modelFluidStorage

Model of a thermal fluid storage

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Information

This is a model for a thermal fluid storage

Typical use and important parameters

nEle number of layers, enumeration starts at bottom (bottom layer is no. 1)

Options

The thermal fluid storage model has several fluidports. 2 at the bottom and 2 at the top. It is possible to have different configurations:

Switch on fluidports connected to each of the intermediate fluid layers.
2 optional and freely placeable internal heat exchangers (identified as "1" and "2").
Specify the layer at which the HX are connected.
Set PerfectlyIsolated to true to switch off the heat losses to the environment, i.e. the thermal fluid storage is perfectly isolated.
Note that if PerfectlyIsolated is set to false and no boundary condition is connected to the heatPort, the external heat flow rate will also be 0. However, because all layers are connected to the external heat port, a non-physical internal heat flow transfer between volumes takes place.

Notes

The thermal fluid storage uses a model to increase heat exchange betweeen layers accounting for buoyancy effect, see BuoyancyModels

Assumption and limitations

Up to date the model does not take into account the mixing caused by in and outflows and there is no model for a stratified inlet.

Parameters

Type	Name	Default	Description
Integer	nEle	3	Number of fluid layers
Geometry
Modelica.Units.SI.Length	height	1.0	Height of the storage
Modelica.Units.SI.Volume	V	1.0	Fluid volume of the storage
Modelica.Units.SI.Thickness	thickness_ins	0.005	Insulation thickness
Modelica.Units.SI.Thickness	thickness_wall	1	Wall thickness
Thermal properties
Modelica.Units.SI.CoefficientOfHeatTransfer	alpha_out	800.0	Coefficient of heat transfer outside of the storage
Modelica.Units.SI.CoefficientOfHeatTransfer	alpha_in	3000.0	Coefficient of heat transfer inside the storage
Modelica.Units.SI.ThermalConductivity	lambda_ins	0.05	Thermal heat conductivity of insulation material
Modelica.Units.SI.ThermalConductance	UA_wall	(Modelica.Constants.piheight)/(1.0/(alpha_outdiameter_ext) + log(diameter_ext/diameter_int)/(2lambda_ins) + 1/(alpha_indiameter_int))	Thermal conductance walls
Modelica.Units.SI.ThermalConductance	UA_top	1.0/(thickness_ins/(lambda_insASec) + 1.0/(alpha_inASec) + 1.0/(alpha_out*ASec))	Thermal conductance top
Modelica.Units.SI.ThermalConductance	UA_bot	UA_top	Thermal conductance bottom
Storage configuration
Boolean	HX_2	true	Set to true to add heat exchanger at the top layer
Boolean	HX_1	true	Set to true to add heat exchanger at the bottom layer
Boolean	PerfectlyIsolated	false	Set to true to avoid heat losses
Boolean	AdditionalFluidPorts	false	Set to true to add aditional fluid ports connected to intermediate layers
HX definition
Modelica.Units.SI.ThermalConductance	UA_HX_2	100.0	Constant thermal conductance of material
Integer	Ele_HX_2	2	Layer at which HX_2 is connected
Modelica.Units.SI.ThermalConductance	UA_HX_1	100.0	Constant thermal conductance of material
Integer	Ele_HX_1	1	Layer at which HX_1 is connected
Initialization
Modelica.Media.Interfaces.Types.Temperature	T_start	Medium.T_default	Initial storage temperature

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPorts_a[nEle - 2]	port_a	Ports to the intermediate layers
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	heatPort	Thermal boundary condition to environment
Modelica.Fluid.Interfaces.FluidPort_a	port_HX_1_a	Port a to the HX at the bottom of the storage
Modelica.Fluid.Interfaces.FluidPort_b	port_HX_1_b	Port b to the HX at the bottom of the storage
Modelica.Fluid.Interfaces.FluidPort_a	port_HX_2_a	Port a to the HX at the top of the storage
Modelica.Fluid.Interfaces.FluidPort_b	port_HX_2_b	Port b to the HX at the top of the storage
Modelica.Fluid.Interfaces.FluidPort_b	port_b1	Port to the top of the storage n=nEle
Modelica.Fluid.Interfaces.FluidPort_b	port_b2	Port to the bottom of the storage n=1
Modelica.Fluid.Interfaces.FluidPort_a	port_a1	Port to the bottom of the storage n=1
Modelica.Fluid.Interfaces.FluidPort_a	port_a2	Port to the top of the storage n=nEle
Modelica.Blocks.Interfaces.RealOutput[nEle]	T	Starting at bottom

Components

Type	Name	Description
BuildingSystems.Fluid.MixingVolumes.MixingVolume[nEle - 2]	vol
Modelica.Thermal.HeatTransfer.Components.ThermalConductor	HeatThroughTop
Modelica.Thermal.HeatTransfer.Components.ThermalConductor[nEle]	HeatThroughWalls
Modelica.Thermal.HeatTransfer.Components.ThermalConductor	HeatThroughBottom
Modelica.Thermal.HeatTransfer.Components.ThermalConductor[nEle - 1]	HeatBetweenLayers	Normal heat transfer due to conductivity
BuildingSystems.Technologies.ThermalStorages.BaseClasses.BuoyancyModels.Buoyancy1	HeatBuoyancy
Modelica.Thermal.HeatTransfer.Components.ThermalCollector	thermalCollector
BuildingSystems.Fluid.MixingVolumes.MixingVolume	vol_HX_1
Modelica.Thermal.HeatTransfer.Components.ThermalConductor	ThermalConductanceHX_1
BuildingSystems.Fluid.MixingVolumes.MixingVolume	vol_HX_2
Modelica.Thermal.HeatTransfer.Components.ThermalConductor	ThermalConductanceHX_2
BuildingSystems.Fluid.MixingVolumes.MixingVolume	vol_bot
Fluid.MixingVolumes.MixingVolume	vol_top
Fluid.FixedResistances.LosslessPipe[nEle - 2]	pip

Name	Description
Medium	Medium of the storage content
Medium_HX_1	Medium of the internal heat exchanger 1
Medium_HX_2	Medium of the internal heat exchanger 2

Revisions

August 18, 2018, by Christoph Nytsch-Geusen:
Adapted to possible different media for the storage content and the two internal heat exchangers.
May 23, 2015 by Carles Ribas Tugores:
First implementation.