[Dr Van Nostrand]

So an astronaut floating in space can throw a baseball and it'll fly away from him.  But if he sets that baseball on a hand grenade and detonates it, the baseball will stand still?

[stack]

Okay will do!

I’ll probably start with those same articles. They seem to know about it.

Unless you have some other sources about entropy that might help me learn about it in the way you do?

Simply put, entropy is a quantity representing the availability of the thermal energy in a system to be converted into work.

A rocket cannot possibly maintain constant entropy.

Incorrect, as you will see in a moment.

As stack writes falsely:

Rocket engines are considered Isentropic systems where entropy remains unchanged.

Isentropic nozzle flow
"Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approximates the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids.”

So you see, a Nonisentropic process, like Free Expansion, does not apply to an Isentropic system. Apples and oranges.

...it is obviously written by someone trying to engage in double speak...

And stack, while he talks of the rocket engine, does NOT want you to look behind the curtain containing the rocket exhaust, which is where the meat and potatoes is at.

A rocket has a fixed amount of fuel and a fixed amount of potential energy.

Rockets have a fixed rate of discharge at any particular point of time.

Sooner or later, there is no more more potential energy available.

Therefore, rockets cannot maintain unchanged entropy when in operation.

And that process is not "reversible," nor can it possibly be "adiabatic," as described in stacks' ridiculous post, once initiated. Rockets experience no reverse flow of fluids or exhaust. The exhaust is supposedly taking place in the vacuum of outer space...again, where all the fakers want you to believe that gas, just because it is coming from a rocket, can somehow, someway...be different...but it, of course...cannot.

Gas released into a vacuum...does no work.

All of what you wrote is false and backed by zero evidence or science. Regarding Rockets and Isentropic Flow:

"As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas. The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy. Engineers call this type of flow an isentropic flow; a combination of the Greek word "iso" (same) and entropy."

More information and equations can be found here:
https://www.grc.nasa.gov/WWW/k-12/airplane/isentrop.html

You see, engineers call this type of flow an isentropic flow. You are neither an engineer, nor a rocket scientist, nor an expert in thermodynamics yet you claim to know more than people who are without providing any evidence. Your "free expansion does no work" is nonisentropic and does not apply here to rocket engines, so that argument you originally had is toast.

For once, please provide some evidence for you claims rather than just ignorant unfounded bluster.

[totallackey]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

[totallackey]

Okay will do!

I’ll probably start with those same articles. They seem to know about it.

Unless you have some other sources about entropy that might help me learn about it in the way you do?

Simply put, entropy is a quantity representing the availability of the thermal energy in a system to be converted into work.

A rocket cannot possibly maintain constant entropy.

Incorrect, as you will see in a moment.

As stack writes falsely:

Rocket engines are considered Isentropic systems where entropy remains unchanged.

Isentropic nozzle flow
"Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approximates the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids.”

So you see, a Nonisentropic process, like Free Expansion, does not apply to an Isentropic system. Apples and oranges.

...it is obviously written by someone trying to engage in double speak...

And stack, while he talks of the rocket engine, does NOT want you to look behind the curtain containing the rocket exhaust, which is where the meat and potatoes is at.

A rocket has a fixed amount of fuel and a fixed amount of potential energy.

Rockets have a fixed rate of discharge at any particular point of time.

Sooner or later, there is no more more potential energy available.

Therefore, rockets cannot maintain unchanged entropy when in operation.

And that process is not "reversible," nor can it possibly be "adiabatic," as described in stacks' ridiculous post, once initiated. Rockets experience no reverse flow of fluids or exhaust. The exhaust is supposedly taking place in the vacuum of outer space...again, where all the fakers want you to believe that gas, just because it is coming from a rocket, can somehow, someway...be different...but it, of course...cannot.

Gas released into a vacuum...does no work.

All of what you wrote is false and backed by zero evidence or science. Regarding Rockets and Isentropic Flow:

"As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas. The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy. Engineers call this type of flow an isentropic flow; a combination of the Greek word "iso" (same) and entropy."

More information and equations can be found here:
https://www.grc.nasa.gov/WWW/k-12/airplane/isentrop.html

You see, engineers call this type of flow an isentropic flow. You are neither an engineer, nor a rocket scientist, nor an expert in thermodynamics yet you claim to know more than people who are without providing any evidence. Your "free expansion does no work" is nonisentropic and does not apply here to rocket engines, so that argument you originally had is toast.

For once, please provide some evidence for you claims rather than just ignorant unfounded bluster.

For once, understand what the hell you are reading and where the flow is taking place.

I mean, read the whole thing...

And make note of the word TUBE!

Gas...in a...TUBE...

Not gas...in a...nozzle.

Now, goodbye to your lack of understanding.

[iCare]

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Indeed, a rocket's exhaust will not reverse back into the rocket.
However, that doesn't matter, because the overall process doesn't need to be reversible for the relevant thermodynamic process to be reversible.

A rocket is not an isolated experiment with only one thing happening or one parameter changing at one time.
It is a real world application with multiple factors and processes influencing and interacting with each other.
In this case at least three processes, that happen both sequentially and in parallel:

• An exothermic chemical reaction creates (lots of) hot gas.
• That gas is then - in accordance with the laws of thermodynamics - expelled through the nozzle creating thrust.
• After leaving the rocket the exhaust dissipates (regardless, if this happens in an atmosphere or in a vacuum).

The chemical part (1) of the process is obviously not reversible as the gas will not turn back into fuel.
Also, the dissipation part (2) is not reversible - once the exhaust has left the rocket it is no longer available to be "sucked back in" (as it has dissipated).
The thermodynamic part (3), however, is reversible.
If the gas were to cool down to its original temperature in an experimental setting (i.e. no other influences, constant amount of gas, no dissipation) it would eventually contract again and fill the original volume.
That this does not happen due to (1) and (2) doesn't change its basic nature of being reversible.

So, as stated initially, the overall process is not reversible, but the thermodynamic process is reversible. In the end confirming, that work is done and the rocket accelerates in a vacuum.

In contrast free expansion (which has been thoroughly discussed in this thread and is not applicable to rocket propulsion) is not reversible.
Gas will freely expand into an available vacuum and it will not evacuate that volume again to return to its original volume.

iC

[totallackey]

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Indeed, a rocket's exhaust will not reverse back into the rocket.
However, that doesn't matter, because the overall process doesn't need to be reversible for the relevant thermodynamic process to be reversible.

A rocket is not an isolated experiment with only one thing happening or one parameter changing at one time.
It is a real world application with multiple factors and processes influencing and interacting with each other.
In this case at least three processes, that happen both sequentially and in parallel:

• An exothermic chemical reaction creates (lots of) hot gas.
• That gas is then - in accordance with the laws of thermodynamics - expelled through the nozzle creating thrust.
• After leaving the rocket the exhaust dissipates (regardless, if this happens in an atmosphere or in a vacuum).

The chemical part (1) of the process is obviously not reversible as the gas will not turn back into fuel.
Also, the dissipation part (2) is not reversible - once the exhaust has left the rocket it is no longer available to be "sucked back in" (as it has dissipated).
The thermodynamic part (3), however, is reversible.
If the gas were to cool down to its original temperature in an experimental setting (i.e. no other influences, constant amount of gas, no dissipation) it would eventually contract again and fill the original volume.
That this does not happen due to (1) and (2) doesn't change its basic nature of being reversible.

So, as stated initially, the overall process is not reversible, but the thermodynamic process is reversible. In the end confirming, that work is done and the rocket accelerates in a vacuum.

In contrast free expansion (which has been thoroughly discussed in this thread and is not applicable to rocket propulsion) is not reversible.
Gas will freely expand into an available vacuum and it will not evacuate that volume again to return to its original volume.

iC

LOL!...

Paraphrasing your reply...

"Allow me to state I know that gas will freely expand into a vacuum but this does not apply to a rocket. Even though the videos here of rockets attempting to work in a vacuum show they do not work until such time there is adequate surrounding pressure to allow for functioning."

Thanks!

The processes which you refer to that are reversible and therefore isentropic processes take place in the tubes, not the exhaust.

[iCare]

Paraphrasing your reply...

"Allow me to state I know that gas will freely expand into a vacuum but this does not apply to a rocket.

That doesn't require paraphrasing.
I have repeatedly stated, that while I do not doubt free expansion, it does not apply in that case of firing a rocket, as the scientific requirements for free expansion are not met.

Even though the videos here of rockets attempting to work in a vacuum show they do not work until such time there is adequate surround pressure to allow for functioning."

That is not what the videos show, but simply your interpretation of it.
That interpretation has been convincingly challenged several times by various people.

The processes which you refer to that are reversible and therefore isentropic take place in the tubes, not the exhaust.

What law states, that a thermodynamic process requires a tube to be reversible?
Where, exactly, is "in the exhaust"? Still in the combustion chamber, in the nozzle, outside the rocket, all of the aforementioned or something different? 

iC

[totallackey]

Paraphrasing your reply...

"Allow me to state I know that gas will freely expand into a vacuum but this does not apply to a rocket.

That doesn't require paraphrasing.
I have repeatedly stated, that while I do not doubt free expansion, it does not apply in that case of firing a rocket, as the scientific requirements for free expansion are not met.

Yeah, we know...you simply deny.

The part of gas being being released into a vacuum doing no work somehow escapes you.

Even though the videos here of rockets attempting to work in a vacuum show they do not work until such time there is adequate surround pressure to allow for functioning."

That is not what the videos show, but simply your interpretation of it.
That interpretation has been convincingly challenged several times by various people.

Nah...not even challenged...because the people know what they see.

They know it is not even a vacuum when the rockets are finally able to work.

The processes which you refer to that are reversible and therefore isentropic take place in the tubes, not the exhaust.

What law states, that a thermodynamic process requires a tube to be reversible?
Where, exactly, is "in the exhaust"? Still in the combustion chamber, in the nozzle, outside the rocket, all of the aforementioned or something different? 

iC

You read the source material.

The source material states the word TUBE.

You know where the exhaust of a rocket is...it certainly isn't a tube.

And the exhaust is not inside the rocket.

A rocket certainly works, but it certainly cannot work in a vacuum.

The evidence and science are clear.

[BRrollin]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Why not? If free expansion of the exhaust into a vacuum does no work, then reversing the process is thermodynamically trivial.

Or did you think that “reversible” means you need to successfully build a time machine and watch it rewind?

That’s the problem, you don’t understand the basics, but you’ve somehow convinced yourself that you’ve found a flaw in the thinking of experts, by sounding out the words and assuming you thus know their definitions.

[totallackey]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Why not? If free expansion of the exhaust into a vacuum does no work, then reversing the process is thermodynamically trivial.

Or did you think that “reversible” means you need to successfully build a time machine and watch it rewind?

That’s the problem, you don’t understand the basics, but you’ve somehow convinced yourself that you’ve found a flaw in the thinking of experts, by sounding out the words and assuming you thus know their definitions.

Actually, what it shows is the whole source introduced by stack wasn't even relevant to the discussion that is taking place.

I also pointed out to stack that just because a process that takes place within a specific point of operation while the rocket is functioning, does not mean that process is taking place throughout the entirety of the rocket.

That is why what he introduced is not relevant to the part of the rocket (i.e., exhaust) exposed to the vacuum.

I do understand what I am writing.

Gas, when released to a vacuum, does no work.

Have a great day.

[BRrollin]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Why not? If free expansion of the exhaust into a vacuum does no work, then reversing the process is thermodynamically trivial.

Or did you think that “reversible” means you need to successfully build a time machine and watch it rewind?

That’s the problem, you don’t understand the basics, but you’ve somehow convinced yourself that you’ve found a flaw in the thinking of experts, by sounding out the words and assuming you thus know their definitions.

Actually, what it shows is the whole source introduced by stack wasn't even relevant to the discussion that is taking place.

I also pointed out to stack that just because a process that takes place within a specific point of operation while the rocket is functioning, does not mean that process is taking throughout the entirety of the rocket.

That is why what he introduced is not relevant to the part of the rocket (i.e., exhaust) exposed to the vacuum.

I do understand what I am writing.

Gas, when released to a vacuum, does no work.

Have a great day.

Focus. I wasn’t challenging you on that point. You’re getting your conversations mixed up.

“Gas, when released to a vacuum, does no work.”

No. The free expansion of a gas into a vacuum does no work. This is not the same as a gas “released” into a vacuum.

But it doesn’t even matter, because if the exhaust does no work, then reversing the process is not a problem.

So you’ve argued yourself into a corner.

[totallackey]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Why not? If free expansion of the exhaust into a vacuum does no work, then reversing the process is thermodynamically trivial.

Or did you think that “reversible” means you need to successfully build a time machine and watch it rewind?

That’s the problem, you don’t understand the basics, but you’ve somehow convinced yourself that you’ve found a flaw in the thinking of experts, by sounding out the words and assuming you thus know their definitions.

Actually, what it shows is the whole source introduced by stack wasn't even relevant to the discussion that is taking place.

I also pointed out to stack that just because a process that takes place within a specific point of operation while the rocket is functioning, does not mean that process is taking throughout the entirety of the rocket.

That is why what he introduced is not relevant to the part of the rocket (i.e., exhaust) exposed to the vacuum.

I do understand what I am writing.

Gas, when released to a vacuum, does no work.

Have a great day.

Focus. I wasn’t challenging you on that point. You’re getting your conversations mixed up.

“Gas, when released to a vacuum, does no work.”

No. The free expansion of a gas into a vacuum does no work. This is not the same as a gas “released” into a vacuum.

But it doesn’t even matter, because if the exhaust does no work, then reversing the process is not a problem.

So you’ve argued yourself into a corner.

Focus.

You cannot even interpret the things written in the discussion.

You are not even arguing in the same room, let alone aware enough to see if I am in a corner.

Gas has no choice but to freely expand when released to a vacuum.

[BRrollin]

Okay, so then why do the sources that I gave all say that it is isentropic? Are they all wrong?

A rocket engine, yes...

Rocket exhaust cannot be isentropic because of the physical conditions.

How do you reverse the exhaust of a rocket?

Well why don’t you look that up? I think it’s much more likely that you just don’t understand the science rather than the scientists being wrong about a science process. Lol. That’s what folks do: when something doesn’t make sense to them they look it up.

Instead, you’re approach seems to be that since you don’t understand it then the science is wrong.

I mean, if I had to bet on it, I’d put all the money on you just not knowing what you’re talking about.

Written by the type guy who wants to point out he doesn't understand his own sources, yet miraculously believes them anyway.

You can't reverse the exhaust of a rocket...I don't need to look anything up.

Why not? If free expansion of the exhaust into a vacuum does no work, then reversing the process is thermodynamically trivial.

Or did you think that “reversible” means you need to successfully build a time machine and watch it rewind?

That’s the problem, you don’t understand the basics, but you’ve somehow convinced yourself that you’ve found a flaw in the thinking of experts, by sounding out the words and assuming you thus know their definitions.

Actually, what it shows is the whole source introduced by stack wasn't even relevant to the discussion that is taking place.

I also pointed out to stack that just because a process that takes place within a specific point of operation while the rocket is functioning, does not mean that process is taking throughout the entirety of the rocket.

That is why what he introduced is not relevant to the part of the rocket (i.e., exhaust) exposed to the vacuum.

I do understand what I am writing.

Gas, when released to a vacuum, does no work.

Have a great day.

Focus. I wasn’t challenging you on that point. You’re getting your conversations mixed up.

“Gas, when released to a vacuum, does no work.”

No. The free expansion of a gas into a vacuum does no work. This is not the same as a gas “released” into a vacuum.

But it doesn’t even matter, because if the exhaust does no work, then reversing the process is not a problem.

So you’ve argued yourself into a corner.

Focus.

You cannot even interpret the things written in the discussion.

You are not even arguing in the same room, let alone aware enough to see if I am in a corner.

Gas has no choice but to freely expand when released to a vacuum.

We’ll sure. Once it’s in the vacuum, that’s what it will do. But that isn’t what is relevant here.

If you fart in space, your fart gas, once farted, will freely expand.

But you squeezing those pasty white cheeks is mechanical work. That’s how the fart gas gets into the vacuum from your body.

Now let’s try to keep the fart gas coming out of the right orifice. It’s tiresome reading your mouth flatulence.

[totallackey]

We’ll sure. Once it’s in the vacuum, that’s what it will do. But that isn’t what is relevant here.

If you fart in space, your fart gas, once farted, will freely expand.

But you squeezing those pasty white cheeks is mechanical work. That’s how the fart gas gets into the vacuum from your body.

Now let’s try to keep the fart gas coming out of the right orifice. It’s tiresome reading your mouth flatulence.

No one is denying it takes work to get gas into its original container.

No one is denying the gas has the potential to do work once it is released from its container.

But science states gas released into a vacuum does no work.

And no amount of your dull attempts at humor allow for the science to be invalidated.

Buh bye...

[BRrollin]

We’ll sure. Once it’s in the vacuum, that’s what it will do. But that isn’t what is relevant here.

If you fart in space, your fart gas, once farted, will freely expand.

But you squeezing those pasty white cheeks is mechanical work. That’s how the fart gas gets into the vacuum from your body.

Now let’s try to keep the fart gas coming out of the right orifice. It’s tiresome reading your mouth flatulence.

No one is denying it takes work to get gas into its original container.

No one is denying the gas has the potential to do work once it is released from its container.

But science states gas released into a vacuum does no work.

And no amount of your dull attempts at humor allow for the science to be invalidated.

Buh bye...

Science doesn’t state that at all. It states the free expansion of gas in a vacuum does no work.

The fact that you cannot see the difference between those two things is about as much humor as we can stand.

[iCare]

I have repeatedly stated, that while I do not doubt free expansion, it does not apply in that case of firing a rocket, as the scientific requirements for free expansion are not met.

Yeah, we know...you simply deny.

When I state something, I usually provide the reasoning behind that statement.
If you review this thread, you will find several posts in which I provided detailed explanations why free expansion does not apply to how rockets work.
You will also find others agreeing with my reasoning.
=> Stating I would "simply deny" is obviously a false claim. Please do not do that. 

To refresh your memory, here a three reasons:

• Free expansion requires a constant temperature of the gas. In rocket motors the gas gets (a lot) hotter.
• Free expansion requires a constant amount of gas. In rockets the amount of gas increases (dramatically).
  (Note: Free expansion requires the gas to actually being present "as gas" at the beginning; this is not about the total amount of gas "potentially" available as fuel.)
• Free expansion requires free expansion, i.e. not through a nozzle/valve - which by definition restricts expansion.

Rockets do not meet (at least) three requirements Joule set for free expansion. => Free expansion does not apply. Gas being expelled from a rocket can do work.

The part of gas being being released into a vacuum doing no work somehow escapes you.

It does not. But - as explained above - rockets do not "freely release" gas, they "forcefully eject" it. Different story.

That interpretation <of videos> has been convincingly challenged several times by various people.

Nah...not even challenged...because the people know what they see.

Maybe you have a different interpretation of challenge than I do, but I recall several people making a convincing case against your interpretation.

The source material states the word TUBE.

Indeed it does.
However, it does not state, that it has to be a closed/endless tube, does it?
The source states that gas is forced through a tube and that is obviously true for a rocket.

• Gas is in the combustion chamber. => "Beginning" of the tube.
• Gas is forced through the nozzle. => Still a tube, smaller diameter.
• Gas is expanding in the => Still a tube, increasing diameter.
• Gas leaves the restraints of the rocket completely. => Tube ends, gas dissipates, isn't relevant to propulsion anymore.

This is the same in an atmosphere and in a vacuum.
If rockets wouldn't work, because there "is no tube" they shouldn't work in an atmosphere either.

You are ignoring relevant restrictions  (see the three examples above) to make it look like free expansion would support your point of view.
On the other hand you unduly dismiss valid laws by extending restrictions beyond their relevance (requiring a tube a point of the process, where it does no longer matter).   

A rocket certainly works, but it certainly cannot work in a vacuum.

Atmosphere or vacuum makes no difference for the workings of a rocket. None of the relevant laws makes a distinction between atmosphere being present or not.

The evidence and science are clear.

Indeed, they are. And they clearly show, that rockets will work both in an atmosphere and in a vacuum.

iC

[stack]

Okay will do!

I’ll probably start with those same articles. They seem to know about it.

Unless you have some other sources about entropy that might help me learn about it in the way you do?

Simply put, entropy is a quantity representing the availability of the thermal energy in a system to be converted into work.

A rocket cannot possibly maintain constant entropy.

Incorrect, as you will see in a moment.

As stack writes falsely:

Rocket engines are considered Isentropic systems where entropy remains unchanged.

Isentropic nozzle flow
"Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approximates the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids.”

So you see, a Nonisentropic process, like Free Expansion, does not apply to an Isentropic system. Apples and oranges.

...it is obviously written by someone trying to engage in double speak...

And stack, while he talks of the rocket engine, does NOT want you to look behind the curtain containing the rocket exhaust, which is where the meat and potatoes is at.

A rocket has a fixed amount of fuel and a fixed amount of potential energy.

Rockets have a fixed rate of discharge at any particular point of time.

Sooner or later, there is no more more potential energy available.

Therefore, rockets cannot maintain unchanged entropy when in operation.

And that process is not "reversible," nor can it possibly be "adiabatic," as described in stacks' ridiculous post, once initiated. Rockets experience no reverse flow of fluids or exhaust. The exhaust is supposedly taking place in the vacuum of outer space...again, where all the fakers want you to believe that gas, just because it is coming from a rocket, can somehow, someway...be different...but it, of course...cannot.

Gas released into a vacuum...does no work.

All of what you wrote is false and backed by zero evidence or science. Regarding Rockets and Isentropic Flow:

"As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas. The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy. Engineers call this type of flow an isentropic flow; a combination of the Greek word "iso" (same) and entropy."

More information and equations can be found here:
https://www.grc.nasa.gov/WWW/k-12/airplane/isentrop.html

You see, engineers call this type of flow an isentropic flow. You are neither an engineer, nor a rocket scientist, nor an expert in thermodynamics yet you claim to know more than people who are without providing any evidence. Your "free expansion does no work" is nonisentropic and does not apply here to rocket engines, so that argument you originally had is toast.

For once, please provide some evidence for you claims rather than just ignorant unfounded bluster.

For once, understand what the hell you are reading and where the flow is taking place.

I mean, read the whole thing...

And make note of the word TUBE!

Gas...in a...TUBE...

Not gas...in a...nozzle.

Now, goodbye to your lack of understanding.

Just how you never provide evidence you apparently don't read evidence either. Here's the next paragraph after the one the one I cited above:

"Isentropic flows occur when the change in flow variables is small and gradual, such as the ideal flow through the nozzle shown above. The generation of sound waves is an isentropic process. A supersonic flow that is turned while the flow area increases is also isentropic. We call this an isentropic expansion because of the area increase."

Here's the image 'shown above' that it refers to:



You really have to start providing some evidence rather than just jibber-jabber. For once and for all the nonisentropic law of free expansion where gas in a vacuum 'does no work' does not apply to rockets. Rockets are isentropic, period. Read the literature. If you disagree, provide some evidence to back up your claims, not just your own ignorance of the subject.

[DuncanDoenitz]

Lackey, JP Joule would be turning in his grave at how some people are misinterpreting his work and claiming his support for their own theories. 

I think everyone is happy with his "free-expansion into a vacuum" experiment.  In the demonstration normally presented, the gas is released from its containment on the left, along the x-axis, into the evacuated containment on the right, such that it then occupies both parts of the vessel.  The gas comes to rest.  The vessel is insulated.  The internal mass and energy and heat remain unchanged during the process.  No work.

Lets consider the first individual molecule of gas to make that journey.  When the gas is released, that molecule is accelerated through the aperture into vacuum.  It has velocity.  That velocity is the result of the pressure of all its fellow molecules pushing against it.  It is an action to the right, and at some point will produce a reaction to the left. 

The next molecule does the same thing; same action, same reaction.  But now there are 2 molecules in the right hand containment, and they ADDITIONALLY repel each other, so also accelerating along the y- and z-axes.  They are expanding freely in a vacuum.  But they still have their initial velocity to the right on the x-axis. 

Pretty soon, roughly half of the remaining molecules will join their colleagues on the journey.  The acceleration of each along the x-axis will be infinitesimally less than the first, because the right-hand containment is beginning to pressurise.  Each will accelerate to the right on the x-axis, an action, creating the need for a reaction.  They will also expand freely along the y- and z-axes.  But you have to remember that whatever acceleration they receive through free-expansion is ADDITIONAL to the velocity they had to the right initially. 

Meanwhile, our first molecule has hit the right-hand wall af the containment, and comes to rest.  By reducing its velocity to zero, it has accelerated to the LEFT on the x-axis.  This is an action to the left, and will produce a reaction to the right.  But just a minute, we left an action/reaction pair hanging a few paragraphs back, which is convenient because when we dial that in, then the algebraic equation for all the force applied to Molecule #1 is zero.  It started at rest and finished at rest.  No action.  No reaction.  No work.  Thank you JPJ. 

Now lets transfer the left-hand containment to the infinite majesty of space.  When released, our molecules accelerate to the right, an action.  Yes, the gas disperses freely in 3 dimensions into the vacuum but the individual molecules retain their velocity along the x-axis.  Although the gas is very, very, very dispersed, it hasn't ceased to exist, the molecules still have mass and velocity.  They got that velocity by being accelerated out of the containment; an action to the right, producing a reaction of the containment to the left.  And because they don't hit the wall of a right hand containment, so there is no second action/reaction pair, they keep going.  For ever. 

As does the containment, to the left.  For ever. 

Work done. 

[totallackey]

Okay will do!

I’ll probably start with those same articles. They seem to know about it.

Unless you have some other sources about entropy that might help me learn about it in the way you do?

Simply put, entropy is a quantity representing the availability of the thermal energy in a system to be converted into work.

A rocket cannot possibly maintain constant entropy.

Incorrect, as you will see in a moment.

As stack writes falsely:

Rocket engines are considered Isentropic systems where entropy remains unchanged.

Isentropic nozzle flow
"Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approximates the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids.”

So you see, a Nonisentropic process, like Free Expansion, does not apply to an Isentropic system. Apples and oranges.

...it is obviously written by someone trying to engage in double speak...

And stack, while he talks of the rocket engine, does NOT want you to look behind the curtain containing the rocket exhaust, which is where the meat and potatoes is at.

A rocket has a fixed amount of fuel and a fixed amount of potential energy.

Rockets have a fixed rate of discharge at any particular point of time.

Sooner or later, there is no more more potential energy available.

Therefore, rockets cannot maintain unchanged entropy when in operation.

And that process is not "reversible," nor can it possibly be "adiabatic," as described in stacks' ridiculous post, once initiated. Rockets experience no reverse flow of fluids or exhaust. The exhaust is supposedly taking place in the vacuum of outer space...again, where all the fakers want you to believe that gas, just because it is coming from a rocket, can somehow, someway...be different...but it, of course...cannot.

Gas released into a vacuum...does no work.

All of what you wrote is false and backed by zero evidence or science. Regarding Rockets and Isentropic Flow:

"As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas. The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy. Engineers call this type of flow an isentropic flow; a combination of the Greek word "iso" (same) and entropy."

More information and equations can be found here:
https://www.grc.nasa.gov/WWW/k-12/airplane/isentrop.html

You see, engineers call this type of flow an isentropic flow. You are neither an engineer, nor a rocket scientist, nor an expert in thermodynamics yet you claim to know more than people who are without providing any evidence. Your "free expansion does no work" is nonisentropic and does not apply here to rocket engines, so that argument you originally had is toast.

For once, please provide some evidence for you claims rather than just ignorant unfounded bluster.

For once, understand what the hell you are reading and where the flow is taking place.

I mean, read the whole thing...

And make note of the word TUBE!

Gas...in a...TUBE...

Not gas...in a...nozzle.

Now, goodbye to your lack of understanding.

Just how you never provide evidence you apparently don't read evidence either. Here's the next paragraph after the one the one I cited above:

"Isentropic flows occur when the change in flow variables is small and gradual, such as the ideal flow through the nozzle shown above. The generation of sound waves is an isentropic process. A supersonic flow that is turned while the flow area increases is also isentropic. We call this an isentropic expansion because of the area increase."

Here's the image 'shown above' that it refers to:



You really have to start providing some evidence rather than just jibber-jabber. For once and for all the nonisentropic law of free expansion where gas in a vacuum 'does no work' does not apply to rockets. Rockets are isentropic, period. Read the literature. If you disagree, provide some evidence to back up your claims, not just your own ignorance of the subject.

Holy crap...isentropic relative to the sound?

LOL!

Like, A: Sound could even travel in a vacuum...

2) Gas does no work when released to a vacuum...

Take your nonsense peddling show elsewhere.

[totallackey]

Lackey, JP Joule would be turning in his grave at how some people are misinterpreting his work and claiming his support for their own theories. 

I think everyone is happy with his "free-expansion into a vacuum" experiment.  In the demonstration normally presented, the gas is released from its containment on the left, along the x-axis, into the evacuated containment on the right, such that it then occupies both parts of the vessel.  The gas comes to rest.  The vessel is insulated.  The internal mass and energy and heat remain unchanged during the process.  No work.

Lets consider the first individual molecule of gas to make that journey.  When the gas is released, that molecule is accelerated through the aperture into vacuum.  It has velocity.  That velocity is the result of the pressure of all its fellow molecules pushing against it.  It is an action to the right, and at some point will produce a reaction to the left. 

The next molecule does the same thing; same action, same reaction.  But now there are 2 molecules in the right hand containment, and they ADDITIONALLY repel each other, so also accelerating along the y- and z-axes.  They are expanding freely in a vacuum.  But they still have their initial velocity to the right on the x-axis. 

Pretty soon, roughly half of the remaining molecules will join their colleagues on the journey.  The acceleration of each along the x-axis will be infinitesimally less than the first, because the right-hand containment is beginning to pressurise.  Each will accelerate to the right on the x-axis, an action, creating the need for a reaction.  They will also expand freely along the y- and z-axes.  But you have to remember that whatever acceleration they receive through free-expansion is ADDITIONAL to the velocity they had to the right initially. 

Meanwhile, our first molecule has hit the right-hand wall af the containment, and comes to rest.  By reducing its velocity to zero, it has accelerated to the LEFT on the x-axis.  This is an action to the left, and will produce a reaction to the right.  But just a minute, we left an action/reaction pair hanging a few paragraphs back, which is convenient because when we dial that in, then the algebraic equation for all the force applied to Molecule #1 is zero.  It started at rest and finished at rest.  No action.  No reaction.  No work.  Thank you JPJ. 

Now lets transfer the left-hand containment to the infinite majesty of space.  When released, our molecules accelerate to the right, an action.  Yes, the gas disperses freely in 3 dimensions into the vacuum but the individual molecules retain their velocity along the x-axis.  Although the gas is very, very, very dispersed, it hasn't ceased to exist, the molecules still have mass and velocity.  They got that velocity by being accelerated out of the containment; an action to the right, producing a reaction of the containment to the left.  And because they don't hit the wall of a right hand containment, so there is no second action/reaction pair, they keep going.  For ever. 

As does the containment, to the left.  For ever. 

Work done.

Wrong...just totally wrong...

Any gas released to a vacuum does 0 work.

No matter how you try to fluff it up or otherwise hold on to your fantasy.

Look at all the videos provided here for plain visual proof you are wrong.