Low-fin tube question. 2

[Christine74]

In a low-fin tube, is the I.D. typically made larger in the unfinned portion of the tube, as is shown in the diagram below:

http://www.furukawa.co.jp/copper/img/efl_ef1.gif

If so, why? I thought the fin grooves were machined out of a piece of tubing of uniform thickness.

Thanks.

-Christine

 

[MikeHalloran]

I have _no_idea_ if they actually do it this way, but it looks like you _could_ make that article by rolling the grooves between the fins, using a tool like a dull pipecutter. I.e. in a very narrow region, you push the o.d., and the i.d., in, leaving the adjacent metal mostly undisturbed, _forming_ fins without cutting the metal.

So it isn't that the i.d. is made larger in the unfinned portion, it's that the starting i.d. is left undisturbed in the unfinned portion.

Hypothetically.


Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

One reason for this form is that if you need additional surface area in an existing bundle you can get this by using a low fin tube as you describe.

We use this type several time in service where we couldn't change the footprint of an exising exchanger.

 

[TXiceman]

As indicated, the tubes have the fins rolled not the surface and there is zero machining on a Lo-fin tube. The ends are unfinned and are for rolling the tubes into the tube sheet. When you roll the tubes, you do make a slight increase on the ID.

When the tube is rolled, the ID is basically unchanged. The material for the tubes in basically take from the OD and the OD is the same as the plain end. The tune wall under the fine is generally one gauge less than the tube wall on the plain end.

Ken

Ken
KE5DFR

 

[sterl]

Otherwise, you couldn't insert the tube into tube sheet in a conventional tube/tube sheet/baffle bundle. The plain end OD has to be at least as large as the OD in the finned portion.

That just a restate of unclesyd and txiceman, I think.