HomeRoast Digest


Topic: Mini turbo charged mod for the RK drums (3 msgs / 91 lines)
1) From: Douglas H. Boutell
  I made a modification to the RK Drum with a
air scoop that seems  to make an improvement
in roasting time and flavors. So far I have tested
three Kenyas and all have benefited from the
air scoop. Yes the workmanship is sloppy but it's
still in the testing stage and more mods will be
needed to determine the final size.http://www.homeroasters.org/php/forum/viewforum.php?forum_idDoug

2) From: Scott Marquardt
I'll tell you something though, the improvement isn't happening for the
reason you think.
Against all intuition, I assure you that the scoop is actually causing air
to flow exactly in the opposite direction than you expect.
:-\
Weird, but true. But the funniest part is that if you're seeing better
efficiency, it's on account of increased airflow through the drum resulting
from a flow path that's contrary to what you were trying to achieve.
When you think about it, though, that makes sense. An exact opposite flow
would have the same effect.
However, this means that your first crack is actually your second, and your
second is actually your first. This makes stopping a roast between first and
second crack impossible unless you spin the drum in reverse. In that case,
be sure to reverse the polarity on your thermocouple connector.
;-)
In all seriousness, when my machinist and I built the ring roaster (http://scott.marquardt.googlepages.com/openskyroaster) we implemented 6
substantial scoops on the outside of the drum halves (if you look at the
picture of the entire drum assembly, the two inner donut rings that extend
an inch beyond the drum radius [on either side of the stationary ring in the
middle] were the anchor for the vanes, six on either side, with closed ends
at the outer extremity of the dum halves). We imagined we'd then use the
fill port in the top of the stationary ring as the exhaust. But lo, we
discovered that our "exhaust" was exhibiting a minor suction. Far from
creating the howling turbine we gleefully thought this would be, we
discovered that we didn't know jack about how this stuff works.
We even extended the scoops dramatically around the circumfrence -- no
change. Instead of making air flow inward, they made it flow outward.
This was one of the most bizarre experiences we had, in an otherwise very
successful engineering effort. I think the both of us are still needing
serious therapy for our intuitions, which were left pretty much in tatters.
You could probably improve the efficiency by just making a flat vane
sticking straight up from he drum surface.
Seriously. Don't be incredulous, trust me. This is weird stuff.
- Scott
On 11/11/06, Douglas H. Boutell  wrote:
<Snip>

3) From: Douglas H. Boutell
This is a multi-part message in MIME format.
Scott Marquardt wrote:
<Snip>
Scott,
The only thing I was trying to achieve was airflow through the drum and 
nothing else.  I designed  a smaller  drum
  5" dia by 8" length  and  the optimum load was for 12 oz of dry beans 
which met my needs.  Before I added the scoop I  roasted
16 ounces with my  profile for the 12 oz setup the roast would took  
about 19 :15 min and tasted flat.
I tried 18 oz this weekend with my standard profile  and the roast 
finished 15:45 roast time  about 20 sec longer than than
my 12 oz setup . The scoop seems  to  improve the  caramelized  flavors 
and  efficiency. I also roasted one of Tom's
screaming bright Kenya's to  a Cinnamon Roast and the acidity, well was 
not the screaming bright that you would expect
but very good.
Doug
<Snip>


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