Olle P wrote:
I'd say you don't need to guide the air, but your solution for oil flow management seems great!
Maybe I'll be able to design the tank to have removable guides, so we'll be able to test that hypothesis. That would be fun. I'm guessing that forced convention will make a significant difference. I predict, um, 10C lower oil temp with forced air versus passive. That's a total SWAG, of course. It's not like I know what I'm doing, or anything. ;-)
Olle P wrote:
Your flat vanes have a couple of disadvantages:
1) They're probably too thin to get an even oil flow distribution over the surfaces.
2) They're pretty difficult to manufacture.
Sounds like you know more about metal work than I do, so I can't really dispute your second point.
About your first point -- I originally considered a zig-zag pattern. The evolution of my thinking, from start to finish, went like this:
1 - A 12" high, 16" wide flat tank wall has 1.3 sq ft of surface area. Ok.
2 - What about adding fins? A 1" vertical fin spaced every 1/2" along the wall will triple the surface area of the air-tank interface to 4 sq ft! Woot!
3 - Oh, but wait, if the interior of the tank is just a flat wall, it will have just 1.3 sq ft for oil-tank interface. That may be the bottleneck for heat transfer from oil to wall to air.
4 - Fine, so I will put fins on the inside too.
5 - Ick. That's a lot of fins. A lot of welding. Or gluing? They might be breaking off and stuff.
6 - Hmm, fins on the inside and fins on the outside rely on the metal to conduct a lot of heat along it's thin cross section. And if the fin is "wide" - that is, sticks out a long way, like 4 inches instead of just 1 inch, then we need even MORE heat flow through that thin cross section of metal. What metals are heat conductive? Copper rocks. But too expensive. Aluminum is half as conductive as copper. Not so expensive. But hard to weld (so I'm told). Steel has about 1/5th the conductivity of copper. And cheap. And workable (so I hear). Hm. But is it conductive enough for super wide fins? This sounds like a manufacturing nightmare.
7 - Hmm, thicker metal means more heat conductance. So what if I make the fins super thick? Like, maybe 1/8" thick? Actually, what if I make them SUPER thick - like 1" thick and 4" wide? Or go with metal wedges as fins, 1/2" at base, 4" wide, packed along the side of the tank. That's certainly enough metal to conduct the heat along their length. Hmm, but expensive. And heavy. Ridiculously heavy.
8 - Oooh, what if I make the fins HOLLOW! Let the oil flow INSIDE the fins, to supply them with heat. Made how? Hollow out blocks of steel. No, of course not. Buy rectangular tubing and join them together? Hmm, maybe. Then the heat flows transversely THROUGH the hollow fin's metal wall, instead of ALONG the metal. In which case thin metal is GOOD, not BAD. Jeez, how will I avoid leaks after joining all these hollow things together?
9 - Oh, of course, let's just take a big sheet of metal and fold it like an accordion. No joints, no welds, no chances of leaks. The more extreme the folding, the more surface area we get. But two questions: what shape for the folds/vanes, and how closely spaced (how thin), and how wide (how much does a vane "stick out" away from the tank) ?
10 - First, what amount of surface area are we aiming for here? I want extreme surface area -- like about 10x what you'd get with an ordinary tank. Increasing surface area requires either using more closely spaced vanes (and therefore more of them) or using wider vanes (so each vane has more surface area). So, let's consider wide, closely spaced vanes, for lots of surface area.
11 - Now, rectangle or triangle? My feeling is that a triangular cross section with a narrow base will cause oil to flow poorly in the pointy end -- that would be a fair bit of surface area not being given heat. My feeling is that a rectangle, even one with the same "average" thickness as the triangle (that is, half the base width) would do better. That's just intuition though. I can't back that up with real science.
So, I'm trying rectangles, as shown in the design illustration I gave earlier. Unless I cannot manufacture it. I don't know how to do it yet.
Olle P wrote:
My suggestion is to do a nice blueprint of the design, and let some professional metal shop do the physical work.
I'm doing myself. That's part of the purpose of the project - I do it myself. I WILL learn how to work with metal.
Olle P wrote:
Spring steel is definitely the wrong quality. Too hard to work with!
These are the thicknesses to go for. .022 should suffice, .035 is very good.
... But again: Do see what the professionals say! They have the know-how, the skills, the tools and the material needed.
Personally I think it's too difficult for me as a novice to get the construction sealed at the bottom and at every junction.
Good to know, and good advice. Thank you!