External Fins for Heat Transfer

[drax]

I need to add some fins for heat transfer on a Mild steel tank. Can anyone suggest a good material to make the fins out of or maybe can suggest a preferred shape of the fin for the best transfer.

 

[Jonkatz]

Is this for outdoor use or indoor use? If you expect the fins to hold up to weathering, its best to use a corrosion resistant material (i.e. stainless steel or such)
If contact with water is not expected and temperatures permits you could use medium carbon steel fins. If you expect high fin temps, then you should use a high temp alloy (for example 2.25% Cr or something like that).
THere are endless possibilities for shapes of fins. THin strips of metal (~0.05" thick) make for pretty good fins, but cylindrical studs (for example) would be more durable if thats an issue. Hope this help you..

 

[butelja]

How large is your tank?

 

[Haf]

Hello,

Butelja and Jonkatz asked two good questions. Is the tank indoor or outdoor? How large is the tank (and what is its geometry)? In addition, how much heat do you want to dissipate? How hot is the material in the tank? These questions will all determine the best fin design. Remember, you don't necessarily want the design that dissipates the most heat, as this could be extremely expensive. Presumably, you want the simplest design that will meet your needs.

When it comes to fin efficiency, three factors dominate: surface area, geometry, and thermal conductivity. Obviously, you want high surface area, which can be controlled by the geometry and number of fins used. If the tank is cylindrical, it is common to use annular fins, but this may not be practical if the tank is large. In terms of fin material, pick something with low thermal conductivity: copper and aluminum are common. Aluminum is usually preferred since it is light and relatively inexpensive.

Heat dissipation with and without fins can readily be estimated with the help of a decent heat transfer text book (I recommend "Fundamentals of Heat and Mass Transfer" by Incropera and DeWitt, John Wiley and Sons, ISBN 0-471-30460-3).

Remember, as Jonkatz pointed out, whether or not the tank is located indoors or outdoors will limit material selection. Also, you have to take into account seasonal changes in temperature vs. a more stable indoors temperature. Your preferred method for attaching the fins (welding, bolting, brazing, etc.) may also limit material selection. To solve this problem rigorously, I would perform some relatively detailed calculations. Otherwise you may end up spending too much money, or you may end up with a design that does not enhance heat transfer (arbitrarily adding fins does not guarantee increased heat transfer).

Good luck, and if you need more help, please post with some more details.

Haf