AixLib.Fluid.DistrictHeatingCooling.Pipes.DHCPipe

# .AixLib.Fluid.DistrictHeatingCooling.Pipes.DHCPipe

Generic pipe model for DHC applications

## Information

This pipe aims to enable the representation of all one pipe district heating and cooling pipe applications for dynamic simulation of district heating and cooling grids.

Pipe with heat loss using the wether the time delay based heat losses and transport of the fluid using a plug flow model, applicable for simulation of long pipes such as in district heating and cooling systems, or the more staty-state based approach with the static core.

This model takes into account transport delay along the pipe length idealized as a plug flow. The model also includes thermal inertia of the pipe wall. This model determines the pressure drop either through a static factor or using the sum of zeta values.

In addition this model is able to represent a very simplified soil around the pipe. With 3 capacities and the possibility to define the soil properties, this enables the user of this pipe model to account for heat losses in a more accurate way.

#### Implementation

This model is based on AixLib.Fluid.FixedResistances.BaseClasses.PlugFlowCore or on AixLib.Fluid.DistrictHeatingCooling.Pipes.BaseClassesStatic.StaticCore .

The spatialDistribution operator is used for the temperature wave propagation through the length of the pipe.

Heat losses are implemented by AixLib.Fluid.FixedResistances.BaseClasses.PlugFlowHeatLoss at each end of the pipe (see AixLib.Fluid.FixedResistances.BaseClasses.PlugFlowCore). Depending on the flow direction, the temperature difference due to heat losses is subtracted at the right fluid port.

The pressure drop is implemented using AixLib.Fluid.FixedResistances.HydraulicDiameter.

The thermal capacity of the pipe wall is implemented as a mixing volume of the fluid in the pipe, of which the thermal capacity is equal to that of the pipe wall material. In addition, this mixing volume allows the hydraulic separation of subsequent pipes. Thanks to the vectorized implementation of the (design) outlet port, splits and junctions of pipes can be handled in a numerically efficient way.

This mixing volume is not present in the PlugFlowCore model, which can be used in cases where mixing volumes at pipe junctions need to be added manually.

If Boolean use_zeta is set "true" HydraulicResistance is used.

HydraulicResistance takes into account additional pressure drops due to bends/valves/etc. Therefore the sum of zeta values has to be given prior.

If Boolean use_zeta is set "false" the pressureloss is determine through a static factor which has to given prior.

The Soil model is represented by three capacities which can be parameterized in the Soil Tab of the model.

#### Assumptions

- Heat losses are for steady-state operation.
- The axial heat diffusion in the fluid, the pipe wall and the ground are neglected.
- The boundary temperature is uniform.
- The thermal inertia of the pipe wall material is lumped on the side of the pipe that is connected to ports_b.

## Revisions

- November 12, 2020, by Michael Mans:
  First implementation

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