Analysis of a Cold-Plate Model with Non-Conformal Meshing using Ansys Icepak
Objective:
To perform the analysis for a two heated plates model, cooled by water circulating inside the cold-plate cavity, as well as by air driven by natural convection externally. And separately meshed assemblies will be employed to reduce the overall mesh count in the domain.
Introduction:
A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in
- Space heating
- Refrigeration
- Air conditioning
- Power stations
- chemical plants
- Petrochemical plants
- Petroleum refineries
- Natural gas processing
- sewage treatment.
The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Another example is the heat sink, which is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant.
Geometry creation:
Cabinet:
First, we need to create the cabinet with the dimension 400 mm X 300 mm X 200 mm and the cabinet as an enclosure for the total geometry
Cold plate solid block:
The cold plate solid block was created accordingly as per the given dimensions in the challenge with a start point (50 mm, 80mm, 70 mm), Endpoint(350mm, 220 mm, 130 mm) made of aluminum extruded. and the two pipes were created for the pass of the fluid domain into the cold plate and the dimensions are as follow
Incoming pipe: thickness : 5mm, connected @ (100mm, 0 mm, 100mm) and radius 15 mm, the inlet water velocity is 0.2 m/s
Outgoing pipe: thickness : 5mm, connected @ (300mm, 0 mm, 100mm) and radius 15 mm
Cold plate fluid block:
The cold plate Fluid block was created accordingly as per the given dimensions in the challenge with a start point (60 mm 90mm, 80 mm), Endpoint (340mm, 210 mm, 120mm)
Plates:
The cold plate solid block was created accordingly as per the given dimensions in the challenge with a start point
Plate 1: conducting thick 10mm, 200W, located at 60mm having dim (260 mm X 100 mm) in Z plane
Plate 2: conducting thick 10mm, 200W, located at 130mm having dim (260 mm X 100 mm) in Z plane
Cabinet opening:
Openings at the liquid inflow and outflow regions of the cold-plate are MinX and Max X
Final geometry:
We finally end up with the geometry as shown below after total set up.
Generate the Mesh:
Create a non-conformal mesh assembly:
we have generated the non-conformal mesh without the slack values then we can see the number of the elements was 23360 and the no of the nodes is 26772.
Use mesh separately option with slack values:
The bounding box of the assembly is larger than the original assembly by 0.01 m on five sides. The slack value for the min Y side of the assembly is set to be 0 m since the min Y side of the assembly is at the bottom surface of the cabinet.
To create a separate meshed assembly, highlight all the objects in the model tree other than the cabinet, opening.3, and opening.4.To enable separate meshing for the assembly, double-click on assembly.1 to edit the assembly. Under the Meshing tab, toggle on the Mesh separately button and then enter the slack values as follows
Use object parameters:
we have used the object parameters option for the required count as shown below.
Click Accept “change value\" checks in the Mesh control panel and click on Generate mesh to mesh the model. Visualize the mesh at plane cuts and surface displays.
Generate mesh:
The mesh generation on the total solid domain in the geometry.
The mesh generation on the total fluid domain in the geometry.
After using the slack values we can see an improvement in the mesh elements to 27528 and the number of nodes is 31038.
The final mesh generation for the total domain including the solid and fluid together and the cut plane was in the z-axis with mesh elements to 27528 and the number of nodes is 31038.
Numerical setting:
Use problem set up wizard:
A software wizard or setup assistant is a user interface type that presents a user with a sequence of dialog boxes that lead the user through a series of well-defined steps. Tasks that are complex, infrequently performed or unfamiliar may be easier to perform using a wizard.
set no of iterations and convergence criteria:
The total number of iteration was set to be 300 iterations and coming to the convergence criteria the flow was set to 0.00001 and joule heating, the energy was 1e-15, and the turbulent kinetic energy and turbulent dissipation rate were 0.001
Advanced solver setup:
In applied mathematics, discretization is the process of transferring continuous functions, models, variables, and equations into discrete counterparts. This process is usually carried out as a first step toward making them suitable for numerical evaluation and implementation on digital computers.
Select the Basic settings panel from the Solution settings branch of the tree and set the number of iterations to 300. Go to Advanced settings and specify Under-relaxation factors for Pressure, Momentum, and Temperature as 0.3, 0.7, and 1.0, respectively. Select Double for the Precision drop-down list. The recommended basic settings and advanced solver setup for this model are shown above.
Solve for Flow and Temperature and Radiation is off. The turbulence model is the Zero equation model:
Basic parameters and choose the Zero equation turbulence model for the flow regime in the General setup tab.
The heat-transfer due to the radiation was Ignore for this simulation. The radiation parameter was also disapplied.
Set up the gravity vector:
Gravity acts in the negative x-direction in this problem. To set up the effects of gravity, toggle on the Gravity vector in the General setup tab. Enter the new values for the gravity vector as x = -9.80665, y = 0 and z =0. Now go to the Transient setup tab and set an initial velocity X velocity = 0.005 m/s in the x-direction.
Accept all other defaults in the Basic parameters panel. These are shown in the Figure above.
Setup transient simulation with an initial velocity of 0.005 m/s in antigravity direction.
We have set an initial velocity of 0.005 m/s in the x-direction for the antigravity in the transient setup.
Set up monitor points in the model:
Add four monitor points to the Points folder, the four monitor temperatures are at the center of the opening.1 (outlet opening) opening-4 (Outlet), and at the center of block.2 and plate.2
Save the model:
ANSYS Icepak will save the model for you automatically before it starts the calculation, but it is a good idea to save the model (including the mesh) as well. If we exit ANSYS Icepak before you start the calculation, we will be able to open the job that we saved and continue with our analysis. If we start the calculation in the current ANSYS Icepak session, ANSYS Icepak will simply overwrite your job file when it saves the model.
Solve the model:
There are no universal metrics for judging convergence, a good indicator is when the solution no longer changes with more iterations, and when the residuals have decreased to a certain degree. The default criterion is that each residual will be reduced to a value of less than 10^-3 except the energy residual, for which the default criterion is 10^-7. It is a good idea to judge convergence not only by examining residuals levels but also by monitoring relevant integrated quantities.
ANSYS Icepak will begin to calculate a solution for the model, and a separate window will open where the solver will print the numerical values of the residuals. ANSYS Icepak will also open the Solution residuals graphics display and control window, where it will display the convergence history for the calculation.
Examine and post-process the results:
Residual plot:
Select the Basic settings panel from the Solution settings branch of the tree and set the number of iterations to 300. Go to Advanced settings and specify Under-relaxation factors for Pressure, Momentum, and Temperature as 0.3, 0.7, and 1.0, respectively. Select Double for the Precision drop-down list.
From the residual plot provided above it is clear that the simulation has reached the converged stage and also obtained the convergence, and they are no fluctuations in the plot.
Temperature monitoring points:
The four monitor points to the Points folder, the four monitor temperatures are at the center of the opening.1 (outlet opening) opening-4 (Outlet), and at the center of block.2 and plate.2.From the above graph, it clearly shows that the obtained temperatures for the inlet temperature for the cabinet were at 25°C and the outlet temperature for the cabinet was at 20°C. The block-2 temperature was at 23°C and the plate-2 temperature was at 35°C
Plane cut:
The cut plane was created for the cold plate model and the axis for the cut-plane used was the Z plane through the center.
Pressure contour representation for the cut-plane:
For the cut plane representation, we have shown the pressure contour on the z plane for the model.
Vector plot:
The Vector plot was set to the z plane through the plane and it is clearly seen that the inlet velocity for the opening was at the initial value of 0.02m/sec and a maximum velocity was at the value of 0.23m/sec was obtained in the domain and the velocity inside the sidewall domain was nearly at 0.145m/sec.
Animation for the Velocity Vector profile on the Cut plane in the z-axis:
The vector animation which represents the flow of the velocity magnitude over the cold plate model surface was shown in the above animation.
Temperature contour:
The Temperature Contour was set to position accordingly to the z plane through the plane and it is clearly seen that the inlet temperature for the opening was at the 20°C and a maximum temperature of 33.5°C was obtained in the domain and the temperature inside the solid domain was nearly at 30°C.
Animation for the Temperature profile on the Cut plane in the z-axis:
The Temperature animation which represents the temperature magnitude over the cold plate model surface was shown in the above animation.
Velocity contour:
The Velocity Contour was set to position accordingly to the z plane through the plane and it is clearly seen that the inlet velocity for the opening was at the initial value of 0.02m/sec and a maximum velocity was at the value of 0.23m/sec was obtained in the domain and the velocity inside the sidewall domain was nearly at 0.145m/sec.
Animation for the Velocity profile on the Cut plane in the z-axis:
The velocity animation which represents the velocity magnitude over the cold plate model surface was shown in the above animation.
Object face:
An object-face view allows you to examine the distribution of a solution variable on one or more faces of an object in the model. To generate an object-face view, you must select the object and specify both the variable to be displayed (e.g., temperature, Velocity, Pressure) and the attributes of the view (e.g., shading type).
Object face to display temperature contour on overall Cold-Plate Model:
The overall temperature distribution throughout the cold-plate model was shown in the above Figure.
Object face to display velocity contour on overall Cold-Plate Model:
The overall Pressure distribution throughout the cold-plate model was shown in the above Figure.
Conclusion:
We have successfully performed the analysis for a two heated plates model, cooled by water circulating inside the cold-plate cavity, as well as by air driven by natural convection externally. And separately meshed assemblies will be employed to reduce the overall mesh count in the domain.
Parameters like temperature, pressure, and velocity were plotted. And monitor points were considered at the plates and blocks, inflow, outflow boundary conditions to obtain the temperature that has generated in the model.