2011

Thermal Management Solutions for Medical Applications

Thermoelectric Assemblies (TEAs) offer precise temperature control for applications with tight space constraints and low weight requirements.

Thermal management of medical electronic devices and systems is now more challenging. Power densities continue to increase while product form factors continue to shrink. Simple thermal management solutions, such as passive cooling (adding a fan and heat sink), are no longer typically viable to meet required performance and reliability specifications. In today’s complex medical operating environment, Thermo electric Assemblies (TEAs) are necessary to provide precise temperature control via cooling and heating in a variety of modular platforms.

TEAs combine special benefits that make them an effective solution for many medical thermal management applications by offering greater performance, higher reliability, and low cost of ownership. Their advanced capabilities are aided by new material technologies, thinner profiles, and automated assembly. A wide range of small- and medium-sized heat pumping units handle most applications, including temperature regulation of samples and stabilization of sensitive instruments with the use of temperature controllers.

Medical devices require strict temperature control; TEAs offer precise temperature control with tolerances of ±0.1 °C under steady-state conditions. DC operation with reverse polarity allows heating and cooling in thermal cycling applications, as well as rapid cooldown to below ambient temperature.

Most medical applications have tight space constraints and low weight requirements. The units have fewer components and run on solid-state operation that yields high reliability and minimizes downtime of the medical device over its product lifecycle.

TEAs are suitable for electrophoresis applications due to the ability to easily adjust temperature to either above or below ambient. This cannot be accomplished by any other means without a complex heating and cooling system. Other advantages include high reliability, maintenance-free operation, and compact size.

Optics used in laser systems can obtain peak performance by stabilizing temperature at or below ambient. TEAs dissipate heat generated by a CO2 or YAG laser that ranges from 15 to 100 Watts. They can maintain the temperature of the laser system to within ±0.5 °C, while the ambient condition may fluctuate from 20–32 °C.

TEAs maintain the control temperature of a reagent tub used in clinical diagnostic systems to 4–6 °C from an ambient temperature that can fluctuate from 23–30 °C. Heat load cooling requirements can range from 30–150 Watts. TEAs are used due to tight geometric space constraints, low cost of ownership through solid-state construction, and DC operation.

Digital radiography uses imaging systems with detector heads. TEAs cool the thermal output of the detector head to keep the temperature stable, while environmental temperature can range from 20–38 °C. This allows the detector to capture an image with very high resolution. TEAs also dramatically reduce the cooling noise vs. compressor-based systems.

Detectors used in MRIs obtain high-resolution images by controlling the temperature to a specific point, while the ambient temperature may fluctuate from 15–38 °C. TEAs are used in a closed-loop system with feedback to the temperature controller, removing 30 to 50 Watts of heat at the source. They maintain the temperature of the detector to within ±0.25 °C under steady-state conditions or offset control temperature from an ambient set point.

In medical centrifuges, TEMs maintain the control temperature of the centrifuge tub to below 0 °C from an ambient temperature up to 32 °C. Heat load cooling requirements can range from 30–150 Watts.

Given the need for seamless mobility in a healthcare environment and battery requirements that need to last an entire 12- hour shift, TEMs allow portable medical cockpits to keep cool while meeting compact size constraints, low power consumption requirements, and low heat load.

Heat Dissipation

TEAs use thermoelectric modules (TEMs) to dissipate heat. TEMs are solidstate heat pumps that require a heat exchanger to dissipate heat utilizing the Peltier effect. During operation, DC current flows through the TEMs and creates heat transfer and a temperature differential across the ceramic surfaces. Thus, one side of the TEM will be cold, while the other side is hot. A single-stage TEM can achieve temperature differentials of up to 70 °C and can transfer heat at a rate of up to 150 Watts. In order to increase the amount of heat pumping capacity, the TEM’s modular design allows for the use of multiple TEMs mounted side-byside, which is called a TE Array.

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