Segmented Fin Air-Cooled HEX 1

[AggieCHEN04]

Does anybody have any experience split fin or segmented fin air coolers? It's also called High Performance or Wheelfin depending on the manufacturer. Basically the fin is a regular L-tension wound aluminum fin with a notch cut on the outside edge to increase air turbulence and help heat transfer.

How well does this work? The thermal designer of a particular air-cooler has stated that use of this type of fin makes approximately 20% to 25% difference in the overall heat transfer for this particular application.

 

[speco]

Dear Aggie,

Please take what I say here with a very large block of salt. I have been working with air-cooled exchangers for about 25 years or so, and have developed various opinions based on the mythologies of the people with whom I have worked. Some mythologies have turned out to be much better than other in the long run. So much for the disclaimer.

Here's what I believe. These kinds of "enhanced" fins are little more than a smokescreen for intentionally undersizing coolers. While there might be a slight increase in air-side performance, it would be at the cost of additional static pressure across the tube bundle. Increased static means incresed fan horsepower.

In a "normal" air cooler, there is uaually an approximate balance between the fin-side thermal resistance and the tube-side resistance. That is, they are approximately equal when evaluated on a similar basis (either finned or bare surface). Therefore, in order to increase the overall heat transfer coefficient by 25%, the air-side coefficient would have to be doubled. In my opinion, this is too fantastic to be credible. The secondary effect of some kinds of "enhanced" fins is to make the fins really good filters by greatly increasing the places where any airborne materials will be caught in the fins.

I am told that there are some manufacturers whose normal policy is to undersized coolers by as much as 20%. They probably work fine until the ambient air temperature gets as high as the design point. It's only then that the end user begins to notice a problem with performance.

Other people will have different opinions, I am sure.

Regards,

speco (

http://www.stoneprocess.com)