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With recent growing interest in biomimetic smart nanochannels, a biological sensory transduction in response to external stimuli has been of particular interest in the development of biomimetic nanofluidic systems. Here we demonstrate the MXene-based subnanometer ion channels that convert external temperature changes to electric signals via preferential diffusion of cations under a thermal gradient. In particular, coupled with a photothermal conversion feature of MXenes, an array of the nanoconfined Ti3C2Tx ion channels can capture trans-nanochannel diffusion potentials under a light-driven axial temperature gradient. The nonisothermal open-circuit potential across channels is enhanced with increasing cationic permselectivity of confined channels, associated with the ionic concentration or pH of permeant fluids. The photothermoelectric ionic response (evaluated from the ionic Seebeck coefficient) reached up to 1 mV·K-1, which is comparable to biological thermosensory channels, and demonstrated stability and reproducibility in the absence and presence of an ionic concentration gradient. With advantages of physicochemical tunability and easy fabrication process, the lamellar ion conductors may be an important nanofluidic thermosensation platform possibly for biomimetic sensory systems.

Salinity-gradient is emerging as one of the promising renewable energy sources but its energy conversion is severely limited by unsatisfactory performance of available semipermeable membranes. Recently, nanoconfined channels, as osmotic conduits, have shown superior energy conversion performance to conventional technologies. Here, ion selective nanochannels in lamellar Ti3C2Tx MXene membranes are reported for efficient osmotic power harvesting. These subnanometer channels in the Ti3C2Tx membranes enable cation-selective passage, assisted with tailored surface terminal groups, under salinity gradient. A record-high output power density of 21 W·m-2 at room temperature with an energy conversion efficiency of up to 40.6% is achieved by controlled surface charges at a 1000-fold salinity gradient. In addition, due to thermal regulation of surface charges and ionic mobility, the MXene membrane produces a large thermal enhancement at 331 K, yielding a power density of up to 54 W·m-2. The MXene lamellar structure, coupled with its scalability and chemical tunability, may be an important platform for high-performance osmotic power generators.

Reflood experiments at elevated pressures for small and medium break loss-of-coolant accidents were performed to investigate the influence of fuel deformation on the peak cladding temperature and local quenching behaviors. The typical experimental parameters such as initial water level, power, reflood rate, system pressure, initial wall temperature, and fluid temperature were varied to cover a wide range of flow conditions under a medium and high pressure. The experimental results showed remarkable differences in the peak cladding temperature and local quenching behaviors between the intact and deformed rod bundles due to the flow blockage effect. The present results implied that the fuel rod deformation can enhance the coolability of fuel rods by the flow blockage in the present fully blocked channel. Any bypass in a partially blocked channel may change those results due to a crossflow between intact and deformed rods. The experimental results were then used to validate the system analysis code, Multi-dimensional Analysis of Reactor Safety-KINS Standard (MARS-KS). The MARS-KS code showed good prediction of the present experimental data for most of the flow conditions.

Solar steam generation, due to its capability of producing clean water directly by solar energy, is emerging as a promising eco-friendly and energy-efficient technology to address global challenges of water crisis and energy shortage. Although diverse materials and architectures have been explored to improve solar energy utilization, high efficiency in solar steam generation could be accomplished only with external optical and thermal management. For the first time, we report a deployable, three-dimensional (3D) origami-based solar steam generator capable of near full utilization of solar energy. This auxetic platform is designed based on Miura-ori tessellation and is able to efficiently recover radiative and convective heat loss as well as to trap solar energy via its periodic concavity pattern. The 3D solar steam generator device with a nanocarbon composite of graphene oxide and carbon nanotubes being photothermal component in this work shows a very strong dependence between its solar energy efficiency and surface areal density. The device yields an extraordinary solar energy efficiency close to 100% under 1 sun illumination at a highly folded configuration. The 3D origami device can withstand a great number of folding and unfolding cycles and shows unimpaired solar steam generation performances. The unique structural feature of the 3D origami structure offers a new insight into the future development of highly efficient and easily deployable solar steam generator.

Solar-driven water evaporation is emerging as a promising solar-energy utilization process. In the present work, a highly stable, flexible and washable nonwoven photothermal cloth is prepared by electrospinning for efficient and durable solar steam evaporation. The cloth is composed of polymeric nanofibers as the matrix and inorganic carbon black nanoparticles encapsulated inside the matrix as light absorbing components. The photothermal cloth with an optimized carbon loading shows desirable underwater black properties, absorbing 94% of the solar spectrum and giving rise to a state-of-the-art solar energy utilization efficiency of 83% during the pure water evaporation process. Owing to its compositions and special structural design, the cloth possesses anti-photothermal-component-loss properties and is highly flexible, mechanically strong, and chemically stable in various harsh environments such as strong acid, alkalis, organic solvents and salty water. It can be hand-washed more than 100 times without degrading its performance and thus offers a potential mechanism for foulant cleaning during practical solar steam generation and distillation processes. The results of this work stimulate more research in durable photothermal materials aiming at real world applications.

Coolability of the partially blocked core in a large break loss-of-coolant accident (LB LOCA) is one of the most important thermal-hydraulic concerns for nuclear reactor safety analysis. During blowdown phase and early stage of reflooding phase in the LB LOCA, the prevailing wall-to-vapor convective heat transfer plays an important role on the decay heat removal process. Experiments on single-phase convective heat transfer to vapor were conducted in 5 × 5 heater rod bundles containing 3 × 3 ballooned rods of 90% flow blockage ratio with consideration of fuel relocation phenomenon. The obtained experimental data were used to assess the single-phase heat transfer enhancement models of the COBRA-TF code. The assessment results showed underprediction of local heat transfer downstream of the flow blockage. Therefore, a new correlation has been proposed to improve the prediction capability of the conventional models by more accurately describing the flow blockage effect. The new correlation predicted the local heat transfer satisfactorily within a 20% discrepancy of the experimental data for various kinds of flow blockage configurations.

Nanostructured graphene-oxide (GO) laminate membranes, exhibiting ultrahigh water flux, are excellent candidates for next generation nanofiltration and desalination membranes, provided the ionic rejection could be further increased without compromising the water flux. Using microscopic drift-diffusion experiments, we demonstrated the ultrahigh charge selectivity for GO membranes, with more than order of magnitude difference in the permeabilities of cationic and anionic species of equivalent hydration radii. Measuring diffusion of a wide range of ions of different size and charge, we were able to clearly disentangle different physical mechanisms contributing to the ionic sieving in GO membranes: electrostatic repulsion between ions and charged chemical groups; and the compression of the ionic hydration shell within the membrane's nanochannels, following the activated behavior. The charge-selectivity allows us to rationally design membranes with increased ionic rejection and opens up the field of ion exchange and electrodialysis to the GO membranes.

Clean water shortage has long been a challenge in remote and landlocked communities especially for the impoverished. Atmospheric water is now considered as an unconventional but accessible fresh water source and sorption-based atmospheric water generator (AWG) has been successfully demonstrated a reliable way of harvesting atmospheric water. The water vapor sorbents with high water uptake capacity and especially fast vapor sorption/desorption kinetics have become the bottleneck to a desirable clean water productivity in AWG. In this work, we developed a new nano vapor sorbent composed of a nano carbon hollow capsule with LiCl inside the void core. The sorbent can capture water vapor from ambient air as much as 100% of its own weight under RH 60% within 3 h and quickly release the sorbed water within just half hour under 1 kW/m2 sunlight irradiation. A batch-mode AWG device was able to conduct 3 sorption/desorption cycles within 10 h during one day test in the outdoor condition and produced 1.6 kgwater/kgsorbent. A prototype of continuous AWG device was designed, fabricated, and successfully demonstrated, hinting a possible way of large-scale deployment of AWG for practical purposes.

A test facility to investigate the flow characteristics inside reactor vessel for the Prototype Gen-IV Sodium-cooled Fast Reactor was constructed. In the test facility, reactor vessel and the main in-vessel components are linearly reduced at a scaling ratio of 1/5 and water is used as the working fluid. In the reactor vessel of the test facility, the main components such as core, UIS, PHTS pump and IHX are installed. The exteriors of the main components are conserved following the scaling ratio of 1/5, but the internal flow paths inside the fuel assemblies and IHXs are uniquely designed for precise measurement of flow rate and conserving the pressure drop characteristics. In order to determine the configuration and specific dimension of the internal flow path, separate analysis and experiment for validation are required. In the present paper, the basic design concept of internal flow path for fuel assembly simulator used for the reactor flow distribution test was established, and the detailed size of main design factors were estimated using commercial CFD code. The internal flow path of the simulator is composed of a receptacle, variable-resistance rotating orifice spool, venturi tube, and connection lines. The flow rate through the simulator could be estimated by measuring the differential pressure between inlet section and the throat of the venturi tube. The orifice spool is installed at the downstream of the receptacle, by which entire pressure drop through the simulator is controlled. A series of CFD analysis was conducted to estimate the throat diameter of the venturi tube and the size of the holes at the orifices. The geometry of the orifice is determined to obtain target pressure drop when the angle between two orifice plates is from 0° to 45°. The design specifications were applied to the fabrication of the fuel assembly simulators, and the performance of them was verified experimentally. The pressure drop of 112 fuel assembly simulators was successfully adjusted to be within ±1% of the target pressure drop. The relationship between the mass flow rate and differential pressure of the venturi tube was also obtained, and empirical correlation was suggested.

Theoretical calculations predict that by coupling an exothermic chemical reaction with a nanotube or nanowire possessing a high axial thermal conductivity, a self-propagating reactive wave can be driven along its length. Herein, such waves are realized using a 7-nm cyclotrimethylene trinitramine annular shell around a multiwalled carbon nanotube and are amplified by more than 10(4) times the bulk value, propagating faster than 2 m s(-1), with an effective thermal conductivity of 1.28+/-0.2 kW m(-1) K(-1) at 2,860 K. This wave produces a concomitant electrical pulse of disproportionately high specific power, as large as 7 kW kg(-1), which we identify as a thermopower wave. Thermally excited carriers flow in the direction of the propagating reaction with a specific power that scales inversely with system size. The reaction also evolves an anisotropic pressure wave of high total impulse per mass (300 N s kg(-1)). Such waves of high power density may find uses as unique energy sources.

The gas-polymer and liquid-polymer interfacial reactions of photosensitive polyimide can annihilate photo-reactive carbon–carbon double bonds, which remain after photo-alignment process. The annihilation processes dramatically affect voltage holding ratio and reorientation of photo-active functional groups. Photochemical dimerizations were identified using UV-visible and FT-IR spectroscopy. Polyimide films containing cinnamate groups were irradiated by linear polarized ultra violet (LPUV) light. Schadt et al. claims that the photo-alignment results from the anisotropy depletion of the cinnamate side chains as a consequence of the (2 + 2) cycloaddition reactions.1 The photoaligned polyimide induces the orientation of nematic liquid crystals perpendicular to the polarization axis.1,2 However, the un-reacted photo-sensitive functional groups generate problems such as image sticking and reduced contrast ratio. Voltage holding ratio and photo-fading observed from photo-alignment layer can be dramatically improved by annihilation process of remnant photoreactive groups.

It is known that single-walled carbon nanotubes (SWCNTs) can be functionalized by fluorine gas. Here, we report neutralized fluorine radical detection using a matted sheet of SWCNTs, prepared by alternating current dielectrophoresis. Upon exposure to neutralized radicals containing fluorine atoms in a plasma, as model analytes, the conductance of the SWCNT matt showed fast modulation. The transduction mechanism was investigated by electrical transport measurements, X-ray photoelectron spectroscopy and Raman spectroscopy. Metallic nanotubes were shown to react covalently to the near exclusion of semiconducting species. The selectivity was promoted by the curvature-induced strain of the nanotubes. The results open new opportunities for the detection of fluorine radicals at specific locations inside the reaction zone using a simple, miniaturized carbon nanotube network.

The surface conductivity of colloidal nanotubes, induced by ionic surfactants, is known to affect alternating current dielectrophoresis, which has been actively investigated with regard to separating single-walled carbon nanotubes according to electronic type. The nanotube-to-suspending medium conductivity ratio is a primary factor for determining the dielectrophoretic behavior of semiconducting nanotubes. In this study, our theoretical and experimental analysis revealed that the suspending medium conductivity also plays an important role in controlling the conductivity ratio. This work elucidates the effects of several surfactant systems on the conductivity ratio and therefore the degree of separation between metallic and semiconducting nanotubes. The equimolar mixture of anionic and cationic surfactants was more effective than a nonionic polymer in reducing the conductivity ratio because the conductivity of colloidal nanotubes was decreased and that of the suspending medium was increased. Besides, the surfactant mixture provided a better dispersion of nanotubes. The dielectrophoretic separation was carried out using microelectrodes with a gap size of 4 mum at an electric field frequency of 10 MHz. The complete separation of nanotubes at the reduced conductivity ratio was confirmed by Raman spectroscopy and electrical transport measurements.

Alternating current dielectrophoresis in water was used to position graphite oxide soot (GO-soot) particles generated by rapid thermal expansion of graphite oxide under inert gas. The dielectrophoretic deposition was carried out at a frequency of 10 MHz and a peak-to-peak voltage of 10 V, and the deposited particles were analyzed using scanning electron microscopy. The vertical cross section, obtained by focused ion beam cutting, shows the wrinkled layers of the GO-soot particles and cavities between the layers. The electrical transport measurements show typical characteristics of metal-like pathways. The improved electrical contact between electrodes and GO-soot, probably due to the thin platelet structure of GO-soot, makes the material favorable for electrical device applications. The results demonstrate that AC dielectrophoresis can be used to selectively deposit graphite oxide soot particles at desired locations.

Alternating current dielectrophoresis has attracted considerable attention as a possible candidate to separate single-walled carbon nanotubes according to electronic types. Recently, the significant effect of surface charge on the polarizability of semiconducting nanotubes was demonstrated using comparative Raman spectroscopic studies. Here we present electrical transport characteristics of surface-charge-controlled, dielectrophoretically deposited nanotube arrays. The surface charge was controlled using cationic/anionic surfactant mixtures. Complete separation between metallic and semiconducting species was achieved at the electric field frequency of 10 MHz only when the surface charge of nanotubes was neutralized, which is consistent with previous Raman investigation. A theoretical analysis, using zeta potential information as input, further supported the experimental observation.