From imaging equipment to surgical instruments to autoimmune, the powerful medical technology of the 21st century is impressive, thanks in large part to the increased computing power of microprocessors. However, for the cooling engineers, these advances have also paid a corresponding price. The greater the power of the device, the greater the heat it generates, and in general, the heat dissipation in smaller and smaller spaces (because the size of the device becomes smaller and smaller). As we become more demanding on the accuracy and reliability of medical devices, thermal control becomes even more important. Another challenge stems from the fact that medical devices have certain special requirements due to high risks. For example, because of the intimacy of some materials and the human body, some common materials in thermal solutions (eg, copper) cannot be used in many medical applications (in addition to causing inflammation of human tissue, copper can cause serious problems). , irreversible neuronal degeneration). Some medical applications may compress the space used for the cooling solution to the point of almost disappearing due to the need for precision—some surgical instruments require heat management to avoid damage to human tissue, but they are only designs. Personnel provide a 0.5 mm position to deploy heat transfer technology. Another area that requires ultra-small thermal management solutions is the design of implantable devices. Smaller implants require a small temperature coefficient of variation (?T°) to protect human organs. Finally, rapid temperature changes (with temperature fluctuations up to 50 °C in a few milliseconds) are common features of many laboratory equipment such as DNA splicers. All of these factors related to accuracy, reliability, size constraints, and rigorous material selection make medical thermal engineering design a difficult task for designers. Heat transfer design engineers must make trade-offs between efficiency and size Vs cost, and increasingly trade off between heat dissipation performance and low noise (which means that the fan's high volumetric airflow makes it optimal. Thermal performance, but in some applications you can't use a fan). Heat transfer Thermal engineers have increasingly turned to passive heat transfer devices (eg, heat pipes) to address these challenges. Because the working fluid in the heat pipe has two forms of liquid and water vapor, the heat pipe is a two-phase cooling device. The transfer of working fluid from liquid to water vapor enables heat transfer. The working fluid in the heat pipe is sent to the evaporation zone for a continuous period of evaporation, transfer (heat), condensation and condensation. There is no transmission component failure during this work – this is a core consideration in applications where reliability is extremely important to achieve accurate results or to achieve patient recovery. The design of the passive heat transfer assembly is simple and straightforward, and generally involves a vacuum sealed tube that is filled with a working fluid and is relatively easy to miniaturize. The ever-increasing capillary structure technology helps ensure that the cooled and condensed working fluid is resistant to gravity and is effectively and reliably returned to the heat input section of the heat pipe. This allows the heat pipes to work in different orientations. Designers can even use flexible heat pipes with more design freedom. Another commonly used cooling solution is the heat sink. The heat sink can work in forced or natural convection. But again, no matter which option you use, it means making trade-offs. If the airflow for cooling is increased, it means that the number of fins can be reduced or the area of ​​the fins can be reduced. However, if the airflow generated by the fan is larger, the noise generated by the fan is larger; if the airflow generated by the fan is small, the fan runs quieter and the size can be made smaller, but this means that the heat sink must have more Or larger heat sink fins. Therefore, it is not easy to make the heat sink components smaller and quieter in the same device at the same time. In the heat pipe heat exchanger, heat is conducted through the heat pipe to the heat sink fins and then to the surrounding air. But it can also be done. At the same time, the way to reduce the size and reduce the noise is to make the radiator piece more isothermal. The heat sink previously cooled with a single thermoelectric cooler (TEC) can be redesigned to use multiple TECs to transfer heat evenly through the surface of the heat sink instead of relying solely on heat transfer for heat transfer. However, in addition to the need for maintenance, such solutions add complexity and cost to the electronics. The rack heat pipe assembly provides complete thermal stability and minimal technical maintenance. There is also a simpler cooling solution that uses passive heat dissipation technology to combine the heat sink with the embedded steam chamber (essentially a flat heat pipe that is flattened to a flat heat pipe), or a surface-integrated heat pipe Heat sink. Both solutions can transfer heat quickly and evenly by evaporating the working fluid in the embedded heat pipe or vapor chamber. The water vapor carries heat evenly through the entire bottom surface of the heat sink and the heat sink fins, avoiding the appearance of hot spots. Because the heat sink is isothermal, the flowing air passing through the heat sink fins carries the most heat. In general, the trend toward medical devices turning to passive heat sinks (eg, heat pipes, heat sinks, and steam chambers) reflects the evolution of smaller, more powerful, and more miniaturized electronics. Although more traditional cooling solutions (refrigeration, TEC, liquid cooling plates, etc.) are still the most appropriate choice for some medical devices, designers have found that with the development of passive cooling technology, it will become more and more The more attractive. A series of advances in material construction have also made passive cooling solutions more attractive to medical device designers. For example, with the advent of pyrolytic graphite (APG), it has become possible to make heat sinks that are smaller in size, lighter in weight, and more efficient in heat dissipation than conventional aluminum or copper fins. As products move toward more miniaturization and the miniaturization of electronic housings, materials with higher thermal conductivity can help designers. The effective thermal conductivity of APG is 1000 W/m?K, which is 5 times that of solid aluminum and 2.5 times that of solid copper. APG can also be packaged for applications such as surgical instruments. In such applications, it is important to avoid contact between APG and human tissue for structural damage, scarring or infection. The development of materials such as APG helps explain why medical device designers have more choices for passive thermal control systems. Because these systems not only offer a wider range of options, but in many cases provide better thermal management options. Passive cooling systems are more reliable than traditional liquid cooling solutions (less transfer parts mean lower risk of failure), reduced maintenance, more flexible design, quieter operation, and easier management costs in many cases . Below is an example of several passive thermal management concepts integrated into some important medical device applications. Diagnostic imaging Because the performance of electronic products drops rapidly after reaching critical temperatures, case cooling is critical to technologies that use more electronic components such as magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, and X-ray ( X-ray). Fine microwave motion of the temperature will affect calibration and results, resulting in costly downtime and maintenance. The FDA has played an important role in driving the reproducibility and reproducibility of medical device test results such as scanners, biotechnology equipment, and laboratory microassays toward near perfection (≥95%). To ensure accuracy, only a single diagnostic imaging machine (21 CFR 900.12), the specification mandates 31 separate tests, many of which are subject to thermal performance. The competitive diagnostic medical device market makes strict thermal control a more important factor in electronic product design. Designers typically work within a narrow temperature range (ΔT), with internal and external ambient temperatures typically 10 °C. Multiple sources of heat (such as equipment power supplies and other discrete electronic components) can produce a total output power of 1200 watts or more, of which 400 watts is the waste heat that needs to be discharged. In order to limit the fan size and wind speed, it is more complicated to achieve silent work. These problems are often solved to the greatest extent by heat pipe heat exchangers. In the heat pipe heat exchanger, heat is conducted from the inside of the device to the outside of the device through the heat pipe and then discharged into the surrounding air through the fin fins. If the fin area of ​​the heat exchanger is larger and the heat pipe is more efficient, a smaller, quieter fan can be used, and the strict heat dissipation requirements in regulatory and clinical environments can be met. In some cases, heat pipe technology can also be used for the heat pipe itself to utilize the laws of thermodynamics rather than electronics or fans to accomplish heat transfer. Similar heat pipe technology is used to cool the display in important care monitoring equipment. As shown in the figure, a rack-mounted heat pipe assembly provides perfect thermal stability with minimal technical maintenance. Since the transfer parts are not used, this allows the heat pipe to have a normal working life of several million hours, making it almost impossible to fail in critical care operations. 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