Week 5.1 - Non-Conformal Meshing and Solving a Cold plate model

AIM

The objective of the project is to perform CFD analysis for the Cold plate and also create the non conformal mesh for the model.

TASK

• Create non-conformal mesh assembly.
• Solve for Flow and Temperature model & choose zero equation turbulent model and setup gravity vector.
• Setup transient simulation with an initial velocity of 0.005 m /s in antigravity direction and create monitor points.
• Post process the results using the Plane cut, Vector plot, Temperature contour and object face.

MODEL

The following objects are created in Icepak using the design specification.

Cabinet : It creates a fluid region around the model for which the governing equations are solved.

i) Geometry

Shape - Prism.

Specified By - Start/end.

Start Xs - 0

Start Ys - 0

Start Zs - 0

End Xe - 400 mm.

End Ye - 300mm.

End Ze - 200mm.

ii) Properties - The wall type for the cabinet is defined.

Min X - Opening.

Max X - Opening.

Min Y - Default.

Max Y - Default.

Min Z - Default.

Max Z - Default.

Block 1

i) Geometry

Shape - Prism.

Specified By - Start/end.

Start Xs - 50 mm.

Start Ys - 80 mm.

Start Zs - 70 mm.

End Xe - 350 mm.

End Ye - 220mm.

End Ze - 130mm.

ii) Properties

Block type - Solid.

Solid Material - Default.

Block 2

Geometry

Shape - Prism.

Specified By - Start/end.

Start Xs - 60 mm.

Start Ys - 90 mm.

Start Zs - 80 mm.

End Xe - 340 mm.

End Ye - 210mm.

End Ze - 120mm.

ii) Properties

Block type - Fluid.

Fluid Material - Water.

Plate 1

Geometry

Shape - Rectangular.

Plane - X-Y.

Specified By - Start/end.

Start Xs - 70 mm.

Start Ys - 100 mm.

Start Zs - 60 mm.

End Xe - 330 mm.

End Ye - 200mm.

ii) Properties

Thermal model - Conducting thick.

Thickness - 10mm.

Solid Material - Default.

Total power - 200W.

Plate 2

Geometry

Shape - Rectangular.

Plane - X-Y.

Specified By - Start/end.

Start Xs - 70 mm.

Start Ys - 100 mm.

Start Zs - 130 mm.

End Xe - 330 mm.

End Ye - 200mm.

ii) Properties

Thermal model - Conducting thick.

Thickness - 10mm.

Solid Material - Default.

Total power - 200W.

Inlet Pipe

Geometry

Shape - Cylinder.

Plane - X-Z.

Center xC - 100 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Height - 90mm.

Radius - 20mm.

Int Radius - 15mm.

ii) Properties

Block type - Solid.

Solid Material - Default.

Inlet Fluid region

Geometry

Shape - Cylinder.

Plane - X-Z.

Center xC - 100 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Height - 90mm.

Radius - 15mm.

ii) Properties

Block type - Fluid.

Fluid Material - Water.

Inlet Opening

Geometry

Shape - Circular.

Plane - X-Z.

Center xC - 100 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Radius - 15mm.

Properties

Temperature - Ambient.

Y velocity - 0.2m/s.

Outlet Pipe

Geometry

Shape - Cylinder.

Plane - X-Z.

Center xC - 300 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Height - 90mm.

Radius - 20mm.

Int Radius - 15mm.

ii) Properties

Block type - Solid.

Solid Material - Default.

Outlet fluid region

Geometry

Shape - Cylinder.

Plane - X-Z.

Center xC - 300 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Height - 90mm.

Radius - 15mm.

ii) Properties

Block type - Fluid.

Fluid Material - Water.

Outlet Opening

Geometry

Shape - Circular.

Plane - X-Z.

Center xC - 300 mm.

Center yC - 0 mm.

Center zC - 100 mm.

Radius - 15mm.

Properties

Temperature - Ambient.

The Non conformal mesh for the model is created by creating 3 assemble.

Assemble - 1

Select inlet pipe, inlet fluid region and inlet opening, create --> assembly.

Under the meshing tab choose Mesh separately,

i) Slack setting

Min X - 2 mm.

Max X - 2 mm.

Min Y - 0.

Max Y - 0.

Min Z - 2mm.

Max Z - 2mm.

ii) Mesh type

Max element size X - 2mm.

Max element size Y - 5mm.

Max element size Z - 2mm.

Min Gap X - 0.02 mm.

Min Gap Y - 0.05 mm.

Min Gap Z - 0.02 mm.

Assemble - 2

Select outlet pipe, outlet fluid region and outlet opening, create --> assembly.

Under the meshing tab choose Mesh separately,

i) Slack setting

Min X - 2 mm.

Max X - 2 mm.

Min Y - 0.

Max Y - 0.

Min Z - 2mm.

Max Z - 2mm.

ii) Mesh type

Max element size X - 2mm.

Max element size Y - 5mm.

Max element size Z - 2mm.

Min Gap X - 0.02 mm.

Min Gap Y - 0.05 mm.

Min Gap Z - 0.02 mm.

Assemble - 3

Select block 1, block 2, plate 1, plate 2, assemble 1 & assemble 2, create --> assemble.

Under the meshing tab choose Mesh separately,

i) Slack setting

Min X - 2 mm.

Max X - 2 mm.

Min Y - 0.

Max Y - 2 mm.

Min Z - 2mm.

Max Z - 2mm.

ii) Mesh type

Max element size X - 10mm.

Max element size Y - 7.5mm.

Max element size Z - 5mm.

Min Gap X - 0.1 mm.

Min Gap Y - 0.075 mm.

Min Gap Z - 0.05 mm.

• Macros --> Productivity --> Validation --> Automatic case check tool - It checks the assembly interface between the varies objects and assembly.

Mesh Control

Mesh along X plane

Mesh along Y plane

Mesh along Z plane

Mesh Verification

Face alignment

• It is the measure of mesh quality defined by face alignment index = C0C1.f
• C0 & C1 are the centroids of two adjacent elements are normal vector to the face between the two elements.
• Range of face alignment 0 (bad) to 1 (good) & value greater than 0.1 (preferred) & value greater than 0.15 provide better results.

The min value of the model is 0.6 which provide better results.

Volume

• Preferable volume of mesh to be greater than 1e-13 for single precision solver & greater than 1e-15 for double precision.
• Max / Min cell volume should be less than 10^7 for single precision & must be less than 10^12 for double precicion since very small volume create divergence of the solution.

The volume of the mesh greater than 10^-13 & Max / Min cell ratio is around 1000 which is in required range & the single precision is used for this model.

Skewness

It determines how close to the ideal & based on the equilateral volume. The value greater than 0.5 provide good cell quality.

The min value of the skewness is 0.44 and it produce good cell quality.

Solver

The three dimensional steady state Navier stokes equations for the model are solved within the computational domain.

General Setup

• Variables solved - flow and temperature.
• Radiation - Off.
• Flow regime - Turbulent - The zero equation are solved for the turbulent model.

Natural convection are consider for this model.

Gravity vector for the y axis is set to -9.81 m/s2.

The defaults value of the parameters are set to default.

Transient Setup

• Time variation - Steady

Solution Initialization

X velocity - 0.

Y velocity - 0.005 m/s.

Z velocity -0.

Temperature - ambient.

Basic settings

No of iterations - 500.

Convergence criteria

Flow - 0.001.

Energy - 1e-7.

Joule heating - 1e-7.

Parallel Settings

Configuration - parallel.

Parallel options - 4 processors.

Advance Solver Setup

Results

The residuals for the following equations are plotted against the number of iterations:

• Continuity equation.
• X-momentum equation.
• Y-momentum equation.
• Z-momentum equation.
• Energy equation.

The solution gets converged around 125 iterations and the contiuity and momemtum equation gets converged.

Plot

Temperature Contour

Y cut plane

Z cut plane

X cut plane

The maximum temperature within the computational domain is 31.247 degC. The plate provide the heat source of the model interacts with the aluminium block due to the heat transfer from them and the fluid region inside the block and the fluid flows from the inlet to the fluid block & to the outlet. The temperature at the other end of the model is at the ambient condition.

Velocity Contour

The contour plot of the velocity is highest around 0.238 m/s. The initial velocity is set to 0.005 m/s & the maximum velocity is at outlet since it in the direction of the gravity.

Object contour

The maximum temp is at the center of the plate in 31.28 degC. The inlet is at 20 degC & the outlet is at 22 degC.

Particle tracer plots

The vector plots for the velocity for the air at 100 points distributed uniformly through the X plane. The vectors the water achieves maximum velocity at the outlet. The velocity vector are able to capture the recirculation zones established on the Z plane.

Conclusion

In this project the given model of the cold plate was meshed using ANSYS Icepak using the non-conformal meshing, per-object meshing parameters and multi-level meshing. The three dimensional steady-state governing equations for the model were solved for flow and temperature within the computational domain in the Icepak.

• The maximum temperature within the computational domain is 31.247 deg.C.
• The maximum air velocity within the computational domain is 0.238 m/s.