tube size and placement

[jakeharder]

I am working on a design of a small (8" dia.) HRT three pass boiler. I am wondering what effect the proximity of the tubes to each other might have on water circulation, also, by how much should the total cross sectional area of the tubes be reduced for each pass to allow for cooling of the flue gasses. If I add a steam dome, how much steam space do I need in the drum? I was thinking a 2" morrison tube for the first pass. woould I be better off using 3/8" or 1/4" tubes? Thank you in advance for any replies.

[watt-steam]

Huh?

HRT? Morrison tubes? 3 pass?

[jakeharder]

HRT-Horizontal Return Tube. The morrison tube is a larger tube with the burner at one end with the flame taking up almost all the area of the tube. The flue gasses pass through the morrison tube, return through the first bank of tubes, make another change of direction, passing back to the rear of the boiler, and up the stack, hence the term three-pass. As the flue gasses cool, they contract, requiring less total cross sectional area to keep them traveling at the same speed. I hope this clears up any questions. Thank you for your reply.

[watt-steam]

Very interesting stuff Jake. Thanks for explaining. I don't have any wisdom for you though about what tubes to use.

[Bill Shields]

I am assuming that you are going to stack the passes on top of each other, rather than go side to side..??

[jakeharder]

Bill, yes the passes would be from bottem to top, with baffels to direct the flow. Another question I have is how does one calculate the air flow required, and how big to make the fan?