Thermal Management
Microvascular composites that contain a circulatory system are being developed to expand the temperature range for their use in structural applications. By circulating coolants within the vascular network these materials are able to maintain lower temperatures even when exposed to high thermal flux. Alternatively, when exposed to low temperature environments they can maintain higher temperatures by circulating heated fluids or chemical components that undergo an exothermic reaction.
Advanced fiber-reinforced composite materials are desirable for weight critical applications, such as cars and aircraft, but are often limited by the low temperature stability of the polymer matrix. To extend the temperature range of these materials we can use a biologically-inspired approach. Just like the human body uses blood pumped through the circulatory system to regulate temperature, fluid pumped through microchannels can add or remove heat, changing the material's temperature. In addition, the system can be used to cool or heat external systems, allowing for adaptation to changing conditions, such as increased heat generation in electronics. Areas of study include manufacturing of complex 2D and 3D channel architectures, enhancement of cooling through thermally induced flow control and perspiration, and preservation of structural performance.
Thermal cooling performance of microvascular composite specimen. The IR camera captures the temperature field on the top of a specimen exposed to thermal flux from below (Left image). IR camera images for no flow (middle) and actively cooled (right) cases. Active cooling dramatically reduces the temperature, in this case from an average of 80°C to just around 30°C for a flow rate of 1 ml/min.
Embedded thermally triggered valves can redirect flow, allowing the system to adapt to changing environmental conditions. This image shows a 3D vascular network embedded in epoxy with a flow control valve in the center. (Left) At low temperatures flow is directed through the central artery, which has a large diameter and minimizes pumping power. (Right) As the temperature increases, the valve closes off flow through the central artery, redirecting it into the outer capillary beds to improve heat transfer.
Branched networks with multiple channel sizes can be used to maximize the efficiency of fluid delivery and optimize the transfer of heat.