Stirlingengineforum.com

Entropy.

The thermodynamics definition boils down to:
S = ∆Q/T

Energy transfered, Joules, divided by Temperature, Kelvin. Both being real values therefore, Entropy S is a real concept and value, too.

The following link does a fairly good job of introducing entropy.

https://m.youtube.com/watch?v=DxL2HoqLb ... bmVyZ3k%3D

Enjoy. I hope it helps.

One thing I'd like to add is that heat traveling to an equilibrium temperature is more likely than just the dice rolling probability described in the video. It, also, is forced there buy a thermal "pressure" enacting a outward direction for heat. That pressure is measured by temperature and kinetic pressure. If the outward force, temperature, is greater in one area than another heat flow from hotter to colder will be the direction.

Dark energy may just be the heat of the universe expanding the universe outwards rasing the total entropy as it goes.

Fool wrote: ↑Mon May 13, 2024 11:59 am Entropy.

The thermodynamics definition boils down to:
S = ∆Q/T

Energy transfered, Joules, divided by Temperature, Kelvin. Both being real values therefore, Entropy S is a real concept and value, too.
...

Not necessarily

2 hamsters / 2 cups of milk = 1 Milkster.

7 dinosaurs x 3 grapefruits = 21 grapasaurs

Joules / temperature = temprajoules

Are you guys working on a molecular reactor, or a piston engine?

Temperature is a measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. So, kinetic energy transferred to the thermometer bulb. But Joules are also representative of energy transfer. So this is all about energy transfer, and the idea that it'll all spread out until it's uniformly distributed.

This is all predicated on the beginning - middle - and end version of our currently favoured creation myth, the Big Bang. In the realm of astrophysics, I'm as skeptical of 'end of the universe' stories as I am of 'beginning of the universe' stories. And don't get me started on 'dark matter'.

Edit to add: Thanks Vincent, for bringing us back down to Earth, and to the matter in hand. Understanding and improving our Stirling engines.

Stroller wrote: ↑Mon May 13, 2024 2:04 pm Temperature is a measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. So, kinetic energy transferred to the thermometer bulb. But Joules are also representative of energy transfer. So this is all about energy transfer, and the idea that it'll all spread out until it's uniformly distributed.

...

So, fool says: S = ∆Q/T

∆Q I assume = joules transfered? From what to what? Into an engine?

T is the temperature at which the joules are transfered?

If we transfer say 1000 joules at 400 K

S = 2.5 ?

If correct, that number represents what exactly?

Like the Carnot limit, this appears to be just another meaningless ratio with no context.

I enjoyed the additional historical context around Carnot in the linked video. It tells us that following the invasion of France by the Germans, Ruskies and Prussians he puzzled out his ideal powerless reversible engine in an attempt to give his native France the upper hand in steam engine development and overtake Great Britain's lead in the industrial revolution. The idea was that this would enable France to become militarily strong and not get invaded by the Germans again. Sadly, the French military turned out to be be powerless and reversible in the face of the Germans in 1915 and again in 1940.

Adrian Bejan: Entropy generation minimization: The new thermodynamics of finite‐size devices and finite‐time processes.

Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics. These simple models are used in the optimization of real (irreversible) devices and processes, subject to finite‐size and finite‐time constraints.
The review traces the development and adoption of the method in several sectors of mainstream thermal engineering and science: cryogenics, heat transfer, education, storage systems, solar power plants, nuclear and fossil power plants, and refrigerators. Emphasis is placed on the fundamental and technological importance of the optimization method and its results, the pedagogical merits of the method, and the chronological development of the field.

https://pubs.aip.org/aip/jap/article-ab ... on-The-new

Bejan later went on to develop a theory of the anti-entropic self organisation of biological and inanimate systems from which he derived his 'constructal law'.

He's cited by Buchar (Ref 13): https://www.researchgate.net/publicatio ... not_engine

And Bejan cites Chambadal 1957 and Novikov 1958 in the quoted paper above. I've been discussing their development of the Carnot theory to include irreversible energy flow and power output in my thread here; https://www.stirlingengineforum.com/vie ... php?t=5661

Fool wrote: ↑Mon May 13, 2024 11:59 am Entropy.

The thermodynamics definition boils down to:
S = ∆Q/T
...

The equation appears to be incorrect, or at least there is some debate about it:

One person says the correct form of the equation is:

∆S = Q/T

Another says:

∆S = ∆Q/T

Someone else:

T∆S = ∆Q

https://www.quora.com/How-was-the-entro ... eptualized

This explanation someone provided actually makes some sense. Applied to steam engines or processes involving phase change. i.e. boiling water.

A good example of this behavior is provided by a phase transition, such as the melting of ice. If a glass of ice-water is left in a warm room, it will gradually absorb heat from the room leading the ice to slowly melt. A thermometer measuring the temperature of the ice-water will not record an increase in temperature during this process; under standard conditions, the temperature will remain at 0 °C as long as there is at least some ice left. The heat that is absorbed from the room goes to achieve the release of water molecules from the ice crystal, allowing them to move more freely as liquid water. The average thermal energy of the water molecules in ice at 0 °C or in water at 0 °C is identical, but in the solid state this energy is manifested as vibrational motions of atoms, whereas in liquid water the energy is stored in a combination of bond vibrations and molecular translations, rotations and librations. The liquid water has much more entropy, however, and thus represents a higher energy state of the system. The process of melting has thus involved a transfer of heat from the surroundings (the room) to the system (the ice water) without changing the temperature of the system. All of the energy transferred to the system as heat has gone directly to increase the entropy of the system.

The gaseous form of H2O is more "chaotic" more "entropy".

But does this apply to a hot air engine where there is no "latent heat"?

We learned earlier that in an isothermal expansion of a gas the heat is transformed 100% into work (not entropy).

This is similar to the Carnot cycle, which really only seems to make sense in the realm of steam engines.

Adding or removing heat isothermally with no increase or decrease in temperature does not take an "infinite" amount of time if you're talking about boiling or condensing water.

https://en.m.wikipedia.org/wiki/Entropy

Entropy is defined by calculus specifically a differential equation. The following is a line from Wikipedia:

"So we can define a state function S called entropy, which satisfies 𝑑𝑆 = (𝛿𝑄rev)/𝑇 ."

This when integrated on both sides becomes S=∆Q/T .

But you already knew that, it's just simple calculus/differential-equations, right?

Entropy IMHO is more easily thought of as uselessness of heat, and or dispersion. The same amount of heat at a lower temperature is more useless, higher entropy, lower pressure, larger volume. Able to do less work. Can't heat up your coffee, warm you in the winter, melt an ice cube. Temperature needs to be above those to even be possible.

Colder equals, less usefulness lower enthalpy, and, higher uselessness, higher entropy more dissipated.

Hotter, more useful, higher enthalpy, and lower uselessness, lower entropy, able to do more work.