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Author Topic: Definition of Thermal Energy and the BTU  (Read 7511 times)


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Definition of Thermal Energy and the BTU
« on: December 01, 2017, 01:20:41 AM »
Hi guys. I’m putting this in the do-it-yourself category,
Because we don’t really have a category for this.
Attached to this is I guess you would call the oldest
Do-it-yourself project in human history.

I’m talking about the camp fire, and from a time when fire
Could have very well meant life or death.

And Ancient Metal Smelting
(And yes I will give you the device)

From a time, the historians tell us, was 230-250 thousand
Years ago...

This came to me from a friend, who had a stack of old photos
1970’s sometime, and research papers done from his dads
tour of museums at that time. The subject of interest was in these
particular fire pits that, according to the exhibits, would stay lit
for a week, sometimes more. And my friend wanted me to explain
to him how it worked.

Well, I was an Eagle Scout, so I knew a thing or two about campfires,
(or so I thought), and the best of mine, I could go out two or three days
later and stir the coals and find something lit, but a week sounded ridiculous.

So I told him I would read through what he had and see if I could dig up any other
stuff on these.

Well, what I found, places Heat Energy into a category that more closely resembles
light and sound, and electromagnetism.

I’ll do my best to explain:  we can define heat in terms of a group of thermal energy,
and by doing so, we give this volume of energy a sort of linear definition in terms of
transfer of energy, through solids and through gas.

But less talked about, is that we can also define heat energy in terms of a wave.
We can see heat waves when light hits them and reflects to our eyes.
On a hot road, or coming out of our ovens.

We can measure them, and catalog the data of waves of packets of heat.
But nowhere do I see anyone talking about the frequency of these waves.
At least not in any definitive manner applicable to the quantity of heat energy.

I did find studies done on the interference patterns of heat waves, but
nothing that applied to this guys question.

The reason I’m mentioning heat waves and ancient caveman technology,
Is because that is where the research led me. As it turns out, frequency and
Heat waves had nothing to do with the fire staying hot, as that technology had developed
much earlier than the furnaces he gave me.

What THESE people were doing, clearly had nothing to do with cooking food.
There is only two things a person would conceivably do with these temperatures
And those are to smelt metals, or make your own sort of personal lava / obsidian.

We’ll get to that, but first I will walk you through the origins of this stuff.
These fire pits were found in Cave Man exhibits in museums across the US and Europe
In the 1970’s.
I don’t remember paying much attention in the 80’s so I don’t know if they were still there
when I was a kid, but they are nowhere to be found now, and no one in the museums will
give me any info. I am told only that I can bring them cataloge numbers or something and fill
out a request to view a catalogued artifact.
The problem is, we don’t have lists of all of the stuff they keep in their basements.

So, this technology is known as ashenware, which later developed into ashenclay, or clay ash.
The modern official description states that the cavemen mixed ashes with clay and made these mounds
To cook their food.

Well, that’s not what the historians said in the 70’s.

First: the ashenware was always placed first. As if the base structure was created first,
From rocks and ashes mixed with water to form a brittle clay.
The Actual clay was placed on top of these structures, and in the layer where they touched
Yes, there was some “mixing”. Then was just clay.

And not just clay, but specifically measured, flat interiors of the furnace.
With strange notches, which made these particular furnaces a unique type.


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Re: Definition of Thermal Energy and the BTU
« Reply #1 on: December 01, 2017, 01:53:52 AM »
They were built different sizes and I did not see the correlations
until I started reading the technical descriptions made by this guys dad.

These furnaces, no matter their size, were build with explicit proportions,
and always this shape in the bottom.

I also noticed that there was nowhere
To cook food

You had a place to put coals or wood into, but the top was, what the historians
refered to as an exhaust vent that produced temperatures over 2000 degrees.

Which, as a chef, I assume would destroy your food.

And there was always these 3 proportions, and a 4th which
was mostly proportional but varied slightly.

Why did they need such heat?
Well 1200 years later in time, the same furnaces were found
With additional mounding on top of the original style furnaces,
and a large square oven on top, whose dimensions were perfectly
divisible by the previous dimensions.

Anyways, the ashenware technology that predates these by a few
tens of thousands of years, does stay hot for a week. You go to it
7-9 days later, stir the ashes and the whole pit lights back up.
How do I know? Because I built one.

Next, I added a layer of clay. And made the witch-furnace.
I call it a witch furnace because it reminds me of an old timey
American fire pit with a open face chimney, often found in places
where witches were rumored to live. In actuality was probably old
loners who lived in the woods..... anyways they look like that.
Except they don’t have an open face. They are just an ugly mound, or
square or conical chimney, at the edge of a large fire pit.

But inside is a chamber, the height varied but was the bottom section
of these devices. And inside was a square design that was two over-layer squares.
Or a square with cut-outs on 3 walls of specific length and depth, and both of those
Dimensions were proportional to the height of the base+chimney to a narrow opening
on the top.

Now - the dimension of the (later) cube on top was always divisible by a common factor.


Well, as it turns out, there is a frequency effect inside this thing.
And even without heat (and I waited two weeks to be sure)
A vortex of air forms inside with even the slightest movement of air outside.
It does it when I cannot even detect wind, but I assume there must be “some wind”.
You can see ashes or cig smoke just tornadoe up the chimney.
But when there IS heat, just a small handful of twigs or grass can send fire 4 ft out the top
And heat steel to a glowing red. I’ve melted alumin and glass. And as I perfect my construction
I will update you guys on this.

There are no bellows
No hair dryer
And I haven’t even build a lid.

The thing sounds like a rocket engine

I’m trying to get a video onto my YouTube but google is being a $&@!!

Worse case I will upload a schematic to show the dimensions.

The real topic that is risen here is not that we can make our own forge,
Or even wether or not that is what the cavemen were doing with this.

But it is concerning this frequency effect of convection and heat generation.
And how this applies to our definition of a quantity
Of heat energy.

If you have access to a convection oven, place the blower fan on a timer circuit.
And pulse it across a frequency sweep.
Find the peaks and troughs of the rate of change of the oven temp vs freq.
Now take the frequencies where rate of change peaks, and compare those wavelengths
to the internal dimensions of your convection oven.

I think you will quickly see that that situation resembles what happens in
your microwave.


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Re: Definition of Thermal Energy and the BTU
« Reply #2 on: December 01, 2017, 03:00:45 PM »
sorry about the delay, finally got access to my youtube channel.

here is a short video of my first successful melting of Aluminum.

i'll upload a schematic tonight.

but I want to talk a little more about these dimensions, and why they do what they do.

the insets (square within a square), are cut back into the walls, on 3 sides. open in the front, up to the height of the chamber. The depth of the inset is 1/16 of the length of the inset.
mine are based on the earliest version I could find, which is 1/2 inch inset and 8 inches in length.
the inner square is 4 inches smaller, which leaves these square corners sticking about, which are about 2 inches, I say about, because the exact dimensions of those squares seemed less important
to the cavemen, as they varied by up to 1/4 of an inch.
that doesn't seem like much variance, but when you compare the precision of the other dimensions,
you can see that these guys didn't make a mistake by even 1/20th of an inch. they were all exact.
the historians measured with micrometers, and I don't have that sort of thing. I converted it to inches and rounded off a tiny fraction, but kept the proportions the same.

the height of the chamber had no direct correlation to anything, as it was anywhere from 8-14 inches, and was different from device to device. mine is ~10 inches tall.

chimney is smooth walled and becomes more narrow as it rises. some groups of cavemen made them round, others made them square or flat walled inside. but the total height was important.

in the example I recreated, the height is 32 inches, or 4x the 8-inch dimension.

in the later ovens, which had a square chamber on top of the chimney
it's length and width and height were 24 inches, or 3x the 8-inch dimension.
im assuming they had some kind of door, but that wasn't talked about in any of the papers I read.
otherwise, how would they make use of it?

I haven't gotten to the upper chamber yet, as I want to perfect the bottom part of this device,
before I move on to more advanced versions.

but as you can see in the video, this device is able to reach incredible temperatures with very little
fuel, and no forced air. the air-flow is completely natural, and built-in.
the hotter I get it, the stronger the air-flow of the vortex, but the frequency (the hum it makes)
is always the same tone when it gets going. sounds like a jet engine or something.
reminds me of those pulse-rockets.


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Re: Definition of Thermal Energy and the BTU
« Reply #3 on: December 05, 2017, 05:49:58 PM »
What does this have to do with the BTU?
Well, a lot actually. But before I start making outrageous claims,
which, if true, could upset the realm of physics...

Let’s talk about how we USE the BTU.

When we measure the BTU (or energy of the combustible content)
Of Wood: this is traditionally done with a wood stove.
Greater accuracy is obtained by pelletizing the wood
For more consistent burning.
In almost every example, the approximate BTU for wood
Comes out to around 7000 /Lb.
In fact, most plant debris is measured close to that.

When we consider a quantity of water, heated to a boil,
By a quantity of fuel, in a traditional wood stove,
We find the estimate of the BTU of wood to be consistent
with the scientific standard values.

I’ve tested similar quantities of wood (small sticks/twigs)
In a variety of small fire containers and wood burning stoves.

How much heat energy are we talking about?
One gallon of water requires approx 8.34 BTU’s
Per degree of temp. increase. 212-60= 152
152x8.34= 1268 BTU’s to bring a gallon to boiling.
0.18 Lbs of wood, burnt at maximum efficiency.
Or ~2.88 ounces of sticks.
The cedar that grows around here, this is about 3 cups of
1-2 inch twigs. Avg 1/4 inch diameter.

In a variety of modern wood stoves,
Commercial and homemade, this amount would barely heat the water.
In fact, in most stoves the twigs burn up so fast that it is nearly
Impossible to harness 100% of the woods energy.
And in most cases, it took 3 or 4 times that BTU’s worth of wood
To boil a gallon of water.
A lot of heat is lost due to inefficienties of the stoves.

With the caveman furnace I can easily boil the water in a couple of minutes.
It is in fact, faster than my gas powered store be inside by 2 mins.

Turning off my water heater, and watching the meter, I was able to get a number
for the quantity of gas used, and reverse engineering the BTU I find that
my gas stove runs at about 40% efficiency.
This is better than the 20-30% of a wood stove.

This is where the problems begin.
These “cavemen” that lived some 230-250,000 yrs ago, somehow managed to
Make a furnace that operates at ~120% efficiency.

Wtf?  Ok well, it can’t be greater than 100%, at best.
So let’s look for another solution.
Is our value of the BTU of wood correct?
Is the value of the BTU itself correct?

We’ll deal with the second one, but first things first.

How did we come up with 7,000/lb?

It appears, upon lots of digging, that this number is inherented.
And by that I mean: passed along from source to source, making it
difficult to find the origin.

Until you get back into the 1980’s and older research
There we find intense measurements done, with ranges of
5000 to 11000 BTU’s per lb of wood.
And that density is only one of several factors, including oil content,
Hydration, and chemical composition of the plant.

The local firewood salesman tells me the accepted standard is 8600/lb
And he uses that fact to sell his different woods based on their density,
and various characteristics of the flames each type produces.

Wait what? Different wood produces different flames?
Well, it turns out those chemicals actually burn at different temperatures!!
The color of the flame presents itself as a scale by which we can grade our wood.

A physicist at the University of Texas tells us that the temperature the wood burns at
does not affect the actual BTU values, but that hotter flames simply burn more BTUs faster....
My barrage of questions that followed that statement went unanswered, he was unable to
explain this line of reasoning, that it was “what he was taught”.

Ok, back to the caveman stove, if our value of BTU’s per lb
actually has a range of several thousand BTU’s, we not only don’t know the true efficiency
of our wood burning devices, but we also can’t compare it to a gas stove.

Let’s assume that this local cedar or medium wood density, was the maximum of 11000/lb.
This means the caveman furnace is operating at ~85%.
Ok this sounds more within reason.

The problem still exists, that these “cavemen” made stoves that we’re 2-3 times more efficient
than our modern stoves.

And this physicist had no comments on the vortex.
he said that rising convection currents have two main components
Thermal Displacement (the whole heat rises thing)
and air drawn upwards by the ‘licking’ of the flames.
And that they sometimes cause the flame to take on circulation patterns.
Also, he told me that frequency has nothing to do with convection
And that wood flames don’t ‘lick’ at a set frequency, they are random.

Thanks Doc,

However, the caveman furnace CLEARLY makes the same tone,
regardless of what is burnt in it. Paper, wood, charcoal, cardboard, gasoline, alcohol
paint thinner...

And why would a primitive race of cavemen build meticulously intricate interiors
for a useless chimney......
And the heat!!??!! Why did cavemen need all that heat?
Then we find in a museum in Columbus, Ohio - 40,000 yr old metal arrowheads.

They were smelting 250,000 yrs ago.
(No I didn’t find any metal artifacts that old)
But the fact that these furnaces existed proved they were doing a lot more than
we give them credit for.

Even my crappy replication gets plenty hot enough to melt a several different metals.

I am experimenting with this tech to see if other frequency (or spatial dimension) related effects occur.
I’ll keep you guys posted with what I find.


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Re: Definition of Thermal Energy and the BTU
« Reply #4 on: December 07, 2017, 01:21:38 PM »
Hello sm0ky2!
Could you please post a schematic with the dimensions (and ratios)? I'm interested in the workings of this caveman stove.

Thanks for sharing!


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Re: Definition of Thermal Energy and the BTU
« Reply #5 on: December 08, 2017, 02:07:57 AM »
i suck at art, but here goes


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Re: Definition of Thermal Energy and the BTU
« Reply #6 on: December 08, 2017, 02:23:11 AM »
Ok so,
We have 4 basic dimensions in the earlier versions of this tech

D is the one that doesn't always fit a set proportion, it is sometimes close,
But seems like an arbitrary value for the height of the burn chamber.
I went with 10-inches here, which is within the 2.5 inches from the value A
As the dimension D was always with a range of 2.5in +/- of A

B = 1/4 A
A = 1/4 C
C is the total height from the bottom of the burn chamber to the top aperature
The chimney gets narrower from the top of the chamber towards the top.
I didn't find any set angle, some were conical, some were angled-flat sides.
The size and shape of the top opening varied drastically as well.

I've built mine for the 4th time recently (overheats and destroyed itself)
It gets too hot for plaster, so I went back to clay. This time mixing sand and
crushed (used) plaster as an aggregate. Hoping this will help.
I think the clay I used he first time had too low ceramic content, so I went with a different
type of colliche, also found locally in the ground.
I'm making some clay extracted from crushed granites.
To test the heat tolerance. If that holds well, I may use that for my next one.

I tried playing with the dimensions of the (later advancement) upper chamber
Mostly because I didn't have enough materials to make that large of a box.
I tried 1/2 A, the vortex is still present but the air flow went way down, and it doesn't no get as hot.
With this new mod it takes about 20 mins to heat up, and barely will melt aluminum.
(got hot in under 2 mins before)
So I will knock the little box off and try again.

I want to try 1/3 A, but if that do sent work I will collect the materials to build the 3A dimension
used by the ancients. (Cube oven)
I assume it had a removable door, as the top vent was too small to insert a crucible.
My current top-box has no lid, and no door.
I drop the crucible in from above.
I think it constricts the airflow too much, still hums the same tune
But the flame-jet dropped to 3-4 inches out the top, instead of the original 4-feet into the air

I'll update this thread when I get the new chamber built


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Re: Definition of Thermal Energy and the BTU
« Reply #7 on: December 08, 2017, 10:12:42 AM »
Sorry, my drawing is missing a detail

The front part of that shape is open
So you can put the wood or coals in
I drew it there but forgot to go back and
erase the front side of the chamber
It’s a 3-sided shape


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Re: Definition of Thermal Energy and the BTU
« Reply #8 on: December 10, 2017, 12:30:05 AM »

Thanks for the details.
What should be the dimensions of the front opening? Should the width be A or A+2B? What about the height and shape of the opening?

Wish you good luck with the construction and testing.


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Re: Definition of Thermal Energy and the BTU
« Reply #9 on: December 10, 2017, 01:13:36 AM »
Basically, the front is A, as if A was missing
And the B’s stand as pillars at the corners
I think it’s to form the boundaries of the side A’s
The height is the same as the chamber height on
the examples I saw.

It looked like a separate piece that the chimney
and outer structure was built around.
I built my base first then sort of stuck the chamber
inside as I got close to the inner dimension.
I just framed it with wood paneling, and burnt it out
after the clay hardened.

Mine didn’t turn out nearly as pretty as the ancient
promethian culture.
not sure their techniques, but they were better at it
than my first attempt. my surface is all cracked with
pits and whatnot. I just kinda fill it in as it falls apart.


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Re: Definition of Thermal Energy and the BTU
« Reply #10 on: December 12, 2017, 12:12:02 AM »
been enjoying all your contributions ,and this one is very interesting indeed ,[an association between frequency and heat ??]

Here is something which  is also frequency dependent [resonance too]  fascinating and perhaps has plenty of room for  improvements and "what ifs"

imagine getting one of your furnaces to howl and make power too ??  [contribution from Tinsel at another thread]

Chet K


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Re: Definition of Thermal Energy and the BTU
« Reply #11 on: December 12, 2017, 12:33:54 PM »
Thanks Chet

That is a ‘thermal displacement engine’
Basically an advancement to Sterling Engine technology
Also called acoustic piston, thermo-acoustic resonator, etc.

This definitely opens the door for some more detailed
analysis of this device. Since we already have the math
available for thermo-acoustics, from these and from the
pulse rocket tech.

I need some time to convert my data into a format I can
plug in. I was heading in a whole other direction with this
before your post, thinking along the lines of convection and
thermal expansion of an air mass in an open cylinder.

What you just brought to the table, not only makes more sense
(to me), but is a lot simpler, physics-wise.
Eliminates the need for reiterating redundant equations.

So, if we have a situation like these engines or the pulse rocket,
It stands to reason that their knowledge was acoustic in nature,
From the very beginning, with the advent of fire......

These furnaces could possibly be the early stages of the ancient
acoustic stone art found all over the world??
(maybe that’s too much of a stretch)

There is definitely a spacial aspect to the vortex as well as the
time or ‘humm’ of the furnace jet.
I can easily make it fail by going too far away from the proportional
relationships used by the cavemen.

Still trying to understand the how/why of that mess.
I broke it by making assumptions and trying new things.

So I’m experimentally searching for a hint of the right path
maybe if I play with different proportional dimensions of the
base dimensions (dimensions of the base portion) I can find the
acoustic cavity size(s) coherent with the foundation.
Having the wrong dimensions of a connected cavity disrupts the

If we apply thermo-acoustics to that, we would call it
“Destructive Interference”??

Let me set up some equations and see if I can figure out what
would be the situation if this were a giant thermo-acoustic /
thermal displacement engine.

Also, take a look at the old church organ pipes.
There’s 2 ways those can be made

Half-wave or full wave
If this were viewed like that, it kind of resembles a full wave organ pipe
If we were to take that and apply it to the queens chamber of the great pyramid
And the smaller ante-chamber, and the similar situation found in Malta
I should be able to raise my second chamber to a half-wave....
I’ll make a video of that later, whether or not it “works”.
Before I tear it down and start over.

I was trying to hit the 1/4 wave, but either that’s NOT the right approach,
or the small dimensions require more accurate construction than my hands
like to perform.... There’s something I seem to have missed in the early
stages of schooling, when it comes to sound waves. Some people get this
music stuff, I keep trying to relate it to emf, but there’s something I’m missing.

I tell myself it’s to do with the mass of air, and moving it around,
but it’s probably something more humbling, one of those ‘make you feel stupid
when you hear it’ kind of things....

Anyways, thanks again for your contribution, it seems like the right approach.


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Re: Definition of Thermal Energy and the BTU
« Reply #12 on: December 12, 2017, 01:04:43 PM »
An audio engineer just sent me this

Wavelength =1/(2xFreq)

He said basically if we divide 1 by the dimension
Then double that, then divide 1 by that number
We get the next dimension?

And that all dimensions larger or smaller on that list
Will “work”. (I guess that means we take half instead of
double to go downwards)

He said we don’t really need to know if it’s A,B,C,D,E
Sharp/flat, or all that jazz
He said get a guitar tuner if I really wanted to know.

But he said
Just convert the size to freq. do your math from there,
Then convert it back to size.
(can anyone tell me why I don’t just divide the inches??)
this is why I’m not a musician.....

Anyways, looking at the caveman furnace

1/8 = 0.125, x4, divide it back out
I get =4 (32, divided by 8 to reduce)
We already knew that from the caveman proportions

It stands to reason I could just x or / the measurement
But it doesn’t work like that for some reason

Maybe that’s why every sound isn’t resonant to a 1-inch cavity?
or maybe a 1m cavity?
Or a cavity of 1 kos?

Is there a base wavelength for sound?
Like the plank constant?


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Re: Definition of Thermal Energy and the BTU
« Reply #13 on: December 12, 2017, 03:46:22 PM »
The math is all stupid on this, I’m coming up with something like

Unless there’s some kind of Schumann effect
Which would make this the caveman TPU


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Re: Definition of Thermal Energy and the BTU
« Reply #14 on: December 12, 2017, 03:58:22 PM »
the beauty is the simplicity [in your caveman furnace] it did however leave me wanting for a smaller version to play with.

and then I noticed Tinsel's contribution [serendipity ??]

would be hard to imagine a simpler device to Fuss with and try all manner of ideas

its like a gift to the community IMO .

and as you so rightly point out.. opens other "easy peasy" places to play ..cavity resonance
for one.

and here is another interesting thought experiment from our friend Johan 1955

creating a water hammer effect thru Vacuum resonance [minimal input] to make an entirely different source of heat ......sono/water hammer ?

But who knows ? this huge pressure might manifest in these other experiments too ??

you are very inspiring Sm0ky2
and it is indeed contagious

Chet K