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Is Carnot efficiency valid?


Tom Booth
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31 minutes ago, Tom Booth said:

What is the predicted outcome?

An efficiency of zero because you seem to have no means of extracting work from the system.

31 minutes ago, Tom Booth said:

My IR camera barely read above ambient after 15 minutes at the top of the Aerogel blanket. What do you conclude from that?

Why doesn't the engine overheat in your opinion, when the sink is insulated ? I know, Aerogel is no different than air, or it conducts heat or absorbs it or something.

The machine still operates therefore there is enough heat flow to keep it operating. 

Edited by sethoflagos
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3 minutes ago, sethoflagos said:

An efficiency of zero because you seem to have no means of extracting work from the system.

The machine still operates therefore there is enough heat flow keep it operating. 

At zero efficiency then, 100% of the heat should go straight through to the sink ?

The top of the engine should get as hot as the bottom heated side. Correct ?

But IMO the working fluid IS doing work driving the piston, creating friction, agitating the air, making noise, doing "work".

The discussion is about Carnot efficiency.

Occasionally I forget to insert "Carnot" before the word "efficiency" but in most cases in this context I'm talking about Carnot efficiency.

 

2 minutes ago, studiot said:

Pity, just when I though we starting to get on well.

What are you talking about?

This thread is moving very fast and I'm trying to get off here for a while to get some things done today.

Sometimes there is cross posting and I miss something but I'm not "stopped talking" to you again. Assuming you are addressing me.

3 hours ago, studiot said:

I thought so.

You said you are an engine mechanic - a very respectable trade I know such people who have many innate skils I don't possess. They find it easy to for instance dissemble, fix and reassemble aBorg-Warner auto box whilst I know from personal experience of much simpler mechanics that I would struggle for days and probably not succeed with a B-W.

However you anser brings us to appreciating the difference between power and energy.

I have assumed you know this.

 

Total energy (you have a total energy meter ?) used to keep the waterbath temperature constant for 15 minutes.

Do you think 15 minutes is enough ?

I don't.

 

So over a longer period you can measure the energy to maintain that waterbath temperature.

So what ?

How do you know what proportion of that input actually goes into the working fluid ?

And over that time how many cycles has you engine completed ?

The above post?

Are you arguing that keeping some account of energy input is impossible or something?

My electric company sends me a bill every month. It's not rocket science.

 

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36 minutes ago, exchemist said:

Wrong. Industrial diesel engines (low speed, two stroke, with an energy recovery turbine in the exhaust) can get over 50% efficiency, and combined cycle turbine installations even getting on for 60%: https://en.wikipedia.org/wiki/Combined_cycle_power_plant 

The opening few paragraphs go into this a bit and even refer to how close to Carnot cycle efficiency they can get.

Since I was Lead Process Engineer for Stone & Webster on the design of https://en.wikipedia.org/wiki/Sutton_Bridge_Power_Station, I can confirm this. The minimum required thermal efficiency was written into the contract, and was no small challenge to meet given they insisted we used an air-cooled condenser for the steam cycle.

As a side note this was the last CCGT plant to be built in the UK before the government put a moratorium on gas-fired power plant, which was one of the factors that encouraged me to leave for sunnier shores.

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14 hours ago, Tom Booth said:

What I mean is, by introducing cold water into a warmer environment, the water will heat up because of the higher temperature surroundings, AS IF placed in an oven, regardless of what the engine does or doesn't do.

Which is why you do a control experiment, which measures the effect of the surroundings.

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21 minutes ago, Tom Booth said:

But IMO the working fluid IS doing work driving the piston, creating friction, agitating the air, making noise, doing "work".

No shaft work exiting the system so your 'work' is just more heat.

23 minutes ago, Tom Booth said:

The discussion is about Carnot efficiency.

Occasionally I forget to insert "Carnot" before the word "efficiency" but in most cases in this context I'm talking about Carnot efficiency.

Deja vu.

On 1/25/2023 at 5:25 PM, sethoflagos said:

You're conflating the Carnot limit with actual machine isentropic efficiency. They are entirely different concepts. Confusing the two leads to absurd conclusions. 

 

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6 minutes ago, sethoflagos said:

Since I was Lead Process Engineer for Stone & Webster on the design of https://en.wikipedia.org/wiki/Sutton_Bridge_Power_Station, I can confirm this. The minimum required thermal efficiency was written into the contract, and was no small challenge to meet given they insisted we used an air-cooled condenser for the steam cycle.

As a side note this was the last CCGT plant to be built in the UK before the government put a moratorium on gas-fired power plant, which was one of the factors that encouraged me to leave for sunnier shores.

Not sure what the relevance of your work history is to the little LTD Stirling operating on a the steam from a facial sauna.

The formula in question is the Carnot efficiency formula. It is based on the temperatures of the steam (something under 100°C and ambient sink (about 70° F)

Do you contest that the Carnot efficiency would be about 20% or less ?

That the heat rejection would be 80% or more ?

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5 hours ago, Tom Booth said:

If a billiard ball, slow moving or otherwise strikes a stationary billiard ball, 100% of the force is transmitted to the second ball, subtract a bit for the sound vibrations emitted, friction on the felt table top, etc. but the second ball basically takes off at the same speed as the ball that struck it and the first ball comes to a stop.

Rationalizations aside, where is the empirical data? Who did experiments that conclusively established this exact supposed limit?

College students do similar experiments every year in introductory physics classes. It’s not noteworthy, so nobody is going to publish these results.

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12 minutes ago, Tom Booth said:

Not sure what the relevance of your work history is to the little LTD Stirling operating on a the steam from a facial sauna.

That post wasn't addressed to you.

But perhaps there's no harm in reminding you that this body of theory that you are constantly sneering at is in everyday use in the design of serious real world applications where getting it wrong can seriously damage your career. Steep learning curve.  

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12 minutes ago, swansont said:

College students do similar experiments every year in introductory physics classes. It’s not noteworthy, so nobody is going to publish these results.

Certainly if such experiments are carried out continually on Colleges all over the world on a routine basis, there should be some well worn procedural outline to follow.

Materials required, setup, etc. 

There should be textbook procedures to follow. Every student gets a little engine to test and some temperature probes.

To say "It’s not noteworthy, so nobody is going to publish these results." Is IMO absurd. No disrespect, but if that is the case the procedure should be well known and available. Published somewhere.

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Just now, Tom Booth said:

Certainly if such experiments are carried out continually on Colleges all over the world on a routine basis, there should be some well worn procedural outline to follow.

Materials required, setup, etc. 

There should be textbook procedures to follow. Every student gets a little engine to test and some temperature probes.

There are. The lab description, and the writeup done by the students. But you’d have to take the class to have access.

 

Just now, Tom Booth said:

To say "It’s not noteworthy, so nobody is going to publish these results." Is IMO absurd. No disrespect, but if that is the case the procedure should be well known and available. Published somewhere.

I’m sure someone will get right on that, right after you publish the torque values for every bolt you’ve tightened.

Go take a physics class.

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35 minutes ago, swansont said:

Which is why you do a control experiment, which measures the effect of the surroundings.

OK.

I don't personally see what difference it makes what the starting cold side temperature is so why not?

Put some ice water on top of an inoperative engine (heated by the facial sauna or some other heat source ???) and measure the temperature change, plot a graph. Sounds interesting.

Then do it a second time letting the engine run.

What about the Arduino. Do you agree the inoperative engine should have the displacer actuated by a servo motor?

5 minutes ago, swansont said:

There are. The lab description, and the writeup done by the students. But you’d have to take the class to have access.

 

I’m sure someone will get right on that, right after you publish the torque values for every bolt you’ve tightened.

Go take a physics class.

Right.

The routine experiment every physics student knows is very very super secret. Every student has to sign an NDA and promise to destroy all notes and materials before leaving class.

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1 hour ago, Tom Booth said:

The above post?

Are you arguing that keeping some account of energy input is impossible or something?

My electric company sends me a bill every month. It's not rocket science.

I.m not arguing anything at the moment.

I am trying to keep my posts short, especially as you keep avoifing the pertinent questions I ask in each one.

In response to your question I am not arguing anything I am seeking factual information about the numbers you are claiming.

 

It is quite insulting that you only bother to reply after I remind you twice this last time.

 

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30 minutes ago, studiot said:

I.m not arguing anything at the moment.

I am trying to keep my posts short, especially as you keep avoifing the pertinent questions I ask in each one.

In response to your question I am not arguing anything I am seeking factual information about the numbers you are claiming.

 

It is quite insulting that you only bother to reply after I remind you twice this last time.

 

When I have more time I'll go back and read through all this mess, right now I'm trying to run wires, install breakers, drill holes etc. so my wife can use the kitchen.

There's quite a few questions I've asked in here that haven't been answered, and other posts beside yours I need to go back and address as well. aside from the experiments I'm trying to squeeze in.

Edited by Tom Booth
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39 minutes ago, Tom Booth said:

When I have more time I'll go back and read through all this mess, right now I'm trying to run wires, install breakers, drill holes etc. so my wife can use the kitchen.

There's quite a few questions I've asked in here that haven't been answered, and other posts beside yours I need to go back and address as well. aside from the experiments I'm trying to squeeze in.

A lot of different possible 'experiments' have been suggested and you have rushed off once or twice to start on some.

I seriously suggest you do some collecting and collating before starting any more and plan a course of action.

Otherwise you will be doing a lot of tail chasing and probably unneccessary work.

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2 hours ago, Tom Booth said:

OK.

I don't personally see what difference it makes what the starting cold side temperature is so why not?

0 is easy to replicate. The goal is to change only one parameter at a time, e.g. doing work vs not doing work

2 hours ago, Tom Booth said:

Put some ice water on top of an inoperative engine (heated by the facial sauna or some other heat source ???) and measure the temperature change, plot a graph. Sounds interesting.

Then do it a second time letting the engine run.

Having ice water means tracking how much energy goes into melting the ice

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38 minutes ago, swansont said:

0 is easy to replicate. The goal is to change only one parameter at a time, e.g. doing work vs not doing work

Having ice water means tracking how much energy goes into melting the ice

Melting the ice?

I thought you said NOT to use ice.

Perhaps a miss-statement?

Ice can be below 0°C possibly different temperatures at different parts. (Extremity, center). I had assumed the idea of only using near 0° ice water was to avoid all that potential ambiguity. The ice could take in unknown quantities of latent heat before begining to melt.

But you did say "ice water" above.

Rather than speculate, I'll just allow you to clarify.

If the goal is to only change one parameter at a time. Why change the given (ambient) temperature of the cold side ? To my mind, as I said before, this just introduces an additional needless variable to no purpose rendering any results ambiguous.

Quote

Having ice water means tracking how much energy goes into melting the ice

Aside from the obvious clarification needed. Why? Seems like redundant data unrelated to the issue under investigation. Or if you believe it is related, how so?

 

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I agree that playing around with ice water / electric heaters / and other devices opens too many cans of worms for satisfactory simple experimentation.

You need to arrange both reservoirs so that the heat transferred through the fluid is les than 1% - preferably less than0.1% - of the heat content ofeach reservoir.

Do you understand the difference between specific heat (also called heat capacity) and heat content ?

For instance using the ocean or a lake etc as the cold reservoir would be really good.

Stirling in his original devices used a blast furnace as the hot reservoir.

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 Not ignoring you Studiot. Just responding in general.

The purpose behind the experiment, originally, is to see what happens to the engine with the "sink" blocked.

The "natural" existing sink, (if we are going to apply steam/heat as the heat source) is the ambient atmosphere.

Introducing ice or ice water creates a mixed sink. Partly ice or cold water and partly ambient, and it would be difficult to distinguish what's what, I would think, and the heat melting the ice or warming the water can then be originating from multiple sources: the ambient surroundings, the heat from the steamer or the engine itself.

But, IMO additional data does no harm. Experiments can be run over and over in various ways. Sometimes unexpected results emerge.

My only problem is finding the time, so I try to make experiments as simple and quick as possible and with meaningful results. I'm not just experimenting for the sake of experimenting to waste time.

My question I want answered is where is the "waste heat" that the Carnot (so-called) equation suggests should be there.

So how does melting ice, or warming cold water help answer that question?

 

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45 minutes ago, Tom Booth said:

Melting the ice?

I thought you said NOT to use ice.

I did. YOU said ice water. I explained why that’s not a good idea. 

45 minutes ago, Tom Booth said:

Perhaps a miss-statement?

Ice can be below 0°C possibly different temperatures at different parts. (Extremity, center). I had assumed the idea of only using near 0° ice water was to avoid all that potential ambiguity. The ice could take in unknown quantities of latent heat before begining to melt.

But you did say "ice water" above.

After you said it.

 

45 minutes ago, Tom Booth said:

Rather than speculate, I'll just allow you to clarify.

If the goal is to only change one parameter at a time. Why change the given (ambient) temperature of the cold side ? To my mind, as I said before, this just introduces an additional needless variable to no purpose rendering any results ambiguous.

Then you come up with a way to track the heat flow into the cold reservoir.

 

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25 minutes ago, swansont said:

I did. YOU said ice water. I explained why that’s not a good idea. 

After you said it.

 

Then you come up with a way to track the heat flow into the cold reservoir.

 

This was your earlier suggestion.

I read: "no ice".

Polish_20230129_183400765.thumb.jpg.22f980aa0d22a32a8ea3769d1ef89afa.jpg

Are you suggesting conducting the experiment in an ice box ?

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10 minutes ago, Tom Booth said:

This was your earlier suggestion.

I read: "no ice".

Yes, I said no ice. This seems to be confusing to you. 

If you measure how much the temperature goes up, you can see how much heat has flowed in. You do this just with ambient air, to see what its contribution is. Then you do it with the engine. 

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2 minutes ago, swansont said:

Yes, I said no ice. This seems to be confusing to you. 

If you measure how much the temperature goes up, you can see how much heat has flowed in. You do this just with ambient air, to see what its contribution is. Then you do it with the engine. 

I guess I automatically thought of "0°C" as the freezing temperature of water, so if not ice, than ice-water.

Sorry for the misunderstanding.

You said "the cold reservoir" should start out colder than ambient, perhaps 0°C

What "cold reservoir"?

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1 hour ago, Tom Booth said:

I guess I automatically thought of "0°C" as the freezing temperature of water, so if not ice, than ice-water.

Sorry for the misunderstanding.

You said "the cold reservoir" should start out colder than ambient, perhaps 0°C

What "cold reservoir"?

We’re six pages into a discussion of heat engines and you don’t know what the cold reservoir is? 

It’s whatever connects with the plate opposite the hot reservoir. 

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59 minutes ago, swansont said:

We’re six pages into a discussion of heat engines and you don’t know what the cold reservoir is? 

It’s whatever connects with the plate opposite the hot reservoir. 

"Cold reservoir" or heat "reservoir" generally is a product of Sadi Carnot's imagination.

You, or someone in here said I'm obsessed with "caloric theory" which has long ago been abandoned but the language of thermodynamics harkens all the way back to it and the language influences thinking on the subject of heat still to this day.

What is in contact with "the plate opposite the hot plate" in the last experiment was silica Aerogel and beyond that the surrounding ambient air.

You said:

Quote

"the cold reservoir" should start out colder than ambient, perhaps 0° C"

Implying the "reservoir" should be something other than the ambient (which is "colder" than the ambient).

Talking abstractions like "reservoir" is fine when discussing theory but this is actual, not some thought experiment, this has to be implemented in the real world in real life.

 

Edited by Tom Booth
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