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The internal convective heat transfer characteristics of n-decane at supercritical pressure in a vertical square tube with a hydraulic diameter of 1.8 mm were experimentally investigated. The external wall temperatures of the square tube were measured with welded thermocouples whereas the internal wall temperatures were calculated with space marching method. In this experiment, the operating pressure ranged from 3 to 5 MPa and the heat flux from 100 to 500 kW/m2. Besides, the flow direction in the vertical tube was also switched in order to examine the effects of buoyancy. Moreover, the circumferential uniformity of heat transfer was also discussed. The results showed that the effects of buoyancy on the heat transfer were negligible once the local buoyancy number was less than a threshold. After the threshold, the buoyancy promoted the heat transfer in the downward flow configuration, but weakened the heat transfer in the upward flow one. The reason could be inferred that the buoyancy would influence the intensity of turbulent kinetic energy and the heat transfer near the wall. Finally, new heat transfer correlations for vertical upward and downward flow in square tubes were proposed.

The conventional cross-slot fed dielectric resonator antenna can only provide a narrow axial-ratio beamwidth over a limited bandwidth. As a novel approach, the compact ground plane is utilized for the simultaneous enhancement of beamwidth and bandwidth with simplicity in structure. For demonstration, a wideband circularly polarized dielectric resonator antenna was designed, fabricated and measured. Reasonable agreement between simulation and measurement can be observed. A wide 3-dB AR angular beamwidth larger than 175° was obtained across a 8.1% bandwidth.

We propose and demonstrate a directional bend sensing based on Mach-Zehnder interferometer in a high birefringence dual-core photonic crystal fiber. Its curvature sensitivity is up to 4.24 nm/m–1 within the curvature range of 2.19-3.99 m–1.

The reaction mechanism of CO methanation on the Ni4/3C-SiC(1 1 1) catalyst surface was explored by the density functional theory in this paper. The configuration of Ni4/3C-SiC(1 1 1) is built and the binding energy of Ni4 cluster on Ni4/3C-SiC(1 1 1) is higher than that on Ni4/t-ZrO2 and Ni4/Al2O3 surface, which may be contributed to improve the dispersion and stability of Ni-based catalyst. And the main pathway of CH4 formation on Ni4/3C-SiC(1 1 1) surface is CO + H → CHO + H → CH2O + H → CH3O → CH3 + H → CH4. The results show that the rate-determining step for CO methanation on Ni4/3C-SiC(1 1 1) is the formation of CH3 from CH3O dissociation with an energy barrier of 241.3 kJ/mol, which is lower than that on Ni4/t-ZrO2. In addition, the activation energy of CH3OH formation is higher than that of CH4 synthesis on Ni4/3C-SiC(1 1 1) surface (254.5 vs. 241.3 kJ/mol). Different from Ni(1 1 1), Ni4/γ-Al2O3, and Ni4/t-ZrO2 catalysts, the Ni4/3C-SiC(1 1 1) catalyst has a much higher selectivity for CH4 in the reaction of CO methanation, which may be attributed to the lower activation energy of CH3O dissociation to CH3 than that hydrogenation to CH3OH. Therefore, Ni4/3C-SiC(1 1 1) can be recommended preferentially for CH4 synthesis via CO hydrogenation, rather than CH3OH formation.

The mechanism for dimethyl carbonate (DMC) synthesis by oxidation carbonylation of methanol on a single-atom Cu1/graphene catalyst was investigated by density-functional theory calculations. Carbon vacancies in graphene can significantly enhance the interaction between Cu atoms and graphene supports, and provide an increased transfer of electrons from Cu atoms to the graphene sheet. Compared with Cu-doped divacancy graphene (Cu/DG), Cu-doped monovacancy graphene (Cu/MG) provides a stronger interaction between adsorbents and the catalyst surface. Among the reaction processes over Cu1/graphene catalysts, CO insertion into methoxide was more favorable than dimethoxide. The rate-limiting step on the Cu/DG surface is the carbomethoxide reaction with methoxide, which is exothermic by 164.6 kJ mol−1 and has an activation barrier of 190.9 kJ mol−1 energy. Compared with that on the Cu crystal surface, Cu4 and Cu3Rh clusters, and the Cu2O(111) surface, the rate-determining step for DMC formation on Cu/MG, which is CO insertion into methoxide, needs to overcome the lowest barrier of 73.5 kJ mol−1 and is exothermic by 44.6 kJ mol−1. Therefore, Cu/MG was beneficial to the formation of DMC as a single-atom catalyst.

The synthesis of dimethyl carbonate (DMC) by oxidative carbonylation of methanol on atomic Cu supported on N-doped graphene (Cu1/NG) was explored by density-functional theory. The configurations with which the Cu atom is anchored to pyridinic- (Cu/PNG), graphitic- (Cu/GNG) and amino-N (Cu/ANG) doped graphene have been systematically investigated and compared with Cu-doped monovacancy graphene (Cu/MG) and pristine graphene (Cu/PG). The binding energy of the Cu atom was found to decrease in the order Cu/GNG > Cu/ANG > Cu/MG > Cu/PNG > Cu/PG. On Cu1/NG, DMC can be formed via CO insertion into CH3O to form CH3OCO, which then reacts with additional methoxide. The barrier energies of the rate-limiting reaction of CO insertion into methoxide on Cu/PNG, Cu/GNG, Cu/MG, and Cu/ANG surfaces have been found to be 31.0, 52.1, 73.5, and 92.0 kJ/mol, respectively. And the corresponding reaction energies are −38.2, −51.3, −44.6, and −63.4 kJ/mol, respectively. The activity of the Cu1/NG catalysts increases in the order Cu/PNG

In order to improve the catalytic activity, the screening of optimal potential additives to Ni/Al2O3 catalysts for CO methanation was performed by data mining techniques with a combination of principal component analysis, K-means algorithm and Gaussian process regression (GPR). Based on a tremendous amount of data from previous studies, 63 elements excluding gaseous, poisonous and radioactive ones were selected as initial candidates. After the screening by element clustering, the activities of Ni/Al2O3 catalysts promoted by 9 representative elements including Na, Ca, Cr, B, La, Ru, Cu, Zn, and In were measured, and the catalytic activity was analyzed in terms of T50, which represents the temperature at a CO conversion rate of 50%. The activities and physicochemical properties of the nine elements were used to construct regression models by GPR. The regression models predicted that as a potential additive, Re promotes the activity; we experimentally verified that the T50 dropped by 78 °C relative to that of the unmodified Ni/Al2O3 catalyst. It can be considered to be the most effective one of all additives. The advantages of using data mining techniques in catalyst research are that they reduce the number of catalysts to be empirically analyzed and they accelerate the discovery of new catalysts.

The mechanism of methane synthesis from syngas on a Ni4/t-ZrO2(101) surface, as well as the effect of oxygen vacancies and hydroxyl groups, was systematically investigated using density functional theory. Our results showed that CO hydrogenation to a CHO intermediate was more favorable than direct CO dissociation on both perfect and defect surfaces; the main pathway for CH4 formation on Ni4/t-ZrO2(101), Ni4/VO-t-ZrO2(101) and Ni4/H-t-ZrO2(101) surfaces were as follows: CO + 4H → CHO + 3H → CH2O + 2H → CH3O → CH3 + H → CH4. The highest barrier energies during CH4 formation on Ni4/t-ZrO2(101), Ni4/VO-t-ZrO2(101) and Ni4/H-t-ZrO2(101) surfaces were 258.0, 147.6 and 233.6 kJ mol−1, and the corresponding reaction energies were −77.4, 85.1 and −84.5 kJ mol−1, respectively. Hydroxyl groups and oxygen vacancies on Ni4/t-ZrO2 surfaces were beneficial to the formation of CH4, and the selectivity of methane was significantly improved because of the oxygen vacancies.

In this paper, a dielectric resonator antenna (DRA) with self-diplexing property is proposed for the first time. Based on the high flexibility of a dielectric resonator, two modes of a rectangular dielectric resonator (TE δ11 and TE δ13 ) are utilized to implement two independent operating modes of an antenna. By introducing two pairs of open stubs on the feed lines, good isolation between two input ports is achieved together with improved bandpass characteristics. For demonstration, a self-diplexing DRA operating at 1.8 GHz and 2.45 GHz was designed, fabricated and measured. Reasonable agreement between simulation and measurement can be observed. The diplexing function has been successfully implemented without introducing extra filters. In addition, similar radiation properties have been realized for the two operating modes.

The pump-induced bleaching effects upon luminescence of Bi/Er co-doped optical fiber (BEDF) have been investigated. The bismuth related luminescence is significantly bleached, especially BAC-Si, and can hardly recover to the initial level.

The regenerative cooling technology has become the most effective method to reduce the high-temperature of the scramjet engine. With physical and chemical heat sink, the endothermic hydrocarbon fuel has excellent performance in the regenerative cooling system of the scramjet engine which operates under extremely high temperature. The pyrolytic reactions not only absorb a large amount of heat, but also produce some kinds of coking precursors, mainly alkenes and aromatics. Because of the coking precursors and the coking reactions, a lot of coke would be generated on the wall and exert strong impact on the heat transfer, as the conductivity of the coke is much lower than that of the metal wall. Meanwhile, the surface coking changes the geometric parameters of the cooling tube, which leads to the flow field variations with the thickening coking layer. So, it is needed to find out the interaction between these variations. In this paper, a one-dimensional (1D) model has been developed to calculate the flow and heat transfer parameters distributions of the pyrolytically reacted RP-3 along the regenerative cooling tube with the pyrolytic coking. The 24-step pyrolytic reaction model and the coking kinetic model are applied to predict the pyrolysis and pyrolytic coking process of RP-3, with accurate computations of the physical properties of fluid mixture which undergo drastic variations during the transcritical process. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. Calculations on the coupling relationships between the flow, heat transfer, pyrolysis and pyrolytic coking within 20 min in the circular tube have been conducted. With the heat flux increased, the coke mass is rising sharply and the temperature of the outer tube wall rises rapidly owing to the increasing thermal resistance of the coke layer. Moreover, the flow velocity becomes faster during the narrowing process of the tube caused by surface coking. In order to better understand the coking characteristics, further investigations on distributions of the surface coking under heat fluxes of 1.2–2.0MW/m2, pressures of 2.6–7.4 MPa and with inlet velocities of 0–5m/s have been performed. Results reveal that all these factors play an important role in the pyrolytic reactions and the coking rate distributions. The results in this paper have significant reference value in the design of the regenerative cooling system.

The resistance to sintering of Ni/Al2O3 catalysts with different additives for methanation reaction was modeled and predicted by data mining. In the screening, the resistance to sintering of Na, Ca, Ce, Mg, La, Cu, Zn, Zr, In, Mo, and Ti promoted Ni/Al2O3 catalyst were measured in terms of the increased rate of the size of the metallic nickel particles. The resistance to sintering of catalysts, described by the increased rate of Ni particle size as well as basic physicochemical properties of the 11 selected elements, was adopted for optimization model construction by data mining. Through regression model prediction and experimental verification, Cs was found to be an additive, and promotes the resistance to sintering mostly for Ni/Al2O3 catalysts. This result provides further evidence that data mining techniques can be employed as a highly efficient tool for the discovery of new catalysts in comparison with the traditional experimental method.

This paper aims at the interfacial phenomena of liquid-liquid mass transfer and its characteristic. By using the real-time holographic technique, the concentration distributions on the aqueous side were obtained according to holographic diagrams of mass transfer of ethanol through the interface of oil and water at different initial concentrations. Furthermore, the concentrations near the interface and the mass transfer coefficients were attained. A correlation of concentration near the interface to the concentration of the solute in the oil side was proposed. An approach of interfacial energy with solute concentration was established, and the calculated results are at good agreement with the experimental data. It is indicated that the liquid-liquid mass transfer process is approximately in accordance with two-film theory, the interfacial performance may be changed by the addition of the solute, and the interface of liquid-liquid is nonequilibrium thermodynamically during the mass transfer process.