modelHEXtubes
Extends from HEXtubesDefinition.
Information
Here come the equations missing in the HEXtubesDefinition model. The model has the elements and equations common to forced convection and gas condensation.It is not clear how to calculate the average wall temperature used to introduce corrections in the calculated heat transfer coefficient. I see three possibilities:
· The average temperature of both streams at both ends.
· Split the temperature difference (between the two streams average temperatures) according to the respective heat trasfer resistance of each flow. It seems better, as it is clear that the wall temperature will be closer to the stream with less heat transfer resistance.
· Calculate a wall temperature that will produce the same heat transfer considering the LMTD between this temperature and one of the streams. This is a more complex calculation, and I have not checked that the obtained temperature is the same for both streams.
For now, split the temperature according to the resistance seems the best option.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Flow data | |||
| Modelica.Units.SI.Distance | iElevDiff (from HEXtubesDefinition) | 0 | inner pipe differential elevation: out elev. - in elev. |
| Modelica.Units.SI.Distance | oElevDiff (from HEXtubesDefinition) | 0 | outer flow differential elevation: out elev. - in elev. |
| Real | iNumVelocityHeads (from HEXtubesDefinition) | 2*iNumSerial | inner flow number of velocity heads to consider in pressure loss |
| Integer | iNumUturns (from HEXtubesDefinition) | iNumSerial - 1 | number of U turns in each exchanger |
| Inner pipe data | |||
| Boolean | iIsCircular (from HEXtubesDefinition) | true | if false, the inner pipe is not circular |
| Modelica.Units.SI.Distance | iDi (from HEXtubesDefinition) | 0.0 | inner pipe internal diameter, if circular |
| Modelica.Units.SI.Area | iSection (from HEXtubesDefinition) | 0 | inner pipe flow section, if not circular |
| Modelica.Units.SI.Distance | iPerimeter (from HEXtubesDefinition) | 0 | inner pipe perimeter, if not circular |
| Modelica.Units.SI.Distance | iThickness (from HEXtubesDefinition) | 1e-3 | inner pipe thickness |
| Modelica.Units.SI.Distance | iRoughness (from HEXtubesDefinition) | 1.5e-005 | inner pipe roughness. SS:1.5e-5, Steel new:4.6e-5, Steel old:2.0e-4, Concrete:1.5e-3 |
| Modelica.Units.SI.Density | iRhoWall (from HEXtubesDefinition) | 8000 | inner pipe wall density |
| Modelica.Units.SI.ThermalConductivity | iKwall (from HEXtubesDefinition) | 16 | inner pipe wall thermal conductivity. Al=210, Cu=390, Steel=50, SS=17 |
| Modelica.Units.SI.Distance | iLTube (from HEXtubesDefinition) | 0 | stright length of each individual inner pipe |
| Integer | iNumPipes (from HEXtubesDefinition) | 1 | number of inner pipes that form a common pass |
| Integer | iNumParallel (from HEXtubesDefinition) | 1 | number of parallel inner passes. Normally it is the number of exchangers |
| Integer | iNumSerial (from HEXtubesDefinition) | 2 | number of serial inner passes (Each hairpin has two serial passes) |
| Heat transfer | |||
| Modelica.Units.SI.ThermalInsulance | iFoulingF (from HEXtubesDefinition) | 0.0002 | inner pipe side fouling factor.Typical: 0.00018 for thermal oil, or treated cooling water |
| Modelica.Units.SI.ThermalInsulance | oFoulingF (from HEXtubesDefinition) | 0.0002 | outer flow fouling factor.Typical: 0.00018 for thermal oil, or treated cooling water |
| Boolean | useHTcorr (from HEXtubesDefinition) | true | if true, the heat transfer correction factor is used |
| Boolean | counterCurrent (from HEXtubesDefinition) | true | true if flow is counter-current, otherwise it will be considered co-current |
| Fins data | |||
| Boolean | useFins (from HEXtubesDefinition) | false | if true, fins are taken into account in calculations |
| Modelica.Units.SI.Density | finRho (from HEXtubesDefinition) | 0 | fin density. Al=2700, Cu=8930, Steel=7830, SS=8000 |
| Modelica.Units.SI.ThermalConductivity | finK (from HEXtubesDefinition) | 0 | fin thermal conductivity. Al=210, Cu=390, Steel=50, SS=17 |
| Modelica.Units.SI.Distance | finThickness (from HEXtubesDefinition) | 0.0 | fin thickness |
Connectors
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | ItotalNumPipes (from HEXtubesDefinition) | total number of individual inner pipes | |
| Modelica.Units.SI.Distance | IiPerimeter (from HEXtubesDefinition) | inner pipe internal wetted perimeter | |
| Modelica.Units.SI.Area | IiSection (from HEXtubesDefinition) | inner pipe internal flow section | |
| Modelica.Units.SI.Distance | IDh (from HEXtubesDefinition) | internal pipe hydraulic diameter | |
| Modelica.Units.SI.Area | IiArea (from HEXtubesDefinition) | total inner pipes internal heat transfer area | |
| Modelica.Units.SI.Distance | IoPerimeter (from HEXtubesDefinition) | inner pipe external perimeter | |
| Modelica.Units.SI.Area | IoSection (from HEXtubesDefinition) | inner pipe external section | |
| Modelica.Units.SI.Area | IoArea (from HEXtubesDefinition) | total inner pipes external heat transfer area | |
| MediumI.ThermodynamicState | IStateIn (from HEXtubesDefinition) | inner flow inlet state | |
| MediumI.ThermodynamicState | IStateOut (from HEXtubesDefinition) | inner flow outlet state | |
| Modelica.Units.SI.Temperature | ITin (from HEXtubesDefinition) | inner flow inlet temperature | |
| Modelica.Units.SI.Temperature | ITout (from HEXtubesDefinition) | iiner flow outlet temperature | |
| Modelica.Units.SI.Temperature | IT (from HEXtubesDefinition) | inner pipe average temperature | |
| MediumI.ThermodynamicState | IStateWall (from HEXtubesDefinition) | inner pipe wall state for correction factors calculation | |
| Modelica.Units.SI.Temperature | ITwall (from HEXtubesDefinition) | inner pipe wall temperature | |
| Modelica.Units.SI.DynamicViscosity | IMuWall (from HEXtubesDefinition) | inner pipe wall dynamic viscosity | |
| Real | IPlossCorr (from HEXtubesDefinition) | internal pipe pressure loss correction factor | |
| Modelica.Units.SI.AbsolutePressure | IPloss (from HEXtubesDefinition) | internal pipe pressure loss by friction, without taking into account the nozzles | |
| Real | IHTcorr (from HEXtubesDefinition) | internal pipe heat transfer correction factor | |
| Modelica.Units.SI.NusseltNumber | INu (from HEXtubesDefinition) | inner pipe Nusselt number | |
| Modelica.Units.SI.CoefficientOfHeatTransfer | IH (from HEXtubesDefinition) | inner pipe average heat transfer coefficient | |
| MediumO.ThermodynamicState | OStateIn (from HEXtubesDefinition) | outer flow inlet state | |
| MediumO.ThermodynamicState | OStateOut (from HEXtubesDefinition) | outer flow outlet state | |
| Modelica.Units.SI.Temperature | OTin (from HEXtubesDefinition) | outer flow inlet temperature | |
| Modelica.Units.SI.Temperature | OTout (from HEXtubesDefinition) | outer flow outlet temperature | |
| Modelica.Units.SI.Temperature | OT (from HEXtubesDefinition) | outer flow average temperature | |
| Modelica.Units.SI.Length | IEquivLength (from HEXtubesDefinition) | internal pipe equivalent length for pressure drop | |
| Real | OPlossCorr (from HEXtubesDefinition) | outer flow pressure loss correction factor | |
| Modelica.Units.SI.AbsolutePressure | OPloss (from HEXtubesDefinition) | outer flow pressure loss by friction | |
| Modelica.Units.SI.Area | OiArea (from HEXtubesDefinition) | total outer flow internal area for heat transfer | |
| Fraction | OiEfficiency (from HEXtubesDefinition) | outer flow internal area efficiency | |
| Modelica.Units.SI.NusseltNumber | ONu (from HEXtubesDefinition) | outer flow nusselt number for internal heat transfer | |
| Modelica.Units.SI.CoefficientOfHeatTransfer | OHi (from HEXtubesDefinition) | outer flow average heat transfer coefficient to inner pipe | |
| Modelica.Units.SI.ThermalResistance | TRii (from HEXtubesDefinition) | total resitance for the transfer between inner fluid and inner wall | |
| Modelica.Units.SI.ThermalResistance | TRio (from HEXtubesDefinition) | total resitance for the transfer between outer fluid and inner wall | |
| Modelica.Units.SI.ThermalResistance | TRi (from HEXtubesDefinition) | total resitance for the transfer between inner and outer fluids | |
| Modelica.Units.SI.CoefficientOfHeatTransfer | Ui (from HEXtubesDefinition) | global heat transfer coefficient referenced to total inner flow area | |
| Modelica.Units.SI.TemperatureDifference | ILMTD (from HEXtubesDefinition) | LMTD between inner and outer fluids | |
| Fraction | ILMTDcorr (from HEXtubesDefinition) | internal LMTD correction factor | |
| Real | Rntu (from HEXtubesDefinition) | ||
| Real | NTU (from HEXtubesDefinition) | ||
| Modelica.Units.SI.Power | IW (from HEXtubesDefinition) | heat exchanged between inner and outer fluids. Positive if heat enters the inner fluid | |
| Modelica.Units.SI.Area | IiArea1 (from HEXtubesDefinition) | total inner pipes internal heat transfer area used in first stage transfer | |
| Modelica.Units.SI.ThermalResistance | TRi1 (from HEXtubesDefinition) | total resitance for the transfer between inner and outer fluids in the first stage |