  Art__s_Process_Spec_Sheets.xls   852KB   537 downloads