Membrane-based osmotic power harvesting is a strategy for sustainable power generation. 2D nanofluids with high ion conductivity and selectivity are emerging candidates for osmotic energy conversion. However, the ion diffusion under nanoconfinement is hindered by homogeneous 2D membranes with monotonic charge regulation and severe concentration polarization, which results in an undesirable power conversion performance.Here, an asymmetric nanochannel membrane with a two-layered structure is reported, in which the angstrom-scale channels of 2D transition metal carbides/nitrides (MXenes) act as a screening layer for controlling ion transport, and the nanoscale pores of the block copolymer (BCP) are the pH-responsive arrays with an ordered nanovoid structure. The heterogeneous nanofluidic device exhibits an asymmetric charge distribution and enlarged 1D BCP porosity under acidic and alkaline conditions, respectively; this improves the gradient-driven ion diffusion, allowing a high-performance osmotic energy conversion with a power density of up to 6.74 W m −2 by mixing artificial river water and seawater. Experiments and theoretical simulations indicate that the tunable asymmetric heterostructure contributes to impairing the concentration polarization and enhancing the ion flux. This efficient osmotic energy generator can advance the fundamental understanding of the MXene-based heterogeneous nanofluidic devices as a paradigm for membrane-based energy conversion technologies.

Electrical capacitance tomography (ECT) provides a non-intrusive means to visualize cross-sectional material distribution of gas-solid bubbling fluidized beds. Successful application of ECT strongly depends on the image reconstruction algorithm used. For on-line measurements of bubbling fluidized beds, employing an algorithm that can produce highquality images without extensive computation is necessary. Using the conventional Tikhonov regularization algorithm, image quality in the central area is basically satisfied but suffers from artifacts in the near-wall region. To solve this problem, a similar division operation learned from linear back projection was introduced to modify the conventional Tikhonov algorithm. Both numerical simulations and experiments were performed to evaluate the modified technique.The results indicate that the artifacts can be effectively removed and the reconstructed image quality is similar to Landweber method with dozens of iterations. Furthermore, the modified Tikhonov technique shows high accuracy when obtaining important hydrodynamic parameters in gas-solid bubbling fluidized beds. V C 2017 American Institute of Chemical Engineers AIChE J, 64: 29-41, 2018

The mechanisms underlying homogeneous fluidization of Geldart A particles have been debated for decades. Some ascribed the stability to inter-particle forces, while others insisted a purely hydrodynamic explanation. Valverde et al. (2001) fluidized 8.53-μm (i.e., Geldart C) particles by the addition of fumed silica nanoparticles and found that even during homogeneous fluidization both solid-like and fluid-like behavior can be distinguished. However, it is still unclear whether both states exist for true Geldart A particles. In this paper, particulate fluidization characteristics of three typical Geldart A powders were studied by camera recording, electrical capacitance tomography, and pressure fluctuation. For the first time, the existence of both solid-like state dominated by inter-particle forces and fluid-like state by fluid dynamics during homogeneous expansion of Geldart A particles was experimentally verified. Furthermore, the ability and performance of the used measurement techniques to identify different flow regimes were compared.

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The methanol to olefins (MTO) process has been successfully commercialized in China and will potentially become an important route for light olefins production. In this work, a modeling approach is presented for MTO fluidized bed reactor design and operation optimization. The two-fluid model (TFM) where the solid phase shear viscosity and solid phase pressure are derived from kinetic theory of granular flow has been used to model the solid−gas two-phase flows. The interphase drag force is calculated by either the traditional Gidaspow model or a recently developed EMMS-bubble model. The simulation study has been performed for a fluidized bed reactor in a 16 kt/a DMTO unit. It has been shown that the Gidaspow model cannot predict a stable dense bed, while the EMMS-bubbling model could simulate the solid fraction distribution in the reactor reasonable well. A reaction model based on the simple MTO reaction kinetics has been implemented to test the effectiveness of the model approach. The simulation results show that the methanol is converted rapidly just above the gas inlet. The selectivity of ethylene and propylene however are underpredicted, while the selectivity of CO 2 and other products are overestimated. It is suggested that a further extension of the EMMS model to a turbulent fluidized bed is important in order to get more quantitative results. Also the MTO reaction kinetics for a commercial DMTO catalyst, in which the coke formation kinetics should be included, is highly desired.

Ocean waves are the richest texture on the sea surface, from which valuable information can be inversed. In general, the Synthetic Aperture Radar (SAR) images of surface waves will inevitably be distorted due to the intricate motion of surface waves. However, commonly used imaging algorithms do not take the motion of surface waves into consideration. Therefore, surface waves on the obtained SAR images are rather blurred. To solve this problem, an airborne SAR imaging algorithm for ocean waves based on optimum focus setting is proposed in this paper. Firstly, in order to obtain the real azimuth phase speed of dominant wave, the geometric and scanning distortion in the blurred SAR image is calibrated. Subsequently, according to the SAR integration time and wavelength of the dominant wave, a proper focus setting variation section is selected. Afterwards, all the focus settings in this variation section are used to refocus the image, which are then compared to decide the optimum focus setting for dominant wave. Finally, by redesigning the azimuth matched filter using this optimum focus setting, a well-focused SAR image for the dominant wave can be obtained. The proposed algorithm is applied to both simulation and field data, and SAR images of surface waves are obtained. Furthermore, the obtained images are compared with those obtained with a zero-focus setting. The comparison shows that the focus of surface waves is significantly improved, which verifies the effectiveness of the proposed algorithm. Finally, how to choose the appropriate focus setting variation section under different parameters and the applicability of the algorithm are analyzed.

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