modelTestWaterFlow1DFV_AdaptiveAverageTemp
Extends from Modelica.Icons.Example (Icon for runnable examples).
Information
This model is designed to test the adaptive average temperature mechanism of the FlowDependentHeatTransferCoefficient model.
This model represent the fluid side of a heat exchanger with convective thermal exchange against an external source of constant and uniform temperature. The number of transfer units at the beginning of the transient with the nominal flow rate is NTU = 2.42.
By computing the heat transfer with the average volume temperatures, using three finite volumes the outlet temperature is computed at 66.17 degC, which is very close to the theoretical value 20+50*(1-exp(-NTU))=65.55.
After 10 seconds, the mass flow rate is rapidly reduced to zero. Thanks to the adaptive average temperature feature, when the flows gets below 10% of the nominal value, the heat transfer is computed as a function of the volume outlet temperatures instead of the average inlet/outlet temperature. As a consequence, all the temperatures correctly move to the value of the heat source
If the adaptiveAverageTemperature parameter of the heat transfer model is set to false, the values of the temperature along the heat exchanger approach non-physical values, some of them above the source temperature, and lead to a singularity when the flow rate is exactly zero.
Simulation Interval = [0...200] sec
Integration Algorithm = DASSL
Algorithm Tolerance = 1e-6
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | Nnodes | 4 | Number of nodes |
| Integer | Nt | 5 | Number of tubes |
| Modelica.SIunits.Length | Lhex | 2 | Total length |
| Modelica.SIunits.Diameter | Dihex | 0.02 | Internal diameter |
| Modelica.SIunits.Radius | rhex | Dihex/2 | Internal radius |
| Modelica.SIunits.Length | omegahex | Modelica.Constants.pi*Dihex | Internal perimeter |
| Modelica.SIunits.Area | Ahex | Modelica.Constants.pi*rhex^2 | Internal cross section |
| Real | Cfhex | 0.005 | Friction coefficient |
| Modelica.SIunits.MassFlowRate | whex | 0.31 | Nominal mass flow rate |
| Modelica.SIunits.Pressure | phex | 3e5 | Initial pressure |
| Modelica.SIunits.SpecificEnthalpy | hs | Medium.specificEnthalpy_pT(phex, 293.15) | Initial inlet specific enthalpy |
| Modelica.SIunits.CoefficientOfHeatTransfer | gamma | 5000 | Fixed heat transfer coefficient |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Real | cp | Medium.specificHeatCapacityCp(hex.fluidState[1]) | |
| Real | NTU | (Nt*Lhex*Dihex*3.1415*gamma)/(whex*Medium.specificHeatCapacityCp(hex.fluidState[1])) | Number of heat transfer units |
| Real | alpha | 1 - exp(-NTU) | Steady state gain of outlet temperature vs. external temperature |
| Water.ValveLin | valve | ||
| Water.SourceMassFlow | fluidSource | ||
| Water.SinkPressure | fluidSink | ||
| Modelica.Blocks.Sources.Constant | temperature | ||
| Modelica.Blocks.Sources.Constant | valveOpening | ||
| Water.SensT | T_in | ||
| Water.SensT | T_out | ||
| System | system | ||
| Thermal.TempSource1DFV | tempSource | ||
| Water.Flow1DFV | hex | ||
| Modelica.Blocks.Sources.Ramp | massFlowRate |
Contents
| Name | Description |
|---|---|
 Medium |
Revisions
- 18 Feb 2017 by Francesco Casella:
First release.