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The rapid development of wearable electronics highlights the urgence to develop the portable energy harvester with excellent output performance, comfortability, and sustainability. This work designs an electromagnetic walking energy harvester based on water turbine that can be embedded in shoes with good comfortability. Its working principle is that the walking generated pressure energy drives a miniature hydraulic turbine to output electricity. Experimental results show that an average power of 300 and 180 mW can be produced at heel and toe, respectively, when a man of 80 kg walks at a speed of 1.8 m s−1. This power output exceeds the piezoelectric, triboelectric, and electromagnetic walking energy harvesters reported in the past. Additionally, the simpler structure endows it better comfortability as compared with the electrostatic capacitances. Computational fluid dynamics simulations provide a further insight that the efficiency of turbine can reach 13.5% by optimizing parameters of blade number and outlet flow ratio. Finally, user real-time positioning and trajectory recording are successfully demonstrated via a wearable GPS means Global Positioning System module powered by the harvester. Due to the combination of high output performance, simple structure and low discomfort, the water turbine based walking energy harvester will provide a wide application potential in wearable devices. [ABSTRACT FROM AUTHOR]

• The erosion of runner is contributed to the inter-blade vortices. • Erosion distributions are highly consistent with the actual site observations. • Maximum average erosion rate occurs when particle diameter is 0.2 mm. Sediment erosion is a prevalent and significant challenge to hydro turbines in mountainous rivers. In order to gain an insight into the erosion characteristics of Francis turbines, this study considers the influence of actual sediment gradation and emphasizes the erosion mechanism from the perspective of flow structure. Numerical results reveal a significant correlation between erosion distributions and the location of inter-blade vortices, which is dependent on operating conditions. Specifically, at small or optimal openings, inter-blade vortices predominantly form on the suction side of blades, which coincidentally experiences the most severe sediment erosion. Conversely, at a large guide vane opening, sediment erosion and vortices are primarily distributed at outlet of pressure side, aligning closely with actual site observations at a hydropower station. With increase of operating heads, the average erosion rate of suction side decreases at all guide vane openings, while that of pressure side elevates significantly. In addition, the effect of particle size on sediment erosion was discussed and the maximum erosion rate is demonstrated to be proportional to sediment diameter. These findings would provide important engineering insights for operation optimization to reduce sediment erosion. [ABSTRACT FROM AUTHOR]

[Display omitted] • An effective strategy to prevent Cassie-wetting failure of structured hydrophobic surface was proposed by simply coating a single-layer graphene. • Droplets exhibit a stable Cassie-state wetting on graphene-coated surface due to the wetting transparency and water impermeability of graphene. • The modified surface showed a 40–100% increase in condensation rate in 5 h at a subcooling of 40 °C. Structured hydrophobic surfaces often suffer from Cassie-wetting failure due to trapped water in structure gaps for a long-term operation. Sustainable Cassie-wetting on such surface could be achieved by coating an atom-thick and moisture-impermeable graphene on it. Water contact angles were measured to clarify the effect of graphene on wetting, and water impermeability was verified by moisture deposition and evaporation. Sliding angle measurements and vapor condensation were carried out to demonstrate the stable Cassie-state wetting and application. Interestingly we found the graphene does not significantly disrupt the wetting behavior of the structured hydrophobic surface, showing a wettability transparency. Moreover, the impermeability of graphene keeps moisture away from the structure gaps. Owning to the combination of these two properties, droplets on the graphene-coated structured surface exhibit a stable Cassie-state hydrophobic wetting, even under the situation of moisture deposition and evaporation. Using the modified surface, we also found a 40–100% increase in condensation efficiency for a 5-hour vapor condensation at a subcooling of 40 °C. These results suggest an effective strategy to prevent Cassie-wetting failure of structured hydrophobic surface and are expected to promote its further application in more complex conditions. [ABSTRACT FROM AUTHOR]

Low-grade heat energy is enormous and widely distributed around the world, but it cannot be effectively converted to electricity owing to the small temperature difference and fluctuating heat source. As a promising technology that can convert low-grade heat energy into electricity while obtaining additional freshwater, thermo-osmotic energy conversion has attracted attentions of numerous researchers. However, traditional thermo-osmotic energy conversion technologies lack the utilization of the accompanying variation in salinity gradients throughout the process. In this study, a hybrid system was presented to achieve simultaneous freshwater production and electricity generation by combining thermo-osmosis system with a salinity gradient power recovery module. Continuous operation of the thermo-osmosis system will naturally produce a range of salinity differences, which will then be converted into electricity by the salinity gradient power recovery module. Our results show that this hybrid system can optimally increase the electricity output by ∼0.99 W m−2 over the conventional thermo-osmotic energy conversion system. Overall, our research demonstrates a promising device to harvest low-grade waste heat for co-generation of electricity and freshwater. This innovative approach has the potential to broaden the application possibilities of thermo-osmosis technology. • Salinity gradient recovery combined thermal-osmosis hybrid system was proposed. • A theoretical model was developed to predict electricity output of the system. • Comparing to traditional TOEC, increasing electricity output by ∼0.99 W m−2. • Co-generation of freshwater and electricity was achieved under real seawater. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Permeation across GO membranes for mixed solution was concerned. • Concentration and recovery of Cu2+ with GO membranes was investigated. • Inhibitory effect of hydrogen ion on the transport of copper ions was demonstrated. Abstract Graphene-based materials have many unique features including atomic thickness and well-defined nanochannels, making their great properties for filtration and separation. The removal of low-level heavy-metal ions (e.g. Cu2+) by graphene oxide sheets has been discussed to ascertain their adsorption capacity, but separation and recovery of massive copper ions with graphene oxide (GO) membranes remain to be further studied. Besides, the permeation across GO membranes involving different ions in the very same solution is rarely investigated. Hence, the permeation properties of GO membranes concerning single and mixed solutions of acid and salt were examined in this study, and inhibitory effect of hydrogen ion on the copper ions transport was observed. Expectedly, GO membranes perform obvious permeation rate differences to acid (i.e. H 2 SO 4 , HCl) and copper salts (i.e. CuSO 4 , CuCl 2) when they are tested individually. The diffusion coefficient of H+ is 16 times larger than that of Cu2+ when the anion is SO 4 2−, and twice in the case of Cl−. The differences are mainly determined by physical screening of the capillary channels in the film for ions with different hydration radii and the rapid migration of hydrogen ions in solution. Furthermore, Experiments were carried out using mixed solution of acid and copper salt with the same anion and concentration. It was shown that the existence of H+, whose own transmission decreased by only 1.6 times, reduced the penetration of Cu2+ by an order of magnitude in the same time interval. We supposed this remarkable inhibitory effect is associated with shrink of interlayer spacing and competitive adsorption of H+ against Cu2+ on the surface of GO membranes in mixed solution. The properties of GO membranes show great application prospects in separation and wastewater reuse. [ABSTRACT FROM AUTHOR]

Harvesting solar energy for water desalination is considered as one of the most important technologies to effectively address global water scarcity. Recently, it was found that water droplets on azobenzene modified anodized alumina membranes and disperse red 1 modified PTFE (polytetrafluoroethylene) membranes can permeate the membrane to be purified and desalinated under light irradiation. Herein, in order to efficiently collect vaporized and condensed water, we demonstrated the immobilization of graphene-based material n hydrophobic PTFE membrane surface for water desalination via photothermal membrane distillation (PMD). An ultrathin graphene-based film, fabricated by a scalable process, serves as efficient solar absorbers (absorption efficiency of rGO/pDA-rGO > 80%), ultrafast water permeable channels, and high salt resistance network. Compared with bare PTFE membrane, water transmembrane flux on the pDA-rGO material modified PTFE membrane can achieve as much as 78.6% enhancement under normal solar illumination. Due to high salt rejection of graphene-based films, the evaporation rate of graphene-based material modified PTFE membrane was unaffected by 4% NaCl solution, which indicated that concentration polarization effect can obviously be eliminated. These results provided new insights into the design and utilization of graphene-based films for effectively solar desalination via PMD. [ABSTRACT FROM AUTHOR]

On-site sample preparation is highly desired because it avoids the transportation of large-volume samples and ensures the accuracy of the analytical results. In this work, a portable prototype of tip microextraction device (TMD) was designed and developed for on-site sample pretreatment. The assembly procedure of TMD is quite simple. Firstly, polymeric ionic liquid (PIL)-based adsorbent was in-situ prepared in a pipette tip. After that, the tip was connected with a syringe which was driven by a bidirectional motor. The flow rates in adsorption and desorption steps were controlled accurately by the motor. To evaluate the practicability of the developed device, the TMD was used to on-site sample preparation of waters and combined with high-performance liquid chromatography with diode array detection to measure trace estrogens in water samples. Under the most favorable conditions, the limits of detection (LODs, S/N = 3) for the target analytes were in the range of 4.9–22 ng/L, with good coefficients of determination. Confirmatory study well evidences that the extraction performance of TMD is comparable to that of the traditional laboratory solid-phase extraction process, but the proposed TMD is more simple and convenient. At the same time, the TMD avoids complicated sampling and transferring steps of large-volume water samples. [ABSTRACT FROM AUTHOR]

A flow injection method combined with an on-line UV and thermal digestion for simultaneous determination of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in natural waters was established in this study. A novel flow manifold made the proposed system compact and automatic. The conversion rates of various nitrogen and phosphorus compounds to their nitrate and phosphate forms with different digestion models and different concentrations were well investigated using the flow injection technique. The reagent concentrations for colorimetric analysis were optimized based on a univariate experimental design. The detection limits were 0.8 μmol L −1 and 0.2 μmol L −1 , and linear analytical ranges were up to 300 μmol L −1 and 25 μmol L −1 for TDN and TDP, respectively. The sample throughput was ~ 5 h −1 . The recovery of spiked natural water samples varied from 86.8% to 102.6% for TDN and 88.0% to 102.0% for TDP. The present approach was successfully applied for the determination of TDN and TDP in natural water samples and was found to have good agreement with reference methods. The outcomes of present study indicated that the proposed method is suitable for routine analysis as well as for potential on-line monitoring. [ABSTRACT FROM AUTHOR]

Currently, energy conversion methods in nanochannels have been developed for both fundamental sciences and technological applications. Graphene oxide membranes with excellent properties possess potential applications in numerous fields. Due to the confinement of nanocapillaries within graphene oxide membranes and the mobility difference of ions, an electricity generation process has been achieved using graphene oxide membranes. In this study, for the first time, the influence of source concentration, applied pressure and membrane thickness was investigated on electricity generation in aqueous environment. The results revealed that these three factors could successfully control the electricity generation with graphene oxide membranes. Electrical potential difference would become larger with increasing the source concentration and membrane thickness. In contrast, the applied pressure was not well-suited to capture energy from sources. This provided new insights into the design and utilization of graphene oxide films for highly efficient energy harvesting. [ABSTRACT FROM AUTHOR]

In this paper, a numerical computation method combining a high-order compact difference scheme and immersed boundary method is used to simulate the flow around a hyperbolic cylinder with different aspect ratios and eccentricity. It is found that compared to the circular cylinder, the vortex-separation point in the wake of the hyperbolic cylinder moves backward, and the corresponding drag coefficient decreases by 27.6%. More interestingly, the time-averaged drag coefficient of hyperbolic cylinder behaviors parabolic relationship with cross-section aspect ratio and hyperboloid eccentricity, respectively. As the aspect ratio decreases from 1 to 0.6, the flow drag parallel to the long-axis reduces dramatically to 42.9%. Especially, there is no obviously low pressure region behind the hyperbolic cylinder when r = 0.4, which leads to the drag coefficient is only 0.0249 and close to zero. Besides, the average drag coefficient diminishes in a parabolic trend with the eccentricity that has a monotonously positive correlation with two parameters, and an increase in eccentricity e by varying a or c will also reduce the drag, but the effect of parameter a is more obvious than parameter c. The results presented here are expected to suggest a strategy for drag reduction in flow around the cylinder and provide theoretical guidance for the design and optimization of hyperbolic structures in flowing fluid. •Flow over a hyperbolic cylinder with different aspect ratio and eccentricity is investigated •Drag coefficient of hyperbolic cylinder decreases by 27.6% compared to circular cylinder; •Time-averaged drag has a parabolic relationship with the aspect ratio and eccentricity [ABSTRACT FROM AUTHOR]

Passive cooling for thermal comfort improvement has received extensive attention for its low energy consumption. However, most of the existing passive cooling technologies require a complex system design and supporting equipment, since they cool the ambient air. Herein, we propose a hybrid evaporative and radiative cooling membrane with a hygroscopic hydrogel sandwiched by two layers of a porous polyethylene aerogel (PEA). The hydrogel implements evaporative cooling. Combining the high solar reflection of PEA and the high infrared emissivity of hydrogel, this hybrid membrane also possesses radiative cooling. In addition, the high infrared transmittance and low thermal conductivity of PEA allow direct heat transfer between the hydrogel and human body, instead of the ambient air. Through comparative experiments and theoretical calculations, it is indicated that the net cooling power delivered by the hybrid membrane to the human body is up to 78.45 W m−2, which is much higher than that of conventional radiative cooling materials. Outdoor demonstration shows that emission below the hybrid membrane can achieve an average sub-ambient temperature drop of 6 °C, with a maximum of 14 °C, showing great potential for passive building cooling and human personal cooling. [ABSTRACT FROM AUTHOR]

The analysis of time-series concentrations (C TS) is of great importance when investigating the biogeochemical processes of nutrients in aquatic environments. However, obtaining C TS of nutrients remains a challenge using current sampling techniques. In this study, a novel in situ sampler was constructed using reverse osmosis membrane (ROM) osmotic pumps (OP) (ROM-OP sampler), and was used to obtain the C TS of nutrients in surface waters. The sampler consisted of a sampling OP, sample storing coil, filter, bubble injection module, and preservative adding module. When deployed, the sampling OP continuously draws ambient water through the filter into the sample storing coil, while simultaneously the preservative adding module continuously delivers preservative (H 2 SO 4 solution) into the water flow. The bubble injection module periodically injects air bubbles into the sample storing coil, to segment the sample and create time stamp indicators that allow the sample age to be defined. Upon retrieval, the sample segments in the coil are sequentially pumped out of the sample storing coil and transferred into different vials for further analysis. The sampler was applied to measure the C TS of various nutrients, including dissolved total nitrogen, dissolved total phosphorus, dissolved reactive phosphorus, and nitrate in a river over a 20 day period and in municipal sewage treatment plant effluent for a 36 h period. Results showed that the ROM-OP sampler successfully obtained C TS of nutrients, capturing nutrient variations at a high temporal resolution. This sampler is relatively low-cost (~USD 300), small in size, lightweight, robust and does not require an external power source, showing high promise as an effective and efficient tool for monitoring nutrient C TS in aquatic environments. Unlabelled Image • Time-series sampler developed using osmotic pumps with reverse osmosis membrane. • Air bubbles were used to segment the water sample, with H 2 SO 4 as a preservative. • Obtained a high temporal resolution time-series of nutrient concentrations. • Excellent agreement was achieved between sampler-collected samples and spot samples. • The sampler is cheap, small size, robust and requires no external power source. [ABSTRACT FROM AUTHOR]

• A new stable and cost-efficient solar absorber for solar-based applications. • Reveals the influencing factors of photothermal conversion efficiency of nanofluid. • The highest relative efficiency reaches 91.6% at 3 suns. For high-temperatures surfaces, surface absorbers possess a higher evaporation rate while volumetric receivers have a higher solar vapor generation efficiency by localizing high temperatures to the interior of the receiver and thus reduce surface losses. In this work, the solar vapor generation rates and efficiencies of several direct absorption solar collectors were compared by using reduced graphene oxide/graphene oxide and silver nanofluids as evaporators, two of which deserve to be noticed. One is the hybrid nanofluids containing reduced graphene oxide decorated with silver nanoparticles in volumetric solar absorbers and the other one is hybrid nanofluids containing reduced graphene oxide with silver floating on the surface, combining surface absorbers and volumetric ones. The results show that relative efficiency monotonously increases with the light density (e.g. correspondingly changes within 61.5% at 1 sun, 62% at 2 suns, 64% at 3 suns and 69% at 4 suns for 0.45 mg/ml reduced graphene oxide) and nanofluid concentration. The further experiments reveal that nanofluid-assisted vapor generation efficiencies of hybrid nanofluids containing reduced graphene oxide with silver floating on the surface were higher, reaching 91.6% at 3 suns, than the others due to its higher absorbance and plasmonic effect of the nanoparticles and high thermal conductivity of graphene nanosheets. This demonstration of hybrid nanofluids containing reduced graphene oxide with silver floating on the surface holds the promise of significantly expanding the potential applications in desalination, water treatment and power generation. [ABSTRACT FROM AUTHOR]

A micro hydrokinetic turbine is a device for extracting energy from rivers or tides, and this device represents one of the frontiers for renewable energy technology. A detailed analysis of the acoustic characteristics of these turbines is of great significance for their cleaner production, further development, and use. Based on the Ffowcs Williams and Hawkings integration method, the acoustic characteristics of the horizontal axis of a micro hydrokinetic turbine are numerically studied in this work, with emphasis on the acoustic distribution, the acoustic spectrum in the time and frequency domains, and the acoustic directivity in different regions. It is found that the noise of a horizontal axis micro hydrokinetic turbine mainly occurs at the leading edge and tip of the blade due to the appearance and separation of vortices at these locations. The noise signal is mainly caused by the blade passing frequency, especially the first-order frequency, and with the features of a low frequency and broad band. In the progress of downstream propagation, rapid energy dissipation leads to the gradual decrease of the sound pressure level. Furthermore, the noise radiation of the blade has obvious dipole characteristics in the flow direction. The results presented here will contribute to a fundamental understanding of the acoustic characteristics of a turbine. • High intensity noise sources are near the leading edge and tip of the blade. • Acoustic pressure show obvious periodicity. • Peak value of SPL is mainly located at the first order BPF and its harmonic frequency. • Noise radiation of blade has an obvious dipole characteristic. [ABSTRACT FROM AUTHOR]