Last Single-Mirror Solar Oven Simulation Test

by Curlydock
Nov 24, 2007

In my previous couple of posts I showed some of the results of tests of a program I wrote to simulate what I call a “kaleidoscopic” type solar oven. In earlier posts I detail the actual oven I use to bake bread. I wanted to see how to build a better oven of this type, so I wrote the simulation for ray-tracing various reflector sizes, shapes, quantities and configurations.

This post will cover what I hope is the last of the one-reflector tests. I wish to begin tests of two-mirror simulations in the next post.

nov1026a.jpg

Graph “nov1026a” shows the results of five runs with a single equilateral triangular reflector in the plane of the horizon. That reflector I frequently refer to as “R3”. Five sweeps of the sun from zero degrees (horizon) to 90 degrees (zenith) are shown, one sweep for each size of R3. The sides are all equal and are measured in cavity diameters. The smallest R3 is 2.0 and the largest is 8.0 cavity diameters on a side. The cavity bounding sphere is represented by the ball that is aways in the corner farthest from the sun when the sun is on the horizon.

Observe that the gain never exceeds 2.0 and never falls below 1.0. This is consistent with my expectations of what happens with only one mirror and increases my confidence in the simulator.

Rule 1026a

Also observe that the increment of improvement in gain decreases as R3 gets larger. Large mirrors increase the gain when the sun is at lower angles but the reflector has to get perhaps impractically large to produce these gains. At solar angles above about 20.0 degrees, it hardly seems worth having a floor reflector larger than 4.0 cavity diameters on a side. This is more than my prejudice up until now, which was that 3.0 cavity diameters on a side was the practical limit. The actual oven I made has only 3.0. So, the next time I build one of these ovens I will probably go with 4.0. It depends on what else we learn when more reflectors are in play.

“Rule 1026a” is, then: the triangular reflector always parallel with the plane of the horizon, that is the one the cavity is above, should be sized to about 4.0 cavity diameters on a side, physical practicality permitting, and probably not less than 3.0.

Now I combine this rule with rule 1010a from the previous post, which said the cavity should be elevated. That results in chart “1027a”:

nov1027a.jpg

For this run I kept the mirror sized to 8.0 cavity diameters on a side and elevated the bottom of the cavity from just touching R3 to where the bottom of the cavity is 0.5 cavity diameters over R3. Otherwise the run and chart calibration are the same.

Again, the gain never exceeds 2.0 and never falls below 1.0, which is good.

Also note that elevating the cavity improves gain when the sun is at higher angles. This is consistent with what we learned in the prior post and was to be expected. The simulation still seems to work. For this configuration, with the cavity elevated, the range of sun angles with the maximum gain of 2.0 is much larger.

In a prior post I expressed some doubt about whether the simulation was following the ray trace through an arbitrary number of reflections or breaking off too soon. I later discovered that was indeed a problem. But it only affected simulations of more than one mirror, none of which I had published yet. I fixed the bug and am now confident that I am ready to do multi-mirror tests. In the next post we will see some results using two reflectors. Those reflectors are the ones I have named “R1” and “R2” in prior posts. They are linked by a vertical hinge and open like a book over the plane of R3. R3 will be put aside while we consider only R1 and R2 and will return probably much later when three-mirror tests begin.

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Sourdough Starter as Ecological Model

By Curlydock

Ever wonder what your sourdough starter gets up to when you are not looking? I spied on mine with a web-cam for about a day. Now I know the shocking truth of its secret life and will show and tell all in this installment.

Why care

about this? There are several parallels between what happens when you feed your sourdough starter and what has happened on this very planet Earth when the human population began to explode.

In both cases, there is a population of living things in an environment that is limited in size and resources.

The sourdough starter is populated with yeast and bacteria in symbiosis. It needs flour for the population to grow and will consume it all if you do not replenish it. Then, there is a die off or crash in the population as a result of starvation, resource exhaustion and poisoning by the accumulation of waste material. Sound familiar?

Earth is populated with people, all the species that people depend upon, and many species relegated to “weed” category, thought of as expendable because we have not yet figured out how to exploit them. Ecologists and those who understand the need for organic farming methods are among the precious minority who value species diversity. As much as we like to think we can dominate nature, the real truth is that we are also symbiots. Our determination to dominate instead of live in harmony is driving the planet and all its populations into a dead-end.

The sourdough starter cannot grow out of it’s jar. (Well, it can but is not likely to find more flour if it does.) The human population cannot leave this planet in any significant numbers any time soon. (And, even if it does, how much organic coffee can we grow on the moon?)

Perhaps the sourdough starter can teach us something about mindless consumption and procreation. “But”, you may protest, “Unlike yeast, people have minds!” I will counter: “A person in a state of denial behaves automatically and just as if they do not have a mind.” Mindless consumers. Purchase what you don’t need. Throw the left-overs in the gutter. Make babies like the world was going out of style. Well, perhaps it is.

The sourdough starter needs flour. Unless you replenish it, the starter will consume all that is available.

The human population of Earth has developed a crippling dependance on oil and other limited resources. Even if we don’t run out of coal and oil, we cannot continue to use them because their use in this already over-populated planet is what is triggering global warming. So, discovering vast new supplies of cheap oil is no solution. In fact, it could aggravate the real problem. Irony.
Procedure

I mixed 54 g of flour with 103 g of water. To that I added 68 g of vigorous starter. Of that 225 g total mixture, I poured 122 g into a glass jar and loosely coverd with a plastic lid. The glass jar was placed in a temperature controlled chamber in front of a camera. The temperature was monitored and never significantly deviated from 79 deg. or 80 deg. F. For a period of about 12 hours, one picture was taken every 5 minutes, resulting in 150 images.

Results

I selected eight of the 150 images to put here. In each image, you will see that I have inserted a set of numbers at the top center. These numbers represent the duration, in hours and minutes, at the time the image was recorded. So, the first image is “00:00”:

00 hours 00 minutes

The next image is after 2 hours and 26 minutes have elapsed:

snapshot-20070105-140039.jpg

At 02:26 you see the normal layer of “hooch” forming. I did not know until I did this experiment that it first forms at the top of the starter. You also see the bubbles of gas forming in the starter, causing the starter to “rise” as it would when used to leaven bread dough. The hooch and gas are the waste products from the yeast and bacteia, the populations of which are beginning to grow rapidly.
At 03:16 the starter has risen a good bit. The hooch layer is
snapshot-20070105-145044.jpg

getting pushed to one corner as the center bulges.

At 03:26 there is another unexpected phenomenon.

snapshot-20070105-150044.jpg

The corner where the hooch was is foaming violently. I say violently because this all took place on a time scale of 5 or10 minutes. This is after almost an hour and a half of liesurly, predictable rise in the starter volume and number of gas bubbles (correlate with population of micro-organisms). I watched this occure on the monitor, bemoaning the fact that all this excitement would be lost to posterity because I had decided to record only one image every 5 minutes. I would have needed a couple of images a second to capture all this short-term activity, which began suddenly and without warning and did not last long at all. I gripped the edge of my seat and practically left greasy nose-marks on my monitor, wondering what this portended for my little microbe-cosm.

At 03:46 the foam is leaving. Where did the hooch go?
snapshot-20070105-152048.jpg

If you look closely you can see the hooch is now all the way at the bottom of the jar.

At 06:26 you see you can’t keep good hooch down.

snapshot-20070105-180107.jpg

Now there are three distinct layers. Under the hooch is a layer of starter that seems to be inactive because there are no bubbles in it. You can’t see it in a few images, but I can tell you it was still very active. Small chunks and particles were seen both rising and falling in the hooch layer. Since the bottom layer was growing, it must be that more was falling than rising. Does this remind you of the economy and the extinction of the middle class?

At 07:01 you can see the first settling of the top layer.
snapshot-20070105-183612.jpg

This tells us that the yeast and bacteria are beginning to die off. They have used up their resource (flour) and are now starving and succumbing to the poisonous effects of their waste products. It looks like the peak occured a bit after six hours in this experiment.

At 14 hours and 30 minutes I ended the experiment.
snapshot-20070106-000205.jpg

The top layer is at its lowest level since its peak. Once it started falling, the fall was pretty monotonous. I could have let it run longer but it had been a long day and this felt very much like the end of history.

Conclusion

Can we take any macro lessons from this micro-biological model? There are some important differences. Our planet, unlike the starter jar that got only one charge of flour, is being re-charged daily with “free” energy from the sun.

The trouble is, we have not been living within the energy budget of the sun since technology allowed us to exploit oil and greed made it inevitable. The energy density of “black gold” cannot be matched by solar, wind, geothermal, etc. Nuclear has a waste problem and the likelihood of catastrophic accidents increases with time and the number of reactors in use.

We may be running out of time to reverse the toxic byproduct of burning fossil fuels: global warming. It may be too late. It could accelerate tenfold or more without warning (remember the foam and the inversion of the hooch layer happened catastrophically). Indeed, there may be evidence of such an acceleration now, see: “Global Warming Already Causing Extinctions, Scientists Say“, by Hannah Hoag for National Geographic News, Nov. 28, 2006.

These sudden accelerations and unpredictable changes can happen in non-linear systems that are under stress. A little push in a certain direction causes changes that themselves add to the push and you get exponential acceleration. The hooch layer suddenly inverts. The die-off caused by global warming or the loss of oil as an energy source could also happen more quickly than predicted by the most dire of doomsayers.

Here is a very good reference for those interested in reading more on the topic of ecosystems that experience overshoot and sudden extinction: “Overshoot in a Nutshell” by David M. Delany.

Seedling Identification Revisited

by Curlydock

This is the start of my second attempt at seedling identification. This time I have a technique that should remove doubt about what sprouted.

Most of the unwanted volunteers from my previous effort turned out to be tomato seedlings. I fed a lot of tomatoes to the worms, so the seeds were still viable in the vermicompost.

I still want to keep the purported advantages of organic living soil so I still have not sterilized the potting medium. In fact, I am using the same pots I used before. This time, however, the seedling of interst is clearly flagged by a ring of newspaper around the seedling. Any sprout that is outside of that ring can be “weeded out”.

Day 6 Rapini

The ring of newspaper is the top rim of what I call a “tiny pot”. The tiny pots are made from 2-inch squares of newspaper wrapped around the end of a pencil. The small cylinder thus created stays intact when the end of it is crushed closed. The seeds are planted in the open end after the tiny pots are placed into the cells of an ice cube tray and moistened.

Sprouter Tray

To get one and only one seed in each tiny pot, I used a bamboo skewer moistened on the end. Small seeds adhere to the sharp end and larger seeds will adhere to the blunt end. Don’t stick the moist skewer into your packet of seeds. The moisture on the skewer is probably not good there. Sprinkle a few seeds from your main pack into another container and pick the seeds from the other container with the wet skewer. The smallest seeds may be repelled instead of attracted to the skewer at first, but they will soon give up their static charge and stick to it.

sprouter

The particular ice cube tray used was one with a five-by-twelve grid of cells. It makes very small round ice cubes. The tray is kept in a plastic shoe box with a lid to keep the tiny pots moist. I had to use a medicine dropper to remove excess moisture from the tiny pots. You want the tiny pots damp but not soggy. I would not have had to use the medicine dropper if I had drilled a small drainage hole in each of the ice cube tray cells.

Day 6 broccoli

The seeds are carfully selected and metered. Only one seed is planted per tiny pot. However, five seeds of the same type are plated in a row. That allows 12 different types of seed to be sprouted in one ice cube tray. Of the five seeds of one kind in any one row, only the largest or most vigorous sprout is selected to plant in the larger pots cotaining the medium of unsterilised vermicompost. The others are kept for a while in case the first one did not take.

Day 6 Chard

The sprout, tiny pot and all, is moved from the ice cube tray cell and planted into the larger containter of potting medium. Do this as soon as it is obvious the seed has sprouted. Leave enough of the tiny pot visible so it will serve as a flag saying “this is the one you planted”. Pull up anything else that comes along.

Tiny Pot

The tiny pots should decay and return to the soil eventually. The piece of paper they are made from is so small that the decaying paper should not significantly deplete the fertility of the potting medium.

Seedling Identification Concluded by Curlydock

Yes, I am already halting the project I started in the previous post.

It is a bit ironic, really.

I took pictures of seedlings growing in little pots kept on this winter’s windowsill. I wanted to refer to the images when I needed to identify what was sprouting in the garden. That way I could tell the difference between what I planted and any volunteers (also known as “weeds”).

Well, the volunteers are now vigorously raising their heads in my little pots. I cannot even be certain of the identification of what is growing on my windowsill.

Go ahead, laugh.

The mistake I made: I should have sterilized the germination medium. I did not.

I knew I should have sterilized it, but chose not to. I didn’t sterilize because I wanted to keep the reputed organic benefit of the microbes that are naturally in the vermicompost.

Also, long ago I observed seeds sprouting in the worm bin and in other compost piles I have kept. Since the vermicompost I used was about a year old I assumed anything that was going to sprout in it had already done so. Then, I reasoned, the sprouts died back because there was not enough light and the worms and microbes feasted off them as “green manure”. Apparently this was not true of the volunteers.

Perhaps some seeds are not fooled into germinating in what seems to be an ideal place to do so: the moist and nutritious old compost. Perhaps they wait for some clue to know the time is right, like a change in ambient oxygen or other chemical or momentary exposure to light. Perhaps they could sense the physical disturbance when I combined the vermicompost with peat moss and egg shells to make the potting medium. I really don’t know. If any reader has an idea or a clue, please post a comment.

The next time I attempt this project (and I probably will attempt it again) I plan to germinate the desired seeds in very small plugs of potting medium after baking the medium in an oven to sterilize it. That way the desired seedling will get a head start. Then, as soon as possible, I will plant the plugs in the very center of the small pot of unsterilized medium. It won’t matter what volunteers then because the desired seedlings are already identified. The volunteers can be uprooted as they appear.