modelAirDuct
model of the air duct
Extends from Interfaces.PartialTwoPortInterface (Partial model with two ports and declaration of quantities that are used by many models), AixLib.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).
Information
This model provides the definition of the air duct in a parallel membrane enthalpy exchanger. It is based on the PartialTwoPortInterface model.
This model defines the geometry of the air duct, as well as the convective heat and mass transfer processes in the air duct. The model can be discretized in flow direction using finite volumes.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | nNodes | 2 | number of discrete volumes (over length) in the air duct |
| Integer | nParallel | 2 | number of parallel air ducts |
| Integer | nWidth | 1 | number of segments in width direction |
| 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 |
| Boolean | homotopyInitialization | true | = true, use homotopy method |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialTwoPortInterface) | false | = true, if actual temperature at port is computed |
| 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 |
| Geometry | |||
| Modelica.Units.SI.Length | lengthDuct | length in flow direction of duct | |
| Modelica.Units.SI.Length | widthDuct | width of duct | |
| Modelica.Units.SI.Length | heightDuct | height of duct | |
| Boolean | couFloArr | true | true: counter-flow arrangement; false: quasi-counter-flow arrangement |
| Heat and Mass transfer | |||
| Boolean | uniWalTem | true if uniform wall temperature, else uniform wall heat flux | |
| Boolean | local | true if local Nusselt/Sherwood number, else average | |
| Boolean | recDuct | true if rectangular duct is used for Nusselt/Sherwood number calculation, else flat gap is used. | |
| Dynamics › Equations | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamics.DynamicFreeInitial | Type of energy balance: dynamic (3 initialization options) or steady state |
| Modelica.Fluid.Types.Dynamics | massDynamics | energyDynamics | Type of mass balance: dynamic (3 initialization options) or steady state |
| Initialization | |||
| Medium.AbsolutePressure | p_a_start | Medium.p_default | Start value of pressure at port a |
| Medium.AbsolutePressure | p_b_start | p_a_start | Start value of pressure at port b |
| Medium.AbsolutePressure | p_start | Medium.p_default | Start value of pressure |
| Medium.Temperature | T_start | Medium.T_default | Start value of temperature |
| Medium.MassFraction[Medium.nX] | X_start | Medium.X_default | Start value of mass fractions m_i/m |
| Medium.ExtraProperty[Medium.nC] | C_start | 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 | coeCroCouSens | coefficient for heat transfer reduction due to cross-flow portion | |
| Modelica.Blocks.Interfaces.RealInput | coeCroCouLats | coefficient for mass transfer reduction due to cross-flow portion | |
| Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a[nNodes] | heatPorts | ||
| Utilities.MassTransfer.MassPort[nNodes] | massPorts |
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 |
| Modelica.Units.SI.Length | lengths | {i*(lengthDuct/((nNodes + 1)*nNodes/2)) for i in 1:nNodes} | length of segements in flow direction |
| Modelica.Units.SI.Area | croSecs | fill(heightDuct*widthDuct, nNodes) | cross section of duct segments |
| Modelica.Units.SI.Velocity | vs | {port_a.m_flow/Medium.density(states[i])/croSecs[i] for i in 1:nNodes}/nParallel | velocity in air duct segments |
| Modelica.Units.SI.PartialPressure | ps | {vol[i].p*vol[i].X_w*(Ms[i]/M_steam) for i in 1:nNodes} | |
| Modelica.Units.SI.MolarMass | Ms | {1/(vol[i].X_w/M_steam + (1 - vol[i].X_w)/M_air) for i in 1:nNodes} | |
| Medium.ThermodynamicState | states | {Medium.setState_pTX(vol[i].p, vol[i].T, vol[i].Xi) for i in 1:nNodes} | |
| Modelica.Units.SI.SpecificEnthalpy | dhAds | adsorptionEnthalpy.dhAds | adsorption enthalpy |
| HeatTransfer | heatTransfer | ||
| MassTransfer | massTransfer | ||
| AixLib.Fluid.MixingVolumes.MixingVolumeMoistAir[nNodes] | vol | Volume for fluid stream | |
| AixLib.Fluid.FixedResistances.PressureDrop | preDro | Flow resistance | |
| Modelica.Thermal.HeatTransfer.Sources.PrescribedHeatFlow[nNodes] | prescribedHeatFlow | ||
| Modelica.Blocks.Sources.RealExpression[nNodes] | Q_flow | ||
| Modelica.Blocks.Sources.RealExpression[nNodes] | mWat_flow |
Contents
| Name | Description |
|---|---|
 HeatTransfer | |
 MassTransfer |
Revisions
- November 23, 2018, by Martin Kremer:
Changing adsorption enthalpy dhAds from parameter to input for usage of adsorption enthalpy model. - August 21, 2018, by Martin Kremer:
First Implementation