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http://www.worldaware.org.uk/awards/awards2001/mobah.html

Have a look at this great invention from:
Mohammed Bah Abba

hmm i am surprised thet they haven't used it already there :o this invention is at least a few hundred years old,in greece and roman empire they used it a lot.I remember constructing one of those for myself from a pot for flowers,when inspired by history classes book (i was mybe 12 years old that time )  :)
So at least it is wel tested ;) i hope they will use it!

What's interesting here is that we have a sustained and confined heat differential.
How do you turn a heat differential into an energy generator? Personally I don't know how to do that, but maybe someone has an idea.

Let's brainstorm everyone. Throw out some ideas if you have any.

Just a silly idea, running a pipe filled with liquid through a large apparatus, the cooling would cause the liquid to flow downward,  heat on the outside would cause the liquid to warm and rise, producing a liquid flow that might move a water wheel (fan?). The sun would power the whole unit by evaporating the water from the pots.

Just an idea, even though the sketch it very crude, I think you get the gist of it.

Thanks for your interest.

ResinRat2:

Why not simply have a matrix of pipes painted pitch black (or covered with tar paper or something to absorb heat), joined to another matrix, either buried in the ground or at least in the shade. Fill that with whatever fluid. Plop a turbine in the middle. You gotta heat-diff turbine. Hook the turbine to a generator........
Hmm....what if there was no sun out? Then maybe the option to bury the cooler side in the ground would be better. As long as there was a difference in temp between either side, there will be a movement of the fluid.

8)

Quote from: ResinRat2 on April 29, 2008, 10:21:12 PM
What's interesting here is that we have a sustained and confined heat differential.
How do you turn a heat differential into an energy generator? Personally I don't know how to do that, but maybe someone has an idea.

Let's brainstorm everyone. Throw out some ideas if you have any.
[/quote

Hi ResinRat2,

  Try to get the solar cooling out of your head, but I have a working idea as to how you turn a heat differential into an energy generator>
  Heard about the Seebeck effect? There you get DC from a very simple model of heat differential.
  19th century discovery, college level physics.

  Regards,

    laci

Quote from laci:

"Hi ResinRat2,

  Try to get the solar cooling out of your head,"

Actually, I am obsessed with this notion. Many people here are searching for the elusive "zero-point" energy, but I believe we need to focus our attention on the SUN. It runs this planet and drops kilowatts of energy per square meter on the earth's surface each day. I believe even Linnard Griffin's Electrolysis Process uses its endothermic nature to take advantage of the sun's heat. So I am inclined to be drawn toward exploiting the sun's naturally available power to run the world on. Anything that produces a temperature difference can be used to produce power.

Thanks for the Seebeck idea. It looks interesting and could easily apply to this "solar cooler"

I was just throwing out ideas, not necessarily something that I would pursue, just something that looked simple and easy to experiment with. Heck, I even went out and bought two clay flower pots, one that fits inside the other, and some sand to see if I can duplicate this temperature differential and take some measurements just for fun. I am still working on my hydrogen reactor, but this is just something quick and dirty that I could look at. I guess I just like to research stuff; even in my spare time. I guess you can see that I'm not a "party" type of guy. LOL!

Although I don't really follow how exactly a simple two pot setup is used
to provide cooling from sunlight (couldn't run the .mov for some reason),
it seems to me that a sustained temperature difference should allow
for the use of a simple thermocouple to produce electrical output?
Depends on the temperature difference, of course... ;)

Hi Koen1,

The simple process involved is merely cooling by water evaporation. The center pot is cooled by the water evaporating from the sand around it. Apparently it is cool enough to preserve vegetables for three weeks that normally spoil in three days. So it must be in the very low 50 or mid 40 degrees F; and it looks like this is in a very hot region of the earth. So we could probably guess a 25-35 degree difference in temperature at least. Probably even more on a hot day.

Based off your noted Seebeck effect, I wonder what kind of current is possible from this temperature differential?

This is just an idea, something I probably wouldn't be pursuing at this moment in time; but maybe possibly later on. I still need to do my experiment with the clay pots just for fun. I am curious what kind of temperature difference I could see.

ResinRat2,

I was inspired by your interest in this 2 clay pots thread to post the item on Donkey's solar refridgerator.

In that system, the stovepipe is painted black and powerfully draws the air into the lower part of the system, and across the water evaporator which is the burlap bag. This cools the air inside the walk-in cooler. In fact there is even a draft controller to slow down the breeze to keep things from freezing.

But in addition to this cooling, The moist breeze is drawn across the aluminum cans that are sticking out of the entire inside wall of the walk-in cooler.

I am not sure what it is called, but cold moist aluminum boosts the cooling process.

The proximity of the cold cans and the hot stovepipe would make it easy to rig up a thermocouple, I should think.

I just thought I would draw your attention to the design, in case you missed it.

thank you,

jeanna

Well, here is my attempt at a simulation of the two-pot cooler.

The larger clay flower pot it 11 inches across and tall, the smaller clay pot is 9 inches across and tall. The space between them was filled with fine playbox sand. I covered the bottom holes with plastic, but the inside pot water bubbles into the pot so I placed a layer of aluminum foil on the inside to protect the contents. Aluminum has a fantastic heat transfer rate so this should work well.

The first thing I noticed was that the water soaked from the inside to the outside surface of the clay pot, so this is how this unit is working. The water evaporates from the outside large surface area of the outer clay pot and evaporates, drawing heat from the center inside pot. I covered the top with a shami type rag that I soaked with water. I want to see what type of temperature differential I can cool the soda-pop cans down to after a day or so. Also, I am keeping the unit in my basement so I can maintain a somewhat controlled temperature and humidity environment.

I will keep you all periodically posted on what I find.

Thanks for your interest.

P.S. Now I am going to work on my hydrogen reactor. Wish me luck.

Thanks for your interest

G'day all,

I don't know why everyone gets so excited about this. Evaporative cooling has been used since antiquity. Unglazed pottery has been used from Babylonian times to cool liquids, so have goatskin bladders. In Australia the technology is used in the outback. The typical "bush fridge" is no more than a wire cage with a cloth wrapped around it that trails in a container of water. When outside temperatures are beastly hot (It can get to 55 degrees centigrade in some places) we hang a bed-sheet over the windows inside, like a curtain, and put the bottom end into a bucket of water. It works a treat.

Am I missing something here?

Hans von Lieven

I wonder how well this would run a Sterling Stirling engine.

After all, I had one made from a tuna tin that ran from the heat off the palm of my hand. All it needs in a differential. Sounds like there is differential with this.

If interested there are plenty of web sites for this engine.

Hi Hans,

The purpose of this experiment is to determine the actual heat differential that can be achieved. Then see if the localized heat sink can be used with the Seebeck effect to produce an electrical current from the heat differential.

It's just an investigation into converting evaporation of the water directly into a constant electrical current, that's all. This is the first time I have heard of this effect, so please don't be too hard on my ignorance on this subject.

I just found it interesting. Thanks.

Sorry Dave,

I didn't mean it like this. I was just surprised that evaporative cooling was such a new area for so many. You can get much bigger effects if you use liquids other than water, like alcohol, ammonia or ether. Ammonia was used in absorber fridges and in ice production in the old gas works that used the waste heat to produce ice. Fascinating technology.

Hans

I just found it interesting. I could use just water to produce the heat differential. Since the Seebeck effect that laci mentioned can produce a current from a heat differential, I just figured that something like this, with the localized heat differential, could produce an electrical current for FREE. You know, like power produced from a natural, renewable resource. LOL!  Namely, the Sun's heat.

HEY! That's called overunity. :D

That's why I was interested. I just have not heard of anyone putting these two technologies together to produce a constant electrical output.

Just some crazy idea that crossed my already overloaded mind. :D

Quote from: hansvonlieven on May 08, 2008, 09:19:50 PM
I was just surprised that evaporative cooling was such a new area for so many.

Hans, I guess many people have grown so accustomed to refrigerators that they
don't really know the old technology anymore...
Your example of hanging sheets in front of the windows with the bottom sticking in a
bucket of water is one I hadn't really heard before. I suspect it doesn't work as well
in very humid areas (like the Townsville region for example) ? Nice application though.
I was told stories of similar "bush fridges" when I lived in South Africa, by old people
who still remembered the days they didn't have any electricity nor electrical cooling.
A few described a cooler box that had cloth wrapped around it which was either regularly
watered by hand, or was hung in a vessel containing water to soak it up. The box itself
would be either fine wire mesh to allow air to move through the box, or it would be
a metal box. One old lady told me how they used a slightly different mechanism
where water from a container on top of the box was allowed to flow down the fine
wire mesh box and collected at the bottom, and part of the water would evaporate
during the downflow of course, cooling the box and contents.
Works like a charm, if you have enough water to waste on evaporation. :)

Well I have some results from my two pot experiment.

I took four readings over the last 36 hours.

The first was about two hours after the unit was built, then I took another 12 and 24 hours after starting. This test as run in my basement which has a pretty constant temperature and because I have a dehumidifier going constantly, the humidity level should be pretty well controlled and constant.


Elapsed Time (hrs:min)         Air Temp(F)                     Inner Pot Temp(F)                     Differential(F)
    2:00                                             63                                     57                                        6
   12:00                                            63                                     57                                        6
   24:00                                            65                                     57                                        8
   36:00                                            65                                     57                                        8

So It appeared to have stabilized at 57 F.

I then transferred the unit outside into the sunlight. It sat in the sun for an hour and I took the following readings.

Elapsed Time (hrs:min)      Air Temp(F)                     Inner Pot Temp(F)                    Differential(F)   
  1:00                                         75                                     60                                        15
  2:00                                         75                                     61                                        14
Which is where it stands now. I want to let it sit in the sun for several hours to allow the unit to equilibrate. I was actually hoping the temperature would drop, but so far this did not happen.

Just out of curiosity, does anyone know what type of heat differential is required to run a Stirling engine?
I'll see if I can find the information.

Thanks for your interest.

Here's a link:
http://www.howstuffworks.com/framed.htm?parent=stirling-engine.htm&url=http://www.stirlingengine.com/

This unit runs on a temperature difference of only 7.2 degrees F.

Could this have possibilites?

Hmmmm... I'll have to think about it for a bit to see if I could dream up a configuration that could utilize this temperature difference with a small stirling engine.

Thanks for your interest.

Actually, reading on how the Stirling engine works, all I would have to do is place the base of the engine on the moist rag that covers over the top of the unit. This temperature differential should then start the engine operating.

Could it be that simple?

I wonder what type of differential a really LARGE pair of pots would create.

Does anyone out there own a small Stirling engine and would be interested in trying this?

Thanks for your interest.

G'day Dave,

The answer is yes, Stirling motors have been built that use evaporative cooling to increase output. The so called dipping bird or its more modern version the Minto wheel also rely on evaporative cooling for their effect.

Hans von Lieven

Hi Hans,

I think I remember you saying something about submarines that used stirling engines. What was the substance that it used to store the heat? Something about a tank filled with this component that held heat for the engine. I'm thinking of filling the center pot with whatever that was, that way it would be easier to hold the temperature difference.

Thanks

Aha!!  Found it:

aluminium oxide pellets

Thanks Hans!!

G'day Dave,

From memory the medium to store heat were aluminium oxide pellets.

Hans

LOL  ;D ;D ;D ;D ;D ;D ;D

I love those simultaneous posts

Sure the application has been around for ages...

Swamp Coolers are used in dry regions to add water to the air for cooling...

While AC is used in damp regions to remove dampness from the air...

But the idea is not bad at all clay pots enable a similar reaction without the need for electricity this is the importance of this discussion.

No electricity and cooler temperatures!

That is the punch line folks and that is what interests people!
-----------------------------------------------------------------------------------------------------------

I have an excellent solar expirament I wish to share with everyone.

I will gladly do so in another thread soon.

I guess though that people in regions with a lot of available water all know
similar traditional and relatively intuitive ways of using evaporative cooling...

And it seems to me that the main areas where cooling is needed,
the very dry and hot zones of the world, also have very little water
to go around, and thus they also have less water available for
evaporative cooling systems...
So it's still not a solution for the Sahara for example.

In such regions a form of cooling that converts heat directly into
electrical energy would be much more usefull. But those systems
are still far from available. The only system I know of that actually
converts ambient air temperature into additional electrical output
is this: http://jnaudin.free.fr/html/nzaevncp.htm (http://jnaudin.free.fr/html/nzaevncp.htm)
And that needs special ferroelectric capacitors that are apparently
not available at all...

Hi Koen1,

In desert areas this won't be an option. I am thinking more along the lines of it working in more temperate regions where water is available. It doesn't have to necessarily be drinking quality water either. All I am looking for is a sustained temperature difference.

The Seebeck effect looks like it produces very small amounts of output. So maybe a Sterling Engine may be more of a possibility. Even these seem to be very weak, from what I have read so far. Aluminum oxide pellets were mentioned as holding heat. I am thinking that it would be better if the material in the center pot would give up its heat quickly rather than slowly. That way the center would give up heat faster and produce and maintain a temperature differential at a faster rate. Filling it with aluminum, which gives off its heat quickly, would probably work well. This is something I will try in the future. Maybe even just putting a aluminum sided pot, or aluminum pellets in the center pot would work better. That way a larger heat differential would form more quickly and keep up with changing air temperatures.

Just some thoughts I had. Right now I want to work on my other project, so I will return to this at a later date.

Thanks everyone for your interest.

G'day Dave and all,

The best evaporative coolers used to be the old fashioned canvas bags. Here is a picture of a really pretty one, most were without decorations. (https://overunityarchives.com/proxy.php?request=http%3A%2F%2Fi16.ebayimg.com%2F06%2Fi%2F000%2Fef%2F58%2Fccb3_1.JPG&hash=a6a35eddca1d13f1a1b92b5ba96073c397cc08d1) You simply fill it with water, a little keeps seeping through the canvas and the evaporation cools the water inside. In Australia they are still in use in the bush. People hang them from bullbars, motorcycle handlebars and horse saddles.

The best temperature differential can be achieved by using the liquid itself for lower temperature source. As far as I can see the two pot system is only there so that dry matter can be cooled without getting wet. It is not as efficient as direct evaporation.

Hans von Lieven

Hi Hans,

Yes, that bag is very pretty indeed. LOL!     :D

So how could this bag be designed to run a Sterling Engine from the heat differential? That's the question.

Simply by using the bag as a reservoir and feed the cool water into the jacketed working cylinder, than recirculate it back into the bag. The bag would need to be large with a big surface area.

Hans

EDIT Or simply wrap a rag around the working cylinder and dribble water on it

What about using a peltier junction along with these systems to produce free electricity?  Put the cold side to the cold, generate power, put the hot side toward the hot, more power.  Just a thought.

Bill

Hi Bill,

That was mentioned earlier in the thread by laci as the Seebeck effect. You mentioning the Peltier effect, or it's related title of  the Peltier?Seebeck effect. Personally I am not sure how to do this. What specific piece of equipment would be used to initiate the electron flow?
I assume you mean a thermocouple. I am just not sure what type of thermocouple to use, and from what I have read so far, the amount of electricity produced would be very small. I might be wrong.

Any suggestions that anyone has I am open to right now. To me this is interesting that you can have the sustained temperature differential.

ResinRat2:

I don't know any more about them except I have seen them in a few surplus catalogs for reasonable prices.  I know they are used in the 12 volt cooler technology (we made some of the original ceramic parts for that) and also, the small things that keep coffee hot.  I know you can power them to have a cold side and a hot side and with no power, if you heat and/or cool the appropriate sides, it produced electricity.  I know nothing of the efficiency ratings for these devices, or, if they are indeed related to thermocouples.  Thanks for telling me the complete name, I did not recognize it by the Seebeck name. I learn something new here every day.

Bill

@Hans: nice pic of a waterbag :D
When I lived in South Africa I used to go out camping and fishing etc
in the bush every weekend with some friends, and one of them
always brought a couple of oldfashioned leather waterbags along.
He hung them off his bullbar and a tiny bit of water would seep out
and evaporate, that and the cooling effect of the air rushing past it
kept the water nice and cold.

Another 'trick' I saw that guy pull was to dig a shallow hole in the ground,
put your beer cans in the hole, cover it up with sand again, and then just
pour some water over the spot every now and then. The water evaporated
and cooled the sand layer just under the surface enough to keep your
beer cool. ;D

Although of course if you have enough water it is easier to just put the
water in the shade and put your beer cans in the water...

Funny enough the native bushfolk seemed to know the principle of
evaporative cooling too, but they apparently didn't grasp the concept
of condensation to obtain clean drinking water...

@ Koen1:

Who needs clean drinking water when you have cold beer? (ha ha)


Bill

Quote from: Pirate88179 on May 14, 2008, 12:01:58 PM
Who needs clean drinking water when you have cold beer? (ha ha)

:D Hehehehe Good point Bill! ;)

I  always knew I would return to this project someday. I was looking at a posting by member jeanna at :

http://www.overunity.com/index.php?action=dlattach;topic=4627.0;attach=23007

that showed Donkey's solar refrigerator. This led me to consider using a stirling engine on top of the flowerpot system to see if it could give a continuous running motor that kept the temperature differential intact even with a stirling motor running on the top of the system.

The first picture shows the two clay flowerpot design that has aluminum oxide filling the center pot and sand and water filling the outer ring between the first and second flowerpots. The hope here is that the aluminum oxide center will cool or heat up at a different rate than the outer ring of sand and water as that area cools. This should draw heat away from the center and always keep the temperature difference as the water freely evaporates.

The second picture shows the same system except that now a stirling engine is resting on top of the aluminum oxide center and the area around the engine base is insulated with a wool ring to isolate it from the environment. That way all the cooling will be from the water and sand ring around it, and all heating will be from the stirling engine. I researched the specific heat values of aluminum oxide, clay, and quartz sand. These gave values of 0.21, 0.33, and 0.19 (cal/g/^oC) respectively. I am hoping this will allow the outside pot to always cool faster than the inner core.

My hope is that no matter what the outside temperature is, there will always be a temperature differential that will keep the stirling engine operational. As long as the whole system is above freezing temperatures of water that is. Although it might even work below freezing, I don't know for sure until it is tested.

I should receive my aluminum oxide in three days. At that point I will put the system together without a stirling engine and run it for several days with a temperature probe in the center. I will record the temperature differential between the system center and ambient temperature and see what kind of difference will result. This will let me know if it is worth it to purchase the engine. I saw one for about $100 US dollars that doesn't seem too unreasonable.

Thanks for your interest.

RR2

Interesting idea, that. :)

It reminds me of an idea, not sure who came up with it first, but
it is beginning to see a bit of revival recently in the sustainable energy
industry, anyways, an idea where the heating or cooling is done by
using the earth as reservoir.
Basically, in summer when air and surface temperatures are relatively
high, temperature a few meters under ground is relatively low (as
that remains fairly constant around 18 degrees or so). A water reservoir
placed a couple of meters under ground could be used as a heat sink
and a stirling engine or thermocouple could be used to produce energy
from the thermal energy flow.
Similarly, in winter the air and surface temperature in most places is
a fair bit lower than the temperature under ground, and now the under-
ground water reservoir will be warmer than the outside air, so now
the outer environment can be used as a heat sink and thermal energy
from underground can flow out, producing energy again via the same
stirling engine or thermocouple.
This is what they're doing in many new housing projects, using the ground
as heat or cold supply.

Regards,
Koen

Hi Koen,

Yes, similar principle. Spelunkers and well-water users know how cold water underground can be.

If this unit works like I think it will, there should be a good temperature differential (perhaps 40°F or so.) That should give a good boost to the Stirling and maybe give enough torque to perhaps run a very small motor as a generator. Those Stirlings are notoriously weak, but if the motor it powers is very small it could prove the viability of the concept. I would like to scale it up a bit in the future if good results could be obtained.

What I like is that this type of system would work even when the sun goes down. Unlike the solar-powered Stirling units they have developed that stop when the clouds block out the sun.

If you fill a jar or aquarium with carbon dioxide gas.That greenhouse gas(the carbon dioxide) will be 4 F degrees warmer than the outside of the jar or aquarium.I have heard that methane gas(being a super greenhouse gas absorbs 20 times the heat that CO2 will .So does that mean a jar or aquarium full of methane will be 80 F degrees warmer than outside the container?Just throwing out some thoughts I had on the subject.If its true maybe clothes made out of material full of methane bubbles would keep us warm in the coldest places? Like in outer space? Triffid

If you use natural gas to cook with,It's mostly methane.I use all electric myself.Triffid

Mixing baking powder from the store with water releases carbon dioxide gas.Baking powder is not the same as baking soda.So now we have have a very cheap source of these two greenhouse gases for someone here to try to experiment with.Triffid

triffid:

An even cheaper source of this so called "greenhouse gas" CO2, is to just exhale.  This is why I think all this carbon tax bs is full of crap.  Every time someone opens a soda (like Coke) now, they will have to pay a carbon tax for emitting a "greenhouse" gas.  If it were not for these gases in the atmosphere, our planet would be about 100 degrees or more colder.  Talk about high heating bills.

Bill

I agree we exhale carbon dioxide but its not much percentage wise.Which is why we can do mouth to mouth on someone who needs it.Triffid

I thought we don't do mouth to mouth anymore? Only chest compression? AHHHHH now I see why they changed the procedure for CPR. It's because of GLOBAL WARMING!!! LOL!

Carbon dioxide and greenhouse gasses aside, I have been running the flowerpot unit in my basement with the aluminum oxide in the middle pot. I am going to let it run for a week or so before I buy the stirling engine. I can't run it outdoors yet because we have snow on the ground and cold conditions.

The aluminum oxide is in powder form and I purchased five pounds, but that was only enough to halfway fill the center pot. It will have to do for the experiment. I will add water to the unit once per day and I will report numbers and observations in about a week.

Thanks for your interest everyone.

Dave (RR2)

The best way to generate carbon dioxide is to put some sugar water in a flask and add some yeast. Bingo, pure carbon dioxide in minutes.

Hans von Lieven

Quote from: hansvonlieven on March 30, 2009, 03:10:27 PM
The best way to generate carbon dioxide is to put some sugar water in a flask and add some yeast. Bingo, pure carbon dioxide in minutes.

Hans von Lieven

Whoa, don't tell the Government. They'll have to put an extra Global-Warming Tax on every loaf of bread and every pastry product that uses yeast as one of its ingrediants.

Not to mention beer  ;D ;D ;D ;D

Hans

@ Hans:

That is exactly what I was thinking.  I hope they don't read this.  They just raised my beer tax here $3.00 and they don't need any more ideas, ha ha.

Bill

They are way ahead of you. LOL!

LOL yeah well before you know it, they'll
implement legislation forcing breweries to
replace the CO2 bubbles with something like
Helium or something... ;D

Can we do it? YES WE CAN! lol ;)

Next thing you know, they're going to make us all
wear exhalation filters to filter the CO2 out of our breath...
;D

That will be fun Koen, we will all be talking like Donald Duck  ;D ;D ;D

Hans

LOL well, Alvin and the Chipmunks probably sounds more heliumy
but yeah, could be fun! ;D

Ah, we'll see what "they" do eh...

It's great to have democracy, where the government does what the people want.
Every morning I am astonished to read in the newspaper what I want today.
It's amazing how many things I want that I never knew I wanted. Or even
thought I did not want. But hey, there's more of me that want it than that don't,
apparently.

LOL ;D

I guess one could make all kinds of money selling "carbon credits".Afterall everyone seems to be a potential customer.Triffid

I too have read about Donkey's solar icebox and am curious about that natural building material"cob",I would love to learn more about it.I also wonder how much heat those al oxide pellets can hold?
Anyone here have the answers?Triffid

Well the solar pot experiment has been running eight days in my basement. I have been recording temperatures every 24 hours and adding water as needed to the sand. The center is half-filled with aluminum oxide powder.

Air temperature for my basement has varied from 66 down to 59 during the week and the temperature differential between the ambient air and the center pot has remained very steady at 3.9°F. So in my dark, reasonably temperature-controlled basement the unit maintains a sustained and almost four degree (°F) temperature difference. Not much, but it is consistent and not being driven by anything except evaporation alone.

I am anxious to get it outside in the sun where it can really rock, but we have had freezing temperatures and snow lately, so once there begins a warmer stretch of weather I will begin recording the numbers.

I am hoping to achieve a forty to fifty degree temperature differential in the hotter weather, strong enough to get a low temperature Stirling Engine going at a good and hearty clip, hopefully enough to power a small motor generator.

Thanks for your interest, RR2

ResinRat2 interesting results !

Glad to hear you are attempting this haven't seen you post as much as you used to.

Maybe I'm just not reading the threads your posting in could be but anyhow keep us posted on your progress ...

Do you have a digital camera if so mind taking some snapshots of your setup?

The larger clay flower pot is 11 inches across and tall, the smaller clay pot is 9 inches across and tall. The space between them was filled with fine playbox sand. I covered the bottom holes with plastic, but the inside pot water bubbles into the pot so I placed a layer of aluminum foil on the inside to protect the Aluminum Oxide Powder contents. Aluminum has a fantastic heat transfer rate so this should work well.

Right now I am keeping the top covered with plastic so all the cooling comes from the water that permeates the sides of the outer clay pot and evaporates. This is the cooling mechanism. The aluminum oxide center should resist temperature changes.

The goal is to set the unit in the sun so that the heat differential cools the center al. oxide below ambient and keeps a Stirling motor set on top of the al. oxide powder running. A motor that runs off the water evaporation. When the sun goes down the whole unit cools with the ambient temperatures, but the aluminum oxide should always cool at a different rate, thus again creating and maintaining the heat differential. My fingers are crossed that I can develop a unit that runs the motor continuously both night and day.

This unit is small, but larger units should have greater potential for developing and maintaining a heat differential that should be able to power larger Stirling Engines. That is what I am hoping for.

Too sweet finally a good sterling approach ! We hope ;)

Thanks bud!

I wonder if you couldn't couple this system with say a solar heater on one end to gain more power at peak sun time or even a Fresnal lens maybe... Well I suppose each project is always a step at a time but your results are rather interesting.

I thought about focusing the sunlight too, but I was debating whether it would have a helpful effect up to a point, and then it might be counter-productive and heat up the inner sand layer. This might actually heat the center aluminum oxide mass. Who knows, it might actually help; but I would say it is something to try.

I am going to purchase more aluminum oxide so the center pot is filled to the top and I will have a nice 10-15 pounds of thermal mass to work with. This should help with maintaining a heat differential.

Most people would probably dismiss this concept, but I find it interesting.

Aluminum oxide has a very good (for this application) thermal conductivity number. (Meaning low conductivity)  But, there are many, many types of Al203.  We used to purchase a number of different mixtures and purity in the ceramics business.  Purities of 99.7% vary greatly from purities of 99.8%, and 97% and 96% as well as 95%.  Each, like steel, has their own set of physical properties and vary greatly from each other.  Usually, depending on the manufacturer, (we purchased most of ours from Coors) the remaining ingredients in the Al203 is usually glass.  That is why, for metalization purposes, we used 95% because the glass allowed the metal to bond with the Al203.

So, I would make sure you know the content of the aluminum oxide you are using as just a little bit of difference make a huge change in physical properties.  And, if your supplier tells you it is 100% Al203, do not believe them as Coors 99.8% cost us (20 years ago) $100.00/ft of 1/4" rod.  This is very specialized stuff.

I don't know if this helps or not but, I was tossing it out there.

I can post the specs on this stuff if I can dig them out of my library.

Bill

Why not taking a propane fridge and replace the propane flame by some kind of solar oven?
this could maybe work!

Regards.

electrospark