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A leetle thermodynamics!

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Peter Lissaman

A leetle thermodynamics!

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.

============================================================
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

Victoria Hughes

Re: A leetle thermodynamics!

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.
>
> ============================================================
> 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
>

Owen Densmore

Re: A leetle thermodynamics!

Administrator

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.
>>

Robert Howard-2-3

Re: A leetle thermodynamics!

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

-----Original Message-----
From: [hidden email] [mailto:[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:

============================================================
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

Steve Smith

Re: A leetle thermodynamics!

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.


============================================================
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