Posted by
Steve Smith on
Apr 13, 2009; 2:18am
URL: http://friam.383.s1.nabble.com/A-leetle-thermodynamics-tp2618412p2626055.html
Robert Howard wrote:
Microwave ovens, gas stoves, coal stoves, fireplaces, and solar cookers; all
have a price-time tradeoff. The solar cooker is slow and cheap. Most people
would rather have an option and the freedom not choose it, than no option at
all. For a $50,000 prize, I wish I invented it. -- Rob
I *did* invent it. In 1970. Where's my $50K?
After our Jr. Hi teacher showed us how to make a parabolic reflector
from cardboard, and then cover it in aluminum foil... I went home and
made my own bigger one to see if I could "melt things", not just boil
water.
I still have some scars on my foot from when the coffee can filled with
old bullets dug out of the backstop at the local firing range gave way
at the seams... it seems the solder melts at just a slightly higher
temperature than lead... just enough to carry the can a couple of feet
with some tongs before it gives out and splashes hot lead down your
pants-leg and into your shoe.
Impatient and curious, and with lots of cardboard/aluminum foil on
hand, I did almost exactly what this new "invention" showed. I painted
the inside of a box black, I put it inside of another box stuffed with
newspaper but lined with aluminum foil (having been taught that the
aluminum foil would reflect infra-red radiation (heat) back into the
box as the "black body" heated up. I covered the box-lid (as with
the example here) with aluminum foil but I also made aluminum covered
"gussets" to fill the corners and hold the lids open like petals at
what I calculated (geometrically by folding cross-sectional models) to
be the optimal angle for directing extra sunlight into the box. I
covered the "cooking chamber" with Saran Wrap the first time... that
did not turn out too well... Then I found abroken window pane and
made my father teach me how to cut glass (he was quite pleased to get
to teach me something since I normally didn't like letting him teach me
anything) and when fitted to the box, I was able to heat any number of
things to "cooking" temperature in an hour or so... It was late spring
in the desert, so it really wasn't that much fun, you could have nearly
the same effect just by piercing the top of a can of "lunch" and
leaving it on the dashboard of your car. It was at least as much fun
to wrap up some stew meat with some potatoes and carrots in aluminum
foil and put it on the manifold of your parents truck and then surprise
them when you got to the camping destination with the smell of
(usually, mostly) cooked stew. The overtone of burned oil from the
leaky valve-cover gasket was a bit distracting, but what the hey.
I applaud the first world's desire to solve the third world's
"problems" with cleverisms like this, unfortunately, I think the
results are hugely confounded by lots of non-technical factors, and
when we *do* manage to resolve one set of overt problems with our
technology, we often create other, less obvious, unintended ones.
In more than one location in the deserts of the middle east, the
villagers who used to have to walk miles to a centralized hand dug well
where they exchanged gossip (aka news) every day suddenly could stay in
their own villages because of wells with hand pumps within a hundred
yards. They spent less time gathering water and became completely
alienated from their neighbors and with the addition of
draft-animal-drawn pumps, became more wasteful (or generous as you
might want to call it) with the water, lowering the water table far
enough that the shallower wells had to be drilled deeper which just
aggravated the problem.
In Bangaladesh the people all took their water from standing, bacteria,
virus and parasite infested waters and had high death rates and often
miserable lives. We came in and drilled them wells deep enough to
avoid contamination, and it took 20 years or more to realize that there
was a new set of horrible symptoms caused by the arsenic in the water
that we didn't know or think to look for. Maybe they were better off
dying of arsenic poisoning in their early adulthood rather than various
diseases in their infancy. It is hard to tell.
In Africa, we provided wonderful high-quality hybrid Sorghum plants to
replace the low-yield sulfurous Sorghum the natives used. Once a
number of seasons had gone by and all of the "yucky, low yield" Sorghum
had been displaced entirely and the locals were enjoying significant
increases in wealth, a periodic plague of locusts came through and
completely destroyed the crops that year... yielding an overwhelming
famine. In the past, the sulfurous, low-yield sorghum survived the
locusts enough that not only did nobody starve, but there was seed for
the next year's crop.
In Mongolia, the Soviet Union built concrete apartment buildings heated
by the plentiful fossil fuels they brought in by pipeline. Most of the
folks living nomadically in their age-old way with yak-felt Ger's
(Yurts) gave over and learned to live in concrete apartments with
central heat and food from the markets. Several generations (50
years) passed and all of the old ways were forgotten. The Soviet
Union collapsed and not only did the well-meaning Soviet Bureacrats
leave, but they took their natural gas and oil with them, leaving a
people with inherently unlivable concrete caves to live in and no
residual skills for living in "the old ways".
It is bad enough when we outrun our own headlights but when we
encourage people who have steady-state ways of living to join us in our
breakneck rush into the future, we are not always doing them favors.
I'm not saying it never works out, I suspect it often does, I'm not
really trying to be a wet blanket nor a Luddite, but I am chiding us on
"local optimizations" like assuming that trading in the burning of wood
or charcoal gathered or made nearby for something very low tech by our
standards (but high tech by theirs) like cardboard boxes, aluminum foil
and acrylic or glass covers is not always the win we assume it is. And
I also don't think most of us think about how these new technology
"prizes" are going to be integrated into everyday life and culture.
If/when/as such things *do* get integrated, they surely have the chance
of improving lives, decreasing long term degradation of resources, etc.
Wikipedia gives "the 1973 fuel crisis" as the date of emergence of the
term
Appropriate
Technology and proceeds to define it mostly in terms of lowering
the capital investment and maintenance aspects of technology (in
natural reaction to the huge amounts of unsustainable tech we exported
during our various waves of colonization). I heard about it in the
late 70's from some friends working in South America trying to
introduce the "Coffee Can Twig Stove" as an alternative to other forms
of cooking/heating. They used the term to focus on both technological
and cultural "appropriateness" and were struggling to understand the
various peoples they were interacting with enough to know whether these
"twig stoves" made from a simple tin can (nominally a coffee can, but
usually a large can of other rations) could ever catch on. Sometimes
they did, sometimes they didn't, and often for reasons they could never
have guessed.
It is interesting (to me) that many of these "low tech" solutions are
centered around high-tech materials we consider to be waste (cardboard
boxes and steel food cans)... perhaps there is a hint in there
somewhere. It is also interesting that we seem to be most concerned
about the "energy use" in the third world everytime our own energy
sources get threatened (1973 crisis, current crisis).
I think I'll go see if my dinner is done, my truck has been idling for
most of an hour... surely the stew is done by now!
- Steve
-----Original Message-----
From: [hidden email] [[hidden email]] On Behalf
Of Owen Densmore
Sent: Saturday, April 11, 2009 4:04 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: Re: [FRIAM] A leetle thermodynamics!
As usual, Wikipedia has some info:
http://en.wikipedia.org/wiki/Solar_cooker#Using_a_solar_cooker
Looks like Peter is right about the time it takes. Pretty slow
process, but that may not be as big an issue for the users compared to
gathering fuel etc.
-- Owen
On Apr 10, 2009, at 8:40 PM, Victoria Hughes wrote:
Hey, that is a pretty cool bunch of information.
Egyptian Ice, eh - a new delicacy, only for heirophants.
How did they know to do that? Arabs?
Sounds Tom Robbins-y. Love it.
Tory
On Apr 10, 2009, at 3:25 PM, Peter Lissaman wrote:
Solar cookers can break your heart, but not the laws of
thermodynamics. Consider this elementary fact, my dear Dr. Watson.
The insolation on earth near the equator is about 800 W/m2, it is
less at the end of the day, and much less after sunset. For an
aperture of 0.1 m2, you getting about 80 W black body, ignoring
losses. Concentrators have nuttin to do with it! This amounts to
about 270 BTU/hr from which you could boil a bit less than 2 pints
of water in an hour, assuming no losses.
BTW, you can, with care and ceremony, make ice in the Egyptian
deserts every cloudless night, by exploiting radiation to the stars
from shallow water trays, and careful control of nucleation,
convection and vaporization. In fact, the temple priests used to do
it on the flat roofs of the temples to impress the unwashed on the
bounty of whatever God they were scamming that week. Much hoopla,
involving sanctified water brought up from the basement (where it
had got pretty cool, mixed with yesterday's ice), throwing holy
dust on the surface (to provide nucleation particles) and wafting
the surface at just the right time and rate with magic ostrich
featherwands to actually control heat transfer due to convection
and vapors. It's just thermodynamics, Nefertiti! And if sometimes
the ice didn't form, it was because someone's mother-in-law was a
witch! It's amazing what them religious guys know!!
I usedta teach elementary courses in thermo in CA and the
conversion constants are from memory and only roughly correct.
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FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at
http://www.friam.org