2 replies to this topic

[fiqahbidamkil]

haii. im designing heat exchanger. i calculated the no. of tubes and i got 8000+ using the assume heat transfer coefficient (10-50). is it normal to get that value?  My Q used to calculate the tube no is also very high. 

and to calculate Reynold number, im not sure what what viscosity to use since both tube and the shell side contains mixture of gases and at what temp. same goes for density and fluid thermal conductivity to find the Prandtle no. And for the baffle cut, what % should i use? 

And are fluid viscosity at the wall (U) and fluid viscosity at the bulk fluid temperature (Uw) considered the same for this design?

I really need your help, Thank YOU.

[Art Montemayor]

fiqahbidamkil:

 

If you are a chemical engineering student, I am going to assume that you have passed rigorous entrance qualifications to study engineering: you have achieved high marks in chemistry, physics, mathematics, and other studies showing that you have the ability to use clear and concise logic as well as rational common sense.  Your prior achievements should have prepared you for what you are confronted with.

 

I am going to give you some help in engineering problems - but it has little to do with heat transfer specifically.  The help I offer is one of using your prior studies, your common sense, and communicating with others (particularly future colleagues).  This has to do with what a lot of our student forum members fail to do or exercise - the art of communicating specifically, logically, and in accurate detail.  The most important rule in engineering is knowing how to describe your problem(s).  This is so because if you don’t know how to explain or describe your problem logically, in detail, and accurately, you haven’t understood what the problem is about - and much less how to solve it.  This is an important facet of your professional preparation and I present your queries as follows:

 

Query: I calculated the no. of tubes and I got 8000+ using the assume heat transfer coefficient (10-50).  Is it normal to get that value?
Response: What value is questioned - the tube quantity or the coefficient?  Be clear and specific.  How can either point be addressed if you haven’t defined the heat duty, the fluids involved, the temperatures, the pressures, the type of heat exchanger?

 

Query: My Q used to calculate the tube no is also very high.

Response: Without seeing the detailed calculations, how can anyone determine what is relatively “high” or “low”?  Without detailed basic data and the calculations, nothing can be surmised.

 

Query: to calculate Reynolds Number, I’m not sure what viscosity to use since both tube and the shell side contains mixture of gases and at what temp. same goes for density and fluid thermal conductivity to find the Prandtl No.
Response: If your instructor(s) have assigned you a heat transfer problem it must be because you are taking a heat transfer course and have already attended lectures and read all the assigned text and theory.  Your instructor(s) should already have gone through an example of a heat exchanger calculation or furnished you with a text or document showing such a calculation.  If your instructors and/or your university are deficient in this, there are abundant sources of heat exchanger calculations in your library as well as in the internet.

 

You should have no problem in gathering and studying example problems in detail that will show you how each equation is derived and employed.  Donald Q. Kern, in his famous book - “Process Heat Transfer” - shows all these details in numerous example problems.  You should go through all these example problems, doing the detailed step-wise calculations.

 

There is a lot of information on heat exchanger design to be found within our Forum - but it is up to you to locate it, download it, and study it diligently.  You will find copies of detailed calculations as well as much information on exchanger types, orientations, and comparisons.  You have to put in the required man-hours of researching, studying, and working typical problems.

 

The best way to define your heat exchanger application is to fill in a heat exchanger Data Sheet.  You can find this valuable document in our website for download.  If you have questions as to what type of baffle to employ, your instructor should have lectured on this.  If not, then go to him/her and ask for their advice and recommendations.  We don’t know anything about your application except that your calculation results don’t seem “right”.  We need specifics and that is what you should concentrate on in communicating your query.  Refer to the attached documents and study them in detail.

 

I hope you follow my advice and re-submit your query with all the required basic data and your detailed calculations so that our members can fully know what your query is and what it is based on.

 

Good luck.

 

 Shell and Tube Heat Exchanger Design.pdf   7.18MB   113 downloads

 How to Design a Shell&Tube Heat Exchanger.pdf   54.23KB   84 downloads

 Effectively Design Shell&Tube Heat Exchangers.pdf   185.85KB   95 downloads

[Art Montemayor]

Everyone (especially students):

 

I consider the previously submitted article, "Effectively Design Shell&Tube Heat Exchangers.pdf " as such a good discussion of heat exchanger design that I have taken the time to finish editing and formatting the article into a Word for Windows document that is much easier to read, follow, and study.  I started this work sometime ago and finally resolved myself to finish what I started.  This product is found attached.

 

I have taken the liberty to include some footnotes to comments made by the author.  This is done not to contradict the authors good explanations, but rather to add some field experience in the fabrication, operation, and maintenance of heat exchangers.

 

I hope this serves to help young chemical engineers - as well as students - who are beginning to get their "feet wet" in the process heat transfer arena.

 

 Effectively Design Shell&Tube Heat Exchangers.docx   2.73MB   76 downloads