Why a temperature differential?

[Tom Booth]

So, is this right?

You want to start with a gas confined in a cylinder at 300°k

Heat the gas to 600°k

Then expand it until it reaches 300°k and stop the expansion at that point?

Then you want to know the volume and pressure at the conclusion?

From what VincentG quoted earlier:

You said:

What happens to a fluid when heated up and how does manipulating either temperature, volume or pressure change that.

So if you heat a liter of air, expand it until it's back to starting temperature, what do you end up with? Bigger volume, lower density, same pressure?

You have multiple open ended questions there.

Heated up and then "manipulating either temperature, volume or pressure".

No real idea what you're after.

Are you also excluding/including "work".

A gas expanding does work in the process of expanding as well, unless expanding into a total vacuum.

[Tom Booth]

If you convert the starting gas, volume, pressure and temperature to moles, then you could probably get a ballpark answer to your question, (whatever it is) using an ideal gas calculator

https://www.calculatorsoup.com/calculat ... as-law.php

[Tom Booth]

I get:

Answer:
n = 0.040621987915681 mol
moles

Using 1atm, 1 L, (I assume to be liters) at 300°K

0.040621987915681

You can use that to calculate whatever else you want to know

[Tom Booth]

According to the calculator:

0.040621987915681 moles at 300°k (the temperature expanded to) back to 1 ATM will end up as 1 liter again

Compress_20240629_142311_1475.jpg (40.95 KiB) Viewed 3288 times

[Jack]

I'm trying to get an understanding of what air, or any other fluid, does when heated up. How that turns into internal energy and how that manifests itself.

The theoretical example I thought of would give me an insight into that. And I don't think it's that complicated.
But it seems nobody can give me a straight simple answer. I'm not blaming anybody here, but in stead of flailing around saying my question doesn't make sense, tell me what you need to know then to answer it.

For the sake of imagination, yeah let's say I have a cylinder with a liter of air. 1 bar pressure. I heat it up by 300k (from 300k to 600k) The pressure rises.

Now I expand the cylinder until the air is back to 300k, its starting temperature.
What pressure do I end up with?

Before I was asking this in a very general way because I don't need an exact answer to my question. I just wanted to know if the pressure is higher, lower or the same in the end. That's all.
If this is not answerable, let me know what else you need to know.

“If you can't explain it to a six year old, you don't understand it yourself.”
Einstein (apparently)

[Jack]

For the sake of clarity. Assume no friction losses or work output. Also no temperature loss through conduction.

[matt brown]

Jack if you heat 1 liter of 300k air to 600k and expand it adiabatically, it will reach 1 bar well before it lowers to 300k.

I'll try to find the real values fir you but maybe Matt will beat me to it.

Jack, Vincent is correct and here's my cheat sheet from an older post

adi index.png (28.33 KiB) Viewed 3267 times

It's indexed to changes in volume ratio. This was required ME homework pre-war (pre WWII) but disappeared post-war. Anyone scheming adiabatic processes needs to know how to calculate adiabatic process values to validate cycle scheme. No doubt KIA Tom will dismiss this as just useless mumbo-jumbo.

The Lenoir cycle (ICE Otto-Langen engine) has isochoric input with adiabatic expansion and isobaric exhaust, but very low efficiency due to high temperature exhaust. This was the last successful non-compression cycle engine, since Otto himself was adjusting the valves on one when he had his Eureka moment and the rest is history...

Otto-Langen.png (322.29 KiB) Viewed 3267 times

[matt brown]

I'm trying to get an understanding of what air, or any other fluid, does when heated up. How that turns into internal energy and how that manifests itself.

“If you can't explain it to a six year old, you don't understand it yourself.”
Einstein (apparently)

I'm working on a simple chart that shows the relationship of PVT and QWU via process. This is no problem for isochoric, isothermal and isobaric, but including adiabatic will likely require a second chart with different values. I've been working on this for days just so it follows that Einstein quote !!! Stay tuned, I'll post this later today.

[matt brown]

Unfortunately it fails to show work input. That is work necessary for pulling a vacuum, and for compression. I've added the areas that add up to 'negative work' to the photo:

The effective expansion is that to the left of the area I put the red squiggly line.

Xlnt graphic mod, but you forgot to callout

(1) Wneg is "above" the work area at the tail vs "below" the work area at the head

(2) the visual "hipshot" of Wpos vs Wneg

(3) 30w output from 400cc is nothing to write home about, but this is only 200rpm

(4) if this was 1000rpm then 150w appears possible, and I don't see how this would be possible or these buggers would be everywhere. 150w from any 400cc vacuum eng at 1000rpm is beyond belief when ambient compression restrains thermal ratio = volume ratio


Hey Fool, here's a couple more similar plots with the second one just for you LOL

forced work PV plot_1.png (31.14 KiB) Viewed 3257 times

forced work PV plot_2.jpg (14.29 KiB) Viewed 3257 times

[matt brown]

If you convert the starting gas, volume, pressure and temperature to moles, then you could probably get a ballpark answer to your question, (whatever it is) using an ideal gas calculator

https://www.calculatorsoup.com/calculat ... as-law.php

I good calculator includes QWU values, and like the layout of this one (CalcTool)


https://www.calctool.org/thermodynamics ... -processes

[Tom Booth]

I'm trying to get an understanding of what air, or any other fluid, does when heated up. How that turns into internal energy and how that manifests itself.

The theoretical example I thought of would give me an insight into that. And I don't think it's that complicated.
But it seems nobody can give me a straight simple answer. I'm not blaming anybody here, but in stead of flailing around saying my question doesn't make sense, tell me what you need to know then to answer it.

For the sake of imagination, yeah let's say I have a cylinder with a liter of air. 1 bar pressure. I heat it up by 300k (from 300k to 600k) The pressure rises.

Now I expand the cylinder until the air is back to 300k, its starting temperature.
What pressure do I end up with?

Before I was asking this in a very general way because I don't need an exact answer to my question. I just wanted to know if the pressure is higher, lower or the same in the end. That's all.
If this is not answerable, let me know what else you need to know.

“If you can't explain it to a six year old, you don't understand it yourself.”
Einstein (apparently)

What's wrong with the online calculator?

Did you see my post? As I said, you can pretty much use that to answer such questions.

The one Matt linked to looks good also, but probably not necessary, either one should work

air, or any other fluid

You don't want much do you?

All combined you've asked about maybe 100 different questions.

Tell me now. What you can't answer?

You haven't asked a specific identifiable question, just these vague generalizations. You get a response and add more complications.

Anyway Matt's link has several "fluids" to choose from. But not "Any".

[Tom Booth]

I mean you may as well ask; what do you get when you add up or multiply or divide any combination of numbers?

It's impossible to answer.

So here's a calculator.

[Fool]

To all, please disregard my calculations a few pages back. They seem in error. It was late last night and I was too tired to double check them. I think the numbers got entered into my calculator incorrectly. But I don't know for sure. Will check them myself and get back here to answer Jacks question. I'm skeptical of the 15 times.

I am sorry. Please continue on until I can effect a correction.

Jack, the mathematical Dyslexic can become good at this mathematics, it takes a lot more work, and perhaps better lessons. Don't give up the effort. Please. If I can learn it anyone can.

Matt, yes the area under the curve flips sides when the curve crosses over zero, even if zero is displaced by a constant. I'm glad someone here has the education to understand Integral Calculus too. Thanks for the input.

I think Jack wants to verify gas behavior empirically. The gas equations and gas calculators are based on information that was gathered by scientists years ago and are excellent predictors of what Jack will again rediscover.

Jack if you take a sealed cylinder and pre pressurize it at Tc for an initial value. Put it into a warm space, like an oven with a calibrated Th, it will eventually come into equilibrium. T inside will equal T outside. The pressure can be read at this point. Different initial pressures and Temperatures can be tested and measured.

To measure an adiabatic temperature drop will be much more difficult. The temperature of just the gas needs to be measured. Unfortunately the gas changing pressure will have a different temperature between it and the thermometer, and the cylinder walls. So it won't stay at the new temperature.

Using the ideal gas equations allows calculating the gas temperature from volume and pressure. This is often done inside engines using what's called an indicator diagram.

It might be easier to learn the thermodynamics like everyone else, or how to use an online calculator. Good luck Cary on Sir.

[Jack]

Thanks for the help everyone. I'll try to sort this in my head.

[Jack]

air, or any other fluid

You don't want much do you?

All combined you've asked about maybe 100 different questions.

Tell me now. What you can't answer?

You haven't asked a specific identifiable question, just these vague generalizations. You get a response and add more complications.

Anyway Matt's link has several "fluids" to choose from. But not "Any".

You have an incredible talent to trip over one word and forget everything else I said.
"Any", as in "just pick one" as they'll be similar enough in behavior for my purpose.
It doesn't mean "every" or "all". I'm asking to just give an example. And I'm not asking for exact numbers, just general behavior.
Again, my English might not be perfect here and your understanding of my question might be lacking because of it. But I don't think I asked something ridiculous that you can't read into.