Timeline for Why is a throttling valve isenthalpic whilst a nozzle is not?
Current License: CC BY-SA 4.0
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| Jul 31, 2021 at 22:25 | comment | added | David White | @SalahTheGoat, it's not done that way. What you are describing is an eductor, which "pulls a vacuum on a side stream" in order to entrain liquid from a lower pressure source. Also, note my previous reply ... the conclusions of the author are based on the standard way of drawing control volumes for the given devices, but that's not the only way to select a control volume. The selection of the control volume will influence your answer. | |
| Jul 31, 2021 at 18:59 | comment | added | SalahTheGoat | Thanks. Just a quick question: suppose we have a throttle valve set up in a 8'' pipe as you describe with a perfectly incompressible fluid flow through it so that $V_{out}=V_{in}$. In this case we have that $u_f+P_fv=u_i +P_iv$ where $v$ is the constant specific volume. Throttle valves decrease the pressure ($P_f<_P_i$) which implies that $\Delta u = u_f-u_i=(P_i-P_f)v > 0$ (i.e the fluids internal energy increases as it passes through the valve). Surely this means that the fluid temperature will always increase in a throttle valve if we have an incompressible fluid (i.e any liquid)? | |
| Jul 31, 2021 at 15:49 | history | answered | David White | CC BY-SA 4.0 |