Turbulator Question

[chuck172]

If adding turbulators cools the exhaust and transfers more heat to the water jacket by slowing down the hot exhaust gases, wouldn't a standard cast iron stovepipe damper mounted above the boiler do the same thing?

 

[Singed Eyebrows]

I use one of these on the Atmos because of my 50hz fan pulling flue gas through too fast on 60hz. Even though I can throttle down to .1WC with the damper this is not the same as having a proper drafting fan & I don't believe the damper would do what properly sized turbs would do. I needed to bend the impeller vanes & my guess is this drops velocity. If it were me, I would add the turbs(if not already installed) & the damper & run at the WC that Tarm recommends, Randy

 

[chuck172]

I don't understand what turbulators can do that a damper can't. I have chain turbulators, I haven't tried a damper yet.

 

[sweetheat]

Hot gases going up through the Hx tubes are traveling straight and fast, they need to be redirected or deflected to allow for more btu's to reach the tube walls. A damper is not directly in the tubes path of flow it's past it in the smoke pipe, I don't think the turbulators cool the exhaust. They just allow the boiler tubes to receive more heat. Do you mean a manually controlled damper? I'm no expert but thats my take on it. Sweetheat

 

[pybyr]

I don't understand what turbulators can do that a damper can't. I have chain turbulators, I haven't tried a damper yet.

It's all about disrupting the "laminar flow" (smooth, layered flow) that would otherwise occur (without turbulators) and which impedes heat transfer:

""Fluid can flow in laminar, transitional, and turbulent modes. When flow is laminar and at low velocities in a tube, there is little or no fluid movement immediately next to the tube wall. This layer of stagnant fluid hinders heat transfer and acts as insulation. Faster, turbulent flow has no smooth velocity gradient. The jumbled, tumbled flow pattern can disrupt much of the stationary fluid film. Built-in obstructions to flow, called turbulators, disrupt laminar flow, thereby improving heat transfer. Although these obstructions to flow increase pressure drop through the heat exchanger, the improvement in heat transfer more than compensates for the higher pressure drop.

from

http://www.hydraulicspneumatics.com...es/Article/True/6451/TechZone-FluidPowerAcces

[the article deals with fluid heat exchange, but the principles are the same with hot gases]

A damper will slow things by reducing the flue's pull, but it won't do anything about the flow patterns in the HX tubes.

 

[Singed Eyebrows]

Well said Trevor & this explains why the turbs work. I sure wish I understood what was happening with my Atmos even though the problem is solved, Randy

 

[RobC]

One other thought with a Tarm is the HX cover doesn't have a real positive seal. By blocking chimney draft you have the potential of pushing exhaust past HX cover cover due to back pressure from damper.
Might have an adverse affect on chimney too from not letting the flue gas move along, up and out.

 

[jebatty]

One other thought with a Tarm is the HX cover doesn’t have a real positive seal.

I've never noticed any evidence of flue gases getting past the smoke box/HX cover. It is steel on steel, and mine appears to be flat against flat.

 

[RobC]

Had blue covers off for cleaning and lit stove. Wanted to adjust primary air etc. I have negative draft some times and blow back when closing lever for gasification sometimes. That was when I saw smoke getting out. Once I get stove going chimney draws fine.
Anyway just a thought.
I'm thinking that the damper idea, although it might help, would be kinda like putting a potato in a car exhaust. The primary air and barometric damper working together would give the best result for hot secondary burn and reduced draft up chimney. Chains, Tarm turbulators or whatever to disrupt the flow in the HX tubes is doing something different than changing pressures in stove in an attempt to hold the heat in boiler longer.