Cool ways to confront thermal issues
When nonengineers hear that you're "in electronics," they often assume you simply design circuits, or just do software. They fail to realize the multidisciplinary skills it takes to put a real project together, whether it's for a cell phone or an industrial control system. Yet almost every real design calls on other specialties, such as thermal and mechanical engineering, to be reliable.
A good engineer can, at the very least, work across these disciplines simultaneously, even if not expert in them. Even in this day of superspecialization, the ability to integrate those other areas is critical to a product design that balances conflicting marketing objectives and consequent engineering trade-offs. For example, perhaps incurring the cost of a fan will allow use of more suitable components that, unfortunately, dissipate more heat.
Of course, each of these nonelectronics areas has its own culture, tools and techniques. For thermal management, we have heat sinks to draw heat away from the source component, as a starting effort. The heat sink can have passive convection cooling or active forced-air cooling, usually with a fan. Minimizing the power consumed by the fan then ripples back as an electronics challenge.
Plates and pipes
But why stop with just a sink, when you can go for the plate? Using a cold plate--a metal plate with internal channels--water or other working fluid flows through to conduct heat away more effectively than convection airflow can via the heat sink. Then there are heat pipes, simple yet clever passive devices that conduct heat away from its source very effectively (but do not dissipate it). As a vivid science demo for lower-grade students, I take a heat pipe and an equivalent-size metal rod, stick both in a hot cup of coffee and let students feel how fast the dry, cool end of the pipe gets hot, compared with the plain rod.
The thermal challenge intensifies when IC vendors put thermal slugs under the package to conduct heat from the die. That seems simple, but it turns their problem of a hot IC into your problem of having enough surrounding pc-board area, and with good airflow, to act as a heat spreader. The layout challenge intensifies when each such IC in a tightly packed group demands several square inches of pc board for its own dissipation.
When all else fails, try a vortex tube chiller, which operates entirely from a high-pressure air stream. These specially shaped, tornado-like cylinders produce a stream of cold air without moving parts, electricity or refrigerant. They're a clever application of the laws of thermodynamics and conservation of energy.
Bill Schweber (bschweber@cmp.com) is the editor of sister publication PlanetAnalog.com, an online resource of design, news and product information.
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