A sinking feeling?

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There has been recent speculation as to whether the engineered heat sink has had its day. Nic Smith, head of sales and marketing at PSL Assemblies Ltd, takes a closer look into the future of the technology and explores whether there is any weight behind these claims. 

A few months ago, I attended an industry conference which included several presentations on the subject of thermal management in power electronics. In my desperate bid to stay up-to-date with the often bewildering advances in technology and power innovations, I do try to attend as many of these lectures as possible – but sadly some of these presentations are, at their very best, somewhat less than entertaining. 

Seasoned technical directors and graduate design engineers alike are coerced into preparing a technical presentation, and soon they find themselves in front of an audience, laser pointer in hand, and expected to inform and educate a room containing potential buyers, salespeople and other hitherto industry experts. 

As a time-served salesman, I have prepared many similar PowerPoint creations, and over several years I have learned to enjoy my time on stage – trying everything possible to keep the presentation light-hearted and interesting, but at the same time keeping the audience absorbed in the product information with the ultimate aim of winning new clients and selling more product.

At the thermal management conference mentioned earlier, only one of the presentations held my interest for more than a few minutes – in actual fact I was spellbound and bewitched by the subject matter and the speaker’s narrative. Indeed, it was the opening line that first arrested my attention – “The engineered heatsink is dead!”

Of course, as a sales manager for a thermal management company which specialises in engineered heatsinks for power electronics, this statement was definitely not what I wanted to hear! The entire lecture also focused on topics such as reducing footprint, reducing weight, recycling dissipated energy and low carbon initiatives. As much as the opening phrase was somewhat alarming, the University Professor delivering the presentation did eventually confess that a heatsink-free world may indeed never happen – but he insisted that we do need to find ways to reduce our use of aluminium profiles and copper tubing – thus challenging electronic engineers to eliminate large heatsinks and cooling plates from their new designs. 

In consumer electronics, for the last few decades, small is best. Except if you are a marketeer in the mobile phone industry – then you can convince your target audience that either small is best or bigger is better – depending on the current trend and your marketing budget. 

Indeed, in power electronics, reducing physical size and weight from electric road vehicles and electric trains is essential if we are to improve on energy efficiency. But, it’s not always about efficiency – we still have a desire for increased speed (HS2 for example), and there is always a need for more power in the grid. We know that there are simply not enough sources of electrical power in the grid at the moment, and our scientists are desperately trying to build energy-efficient power stations and minimum-emission energy generators before the need for electric vehicles ultimately overtakes the availability of electricity. 

When trains are designed to travel faster, equally the traction electronics have to be designed to generate massive increases in power, but in a controlled and energy-efficient manner. Similarly, our hospitals, hotels and commercial buildings are becoming more energy efficient but at the same time needing more power, more efficiency, more reliability. 

Batteries are becoming more efficient, but it will be quite some time before genuine miniaturisation of batteries is achieved. Even the most efficient of industrial batteries for high power lasers, electric buses, hybrid and battery-powered trains etc, all generate huge amounts of heat – and we all know that hot electronics are inefficient electronics, and over-heated electronics are extremely dangerous to say the least.

We were asked some years ago to help design a 3,000A static-transfer switch with a brief to minimise the weight and physical footprint. By simply changing the design from a heavy extruded-profile heatsink to a much lighter bonded-fin heatsink we created a much larger surface area to allow for increased heat dissipation. 

Shortly afterwards, our client decided that a 6,000A switch was needed, but again without any allowance for a larger footprint or weight heavier than the original 3,000A unit. The challenge was always the heat dissipation – we could manufacture any design of switch, with any size of thyristor, and we had our own innovative clamping solution – but to double the rating of a static transfer switch in the same footprint at first appeared impossible. 

Sometimes, energy efficiency does not require innovative solutions, and that basic physics combined with over 40 years of experience in thermal management can produce an equally effective energy-efficient answer. Although we do not manufacture heat-exchangers, we do use manipulated tubes (heat pipes) in our cooling plate designs and by the use of an appropriate fluid we can determine the point of evaporation and condensing points that would give us the additional thermal capacity to accommodate the increase in the losses. This simple use of physics sufficiently improved the cooling of the 6,000A unit, and this design continues to be supplied to our client – a global manufacturer of high-quality whole-building UPS systems.

As batteries for electric vehicles become more efficient, the desire for battery power inevitably meets with the challenges of weight and footprint. It is ironic that some of the EV industry is actually looking backwards, not forwards, incorporating thin lightweight aluminium cooling plates with pressed-in recesses instead of cooling pipes – somewhat similar to the cooling pipe configuration on the back of old domestic refrigerators. 

Our clients are interested in high power, high efficiency and maximum safety – they supply innovative and highly technical equipment for trains, laser and welding machines, electric buses and coaches, and critical back-up power UPS systems. They will continue to design energy efficiency into their power electronic equipment, and they acknowledge the constant limitations on weight and footprint. But, our clients also continue to incorporate heavy-duty engineered heatsinks and liquid-cooled plates into their designs, and we are therefore quite sure (hopefully at least for many more years into the future) that thermal management and engineered heatsinks for power electronics are definitely not dead!