Passive thermal management programmes to promote the development of medical electronics equipment (1)

Device from the imaging to the surgical instruments to auto-immune, twenty-first century powerful medical technology for impressive, in large part thanks to the microprocessor capable of improvement.

However, for thermal engineers, these advances also have paid the corresponding price. Equipment of power, the greater its calorific value greater means and overall, but also in smaller space for thermal (because the device volume becomes smaller). With our medical equipment for precision and reliability of increasingly demanding, thermal control becomes more important.

Another challenge stems from the medical device which involve high risk and there are some specific requirements of this fact.

For example, to some of the material and human intimacy, thermal solution of some common materials (e.g. copper) in many medical applications cannot use (copper in addition to causing human tissue inflammation, it can cause serious, irreversible nervous tissue degradation). Some medical applications for accuracy, may be used for cooling solution space compression to almost disappear anymore — some surgical instruments need to be heat emission management to avoid causing damage to body tissues, but they only designers 0.5 mm heat transfer technology for deployment.

Another call for ultra-small thermal management programme areas are human implantable device design, Implantable devices that require small size also requires a precise temperature coefficient (∆ T °), in order to protect human organs.

Finally, do cyclical temperature quickly (within a few milliseconds temperature fluctuation range up to 50 ° c) are many laboratory equipment (such as DNA splicer) common characteristics.

All of these and the accuracy, reliability, size limitations and strict material choice related factors make medical thermal engineering on designers, has become a difficult thing.

Thermal design engineers must be efficiency and size Vs cost trade-off between, and increasingly in thermal performance Vs low noise made a choice between (this means that although the fan airflow for high volume so that it has the best thermal performance, but in some applications cannot use the fan).

Heat transfer

Thermal engineers are increasingly turning to passive heat transfer device (e.g., heat pipe) to address these challenges.

Because of the heat pipe of liquid liquid and steam two existing forms, heat pipe for two-phase cooling devices. Working liquid from liquid to vapor change for heat transfer. Duct work liquid after evaporation, transfer (thermal), condensation and cooling after the working fluid being sent back to evaporation area this continuous cycle. In this work process does not have shipping parts fail---in which reliability is extremely important to obtain accurate results or achieving patient rehabilitation applications, this is a core consideration. A passive heat transfer component design simple and straightforward, generally involve a note with working fluid, relatively easy to do miniature vacuum seal. Progressive capillary structure technology helps ensure that have cooling and condensation of a working fluid can resist gravity, it effectively and reliably back heat pipe heat input section. This makes the heat pipe can work in a different direction. More design freedom, designers can use flexible duct.

Another of the more popular thermal programmes is the heat sink.

Heatsink can work in forced or natural convection. But equally, either programmes are meant to make a choice. If you increase the air for cooling, this means that you can reduce the number of fin or reduce cooling fins of the area. However, if you have, the greater the airflow fan, its noise is also bigger; if the airflow fan, fan run quieter and size can be smaller, but this also means that the heatsink must have more or larger fin. Therefore, in the same device to allow cooling components at the same time make it smaller and quieter is not easy.

In the heat pipe heat exchanger, heat conduction through the duct to a fin, and then distributed to the surrounding air.

But also can do it.

At the same time reduce the size and reduce noise is to let radiator more isothermal. Before you can use a single thermoelectric cooler (TEC) cooling heatsink redesign, use multiple TEC, through the heat sink surface heat evenly, no longer purely relying on heat conduction to heat transfer. However, such programmes in addition to the need for maintenance, but also increased the complexity and cost of electronic components.

Rack duct components can provide good thermal stability and technical maintenance workload.