Durable superhydrophobic polyvinylidene fluoride membranes via facile spray-coating for effective membrane distillation

Membrane wetting and fouling substantially limits application and deployment of membrane distillation process. Designing high-performance superhydrophobic membranes offers an effective solution to solve the challenge. In this work, a highly durable superhydrophobic surface (water contact angle of 170.8 ± 1.3°) was constructed via a facile and rapid spray-coating of extremely hydrophobic SiO2 nanoparticles onto a porous polyvinylidene fluoride (PVDF) substrate for membrane distillation. The superhydrophobic membrane coated by fluorinated SiO2 nanoparticles exhibited a superior physicochemical stability in a wide range of extreme environments (i.e., NaOH, HCl, hot water, rust water, humic acid solution, ultrasonication, and high-speed water scouring). During 8-h continuous membrane distillation desalination experiment, the coated superhydrophobic membrane experienced a consistently stable water vapor flux (ca. 19.1 kg·m−2·h−1) and desalination efficiency (99.99 %). Additionally, such a stable superhydrophobicity endowed the spray-coated PVDF membrane to overcome membrane wetting and fouling during membrane distillation of highly saline solutions containing foulants (i.e., humic acid and rust). Results reported in this study provides a useful concept and strategy in facile construction of robust superhydrophobic membranes via spray-coating for effective membrane distillation.</p

Optimal Design of Tuned Mass-Damper-Inerter for Structure with Uncertain-but-Bounded Parameter

International audienceIn this study we focus on the H∞ optimization of a tuned mass damper inerter (TMDI), which is implemented on an harmonically forced structure of a single degree of freedom in the presence of stiffness uncertainty. Posed as a min-max optimization problem, its closed-form solutions are analytically derived via an algebraic approach that was newly developed in this work, and ready-to-use formulae of tuning parameters are provided herein for the optimal TMDI (referred to as the TMD). The accuracy of the derived solutions are examined by comparing them with the existing literature and with numerically solved solutions in both deterministic and uncertain scenarios. Our numerical investigation suggested that compared to the classic design, the proposed tuning strategy could effectively reduce the peak vibration amplitude of the host structure in the worst-case scenario. Moreover, its peak vibration amplitude decreases monotonically as the total amount of the tuned mass and inertance increases. Therefore, the incorporation of a grounded inerter in a traditional TMD could render the deteriorated performance of vibration control less important, thereby protecting the primary system against the detuning effect more effectively. Finally, the effectiveness of the proposed design under random excitation is also underlined

An improved model for thermal conductivity of nanofluids with effects of particle size and Brownian motion

Based on the generalized distribution of the temperature field, an improved model for the thermal conductivity of nanofluid has been derived. The impact of particle size and Brownian motion is modeled through the effective volume fraction, based on particle radius. In the special case, the generalized relationship reduces to the classical Maxwell model. On the other hand, the effect of Brownian movement is equivalent to increasing the effective volume fraction of nanoparticles. The effective radius of the nanoparticle is proposed, where the switching time and the equivalent volume fraction depend on the Brownian velocity of the nanoparticles. Considering the above two effects, an effective model is obtained. Comparison of thermal conductivity for Al2O3-water nanofluid is made between the present model and several theoretical models. Theoretical predictions on CuO-water nanofluid, ZnO-TiO2 hybrid nanofluids and MWCNTs nanofluid are also verified against experimental data