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Resonant-type liner panels are one the primary countermeasures for the fan noise of aircraft engines, though the sound absorption performances of the liners are known to be tolerated by the grazing flow streaming on their surface. Therefore, suppressing the effect of the flow on the liners is greatly important for higher sound absorption efficiency. In this study, liner panels with special surface structures were manufactured and applied to an outdoor test using a small turbofan engine, DGEN 380. A special thin film, Fine-Perforated-Film (FPF), was applied to two liner samples. In the first sample, FPF was applied directly to the surface of a typical liner. In the second sample, a gap was fixed between the FPF and liner surface. In addition, a rigid wall and a typical liner were used for comparison, to investigate the effect of the structures. During the test, the samples were installed to the exhaust bypass duct of the DGEN engine. The acoustic pressure inside the duct and in far field was measured. Analysis and comparison of the results showed that the new structures suppressed the effect of the grazing flow and caused a larger amount of noise reduction, compared to the typical liner sample.

Oxide layers on conductive TiN have recently been investigated to catalyse the oxygen reduction reaction (ORR) in acidic media. The ORR reactivity

This paper deals with a resonant type liner panel with a special surface structure. A typical resonant type liner panel generally consists of a perforated face plate, cells, and a back rigid plate. One of the technical challenges of the acoustic liners applied to the future ultra-high bypass ratio engines is to increase the sound absorption efficiency under grazing conditions because the nacelle, covering of the engine, tends to reduce its length and the lined area. It is known that the sound absorption of the conventional liners tends to deteriorate as grazing flow increases. The authors introduced a special thin acoustically transparent film over the face plate of the acoustic liner. The film, a fine perforated film (FPF), is expected to prevent the interaction of the grazing flow with the opening of the liner face plate. An experimental result with a flow duct rig in JAXA confirmed that the proposed combination of the acoustic liner and the FPF improved the absorption in acoustic energy under grazing conditions, compared with the sole acoustic liner and simple treatment of the FPF.

This study experimentally investigated the evaporation and wetting transition behavior of fakir drops on five different microstructured surfaces. Diamond-like carbon was introduced as the substrate, and the influence of varying the width, height, and pitch of the micropillars was assessed. The results showed that different evaporation modes emerged during the transition, which were influenced by the interfacial properties of the surfaces. In addition, the resistance of superhydrophobic surfaces to the Cassie–Baxter to Wenzel transition was strongly dependent on the depinning ability of the three-phase contact line of the liquid drop. The accuracy of the theoretical models for predicting the critical transition parameters was discussed, and a numerical model was developed in the surface evolver to compute the penetration of the drop bottom meniscus within the micropillars. Finally, a robust superhydrophobic surface capable of suppressing the Cassie–Baxter to Wenzel transition without a hierarchical nanostructure for microdroplets less than 0.37 mm in diameter was demonstrated as the key outcome of this study.

A tapered fiber sensor was developed to detect the presence of condensed water and frost. The rough surface of the tapered fiber efficiently scattered the light propagating through the tapered fiber. The scattering loss is selective to the medium surrounding the tapered region of the fiber. Compared to the transmission intensity in the air, liquid water on the tapered fiber causes a 40% increase in transmission, whereas the presence of frost decreases the light transmission by 15%. Frost induces roughness on the surface of the tapered fiber and as a result increases light scattering and transmission losses. In contrast, liquid water uniformly covers the tapered fiber surface and reduces the light scattering. Furthermore, the amount of frozen water on the tapered surface is related to the duration of the transmission intensity peak during the defrosting process. The proposed detection scheme based on a rough tapered fiber can be utilized in real-time remote monitoring systems of the frost formation in large refrigeration systems.

The transition from nucleate to film boiling on micro/nano textured surfaces is of crucial importance in a number of practical applications, where it needs to be avoided to enable safe and efficient heat transfer. Previous studies have focused on the transition process at the macroscale, where heat transfer and bubble generation are activated on an array of micro/nanostructures. In the present study, we narrow down our investigation scale to a single nanopore, where, through localized Joule heating within the pore volume, single-bubble nucleation and transition are examined at nanosecond resolution using resistive pulse sensing and acoustic sensing. Akin to macroscale boiling, where heterogeneous bubbles can nucleate and coalesce into a film, in the case of nanopores also, patches of heterogeneous bubbles nucleating on the cylindrical pore surface can form a torus-shaped vapor film blanketing the entire pore surface. In contrast to conventional pool boiling, nanopore boiling involves a reverse transition mechanism, where, with increased heat generation, film boiling reverts to nucleate boiling. With increasing bias voltage across the nanopore, the Joule heat production increases within the pore, leading to destabilization and collapse of the torus-shaped vapor film., 18 pages, 7 figures

Electroosmotic flow (EOF), a consequence of an imposed electric field onto an electrolyte solution in the tangential direction of a charged surface, has emerged as an important phenomenon in electrokinetic transport at the micro/nanoscale. Because of their ability to efficiently pump liquids in miniaturized systems without incorporating any mechanical parts, electroosmotic methods for fluid pumping have been adopted in versatile applications—from biotechnology to environmental science. To understand the electrokinetic pumping mechanism, it is crucial to identify the role of an ionically polarized layer, the so‐called electrical double layer (EDL), which forms in the vicinity of a charged solid–liquid interface, as well as the characteristic length scale of the conducting media. Therefore, in this tutorial review, we summarize the development of electrical double layer models from a historical point of view to elucidate the interplay and configuration of water molecules and ions in the vicinity of a solid–liquid interface. Moreover, we discuss the physicochemical phenomena owing to the interaction of electrical double layer when the characteristic length of the conducting media is decreased from the microscale to the nanoscale. Finally, we highlight the pioneering studies and the most recent works on electro osmotic flow devoted to both theoretical and experimental aspects.

Single entity electrochemistry (SEE) has emerged as a promising method for precise measurement and fundamental understanding of the heterogeneity of single entities. Herein, we propose the dual responsive SEE sensing of the silver nanoparticles (AgNPs) collisions through a wireless nanopore electrode (WNE). Given the high temporal resolution and low background noise features, the Faradaic and capacitive currents provide the AgNPs' collision response. The electron transfer between the AgNPs and the electrode surface is identified under a bipolar electrochemical mechanism. Compared to the ultramicroelectrode, multistep oxidation of 30 nm AgNPs is observed due to the decreased interaction of the nanoparticles to the electrode. Moreover, the nanoconfinement of WNE plays a vital role in the repeated capturing of nanoparticles from the nontunneling region into the tunneling region until a complete oxidation. As a comparison, the collision of 5 nm AgNPs with higher interaction at the electrode surface shows great decrease in the multistep events. Thus, we propose a nanoconfined interaction based SEE method which could be used for simultaneously capturing the Faradaic and capacitive response. The nanoconfined interaction based SEE method holds great promise in the better understanding of heterogeneity of single particles.

Oxide catalysts have been developed in polymer electrolyte fuel cell cathodes to replace platinum-group-metal catalysts while retaining moderate oxygen reduction reaction (ORR) activity. Recently, ...

Metal organic frameworks (MOFs) are promising porous materials for the adsorption of CO2. Here, we report the study of a luminescent MOF (LMOF), called LMOF-202. We have employed Grand Canonical Monte Carlo (GCMC) simulations to understand and explain the adsorption phenomena inside LMOF-202, and based on the phenomena happening at the molecular level, we have varied the metal ions in LMOF-202 to increase the CO2 affinity and selectivity of the material. We show that the CO2 adsorption capacity and selectivity can be increased by approximately 1.5 times at 1 bar and 298 K by changing the metal ion from Zn to Ba. We also report the feasibility of using this material to capture CO2 from flue gas under realistic conditions (1 bar and 298 K). This work shows that LMOF-202 merits further consideration as a carbon capture adsorbent.

It has been recently shown that a viscosity gradient could drive electrical current through a negatively charged nanochannel (Wiener and Stein, arXiv: 1807.09106). To understand the physics underlying this phenomenon, we employed the Maxwell-Stefan equation to obtain a relation between the flux of solvent species and the driving forces. Our 1D model, which was derived for both ideal and non-ideal solvents, shows that the ionic current depends on the ideality of the solvent, though both scenarios demonstrated good agreement with experimental data. We employed the model to understand the impact of solution bulk ionic strength and pH on the drift of ionic species with same reservoirs solution properties. Our modeling results unveiled the significant impact of bulk solution properties on the drift of ions which is in agreement with the experiments. Moreover, we have shown that the diffusion gradient along the nanochannel contributes significantly into driving ionic species if we even apply a small ionic concentration gradient to both reservoirs. Our modeling results may pave the way for finding novel applications for drift of ions toward a diffusion gradient., 12 pages, 6 figures

Resistive pulse sensing using solid-state nanopores provides a unique platform for detecting the structure and concentration of molecules of different types of analytes in an electrolyte solution. The capture of an entity into a nanopore is subject not only to the electrostatic force but also the effect of electroosmotic flow originating from the charged nanopore surface. In this study, we theoretically analyze spherical particle electrophoretic behavior near the entrance of a charged nanopore. By investigating the effects of pore size, particle-pore distance, and salt concentration on particle velocity, we summarize dominant mechanisms governing particle behavior for a range of conditions. In the literature, the Helmholtz-Smoluchowski equation is often adopted to evaluate particle translocation by considering the zeta potential difference between the particle and nanopore surfaces. We point out that, due to the difference of the electric field inside and outside the nanopore and the influence from the existence of the particle itself, the zeta potential of the particle, however, needs to be at least 30% higher than that of the nanopore to allow the particle to enter into the nanopore when its velocity is close to zero. Accordingly, we summarize the effective salt concentrations that enable successful particle capture and detection for different pore sizes, offering direct guidance for nanopore applications.

Perovskite solar cells (PSCs) are regarded as the next-generation thin-film energy harvester, owing to their high performance. However, there is a lack of studies on their encapsulation technology, which is critical for resolving their shortcomings, such as their degradation by oxygen and moisture. It is determined that the moisture intrusion and the heat trapped within the encapsulating cover glass of PSCs influenced the operating stability of the devices. Therefore, we improved the moisture and oxygen barrier ability and heat releasing capability in the passivation of PSCs by adding multi-walled carbon nanotubes to the epoxy resin used for encapsulation. The 0.5 wt% of carbon nanotube-added resin-based encapsulated PSCs exhibited a more stable operation with a ca. 30% efficiency decrease compared to the ca. 63% decrease in the reference devices over one week under continuous operation. Specifically, the short-circuit current density and the fill factor, which are affected by moisture and oxygen-driven degradation, as well as the open-circuit voltage, which is affected by thermal damage, were higher for the multi-walled carbon nanotube-added encapsulated devices than the control devices, after the stability test.

Framework flexibility is one of the most important characteristics of metal–organic frameworks (MOFs), making them highly suitable for adsorption applications. There have been a limited number of computational efforts to study flexible MOFs in the literature, and they are mostly focused on MIL-53. We studied a flexible MOF known as LMOF-201, which was found to exhibit guest-induced flexible properties; however, the mechanism of the appearance of flexibility is still unclear. First, we validated our simulation results by reproducing the experimental isotherm and powder X-ray diffraction measurements of experimental structures using grand canonical Monte Carlo (GCMC) and reactive force field (ReaxFF) molecular dynamics (MD) simulations. Then, we demonstrated the importance of the presence of a carbonyl oxygen atom in LMOF-201 to induce flexibility. The mechanism determined in this study will enable LMOF-201 to be considered for adsorption applications in the future.

Hollow poly(Lactic Acid) (PLA) microcapsules were fabricated using the bubble template method. In this method, microbubbles nucleated inside droplets of a dichloromethane solution of PLA which were located in a continuous phase of poly(vinyl alcohol). PLA-covered microbubbles formed when PLA adsorbed to the bubble surface by physisorption. Then, the coated microbubbles were spontaneously released from the droplet´s interior into the continuous phase. To increase the production yield of hollow microcapsules in this method, ultrasound was applied to enhance bubble nucleation inside the droplets. Thus to attain uniform hollow PLA microcapsules, the optimum PLA concentration with ultrasound was 30 g L −1 , which is higher than that without ultrasound (2 g L−1 ). At the optimum concentration, the average radius was 0.54 µm, with a polydispersity index of 21.2%. It was found that the equilibrium size of the microbubble template radius was the same with and without ultrasound. The production yield had a tenfold increase when ultrasound was employed.

A numerical model is presented for the prediction of transient heat and mass transfer characteristics during the regeneration process in a multilayer fixed-bed, binder-free desiccant dehumidifier. Experiments were carried out in a previous study that provided the benchmark data for validation of the current model under different temperatures and velocities of the regeneration air. A spherical microsphere silica gel having a pore diameter of 2.7 nm was used as the adsorbent during the experiments. In the first part of this study, model validation was performed for different temperatures (314.4–325.0 K) and velocities (0.6–0.9 m s−1) of regeneration air. The results showed that at a fixed regeneration temperature (325.0 K), the model predicted mass of the desorbed water as well as the desiccant bed and air temperatures were in a good agreement with the previously reported experimental results. With a decrease in the temperature and velocity of the regeneration air, the model slightly underpredicted the experimentally obtained mass of the desorbed water; however, the deviation remained within a reasonable limit. Upon validation, a parametric study was carried out to show how the heat and mass transfer characteristics of the microsphere silica gel during desorption depended on the intrinsic material properties (e.g., desorption rate constant, diffusivity, and desorption isotherm) and mechanical design parameters of the device (e.g., convective heat transfer coefficient, porosity, and thickness of the desiccant bed).

2D perovskite-stabilized FACsPbI3 (FA = formamidinium) perovskite solar cells were fabricated in both normal-type and inverted-type architectures. While the normal-type devices exhibited a high power conversion efficiency of 20.2%, their reproducibility was limited. On the other hand, the inverted-type devices exhibited an efficiency of 18.2% with a greater stability and higher reproducibility than those of the normal-type devices. The reduced reproducibility of the normal-type devices was associated with the crack formation on the perovskite films during a spin-coating process. The hardness of both the perovskite and the sublayer was directly linked to the crack formation. Inverted-type 2D/3D FACsPbI3 with ozone-treated poly(triarylamine) as sublayer exhibited the highest phase stability owing to the hydrophobic nature of poly(triarylamine) and improved energy level alignment upon an ozone treatment. In addition, strong interaction between phenethylamine cations of the 2D perovskite and of the 3D FACsPbI...

Owing to its high mobility and low sintering temperature, ZnO is a promising electron-transporting layer for flexible and tandem applications of perovskite solar cells. However, ZnO inevitably triggers the degradation of perovskite materials. Such degradation can be inhibited when ZnO films with improved stoichiometry and minimized defects are used. In this work, a high efficiency with substantial stability of ZnO-based perovskite solar cells is achieved using a high-working-pressure sputtering technique. The high-working-pressure sputtering process can produce higher quality ZnO films with fewer surface defects compared with conventional sputtering or sol–gel ZnO solution processes. A power conversion efficiency of 17.3% is recorded. In addition, the stability of these devices is significantly higher than that of the conventional ZnO-based perovskite solar cells. This work showcases that ZnO can be a good candidate for the electron-transporting layer in perovskite solar cells, particularly for flexible a...

Molecular dynamics simulations of water adsorbed in Material Institute Lavoisier MIL-101(Cr) metal-organic frameworks are performed to analyze the kinetic properties of water molecules confined in the framework at 298.15 K and under different vapor pressures and clarify the water adsorption mechanism in MIL-101(Cr). The terahertz frequency-domain spectra (THz-FDS) of water are calculated by applying fast Fourier transform to the configurational data of water molecules. According to the characteristic frequencies in the THz-FDS, the dominant motions of water molecules in MIL-101(Cr) can be categorized into three types: (1) low-frequency translational motion (0-0.5 THz), (2) medium-frequency vibrational motion (2-2.5 THz), and (3) high-frequency vibrational motion (>6 THz). Each type of water motion is confirmed by visualizing the water configuration in MIL-101(Cr). The ratio of the number of water molecules with low-frequency translational motion to the total number of water molecules increases with the increase in vapor pressure. In contrast, that with medium-frequency vibrational motion is found to decrease with vapor pressure, exhibiting a pronounced decrease after water condensation has started in the cavities. That with the high-frequency vibrational motion is almost independent of the vapor pressure. The interactions between different types of water molecules affect the THz-FDS. Furthermore, the self-diffusion coefficient and the velocity auto-correlation function are calculated to clarify the adsorption state of the water confined in MIL-101(Cr). To confirm that the general trend of the THz-FDS does not depend on the water model, the simulations are performed using three water models, namely, rigid SPC/E, flexible SPC/E, and rigid TIP5PEw.

Pore structures and gas transport properties in porous separators for polymer electrolyte fuel cells are evaluated both experimentally and through simulations. In the experiments, the gas permeabilities of two porous samples, a conventional sample and one with low electrical resistivity, are measured by a capillary flow porometer, and the pore size distributions are evaluated with mercury porosimetry. Local pore structures are directly observed with micro-x-ray computed tomography (CT). In the simulations, the effective diffusion coefficients of oxygen and the air permeability in porous samples are calculated using random walk Monte Carlo simulations and computational fluid dynamics (CFD) simulations, respectively, based on the x-ray CT images. The calculated porosities and air permeabilities of the porous samples are in good agreement with the experimental values. The simulation results also show that the in-plane permeability is twice the through-plane permeability in the conventional sample, whereas it is slightly higher in the low-resistivity sample. The results of this study show that CFD simulation based on micro-x-ray CT images makes it possible to evaluate anisotropic gas permeabilities in anisotropic porous media.

Due to the globally occurring recurring waves of COVID-19, a major part of which is taking place through droplet and aerosolized mode of transmission within the indoor environment, it is of utmost importance to design new mode of indoor ventilation system which should be energy economic in one hand and should be capable of preventing indoor transmission of COVID-19 on the other hand. A novel concept of such post-COVID-19 HVAC system to provide virus free clean air for indoor environment in sustainable way is presented in this article. The concept is developed based on the published evidence from the literature. The proposed HVAC system consists of several integral components, such as, ultraviolet germicidal irradiation- and hydroxyl radical-based air purifier unit, MOFs- and nanowire-based air filtration unit and MOFs- and encapsulated phase change material-based hybrid desiccant air conditioning unit. Concept of personalized space ventilation is also proposed to ensure proper isolation between the building occupants. The proposed system is expected to be energy efficient in providing ventilation and thermal comfort for in large indoor spaces, e.g. office floors, restaurants, and patient isolation rooms in health care facilities. Funding Information: This work was supported by JST-CREST Grant No. JPMJCR17I3, Japan Declaration of Interests: The authors declare no conflict of interest.

When applying a voltage bias across a thin nanopore, localized Joule heating can lead to single bubble nucleation, offering a unique platform for studying nanoscale bubble behavior, which is still poorly understood. Accordingly, we investigate bubble nucleation and collapse inside solid-state nanopores filled with electrolyte solutions and find that there exists a clear correlation between homo/heterogeneous bubble nucleation and the pore diameter. As the pore diameter is increased from 280 nm to 525 nm, the nucleation regime transitions from predominantly periodic homogeneous nucleation to a non-periodic mixture of homogeneous and heterogeneous nucleation. A transition barrier between the homogeneous and heterogeneous nucleation regimes is defined by considering the relative free-energy costs of cluster formation. A thermodynamic model considering the transition barrier and contact-line pinning on curved surfaces is constructed, which determines the possibility of heterogeneous nucleation. It is shown that the experimental bubble generation behavior is closely captured by our thermodynamic analysis, providing important information for controlling the periodic homogeneous nucleation of bubbles in nanopores., 15 pages, 11 figures; revised version