modelHeatingRod
Extends from AixLib.Fluid.Interfaces.TwoPortHeatMassExchanger (Partial model transporting one fluid stream with storing mass or energy).
Information
Model for a heating rod.
This model adds heat in the amount of Q_flow = u Q_flow_nominal to the medium. The input signal u and the nominal heat flow rate Q_flow_nominal can be positive or negative. A positive value of Q_flow means heating, and negative means cooling.
The outlet conditions at port_a are not affected by this model, other than for a possible pressure difference due to flow friction.
Optionally, this model can have a flow resistance. Set dp_nominal = 0 to disable the flow friction calculation.
For a model that uses as an input the fluid temperature leaving at port_b, use AixLib.Fluid.HeatExchangers.PrescribedOutlet
As output, the electrical energy required to supply Q_flow is calculated using the efficiency which is a parameter of the model.
Lastly, the number of times the heating rod switches on may be used as an output.
Limitations
This model does not affect the humidity of the air. Therefore, if used to cool air below the dew point temperature, the water mass fraction will not change.
Validation
The model has been validated against the analytical solution in the example AixLib.Fluid.HeatExchangers.Validation.HeaterCooler_u.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | homotopyInitialization (from TwoPortHeatMassExchanger) | true | = true, use homotopy method |
| Modelica.Units.SI.HeatFlowRate | Q_flow_nominal | Heat flow rate at u=1, positive for heating | |
| Modelica.Units.SI.Volume | V | m_flow_nominal*tau/rho_default | Volume of heat exchanger |
| Real | eta | Efficiency of the heating rod | |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialTwoPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate | m_flow_nominal (from PartialTwoPortInterface) | Nominal mass flow rate | |
| Modelica.Units.SI.PressureDifference | dp_nominal (from TwoPortFlowResistanceParameters) | Pressure difference | |
| Advanced | |||
| Modelica.Units.SI.MassFlowRate | m_flow_small (from PartialTwoPortInterface) | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialTwoPortInterface) | false | = true, if actual temperature at port is computed |
| Boolean | use_countNumSwi | true | Turn the counting of the number of heating rod uses on or off. |
| Flow resistance | |||
| Boolean | computeFlowResistance (from TwoPortFlowResistanceParameters) | true | =true, compute flow resistance. Set to false to assume no friction |
| Boolean | from_dp (from TwoPortFlowResistanceParameters) | false | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Boolean | linearizeFlowResistance (from TwoPortFlowResistanceParameters) | false | = true, use linear relation between m_flow and dp for any flow rate |
| Real | deltaM (from TwoPortFlowResistanceParameters) | 0.1 | Fraction of nominal flow rate where flow transitions to laminar |
| Dynamics › Nominal condition | |||
| Modelica.Units.SI.Time | tau (from TwoPortHeatMassExchanger) | 30 | Time constant at nominal flow (if energyDynamics <> SteadyState) |
| Dynamics › Conservation equations | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics (from TwoPortHeatMassExchanger) | Modelica.Fluid.Types.Dynamics.DynamicFreeInitial | Type of energy balance: dynamic (3 initialization options) or steady state |
| Initialization | |||
| Medium.AbsolutePressure | p_start (from TwoPortHeatMassExchanger) | Medium.p_default | Start value of pressure |
| Medium.Temperature | T_start (from TwoPortHeatMassExchanger) | Medium.T_default | Start value of temperature |
| Medium.MassFraction[Medium.nX] | X_start (from TwoPortHeatMassExchanger) | Medium.X_default | Start value of mass fractions m_i/m |
| Medium.ExtraProperty[Medium.nC] | C_start (from TwoPortHeatMassExchanger) | fill(0, Medium.nC) | Start value of trace substances |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPort_a | port_a (from PartialTwoPort) | Fluid connector a (positive design flow direction is from port_a to port_b) | |
| Modelica.Fluid.Interfaces.FluidPort_b | port_b (from PartialTwoPort) | Fluid connector b (positive design flow direction is from port_a to port_b) | |
| Modelica.Blocks.Interfaces.RealInput | u | Control input | |
| Modelica.Blocks.Interfaces.RealOutput | Pel | Electrical power used to provide current heat flow | |
| Modelica.Blocks.Interfaces.IntegerOutput | numSwi | Number of on switches |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.MassFlowRate | m_flow (from PartialTwoPortInterface) | port_a.m_flow | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) |
| Modelica.Units.SI.PressureDifference | dp (from PartialTwoPortInterface) | port_a.p - port_b.p | Pressure difference between port_a and port_b |
| Medium.ThermodynamicState | sta_a (from PartialTwoPortInterface) | if allowFlowReversal then Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) else Medium.setState_phX(port_a.p, noEvent(inStream(port_a.h_outflow)), noEvent(inStream(port_a.Xi_outflow))) | Medium properties in port_a |
| Medium.ThermodynamicState | sta_b (from PartialTwoPortInterface) | if allowFlowReversal then Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) else Medium.setState_phX(port_b.p, noEvent(port_b.h_outflow), noEvent(port_b.Xi_outflow)) | Medium properties in port_b |
| AixLib.Fluid.MixingVolumes.MixingVolume | vol (from TwoPortHeatMassExchanger) | ||
| AixLib.Fluid.FixedResistances.PressureDrop | preDro (from TwoPortHeatMassExchanger) | Flow resistance | |
| Modelica.Blocks.Math.Gain | gai_eta | Divide efficiency | |
| Modelica.Blocks.MathInteger.TriggeredAdd | triggeredAdd | To count on-off cycles | |
| Modelica.Blocks.Sources.IntegerConstant | integerConstant | ||
| Modelica.Blocks.Logical.GreaterThreshold | greaterThreshold |
Revisions
- May 5, 2021, by Fabian Wuellhorst:
Added model.
This is for AixLib, #1092.