The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)

[Tom Booth]

The added energy has increased pressure, but temperature? Possibly, but this is apparently not essential. So how, or in what way is the engine "running on" i.e. powered by a temperature difference?

I think this is the unicorn forest Matt always talks about.

Explain the mechanism where pressure increases without a temperature increase.

Isn't the fact of the matter that a temperature diffential is needed to start the process?

How would an ambient heat powered engine start running without first having colder air to heat with ambient energy?

I think this is true.

You need a "base temperature" or ground energy level to add energy to for expansion.

And to return to.

But it is still the heat added after that that actually powers the engine, expanding the gas and doing work.

You've more or less just provided a kind of artificial "ground state" or base "equilibrium" to launch the process.

The point, however, is, the ambient heat is not "flowing through" to heat up whatever cooled down the working fluid. The cooling step is, or potentially could be a one time affair.

Now, I have a suspicion there is some "gotcha" hiding somewhere that would foil this plan making such a scheme impossible. So, I keep listening to and carefully considering counter arguments, but, so far... experimentally, the "flow through" hypothesis, as far as I can tell, is unsubstantiated.

Blocking the flow does nothing to stop the engine. Often it actually appears to improve performance

Measuring the "waste heat" is also a big zero. Nothing to measure. Possibly I'm seeing NEGATIVE waste heat. i.e. the engine seems to be taking in heat from both ends, much like a Vuilleumier cycle heat pump.

Not that uncommon or unusual a phenomenon actually. Heat can be used as an energy source to produce refrigeration.

You need, of course, SOME starting temperature of the working fluid to add the energy or heat to to produce expansion.

But the gas expands and returns. The heat goes in as heat and goes out as "work".

So yes, it seems to be true, or a fact, that you need a start temperature and a higher temperature heat source to start the process. Just how much a temperature difference needs to be maintained afterwards? Not much apparently. Not externally anyway. Of course, the internal energy of the working fluid, presumably, continues to fluctuate.

It is really quite difficult and a bit strenuous to think in terms other than heat as a "flow" like a river running through the engine.

In my experiments I'm supplying plenty of heat, and the heat is apparently going into the engine, but not much coming out anywhere.

At this point I'm really moving past theorizing and debate into designing engines based on new principles. Finding ways to retain and fully utilize the heat/energy rather than trying to move it through the engine to the "sink" as quickly as possible.

Also the "absolute zero" the colder the better idea is also a fallacy.

If the engine is utilizing two heat sources for energy input. One hot and the other hotter!

[MikeB]

Tom,
The "absolute zero" thing is a core part of the definition of efficiency for a fuel-powered engine - if the exhaust is at any temperature above absolute zero then there is energy being wasted. It's a particularly poor definition for Stirlings, with the many possible energy sources, but its the best one we have, particularly when comparing with ICE or steam.

And its an essential part of the efficiency of the hot-end - if your working fluid runs at 1000C then you're not going to get as much energy transfer in as if the fluid is at zero - that part is surely incontrovertible?

[Tom Booth]

Tom,
The "absolute zero" thing is a core part of the definition of efficiency for a fuel-powered engine - if the exhaust is at any temperature above absolute zero then there is energy being wasted. It's a particularly poor definition for Stirlings, with the many possible energy sources, but its the best one we have, particularly when comparing with ICE or steam.

And its an essential part of the efficiency of the hot-end - if your working fluid runs at 1000C then you're not going to get as much energy transfer in as if the fluid is at zero - that part is surely incontrovertible?

Not if heat is energy.

"Hot" is energy.

"Cold" is just "less hot" i.e. additional heat/energy.

Absolute zero is the complete absence of energy. Useless.

The only way "absolute zero" can be looked at as helpful is the absurd, upside down world of caloric theory where heat is viewed as something that flows "down hill" to cold.

Heat energy isn't utilized by having all the energy sucked down into a "black hole" of absolute cold. It is utilized by preventing it from going into any "sink" and instead converting it to work.

You are, of course, entitled to your opinions.

A heat (Stirling type anyway) engine is an oscillator.

An oscillator requires energy input from both ends, or at least a "spring" at one end and energy input at the other. It is a "bouncing" between two sources of energy input, like a game of tennis. Back and forth.

Absolute zero has no "bounce" no energy to input or return. In a game like ping pong or table tennis, absolute zero would be the ball falling off the table with only one player

[VincentG]

Here's my contention with the absolute zero thing, the best we can do on earth is exhaust down to 1atm at 300k or so.

So chasing "100%" efficiency is like a baseball player chasing a 1.0 batting average, when .300 is considered excellent, and .400 is unheard.

Instead, re-framing "100%" efficiency seems more productive imo.

[VincentG]

I think what is hard to digest is that the 14.7psi atmospheric return stroke helps a typical gas ECE as much as it does an atmospheric Stirling engine.

It's just that the atmospheric pressure adds a significant level of power to the Stirling engine, due to its low output on expansion, whereas the same atmospheric pressure is miniscule compared to the max pressure gained from a combustion event.

[Tom Booth]

...

Instead, re-framing "100%" efficiency seems more productive imo.

The problem I have with the "Carnot Limit" calculation is that it "reframes" efficiency within its own definition of efficiency.

First you add say 1,000 joules or whatever.

Any sane reckoning of efficiency would determine how much of that 1,000 joules is converted to work, not how much of "all the heat" meaning all the internal energy of the working fluid down to absolute zero can be utilized. Let's say the 1,000 joules is 25% you would have to extract 4,000 joules for 100% "Carnot efficiency" though you only supplied 1,000 joules to begin with!

What people don't seem to realize is that "Carnot efficiency" represents full utilization of ALL the "internal energy", not just the heat supplied.

But I think this is misinterpreted. Some academic not very good at math and without much common sense decided that "Carnot efficiency" represents how much of the supplied heat can be utilized.

So the result is that supposedly only 250 joules out of the 1,000 supplied is supposedly available to convert to work, rather than 25% of all 4,000 that it would take to get down to absolute zero, which is, of course, all 1,000 joules actually supplied. 1,000 = 25% of 4,000

Carnot efficiency is 25% of the 4,000 not 25% of the 1,000. (Or should be, in a sane world)

[Fool]

I find it odd that people accept a COP of 300 or 400 for a real heat pump, when the Carnot COP is 600 and 800.

But have great revulsion to the same Carnot engine getting 16.67% or 12.5%, when a real engine gets 8.333% or 6.25%.

It seems like a big incentive to cherry pick, or just plain deny simple science and data.

Giving a total return for combined engine/heat pump of:
6•0.1667= 1, or 100%. Carnot.

3•0.08333 = 0.25 or 25% real engine.

8•0.125 = 1 or 100% Carnot.

4•0.0625 = 0.25 or 25% real engine.

You can't do better than 100%, probably won't do better than 25% trying to run a combination, AKA a cold hole. The deck is stacked against you.

n=(Th-Tc)/Th has never been broken, not even by you. Your experiment has no measurable output, or just lack of measurements. AKA inconclusive. Anomaly yes. Conclusion no.

When the data comes in on your engines for work output and energy consumed you are welcome to talk, otherwise you have very little to stand on.

Measured work output, and measured energy consumed.

[MikeB]

Fool,
My supposition regarding Tom's observations is that we shouldn't consider it to be an engine at all, rather it is a self-powered heat-pump, since it doesn't drive a load, and therefore the only work it can do is 'internal'.

[Fool]

MikeB, I agree with your last two posts.

Tom doesn't seem to want to prove himself wrong. His experiments typically output zero work, meaning that all the heat supplied, whether it makes it into the engine or not eventually ends up in the room's air at that lower temperature. This makes it 100% irreversible. It is a room heater. A small room heater. He is trying to beat Carnot with a room heater. Zero work output. Carnot is about work. If you don't measure work, you can say nothing about Carnot.

He is confusing rpm with work by claiming that faster rpm means more work "runs better". If he were to put a load on the machine he might see different outcomes. Insulate it and be able to only drive a smaller load, heat up the cold plate more, etc... When there is no measurement of both or either, rpm and torque there isn't sufficient data to conclude anything more than an anomaly. In his case a temperature anomaly. He digs further and further into that temperature anomaly, but not into energy supplied verses work out measurement. I thought he'd have done so by now just to shut me up.

People have been very patient trying to explain that to him.

The reason the Carnot limit is so hard to equal is what it doesn't include. All real engines include them. The 'Carnot was optimistic' thread has included some of those oversights. The Carnot limit ignores, friction, heat source inefficiency, T-flame to Th difference, cycle pausing to make sharp corners. Carnot is a very simplistic, thermodynamic only, maximum. Even if perfect an engine will thermodynamically do no better. It's like shooting at the moon. Reality makes it unobtainable.

It simplifies maximum efficiency so much that, if you don't get how and why it works, you won't understand anything else in the science of thermodynamics. In this thread I've tried to demonstrate and derive the how and the why. Unfortunately, Tom has tried to deny it with much misdirection.

Qh = MCvTh, Qc = MCvTc

n = (Qh-Qc)/Qh = (MCvTh-MCvTc)/MCvTh

Canceling MCv top and bottom gives:
n = (Th-Tc)/Th

That is proof enough for most mathematicians/engineers. They can read between the lines, and get it. I've expanded that proof to cover more of the little points.

Tom, in another thread had difficulty accepting that the equation, {ratio of area to volume = 6•x^2/x^3}, got smaller as x got bigger. Most mathematicians get that by simple inspection. Three pages of arguing that it couldn't be true.

Much as I like Tom his rejection of Carnot is inappropriate. Some people here have been very patient with him. Some have left because of him. In this thread he has asked for proof. I have given it several very simple ways.

Again the compression stroke takes away less energy if cooled, just as the expansion stroke provides more energy if heated. No such thing as a gas contracting. Gas always has a positive pressure. It gets hotter and higher pressure when compressed/(smaller volume). Condensation is not a smaller volume. It is lower density and pressure. Volume stays the same, unless the walls move at the same time. This is physics.

[MikeB]

Here's my contention with the absolute zero thing, the best we can do on earth is exhaust down to 1atm at 300k or so.

So chasing "100%" efficiency is like a baseball player chasing a 1.0 batting average, when .300 is considered excellent, and .400 is unheard.

Instead, re-framing "100%" efficiency seems more productive imo.

I have no idea what baseball stats or scores are like - clearly nothing like the stats and batting scores in cricket!

Anyway, I agree that our discussions and investigations would be far more productive if we had/used a metric that measured the efficiency of the actual engine, specifically ignoring the burner/heat source.

[VincentG]

I don't follow baseball but I guess you're from across the pond then?

For starters, I'd like to see a test conducted that proves actual destruction of heat. Not a reduction of, say, internal energy per cubic centimeter, but actual destruction/ conversion of heat energy.

[Stroller]

I don't follow baseball but I guess you're from across the pond then?

For starters, I'd like to see a test conducted that proves actual destruction of heat. Not a reduction of, say, internal energy per cubic centimeter, but actual destruction/ conversion of heat energy.

Take a bicycle pump, extend it, and block the outlet orifice with your finger.
Push the pump handle in and feel the warmth on your finger where it covers the outlet orifice as the air is compressed. That's kinetic energy being converted to heat.
No let go of the pump handle. It is forced outwards by the warm compressed gas and the gas cools at it expands. That's heat being converted back to kinetic energy.

[matt brown]

Stroller - I think Vincent is suggesting a bang-on demo akin a sloooow isothermal expansion lifting a rock. In this manner, the only 'fuzzy belief' required is that an isothermal expansion has no change in internal energy, whereby all heat input 'must be' converted into work, no ands, ifs, or buts. Unfortunately, such a simple test is hard to scheme since pressure drops during an isothermal expansion.

[Stroller]

Stroller - I think Vincent is suggesting a bang-on demo akin a sloooow isothermal expansion lifting a rock. In this manner, the only 'fuzzy belief' required is that an isothermal expansion has no change in internal energy, whereby all heat input 'must be' converted into work, no ands, ifs, or buts. Unfortunately, such a simple test is hard to scheme since pressure drops during an isothermal expansion.

The pressure and temperature won't drop if the right amount of heat/energy is being put into the gas as it expands.

If we simplify our Stirling engine to a tube with a 102g piston inside, the question becomes, how many Joules of heat do we have to add to the air beneath the piston to raise it by 1m while the gas temperature remains the same. We'll know that the kinetic energy generated was equivalent to 1 Joule, because thats how much force is required to lift 102g through 1 meter (at Earth's surface).

The answer will depend on the tube diameter, because that affects air volume. So let's pick a cylinder bore, and warm up the calculator.

[Stroller]

Charles law states V1/T1 = V2/T2
So if we have a 1cm^2 tube with 100cc of air under the piston, then we need to double its volume to lift our piston by 1m. If we start with 300K air then 100/300 = 200/T2 = 600K
3.65 Joules are needed to raise 100cc of air from 300K to 600K
We used 1J raising the 102g piston 1m. That piston now has 1J extra gravitational potential energy.
Is the gas still at 600K having done the work?