[Homeroast] On Topic: Popper-Roasting

Brian Kamnetz bkamnetz at gmail.com
Thu Jul 11 14:37:22 CDT 2013


Martin,

Thanks for looking that up. It's interesting to note that there is an
actual, recognized variance due to moisture content of the air, which
validates my notion that it could have an impact (I wasn't sure before,
just had an untested notion). I had trouble with the last little boost to
first crack, so humidity could have a small, but still significant, effect.
Add a couple other things (e.g., the difference between semi-arid air at
6500 feet above sea level vs. saturation pretty close to sea level; and
maybe some difference in electrical power from the socket) and it could
explain the troubles I was having roasting with poppers in SC vs what I
experienced in NM.

Brian



On Thu, Jul 11, 2013 at 2:04 PM, Martin Maney <maney at two14.net> wrote:

> On Thu, Jul 11, 2013 at 11:04:11AM -0500, Brian Kamnetz wrote:
> > I roasted with a stock West Bend Poppery 2 for several years. First in
> New
> > Mexico, where it worked fine with 1/2 cup of greens. Then I moved to
> > Columbia SC and could hardly get the beans to roast, in two different
> > buildings. The roast would get close to done, but then could barely be
> > coaxed over the top. (I removed the bimetal thermostat.) I finally
> settled
> > on an untested hypothesis that the increased level of moisture in the SC
> > air took more oomph to heat; my analogy, maybe bogus but the best I had,
> > was that if I were to run pure water through the popper it would never
> get
> > close to roasting temps, so as the level of moisture increased (and there
> > was a LOT of moisture in the air in SC compared to NM), it seemed it
> would
> > take more oomph to heat the air. Another possibility, one that I could
> not
> > test, was that the power level in the outlets was lower in SC than in NM.
>
> I've often heard, and have repeated, the "moister air takes more heat"
> (for a given temperature rise), and it's true, but it's always been
> handwavy - no real idea how big a difference it makes.  So I had a few
> minutes and went a-googlin' in search of answers, and if the numbers at
> www.engineeringtoolbox.com aren't all wrong, the difference it makes
> is...  pretty small.  For saturated air at 25°C, the water vapor adds
> about 4%.  The energy per degree of both change somewhat with
> temperature, but ignoring that, let's calculate a bit...
>
> Assume a heater power and volume of airflow with a 200°C rise between
> the inlet and outlet.  If we change that to air with 100% relative
> humidity (which is about 2% water by weight), the outlet temperature
> will be reduced by 7.2°C if I've got this right - call it 13°F, so it's
> the same as if the ambient temperature changed from an afternoon high
> of 85 to an evening roast-time reading of 72.  Or in yet other terms,
> it's as though the heater power were reduced about 4%, equivalent to a
> 2½ volt drop from a nominal 120V.
>
> martin "never met a problem that didn't go better with numbers" maney
>
> --
> Here's my message to the record industry and its allies:
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> thief, I won't be your customer.  -- Dan Gillmor
>
>
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