Can you assume constant volume in a steady flow throttling process?

Answer 1

No I do not think so, at least for compressible flow. You can achieve steady flow in variant volumes by varying the velocity.
Take steady flow of air in a duct. Then increase the duct diameter. The flow will remain the same, it will just slow down. If the duct transitions to a much smaller diameter, flow will remain constant but the velocity will increase. Pressure drop will also, by the way, not remain constant.

For incompressible flow like water, I believe the volume of the stuff flowing does remain constant with flow.

Answer 2

I'm going to guess this is some kind of Thermo problem. I would not assume constant volume as that would be true only for incompressible fluids as noted above.

You can assume that no energy is transfered, or the process is adiabatic. That assumption is good for orifice plates, nozzles and should be fine for a throttling valve. This means that the total energy of the fluid does not change across the throttle, what ever pressure drop occurs across the throttle will increase the velocity, and or temperature of the fluid.

Answer 3

I thought constant volume was for non-flow processes. I believe it's usual to assume adiabatic throttling.

Answer 4

For the first time i am absolutely stumped.
If you have steady flow that would give a constant volume I guess.

Answer 5

Never assume anything, I thought everyone knew that.

Answer 6

Yeah,I managed it with my cat.