Gases and thermodynamics in confinement.

[Juval]

Hi.

Consider a plenum with a small restricting outlet.
Highly heated gas constantly flows through the plenum, and a build-up, or congestion of high-pressure gas exists in the plenum due to the restricting outlet pipe.
The intake flow of gas does not change.

1. A hotter plenum should increase the gas pressure since there is a small amount of
confinement due to the restricted outlet.

2. But, the hotter gas expands more, decreasing pressure/density.

Which of these is true?

 

[gsal]

No, the hotter gas is not free to expand, therefore, pressure increases and possibly pushes more gas out of the restricting outlet and/or starts offering increased opposition to whatever is feeding this plenum

 

[Juval]

No, the hotter gas is not free to expand, therefore, pressure increases and possibly pushes more gas out of the restricting outlet and/or starts offering increased opposition to whatever is feeding this plenum

But look at what you're saying. "therefore, pressure increases", and, "pushes more gas out of the restricting outlet."

If the heat causes more gas to be displaced out of the outlet (remembering that incoming gas flow does not change), the extra gas being displaced is just another way of saying that the gas is expanding, as in example 2.

And would this expansion not mean that the congestion in the plenum becomes less dense since more gas is going out without more gas being put in?

 

[Juval]

Is this a very hard question? Where are all the brains in here??