HomeRoast Digest


Topic: go with the flow (3 msgs / 92 lines)
1) From: dewardh
Dan:
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Actually, Dan, it's what BrightWay says . . . and you still haven't said how to 
describe bean motion in a Rosto . . . (other than "fluidized", as BrightWay 
calls it).
There are more ways than one to "fluidize" . . . ("your" way is one of them) . 
.. . and anyone who has ever observed a Rosto understands that.  In a Rosto the 
beans "flow" around the roast chamber, driven ("fluidized") by airflow.  To be 
sure, the beans just don't go the direction you're used to . . . they "flow" 
horizontally, as well as up and down.  They don't just sit there with air 
blowing through them, they flow.  You don't have to take my word for it . . . 
find someone who has one and see for yourself . . . (if the  hasn't 
glued your eyes shut).
Maybe this will open you mind and broaden your outlook . . .http://www.geology.sdsu.edu/how_volcanoes_work/Pyroflows.htmlDeward
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2) From: Dan Bollinger
Funny, I was thinking about geology examples, too.  Ever see the Grand
Canyon rock flows?  Looks just like water coming down a rapids, but there is
no water present, just sand, stones and rocks.  Anyway,  what that website
and BrightWay have in common is the use of the term fluidized.  Neither use
the term fluidized bed.  It's not my term, as you put it, but a Mr. Gasto's
who invented the fluidized bed in the early 50's.  So, I'm willing to say
the Rosto is fluidized, but I wouldn't call it a fluidized bed.  clear
things up?  Dan
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how to
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BrightWay
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them) .
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the
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To be
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"flow"
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.. .
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3) From: dewardh
Dan:
<Snip>
and BrightWay have in common is the use of the term fluidized.  Neither use
the term fluidized bed.  It's not my term, as you put it, but a Mr. Gasto's
who invented the fluidized bed in the early 50's.  So, I'm willing to say
the Rosto is fluidized, but I wouldn't call it a fluidized bed.  clear
things up?
Sure . . . by that standard (conforming to "Mr. Gasto's invention" and the 
commonly described "fluidized bed combustion" devices used and proposed for 
coal and "waste" burning) there are *no* "fluidized bed" home coffee roasters . 
.. . including not the Hearthware, which only "fountains" the beans in an air 
driven stirring process in which a substantially smaller portion of the beans 
are impacted by the airflow than in the Rosto.  Certainly no home roasters fit 
the narrow description of an entire particle mass fluidized and "levitated" by 
airflow through the (entire) floor (bed) of the roast chamber . . . the common 
characteristic of "fluidized bed" combustor designs.
In the Rosto, although the air does ultimately rise (it's "exhausted" from the 
top of the roast chamber), the bulk of the air's kinetic energy is expended not 
in "lofting" the beans but in swirling ("fluidizing" horizontally ) and 
mixing them.  At the beginning of a roast, before the beans lighten and obvious 
"fluidization" begins, a substantial part of the air-induced bean motion seems 
to be radial (as in the Hearthware, although it's much less vigorous).  Once 
the whole bean mass "fluidizes" (and adopts the predominantly tangential 
"swirling" motion characteristic of the Rosto) that radial motion becomes much 
harder to observe, although it must continue.  It might be an interesting 
experiment to put some "marker beads" or other "visualizer" in with the beans 
to determine actual mixing patterns.  I believe, based on roast outcomes, that 
mixing is sufficient . . . but greater airflow at the beginning of the roast 
(drying phase), and less toward the end when bean motion can become "over 
vigorous" (even throwing beans into the chaff collector) might be worthwhile 
(the Rosto actually does this to some extent itself, as the chaff filter clogs 
and restricts airflow).  Of course any deliberate adjustment of airflow implies 
corresponding adjustment of heater input to maintain proper air temperature . . 
.. and on it goes, in ever increasing complexity . . .
Deward
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