Layered three-dimensional (3D) van der Waals (vdW) structure, as a highly anticipated candidate for next-generation chip cooling solutions, shows extraordinary properties such as high-temperature resistance and high in-plane thermal conductivity (TC). However, the cross-plane TC is greatly limited by weak vdW interactions, making chip-level integration challenging. Here, a strategy of molecular bridge (MB) assembling 3D vdW structure is reported to significantly enhance cross-plane TC. An over 20-fold enhancement is realized through molecular dynamics simulations in multilayer graphene assembled by MB. Through phonon hybridization at the interface between MB and graphene, a novel continuous phonon transmission channel (around 50 THz) is triggered compared with the regular interrupted channel (below 5 THz) induced solely by vdW interactions. In addition, ballistic-diffusive phonon transport is observed with changing lengths of the MB connected to graphene layers. Our work presents an efficient strategy for designing 3D vdW structures with high thermal efficiency and tunable heat conduction through MB.

The organic Rankine cycle (ORC) is a mainstream technology for efficient heat-power conversion of low-to-medium temperature thermal energy below 200℃. Zeotropic mixtures effectively reduce the heat transfer exergy losses, complement the advantages of pure components, and extend the working fluid useful temperature range. Thus, zeotropic mixtures are being rapidly accepted into the ORC field. This paper summarizes the research progress by the authors' team in optimizing the design of ORC systems using zeotropic mixtures. Conventional ORC systems using zeotropic mixtures have been expanded by the introduction of dual-pressure evaporation cycles to improve the temperature matching during evaporation and significantly reduce the heat transfer losses. The liquid-separation condensation method is also used to increase the condensation heat transfer rate of the zeotropic mixtures which greatly reduces the system cost. In summary, zeotropic mixtures can significantly improve the thermodynamics of ORC systems while the liquid-separation condensation method can effectively reduce the large heat transfer areas and improve the poor thermo-economic performance of systems using zeotropic mixtures. Thus, zeotropic mixtures then have favorable prospects for use in ORC systems.

Ultrathin planar absorbers hold promise in solar energy systems because they can reduce the material, fabrication, and system cost. Here, we present a general strategy of effective medium design to realize ultrathin planar broadband absorbers. The absorber consists of two ultrathin absorbing dielectrics to design an effective absorbing medium, a transparent layer, and metallic substrate. Compared with previous studies, this strategy provides another dimension of freedom to enhance optical absorption; therefore, destructive interference can be realized over a broad spectrum. To demonstrate the power and simplicity of this strategy, we both experimentally and theoretically characterized an absorber with 5-nm-thick Ge, 10-nm-thick Ti, and 50-nm-thick SiO₂ films coated on an Ag substrate fabricated using simple deposition methods. Absorptivity higher than 80% was achieved in 15-nm-thick (1/50 of the center wavelength) Ge and Ti films from 400 nm to near 1 μm. As an application example, we experimentally demonstrated that the absorber exhibited a normal solar absorptivity of 0.8 with a normal emittance of 0.1 at 500 ℃, thus demonstrating its potential in solar thermal systems. The effective medium design strategy is general and allows material versatility, suggesting possible applications in real-time optical manipulation using dynamic materials.