Hairpin Heat Exchanger preferred tube layout pattern

[Vicker85]

Hi,

What could be the technical reasons when someone says, "the preferred tube layout pattern for hairpin heat exchangers is 90 degree" ?

What are all the reasons that make the 90 degree tube layout pattern suited for hairpin heat exchangers ?

 

[EdStainless]

Tube layout (TCP vs Square) is often dictated by shell side flow (needed flow area, cross flow velocity) and by cleaning requirements.
You need a square pitch with open lanes if you need to clean the shell side of the bundle.
I have seen various TCP layouts with different tube spacing also based on shell side flow.

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P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

These used to be called "Brown hairpin HXs" and only useful for very specific services.

Since they are true countercurrent HXs, does the tube pattern really make any significant difference ????

http://www.kochheattransfer.com/products/brown-fintube-hairpin-heat-exchangers

MJCronin
Sr. Process Engineer

 

[georgeverghese]

Square pitch pattern (preferably 90deg but possible with 45deg also) is generally easier to clean than with triangular pitch, and is preferred when you have a fouling stream on the shellside. This advantage however, comes at the expense of somewhat lower shellside htc with square pitch (90deg coeff < for 45deg).
For fouling service, tube pitch should also be 1.25x tube od.

 

[Vicker85]

Hello All,

Thank you for your valuable replies and insights into my query.

I could gather that the main reason for 90 degree tube layout is mainly for cleaning purposes!

But, is there more of a mechanical or thermal design reasoning behind this idea ?

I would request your expert comments on this.

Thank you again!

 

[EdStainless]

Since you have lower tube density (layout and pitch related) you end with a larger more expensive HX.
You can get the same thermal performance and mechanical characteristics through the design.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

From a performance perspective, with 90deg square pitch:
a) Shellside htc is the lowest when compared to the other patterns
b) Tube count is also lower for a given shell dia and given tube pitch, so overall surface area is lower than for others.

90deg square pattern is chosen only for shellside mechanical cleaning purposes.

 

[sarahrad]

Tube layout pattern can also address vibration concerns. Triangular layout places the tubes closer together than 90° layout. If you have a vibration prone design due to high shellside velocity, 90° or 45° can help protect against vibration.