Crazy Tube / Fin Relationship Idea

[nikhsub1]

Well it's always scary when I get thinkin', and it hit me last night while looking at the various radiators. Now this could be something that is just stupid, I mean I rarely think of design improvements before others but here goes It seems there is very minimal fin to tube wall contact... sort of like this; >| I then thought why are the fins not designed more like this; ]| as there is much more fin to tube contact. What I do realize is that this will reduce the overall fin surface area in relation to air. The pic below illustrates my point. Thoughts?

[BillA]

look closely at many rads and on a few you will see such
for all the expected reasons, no accident

nice insight Scott

[nikhsub1]

Well that's just it Bill, I've not seen a rad like my example on the right. I must confess, radiator's have not been something I take note to, I have been water cooling almost 5 years now and until recently, the bigger the thicker the better! FPI? WTF is that most would have said 6 months ago (well most like me anyway). When I was looking at the closup of the fins on the new PA series is when this fin idea hit me, but I thought there was absolutely a reason as to why it was NOT done this way.

[mashie]

The contact area isn't too bad on the type to the left since all bends comes with slight radius + solder as a filler.

[Swimming_Bird]

This is sort of how i think of it, grey is fins, black is tubes, red is radiating surfaces, orange is heat transfer points:

[nikhsub1]

Understood mashie, but, the illustration on the right has perhaps 3x more fin to wall contact than conventional rads.

[BillA]

it is a design parameter AND a mfgn variable depending on the equipment used
very small things are additive in a rad

[Swimming_Bird]

the issue is solder is much worse conducter then pure copper, and you dont want to have another medium for the heat to have to transfer though to get to the surface, and coating the copper tube with another copper sheet with solder in between it doesnt seem efficent.

[Marci]

^^ more or less spot on basically...

[nikhsub1]

Originally Posted by Swimming_Bird

the issue is solder is much worse conducter then pure copper, and you dont want to have another medium for the heat to have to transfer though to get to the surface, and coating the copper tube with another copper sheet with solder in between it doesnt seem efficent.

Well depends on how you solder the flat fins. If you solder BETWEEN the fin and the tube then yes, that would suck. However, if the flat fins were flush against the tubes with just a tiny spot solder on the EDGE of the flat fin, that would not reduce fin to tube efficiency one bit.

[nikhsub1]

Another illustration. To be clear, in the flat tube design there is NOTHING in between the fins and tube, it would almost be just like spot welding the edge of the fin to the tube.

[jaydee]

The way I see it is the wall of the tube is a fin. All you are doing is making the tube wall thicker in those spots. I would think that would make heat transfer worst in those spots as you add a joint and make the metal thicker. Certainly could be wrong though. I am far from rad guru.

[maxSaleen]

I see your point. The design on the right gives three times as many POINTS at which heat can be transfered (and thus contact surface area between the tubes). I'd think this would be more efficient, I just see the manufacturing process being much more expensive. Most of the rads I've seen use one long piece of Cu bent many times between the tubes. The design you propose would not be as easy to make.

Solder inefciency is a mute point here because of the fact that both designs must use some bonding mehtod. To be fair we must assume that this is not a variable in comparing the two.

[nikhsub1]

Originally Posted by jaydee

The way I see it is the wall of the tube is a fin. All you are doing is making the tube wall thicker in those spots. I would think that would make heat transfer worst in those spots as you add a joint and make the metal thicker. Certainly could be wrong though. I am far from rad guru.

I'm no rad expert either... are we to assume the fins do little to actually aid in heat transfer? If so, then yes this idea is crap. If they do aid in heat transfer, this idea should work very well, the air flows over the horizontal fins which cool the vertical part of the fins attached to the tubes. I guess we'll never know unless we can find a comparable rad with horizontal fins. I also fail to see how bending the fins in the horizontal fashion is more expensive than bending then into a zig-zag?

And maxSaleen, it's MOOT, not mute. I got razzed about using mute instead of moot and now it's your turn!

[jaydee]

Originally Posted by nikhsub1

I'm no rad expert either... are we to assume the fins do little to actually aid in heat transfer? If so, then yes this idea is crap. If they do aid in heat transfer, this idea should work very well, the air flows over the horizontal fins which cool the vertical part of the fins attached to the tubes. I guess we'll never know unless we can find a comparable rad with horizontal fins. I also fail to see how bending the fins in the horizontal fashion is more expensive than bending then into a zig-zag?

And maxSaleen, it's MOOT, not mute. I got razzed about using mute instead of moot and now it's your turn!

The way I see it the fins are nothing more than expanding surface area that doesn't already exist. The way you have it in the first post on the right you are covering up already used surface area and adding a layer of resistance. I don't think covering up metal with more metal would work to well for optimal heat transfer.


The pic on the left seems better to me as it adds the most surface area not already used. By angling the fins you are lengthening it as well adding more area than just shooting strait across horizontally.

[duh_bing]

think its because the convective heat transfer of air << (much smaller than) the conductive heat transfer of copper. So a larger surface is needed for the air and a much smaller contact surface for the copper fins. No reason to have more fin/pipe contact surface if theres not enought fin surface to "expell" the heat...

[Etacovda]

pretty much what i was thinking.

Gotta be able to make an equation for optimizing it.
Hrm, thinking out loud, wonder if having small recesses/hollows in the tubes to fit the fins, =
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(
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would work well - require less solder as it would 'cup' the fins, holding them in place more, improving surface area without having to solder as much, could help heat transfer as it could be possible to offset the hollows to create turbulence without turbulators restricting the flow so much, and makes the smaller cross-sections of the tube able to be focused to help heat transfer.

Probably a crock, but it might inspire someone. Would require new tooling though, so its probably not an option even if it would work...

"I also fail to see how bending the fins in the horizontal fashion is more expensive than bending then into a zig-zag?"

possibly using more material or a different tooling method required?

[Long Haired Git]

I've always said, like a version of the matrix, what if there were no fins?

[ricecrispi]

The way I see it the fins are nothing more than expanding surface area that doesn't already exist.

True but......

The assumption is the sharp point and brazing to the tube is a bottleneck in performance and limiting the transfer of heat to the fins. I think Nikhsub is proposing straight bends will increase surface area with the tubes to help improve heat transfer into the fins.

The area being overlapped seems to be irrelavent because it is meant to aid more in transfering more heat into the fins.

I think the model makes sense in the diagrams but in real life the diaganol tubing is more like a rounded bend then a point in your diagram. The bend with the brazing probably performs the same as a flat edge bend with the brazing on it.

I'm assuming a rounded bend acts the same as a very small straight flat bend because the brazing is a bigger bottleneck and you will get similiar results.

[maxSaleen]

I'm no rad expert either... are we to assume the fins do little to actually aid in heat transfer?

I've always thought that the exposed surface of the tubes would transfer more heat than the fins. One might find some validation of this theory by looking at the c/w of the PA160 and a similar size HC with a substantially higher FPI (both using very high flow fans so as to negate the core depth difference to a degree).

It would be interesting to take a BIP, cut out all of the fins, and see how it performs. Another interesting experiment would be to make a rad with no fins and more tubes.

The way you have it in the first post on the right you are covering up already used surface area and adding a layer of resistance. I don't think covering up metal with more metal would work to well for optimal heat transfer.

This is exactly what I was thinking. I can't imagine anyone doing this, so I assumed that the perpendicular fins would soldered INDIVIDUALLY. This would greatly increase the cost of production.