Package Modelica.Fluid.Machines.BaseClassesBase classes used in the Machines package (only of interest to build new component models)
Package Modelica.Fluid.Machines.BaseClasses
This icon shall be used for a package/library that contains base models and classes, respectively.
Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).
| Name | Description |
|---|---|
PartialPump | Base model for centrifugal pumps |
PumpCharacteristics … | Functions for pump characteristics |
PumpMonitoring … | Monitoring of pump operation |
Partial Model Modelica.Fluid.Machines.BaseClasses.PartialPump
This is the base model for pumps.
The model describes a centrifugal pump, or a group of nParallel identical pumps. The pump model is based on the theory of kinematic similarity: the pump characteristics are given for nominal operating conditions (rotational speed and fluid density), and then adapted to actual operating condition, according to the similarity equations.
Pump characteristics
The nominal hydraulic characteristic (head vs. volume flow rate) is given by the replaceable function flowCharacteristic.
The pump energy balance can be specified in two alternative ways:
use_powerCharacteristic = false (default option): the replaceable function efficiencyCharacteristic (efficiency vs. volume flow rate in nominal conditions) is used to determine the efficiency, and then the power consumption.
The default is a constant efficiency of 0.8.use_powerCharacteristic = true: the replaceable function powerCharacteristic (power consumption vs. volume flow rate in nominal conditions) is used to determine the power consumption, and then the efficiency.
Use powerCharacteristic to specify a non-zero power consumption for zero flow rate.
Several functions are provided in the package PumpCharacteristics to specify the characteristics as a function of some operating points at nominal conditions.
Depending on the value of the checkValve parameter, the model either supports reverse flow conditions, or includes a built-in check valve to avoid flow reversal.
It is possible to take into account the mass and energy storage of the fluid inside the pump by specifying its volume V, and by selecting appropriate dynamic mass and energy balance assumptions (see below);
this is recommended to avoid singularities in the computation of the outlet enthalpy in case of zero flow rate.
If zero flow rate conditions are always avoided, this dynamic effect can be neglected by leaving the default value V = 0, thus avoiding fast state variables in the model.
Dynamics options
Steady-state mass and energy balances are assumed per default, neglecting the holdup of fluid in the pump; this configuration works well if the flow rate is always positive.
Dynamic mass and energy balance can be used by setting the corresponding dynamic parameters. This is recommended to avoid singularities at zero or reversing mass flow rate. If the initial conditions imply non-zero mass flow rate, it is possible to use the SteadyStateInitial condition, otherwise it is recommended to use FixedInitial in order to avoid undetermined initial conditions.
Heat transfer
The Boolean parameter use_HeatTransfer can be set to true if heat exchanged with the environment
should be taken into account or to model a housing. This might be desirable if a pump with realistic
powerCharacteristic for zero flow operates while a valve prevents fluid flow.
Diagnostics of Cavitation
The replaceable Monitoring submodel can be configured to PumpMonitoringNPSH, in order to compute the Net Positive Suction Head available and check for cavitation, provided a two-phase medium model is used (see Advanced tab).
Extends from Modelica.Fluid.Interfaces.PartialTwoPort (Partial component with two ports) and Modelica.Fluid.Interfaces.PartialLumpedVolume (Lumped volume with mass and energy balance).
| Type | Name | Default | Description |
|---|---|---|---|
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
AbsolutePressure | p_a_start | system.p_start | Guess value for inlet pressure |
AbsolutePressure | p_b_start | p_a_start | Guess value for outlet pressure |
MassFlowRate | m_flow_start | system.m_flow_start | Guess value of m_flow = port_a.m_flow |
final VolumeFlowRate | V_flow_single_init | m_flow_start / rho_nominal / nParallel | Used for simplified initialization model |
final Position | delta_head_init | flowCharacteristic(V_flow_single_init * (1.1)) - flowCharacteristic(V_flow_single_init) | Delta head for a 10% increase of flow at the initialization point |
Integer | nParallel | 1 | Number of pumps in parallel |
AngularVelocity_rpm | N_nominal | Nominal rotational speed for flow characteristic | |
Density | rho_nominal | Medium.density_pTX(Medium.p_default, Medium.T_default, Medium.X_default) | Nominal fluid density for characteristic |
Boolean | use_powerCharacteristic | false | Use powerCharacteristic (vs. efficiencyCharacteristic) |
Boolean | checkValve | false | = true to prevent reverse flow |
Volume | V | 0 | Volume inside the pump |
Dynamics | energyDynamics | Types.Dynamics.SteadyState | Formulation of energy balance |
Dynamics | massDynamics | Types.Dynamics.SteadyState | Formulation of mass balance |
final Dynamics | substanceDynamics | massDynamics | Formulation of substance balance |
final Dynamics | traceDynamics | massDynamics | Formulation of trace substance balance |
final AbsolutePressure | p_start | p_b_start | Start value of pressure |
Boolean | use_T_start | true | = true, use T_start, otherwise h_start |
Temperature | T_start | if use_T_start then system.T_start else Medium.temperature_phX(p_start, h_start, X_start) | Start value of temperature |
SpecificEnthalpy | h_start | if use_T_start then Medium.specificEnthalpy_pTX(p_start, T_start, X_start) else Medium.h_default | Start value of specific enthalpy |
MassFraction | X_start[Medium.nX] | Medium.X_default | Start value of mass fractions m_i/m |
ExtraProperty | C_start[Medium.nC] | Medium.C_default | Start value of trace substances |
Boolean | use_HeatTransfer | false | = true to use a HeatTransfer model, e.g., for a housing |
final Acceleration | g | system.g | |
final Boolean | show_NPSHa | false | obsolete -- remove modifier and specify Monitoring for NPSH instead |
| Type | Name | Description |
|---|---|---|
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
HeatPort_a | heatPort |