This model represents an instantaneously mixed volume.
Potential and kinetic energy at the port are neglected,
and there is no pressure drop at the ports.
The volume can exchange heat through its heatPort
.
The volume can be parameterized as a steady-state model or as dynamic model.
To increase the numerical robustness of the model, the constant
prescribedHeatFlowRate
can be set by the user.
This constant only has an effect if the model has exactly two fluid ports connected,
and if it is used as a steady-state model.
Use the following settings:
prescribedHeatFlowRate=true
if the only means of heat transfer
at the heatPort
is a prescribed heat flow rate that
is not a function of the temperature difference
between the medium and an ambient temperature. Examples include an ideal electrical heater,
a pump that rejects heat into the fluid stream, or a chiller that removes heat based on a performance curve.
If the heatPort
is not connected, then set prescribedHeatFlowRate=true
as
in this case, heatPort.Q_flow=0
.
prescribedHeatFlowRate=false
if there is heat flow at the heatPort
computed as K * (T-heatPort.T), for some temperature T and some conductance K,
which may itself be a function of temperature or mass flow rate.prescribedHeatFlowRate=false
.
The parameter mSenFac
can be used to increase the thermal mass of this model
without increasing its volume. This way, species concentrations are still calculated
correctly even though the thermal mass increases. The additional thermal mass is calculated
based on the density and the value of the function HeatCapacityCp
of the medium state state_default
.
This parameter can for instance be useful in a pipe model when the developer wants to
lump the pipe thermal mass to the fluid volume. By default mSenFac = 1
, hence
the mass is unchanged. For higher values of mSenFac
, the mass will be scaled proportionally.
Set the parameter use_C_flow = true
to enable an input connector for the trace substance flow rate.
This allows to directly add or subtract trace substances such as
CO2 to the volume.
See
BuildingSystems.Fluid.Sensors.Examples.PPM
for an example.
If the model is operated in steady-state and has two fluid ports connected,
then the same energy and mass balance implementation is used as in
steady-state component models, i.e., the use of actualStream
is not used for the properties at the port.
The implementation of these balance equations is done in the instances
dynBal
for the dynamic balance and steBal
for the steady-state balance. Both models use the same input variables:
Q_flow
is used to add sensible and latent heat to the fluid.
For example, Q_flow
participates in the steady-state energy balanceport_b.h_outflow = inStream(port_a.h_outflow) + Q_flow * m_flowInv;where
m_flowInv
approximates the expression 1/m_flow
.
mXi_flow
is used to add a species mass flow rate to the fluid.
For the rationale of selecting different energy and mass balances, and for the
use of prescribedHeatFlowRate
, see the documentation of
BuildingSystems.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume.
For simple models that uses this model, see BuildingSystems.Fluid.HeatExchangers.HeaterCooler_u and BuildingSystems.Fluid.Humidifiers.Humidifier_u.
initialize_p
to final
so that it does not
appear as a user-selectable parameter. This is done because
initialize_p
has been changed from a constant
to a parameter
for
Buildings, issue 1013.
QSen_flow
and
QLat_flow
.protected
block masExc
as
this revision introduces a conditional connector for the
moisture flow rate in the energy and mass balance models.
This change was done to use the same modeling concept for the
moisture input as is used for the trace substance input.
C_flow
.
final
keyword for masExc(final k=0)
.
This addresses
issue 230.
BuildingSystems.Fluid.Interfaces
.
medium
as this is already used in dynBal
.
Removing the base properties led to 30% faster computing time for a solar thermal system
that contains many fluid volumes.
medium
the parameter assignment
preferredMediumStates=true
to
preferredMediumStates= not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState)
.
Otherwise, for a steady-state model, Dymola 2012 may differentiate the model to obtain T
as a state. See ticket Dynasim #13596.
actualStream(...)
, the
inStream(...)
formulation is used.
This changed required the introduction of a new parameter m_flow_nominal
which
is used for smoothing in the steady-state balance equations of the model with two fluid ports.
use_HeatTransfer
as there is
no noticeable overhead in always having the heatPort
connector present.
mC
to avoid wrong trajectory
when concentration is around 1E-7.
See also
https://trac.modelica.org/Modelica/ticket/393.
PartialLumpedVessel
.