Shell-Side Pressure Drop 1

[watwarrior]

I have an exchanger that has 8 baffles, a shell ID of 44" and tubes in the triangular arrangement (15/16" pitch).

I need to know how I can calculate the pressure drop over the shell of this exchanger, if I know the temperatures, flow rate, viscosity and density of the fluid.

This is the first time I have ever had to calculate the shell side pressure drop, I usually only have to do the tube side. So any help would be greatly appriciated.

 

[Ashereng]

Are there pressure readings upstream and down stream of your shell side?

If yes, take the difference, and account for pressure loss in piping. That should get you close.

If not, I defer to my betters.

 

[Ashereng]

Do you have the original documentation? That may have pressure losses on shell side.

 

[watwarrior]

The original Documents are messed, and Im looking to calculate this at variable flow rates, so we have a trend on the pressure drop vs flow rate. And unfortunately there is no pressure instrumentation.

 

[Ashereng]

Have you tried calling the manufactures? They should have original specs for that model. If your's was a custom, the docs may be harder to come by.

I have absolutely no idea how to estimate pressure drop through the shell side, with baffles, etc.

Guess I shall defer to the experts.

 

[25362]

I suggest you get hold of Ludwig's vol. 3 of APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS. There you'd find enough information to enable estimating the [Δ]P_f on the shell side.

 

[MortenA]

if its allready in service why not just note the flow rate and dp at various flow rates. Then plot "superficial velocity" (could be just velocity calculated based on the cross sectional area) vs dP. The inclination would be f*Le/D then use this to make a custom f vs. Renoyld no. as a function of velocity.

Best regards

Morten

 

[Ashereng]

Morten,

I had also suggest that, unfortunately ---

And unfortunately there is no pressure instrumentation.

 

[UmeshMathur]

watwarrior:

The most accurate methods for estimating shell side pressure drop in cross-baffled flow exchangers are based on Tinker's "stream analysis" approach and have been developed by HTRI and HTFS over the years. Unfortunately, these remain proprietary.

The best published method, according to the leading authorities in the field, was developed by Dr. K. J. Bell and is called the "Bell-Delaware" method. This is published in many sources, but a good one is:

Hewitt, G. F., G. L. Shires, and T. R. Bott: "Process Heat Transfer", pp 275-285 (CRC Press, 1994).

This is an encyclopedic work written by the leading authorities in the field, surely a worthy successor to Kern's magnum opus with the same title (McGraw-Hill, 1950). In Hewitt, you will find up-to-date correlations and numerical examples on virtually all aspects of process heat transfer. By the way, Kern's method (and the related procedure in Ludwig, cited above by 25362) for shell side pressure drop is generally acknowledged as being far less accurate than the "Bell-Delaware" method.

You should know that, for serious commercial work, just about everyone uses the HTRI or HTFS suites of computer software. However, it is always good to cross-check vendor designs for critical applications. In my opinion, short of using the HTRI/HTFS codes, you just can't do much better than to study and use Hewitts' book. Since you affiliation is with chemical engineering, this should be no problem.

A key issue is that of finding and using the proper transport properties. For petroleum mixtures, the authority is API's Technical Data Book. For chemical systems, the methods in the DIPPR manuals, supplemented by those in the 5th edition of Poling, Praunitz, and O'Connell's "The Properties of Gases and Liquids" (McGraw-Hill, 2001) are invaluable.

The DIPPR pure component data bank (costly!) is the best evaluated source of data. A good alternative for properties is Professor Carl Yaws' "Chemical Properties Handbook" (McGraw-Hill, 1999).

I trust this provides you the full list of the latest and greatest tools and procedures for such problems.

 

[0707]

Go to

http://www.processassociates.com/Process/heat/dp_shell.htm

And easily you calculate your shell side pressure drop.

Regards

Luis Marques

 

[UmeshMathur]

Hi, 0707:

At this time, the link you provided seems non-functional.

 

[WebWizz]

Hi,

There is a free calculation routine on

http://www.engineeringpage.com

Choose heat exchangers and then the thermal rating routine. You can then choose one of the two calculation forms. Will do thermal and pressure drop calculation for you. Of course this is an elaborate calculation so filling out the form takes some time.

On the website references are made to Bell's method and the book from Hewitt.