1 reply to this topic

[Sadananda Konchady]

When should the triangular 30 degree and rotated triangular 60 degree orientation be used in shell and tube heat exchanger designs?

Is there a significant difference in shell side heat transfer or pressure drop?


Thank you,

[Art Montemayor]

sadananda:

This is difficult to explain without graphics. Perhaps you have a copy of the TEMA standards book and, if so, go to page 24 where you will see the tube layouts you have mentioned: 30 degree triangular & 60 degree rotated triangular. Unfortunately, TEMA only illustrates the layout using a minimal of 3 or 4 tubes to describe the configuration. This is not a good illustration because it doesn't give a broader and more realistic visualization of what is happening. The flow arrows help, but it still takes a lot of conceptualization in my opinion. What I recommend is that you layout the tubes in their respective pitches on an Excel spreadsheet that has been arranged to have practically a square-cell layout. This is done by making your columns 1.71 and leaving your rows at 12.75.

From the created expanded tube layouts you can clearly see that the rotated triangular pitch type leaves an open flow lane for the fluid flow to go through. This obviously results in a reduced pressure drop due to the less rigorous path that the flow has to negotiate. However, as you would expect, the tradeoff of such a benefit is that the shell-side heat transfer coefficient is reduced. I would expect the shell-side Reynolds number may be reduced as well as the related turbulence. With some fluids, such as heavy, viscous types, the rotated pitch might be recommendable. However, everytime you stimulate less turbulence and less pressure drop while using a dirty or solids-containing fluid, you are inviting increased fouling and plugging - coupled with less heat transfer or more area required. Of course, here I am assuming that we are dealing with liquid-to-liquid TEMA type, shell and tube exchangers and not condensers or evaporatos, reboilers, etc.

A decision on picking the proper or best pitch depends a lot on the quality and type of fluid - as well as the physical properties - that you are handling and the maintenance and durability that you expect out of the operation.

I hope my explanation helps answer your question.

Art Montemayor
Spring, TX