@article{gorman_pejman_kumar_patrick_najafi_2024, title={Transient topology optimization for efficient design of actively cooled microvascular materials}, volume={67}, ISSN={["1615-1488"]}, DOI={10.1007/s00158-024-03774-2}, abstractNote={Abstract Microvascular materials containing internal microchannels are able to achieve multi-functionality by flowing different fluids through vasculature. Active cooling is one application to protect structural components and devices from thermal overload, which is critical to modern technology including electric vehicle battery packaging and solar panels on space probes. Creating thermally efficient vascular network designs requires state-of-the-art computational tools. Prior optimization schemes have only considered steady-state cooling, rendering a knowledge gap for time-varying heat transfer behavior. In this study, a transient topology optimization framework is presented to maximize the active-cooling performance and mitigate computational cost. Here, we optimize the channel layout so that coolant flowing within the vascular network can remove heat quickly and also provide a lower steady-state temperature. An objective function for this new transient formulation is proposed that minimizes the area beneath the average temperature versus time curve to simultaneously reduce the temperature and cooling time. The thermal response of the system is obtained through a transient Geometric Reduced Order Finite Element Model (GRO-FEM). The model is verified via a conjugate heat transfer simulation in commercial software and validated by an active-cooling experiment conducted on a 3D-printed microvascular metal. A transient sensitivity analysis is derived to provide the optimizer with analytical gradients of the objective function for further computational efficiency. Example problems are solved demonstrating the method’s ability to enhance cooling performance along with a comparison of transient versus steady-state optimization results. In this comparison, both the steady-state and transient frameworks delivered different designs with similar performance characteristics for the problems considered in this study. This latest computational framework provides a new thermal regulation toolbox for microvascular material designers.}, number={4}, journal={STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION}, author={Gorman, Jonathan and Pejman, Reza and Kumar, Sandeep and Patrick, Jason and Najafi, Ahmad}, year={2024}, month={Apr} } @article{nakshatrala_adhikari_kumar_patrick_2023, title={Configuration-independent thermal invariants under flow reversal in thin vascular systems}, volume={2}, ISSN={["2752-6542"]}, DOI={10.1093/pnasnexus/pgad266}, abstractNote={Abstract Modulating temperature fields is indispensable for advancing modern technologies: space probes, electronic packing, and implantable medical devices, to name a few. Bio-inspired thermal regulation achieved via fluid flow within a network of embedded vesicles is notably desirable for slender synthetic material systems. This far-reaching study—availing theory, numerics, and experiments—reveals a counter-intuitive yet fundamental property of vascular-based fluid-flow-engendered thermal regulation. For such thin systems, the mean surface temperature and the outlet temperature—consequently, the heat extracted by the flowing fluid (coolant)—are invariant under flow reversal (i.e. swapping the inlet and outlet). Despite markedly different temperature fields under flow reversal, our newfound invariance—a discovery—holds for anisotropic thermal conductivity, any inlet and ambient temperatures, transient and steady-state responses, irregular domains, and arbitrary internal vascular topologies, including those with branching. The reported configuration-independent result benefits thermal regulation designers. For instance, the flexibility in the coolant’s inlet location eases coordination challenges between electronics and various delivery systems in microfluidic devices without compromising performance (e.g. soft implantable coolers for pain management). Last but not least, the invariance offers an innovative way to verify computer codes, especially when analytical solutions are unavailable for intricate domain and vascular configurations.}, number={8}, journal={PNAS NEXUS}, author={Nakshatrala, Kalyana B. and Adhikari, Kripa and Kumar, Sandeep Rajendra and Patrick, Jason F.}, year={2023}, month={Aug} }