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Home > News > Industry News > How to keep your cool with hig.....

How to keep your cool with high-rel thermal management

  • Author:Ella Cai
  • Release on:2017-06-29
Efficient thermal management is the key to successful, ‘bullet-proof’ high-reliability design, writes Tom Gregory of 6SigmaET.

The aerospace sector places some uniquely challenging demands on electronics designers – even compared to other applications where reliability is the key priority. 

For a start, the environments that the electronics are exposed to are much harsher than in almost every other scenario. Moreover, the life expectancy of the products is much higher, while the accepted failure rate is easily an order of magnitude lower than typical commercial products. 

In fact, the need for bullet-proof reliability is absolutely critical and cannot be overstated. With aerospace products, in defence applications particularly, there are no simple recalls or RMA processes. 

You cannot “reboot your system to clear issues” on a missile guidance system in the middle of a mission. Product failures always have catastrophic consequences far beyond the loss of market share that might result from a problem with a consumer electronics device. 

When you combine the demand for extremely high reliability with the constant need for higher power and smaller footprints, the result is that thermal design takes on extra importance compared to other industries. 

High reliability aerospace products are high power-density, tightly packed, highly engineered devices which are exposed to very harsh environments. At the same time, designers must find clever ways of dissipating heat away from critical components to make sure the electronics meet the extremely stringent reliability requirements. 

Simply put, when it comes to ensuring high reliability, thermal design and heat removal are the most critical aspects of aerospace electronics design. So designers need the tools to deal with these challenges in the most efficient way possible without sacrificing performance or size in the final products. 

Case study: TEN Tech
The work of TEN Tech, a provider of design and analysis support for embedded high reliability defence and aerospace electronics systems, is an example of the extreme pressures facing aerospace designers when it comes to thermal design and the value of simulation in overcoming design challenges. 

The company needed to design a liquid-cooled airborne radar processing chassis. This was a very high-powered, high ambient temperature design needing a high level of reliability, and had no cooling mechanism other than the liquid cooling loop. Indeed, thermal design was the main driver of the system. A little under 3kW had to be dissipated out to the (already hot) environment for the electronics to be able to function reliably. 

The cold-plate 
The cold-plate
So TEN Tech’s engineers used 6SigmaET – a dedicated thermal simulation tool – throughout the design process. They started with the redesign of one of the cold-plates, as the initial cold-plate design would not have provided enough cooling to be highly reliable in an aerospace environment. The design also had to account for pressure-drop requirements. 

Thermal/computational fluid dynamics (CFD) analysis using the software enabled engineers to understand the flow and focus of the design to maximise cooling and minimise pressure-drop. They were able to quickly create a multi-fluid model of the cold-plate involving free convection and liquid cooling, and to optimise the cooling channels to obtain a good compromise between heat dissipation and pressure-drop through the cold-plate. 

They then moved on to the liquid cooling of the system. This larger chassis included over 25 high-power single board computers (SBCs) and five cold plates of various complexity. TEN Tech had to ensure that the entire chassis was properly cooled, the liquid loop would function correctly and each of the SBCs would be within its temperature requirements. This was a big model, with the added complexity of being multi-fluid with liquid cooling cavities, and in total encompassed around 40 million simulation grid cells. 

By using a dedicated thermal simulation tool the engineers were able to shorten solve-times by 50% compared to general purpose CFD tools. This also meant that they were able to easily simulate several different mission scenarios, corresponding to different altitude, ambient temperature and liquid cooling pump inlet temperature and pressure permutations. 

A design was delivered in a little over three weeks – well under the six week estimate – with more information provided to improve the design for high reliability. 

No short-cuts
Where the demands for reliability and performance are high there is simply no way to short-cut the design process – designers need the right tools for the job if they are to complete projects efficiently, accurately and safely.