Cadmium sulfide photocatalyst was prepared by hydrothermal methods with one-step and two-step methods, respectively. Platinum was loaded on the surface of prepared photocatalysts and its optimal loading amount was exa...
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Cadmium sulfide photocatalyst was prepared by hydrothermal methods with one-step and two-step methods, respectively. Platinum was loaded on the surface of prepared photocatalysts and its optimal loading amount was examined. All the prepared photocatalysts were characterized by XRD, UV-Vis, XRF, SEM and TEM and their pohtocatalytic activity was evaluated by H2 evolution from water under visible light. It was found that the photocatalyst prepared by two-step showed markedly improved hydrogen production activity.
Numerical research was carried out on the convection heat transfer characteristics in bilaterally heated annular channel with narrow gap under the conditions of fully developed flow, where the inner and outer walls ar...
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Numerical research was carried out on the convection heat transfer characteristics in bilaterally heated annular channel with narrow gap under the conditions of fully developed flow, where the inner and outer walls are heated by uniform but unequal heat fluxes. Calculation results show that the ratio of the inner wall heat flux to the outer wall heat flux has great effects on the heat transfer characteristics in bilaterally heated narrow annuli. With the increase of the inner wall heated flux, the heat transfer coefficient at the outer wall of the inner tube will decrease, while the heat transfer coefficient at the inner wall of outer tube will increase. These numerical results are in good agreement with some experimental results in open literatures. Numerical results also show that the decrease of the annuli gap will yield heat transfer deterioration during flowing in narrow annular channels.
A transient one-dimensional two-fluid model is proposed to investigate numerically the interfacial instability and the onset of slugging for liquid-gas flow in a horizontal duct. In the present model, the effects of s...
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A transient one-dimensional two-fluid model is proposed to investigate numerically the interfacial instability and the onset of slugging for liquid-gas flow in a horizontal duct. In the present model, the effects of surface tension and transverse variations in dynamic pressure are taken into account. The evolution of interfacial disturbances is displayed and compared with the linear viscous Kelvin-Helmholtz stability analyses. It shows that interfacial wave is more instable due to the non-linear effect. The model predicts well the stability limit of stratified flow in comparison with the experimental data, and also automatically tracks the onset of slugging. The results show that the initiation of hydrodynamic slugging is related to local interfacial instability. Based on the cycle of slugging, a model for slug frequency is presented, which predicts the trends of slug frequencies with gas/liquid flow rate well in comparison with the available data. The effects of physical properties on slugging have been examined. It is found that with the increase in the gas viscosity and liquid density the slugging would be inhibited, whereas, with the increase in liquid viscosity and gas density, the slugging can be promoted.
A thermal boundary condition for a double-population thermal lattice Boltzmann equation (TLBE) is introduced and numerically demonstrated. The unknown distribution population at the boundary node is decomposed into it...
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A thermal boundary condition for a double-population thermal lattice Boltzmann equation (TLBE) is introduced and numerically demonstrated. The unknown distribution population at the boundary node is decomposed into its equilibrium part and nonequilibrium parts, and then the nonequilibrium part is approximated with a first-order extrapolation of the nonequilibrium part of the populations at the neighboring fluid nodes. Numerical tests with Dirichlet and Neumann boundary constraints show that the numerical results of the TLBE together with the present boundary schemes agree well with the analytical solutions and those of the finite-volume method.
A lattice Boltzmann method is developed for gaseous slip flow at the pore scale in microscale porous geometries. flow characteristics through various porous structures are studied for different Knudsen numbers and inl...
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A lattice Boltzmann method is developed for gaseous slip flow at the pore scale in microscale porous geometries. flow characteristics through various porous structures are studied for different Knudsen numbers and inlet to outlet pressure ratios. It is found that the gas permeability is larger than the absolute permeability of porous media due to the gas slippage effect. Furthermore, the rarefaction influence on the gas permeability is more evident for porous structures with low porosity. The Klinkenberg equation is confirmed for the simulated porous structures. However, the second-order term of the Knudsen number (Kn2) cannot be neglected for gaseous flow with relatively high Knudsen numbers. A model for predicting the pressure drop of the flow through microscale porous media is presented based on the Ergun equation and the Carman-Kozeny equation by taking into account the effects of gas rarefaction and compressibility.
Within the range of pressures from 9 to 28 MPa, mass velocities from 600 to 1200 kg/(m2s), and heat fluxes from 200 to 500 kW/m2, experiments have been performed to investigate the heat transfer to water in the inclin...
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Within the range of pressures from 9 to 28 MPa, mass velocities from 600 to 1200 kg/(m2s), and heat fluxes from 200 to 500 kW/m2, experiments have been performed to investigate the heat transfer to water in the inclined upward internally ribbed tube with the inclined angle of 19.5 degree, the maximum outer diameter of 38.1 mm, and the thickness of 7.5 mm. Based on the experiments, it was found that heat transfer enhancement of the internally ribbed tube could postpone departure from nucleate boiling at the sub-critical pressure. However, the heat transfer enhancement decreased near the critical pressure. At supercritical pressure, the temperature difference between the wall and fluid increased near the pseudo-critical temperature, but the increasing of wall temperature was less than that of departure from nucleate boiling at sub-critical pressure. When pressure was close to the critical pressure, the temperature difference between the wall and fluid greatly increased near the pseudo-critical temperature. Heat transfer to supercritical water in the inclined upward internally ribbed tube was enhanced or deteriorated near the pseudo-critical temperature with the variety of ratio between the mass velocity and the heat flux. Due to the rotational flow of the internal groove reducing the effect of nature convection, the internal wall temperature of the inclined upward internally ribbed tube uniformly distributed along the circumference. The maximum internal wall temperature difference of the inclined upward internally ribbed tube along the circumference was only 10 degree Centigrade when the fluid enthalpy exceeds 2000 kJ/kg. Considering the effect of acute variety of the fluid property on heat transfer, the correlation of heat transfer coefficient on the top of the inclined upward internally ribbed tube have been provided.
As coal was transported homogeneously at high pressure by adding the sodium carboxymethylcellulose (CMC), the hydrogen production from catalytic gasification of coal/CMC in supercritical water (SCW) was investigated. ...
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As coal was transported homogeneously at high pressure by adding the sodium carboxymethylcellulose (CMC), the hydrogen production from catalytic gasification of coal/CMC in supercritical water (SCW) was investigated. The experimental results showed that the molar fraction of hydrogen is higher than that in conventional gasification. H2, CO2 and CH4 are the main product gases, the higher pressure and higher CMC content is advantage of hydrogen production. Longer residence time is favorite to gasification of coal/CMC, but it is not advantage of hydrogen production from coal/CMC gasified in SCW at 20-25 MPa, 15-30 s and 650°C.
The equilibrium sand transport is simulated by Lagrange model combined with the probabilistic distributions of initial speed and angle of ejection sand grain in this paper. Five forms of the possible distributions are...
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The equilibrium sand transport is simulated by Lagrange model combined with the probabilistic distributions of initial speed and angle of ejection sand grain in this paper. Five forms of the possible distributions are summarized from the previous study results published in literature. Since the macro-quantities simulated by rational distribution should be coincident well with experimental result, the rationality of the distributions can be tested by comparing the quantities simulated from these distributions with the experimental quantities. Detailed analysis indicates that the distribution of initial speed and angle of ejected grains in equilibrium sand transport should be a monotonous decline function. According to the experimental data a segmented function comprised by an exponential distribution and a normal distribution is suggested in this paper. This distributions is confirmed by further comparison with experimental data.
Prediction of dryout point is experimentally investigated with deionized water upflowing through narrow annular channel with 1.0 mm and 1.5 mm gap respectively. The annulus with narrow gap is bilaterally heated by AC ...
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Prediction of dryout point is experimentally investigated with deionized water upflowing through narrow annular channel with 1.0 mm and 1.5 mm gap respectively. The annulus with narrow gap is bilaterally heated by AC current power supply. The experimental conditions covered a range of pressure from 0.8 to 3.5 MPa, mass flux of 26.6 to 68.8 kg·m-2·s-1 and wall heat flux of 5 to 50 kW·m-2. The location of dryout is obtained by observing a sudden rise in surface temperature. Kutateladze correlation is cited and modified to predict the location of dryout and proved to be not a proper one. Considering in detail the effects of geometry of annuli, pressure, mass flux and heat flux on dryout, an empirical correction is finally developed to predict dryout point in narrow annular gap under low flow condition, which has a good agreement with experimental data.
The system of ice-making by spraying water in winter and utilizing the ice in summer is pollution-free and economizes the first investment, operating cost, and reduces the peak of electric power in summer. Through est...
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The system of ice-making by spraying water in winter and utilizing the ice in summer is pollution-free and economizes the first investment, operating cost, and reduces the peak of electric power in summer. Through establishing the energy equilibrium equation of sprayed water drop, the relation between the diameter of water droplet and the time of icing at different ambient temperature and coefficient of performance of the system of ice-making by spraying water has been obtained. The errors between the numerical solution and the experimental data lie in a range of 7% to 10%, indicating that the model is reasonable. The method of the ice making is promising in the exercisable region to substitute the mechanical refrigeration system.
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