modelExpansionVessel

Expansion vessel with fixed pressure

Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).

Information

This is a model of a pressure expansion vessel. The vessel has a constant pressure that is equal to the value of the parameter p_start. The model takes into account the energy and mass balance of the medium. It has no heat exchange with the ambient.

The expansion vessel needs to be used in closed loops that contain water to set a reference pressure and, for liquids where the density is modeled as a function of temperature, to allow for the thermal expansion of the liquid.

Note that alternatively, the model Buildings.Fluid.Sources.Boundary_pT may be used to set a reference pressure. The main difference between these two models is that in this model, there is an energy and mass balance for the volume. In contrast, for Buildings.Fluid.Sources.Boundary_pT, any mass flow rate that flows out of the model will be at a user-specified temperature. Therefore, Buildings.Fluid.Sources.Boundary_pT leads to smaller systems of equations, which may result in faster simulation.

Parameters

Type	Name	Default	Description
Modelica.Units.SI.Volume	V_start		Volume of liquid stored in the vessel at the start of the simulation
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics (from LumpedVolumeDeclarations)	Modelica.Fluid.Types.Dynamics.DynamicFreeInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Modelica.Fluid.Types.Dynamics	substanceDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of independent mass fraction balance: dynamic (3 initialization options) or steady state
Modelica.Fluid.Types.Dynamics	traceDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of trace substance balance: dynamic (3 initialization options) or steady state
Advanced › Dynamics
Modelica.Fluid.Types.Dynamics	massDynamics (from LumpedVolumeDeclarations)	energyDynamics	Type of mass balance: dynamic (3 initialization options) or steady state, must be steady state if energyDynamics is steady state
Initialization
Medium.AbsolutePressure	p_start (from LumpedVolumeDeclarations)	Medium.p_default	Start value of pressure
Medium.Temperature	T_start (from LumpedVolumeDeclarations)	Medium.T_default	Start value of temperature
Medium.MassFraction[Medium.nX]	X_start (from LumpedVolumeDeclarations)	Medium.X_default	Start value of mass fractions m_i/m
Medium.ExtraProperty[Medium.nC]	C_start (from LumpedVolumeDeclarations)	fill(0, Medium.nC)	Start value of trace substances
Medium.ExtraProperty[Medium.nC]	C_nominal (from LumpedVolumeDeclarations)	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)
Dynamics
Real	mSenFac (from LumpedVolumeDeclarations)	1	Factor for scaling the sensible thermal mass of the volume

Connectors

Type	Name	Default	Description
Modelica.Fluid.Interfaces.FluidPort_a	port_a		Fluid port

Components

Type	Name	Default	Description
Modelica.Units.SI.Mass	m		Mass of liquid in the vessel

Revisions

May 11, 2022, by Michael Wetter:
Removed nonused parameter p.
This is for IBPSA, #1614.
May 29, 2014, by Michael Wetter:
Removed undesirable annotation Evaluate=true.
March 25, 2014 by Michael Wetter:
Revised the model to use a constant pressure rather than a constant volume of water and gas. This leads to a simpler model.
August 1, 2013 by Michael Wetter:
Updated model to use new connector mWat_flow.
February 7, 2012 by Michael Wetter:
Revised due to changes in conservation equations in Buildings.Fluid.Interfaces.
September 16, 2011 by Michael Wetter:
Set m(stateSelect=StateSelect.always), since setting the stateSelect attribute leads to smaller systems of equations.
July 26, 2011 by Michael Wetter:
Revised model to use new declarations from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations.
May 25, 2011 by Michael Wetter:
Revised model due to a change in the fluid volume model.
Nov. 4, 2009 by Michael Wetter:
First implementation.