'Heat Sink - Conjugate Heat Transfer' simulation project by sjesu_rajendra


#1

I created a new simulation project called 'Heat Sink - Conjugate Heat Transfer':

CHT simulation of heat sink with temperature source


More of my public projects can be found here.


#2

Description


 
Sizeable advancements in electronics have caused them to consume more power as well as heat up to a greater extent. As a result, cooling has become an integral part of electronics design. Oftentimes, heat sinks are used for this purpose. Fundamentally, a heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium. This fluid is usually air or a liquid coolant that carries away heat radiated by the device, thereby regulating the temperature of the device.[1]
 
In practice, a heat sink is designed such that it can dissipate the maximum amount of heat. This can be done by increasing the surface area of the heat sink that is in contact with the air. For the choice of material, it would be best to employ a material that has a high thermal conductivity. A finite element simulation with numerical results would give us a better idea of the performance of different designs and materials.
 

Project Goals


 
With the help of the SimScale platform, we intend to simulate the heat flow from a heat sink to the surrounding cooling fluid. This study would not only give us a deeper insight into the heat transfer mechanism but also would help suggest possible modifications to be made in the heat sink design. The materials selected for this project are:
 

  1. Heat sink: Aluminum
  2. Cooling fluid: Air
     
    Additionally, we will use the CHT (Conjugate Heat Transfer) method for this simulation. CHT allows the simulation of the heat transfer between Solid and Fluid domains by exchanging thermal energy at the interfaces between them. Moreover, this analysis type eliminates the need for the heat transfer coefficient. The typical applications of CHT include simulating heat exchangers, cooling of electronic equipment, and general-purpose heating/cooling systems.
     

Geometry


 
A CHT simulation requires the presence of different geometric solid volumes. In this case, we have 3 - 1 heat source, 1 heat sink and 1 fluid region. These 3 solid volumes should be non-overlapping, with the boundaries in contact in order to set up an interface. The original CAD was provided by @ACH_Likey, which is shown in the image below:
 


 
3 solid volumes
 

 
Isometric view of entire geometry
 

 
Geometry of heat sink (Aluminum)
 

Meshes


 
For the current project, a multi-region mesh is generated. This Hex-dominant Parametric (only CFD) Mesh is mapped onto the entire geometry with 16 computing cores.
 
To capture the heat transfer to the air more accurately, a mesh refinement is made on the entire surface area of the heat sink. The following images depict the mesh of the fluid region (air) and heat sink (aluminium) respectively:
 


 
Meshed geometry
 

 
Internal view of meshed geometry
 

 
Mesh refinement on heat sink
 
 

Simulations


 
A steady-state simulation with an Analysis Type of Conjugate Heat Transfer and a Turbulence model of Laminar is executed.
 
The heat sink is assigned as Aluminium and the cooling fluid is assigned as Air. The boundary conditions are assigned as:

  1. Inlet: Velocity inlet with constant volumetric flow rate
  2. Outlet: Pressure outlet at atmospheric pressure
  3. Zero Gradient: All other surfaces as assigned as zero-gradient walls
  4. Heat Walls: Bottom wall given a constant temperature, acting as heat source to the sink

All the faces faces of the geometry belong to at least one of the previously stated conditions.
 
With 32 Computing Cores, the simulation is run and takes a total of approximately 150 minutes.
 

Results and Conclusions


 
The following images show the temperature contours across the cross-section of the fluid region and the solid domain.
 


 
Temperature contour of solid domain
 
As can be seen in the image above, the fins in the vicinity of the heat wall are hotter than the ones surrounding them. This is due to direct conduction from the heat wall.
 

 
Temperature contour - Cross-section of fluid region
 
From the image, it can be observed that the heat is tranferred from the fins of the sink to the air passing through it. If you notice the temperature scale closely, you may conclude that cold air approaches the heat sink, gets heated and carries away an amount of heat from the sink, which is later dissipated.


#3

Impressive work. A nice work well done!


#4

Dear Rajendra,

First of all, thank you for the impressive work. It is a very nice project.

I was going through your projects to study details for simulation setups. I noticed that in this project, heat transfer coefficient is not specified. I thought for convective projects, heat transfer coefficient should be defined since Q = hAdeltaT. Did I understand in correctly? In addition, I noticed that this is a forced convective problem. If I am trying to solve a problem for natural convection, is it okay if I don’t define heat transfer coefficient? I kept finding articles saying that for natural convection, h should be 5.5 w/m*K. I am confused on if I need this parameter for conjugate heat transfer problem or not.

Hope you could help to answer my question.

Thanks!

Che


#5

Hello Che (@cwo5035 ),

By heat transfer co-efficient, do you refer to the the ones between solid and fluid regions? This is automatically taken up by the solver depending on the type of solid/fluid materials in contact and the velocity of fluid flow. Only for external heat transfer where the solid faces don’t have any fluid region in contact (as per the CAD model definition), a heat transfer coefficient needs to be defined.

I hope this answers your query!

Best,
Sam