Mech-HT 120 WSA1 Phase Change

Workshop (Appendix)

Phase Change

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August 2009Inventory #002667

ANSYS Mechanical Heat Transfer

Workshop (Appendix) - Phase Change

Training ManualProblem Description

• The model represents cooling of molten aluminum contained i n asand cast for a wheel.

– The aluminum has a melting point of 696 ºC.

• To economize the analysis will be conducted using a 2D axisym metrymodel of the wheel and mold.




Training ManualProblem Description

• Since this is a phase change problem we’ll need to include enthalpy as a material property. To do this we need to use a command object. The basic properties are shown below. Later in the workshop we will use this data to construct a table representing ent halpy versus temperature.

• Aluminum Alloy:– Density = 2770 kg/m 3



– Density = 2770 kg/m 3

– Specific Heat (solid) = 876 J/(kg* ºC)– Specific Heat (liquid) = 1050 J/(kg* ºC)– Melting Temperature = 696 ºC– Transition Temperature = 695 ºC– Liquid Temperature = 697 ºC– Latent Heat = 395440 J/kg


Training ManualUnits Setup

• Open Workbench and specify the unit system Metric ( kg, m, s, ºC, A, N, V).

• Choose to “Display Values in Project Units”.




Training ManualModel Setup

1. From the Workbench project page toolbox, select a Transient Thermal analysis system.

2. Double click the Engineering Data.



3. Highlight the Engineering Data cell and enter “Sand” as a new material.



4. From the Toolbox drag and drop Density, Isotropic Thermal Conductivity and Specific Heat onto the “Sand” property.

5. Enter the property values:– Density = 1520 kg/m 3

– Conductivity = 0.346 W/(m* ºC)– Specific Heat = 816 J/(kg* ºC)



– Specific Heat = 816 J/(kg* ºC)

6. Highlight the General Materials library.7. Click the “+” next to “Aluminum Alloy”

to add it to the project.



8. Highlight “Engineering Data” in the Outline filter.

9. Highlight “Aluminum Alloy”

10.Highlight, RMB and delete the properties “Density” and “Specific Heat”.



• Note, for phase change problems, the property enthalpy is used which is defined in terms of density and specific heat. Since this property is not supported in the engineering data application we need to add a command object to define it. We delete density and specific heat here so as not to overwrite the enthalpy definition.



11.Using the properties shown in the table, enter new data for the aluminum alloy thermal conductivity.





12.Return to the project schematic.

13.Highlight the Geometry cell, RMB > Properties.



14. In the Advanced Geometry Options set the “Analysis Type” to 2D.



15.Right click the Geometry cell and import geometry “Sand_Casting_WSA1.x_t”.

16.Double click the Model cell to open the Mechanical application.



17.Highlight the Geometry branch and set the 2D Behavior to “Axisymmetric” .



18.Highlight the part, “Mold” and assign the material “Sand”.

19.Highlight the part, “Wheel” and assign the material “Aluminum Alloy”.– A warning message will be issued (see

below), since we deleted density and specific



below), since we deleted density and specific heat. We will be adding enthalpy so we can ignore the warning.



20.Highlight the “Wheel” part, RMB > Insert Commands.

21.Using the aluminum properties shown earlier and the equations on 7-19 we calculate enthalpy as a function of tempera ture E(T) as:– E(0) = 0– E(695) = 1.6857e9– E(697) = 2.7614e9



– E(697) = 2.7614e9– E(1000) = 3.6626e9

22.Enter the “mptemp” and “mpdata” commands as shown i n the command window:


Training ManualSolution Setup

23.Highlight “Initial Temperature” and set to 30 ºC.

24.Highlight “Analysis Settings” and set auto time stepping as shown below.– This will be a 2 step solution.



• The first step has a duration of 0.01s where the initial temperature load for the aluminum will be applied.

• In the second step (25 minutes or 1500 seconds) the temperature load will be removed and the aluminum allowed to cool to solidification.

• See details on next slide.


Training ManualSolution Setup

• Step 1:– Auto Time Stepping = On– End time = 0.1 s– Initial time step = 1e-3 s– Minimum time step = 1e-3 s– Maximum time step = 0.1 s

• Step 2:



• Step 2:– Auto Time Stepping = On– End time = 1500 s– Initial time step = 1e-3 s– Minimum time step = 1e-4 s– Maximum time step = 5 s


Training ManualBoundary Conditions

25.Highlight the “Transient Thermal” branch.

26.Select the top line on the mold and RMB > Insert > Convection. Details:– Film Coefficient = 5.75 W/(m 2* ºC)– Ambient Temperature = 30 ºC



27.Select the right side line on the mold and RMB > Insert > Convection. Details:– Film Coefficient = 7.5 W/(m 2* ºC)– Ambient Temperature = 30 ºC


Training ManualBoundary Conditions28.Change the selection filter to body select

and select the Wheel part.29.RMB > Insert > Temperature.

30. In the details change magnitude to “Tabular Data”.

31. In the table enter 800 C for time = 0.1s (note



31. In the table enter 800 C for time = 0.1s (note this will automatically fill the temperature for time = 1500s as well).

32.RMB step 2 (t = 1500s) and “Activate/Deactivate at this step!”– Note, deactivating the temperature at this

point removes the temperature load during the second step. This is NOT the same as setting the temperature to zero.


Training ManualSolution and Results

33.Solve the model. – Note depending on hardware, the solution could take 15 minutes.

• When the solution is complete insert temperature re sults for the entire model to review.



Recall from the model setup that the melting temperature of the aluminum

is 696 C. A 3 color legend can be setup to show solidification over time



• A plot of the global maximum temperature shows a re latively flat cooling profile in the aluminum’s transition region (695 – 697 ºC).

• Once solidification is complete the cooling proceed s at an increased rate.

Transition Region



≈ 696 ºC



• By locating coordinate systems at desired locations and attaching temperature probes to the wheel, a chart can be con structed showing temperature over time at each location.



Mech-HT 120 WSA1 Phase Change

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