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modelica / ModelicaStandardLibrary

Free (standard conforming) library to model mechanical (1D/3D), electrical (analog, digital, machines), magnetic, thermal, fluid, control systems and hierarchical state machines. Also numerical functions and functions for strings, files and streams are included.
https://doc.modelica.org
BSD 3-Clause "New" or "Revised" License
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Conservation of kinetic energy in valves and fittings #329

Open modelica-trac-importer opened 7 years ago

modelica-trac-importer commented 7 years ago

Reported by rfranke on 12 Jan 2009 06:47 UTC Pipes.BaseClasses.PartialTwoPortFlow (former distributed pipes) and the main docu in UsersGuide.ComponentDefinition.BalanceEquations contain a notice about not conserved energy if changing fluid velocities are neglected.

Should not a model like Modelica_Fluid.Valves.ValveVaporizing,

Valve for possibly vaporizing (almost) incompressible fluids, accounts for choked flow conditions,

account for the impact of the different density of vapour on the energy balance?

Currently the Valves.BaseClasses.PartialValve formulates an isenthalpic state transformation. This assumptions appears reasonable for ValveIncompressible.

Note that, without further extending the number of parameters, ValveVaporizing and ValveCompressible know the metric flow coefficient Av, which should be a good value for the cross flow areas at inlet and outlet.

Why not extending the energy balance to account for "choked flow conditions"? Also Fittings.SuddenExpansion sounds like a bad model in this regard.

Alternatively, at least the docus should explain why energy is not conserved.

Migrated-From: https://trac.modelica.org/Modelica/ticket/329

modelica-trac-importer commented 7 years ago

Modified by dietmarw on 22 Jan 2009 16:57 UTC

modelica-trac-importer commented 7 years ago

Modified by rfranke on 28 Jan 2009 15:41 UTC

modelica-trac-importer commented 7 years ago

Comment by rfranke on 29 Jan 2009 14:52 UTC It seems we forgot to update the docu of the respective models with modeling assumptions made (see Task 2 of MoMs).

https://svn.modelica.org/projects/ModelicaDesign/trunk/MeetingMinutesMaterial/min60/Slides-and-Documents/MinutesFluid_60_v3.pdf

modelica-trac-importer commented 7 years ago

Comment by msielemann on 23 Mar 2010 11:11 UTC moved from https://trac.modelica.org/Modelica_Fluid/ticket/60

modelica-trac-importer commented 7 years ago

Comment by dietmarw on 27 Jan 2011 12:43 UTC Milestone Modelica_Fluid 1.1 deleted

modelica-trac-importer commented 7 years ago

Modified by ahaumer on 6 Mar 2012 16:32 UTC