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Inspired by the natural fog collection of the Namib beetles and desert cacti, a bioinspired design (BID) needle with a remarkable wettability gradient is introduced. Previous studies about directional water transport have rarely investigated wettability gradients along the azimuthal direction of a needle. Here, we have reported on the fast droplet transportation on a BID needle improved by azimuthally varying Cu nanocolumns on a steel acupuncture needle. We have employed glancing angle deposition (GLAD) to produce gradient porous Cu nanocolumns directly on the curved surface of an acupuncture needle. Due to the engineered gradient on such a surface, a high-speed fog collection of V = 134.8 mm·s–1 and a remarkable acceleration of a = 848.3 mm·s–2 were observed for the droplets on the needle surface. All periodically created droplets were easily swept along the 40 mm needle path in less than 0.5 s. Such efficient fog collection and fast droplet transportation in the proposed azimuthally nonuniform structure have many potential applications, from fog collection in low water regions to water transportation in microsystems.

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The CFD simulation accuracy mostly depends on the appropriate setting of boundary conditions and numerical simulation parameters. This study shows the influence of two types of boundary condition settings on the CFD simulation results of Double-Skin Façade (DSF) for a specific problem. These two boundary settings are the constant temperature on the DSF surfaces called Boundary A, and Boundary B is defined via solar radiation using the Discrete Ordinate radiation Model (DOM). The paper verified both the numerical simulations using the experimental data. Comparing the numerical results of two types of boundaries with experimental data shows that both cases underestimated the values lower than 5.2 K and 0.1 m/s for the temperature and velocity respectively at the regarded measured points. Boundary A gives more accurate temperature prediction results while Boundary B shows velocity magnitude closer to the measurements in the middle height of the cavity; the average temperature and velocity differences between the two boundary types are 0.6 K and, 0.003 m/s respectively which are negligible. Finally, the selection of boundary conditions depends on study purposes, however, when the DSF is equipped with blinds and if there is not enough data in hand but the exact value of solar irradiation, using the Boundary B approach is suggested; it can provide reasonable results associated with multi-type of thermal boundary conditions at the same time. Furthermore, if the goal is to investigate the flow pattern in the DSF, Boundary B is argued to perform better than the constant temperature boundary condition.

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