- #1
Kakashi
- 25
- 1
A gas flows along an insulated pipe (q=0) through a porous plate that separates two sections of the pipe at different constant pressures P1 and P2.
In Thermodynamics we study systems at equilibrium but here the gas is not in equilibrium because there is a pressure difference across the porous plate.If this were not the case, the pistons would accelerate and the pressures would change with time. The pistons are externally constrained so that P1 and P2 are held constant.
I read that gases flow from high pressure to lower pressure to equalize pressure. If gas flows from the left chamber to the right chamber through the porous plate, wouldnt this initially cause the gas pressure in the left chamber to drop so that $$ P_{gas,left}<P_{1} $$ causing the left piston to move inward and compress the gas until the pressure is restored to P1? Similarly, gas entering the right chamber would tend to increase the pressure so that $$ P_{gas, right}>P_{2} $$ causing the right piston to move outward and expand the volume until the pressure returns to P2. After this adjustment, there would still be a pressure difference between the left and right chambers. Does this mean that piston motion continues indefinitely, eventually pushing all the gas from the left chamber through the porous plate so that all the gas ends up on the right side?
View attachment 369235
In Thermodynamics we study systems at equilibrium but here the gas is not in equilibrium because there is a pressure difference across the porous plate.If this were not the case, the pistons would accelerate and the pressures would change with time. The pistons are externally constrained so that P1 and P2 are held constant.
I read that gases flow from high pressure to lower pressure to equalize pressure. If gas flows from the left chamber to the right chamber through the porous plate, wouldnt this initially cause the gas pressure in the left chamber to drop so that $$ P_{gas,left}<P_{1} $$ causing the left piston to move inward and compress the gas until the pressure is restored to P1? Similarly, gas entering the right chamber would tend to increase the pressure so that $$ P_{gas, right}>P_{2} $$ causing the right piston to move outward and expand the volume until the pressure returns to P2. After this adjustment, there would still be a pressure difference between the left and right chambers. Does this mean that piston motion continues indefinitely, eventually pushing all the gas from the left chamber through the porous plate so that all the gas ends up on the right side?
View attachment 369235