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Topic: Tesla's heat engine (split from DDWFTTW) (Read 3987 times) previous topic - next topic - Topic derived from Direct Down Wind Fast...

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Re: Tesla's heat engine (split from DDWFTTW)
Reply #475

Of course such a scheme could never work.

Or could it?

No.  Any system without a source of external energy is never going to create more energy and the working of your system does that.

So no, it won't work continuously.  It will run down and exhaust itself and come to a constant temperature with the environment.  Just as the drinking bird stops working when it runs out of water to evaporate.

And no, I don't feel the need to explain the laws of thermodynamics to you.  They have lots of information on that in college and in textbooks.  Take a course.  Learn why not.  Or waste your time in attempting to violate the laws and become famous  (Just be sure to explain how you did it for consideration for a Nobel Prize with the Prize money).  Either way, no skin off my back.

Windgrins :grin:


In theory, as well as in fact I suppose, the drinking bird could be set next to an inexhaustible water source; river, lake, ocean, toilet bowl tank with a float valve whatever, so it doesn't run out of water. True or no?

What would the above depicted engine run on? What do you suppose it would eventually run out of? Cooling water? Add a water line and a float valve. Problem solved. Or what is it that is in short supply?

You say "Any system without a source of external energy is never going to create more energy..." but the engine has a source of external energy, the same as the bird has. Doesn't it?

Or what is the "system"?

Ambient heat comes from the sun shining on the atmosphere. That seems pretty external to me.

All good questions.  Allow me to help you state it more clearly and to state what won't occur:

1)  What will never occur is to take ambient energy and create more ambient energy than you started with. (COE).

Agreed, but no one is proposing any such thing.

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2)  Can one take ambient thermal energy via some process of conversion and make it into useful energy by lowering the temperature of the environment which gets replenished from an outside source?  (Supposedly one cannot with a heat engine).

But like a flapping flag, one can capture energy from wind by taking the energy of random motion and shaking an attached magnet next to a coil of wire.  This produces a current which can be rectified and used to do useful work.  The energy comes from the wind being slowed by the flag (no energy creation).  The books all balance because the energy of the closed system never increases.  But a type of randomness is used to do useful work.

Can one do it on a thermal molecular level by capturing the energy of vibrating molecules and using it to do useful work?  I don't know the answer to that.

Windgrins :grin:


Re: Tesla's heat engine (split from DDWFTTW)
Reply #476
Harvest yes. Create no.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #477
Like a flapping flag, one can capture energy from wind by taking the energy of random motion and shaking an attached magnet next to a coil of wire.   This produces a current which can be rectified and used to do useful work.  The energy comes from the wind being slowed by the flag (no energy creation).   The books all balance because the energy of the closed system never increases.  But a type of randomness is used to do useful work.

Wind is not random motion.  It's the opposite - it's coherent motion of an air mass (relative to the earth).  That's why it can be used to generate energy.  The equilibrium state of the atmosphere has no wind.

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Can one do it on a thermal molecular level by capturing the energy of vibrating molecules and using it to do useful work?  I don't know the answer to that.

No, at least not if the vibrations are thermal.  Doing so would violate the second law and is impossible (or more precisely, incredibly unlikely).

Re: Tesla's heat engine (split from DDWFTTW)
Reply #478
Like a flapping flag, one can capture energy from wind by taking the energy of random motion and shaking an attached magnet next to a coil of wire.  This produces a current which can be rectified and used to do useful work.  The energy comes from the wind being slowed by the flag (no energy creation).  The books all balance because the energy of the closed system never increases.  But a type of randomness is used to do useful work.

Wind is not random motion.  It's the opposite - it's coherent motion of an air mass (relative to the earth).  That's why it can be used to generate energy.  The equilibrium state of the atmosphere has no wind.

The question is not of the wind, its of the random flapping of the flag.  The wind is the energy source like in the drinking bird scenario.  The flag combined with the circuit described is the way to convert wind energy to electricity.  Molecules clearly have kinetic energy and they can be slowed selectively with lasers as an example.  In that case, we have to use energy to accomplish the entropy decrease.

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Can one do it on a thermal molecular level by capturing the energy of vibrating molecules and using it to do useful work?  I don't know the answer to that.

No, at least not if the vibrations are thermal.  Doing so would violate the second law and is impossible (or more precisely, incredibly unlikely).

I completely understand that a heat engine cannot do that as it runs on statistical principles.  The question becomes is there a way to selectively harness kinetic energy of individual molecules using another type of device such as described (conversion to electrical energy)?  They would certainly cool in the process and have to be reheated by the ambient thermal energy so no issue with COE.

If you take a look at the referenced article, is what they are stating physically impossible?  It does seem like a violation of the 2nd law so I'm confused if there is a catch or not.

Windgrins :grin:
Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

  • ppnl
Re: Tesla's heat engine (split from DDWFTTW)
Reply #479


Sorry Spork but I have not been paying attention. I have not read all the thread since I was here last but you still seem confused.

When you compress a gas you do two things. You heat the gas and you confine the gas to a smaller volume. All the energy you used to compress the gas shows up as heat. You can use that heat to do work but the efficiency will be very low.

But there is another source of energy to do work. By confining the gas to a smaller volume you have lowered it's entropy. Lower entropy means some of the kinetic energy that was already in the gas is now available to do work. You get that work by allowing the gas pressure to push against a cylinder.

Now it seems like you have got more energy out of the gas than you put in - although much of it in the form of waste heat. And you have. But that's ok because the gas is now at below ambient temperature. The energy equation balances.

Think about the air in a room. Statistically it is possible for all the air molecules to find themselves all on one side of the room at the same time. This violates no law of classic physics but is so statistically unlikely that it is unlikely to happen in billions of times the life span of the universe.

If it happened it would be a violation of the second law of thermodynamics. But that's ok because the second law is only statistical in nature.

But one consequence of such a reduction of entropy of the gas in the room is that there is energy available that was not available before. The energy was there it just wasn't available to do work. Now it is. And as the gas re-expands it will do work on the walls blasting them to splinters. 

Entropy is about how matter is arranged and the consequences for the availability of energy to do work. It is a statistical property of a large number of objects.


Re: Tesla's heat engine (split from DDWFTTW)
Reply #480
I completely understand that a heat engine cannot do that as it runs on statistical principles.  The question becomes is there a way to selectively harness kinetic energy of individual molecules using another type of device such as described (conversion to electrical energy)?

No, for the same reason.  The second law applies to everything, so heat engine or no heat engine is irrelevant.

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If you take a look at the referenced article, is what they are stating physically impossible?  It does seem like a violation of the 2nd law so I'm confused if there is a catch or not.

Hard to tell, but not necessarily.  It sounds like the motion of the graphene they're observing is non-thermal.  If so you might be able to extract work from it, but not indefinitely - it will eventually reach equilibrium and then you won't get any more work out of it (unless you "reset" it by doing work ON it).  In other words it might act like a kind of battery or compressed spring.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #481
I completely understand that a heat engine cannot do that as it runs on statistical principles.  The question becomes is there a way to selectively harness kinetic energy of individual molecules using another type of device such as described (conversion to electrical energy)?

No, for the same reason.  The second law applies to everything, so heat engine or no heat engine is irrelevant.

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If you take a look at the referenced article, is what they are stating physically impossible?  It does seem like a violation of the 2nd law so I'm confused if there is a catch or not.

Hard to tell, but not necessarily.  It sounds like the motion of the graphene they're observing is non-thermal.  If so you might be able to extract work from it, but not indefinitely - it will eventually reach equilibrium and then you won't get any more work out of it (unless you "reset" it by doing work ON it).  In other words it might act like a kind of battery or compressed spring.

A diode in effect captures the electricity produced and it is drained away doing work so there is no charge buildup.  The graphene, like the flag, is being "waved" about by thermal energy in the environment.  Each time the matrix is deformed, supposedly they is a charge build up which is drained away.  The molecule gets jostled away and back again so the local environment cools but is replenished from the larger environment.  At least this is the way I understand what they are saying. 

Again, it's sort of like the drinking bird.  As long as the molecules are jiggling and moving charge around, they are producing organized energy.  So COE is definitely not violated.  The material isn't a gas so I don't know if that matters at all.  But one can think of the material as being waved around by sonic energy in the environment and potentially capturing that so its not clear why random thermal energy won't work. 

I'm not saying it will, I just haven't found the "catch" yet.

Windgrins :grin:
Lunatic Fringe, I know you're out there.  You've got to blame someone for your own confusion.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #482
Sorry Spork but I have not been paying attention. 

No worries.  Thanks for checking in.

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I have not read all the thread since I was here last but you still seem confused...

Fair enough.  But the rest of what you wrote seems to agree completely with my current understanding.  Can you tell me what I've posted that I got wrong?  Thanks.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #483
A diode in effect captures the electricity produced and it is drained away doing work so there is no charge buildup.  The graphene, like the flag, is being "waved" about by thermal energy in the environment.  Each time the matrix is deformed, supposedly they is a charge build up which is drained away.  The molecule gets jostled away and back again so the local environment cools but is replenished from the larger environment.  At least this is the way I understand what they are saying. 

Again, it's sort of like the drinking bird.  As long as the molecules are jiggling and moving charge around, they are producing organized energy.  So COE is definitely not violated.  The material isn't a gas so I don't know if that matters at all.  But one can think of the material as being waved around by sonic energy in the environment and potentially capturing that so its not clear why random thermal energy won't work. 

I'm not saying it will, I just haven't found the "catch" yet.

There are a lot of possible catches.  For instance, maybe the graphene is at a different temperature than the environment.  By the way I glanced at the published paper that article is based on and there's really nothing in there about extracting energy.  It's just about measuring the fluctuations of the graphene.  So the article is fluff.

The bottom line is that once the graphene+environment come to equilibrium, it's impossible to do work with the motion of the graphene.  Think about it - "doing work" means moving some macroscopic object a macroscopic distance.  For that to happen a lot of microscopic motions have to conspire.  For instance, a lot more molecules have to hit one side of a piston than the other.  But you can't control those motions because in equilibrium they are random (if you are controlling them, like confining some gas with higher pressure to a syringe, the system is not at equilibrium).  So the only way they can do work is by a coincidence.  But then you can calculate the probability for that coincidence to happen.  A typical result will be probability = 10^(-(10^23)).

Re: Tesla's heat engine (split from DDWFTTW)
Reply #484
These various nano-level apparent 2nd Law violations regarding graphene, gold, micro-circuitry chips, nano-antennas etc. Have appeared over the years, ending up in a kind of limbo of "it looks like" "but maybe" with little follow-up as far as ever settling the 2nd law question.

Like this one for example:


https://www.technologyreview.com/s/427140/graphene-battery-turns-ambient-heat-into-electric-current/

All in all the cumulative evidence suggests that on a nano scale at least, the 2nd law is in the toaster. Or tetering on the edge.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #485
Another example; this was online for many years around 2008 to 2014. I've referenced it many times on other forums over the years.  I can only find a somewhat pared down report archived on the Wayback Machine now. The original article was more extensive, from what I remember. It would be interesting to follow up on this.

https://web.archive.org/web/20080121142844/http://www.theimagingsource.biz:80/en/technology/ambientheatelectricity/

A patent for the technology has been awarded:

Patent #: US20090095908 

http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&s1=20090095908.PGNR.

Thermal image of the chip cooling its surroundings while generating electricity:





The company wrote: "This technology proves that cooling does not require the input of external energy." which I found most interesting.

In theory, if you can cool without external energy input I'd think you should be able to utilize ambient heat without external energy input. We've already seen something like this earlier in the thread involving some material "tuned to deep space" that could be used to cool buildings. This chip works on a different principle. It is apparently "tuned" to the infrared frequency, absorbs heat (infrared light) and converts it to electricity, though the electrical output is unusable as far as I know, other than as a source of some heat. The device simply removes heat from the surroundings and transfers it (the energy/electricity) to a resister of one sort or another.

I sent a message to the company requesting any additional information that might be available.

Nano-antennas are another front:

https://www.youtube.com/watch?time_continue=147&v=BFzGZxqN6eY

"The nanoantennas' ability to absorb infrared radiation makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and re-emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners and fans."

I think this may be different from the information someone posted earlier.

https://www.sciencedaily.com/releases/2008/08/080810214010.htm

This sort of nano-research into utilizing ambient heat has been going on for at least the past 10 years.

When you can get your devices down to the size of individual atoms and electromagnetic waves why shouldn't the kinetic energy of individual molecules be accessible as well? You are no longer limited to statistical sampling.

The problem of Maxwell's demon requiring energy to sort out the molecules doesn't seem to apply as these devices are completely passive or receptive.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #486
https://www.scientificamerican.com/article/second-law-of-thermodynam/

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The truth of the second law is ... a statistical, not a mathematical, truth, for it depends on the fact that the bodies we deal with consist of millions of molecules... Hence the second law of thermodynamics is continually being violated, and that to a considerable extent, in any sufficiently small group of molecules belonging to a real body.  - James Clerk Maxwell

This sort of thing is not really news IMO.

But personally I don't see the difference between something like a nano-antenna and a Stirling Engine's regenerator.

The regenerator is a fine mesh of a certain type of metal. Stainless steel works well (best) for a small model engine. Hobbyists, (model Stirling Engine builders) have experimented with many different materials and there has been general consensus that stainless steel wool, such as a common pot scrubber, absorbs and releases heat just right. It will hold the heat as long as necessary but release it easily when necessary. (I think a Nickle-Titanium alloy might work better as it undergoes an actual solid to solid phase change)

What is hitting these stainless steel fibers other than individual molecules on a nano-level?

A gas or air is composed of individual molecules, if you could get right down there and see what's happening. And how is the heat being released other than to individual air molecules as they pass back through the steel wool? If we knew more about what is really going on, couldn't someone make an even more effective nano-regenerator material?

The type of regenerative heat exchanger or regenerator used in Stirling engines can reach very high efficiency, that is, it will return  practically all the heat it absorbs. I think it is unfortunate though, that today the market is flooded with "toy" so-called Stirling Engines that do not have a regenerator at all.

If you want a "real" Stirling Engine with a regenerator, most likely you will have to make it yourself or make the necessary modifications.

Some people have argued that because Stirling Engines work because heat passes through the engine the regenerator is unnecessary and just ads "dead air space" that saps efficiency. In theory, this should be true, judging by the second law. The faster the heat goes through the engine and gets out the other side to the cold sink the better. As the engine requires not only heating but also cooling. But those who have actually experimented with going back to the old school method of using a regenerator have found that adding a regenerator to a modern so-called Stirling Engine without one, makes for a vast improvement in performance and actual heat utilization.

Flooding the market with so-called "Stirling Engines" that don't actually work seems almost like some kind of intentional misinformation campaign to give people the impression that these engines are useless.

In fact the slower the heat passes through the engine, The more completely the heat is utilized, the more energy is actually converted, the less heat reaches the sink. Ideally, no heat needs to pass through the engine at all. No more than sunshine needs to pass through a photovaltaic panel.

You could run a Stirling engine by putting one side in the sun and the other in the shade. But "SHADE" is not anything but an absence of heat or the absence of sunshine. A lack of energy. It is not a power source.

It is difficult to "SHADE" a heat engine from AMBIENT heat as ambient heat has no specific direction, it is all around on all sides. But it is not "impossible".

The idea of a "Cold Hole" is not using "cold" or ice to run a stirling engine, it is just a way of providing "SHADE" from all the ambient heat.

Internally a displacer and/or or regenerator simply SHADES part of the engine from the incoming ambient heat. The SHADE is necessary, but you don't need energy to maintain shade, you just have to prevent energy from getting past or through whatever is providing the shade and that is what a regenerative heat exchanger does very very well. It can prevent heat from passing through. It traps the heat and sends it back the way it came. If the heat isn't used, it gets sent back.

It may be that any kind of protected "cold hole" is not really necessary as the result of utilizing heat from a gas or air is cold gas or cold air.

Of course you have to make some cold initially. Provide some "SHADE" so to speak. But once established it does not take any additional energy to continue to MAKE SHADE. If you start your Stirling Engine on ICE, it may be that you don't have to continually make more ice to keep it going.

If someone ran a Stirling Engine on Ambient Heat with a Dewar on the other side, I believe the ice or whatever cold substance was in the dewar would not melt, or would melt extremely slowly or would remain cold, as the Engine, in particular the displacer within the engine (assuming your Stirling Engine is a REAL Stirling Engine and actually has a displacer), is shading the ice from the ambient heat, much like a thermoelectric generator might operate just by sitting in the sun, as the device itself would provide the shade to keep the side opposite the sun cooler. You do not necessarily have to actively cool the cold side. But even supposing that you did, why couldn't you use the energy produced by the device to accomplish that, since there is comparatively little heat  to remove compared with the energy gain from the hot side.

It should actually be easier to do "SHADE" a Stirling Engine from ambient heat than to "shade" the cold side of a thermoelectric generator from the sun as there is not any direct connection between the hot and cold sides of a Stirling  engine, (other than the air you are extracting energy from) so heat passage from conduction could be entirely eliminated and heat transfer through the only remaining channel; the regenerator, can be extremely efficient.

Edit: rather preventing heat transfer with a regenerator is extremely efficient.
  • Last Edit: November 29, 2017, 01:39:41 PM by Tom Booth

Re: Tesla's heat engine (split from DDWFTTW)
Reply #487
Tom,  I'm probably not following closely enough, but let me ask anyway...

I think you're proposing a heat engine that operates using the heat of the atmosphere, but no heat "flows through" the heat engine - is that correct?  If so, is it cooling the atmosphere in exchange for the work done?  If so, where does this cooling occur?  Thanks.


Re: Tesla's heat engine (split from DDWFTTW)
Reply #488
Tom,  I'm probably not following closely enough, but let me ask anyway...

I think you're proposing a heat engine that operates using the heat of the atmosphere, but no heat "flows through" the heat engine - is that correct?  If so, is it cooling the atmosphere in exchange for the work done?  If so, where does this cooling occur?  Thanks.



Thanks for taking the time to read the thread and for asking questions. That goes for everyone. I do enjoy debating the subject, but I'm also not doing this just for fun or as a joke. I think the consequense of all this, if I'm right, could have a real impact on the future of our world and I want to do all I can to get the message across as clearly as possible.

I will post a kind of Carnot cycle diagram of what I believe could be going on in the Stirling engine (operating without a flywheel) already.

How we can then improve on that is another issue. I should say I'll compare the Stirling with the Carnot cycle. There really are no proper thermo terms for describing this cycle.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #489
First, maybe someone would like to see the Carnot Cycle:



Note perhaps that this is a description of a completely idealized engine which does not and cannot work in reality. There are no standard thermodynamic terms to describe what happens in a real engine, as far as I know, where heating work and compression all act on the gas simultaneously.


Alright, I ended up making a diagram of a Stirling Cycle WITH a flywheel, but I think it can be seen how the same cycle could take place without a flywheel. (If not I will try to explain further another time)

This diagram explains how (I believe) a REAL Stirling engine actually operates and why a flywheel is not really needed. If the piston is heavy enough or if it does work via a linear alternator the effect would be similar to the engine doing work on the flywheel. It should be noted in particular that the flywheel is NOT what causes the return of the piston as generally supposed which can be proven by removing the flywheel demonstrating that the engine can operate without it.



Explanation of the cycle:

At #1 the internal heat and pressure rise rapidly as piston does work on the gas transferring energy to the gas and raising the temperature of the gas while also the gas is being compressed further raising the temperature while the gas also absorbs heat from the heat source. Energy to compress the gas comes from the atmosphere and momentum of the piston primarily and also from energy(momentum) previously stored in the flywheel if present.

At #2 Gas is at maximum heat and compression. The temperature of the compressed gas has risen higher than the temperature of the heat source. Much heat is temporarily transferred or stored in the regenerator matrix. Excess heat returns to the heat source. Due to the high compression and energy added to the gas, the temperature of the gas may briefly exceed the temperature of the original heat source.

At #3 As the flywheel passes Bottom Dead Center the highly compressed gas at its maximum heat and pressure expands explosively driving the piston upward with great force, transferring energy to the flywheel (if present). It is at this stage when the highly compressed and heated gas expands and the HEAT energy is converted into WORK as ALL the gas molecules under great heat and pressure expand rapidly and simultaneously. There may be some localized transfer of heat energy to the outside atmosphere as the piston pushes atmospheric air out of the cylinder.

At #4 The gas has reached "maximum expansion" upon using up all of the energy it derived from the heat source some heat energy continues to be transferred to the outside atmosphere. At this point the gas would STOP EXPANDING if not for the momentum of the piston itself and the flywheel if attached. This additional mechanical expansion begins to have a refrigerating effect on the gas. The engine is no longer acting as an engine but rather as a refrigerator or "heat-pump" using the "outside energy" stored in the flywheel or the momentum of the piston itself. The temperature of the gas in the cylinder begins to dip below ambient so heat may begin migrating to the cooled cylinder from the outside ambient atmosphere.

At #5 Due to the momentum stored in the piston and flywheel the piston continues up the full length of the cylinder until it reaches Top Dead Center. This action results in a mechanical expansion of the gas which has a refrigerating effect on the gas. The gas cools to below ambient temperature. Heat which has been transferred to the outer atmosphere largely dissipates but outside atmospheric pressure pushes down on the piston. Some heat may transfer from the outside ambient atmosphere to the cool cylinder.

At #6 Having passed Top Dead Center the piston is freed to move inward. It is driven inward by pressure of the outside atmosphere which does work on the piston, which in turn does work on the gas. Put another way the piston is "pulled" inward by the partial vacuum in the cylinder caused by the previous mechanical expansion and refrigeration of the gas..As the piston approaches Bottom Dead Center the temperature and pressure of the gas rise sharply and suddenly and the cycle repeats.

It should be noted that heat only ever leaves the engine by being transferred BACK TO THE HEAT SOURCE. Heat is never transferred to the heat sink, though some heat may be transferred FROM the so-called "heat sink" to the engine while the engine is in its refrigerating stage (#5).



Re: Tesla's heat engine (split from DDWFTTW)
Reply #490
I think you're proposing a heat engine that operates using the heat of the atmosphere, but no heat "flows through" the heat engine - is that correct?  If so, is it cooling the atmosphere in exchange for the work done?  If so, where does this cooling occur?  Thanks.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #491
I think you're proposing a heat engine that operates using the heat of the atmosphere, but no heat "flows through" the heat engine - is that correct?  If so, is it cooling the atmosphere in exchange for the work done?  If so, where does this cooling occur?  Thanks.

I'm guessing you've seen the above cycle.?

Yes, correct

Yes and

See the above. Just make the heat source at the bottom = ambient heat.

That is, between #2 and #4 of the cycle or essentially #3 when the gas expands very rapidly and accomplishes "work" by driving the piston out.
  • Last Edit: November 30, 2017, 06:43:29 AM by Tom Booth

Re: Tesla's heat engine (split from DDWFTTW)
Reply #492
To be clear, heat flows INTO the engine only not Through or out.

The heat flowing into the engine is converted into work.

As the gas does work it loses energy, resulting in a temperature drop.

Some additional cooling takes place at #4 and #5 as a result of mechanical expansion but the gas is not doing work or losing energy there. The cooling (converting heat into work) takes place at #3

Strictly speaking the engine is not exactly cooling the atmosphere as it is an "infinite reservoir". Heat is taken out of it (out of the atmosphere that is) but this does not really cool it (the atmosphere) perceptibly. (as it is very very very large and contains an enormous amount of heat).
  • Last Edit: November 30, 2017, 08:43:44 AM by Tom Booth

Re: Tesla's heat engine (split from DDWFTTW)
Reply #493
Oh... Also there is likely some cooling of the atmosphere at #5 as shown due to the refrigerating effect on the cylinder and also cooling between #6 and #2 due to atmospheric air doing work on the piston. The atmosphere is a gas and when a gas does work it loses heat and there is a drop in temperature - this is represented by the light blue color of the air above the piston at that part of the cycle, though again, the temperature change would likely be scarvely appreciable as again this is a virtually infinite heat reservoir. Nevertheless a conversion of heat into work and a localized cooling of the atmosphere is taking place.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #494
It should probably be noted or added also that when the heat source is ambient the cylindar should be as non-heat conducting as possible and the space surrounding the upper cylinder should be well insulated.

Needless to say, people on Stirling engine forums familiar with laminar flow Stirlings think I'm daft whenever I start talking abour insulating the cylindar on the cold side where it is usual for excess heat to be disipated.
  • Last Edit: November 30, 2017, 08:21:27 AM by Tom Booth

Re: Tesla's heat engine (split from DDWFTTW)
Reply #495

On this diagram where does the heat go in?

Also, it's not clear to me whether the ice-water is cooling the pipe or vice versa.


http://calypso53.com/stirling/Self_Cooling_Stirling_5.jpg

Re: Tesla's heat engine (split from DDWFTTW)
Reply #496

On this diagram where does the heat go in?

Also, it's not clear to me whether the ice-water is cooling the pipe or vice versa.



This is essentially an LTD Stirling Engine running on "Ice" or, in other words, ambient heat. The sketch is admittedly rather rough, sorry.

Similar to this with the ice or cold on the bottom:

https://www.youtube.com/watch?v=fEFZIWtQUWw

The ambient heat would, of course, be entering the engine from the top. The large top metal plate of the engine is taking in heat from the air above it.  The metal plate is warmed by the air above it and that in turn warms the air inside the engine. The top metal plate is basically acting as a heat exchanger.

The engine is pumping air into the pipe which raises the temperature of the air in the pipe. This hot pipe could be used to add additional heat to the top plate of the engine. After some heat has been removed from the pipe by the engine any additional heat can be removed by the cold water bath before the air in the pipe is further cooled by expansion under the engine.

The cold air could then be recirculated, re-compressed, at which point it would then heat up again, but this time it would be more dense and compressed.

Lind recirculated cooled and compressed air over and over in this way as long as it took to get it down to liquid air temperature, several hundred degrees below zero.

I have never run this setup so I really don't know what will happen when and if the air starts to go below freezing UNDER the engine as intended.

Apparently it (the recirculated cold air) can be re-compressed even when hundreds of degrees below zero and heat can then still be removed with a cool water bath. I assume however that this would not be possible with a small model engine. Apparently, with high enough compression the air can be cooled with ordinary water as long as the air continues to remain a gas, that is, until the air condenses into a liquid. For that to happen though, I would assume a much bigger, more powerful engine would be necessary than the small model I have in mind for testing. Though presumably, some kind of similar heating and cooling effect should take place even in a small model engine.

So to put it simply, the cold water bath is intended for cooling the hot compressed air in the pipe, but ideally, much of the heat will already have been removed and utilized by the engine and so converted into work output. The water bath is just to ensure that the air in the pipe is good and cold before it is expanded in the chamber under the engine. From my general reading on the subject such pre-cooling before expansion can result in very cold temperatures on the order of -50 F even with fairly low compression.

As I have never built or actually ran such an engine I'm unsure just how much heat the engine could utilize. The main power source is ambient heat, the hot compressed air is just additional heat that could be utilized. The main purpose of compressing and cooling the air before expansion is to create a "cold hole" under the engine.

I hope this is not too confusing.

Basically the top metal plate of the engine is the HOT side and the bottom metal plate is the cold side.

Of course this arrangement could be reversed and the engine would run either way, but as I mentioned before I think there may be some advantage to keeping the heat on top as this would assist our efforts to prevent heat passing through the engine as hot air has a natural tendency to rise.

I should have erased the words "Heat source - starter" as by this time the "starter" has been removed and the engine is supposed to be running on ambient heat entering through the top plate.

Re: Tesla's heat engine (split from DDWFTTW)
Reply #497
One important detail missing from the illustration is some power output somewhere, like a little generator powering a small light bulb. As if this arrangement were successful at converting heat into another form of energy like electricity, there needs to actually be somewhere for this energy to go.

The electrical load would act as a substitute for the break on the turbine.

An interesting aspect of air cycle cooling with a turbine is that there needs to be a load on the turbine to effect cooling. In otherwords, taking power OUT of the system via an electric load on the system is what effects the cooling which theoretically allows the system to continue operating. If you have ambient heat energy going in and being converted to electricity you also need an equivalent amount of energy going out somewhere in the form of a load on the turbine.

The turbine is primarily where the conversion of energy is taking place. The air is. First compressed in the pipe. The heat removed from the compressed gas leaving pressure. The pressure becomes velocity as the air expands through the turbine. This velosity of the air escaping through the turbine powers the turbine that can drive a generator and produce electricity.

Granted this is no doubt horribly inefficient due to the sheer number of energy conversions but, given that the energy is essentially free from the air, how much does efficiency really matter?


Re: Tesla's heat engine (split from DDWFTTW)
Reply #498
An interesting observation regarding Stirling engines in general is that they start up with quite a bit of apparent labour involved. Faltering, stalling, running slowly.

As they get going and continue to run though, something happens and they seem to get into a grove and run better. Something similar happens when a load is applied. The engine may hesitate and faulter but it will, if it continues running adjust to the load and develop more power and torque as it continues to operate under load.

Load balancing is, or would be a very important factor as far as keeping such an engine going, as it is with any power generating system. But it is important in a strange sort of way with a Stirling engine as the engine cools itself by converting the heat into work.

Without a load, the engine will have a greater tendency to overheat. Or rather, without a load on the engine you get a kind of bottleneck.

This is partly responsible for the apparency that small model Stirling engines are quite feeble and can barely overcome their own friction. This is, I believe, because these engines are for show and are almost never loaded. They are not powering anything, only freewheeling.

It will be found though that given some work to do, heat in the engine finds an outlet. The engine runs cooler. The temperature difference gradually increases and as the engine adjusts to the load it runs stronger and develops more torque and power, whereas without a load it had none.

If you put energy into the system you need a load to take it out or you get a bottleneck and the system will faulter. Build up heat and come to a stop.

  • MikeB
Re: Tesla's heat engine (split from DDWFTTW)
Reply #499
...
This is partly responsible for the apparency that small model Stirling engines are quite feeble and can barely overcome their own friction. This is, I believe, because these engines are for show and are almost never loaded. They are not powering anything, only freewheeling...
This issue with "small" models is likely found in the ratio of frictional area to working volume.  If we assume a fixed stroke and a fixed piston length, the piston frictional area increases in proportion to cylinder diameter, but the volume of working gas (piston stroke times piston area) increases as the square of the cylinder diameter.

More realistically, if we assume piston length and stroke are in direct proportion to the bore, the frictional area of piston against bore is in proportion to the square of the bore and the volume of working gas is in proportion to the cube of the bore.  I believe you can see the implications.