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Flow simulation evaluates cooling methods
 
 

He doesn't need much thinking to answer the question.

 

- It's heat dissipation that's the bigger challenge when it comes to my responsibilities in our embedded projects, says Guido Kats, Mechanical Engineer at Hectronic.

 
He uses SolidWorks Flow Simulation, integrated in the 3D CAD environment, to simulate air flow, temperatures and hot spots. But the actual design is always based on personal experiences.

- The simulation tool is important, for sure. It enables us to show to customers that the concept we are offering is working.
 

Step 1 - Creating a model

The result from the simulation indicates if the cooling of the design is sufficient based on a model. The shape and material of the enclosure, the size of inlets and outlets and consumption and placement of and heat dissipating components are all input to the model.

 

Too many details and the computer is overloaded by massive calculations. Not enough details and the result will be inaccurated or even incorrect. The picture shows components and their respective power consumptions placed in the model of the system in question.

 
Heat sources in the model

Click to enlarge the picture

 

VS: Volume Source. Objects emitting heat from a solid body in all directions.
SS: Surface Source. Objects emitting heat from a  surface.

 

Step 2 - Performing the simulation

The picture shows a section of the system with temperature regions, gradients and hot spots. Some of the components reach the maximum allowed temperature of the system, nearly 90°C. The specifications are consulted to evaluate the temperature of the components individually. In this case a DC/DC converter for the LED LCD exceeded its upper temperature limit of +85°C suggesting that the design needed modifications.

 
Simulation indicating heat problems
 

Step 3 - Design modifications to solve the heat problem

In general, gap pads on critical components may be sufficient cooling for embedded systems in the low power segment, around 5W, even though the enclosure is closed.

 

- If there's some kind of air flow inside the box it may be good enough to take the heat away.

 

If not, as in this case, there are a handful of additional heat dissipation methods: Heat dissipation through a metallic enclosure, heat sinks on components or on the exterior of the box, heat pipes for heat distribution, inlets and outlets in the enclosure to increase the air flow or a fan.

 

Cooling with a fan is sometimes necessary, for example to design a powerful and yet compact system, but there are drawbacks.

 

- It makes noise. It can break down. Airflow comes out and dirty air is forced into the enclosure.

 

The suggested alteration in the example was to introduce holes in the cover. That would enable air to flow in through the bottom of the enclosure, through the interior and electronics and out on the upper side distributing heat for increased cooling.

 
Inlets and outlets for natural convection
 

Step 4 - Simulation to show the effect

The picture below shows the result from the simulation to evaluate heat dissipation after the modifications have been made. 

 
Simulation showing reduced heat
 

The result from the second simulation shows a temperature decrease of approximately 10°C on one the critical components, the DC/DC converter. Thus the design modification proved sufficient to solve the problem.

 

This was a brief example from the work of Mechanical Engineer Guido Kats involving heat dissipation issues. Other duties involve for example EMC protection, protection against solid foreign objects or water (IP-classification), shock and vibration, but that's another story.

 

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