Is Carnot efficiency valid?

[studiot]

Since this thread is about Carnot Efficiency and the Carnot Cycle refers to and was conceived as using only reversible processes I thought I would look around and post this link to a modern publication that claims to achieve Carnot efficiency for an irreversible process, notable the Feynman Ratchet.

https://pubmed.ncbi.nlm.nih.gov/28878219/

 

The paper is downloadble as a pdf at 2.9M

I haven't had time to study it properly yet, but it doesn't seem to avoid mentioning the standard proof of Carnot via a proposed more efficient engine leading to a contradiction.

 

Quote

Carnot efficiency is reachable in an irreversible process

Jae Sung Lee  ¹ , Hyunggyu Park  ²

Affiliations

• PMID: 28878219
• PMCID: PMC5587685
• DOI: 10.1038/s41598-017-10664-9

Free PMC article

Abstract

In thermodynamics, there exists a conventional belief that "the Carnot efficiency is reachable only in the reversible (zero entropy production) limit of nearly reversible processes." However, there is no theorem proving that the Carnot efficiency is unattainable in an irreversible process. Here, we show that the Carnot efficiency is reachable in an irreversible process through investigation of the Feynman-Smoluchowski ratchet (FSR). We also show that it is possible to enhance the efficiency by increasing the irreversibility. Our result opens a new possibility of designing an efficient heat engine in a highly irreversible process and also answers the long-standing question of whether the FSR can operate with the Carnot efficiency.

 

5 minutes ago, swansont said:

The hot reservoir heats up the gas. That’s the Q_H. The gas heats up the cold reservoir. Q_c

It is worth noting that there is no such thing as an ideal hot or cold reservoir in the real world.

The best we can do it to take something where the heat content of the reservoir is many orders of magnitude greater than the heat being used in the engine.

Edited January 26, 2023 by studiot

[sethoflagos]

12 minutes ago, studiot said:

Since this thread is about Carnot Efficiency and the Carnot Cycle refers to and was conceived as using only reversible processes I thought I would look around and post this link to a modern publication that claims to achieve Carnot efficiency for an irreversible process, notable the Feynman Ratchet.

I remember the Brownian ratchet being comprehensively debunked by Magnasco 30 years ago, which was 30 years after Feynman's original debunking. Is someone trying to resurrect the long dead?

[studiot]

8 minutes ago, sethoflagos said:

I remember the Brownian ratchet being comprehensively debunked by Magnasco 30 years ago, which was 30 years after Feynman's original debunking. Is someone trying to resurrect the long dead?

Thank you for that, I had never heard of it before today's search.

The reference I gave is a US government document dated 2017

 

[Tom Booth]

Came up with some temperature probes. A "perfect prime" with four and a multimeter makes one more. Not great and not all in 100% agreement on the temperature, but within a few degrees C.

The multimeter reads a little high and probe #4 seems to have a bad connection reading a little low or sometimes way off or goes blank entirely but comes back and reads good if I wiggle the connector but is not reliable.

Response time for the multimeter is real slow. The perfect prime is better, but the refresh rate of the digital display takes a second.

I can probably get some average temperatures from several points on the engine simultaneously.

Not much hope of getting real time temperature changes of the working gas with compression and expansion with these, but we can see what we can see I guess.

Suggestions about where to place the leads etc. are welcome.

 

[sethoflagos]

There's an interesting interactive site at https://www.flycarpet.net/en/phonline where you can study refrigeration cycles for various refrigerants.

I had a little play this morning with a propane (R290) based cycle between 300K and 250K, and pressures 2 bar and 10 bar.

Assuming isentropic compression/expansion I got Q_H = 351 J for a work input of 61 J (scaled to 1 kg of propane traversing the full circuit).

 ie a thermodynamic advantage of very nearly 6:1.

To put this in context with the OP, we can see that the Carnot limit for a heat pump operating between these temperatures is 0.1667 or 1:6 exactly. This is no coincidence.

If we operate an ideal Carnot cycle between hot and cold sinks generated by the refrigerant cycle, from Q_H = 351 J we can potentially generate a work output of 351/6 =58.5 J. Not quite enough to run our refrigerator. So no free power.

If the Carnot limit was only a little bit of an underestimate, we'd have over unity-machines and all that nonsense. 

Have a play. See if anyone can get a thermodynamic advantage above 6:1  (and break the universe as we know it)

[studiot]

3 minutes ago, sethoflagos said:

There's an interesting interactive site at https://www.flycarpet.net/en/phonline where you can study refrigeration cycles for various refrigerants.

I had a little play this morning with a propane (R290) based cycle between 300K and 250K, and pressures 2 bar and 10 bar.

Assuming isentropic compression/expansion I got Q_H = 351 J for a work input of 61 J (scaled to 1 kg of propane traversing the full circuit).

 ie a thermodynamic advantage of very nearly 6:1.

To put this in context with the OP, we can see that the Carnot limit for a heat pump operating between these temperatures is 0.1667 or 1:6 exactly. This is no coincidence.

If we operate an ideal Carnot cycle between hot and cold sinks generated by the refrigerant cycle, from Q_H = 351 J we can potentially generate a work output of 351/6 =58.5 J. Not quite enough to run our refrigerator. So no free power.

If the Carnot limit was only a little bit of an underestimate, we'd have over unity-machines and all that nonsense. 

Have a play. See if anyone can get a thermodynamic advantage above 6:1  (and break the universe as we know it)

This fits with a worked example I was thinking of posting, if anyone is interested.

 

Quote

Ikg of air is taken through a Carnot Cycle. The initial pressure and temperature are 1.73MN/m² and 300^oC.

From the initial conditions the air is expanded isothermally to three times its initial volume and then further expanded adiabatically to 6 times its initial volume. Isothermal compression followed by adiabatic compression complete the cycle.

a)The pressure, volume and temperature at each corner of the cycle.
b) The thermal efficiency of the cycle.
c) The work done per cycle.
d) The work ratio

 

The thermal efficiency works out at 19% and the last figure , the work ratio at 0.133

This work ratio figure is useful as it tells us exactly how much work we can get out of such a heat engine at maximum compared to tthe total work done during the expansions and contractions.

@Tom Booth

Do you understand that Carnot conceived his cycle using equilibrium processes which are regarded as maximal.

The stirling cycle is of interest because it is one such that can theoretically approach this maximum by arranging parts of the cycle when no work is done (ie at const volume) and parts at equilibrium (the isothermal parts)

?

[Tom Booth]

3 hours ago, sethoflagos said:

There's an interesting interactive site at https://www.flycarpet.net/en/phonline where you can study refrigeration cycles for various refrigerants.

I had a little play this morning with a propane (R290) based cycle between 300K and 250K, and pressures 2 bar and 10 bar.

Assuming isentropic compression/expansion I got Q_H = 351 J for a work input of 61 J (scaled to 1 kg of propane traversing the full circuit).

 ie a thermodynamic advantage of very nearly 6:1.

To put this in context with the OP, we can see that the Carnot limit for a heat pump operating between these temperatures is 0.1667 or 1:6 exactly. This is no coincidence.

If we operate an ideal Carnot cycle between hot and cold sinks generated by the refrigerant cycle, from Q_H = 351 J we can potentially generate a work output of 351/6 =58.5 J. Not quite enough to run our refrigerator. So no free power.

If the Carnot limit was only a little bit of an underestimate, we'd have over unity-machines and all that nonsense. 

Have a play. See if anyone can get a thermodynamic advantage above 6:1  (and break the universe as we know it)

Interesting, though I don't really understand what you are doing, or trying to do.

What do you mean by "between 300K and 250K"? For a refrigeration cycle?

Initially a refrigerator sits in a room at let's say 300k (uniform temperature).

So what does 250k and 300k represent in the real world and which way is the heat being pumped?

For example, are we pumping heat out from a 250k refrigerator box to the 300k environment or from a 300 K environment to a 250k water tank to warm water to take a bath?

In other words, what is the initial temperature before plugging in the heat pump/refrigerator and which way is the heat being moved?

A refrigerator has a condenser that heats up, hotter than the ambient and an evaporator that cools down below the ambient, so is usually not "operating between" those two temperatures. Rather it would be operating in, say, a 300k environment to create a refrigerated space in an insulated box, dumping all the heat into the 300k environment to create a lower temperature in a refrigerated space.

To do that, the condenser coils would have to be much hotter than the 300°k the heat is being moved into. Maybe 375°k ?

If that were the case, how big is the refrigerated box? How long does the unit have to run to bring the temperature down 50° ? How well is the box insulated?

If instead we want to quickly warm cool well water from out of the ground from 250°k up to the ambient 300°k would that take more or less energy than the reverse process? I'm taking heat from a warm environment (ambient air at 300k) and dumping it into a cold environment (water at 250°k)

Or, was it 275°k ambient to generate 250°k and 300°k at the evaporator and condenser respectively?

Then the heat pump would be operating "between" ????

Well, literally, between 275°k and 275°k just pulling heat from point A and dumping it at point B.

Needless to say, I think everyone could agree it is easier to push a car along a flat plane than to push it up a hill and we'll, down hill really takes no effort at all.

Edited January 27, 2023 by Tom Booth
Changed 500°k to a more realistic 375

[sethoflagos]

@Tom Booth

The working fluid, propane in this case, flows around a circuit ABCD

It is arbitrary which point we start at, but let's say it's the inlet to the compressor.

At this point A I picked a pressure of 2 bar and an enthalpy of 550 kJ/kg. This corresponds to a temperature of -22.7 ^oC, entropy of 2.427 kJ/kgK and quality q = 1 (mass fraction in vapour form)

Path AB is isentropic compression to 10 bar. The entropy at point B is 2.427 kJ/kgK when the enthalpy is 626 kJ/kg, temperature 38.5 ^oC and q = 1. The work input required for this stage is W_C = 550 - 626 = -76 kJ/kg

Point C is after heat exchange to atmosphere, still at 10 bar, temperature now 26.9 C, enthalpy 275 kJ/kg, entropy 1.257 kJ/kgK and q = 0.014 (nearly all liquid). Path BC implies an ambient temperature of a little less than 26.9 ^oC which is the fixed point for the system. It will ride up and down on this according to climatic conditions. Under the stated conditions we have an exhaust to the hot sink Q_H = 275 - 626 = -351 kJ/kg.

Path CD is isentropic expansion down to 2 bar, so entropy remains 1.257 kJ/kgK, temperature -25.5 ^oC, enthalpy 260 kJ/kg and q = 0.298. This stage generates a work output WE = 275 - 260 = 15 kJ/kg. 

Path DA is a constant pressure (nearly isothermal) cooling of a refrigerated space. The temperature at A constrains this space to be a little above -22.7 ^oC. Q_C = 550 - 260 = 290 kJ/kg.

You seem to have difficulty with my use of the word 'cycling'. It refers in this case to the changing state of a 1 kg mass of propane cycling around and around the system.

In a real practical system, we would probably lose the turbo expander in path CD (too complicated and problematic for such a small efficiency saving) and replace with a simple adiabatic flash nozzle.

[Ghideon]

On 1/26/2023 at 12:31 PM, Tom Booth said:

It is a continuation of the same line of research.

 

Thanks for your reply. I do not yet have the skills required to dig into the details of the setup and the technical discussion, can you provide a simple statement of a hypothesis you are testing? The topic is "Is Carnot efficiency valid?" and maybe there is some way to state your ideas something like: "An ideal* sterling engine running from an input power X will in a perfectly isolated environment have the output power of Y".

This may help separate any misunderstandings about sterling engines and physics from the technical details of the actual experimental setup.

 

*) Of course not possible to build but maybe useful in stating an idea.

[Tom Booth]

34 minutes ago, sethoflagos said:

@Tom Booth

The working fluid, propane in this case, flows around a circuit ABCD

It is arbitrary which point we start at, but let's say it's the inlet to the compressor.

At this point A I picked a pressure of 2 bar and an enthalpy of 550 kJ/kg. This corresponds to a temperature of -22.7 ^oC, entropy of 2.427 kJ/kgK and quality q = 1 (mass fraction in vapour form)

Path AB is isentropic compression to 10 bar. The entropy at point B is 2.427 kJ/kgK when the enthalpy is 626 kJ/kg, temperature 38.5 ^oC and q = 1. The work input required for this stage is W_C = 550 - 626 = -76 kJ/kg

Point C is after heat exchange to atmosphere, still at 10 bar, temperature now 26.9 C, enthalpy 275 kJ/kg, entropy 1.257 kJ/kgK and q = 0.014 (nearly all liquid). Path BC implies an ambient temperature of a little less than 26.9 ^oC which is the fixed point for the system. It will ride up and down on this according to climatic conditions. Under the stated conditions we have an exhaust to the hot sink Q_H = 275 - 626 = -351 kJ/kg.

Path CD is isentropic expansion down to 2 bar, so entropy remains 1.257 kJ/kgK, temperature -25.5 ^oC, enthalpy 260 kJ/kg and q = 0.298. This stage generates a work output WE = 275 - 260 = 15 kJ/kg. 

Path DA is a constant pressure (nearly isothermal) cooling of a refrigerated space. The temperature at A constrains this space to be a little above -22.7 ^oC. Q_C = 550 - 260 = 290 kJ/kg.

You seem to have difficulty with my use of the word 'cycling'. It refers in this case to the changing state of a 1 kg mass of propane cycling around and around the system.

In a real practical system, we would probably lose the turbo expander in path CD (too complicated and problematic for such a small efficiency saving) and replace with a simple adiabatic flash nozzle.

No, not the word "cycling". 

I was just unsure what the 300°k applied to (in the real world).

From your current elaboration it seems 300°k is the ambient temperature the heat pump is operating in. ("Path BC implies an ambient temperature of a little less than 26.9 ^oC which is the fixed point for the system.")

26.9°C = 300K

So the heat pump/refrigerator is operating in a 300°k environment, is that correct? And taking the temperature of the refrigerator down to 250°k ? Umm.. freezer? That's really cold.

But you say also: "Point C is after heat exchange to atmosphere, still at 10 bar, temperature now 26.9 C"

I assume you mean heat exchange from... atmosphere. (?)

But the system is drawing heat from the freezer box at 250°k not atmosphere. It has to dump the heat into the 300°k

Sorry if I'm groping a bit with all this. I think in terms of Fahrenheit and have to convert Celsius and Kelvin to make sense of anything.

I'm also trying to figure out if your example/calculations make sense in a real world application.

It seems from what you have described that the refrigerator condenser will be just 311°k dumping heat into a 300°k environment. On a hot day could this refrigerator still function?

You say "turbine". What type of refrigeration system are we talking about?

 

 

1 hour ago, Ghideon said:

Thanks for your reply. I do not yet have the skills required to dig into the details of the setup and the technical discussion, can you provide a simple statement of a hypothesis you are testing? The topic is "Is Carnot efficiency valid?" and maybe there is some way to state your ideas something like: "An ideal* sterling engine running from an input power X will in a perfectly isolated environment have the output power of Y".

This may help separate any misunderstandings about sterling engines and physics from the technical details of the actual experimental setup.

 

*) Of course not possible to build but maybe useful in stating an idea.

As far as I understand the forum rules, it is apparently forbidden to bring up a "closed" topic. I believe I was previously banned from the forum as a result of just mentioning a YouTube video of one of my experiments that I had previously posted (in a topic that was closed), so I'm kind of in a bind and I'm probably already walking on thin ice with this topic as well, I imagine.

You might want to look for me on the Stirling engine forum and ask questions there.

In this thread I'm just trying to find out basically, If I supply 500,000 joules of heat to a Stirling engine and  the Carnot efficiency limit calculations reveal that at best, only 100,000 joules of that heat can be converted to work, why can't I seem to find the other 400,000 joules?

Why is my engines "sink" not heating up more than it appears to be, especially when smothered by  insulation?

Maybe it is heating up under the insulation. So why doesn't it stop running?

So... I'm drilling some holes in the dang thing and inserting temperature probes everywhere I can to hopefully find out what's really going on.

I don't really understand exactly why finding that the engine actually utilized one hundred thousand and one joules and only "rejected" 399,998 joules all known laws of the universe would suddenly burn to ashes or something.

[sethoflagos]

1 hour ago, Tom Booth said:

So the heat pump/refrigerator is operating in a 300°k environment, is that correct? And taking the temperature of the refrigerator down to 250°k ? Umm.. freezer? That's really cold.

It's more like a commercial freezer room than a domestic fridge, perhaps. They run typically from -15 ^oC (5 ^pF) down to maybe -35 ^oC (-31 ^pF).

1 hour ago, Tom Booth said:

But you say also: "Point C is after heat exchange to atmosphere, still at 10 bar, temperature now 26.9 C"

I assume you mean heat exchange from... atmosphere. (?)

No. Heat is being exhausted into the (slightly cooler) atmosphere through the condenser.

1 hour ago, Tom Booth said:

But the system is drawing heat from the freezer box at 250°k not atmosphere. It has to dump the heat into the 300°k

Yes. We are extracting Q_C from the (insulated!) freezer, adding the nett shaft work, and exhausting Q_H to atmosphere. 

1 hour ago, Tom Booth said:

Sorry if I'm groping a bit with all this. I think in terms of Fahrenheit and have to convert Celsius and Kelvin to make sense of anything.

Understood.

1 hour ago, Tom Booth said:

I'm also trying to figure out if your example/calculations make sense in a real world application.

My designs were more more scaled for larger industrial applications than perhaps you are familiar with. They all worked moreorless as intended. And the same principles hold at all scales.

1 hour ago, Tom Booth said:

It seems from what you have described that the refrigerator condenser will be just 311°k dumping heat into a 300°k environment. On a hot day could this refrigerator still function?

It's self-adjusting to a certain extent. In hot ambient conditions the cold side temperature will rise until a new equilibrium temperature profile is established. The 50K (90 ^oF) temperature differential is built into the equipment design, but the absolute temperatures will 'float' up and down as necessary on the external temperature seen by the condenser.

In practice, we would design for the warmest anticipated ambient conditions, and provide additional controls (maybe an inverter variable speed drive on the compressor for example) to optimise year round performance. But this isn't the place to go into those details.

1 hour ago, Tom Booth said:

You say "turbine". What type of refrigeration system are we talking about?

Just read 'compressor' or 'expander' as appropriate. The exact type (turbine, positive displacement, screw etc.) is not relevant to this discussion.

Edited January 27, 2023 by sethoflagos
typo

[Tom Booth]

19 minutes ago, sethoflagos said:

It's more like a commercial freezer room than a domestic fridge, perhaps. They run typically from -15 ^oC (5 ^pF) down to maybe -35 ^oC (-31 ^pF).

No. Heat is being exhausted into the (slightly cooler) atmosphere through the condenser.

Yes. We are extracting Q_C from the (insulated!) freezer, adding the nett shaft work, and exhausting Q_H to atmosphere. 

Understood.

My designs were more more scaled for larger industrial applications than perhaps you are familiar with. They all worked moreorless as intended. And the same principles hold at all scales.

It's self-adjusting to a certain extent. In hot ambient conditions the cold side temperature will rise until a new equilibrium temperature profile is established. The 50K (90 ^oF) temperature differential is built into the equipment design, but the absolute temperatures will 'float' up and down as necessary on the external temperature seen by the condenser.

In practice, we would design for the warmest anticipated ambient conditions, and provide additional controls (maybe an inverter variable speed drive on the compressor for example) to optimise year round performance. But this isn't the place to go into those details.

Just read 'compressor' or 'expander' as appropriate. The exact type (turbine, positive displacement, screw etc.) is not relevant to this discussion.

Thanks, that clarifies things. So some form of "bootstrap" system? The expansion turbine drives (assists in driving rather) a turbo-compressor I'm assuming.

Are you familiar with air-cycle systems then?

My journey down this "rabbit hole" started when I was working on designing a solar parabolic dish powered Stirling engine for a military contractor, I think back around, I don't know exactly. 2006-7-ish I'm guessing.

The contractor wrote back to me that the contract or whatever, apparently using my design idea I had labored on for weeks or months, "violated the second law of thermodynamics", according to (whomever), my contractor friend did not supply me with much information.

My design incorporated a kind of bootstrap (open) air-cycle cooling system. In the process of designing this thing I "saw" hot air boiling off the focal point into the air and thought what a big waste of heat.

I believe now, the government was taking bids for a tactical multi-fuel/solar generator for use in Iraq or Afghanistan of some god awful hot desert somewhere. So it had to be as compact and efficient and inconspicuous as possible. That is the dish had to be as small as possible, so I was trying to get as much heat from the dish as possible, thus, air ports around the focal point to suck up this bounty of hot air going to waste. Why not? It could be compressed some, making it even hotter, the cold exhaust from the expander would, of course help cool the back of the heat engine.

Well, running the system in my imagination for hours on end, eventually the sun went down (in my imagination) but the cold side of the engine was already super cold by that time and the air warm, and compressed, it would still be hot. I didn't really THINK, but "saw" in my imagination that the engine kept running after dark, just by compressing the ambient air for heat and using the exhaust from the expander to maintain the temperature differential, at least for a while, into the night, without the sun. With luck it might keep going till the sun came up again. Maybe it didn't need a dish in the daytime either. Maybe just to get it going. Once a differential was well established it seemed it just wanted to keep going.

Without the contract though, I sure don't have the money to build anything like some kind of Stirling-turbine, which is what I started calling it.

To say I was a little disappointed is putting it mildly. I decided I had to find out what this "second law" business was about and why my engine that was running just fine in my head supposedly "violated" it.

Of course, my research traced back to Carnot.

 

 

[sethoflagos]

2 hours ago, Tom Booth said:

I don't really understand exactly why finding that the engine actually utilized one hundred thousand and one joules and only "rejected" 399,998 joules all known laws of the universe would suddenly burn to ashes or something.

Maybe let's return to more familiar ground with Stirling type heat engines. 

Imagine a stack of six of them. The top absorbs 300 kW of heat from the atmosphere at 300 K (80.3 ^oF), the bottom has a cold side at absolute zero.

In between, the cold sink of the upper unit is the hot source for the next one down (and vice versa).

Let us say each is designed for a temperature differential of 50 K (90 ^oF) and performs at the full Carnot limit for their respective temperature band.  

Machine 1: Temp Range 300-250; Input 300 kW; Efficiency 1/6; Output 50 kW

Machine 2: Temp Range 250-200; Input 250 kW; Efficiency 1/5; Output 50 kW

Machine 3: Temp Range 200-150; Input 200 kW; Efficiency 1/4; Output 50 kW

Machine 4: Temp Range 150-100; Input 150 kW; Efficiency 1/3; Output 50 kW

Machine 5: Temp Range 100-50; Input 100 kW; Efficiency 1/2; Output 50 kW

Machine 6: Temp Range 50-0; Input 50 kW; Efficiency 1/1; Output 50 kW

Can you see the beautiful symmetry in this? 300 kW of heat goes in and becomes 300 kW of Work.

If Machine 1 were some how able to extract 50.1 kW, the symmetry would be irredeemably broken. We could potentially get more energy out of the system than was there to begin with. You really are at odds with the most fundamental of our scientific understandings and the countless experimental datapoints that confirm those understandings.  

 

Edit: I've just seen your next post and sympathise. I can't comment on that particular application as I'm not familiar with it. But I've worked for that kind of employer (also in Iraq as it happens) and they can have a very nasty side to them.

Edited January 27, 2023 by sethoflagos
sp

[Tom Booth]

36 minutes ago, sethoflagos said:

Edit: I've just seen your next post and sympathise. I can't comment on that particular application as I'm not familiar with it. But I've worked for that kind of employer (also in Iraq as it happens) and they can have a very nasty side to them.

The funny thing is I still know the contractor. Talked with him not long ago actually. A 3000 watt "NASA" type solar dish Stirling generator was available for purchase, but way out west. Built under government contract I believe, by one of my friends competitors. INFINIA. A prototype "test engine". I thought he might be able to help arrange shipping if I bought it, or perhaps he would want to get it himself. I couldn't see letting it just slip away. My understanding was all those utility scale engines were sold to China for scrap. This one had been stashed away in some university back room and never used since 2008 or some such thing.

While I had his ear I asked whatever happened with his project with the Stirling engine. He changes the subject, then says he has to go on a trip and talk later, but never does. I really get the impression the whole topic is "classified" or some such thing. Originally he had given me the impression the Stirling project was something he wanted to do on the side, for homeowners. The reason for the small dish was not to be too obtrusive in people's residential area back yards.

Anyway, I ended up driving out from New York to Colorado to pick up the engine. Made a vacation out of it.

 

 

1 hour ago, sethoflagos said:

Machine 1: Temp Range 300-250; Input 300 kW; Efficiency 1/6; Output 50 kW

Why not just stop there?

Where are you getting the 300 kw input?

[sethoflagos]

1 hour ago, Tom Booth said:

The contractor wrote back to me that the contract or whatever, apparently using my design idea I had labored on for weeks or months, "violated the second law of thermodynamics", according to (whomever), my contractor friend did not supply me with much information.

Reading between the lines as well as I'm able, I don't think they quite got this right.

Right from day 1 of my chemical engineering course, we were bombarded with the mantra:

                           Output = Input - Accumulation

... until it was ingrained into us as second nature. Until we didn't need to consciously think about it - we just sensed it automatically.

The reason being that it was vital to understand that while an output can be maintained without input via a depletion of reserves (-ve accumulation) this cannot be maintained indefinitely. Sooner or later the reservoir will run dry.

In a complex system, the balance between these three quantities can be impossible to judge without precise calculation, and it can be oh so easy to let a slightly imprecise mental image carry you off on a fool's errand.

It seems to me that you could see that the system kept running through it's accumulation of a high thermal reservoir and thermal inertia, and didn't spot the depletion of resources that was obscured by the systems complexity.

Not only is this quite understandable, but it is actually a breach of the 1st Law not the 2nd.

The correct response would have been to yes, point out the 1st Law transgression, but then acknowledge the value of extending power output into nighttime or at least say that wasn't a necessary consideration. (It has serious global significance now).

I don't know. Without full knowledge of all the details maybe there was a 2nd Law transgression, but by saying so it certainly seems to have made you see the 2nd Law as your enemy and in doing so they did you a great disservice.

The 2nd Law is very much the engineer's friend. A proper understanding of it keeps you on the straight and narrow and saves wasting time on nonsense. Which is a good thing.

Carnot was one of the good guys.

[Tom Booth]

11 minutes ago, sethoflagos said:

Reading between the lines as well as I'm able, I don't think they quite got this right.

Right from day 1 of my chemical engineering course, we were bombarded with the mantra:

                           Output = Input - Accumulation

... until it was ingrained into us as second nature. Until we didn't need to consciously think about it - we just sensed it automatically.

The reason being that it was vital to understand that while an output can be maintained without input via a depletion of reserves (-ve accumulation) this cannot be maintained indefinitely. Sooner or later the reservoir will run dry.

In a complex system, the balance between these three quantities can be impossible to judge without precise calculation, and it can be oh so easy to let a slightly imprecise mental image carry you off on a fool's errand.

It seems to me that you could see that the system kept running through it's accumulation of a high thermal reservoir and thermal inertia, and didn't spot the depletion of resources that was obscured by the systems complexity.

Not only is this quite understandable, but it is actually a breach of the 1st Law not the 2nd.

The correct response would have been to yes, point out the 1st Law transgression, but then acknowledge the value of extending power output into nighttime or at least say that wasn't a necessary consideration. (It has serious global significance now).

I don't know. Without full knowledge of all the details maybe there was a 2nd Law transgression, but by saying so it certainly seems to have made you see the 2nd Law as your enemy and in doing so they did you a great disservice.

The 2nd Law is very much the engineer's friend. A proper understanding of it keeps you on the straight and narrow and saves wasting time on nonsense. Which is a good thing.

Carnot was one of the good guys.

Not an accumulation of heat.

Air-cycle refrigeration is used for cryogenics.

Not particularly an endorsement, I just Googled up "air-cycle" + cryogenic and - well -256°F so they say on this companies website:

https://mirai-intex.com/products/open-cycle/c1

Incidentally, also producing heat at something like 450°F

https://www.sciencedirect.com/science/article/abs/pii/S014070071100079X

 

But unlike household refrigeration where the refrigerator is laboring to extract miniscule amounts of heat from a cold insulated box, an open air-cycle compresses a fresh supply of ambient air (heat of compression) continuously. That is it takes in a fresh supply of WARM air compresses it to get out the heat, then expands it to extract work and produce cryogenic cold.

Now if you have a Stirling engine taking the heat and converting the heat into work, the Stirling engine does part of the cooling which contracts the compressed air, as is is being compressed, which makes compression that much easier, aside from the work output from the expander helping.

[sethoflagos]

22 minutes ago, Tom Booth said:

Not an accumulation of heat.

Air-cycle refrigeration is used for cryogenics.

A cold reservoir is as much a potential energy source as a hot one. It's the existence of a temperature differential that produces the opportunity to output shaft work. In some sense cold sinks are more useful in that they're associated with higher thermal efficiencies.

Air cycles are not particularly part of my repertoire since we tend to look for high energy densities in our working fluids to keep the equipment compact. Phase change latent heats store far more energy per unit volume than just gas heat capacity as used in the typical air cycle HVAC systems used on aeroplanes. But aeroplanes have access to very low temperature ambients and ram air compression so horses for courses.

Edited January 28, 2023 by sethoflagos

[Tom Booth]

At the cold end of the Stirling engine, how much heat is actually being dumped into the accumulated cold reserve? Considering some portion at least of the heat is converted to - whatever. Something that's no longer heat. Drive machinery, generate electricity etc.

That cold reserve isn't going to warm up in a big hurry. Maybe.

So you have the Stirling engine running primarily on cryogenic or near cryo-cold.

The supply of Ambient heat in atmospheric air is almost free for the taking.

The engine converts that heat into work so is a kind of refrigeration system of a sort. The heat that goes in doesn't "ALL" end up at the sink. So, to whatever degree that happens, heat converted to work output, the cold reserve is preserved as the engine runs on ambient heat.

Tesla worked on the same idea but wanted to take it (the air) all the way down to phase change (liquid air).

Personally I think that's going to extremes and unnecessary and probably not really very practical.

 

[sethoflagos]

41 minutes ago, Tom Booth said:

At the cold end of the Stirling engine, how much heat is actually being dumped into the accumulated cold reserve? Considering some portion at least of the heat is converted to - whatever. Something that's no longer heat. Drive machinery, generate electricity etc.

Try not to get distracted by extraneous detail.

Focus on the fundamentals such as this post.

[Tom Booth]

2 hours ago, sethoflagos said:

Try not to get distracted by extraneous detail.

Focus on the fundamentals such as this post.

Well I've read that through several times but, first, I don't think what I've said constitutes "extraneous detail". Second, I can't say I can see any real "beautiful symmetry" to be broken. All I see really is a scheme that has no possibility of working for practical reasons too numerous to go into. I can't honestly even begin to take the proposition seriously (sorry, no offense but what can I say?)

I look at it and see, first of all "absolute zero" and right out of the gate your talking an impossibility, conceptually, even as an interesting thought experiment.

Just as an example of what crosses my mind, well, matter itself, at absolute zero changes state taking on a form that is in no way conducive to building machinery. The elements a Stirling engine generally needs to operate have long since ceased to exist, well before getting anywhere close to absolute zero. I don't even believe Stirling engines operate in a way that would allow such stacking, one on top of the other as proposed.

I could be wrong I suppose. Maybe some such system could be approached using hermetically sealed engines pressurized with helium using solar radiation and the cold of space but then no need for a stack. One engine should do.

Maybe you could elaborate or persuade me to see the light or something somehow but I'm just not getting it at this point.

Maybe I could get away with posting a video I thought was rather interesting (without getting banned I hope?)

I've talked with this guy many times over the years. Online as well as by email and on the phone. But he says a couple of times in this video that he doesn't know anyone working on the stuff he talks about in this lecture. I'll try to give him the benefit of the doubt and say maybe he's just got a bad memory or something, but...

I also think he makes some real miss-statements, like Tesla never talked about heat pumps in his article or in connection with his engine, I guess he didn't actually read the article too carefully, or doesn't understand that a refrigeration system and a heat pump are basically the same thing.

So he bundles up a lot of stuff he and I have been discussing for years and gives a lecture hawking "angel investors" but doesn't know ANYBODY who is actually working on any such thing. Nobody at all.

Oh well. Some food for thought anyway in connection with all this:

 

BTW I'm in no way "depending on" this video for anything. IMO the guy is leaning pretty heavily on ideas he got from me over the years.

Anyway, knowing something about refrigeration systems and compressor-expanders and all that I thought you might find it interesting, but it really kind of just pisses me off when he says he doesn't know me, or "anyone" that has ever done any work on this kind of thing.

 

Anyway, getting back to the experiment, I've made, what I think are a few minor improvements.

I found a section of truck radiator hose that fits the well on the steamer pretty snug.

Elevating the engine on the tube helps contain the steam, keeps the glass from fogging up and, well, I had hoped the steam would condense and drip back down and not boil away as fast, but, the steam still builds up pressure and boils away, but maybe not quite as much.

I taped the glass globe right to the engine which protects it from drafts and from steam. Before steam was rising up through the crack in the insulation which could get under the Aerogel.

Not really much more to report than that at this time but I'm working on it.

Well, I also spent some time trimming the fibers under the flywheel away with some scissors so the flywheel can rotate more freely and did a few test runs to see how all this worked.

Better anyway.

Edited January 28, 2023 by Tom Booth

[Endy0816]

Apologies if this has already been answered, but do you have a tachometer you can use to find RPM?

 

Could directly compare work output that way.

[Tom Booth]

1 hour ago, Endy0816 said:

Apologies if this has already been answered, but do you have a tachometer you can use to find RPM?

 

Could directly compare work output that way.

I've asked around at local auto parts stores but haven't found one so no. Not yet. Any recommendations?

Anyway how could work output be determined by the RPM?

First of all I think I'd need a smoother running engine as these toys with twisted wire for connecting rods and floppy displacers etc. don't always run at a steady RPM but can hang up and slow down or suddenly speed up for a while.

I do have several other engines though.

[Ghideon]

11 hours ago, Tom Booth said:

As far as I understand the forum rules, it is apparently forbidden to bring up a "closed" topic. I believe I was previously banned from the forum as a result of just mentioning a YouTube video of one of my experiments that I had previously posted (in a topic that was closed), so I'm kind of in a bind and I'm probably already walking on thin ice with this topic as well, I imagine.

You might want to look for me on the Stirling engine forum and ask questions there.

In this thread I'm just trying to find out basically, If I supply 500,000 joules of heat to a Stirling engine and  the Carnot efficiency limit calculations reveal that at best, only 100,000 joules of that heat can be converted to work, why can't I seem to find the other 400,000 joules?

Why is my engines "sink" not heating up more than it appears to be, especially when smothered by  insulation?

Maybe it is heating up under the insulation. So why doesn't it stop running?

So... I'm drilling some holes in the dang thing and inserting temperature probes everywhere I can to hopefully find out what's really going on.

I don't really understand exactly why finding that the engine actually utilized one hundred thousand and one joules and only "rejected" 399,998 joules all known laws of the universe would suddenly burn to ashes or something.

Sorry to hear that you feel that forum rules prevents a hypothesis to be posted.

What I read between the lines is that the idea is basically a perpetuum mobile / over unity device (deliberately or by mistake) hidden in lots of engineering details. 

 

[sethoflagos]

7 hours ago, Tom Booth said:

I look at it and see, first of all "absolute zero" and right out of the gate your talking an impossibility, conceptually, even as an interesting thought experiment.

It is not supposed to be a practical machine.

It represents a limiting case that all real world machines will fail to match in performance. Just as the speed of light is the limiting case for particle velocity. 

Your statement shows that you understand at least some of these words.

And yet you persist in claiming that you can produce a machine that outperforms unity efficiency. Apparently you do not understand the meaning of the word 'limit'. Pity because you've reached one of mine.

 

[exchemist]

5 hours ago, Ghideon said:

Sorry to hear that you feel that forum rules prevents a hypothesis to be posted.

What I read between the lines is that the idea is basically a perpetuum mobile / over unity device (deliberately or by mistake) hidden in lots of engineering details. 

 

Yes, Tom is a perpetual motion machine of the second kind devotee. He thinks all heat can be converted to work, with no waste heat rejected.