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Post by craypappy on Oct 31, 2017 18:16:05 GMT -8
Situation: I am nearing completion of an 8” batchbox. My riser height is 10x base. My bell cap is 12” above the top of the riser.
a. Peter recommends a 12” minimum gap above the top of the riser, and comments that more is better. b. Recommended riser height is 8-10x base. I’m assuming that maximum riser height (10x base) is better than minimum (8x base).
Question: which “more is better” recommendation (a or b) dominates?
I could easily shorten the riser to 8x base which would increase the gap above the riser to almost 24”. Or split the difference and go 9x base and 18” gap. Or leave it as is.
Which would give the best predicted performance?
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Post by Orange on Nov 1, 2017 1:20:19 GMT -8
based on what I read here is you can increase the gap more and shorten the riser (up to 4B) to get less gas velocity and more heat extraction by the bell.
leave it as it is or shorten the gap if you need more gas velocity to the secondary bell or horizontal flues.
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Post by pinhead on Nov 1, 2017 5:44:03 GMT -8
Best "predicted" performance would be the longer/taller riser.
With a short riser, there can be times where the flame escapes the riser. In situations where there is high draft and relatively low internal temperature (when compared to "full hot") the short riser can smoke more than the taller riser.
Whether this situation is acceptable to you is a judgement call; the total emissions will only rise slightly and efficiency will likewise be slightly reduced.
However, where space isn't an issue I'd stay with the taller riser and 12-inch gap. With that amount of space there is plenty of room for the barrel to act as a bell and therefore be a very low flow restriction.
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Post by satamax on Nov 2, 2017 13:25:21 GMT -8
12 inches gap is fine. Except if your riser is really tucked in a corner.
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Post by craypappy on Nov 5, 2017 5:22:11 GMT -8
Thanks for input, everyone. I believe I will leave it as is.
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