heat-transfer-from-heating-coil.pdf

Chapter 16: Heat Transfer from a Heating Coil

This tutorial includes:16.1.Tutorial Features16.2. Overview of the Problem to Solve16.3. Before You Begin16.4. Setting Up the Project16.5. Simulating the Copper Coil with a Calcium Carbonate Deposit16.6. Exporting the Results to ANSYS16.7. Simulating the Thin-Walled Copper Coil with Dry Steam

16.1. Tutorial Features

In this tutorial you will learn about:

• Creating and using a solid domain as a heating coil in CFX-Pre.

• Creating a domain interface.

• Modeling conjugate heat transfer in CFX-Pre.

• Using electricity to power a heat source.

• Creating and using a thin-walled fluid domain in CFX-Pre.

• Modeling varying physics between multiple fluid domains.

• Plotting temperature on a cylindrical locator in CFD-Post.

• Lighting in CFD-Post.

• Exporting thermal and mechanical data to be used with ANSYS Multi-field solver.

DetailsFeatureComponent

General modeUser ModeCFX-Pre

Steady StateAnalysis Type

General FluidFluid Type

Multiple DomainDomain Type

k-EpsilonTurbulence Model

Shear Stress Transport

Thermal EnergyHeat Transfer

Conjugate Heat Trans-fer (via Electrical Resist-ance Heating)

Heat Transfer Modeling

291Release 14.5 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

of ANSYS, Inc. and its subsidiaries and affiliates.

DetailsFeatureComponent

Conduction Through aThin Wall

Inlet (Subsonic)Boundary Conditions

Outlet (Subsonic)

Opening

Wall: No-Slip

Wall: Adiabatic

CEL (CFX ExpressionLanguage)

Physical Time ScaleTimestep

ContourPlotsCFD-Post

Cylindrical Locator

Isosurface

Temperature ProfileChart

Changing the ColorRange

Other

Expression Details View

Lighting Adjustment

Variable Details View

Exporting Results toANSYS

16.2. Overview of the Problem to Solve

The first portion of this tutorial demonstrates the capability of ANSYS CFX to model conjugate heattransfer. A simple heat exchanger is used to model the transfer of thermal energy from an electrically-heated solid copper coil to the water flowing around it. The latter section demonstrates the capabilityof ANSYS CFX to model heat transfer through a thin surface. The initial simulation will be altered sothat the heating coil becomes a thin-walled copper tube with dry steam flowing through it.

The first model contains a fluid domain for the water and a solid domain for the coil. The fluid domainis an annular region that envelops the coil, and has water at an initial temperature of 300 K flowingthrough it at 0.4 m/s. The copper coil has a 4.4 V difference in electric potential from one end to theother end and is given an initial temperature of 550 K. Assume that the copper has a uniform electricalconductivity of 59.6E+06 S/m and that there is a 1 mm thick calcium carbonate deposit (calcite) on theheating coil.

The other material parameters for the calcium carbonate deposit are:

• Molar Mass = 100.087[kg kmol^-1]

• Density = 2.71[g cm^-3]

• Specific Heat Capacity = 0.9[J g^-1 K^-1]

Release 14.5 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationof ANSYS, Inc. and its subsidiaries and affiliates.292

Heat Transfer from a Heating Coil

• Thermal Conductivity = 3.85[W m^-1 K^-1]

The second model will maintain the original annular fluid domain, and turn the solid domain into asecond fluid domain. Settings will be adjusted so that these two fluid domains can have separatephysics. The domain interface will be 2 mm of copper. The pipe will contain dry steam at an initialtemperature of 600 K and an initial velocity of 0.25 m/s. The steam outlet will have a relative pressureof 0 psi. All material properties for the dry steam will be set using the IAPWS Library option and usingall default table values.

This tutorial also includes an optional step that demonstrates the use of the CFX to ANSYS Data Transfertool to export thermal and mechanical stress data for use with ANSYS Multi-field solver. A results file isprovided in case you want to skip the model creation and solution steps within ANSYS CFX.

16.3. Before You Begin

If this is the first tutorial you are working with, it is important to review the following topics beforebeginning:

• Setting the Working Directory and Starting ANSYS CFX in Stand-alone Mode (p. 3)

• Running ANSYS CFX Tutorials Using ANSYS Workbench (p. 4)

• Changing the Display Colors (p. 7)

• Playing a Tutorial Session File (p. 6)

16.4. Setting Up the Project

1. Prepare the working directory using the following files in the examples directory:

• HeatingCoil.cfx

• HeatingCoilMesh.gtm

For details, see Preparing the Working Directory (p. 3).



Setting Up the Project

2. Set the working directory and start CFX-Pre.

For details, see Setting the Working Directory and Starting ANSYS CFX in Stand-alone Mode (p. 3).

16.5. Simulating the Copper Coil with a Calcium Carbonate Deposit

In this first part of the tutorial, you will create the simulation with a solid copper coil and a 1 mm thickcalcium carbonate deposit.

16.5.1. Defining the Case Using CFX-Pre

If you want to set up the simulation automatically using a tutorial session file, run HeatingCoil.pre.For details, see Playing a Tutorial Session File (p. 6). Then proceed to Obtaining the Solution usingCFX-Solver Manager (p. 302).

If you want to set up the simulation manually, proceed to the following steps:

1. In CFX-Pre, select File > New Case.

2. Select General and click OK.

3. Select File > Save Case As.

4. Under File name, type HeatingCoil.

5. If you are notified the file already exists, click Overwrite. This file is provided in the tutorial directoryand may exist in your working directory if you have copied it there.

6. Click Save.

16.5.1.1. Importing the Mesh

1. Expand the Case Options sec tion in the Outline tree view.

2. Edit General.

3. Turn off Automatic Default Domain and Automatic Default Interfaces.

Default domain and interface generation should be turned off because you will manually createthe fluid and solid domains and interface later in this tutorial.

4. Click OK to apply this change.

5. Right-click Mesh and select Import Mesh > CFX Mesh.

The Import Mesh dialog box appears.

6. Configure the following setting(s):

ValueSetting

HeatingCoilMesh.gtmFile name

7. Click Open.



8. Right-click a blank area in the viewer and select Predefined Camera > Isometric View (Z up) from theshortcut menu.

16.5.1.2. Editing the Material Properties

1. Expand Materials in the tree view, right-click Copper and select Edit.

2. Configure the following setting(s) of Copper :

ValueSettingTab

Expand the Elec-

tromagnetic

Electromagnetic PropertiesMaterialProperties

Properties frame[1]

(Selected)Electromagnetic Properties >Electrical Conductivity

59.6E+06 [S m^-1]Electromagnetic Properties >Electrical Conductivity > Elec-trical Conductivity

Footnote

1. Expand a section by clicking Roll Down .

3. Click OK to apply these settings to Copper .

16.5.1.3. Defining the Calcium Carbonate Deposit Material

Create a new material definition that will be used to model the calcium carbonate deposit on theheating coil:

1. Click Material and name the new material Calcium Carbonate .


ValueSettingTab

User [1]Material GroupBasic Settings

(Selected)Thermodynamic State

SolidThermodynamic State > Ther-modynamic State

100.087 [kgkmol^-1]

Thermodynamic Properties >Equation of State > MolarMass

Material Prop-erties

2.71 [g cm^-3][2]

Thermodynamic Properties >Equation of State > Density



Simulating the Copper Coil with a Calcium Carbonate Deposit

ValueSettingTab

(Selected)Thermodynamic Properties >Specific Heat Capacity

0.9 [J g^-1 K^-

1] [2]

Thermodynamic Properties >Specific Heat Capacity > Spe-cific Heat Capacity

(Selected) [3]Transport Properties > ThermalConductivity

3.85 [W m^-1K^-1]

Transport Properties > ThermalConductivity > Thermal Con-ductivity

Footnotes

1. The material properties for Calcium Carbonate defined in this table came directly fromthe Overview of the Problem to Solve (p. 292) section at the beginning of this tutorial.

2. Make sure that you change the units to those indicated.

3. You may need to first expand the Transport Properties frame by clicking Roll Down .

3. Click OK to apply these settings.

16.5.1.4. Creating the Domains

This simulation requires both a fluid domain and a solid domain. First, you will create a fluid domainfor the annular region of the heat exchanger.

16.5.1.4.1. Creating a Fluid Domain

The fluid domain will include the region of fluid flow but exclude the solid copper heater coil.

1. Ensure that Flow Analysis 1 > Default Domain does not appear in the Outline tree view. If itdoes, right-click Default Domain and select Delete.

2. Click Domain and set the name to WaterZone .

3. Configure the following setting(s) of WaterZone :

ValueSettingTab

Annulus[1]

Location and Type > LocationBasic Settings

Fluid 1Fluid and Particle Definitions

WaterFluid and Particle Definitions >Fluid 1 > Material



ValueSettingTab

1 [atm]Domain Models > Pressure > Ref-erence Pressure

ThermalEnergy

Heat Transfer > OptionFluid Models

(Selected)Domain InitializationInitialization

Footnote

1. This region name may be different depending on how the mesh was created. You shouldpick the region that forms the exterior surface of the volume surrounding the coil.

4. Click OK to apply these settings to WaterZone .

16.5.1.4.2. Creating a Solid Domain

Since you know that the copper heating element will be much hotter than the fluid, you can initializethe temperature to a reasonable value. The initialization option that is set when creating a domain appliesonly to that domain.

Create the solid domain as follows:

1. Create a new domain named SolidZone .


ValueSettingTab

Coil [1]Location and Type > LocationBasicSet-tings

Solid DomainLocation and Type > Domain Type

Solid 1Solid Definitions

CopperSolid Definitions> Solid 1 > Solid 1 >Material

Thermal En-ergy

Heat Transfer > OptionSolidMod-els (Selected)Electromagnetic Model

Electric Poten-tial

Electromagnetic Model > Electric FieldModel > Option

Automaticwith Value

Domain Initialization > Initial Conditions> Temperature > Option

Initial-ization




ValueSettingTab

550 [K]Domain Initialization > Initial Conditions> Temperature > Temperature

Footnote

1. This region name may be different depending on how the mesh was created. You shouldpick the region that forms the coil.


16.5.1.5. Creating the Boundaries

You will now set the boundary conditions using the values given in the problem description.

16.5.1.5.1. Heating Coil Boundaries

In order to pass electricity through the heating coil, you are going to specify a voltage of 0 [V] at oneend of the coil and 4.4 [V] at the other end:

1. Click Boundary and select in SolidZone from the drop-down menu that appears.

2. Name this new boundary Ground and click OK.


ValueSettingTab

WallBoundary TypeBasic Settings

Coil End 1[1]Location

VoltageElectric Field > OptionBoundary De-tails 0 [V]Electric Field > Voltage

Footnote

1. You will need to click Multi-select from extended list to see a list of all regions.


5. Create a similar boundary named Hot at the other end of the coil, Coil End 2, and apply a voltage of4.4[V].

16.5.1.5.2. Inlet Boundary

You will now create an inlet boundary for the cooling fluid (Water).



1. Create a new boundary in the WaterZone domain named inflow .


ValueSettingTab

InletBoundary TypeBasic Set-tings inflowLocation

Normal SpeedMass and Momentum > OptionBoundaryDetails 0.4 [m s^-1]Mass and Momentum > Normal

Speed

Static Temperat-ure

Heat Transfer > Option

300 [K]Heat Transfer > Static Temperat-ure


16.5.1.5.3. Opening Boundary

An opening boundary is appropriate for the exit in this case because, at some stage during the solution,the coiled heating element will cause some recirculation at the exit. At an opening boundary you needto set the temperature of fluid that enters through the boundary. In this case it is useful to base thistemperature on the fluid temperature at the outlet, since you expect the fluid to be flowing mostly outthrough this opening.

1. Insert a new expression by clicking Expression .

2. Name this new expression OutletTemperature and press the Enter key to continue.

3. In the Definition entry box, type the formula areaAve(T)@outflow

4. Click Apply.

5. Close the Expressions view by clicking Close at the top of the tree view.

6. Create a new boundary in the WaterZone domain named outflow .


ValueSettingTab

OpeningBoundary TypeBasic Set-tings outflowLocation

Opening Pres. andDirn

Mass and Momentum > OptionBoundaryDetails

0 [Pa]Mass and Momentum > RelativePressure

Static TemperatureHeat Transfer > Option




ValueSettingTab

OutletTemperature[1]

Heat Transfer > Static Temperat-ure

Footnote

1. In order to enter an expression, you need to click Enter Expression .


A default no slip, adiabatic wall boundary named WaterZone Default will be applied automaticallyto the remaining unspecified external boundaries of the WaterZone domain.

Two more boundary conditions are generated automatically when a domain interface is created toconnect the fluid and solid domains. The domain interface is discussed in the next section.

16.5.1.6. Creating the Domain Interface

If you have Automatic Default Interfaces turned on, then an interface called Default Fluid Sol-id Interface is created automatically and listed in the tree view. In this case, delete the default in-terface and proceed with creating a new one.

1. Click Domain Interface from the row of icons located along the top of the screen.

2. Set the name to Domain Interface and click OK to accept it.

3. Configure the following setting(s) of Domain Interface :

ValueSettingTab

Fluid SolidInterface TypeBasic Set-tings WaterZoneInterface Side 1 > Domain (Filter)

coil surfaceInterface Side 1 > Region List

SolidZoneInterface Side 2 > Domain (Filter)

F22.33, F30.33, F31.33,F32.33, F34.33, F35.33

Interface Side 2 > Region List

(Selected)Heat TransferAddition-al Inter- Thin MaterialHeat Transfer > Interface Model

> Optionface Mod-els

Calcium CarbonateHeat Transfer > Interface Model> Material



ValueSettingTab

1 [mm] [1]Heat Transfer > Interface Model> Thickness

Footnote

1. Make sure that you change the units to those indicated.


16.5.1.7. Setting Solver Control

1. Click Solver Control .


ValueSettingTab

Physical TimescaleConvergence Control > FluidTimescale Control > TimescaleControl

Basic Set-tings

2 [s]Convergence Control >FluidTimescale Control > PhysicalTimescale

For the Convergence Criteria, an RMS value of at least 1e-05 is usually required for adequateconvergence, but the default value is sufficient for demonstration purposes.


16.5.1.8. Writing the CFX-Solver Input (.def) File

1. Click Define Run .


ValueSetting

HeatingCoil.defFile name

3. Click Save.

CFX-Solver Manager automatically starts and, on the Define Run dialog box, the Solver Input File

is set.

4. If using stand-alone mode, quit CFX-Pre, saving the simulation (.cfx ) file at your discretion.




16.5.2. Obtaining the Solution using CFX-Solver Manager

1. Ensure that the Define Run dialog box is displayed.

2. Click Start Run.

CFX-Solver runs and attempts to obtain a solution. At the end of the run, a dialog box is displayedstating that the simulation has ended.

While the calculations proceed, you can see residual output for various equations in both the textarea and the plot area. Use the tabs to switch between different plots (for example, Heat Transfer,Turbulence (KE), and so on) in the plot area. You can view residual plots for the fluid and soliddomains separately by editing the workspace properties (under Workspace > Workspace Proper-

ties).

3. Select Post-Process Results.

4. If using stand-alone mode, select Shut down CFX-Solver Manager.

5. Click OK.

16.5.3. Viewing the Results Using CFD-Post

The following topics will be discussed:

• Heating Coil Temperature Range (p. 302)

• Creating a Cylindrical Locator (p. 303)

• Specular Lighting (p. 305)

• Moving the Light Source (p. 306)

16.5.3.1. Heating Coil Temperature Range

To grasp the effect of the calcium carbonate deposit, it is beneficial to compare the temperature rangeon either side of the deposit.

1. When CFD-Post opens, if you see the Domain Selector dialog box, ensure that both domains are selected,then click OK.

2. Create a new contour named Contour 1 .


ValueSettingTab

Domain Interface

Side 1 [1]

LocationGeometry

TemperatureVariable

LocalRange



ValueSettingTab

(Selected)Boundary Data > Hybrid

Footnote

1. This is the deposit side that is in contact with the water.

4. Click Apply.

5. Take note of the temperature range displayed below the Range drop-down box. The temperature onthe outer surface of the deposit should range from around 380 [K] to 740 [K].

Change the contour location to Domain Interface Side 2 (The deposit side that is in contactwith the coil) and click Apply. Notice how the temperature ranges from around 420 [K] to 815 [K]on the inner surface of the deposit.

16.5.3.2. Creating a Cylindrical Locator

Next, you will create a cylindrical locator close to the outside wall of the annular domain. This can bedone by using an expression to specify radius and locating a particular radius with an isosurface.

16.5.3.2.1. Expression

1. Create a new expression by clicking Expression .

2. Set the name of this new expression to expradius and press the Enter key to continue.


ValueSetting

(x^2 + y^2)^0.5Definition

4. Click Apply.

16.5.3.2.2. Variable

1. Create a new variable by clicking Variable .

2. Set the name of this new variable to radius and press the Enter key to continue.


ValueSetting

expradiusExpres-sion

4. Click Apply.




16.5.3.2.3. Isosurface of the variable

1. Insert a new isosurface by clicking Location >Isosurface.

2. Accept the default name Isosurface 1 by clicking OK.


ValueSettingTab

radiusDefinition > VariableGeometry

0.8 [m] [1]Definition > Value

VariableModeColor

TemperatureVariable

User Specified [2]Range

299 [K]Min

309 [K]Max

(Selected)Show FacesRender

Footnotes

1. The maximum radius is 1 m, so a cylinder locator at a radius of 0.8 m is suitable.

2. The full temperature range is much larger due to temperature extremes on a small fractionof the isosurface. By neglecting those extreme temperatures, more colors are used overthe range of interest.

4. Click Apply.

5. Turn off the visibility of Contour 1 so that you have an unobstructed view of Isosurface 1 .

Note

The default range legend now displayed is that of the isosurface and not the contour.The default legend is set according to what is being edited in the details view.

16.5.3.2.4. Creating a Temperature Profile Chart

For a quantitative analysis of the temperature variation through the water and heating coil, it is beneficialto create a temperature profile chart.

First, you will create a line that passes through two turns of the heating coil. You can then graphicallyanalyze the temperature variance along that line by creating a temperature chart.

1. Insert a line by clicking Location > Line.

2. Accept the default name Line 1 by clicking OK.



3. Configure the following setting(s) of Line 1

ValueSettingTab

-0.75, 0, 0Definition > Point 1Geometry

-0.75, 0, 2.25Definition > Point 2

(Selected)Line Type > Sample

200Line Type > Samples

4. Click Apply.

5. Create a new chart by clicking Chart .

6. Name this chart Temperature Profile and press the Enter key to continue.

7. Click the Data Series tab.

8. Set Data Source > Location to Line 1 .

9. Click the Y Axis tab.

10. Set Data Selection > Variable to Temperature .

11. Click Apply.

You can see from the chart that the temperature spikes upward when entering the deposit region andis at its maximum at the center of the coil turns.

16.5.3.3. Specular Lighting

Specular lighting is on by default. Specular lighting allows glaring bright spots on the surface of anobject, depending on the orientation of the surface and the position of the light. You can disablespecular lighting as follows:

1. Click the 3D Viewer tab at the bottom of the viewing pane.

2. Edit Isosurface 1 in the Outline tree view.

ValueSettingTab

(Cleared)Show Faces > SpecularRender

3. Click Apply.




16.5.3.4. Moving the Light Source

To move the light source, click within the 3D Viewer, then press and hold Shift while pressing the arrowkeys left, right, up or down.

Tip

If using the stand-alone version, you can move the light source by positioning the mousepointer in the viewer, holding down the Ctrl key, and dragging using the right mouse button.

16.6. Exporting the Results to ANSYS

This optional step involves generating an ANSYS .cdb data file from the results generated in CFX-Solver. The .cdb file could then be used with the ANSYS Multi-field solver to measure the combinedeffects of thermal and mechanical stresses on the solid heating coil.

There are two possible ways to export data to ANSYS:

• Use CFX-Solver Manager to export data.

• Use CFD-Post to export data. This involves:

1. Importing a surface mesh from ANSYS into CFD-Post, and associating the surface with the correspond-ing 2D region in the CFX-Solver results file.

2. Exporting the data to a file containing SFE commands that represent surface element thermal ormechanical stress values.

3. Loading the commands created in the previous step into ANSYS and visualizing the loads.

In this case, you will be using CFX-Solver Manager to export data. Since the heat transfer in the soliddomain was calculated in ANSYS CFX, the 3D thermal data will be exported using element type 3DThermal (70) . The mechanical stresses are calculated on the liquid side of the liquid-solid interface.These values will be exported using element type 2D Stress (154) .

16.6.1. Thermal Data

1. Start CFX-Solver Manager.

2. Select Tools > Export to ANSYS MultiField.

The Export to ANSYS MultiField Solver dialog box appears.


ValueSetting

HeatingCoil_001.resResults File

HeatingCoil_001_ansysf-si_70.cdb

Export File

SolidZoneDomain Name > Domain

(Empty) Domain Name > Boundary



ValueSetting

[1]

3D Thermal (70)Export Options > ANSYS Element Type

Footnote

1. Leave Boundary empty since the entire volume is exported for 3D data.

4. Click Export.

When the export is complete, click OK to acknowledge the message and continue with the nextsteps to export data for Mechanical Stresses (p. 307).

16.6.2. Mechanical Stresses

1. Configure the following setting(s) in the Export to ANSYS MultiField Solver dialog box:

ValueSetting

HeatingCoil_001.resResults File

HeatingCoil_001_ansysf-si_154.cdb

Export File

WaterZoneDomain Name > Domain

WaterZone DefaultDomain Name > Boundary

2D Stress (154)Export Options > ANSYS Element Type

2. Click Export.

When the export is complete, click OK to acknowledge the message and continue.

3. Click Close.

4. Close CFX-Solver Manager.

You now have two exported files that can be used with ANSYS Multi-field solver. When you are finished,close CFX-Solver Manager and CFD-Post.

16.7. Simulating the Thin-Walled Copper Coil with Dry Steam

In this second part of the tutorial, you will modify the simulation from the first part of the tutorial touse a second fluid domain representing a thin-walled copper coil with dry steam running through,rather than the solid copper electric heating coil. Running the simulation a second time will demonstratehow to model multiple fluid domains with varying physics, as well as how to model heat transfer througha thin surface.



Simulating the Thin-Walled Copper Coil with Dry Steam

16.7.1. Defining the Case Using CFX-Pre

If you want to set up the steam coil simulation automatically using a tutorial session file, run Steam-Coil.pre. For details, see Playing a Tutorial Session File (p. 6). Then proceed to Obtaining theSolution using CFX-Solver Manager (p. 314).

1. Start CFX-Pre if it is not already running.

2. Select File > Open Case.

3. From your working directory, select HeatingCoil.cfx and click Open.

4. Select File > Save Case As.

5. Set File name to SteamCoil.cfx.

6. Click Save.

16.7.1.1. Allowing for Fluid Domains with Separate Physics and Enabling Beta Features

In this section, you will disable Constant Domain Physics for this case. This will enable you to createtwo fluid domains with separate physical settings. Since this capability is a Beta feature, you must firstenable the use of Beta features.

1. Edit Case Options > General in the Outline tree view.

2. Select the Physics > Enable Beta Features check box.

3. Clear the Physics > Constant Domain Physics check box.


Note

Make sure to make the changes via Case Options > General in the Outline tree insteadof via the Edit menu (Edit > Options > CFX-Pre > General).

16.7.1.2. Editing Copper Properties

In this section, you will remove the electromagnetic properties of the copper (as defined in the firstsegment of this tutorial).

1. Edit Materials > Copper in the Outline tree view.


ValueSettingTab

Expand the Electro-

magnetic Proper-

ties frame [1]

Electromagnetic PropertiesMaterialProper-ties



ValueSettingTab

(Cleared)Electromagnetic Properties >Electrical Conductivity

Footnote

1. Expand a section by clicking Roll Down .


16.7.1.3. Creating a New Material

In this section, you will create a new material called Dry Steam . This material will represent the drysteam that is going to flow through the hollow copper coil.

1. Right-click Materials in the Outline tree view and select Insert > Material or click Material .

2. Name this new material Dry Steam and click OK.


ValueSettingTab

Dry SteamMaterial GroupBasic Set-tings

IAPWS LibraryOptionMaterialProper-ties

(Selected)Thermodynamic Properties >Table Generation

(Selected)Thermodynamic Properties >Table Generation > MinimumTemperature

273.15 [K]Thermodynamic Properties >Table Generation > MinimumTemperature > Min. Temperature

(Selected)Thermodynamic Properties >Table Generation > MaximumTemperature

1000.0 [K]Thermodynamic Properties >Table Generation > MaximumTemperature > Max. Temperature

(Selected)Thermodynamic Properties >Table Generation > MinimumAbsolute Pressure

1000.0 [Pa]Thermodynamic Properties >Table Generation > Minimum




ValueSettingTab

Absolute Pressure > Min. Abso-lute Pres.

(Selected)Thermodynamic Properties >Table Generation > MaximumAbsolute Pressure

1.0E6 [Pa]Thermodynamic Properties >Table Generation > MaximumAbsolute Pressure > Max. Abso-lute Pres.

(Selected)Thermodynamic Properties >Table Generation > MaximumPoints

100Thermodynamic Properties >Table Generation > MaximumPoints > Maximum Points

(Selected)Thermodynamic Properties >Table Generation > Temp. Extra-polation

(Selected)Thermodynamic Properties >Table Generation > Temp. Extra-polation > Activate

(Selected)Thermodynamic Properties >Table Generation > Pressure Ex-trapolation

(Selected)Thermodynamic Properties >Table Generation > Pressure Ex-trapolation > Activate


16.7.1.4. Editing the SolidZone Domain

In this section, you will modify the SolidZone domain to make it representative of a thin-walled steamcoil.

1. Right-click SolidZone in the Outline tree view and select Rename.

2. Set the new domain name to SteamZone and press the Enter key to apply this new name.

3. Edit SteamZone in the Outline tree view.


ValueSettingTab

Fluid DomainLocation and Type > DomainType

Basic Set-tings



ValueSettingTab

Dry SteamFluid and Particle Definitions >Fluid 1 > Material

1 [atm]Domain Models > Pressure >Reference Pressure

Thermal EnergyHeat Transfer > OptionFluidModels

(Selected)Domain Solver ControlSolverControl Physical TimescaleDomain Solver Control > Times-

cale Control > Timescale Control

5.09 [s] [1]Domain Solver Control > Times-cale Control > Physical Timescale

Footnote

1. The physical timescale is derived from the approximate copper pipe length (10.7 [m])and the average rate at which the steam flows through the pipe (0.21 [m s^-1]).

5. Click OK to apply these changes to the SteamZone domain.

Note

Note that you will see several physics errors appear in the window below the 3D viewer.These are normal because you have just defined a second fluid at the interface, andnow need to modify the domain interface from type Fluid Solid to type FluidFluid.

16.7.1.5. Editing the WaterZone Domain

In this section, you will set a separate physical timescale for this domain since the physical timescalesbetween the two fluid domains are quite different. The physical time scale of a fluid domain should besome fraction of a length scale divided by a velocity scale. For more details on this, see Physical TimeScale in the CFX-Solver Modeling Guide.

1. Edit WaterZone in the Outline tree view.


ValueSettingTab

(Selected)Domain Solver ControlSolverControl Physical TimescaleDomain Solver Control > Times-

cale Control > Timescale Control




ValueSettingTab

0.56 [s] [1]Domain Solver Control > Times-cale Control > Physical Timescale

Footnote

1. The physical timescale is derived from the annular pipe length (2.25 [m]) and the rate atwhich the water flows through the pipe (0.4 [m s^-1]).


16.7.1.6. Editing the Domain Interface

In this section, you will modify the domain interface to represent a thin copper wall.

1. Edit Domain Interface in the Outline tree view.


ValueSettingTab

Fluid FluidInterface TypeBasic Set-tings WaterZoneInterface Side 1 > Domain (Filter)

coil surfaceInterface Side 1 > Region List

SteamZoneInterface Side 2 > Domain (Filter)

F22.33, F30.33,F31.33, F32.33,

F34.33, F35.33 [1]

Interface Side 2 > Region List

No Slip WallMass and Momentum > OptionAddition-al Inter- CopperHeat Transfer > Materialface Mod-els 2 [mm] [2]Heat Transfer > Thickness

Footnote

1. Click Multi-select from extended list and hold down the Ctrl key while selecting eachof the listed regions

2. This thickness is based on the Nominal Pipe Size for a pipe with a 100 mm diameter.

3. Click OK to apply these changes to the domain interface.



16.7.1.7. Editing the Ground Boundary

In this section, you will edit the Ground boundary associated with the SteamZone domain. Thisboundary is currently set up as ground for the electrical heating coil model, and needs to be modifiedto represent the steam coil inlet.

1. Right-click the Ground boundary in the Outline tree view and select Rename.

2. Set the name of this boundary to SteamIn and press the Enter key to apply this change.

3. Edit SteamIn in the Outline tree view.


ValueSettingTab

InletBoundary TypeBasic Set-tings

Cart. Vel. Compon-ents

Mass and Momentum > OptionBoundaryDetails

0.25 [m s^-1]Mass and Momentum > U

0 [m s^-1]Mass and Momentum > V

0 [m s^-1]Mass and Momentum > W

600 [K]Heat Transfer > Static Temperat-ure

Note

The values in this table come directly from the overview of the problem at the beginningof this tutorial.

5. Click OK to apply these changes.

16.7.1.8. Editing the Hot Boundary

In this section, you will edit the Hot boundary associated with the SteamZone domain. This boundaryis currently set up with electric potential for the electrical heating coil model, and needs to be modifiedto represent the steam coil outlet.

1. Right-click the Hot boundary in the Outline tree view and select Rename.

2. Set the name of this boundary to SteamOut and press the Enter key to apply the change.

3. Edit SteamOut in the Outline tree view.


ValueSettingTab

OutletBoundary TypeBasic Set-tings




ValueSettingTab

0 [Pa]Mass and Momentum > RelativePressure

BoundaryDetails

5. Click OK to apply these changes.

16.7.1.9. Writing the CFX-Solver Input (.def) File

1. Click Define Run .


ValueSetting

SteamCoil.defFile name

3. Click Save.

This tutorial makes use of a Beta feature: domain-specific solver control. A dialog box asks if youwant to write the case even though it uses a Beta feature.

4. In the Beta Physics Model Warning dialog box, click Yes.

CFX-Solver Manager automatically starts and, on the Define Run dialog box, the Solver Input File

is set.

Note

If you have used the global options instead of the case options to enable the beta fea-tures, make sure to turn it off because it will cause instability in future sessions.

5. If using stand-alone mode, quit CFX-Pre, saving the simulation (.cfx ) file at your discretion.

16.7.2. Obtaining the Solution using CFX-Solver Manager

1. Ensure that the Define Run dialog box is displayed.

2. Click Start Run.

CFX-Solver runs and attempts to obtain a solution. At the end of the run, a dialog box is displayedstating that the simulation has ended.

While the calculations proceed, you can see residual output for various equations in both the textarea and the plot area. Use the tabs to switch between different plots (for example, Heat Transfer,Turbulence (KE), and so on) in the plot area. You can view residual plots for the fluid and soliddomains separately by editing the workspace properties (under Workspace > Workspace Proper-

ties).

3. Select Post-Process Results.



4. If using stand-alone mode, select Shut down CFX-Solver Manager.

5. Click OK.

16.7.3. Viewing the Results Using CFD-Post

The following topics will be discussed:

• Heating Coil Temperature Range (p. 315)

• Creating a Cylindrical Locator (p. 303)

16.7.3.1. Heating Coil Temperature Range

To examine how the heat transfer through the pipe changes along the length of the coil, it is useful tolook at temperature contour along the outer surface of the coil.

1. When CFD-Post opens, if you see the Domain Selector dialog box, ensure that both domains are selected,then click OK.

2. Create a new contour named Contour 1 .


ValueSettingTab

Domain Interface

Side 1 [1]

LocationGeometry

TemperatureVariable

LocalRange

(Selected)Boundary Data > Hybrid

Footnote

1. This is the deposit side that is in contact with the water.

4. Click Apply.

5. Take note of the temperature range displayed below the Range drop-down box. The temperature onthe outer surface of the deposit should range from around 370 [K] to 540 [K].

Change the contour location to Domain Interface Side 2 (The coil inner coil surface thatis in direct contact with the steam) and click Apply. Notice how the temperature ranges fromaround 370 [K] to 600 [K] on the inner surface of the coil.

16.7.3.2. Creating a Cylindrical Locator

Next, you will create a cylindrical locator close to the outside wall of the annular domain. This can bedone by using an expression to specify radius and locating a particular radius with an isosurface.




16.7.3.2.1. Expression

1. Create a new expression by clicking Expression .

2. Set the name of this new expression to expradius and press Enter to continue.


ValueSetting

(x^2 + y^2)^0.5Definition

4. Click Apply.

16.7.3.2.2. Variable

1. Create a new variable by clicking Variable .

2. Set the name of this new variable to radius and press the Enter key to continue.


ValueSetting

expradiusExpres-sion

4. Click Apply.

16.7.3.2.3. Isosurface of the variable

1. Insert a new isosurface by clicking Location >Isosurface.

2. Accept the default name Isosurface 1 by clicking OK.


ValueSettingTab

radiusDefinition > VariableGeometry

0.8 [m] [1]Definition > Value

VariableModeColor

TemperatureVariable

LocalRange

Footnote

1. The maximum radius is 1 [m], so a cylinder locator at a radius of 0.8 [m] is suitable.



4. Click Apply.

5. Turn off the visibility of Contour 1 so that you have an unobstructed view of Isosurface 1 .

You can see how the temperature along the steam coil gradually decreases along the length of the coil(as some of the heat in the steam is lost via heat transfer through the thin copper wall and to thecooler water on the other side).

Now, you will adjust the temperature range along this isosurface to get a better understanding of theheat transfer from the steam coil to the surrounding water.

• Adjust the settings of Isosurface 1 as follows:

ValueSettingTab

User SpecifiedRangeColor

299 [K]Min

309 [K]Max

Note

The default range legend now displayed is that of the isosurface and not the contour.The default legend is set according to what is being edited in the details view.

You can see how the cool water is heated as it passes directly past the steam coil (the cool watermaintains a steady temperature until it reaches the first loop in the coil).

16.7.3.2.4. Creating a Temperature Profile Chart

For a quantitative analysis of the temperature variation through the water and steam coil, it is beneficialto create a temperature profile chart.

First, you will create a line that passes through two turns of the heating coil. You can then graphicallyanalyze the temperature variance along that line by creating a temperature chart.

1. Insert a line by clicking Location > Line.

2. Accept the default name Line 1 by clicking OK.

3. Configure the following setting(s) of Line 1 :

ValueSettingTab

-0.75, 0, 0Definition > Point 1Geometry

-0.75, 0, 2.25Definition > Point 2

(Selected)Line Type > Sample

200Line Type > Samples

4. Click Apply.

5. Create a new chart by clicking Chart .




6. Name this chart Temperature Profile and press the Enter key to continue.

7. Click the Data Series tab.

8. Set Data Source > Location to Line 1 .

9. Click the Y Axis tab.

10. Set Data Selection > Variable to Temperature .

11. Click Apply.

You can see from the chart that the temperature spikes upward when entering the coil region and re-mains relatively steady across the cross-section of the coil.



heat-transfer-from-heating-coil.pdf

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