Modelica.Fluid.Pipes.BaseClasses.FlowModels

Information

Package Content

Name	Description
PartialStaggeredFlowModel	Base class for momentum balances in flow models
NominalLaminarFlow	NominalLaminarFlow: Linear pressure loss for nominal values
PartialGenericPipeFlow	GenericPipeFlow: Pipe flow pressure loss and gravity with replaceable WallFriction package
NominalTurbulentPipeFlow	NominalTurbulentPipeFlow: Quadratic turbulent pressure loss for nominal values
TurbulentPipeFlow	TurbulentPipeFlow: Pipe wall friction in the quadratic turbulent regime (using mu to regularize laminar region)
DetailedPipeFlow	DetailedPipeFlow: Pipe wall friction in the laminar and turbulent regime (detailed characteristic)

Modelica.Fluid.Pipes.BaseClasses.FlowModels.PartialStaggeredFlowModel

Information

This partial model defines a common interface for m=n-1 flow models between n device segments. The flow models provide a steady-state or dynamic momentum balance using an upwind discretization scheme per default. Extending models must add pressure loss terms for friction and gravity.

The fluid is specified in the interface with the thermodynamic states[n] for a given Medium model. The geometry is specified with the pathLengths[n-1] between the device segments as well as with the crossAreas[n] and the roughnesses[n] of the device segments. Moreover the fluid flow is characterized for different types of devices by the characteristic dimensions[n] and the average velocities vs[n] of fluid flow in the device segments. See Pipes.BaseClasses.CharacteristicNumbers.ReynoldsNumber for example definitions.

The parameter Re_turbulent can be specified for the least mass flow rate of the turbulent regime. It defaults to 4000, which is appropriate for pipe flow. The m_flows_turbulent[n-1] resulting from Re_turbulent can optionally be calculated together with the Reynolds numbers Res[n] of the device segments (show_Res=true).

Using the thermodynamic states[n] of the device segments, the densities rhos[n] and the dynamic viscosities mus[n] of the segments as well as the actual densities rhos_act[n-1] and the actual viscosities mus_act[n-1] of the flows are predefined in this base model. Note that no events are raised on flow reversal. This needs to be treated by an extending model, e.g., with numerical smoothing or by raising events as appropriate.

Parameters

Name	Description
m	Number of flow segments
Re_turbulent	Start of turbulent regime, depending on type of flow device [1]
Advanced
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Connectors

Name	Description
Internal Interface
replaceable package Medium	Medium in the component

Modelica.Fluid.Pipes.BaseClasses.FlowModels.NominalLaminarFlow

Information

This model defines a simple linear pressure loss assuming laminar flow for specified dp_nominal and m_flow_nominal.

Select show_Res = true to analyze the actual flow and the lengths of a pipe that would fulfill the specified nominal values for given geometry parameters crossAreas, dimensions and roughnesses.

Parameters

Name	Description
Re_turbulent	Start of turbulent regime, depending on type of flow device [1]
dp_nominal	Nominal pressure loss [Pa]
m_flow_nominal	Mass flow rate for dp_nominal [kg/s]
Advanced
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Modelica.Fluid.Pipes.BaseClasses.FlowModels.PartialGenericPipeFlow

Information

This model describes pressure losses due to wall friction in a pipe and due to gravity. Correlations of different complexity and validity can be selected via the replaceable package WallFriction (see parameter menu below). The details of the pipe wall friction model are described in the UsersGuide. Basically, different variants of the equation

   dp = λ(Re,D)*(L/D)*ρ*v*|v|/2.

By default, the correlations are computed with media data at the actual time instant. In order to reduce non-linear equation systems, the parameters use_mu_nominal and use_rho_nominal provide the option to compute the correlations with constant media values at the desired operating point. This might speed-up the simulation and/or might give a more robust simulation.

Parameters

Name	Description
Re_turbulent	Start of turbulent regime, depending on type of flow device [1]
dp_nominal	Nominal pressure loss (only for nominal models) [Pa]
m_flow_nominal	Nominal mass flow rate [kg/s]
m_flow_small	Within regularization if |m_flows| < m_flow_small (may be wider for large discontinuities in static head) [kg/s]
Advanced
from_dp	= true, use m_flow = f(dp), otherwise dp = f(m_flow)
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Wall friction
replaceable package WallFriction	Wall friction model
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Connectors

Name	Description
Wall friction
replaceable package WallFriction	Wall friction model

Modelica.Fluid.Pipes.BaseClasses.FlowModels.NominalTurbulentPipeFlow

Information

This model defines the pressure loss assuming turbulent flow for specified dp_nominal and m_flow_nominal. It takes into account the fluid density of each flow segment and obtains appropriate pathLengths_nominal values for an inverse parameterization of the TurbulentPipeFlow model. Per default the upstream and downstream densities are averaged with the setting useUpstreamScheme = false, in order to avoid discontinuous pathLengths_nominal values in the case of flow reversal.

The geometry parameters crossAreas, diameters and roughnesses do not effect simulation results of this nominal pressure loss model. As the geometry is specified however, the optionally calculated Reynolds number as well as m_flows_turbulent and dps_fg_turbulent become meaningful and can be related to m_flow_small and dp_small.

Optional Variables if show_Res

Parameters

Name	Description
pathLengths_internal[n - 1]	pathLengths used internally; to be defined by extending class [m]
Res_turbulent_internal[n - 1]	Re_turbulent used internally; to be defined by extending class [1]
dp_nominal	Nominal pressure loss (only for nominal models) [Pa]
m_flow_nominal	Nominal mass flow rate [kg/s]
m_flow_small	Within regularization if |m_flows| < m_flow_small (may be wider for large discontinuities in static head) [kg/s]
m_flow_turbulent	Turbulent flow starting from |m_flows| > m_flow_turbulent (may be wider for large discontinuities in static head) [kg/s]
Advanced
from_dp	= true, use m_flow = f(dp), otherwise dp = f(m_flow)
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Wall friction
replaceable package WallFriction	Wall friction model
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Connectors

Name	Description
Wall friction
replaceable package WallFriction	Wall friction model

Modelica.Fluid.Pipes.BaseClasses.FlowModels.TurbulentPipeFlow

Information

This model defines only the quadratic turbulent regime of wall friction: dp = k*m_flow*|m_flow|, where "k" depends on density and the roughness of the pipe and is not a function of the Reynolds number. This relationship is only valid for large Reynolds numbers. The turbulent pressure loss correlation might be useful to optimize models that are only facing turbulent flow.

Parameters

Name	Description
pathLengths_internal[n - 1]	pathLengths used internally; to be defined by extending class [m]
Res_turbulent_internal[n - 1]	Re_turbulent used internally; to be defined by extending class [1]
m_flow_nominal	Nominal mass flow rate [kg/s]
m_flow_small	Within regularization if |m_flows| < m_flow_small (may be wider for large discontinuities in static head) [kg/s]
use_Re	= true, if turbulent region is defined by Re, otherwise by m_flow_small
Advanced
from_dp	= true, use m_flow = f(dp), otherwise dp = f(m_flow)
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Wall friction
replaceable package WallFriction	Wall friction model
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Connectors

Name	Description
Wall friction
replaceable package WallFriction	Wall friction model

Modelica.Fluid.Pipes.BaseClasses.FlowModels.DetailedPipeFlow

Information

This component defines the complete regime of wall friction. The details are described in the UsersGuide. The functional relationship of the friction loss factor λ is displayed in the next figure. Function massFlowRate_dp() defines the "red curve" ("Swamee and Jain"), where as function pressureLoss_m_flow() defines the "blue curve" ("Colebrook-White"). The two functions are inverses from each other and give slightly different results in the transition region between Re = 1500 .. 4000, in order to get explicit equations without solving a non-linear equation.

Additionally to wall friction, this component properly implements static head. With respect to the latter, two cases can be distinguished. In the case shown next, the change of elevation with the path from a to b has the opposite sign of the change of density.

In the case illustrated second, the change of elevation with the path from a to b has the same sign of the change of density.

Parameters

Name	Description
pathLengths_internal[n - 1]	pathLengths used internally; to be defined by extending class [m]
Res_turbulent_internal[n - 1]	Re_turbulent used internally; to be defined by extending class [1]
m_flow_nominal	Nominal mass flow rate [kg/s]
m_flow_small	Within regularization if |m_flows| < m_flow_small (may be wider for large discontinuities in static head) [kg/s]
Advanced
from_dp	= true, use m_flow = f(dp), otherwise dp = f(m_flow)
useUpstreamScheme	= false to average upstream and downstream properties across flow segments
use_Ib_flows	= true to consider differences in flow of momentum through boundaries
Diagnostics
show_Res	= true, if Reynolds numbers are included for plotting
Wall friction
replaceable package WallFriction	Wall friction model
Internal Interface
replaceable package Medium	Medium in the component
n	Number of discrete flow volumes
Geometry
nParallel	number of identical parallel flow devices
Static head
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= true to allow flow reversal, false restricts to design direction (states[1] -> states[n+1])
momentumDynamics	Formulation of momentum balance
Initialization
m_flow_start	Start value of mass flow rates [kg/s]
p_a_start	Start value for p[1] at design inflow [Pa]
p_b_start	Start value for p[n+1] at design outflow [Pa]

Connectors

Name	Description
Wall friction
replaceable package WallFriction	Wall friction model