2012

New Thermal Management Strategies for Medical Devices

Vapor Chambers

altVapor Chambers are a subset of heat pipes that spread heat in two dimensions rather than one. More specifically, vapor chambers are planar heat pipes that spread heat from concentrated heat source(s) to a large area heat sink with effective thermal conductivities greatly exceed ing copper. In the most basic configuration, as seen in Fig. 3, the vapor chamber consists of a sealed container, a wick formed on the inside wall of the container, and a small amount of fluid that is in equilibrium with its own vapor. As the heat is applied to one side of the vapor chamber (evaporator), the working fluid vaporizes and the vapor spreads to the entire inner volume and condenses over a much larger surface (condenser). The condensate is returned to the evaporator via capillary forces developed in the wick. Vapor chamber are capable of handling higher heat fluxes (300–500 W/cm2), and are used to transport heat away from high-powered chips and lasers. Another important feature of vapor chambers is that the low flux (condenser) region provides an essentially isothermal surface. This provides an ideal surface to attach heat sinks, because it enables maximum fin efficiency. A view of the key vapor chamber elements can be seen in Fig. 4. Vapor chambers can be used to increase throughput in Polymerase Chain Replicator (PCR) machines. In this process, DNA is replicated through a series of enzymatic reactions. PCRs require fast and precise thermal cycling. Throughput is governed by the rate of uniform temperature change across the device platform. In this application, thermoelectrics are often used to drive the temperature to the set points, typically from 50–95 °C. Vapor chambers can help improve performance by delivering a faster and more uniform thermal response in comparison to conventional metal blocks. Weight optimized vapor chambers can reduce the thermal mass of the sample holder, which also promotes higher cycling rates.

Summary

altAs medical devices become more powerful and compact, thermal management solutions must evolve to ensure optimum performance. Traditional cooling methods such as heat sinks, fans, and pumped liquid cooling systems require augmentation to meet increasingly challenging thermal requirements. Heat pipes and vapor chambers are effective technologies that will play a more frequent role in future medical device thermal management system solutions.

This technology was done by Advanced Cooling Technologies, Lancaster, PA. For more information about thermal technologies for medical applications, visit http://info.hotims.com/40432-165.