Birdman said:
Thanks again for your input. I would like to now let anyone else respond to this concept of the turbulator question. Has anyone out there done this experiment? How does turbulator length effect the efficiency of the Tarm? Does a 22 inch chain do the same thing as a 29 inch chain? And if not... how much less... And if 22 is better.... why ? Sorry to say... I won't be doing the experiment. Guess I will instead.. keep asking questions... in hope that other on this site might have done it already? Or.. that someone who is way better at science and tech will want to take it on? That's why I love this site... so many people on here.. and so smart. I don't have to listen to just one person's opinion..or lack of knowledge... because there may be someone else who has the knowledge.
Speculation here on my part, as I don't own a Tarm, and haven't done the experimenting, but I think logic would suggest an answer...
According to the posts I've seen, Tarms have an optimal exhaust temperature, where the smoke is barely hot enough not to condense going up the flue, but has given up all the heat that it can to the water jacket. They control this temperature by putting in or taking out turbulators from the tubes.
Adding turbulators cools the exhaust and transfers more heat to the water jacket.
The turbulator works by slowing the smoke flow so you have longer "residence time" for heat transfer to take place, and increased turbulence for greater contact with the tube walls.
My assumption, is that given a single tube, the longer the turbulator, the greater the impact that it would have just because it made the turbulence greater.
I would also think that if you had multiple tubes, the effect would be better if all tubes had the same length, short, turbulator as opposed to some tubes having a long one and others having none. With all tubes having the same length, then the exhaust should flow equally through all the tubes since all would have the same resistance. If some tubes had turbulators and others didn't, then the ones without would have lower flow resistance and therefore would see much more flow than the ones with.
Thus my conclusion would be that the optimal solution would be if all tubes had turbulators of the same size and length, with the length chosen to produce the optimal exhaust temperature for that installation.
That said, I don't have any real good ideas on how to predetermine what that optimal length should be - I'm sure there are fluid dynamics formulas that would tell you, but I don't know what they are or how to apply them, and I would note that many of the equations I've seen have involved some very hairy and complex math....
Experimentally I'd see two ways to go - Start with full length turbulators in all tubes, measure the temps, and shorten all of them by uniform amounts until it works. Or start with empty tubes, add full length turbulators a few at a time till you get to the working temperature, and then calculate an average length, put those in and go back to the first method. Given that it is generally easier to make chains or metal strips shorter rather than longer, I'd probably start with the first method...
Gooserider