Aerogels can be used in a broad range of applications such as bioscaffolds, energy storage devices, sensors, pollutant treatment, and thermal insulating materials due to their excellent properties including large surface area, low density, low thermal conductivity, and high porosity. Here we report a facile and effective top-down approach to fabricate an anisotropic wood aerogel directly from natural wood by a simple chemical treatment. The wood aerogel has a layered structure with anisotropic structural properties due to the destruction of cell walls by the removal of lignin and hemicellulose. The layered structure results in the anisotropic wood aerogel having good mechanical compressibility and fragility resistance, demonstrated by a high reversible compression of 60% and stress retention of ∼90% after 10 000 compression cycles. Moreover, the anisotropic structure of the wood aerogel with curved layers stacking layer-by-layer and aligned cellulose nanofibers inside each individual layer enables the wood aerogel to have an anisotropic thermal conductivity with an anisotropy factor of ∼4.3. An extremely low thermal conductivity of 0.028 W/m·K perpendicular to the cellulose alignment direction and a thermal conductivity of 0.12 W/m·K along the cellulose alignment direction can be achieved. The thermal conductivity is not only much lower than that of the natural wood material (by ∼3.6 times) but also lower than most of the commercial thermal insulation materials. The top-down approach is low-cost, scalable, simple, yet effective, representing a promising direction for the fabrication of high-quality aerogel materials.
Thermal management of high-power electronics is often a major obstacle in achieving improved packaging density. Emergence of SiC devices allows higher voltage and temperature limits, but thermal management is still a bottleneck in achieving compact, reliable and high-performance systems. This study introduces the design of an advanced packaging configuration of a dual-active-bridge 10 kW DC-DC converter module with 97% efficiency and ∼1.5 × 104 kW/m3 power density based on preliminary modeling analysis. The proposed packaging scheme allows for significant volume reduction and considerably lighter weight at greater power levels than commercially available converter modules. We introduce an improved placement of high power/high frequency MOSFET switches on the board that enables double-sided cooling, where the dissipated heat is removed from both sides of the switches via manifold-microchannel cooler modules. The cooler modules are additively manufactured monolithic structures made out of a thermally and electrically conductive material, which in turn allows them to double function as electrical terminals for the switches. Their unique shape minimizes footprint utilization on the board while still providing significant area enhancement over the heat dissipating chips’ footprint. Moreover, thermal management of other components with significant heat flux, such as the transformer coils and magnetic core are also accomplished via dielectric liquid cooling with electrically insulating but thermally conductive 3D printed coolers. The overall circuit diagram, assembly configuration and flow routing within the system are demonstrated. The advantages of the proposed design over commercially available modules are discussed in detail.
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