9 replies to this topic

Hi,

I am actually designing a shell tube condenser (diplom thesis), with condensation of "HCFC 123" in the shell.
I wonder how to calculate the pressure drop in the shell, because the mass of vapour gets reduced and so it is hard for me to assume the right data for the formula.

In books I just found ways to calculate pressure drop in regular one phase heat exchangers. Or is it not common or necessary to calculate the pressure drop in condensers?

Could anybody help me?

PS: Sorry for my bad English, I am from Germany.

[Art Montemayor]

Julia:

If you are a Chemical Engineering student, you must have had – or gone through – a heat transfer course or two by now. You also must have had professors or instructors in the matter, as well as lectures. I am going to assume that you have and are not naïve in this subject.

Therefore, how can you be "designing" a shell & tube exchanger without prior knowledge or instruction? You say you are "wondering" how to calculate the pressure drop and don't reveal any prior knowledge of what is required to do so. This is either bad or sad – or both.

We can help, but you must help yourself first. You do this by going back to basic study in the specific matter – such as reading and studying the subject as given in:

1) Ernest Ludwig's "Applied Process Design for Chemical and Petrochemical Plants", Volume 3; pp 137;
2) Coulson & Richardson's "Chemical Engineering", Volume 6; pp 523.

Beside reading and studying the above, you must also do an in-depth study of WHAT constitutes and makes up a shell & tube heat exchanger and why it is designed and fabricated the way it is. This is very important if you are to understand what Ludwig and Coulson & Richardson are writing. If you don't want to do the manual, tedious, and very detailed calculations, then look to do them in a simulator. You can also go to: http://www.inventech.co.uk/CondenserCritique.htm and look at the spreadsheet program that is offered there for approximately 125 Euros. Whether you use a simulator or the spreadsheet, you should always master all that Ludwig and Coulson & Richardson are writing.

P.S. Your English is very good; it is better than USA ChE students.

Thank you for giving me the advice to look in these books. I will try to get them in a library.
After reading that I will be able to ask more precisely. Although I already know a bit about condensers, I hesitated to reveal any prior knowledge because of my weak vocabulary of technical terms. Reading that stuff will be good for me.

thanks

[ashetty]

Thank you for giving me the advice to look in these books. I will try to get them in a library.
After reading that I will be able to ask more precisely. Although I already know a bit about condensers, I hesitated to reveal any prior knowledge because of my weak vocabulary of technical terms. Reading that stuff will be good for me.

thanks

If you could lay your hands on exxon engineering design practice section IX-F:Heat exchange equipment calculation procedure,condensation.It would help.
I have it ,but have not read it in years now as HTRI performs calculations easily and as a result I harldly ever do hand calculations these days.

[fallah]

Thank you for giving me the advice to look in these books. I will try to get them in a library.
After reading that I will be able to ask more precisely. Although I already know a bit about condensers, I hesitated to reveal any prior knowledge because of my weak vocabulary of technical terms. Reading that stuff will be good for me.

thanks

If you could lay your hands on exxon engineering design practice section IX-F:Heat exchange equipment calculation procedure,condensation.It would help.
I have it ,but have not read it in years now as HTRI performs calculations easily and as a result I harldly ever do hand calculations these days.

Dear ashetty
May i have the above mentioned practice,"
Heat exchange equipment calculation procedure,condensation"?If it is possible, my e-mail:n230f@yahoo.com
Thanks

[Art Montemayor]

Ashetty/Fallah:

Any engineering document (especially one involving Practices and design) originating from Exxon-Mobil will certainly have a clearly designated and written declaration that the document is sole property of E-M and no one has the right to copy or transmit the document without the expressed, written permission of the owner.

This is normal, conventional engineering procedure well-known throughout the world. It applies to Shell ("DP" documents), Total, BP, Fluor, Chiyoda, Japan Gasoline, KBR, Snam-Progetti, and every engineering firm or company that I have ever heard of. Engineering intellectual property cannot be negotiated, bargained, transmitted, copied, or used by those who don't own it or have permission from the owner of such property. Our Forums are based on engineering ethics and can't tolerate the use, transmission, exchange, or any involvement with the illegal use of intellectual property. Our reasons for this kind of stance is pretty obvious, I believe, if we are all to respect each other and our own intellectual property among ourselves in an ethical, professional manner.

I bring this subject up once again and direct my comments to all readers - especially students and future professional engineers - because anyone reading this thread would get the impression that we all foster the "sharing" of someone else's intellectual property. We don't, and we can't because it is illegal and unethical to do so. If any member has any problem with this or is taken aback by my statements on this subject, please let me know either through a formal thread in the Professional Industrial Forum or through an email. I will respond.

[sunayana]

HELLO JULIA,

FOR THIS, YOU CAN REF: LUDWIG; VOL 3; PROBLEM NO: 10.8 (DESUPERHEATING AND CONDENSING PROPYLENE IN SHELL

SUNAYANA

[latexman]

Julia,

Many, many years ago I took a graduate course on Process Equipment Design. One of the references that has several empirical pressure drop equations for heat exchangers is an article titled Design of Heat Exchangers by Lord, Minton, and Slusser on page 96 of the January 26, 1970 edition of Chemical Engineering magazine. One of the equations in the article is for shellside condensing pressure drop.

Many thanks for your answers,

I read that books and learned how to figure out the shellside pressure drop and that it seems to be negligible.
In Ernest Ludwig's "Applied Process Design for Chemical and Petrochemical Plants", Volume 3; is an example of a condenser SUNAYANA mentioned.
That condenser has baffles, but there is another example with a condenser ( for amonium) without baffles.
As a rule for baffles I only read that their spacing should be like the shells diameter, but I did not know when they are required or not.
In connection to that question is another question: Does there has to be free space after the inlet nozzle or could the whole shell be full with tubes?



technical Details: In want to condense 3 kg/s of HCFC123 (aka R123), that is a refrigerant. The vapour is overheated 50°C and dew point is 30°C (dew pressure 1,11 bar which is about 6895 psi). The vapour's density is 7.06 kg/cubic m, so there will be a Volume of 2.35 cubic meters per second.
The shell will be about 5.7 m long with a diameter of 0,6 m.
Q= 548 300 W = 160 690 Btu/hr

Thank you for any help

[Art Montemayor]

Julia:

The answer to your specific question is: You don't need baffles to condense a vapor inside the shell of a shell & tube condenser. However, the baffles help in reducing the amount of total heat transfer area required by creating turbulence through a higher Reynolds Number. This turbulence increases the condensing film heat transfer coefficient.

I have operated condensers with and without baffles. Both work. If you have a specific need to condense without baffles, then you can do so.

I hope this addresses your specific query.