Hi guys,
I just don't seem to get this topic fundamentally and also how to actually apply it. Just focusing on compressible flow by the way.
Wikipedia starts by saying "Fanno flow is the adiabatic flow through a constant area duct where the effect of friction is considered."
Basically, I...
"For an ideal gas, the dU term will change due to a change in temperature of the gas."
I'm not saying you're saying. But the question is how come the wiki page says that there's no change in temperature for an ideal gas through an expansion (see the screenshot I posted in my previous post)?
The PdV work we're talking about here is strictly expansion work, not flow work. So could it be that work only needs to be done to expand only in circumstances where there's attractive forces whereas ideal gas has no attractive that are needed to overcome (in a case where it's only a fluid...
Yep agree that dPV = dU for isenthalpic ideal gas expansion. None of the quantities change. Even though there is an expansion. Is your question that how can I say there is no PV work being done at the same time saying there's an expansion?
Yes, one of the fundamental aspects of the Joule Thomson expansion is that it's an irreversible expansion and expansion through the throttle is the most irreversible situation because it happens the fastest (in one step if you will). I mean in fact, all real processes are irreversible and this...
I'm slightly out of my element here as my thermo was always weak :( haha
I think we're conflating two different types of work but unfortunately they're both called PV work which is confusing. Though these might be related in some way I don't well understand. You've been talking about flow work...
Hey, thanks for the input.
I don't believe V has to necessarily be an intensive property here. It is in h=u+Pv (small case, intensive) which seems to be just as valid/applicable as H=U+PV (capital case, extensive) where it is an extensive property. In the wiki link here, they show it in...
...former context is at the "micro" infinitesimal level strictly as a means of calculating the expansion work which would take the generic form of W=P*DeltaV. So at the micro level, P is basically held constant as the volume changes/increases (recall back to how you manually would integrate the...
First of all, thank you for the response. There's a few separate things that need to be parsed out here...
I'll first lay out all the expansion scenarios. I've got this from a wide mix of sources:
Joule-Thomson (JT) expansion effect is isenthalpic, so H=U+PV must be constant. U consists of...
Can anyone tell me if my question makes sense please? I'm not sure if the question is incomprehensible or if you guys aren't sure of the answer either.
Maybe this thread has gotten too deep and messy and maybe I should just make a new clean independent thread with the question?
Thank you!
...flow meaning it could only expand up to 150 (V2 = 150), and if PVk = constant for adiabatic flow meaning PV itself would decrease (i.e., P2*V2 < P1*V1) and so V2 wouldn't be as high as it's in the isothermal case...HOW COME the wiki quote says that PV increases suggesting that V2 would...
Yeah, that struck me too as interesting. I think it reaffirms the saying "You don't know what you don't know". Initially I thought it was rather straightforward but the more we got into it, new questions that I hadn't considered kept popping up.
But the gentlemen here have done an awesome job...
Sure I'm willing to assume they're trying to cover all cases. But the thing is, I don't even see where they cover the usual case of temp dropping AND PV decreasing anywhere. The only time they talk about PV decreasing is here:
"Conversely, a decrease in PV means that work is done on the fluid...
Well no, I'm not saying wiki got it wrong and needs fixing necessarily (unless you're saying that) ... I don't know if it's right or wrong, I'm just seeing a dissonance between what you and katmar have said (volume not increasing sufficiently enough to keep PV constant for adiabatic) and what...
...P multplied by V) would decrease for adiabatic process. The volume doesn't increase sufficiently enough to keep PV constant (like it does in isothermal case). So P2*V2 would be less than P1*V1. So with that being the case, how come wikipedia says (in bold in my earlier post) that PV increases?
Oh no.. I'm not asking this question -> "Since PV must be constant for isothermal flow, how is it that they're saying PV increases in adiabatic flow?" That would be definitely be an absurd question blatantly trying to compare apples to oranges.
It's more like this -> "We recognize that PV =...
