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Topic: Turbo-Crazy/Roaster Design - please help (3 msgs / 138 lines)
1) From: -S
I've been using  a Turbo-Crazy since January and I really like the
performance and capacity.  It matches my usage pattern to roast several
batches of different greens, in say 300gram (~10 ounce) lots of each.  It's
nice to have the flexibility to roast a 500gm (~1.1pound) at a time when I
feel like it.
I think Peter Bishop did a great job of explaining the needed mods, which
are minor.   The (plastic) threaded shaft of the StirCrazy takes 3mm nuts
with a 1mm thread - from Sears hardware for example.  I'd suggest filling
the shaft with metal nuts to increase the heat capacity.  Also use Peters
Copper end-pip and some aluminum foil to cover the center.  A springform pan
~12 inch diameter makes a nice collar - tho' it is not absolutely necessary.
Aside from that it's a mater of replacing the plastic top with a Turbo
cooker.  The Galloping Gourmet unit is out of production, but uses
1450watts.  Most others on the market are around 1200 watts.
Nice to see Ryuji Suzuki's comments; I understand Ryuji is the originator of
the Turbo-Crazy.  I used to pine for a Turbo Suzuki when I was younger, but
I'm almost as thrilled with the coffee roasting variety as the motorcycle.
== == == ==
A project the periodically forces itself into my consciousness is making a
fluid-bed roaster with a max capacity around 500 grams(1.1lb) of greens.
Something like the 1.25lb test unit on the Sivetz website.  I feel it must
be controlled electronically so electrical heating is probably a
requirement.
In Sivetz book, "Coffee Technology", there are several *implications* given
that shorter roasting times make for better coffee.   Yes, these mean less
loss of weight which is important to Folgers, but also supposedly give
better flavor.  They show commercial roasting times dropping from 30 minutes
a century ago to 5 minutes circa 1942 !   Any comments ?   Is 10-13 minutes
too long a roasting period ?  Is shorter really any better ?
When I try decreasing the roasting time on my turbo-crazy the roast comes
out less even - which is a negative.http://www.sivetzcoffee.com/Also the book notes that coffee roast in an environment where the hot
roasting air is recirculated are thermally more efficient, but the resulting
coffee is inferior in flavor - bitter and acrid.  I've seen some amateur
web-designs that intend to recirculate the hot air and it seems like a bad
idea.  Perhaps even the turbo-crazy is a bad idea because it recirculates,
but it leaks like a sieve so I don't think it's quite so problematic.
Fluid Bed Flow Rates:
For anyone interested in designing a fluid-bed roaster, the book confirmed
my estimation that a 3000 ft/sec stream of air is needed to loft a bean
(3000 ft/min * aperture size in square feet  = the fan req in CFM).  IOW
terminal velocity of a bean in air is about 35mph.  A "funnel" with a 1 inch
diameter entry has a cross section of abt 0.0055 sq.ft, so requires a 16 cfm
fan *minimum*.  A 4 inch tube would require a 600cfm air source.  I can now
see why most fluid beds use a small cross section "spouting" area for
lofting and a larger area for re-entry inrto the loft area.  Seehttp://www.sivetzcoffee.com/Fluid%20bed.htmdiagrams.
Energy:
Roasting beans requires about 250BTU per pound applied to the beans.
Heating the air for a continuous commercial system  (sort of a cross between
a buzz-roaster and a fluid-bed) almost doubles that load - bringing it to
about 460BTU/lb.  This is about 485000 Joules/lb [more metrically 1.07
mJoules/kg].  One Watt-second is a Joule of energy, so roasting a pound of
coffee with a 100watt turbo top should require about [485000/1200 = 404
seconds.] 6.75 minutes.  In reality our tiny roasters (like the Turbo-Crazy)
have a lot of heat losses so it's no surprise these take 10-13 minutes.
They must be around 50-60% energy efficient.
The losses in the popcorn poppers must be tremendous.  These have around 1KW
heaters and still take 10 minutes to roast a mere 1/4lb.  That's around 20%
efficient.
If we can keep efficiency around 50% (which may be hard for fluid-bed) and
can accept 10 minute roast times, then we need around 1800 watts of heater
capacity for a 500gm roaster.  Downsizing the unit to 250gram (half pound)
capacity might not decrease the power req too much since efficiency would
drop too.  I probably was a 2KW or 2,5KW heater feeding a smaller diameter
duct.
I'd be very interested on ideas regarding a larger capacity fluid-bed
roaster.   Any ideas or sources for heaters fans and pyrex or borosilicate
roasting chambers  would be appreciated.
-Steve

2) From: Peter Bishop
Steve's post was interesting reading.  Like others, I'm looking at the
(min)500g fluid bed design, and the technical data in the post was
interesting and educational... especially for someone who didn't pay too
much attention when it was being rammed down my throat all those years ago
:)  I'm now trying to get my head around the theory of fluid bed flow rates
and energy figures... although I'll probably go for the "proof of concept"
route with a shop vac, propane burner and various bits of tube :)
Cheers
peter

3) From: Peter Bishop
Thanks for the compliment :)  I've been messing around with my web page, and
if anyone's interested I've got a description (with pictures) of the my
Turbo-Crazy modifications.  The site is the standard "work in progress"...
and has just been stripped down from it's original vanity-publishing concept
:)  The idea now is to use it for sharing useful information... I hope this
is a reasonable start.http://www.bish.ws/coffee/TurboCrazy.htmlCheers
peter


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