Personal cooling technologies locally control the temperature of an individual rather than a large space, thus providing personal thermal comfort while supplementing cooling loads in thermally regulated environments. This can lead to significant energy and cost savings. In this study, a new approach to personal cooling was developed using an infrared-transparent visible-opaque fabric (ITVOF), which provides passive cooling via the transmission of thermal radiation emitted by the human body directly to the environment. Here, we present a conceptual framework to thermally and optically design an ITVOF. Using a heat transfer model, the fabric was found to require a minimum infrared (IR) transmittance of 0.644 and a maximum IR reflectance of 0.2 to ensure thermal comfort at ambient temperatures as high as 26.1 o C (79 o F). To meet these requirements, an ITVOF design was developed using synthetic polymer fibers with an intrinsically low IR absorptance. These fibers were then structured to minimize IR reflection via weak Rayleigh scattering while maintaining visible opaqueness via strong Mie scattering. For a fabric composed of parallel-aligned polyethylene fibers, numerical finite element simulations predict 1 μm diameter fibers bundled into 30 μm yarns can achieve a total hemispherical IR transmittance of 0.972, which is nearly perfectly transparent to mid-and far-IR radiation. The visible wavelength properties of the ITVOF are comparable to conventional textiles ensuring opaqueness to the human eye. By providing personal cooling in a form amenable to everyday use, ITVOF-based clothing offers a simple, low-cost solution to reduce energy consumption in HVAC systems. TOC Graphic

Traditional solar-thermal receivers suffer from high surface temperatures, which increase heat losses to the surroundings. To improve performance, volumetric receivers based on nanoparticles suspended in liquid (nanofluids) have been studied as an approach to reduce surface losses by localizing high temperatures to the interior of the receiver. Here, we report measured vapor generation efficiencies of 69% at solar concentrations of 10 suns using graphitized carbon black, carbon black, and graphenesuspended in water, representing a significant improvement in both transient and steady-state performance over previously reported results. To elucidate the vapor generation mechanism and validate our experimental results, we develop numerical and analytical heat transfer models that suggest that nanofluid heating and vapor generation occur due to classical global heating of the suspension fluid. This work demonstrates highnanofluid-assisted vapor generation efficiencies with potential applications in power generation, distillation, and sterilization.

Due to their unique properties, polymers – typically thermal insulators – can open up opportunities for advanced thermal management when they are transformed into thermal conductors. Recent studies have shown polymers can achieve high thermal conductivity, but the transport mechanisms have yet to be elucidated. Here we report polyethylene films with a high thermal conductivity of 62 Wm −1 K −1 , over two orders-of-magnitude greater than that of typical polymers (~0.1 Wm −1 K −1 ) and exceeding that of many metals and ceramics. Structural studies and thermal modeling reveal that the film consists of nanofibers with crystalline and amorphous regions, and the amorphous region has a remarkably high thermal conductivity, over ~16 Wm −1 K −1 . This work lays the foundation for rational design and synthesis of thermally conductive polymers for thermal management, particularly when flexible, lightweight, chemically inert, and electrically insulating thermal conductors are required.

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