modelGenericPipe

Information

!!! Obsolete, sort of. This model is same as GenericPipe_MultiTransferSurface with the exception that it has one surface for heat transfer. To remove duplciations, etc. this model will be removed in favor of the other

Base model for distributed flow models. The total volume is split into nV segments along the flow path. The default value is nV=2.

The following boundary flow and source terms are part of the mass, energy, species, and trace balances and must be specified in an extending class:

• Qb_flows[nV], heat flow term, e.g., conductive heat flows across segment boundaries
• Wb_flows[nV], work term
• Hb_flows[nV], enthalpy flow
• mb_flows[nV], mass flow
• mbXi_flows[nV], substance mass flow
• mbC_flows[nV], trace substance mass flow

Wall temperature is passed to the flow model as it is needed for some cases. When use_HeatTransfer = false, the wall temperature is assumed to be equal to the medium temperature.

It provides the complete balance equations for one-dimensional fluid flow as formulated in UsersGuide.ComponentDefinition.BalanceEquations.

This generic model offers a large number of combinations of possible parameter settings. In order to reduce model complexity, consider defining and/or using a tailored model for the application at hand, such as HeatExchanger.

In reality this model is not a partial model BUT it is listed as such so different applications of this model will be generated with proper applications of the parameters, icons, etc.

Mass and Energy balances

The mass and energy balances are inherited from Interfaces.PartialDistributedVolume. One total mass and one energy balance is formed across each segment according to the finite volume approach. Substance mass balances are added if the medium contains more than one component.

An extending model needs to define the geometry and the difference in heights between the flow segments (static head).

Momentum balance

The momentum balance is determined by the FlowModel component, which can be replaced with any model extended from BaseClasses.FlowModels.PartialStaggeredFlowModel. The default setting is DetailedPipeFlow.

This considers

• pressure drop due to friction and other dissipative losses, and
• gravity effects for non-horizontal devices.
• variation of flow velocity along the flow path, which occur due to changes in the cross sectional area or the fluid density, provided that flowModel.use_Ib_flows is true.

Model Structure

The momentum balances are formulated across the segment boundaries along the flow path according to the staggered grid approach. The configurable modelStructure determines the formulation of the boundary conditions at port_a and port_b. The options include (default: av_vb):

• av_vb: Symmetric setting with nV-1 momentum balances between nV flow segments. The ports port_a and port_b expose the first and the last thermodynamic state, respectively. Connecting two or more flow devices therefore may result in high-index DAEs for the pressures of connected flow segments.
• a_v_b: Alternative symmetric setting with nV+1 momentum balances across nV flow segments. Half momentum balances are placed between port_a and the first flow segment as well as between the last flow segment and port_b. Connecting two or more flow devices therefore results in algebraic pressures at the ports. The specification of good start values for the port pressures is essential for the solution of large nonlinear equation systems.
• av_b: Asymmetric setting with nV momentum balances, one between nth volume and port_b, potential pressure state at port_a
• a_vb: Asymmetric setting with nV momentum balance, one between first volume and port_a, potential pressure state at port_b

When connecting two components, e.g., two pipes, the momentum balance across the connection point reduces to

pipe1.port_b.p = pipe2.port_a.p

This is only true if the flow velocity remains the same on each side of the connection. Consider using a fitting for any significant change in diameter or fluid density, if the resulting effects, such as change in kinetic energy, cannot be neglected. This also allows for taking into account friction losses with respect to the actual geometry of the connection point.

The model treats the partial differential equations with the finite volume method and a staggered grid scheme for momentum balances. The default value is nV=2. This results in two lumped mass and energy balances and one lumped momentum balance across the model.

Note that this generally leads to high-index DAEs for pressure states if this model are directly connected to each other, or generally to models with storage exposing a thermodynamic state through the port. This may not be valid if the model is connected to a model with non-differentiable pressure, like a Sources.Boundary_pT with prescribed jumping pressure. The modelStructure can be configured as appropriate in such situations, in order to place a momentum balance between a pressure state of the pipe and a non-differentiable boundary condition.

The default modelStructure is av_vb (see Advanced tab). The simplest possible alternative symmetric configuration, avoiding potential high-index DAEs at the cost of the potential introduction of nonlinear equation systems, is obtained with the setting nV=1, modelStructure=a_v_b. Depending on the configured model structure, the first and the last segment, or the flow path length of the first and the last momentum balance, are of half size.

Heat Transfer Structure

The HeatTransfer component specifies the source term Qb_flows of the energy balance. The default component uses a constant coefficient for the heat transfer between the bulk flow and the segment boundaries exposed through the heatPorts. The HeatTransfer model is replaceable and can be exchanged with any model extended from TRANSFORM.Fluid.Pipes.BaseClasses.HeatTransfer.PartialFlowHeatTransfer.

The intended use is for complex networks of pipes and other flow devices, like valves. See, e.g.,

• Examples.BranchingDynamicPipes, or
• Examples.IncompressibleFluidNetwork.

Parameters

Connectors

Components

Contents

Name	Description
Geometry
FlowModel
HeatTransfer
InternalHeatGen
TraceMassTransfer
InternalTraceGen

Revisions

• 5 Dec 2008 by Michael Wetter:
  Modified mass balance for trace substances. With the new formulation, the trace substances masses mC are stored in the same way as the species mXi.
• Dec 2008 by Rüdiger Franke:
  Derived model from original DistributedPipe models
  • moved mass and energy balances to PartialDistributedVolume
  • introduced replaceable pressure loss models
  • combined all model structures and lumped pressure into one model
  • new ModelStructure av_vb, replacing former avb
• 04 Mar 2006 by Katrin Prölß:
  Model added to the Fluid library