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.
A numerical study was performed for incompressible oscillating flow in a two-dimensional channel, the so-called Womersley flow, using lattice-Boltzmann method (LBM). The pressure gradient varies periodically. The majo...
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A numerical study was performed for incompressible oscillating flow in a two-dimensional channel, the so-called Womersley flow, using lattice-Boltzmann method (LBM). The pressure gradient varies periodically. The major results are as follows. When the cycle is short, annular effects exist in the velocity profiles. The amplitudes of the velocity along the centerline are less than those near the wall, and the gradients of the velocity near the wall are larger than those in the center region. However, when the cycle is long the velocity profiles are of parabolic type, and the amplitudes of velocity along the centerline are larger than those near the wall. The results of the velocity fields agree well with the analytical solution. The phase difference between the velocity and temperature, the profiles of the temperature, and the fluctuating characteristics of the temperature mainly depend on the cycle and amplitude of the pressure gradient. From this study, it can be concluded that the LBM is an efficient approach for simulation of oscillating flow.
A new vibrating tube densimeter was developed with a precision of better than ±0.5 kg/m3. Using this apparatus, the saturation liquid density of dimethyl ether was measured from 233.15 K to 320.15 K, and the max ...
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A new vibrating tube densimeter was developed with a precision of better than ±0.5 kg/m3. Using this apparatus, the saturation liquid density of dimethyl ether was measured from 233.15 K to 320.15 K, and the max relative expanded uncertainty was 0.34%(coverage factor k = 2). The experimental data of this work were correlated as a polynomial function of the temperature with the published data of our previous work. The average and maximum relative deviation were 0.13% and 0.37%, respectively.
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.
Through experiments and numerical simulation methods a study has been conducted of the characteristics of convection heat exchange of ridged internal-finned tubes and a comparison of the above characteristics with the...
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Through experiments and numerical simulation methods a study has been conducted of the characteristics of convection heat exchange of ridged internal-finned tubes and a comparison of the above characteristics with the flow and heat transfer characteristics of straight internal-finned tubes is performed. The experimental results indicate that the heat exchange characteristics of ridged internal-finned tubes are better than those of straight internal-finned tubes in terms of intensified heat transfer performance, but at the same time there is a corresponding increase in flow resistance. Through the adoption of a turbulent flow model capable of realizing k-ε equation, the flow and heat transfer process of ridged internal-finned tubes have been simulated. The calculation results are in good agreement with the experimental ones. The calculation results indicate that the periodical ridges inside the finned tubes have changed the distribution of the inner-flow fields and temperature ones. Relative to the straight internal-finned tubes, a secondary vortex flow has emerged, which is conducive to an intensified heat exchange and plays a definite destructive role to the flow boundary layer. Meanwhile, by increasing the turbulent kinetic energy of the flow field, the temperature gradient in the neighborhood of the heat exchange wall surfaces has been enhanced, contributing to an intensification of heat transfer.
An investigation was conducted of the flow distribution characteristics of distribution header water-wall tubes under a supercritical pressure for a home-made 600 MW once-through boiler. The test parameters can be lis...
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An investigation was conducted of the flow distribution characteristics of distribution header water-wall tubes under a supercritical pressure for a home-made 600 MW once-through boiler. The test parameters can be listed as follows: pressure p=23-25 MPa, mass flow rate G=400-1200 kg/(m2·s), working medium temperature t=10-400°C. An experimental study has been conducted of the impact of working medium pressure, mass flow rate and working medium temperature on the vertical water-wall tube flow distribution characteristics of the distribution header. The test results show that with an increase in mass flow rate, the uniformity of flow distribution among the vertical water-wall tubes could be enhanced. The non-uniformity of flow distribution will undergo a step increase near the quasi-critical points. Moreover, with an increasing pressure, the above-mentioned step increase will become weaker. By employing a discrete model of the parallel-connected branch tubes of the distribution header, the flow distribution among the distribution header vertical water-wall tubes was calculated and the calculation results are in good agreement with the test ones.
In this paper, a new numerical procedure is proposed for the steady flow of a viscous, incompressible fluid based on SIMPLER algorithm on a non-orthogonal non-staggered grid, together with Cartesian velocity component...
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In this paper, a new numerical procedure is proposed for the steady flow of a viscous, incompressible fluid based on SIMPLER algorithm on a non-orthogonal non-staggered grid, together with Cartesian velocity components as dependent variables in the momentum equations. The main feature of the algorithm is that the pressure and pressure correction equations are obtained by explicitly treating pressure cross-derivatives terms in interface contravariant velocities. A collocated arrangement of variables is introduced on numerical grids, and the cell face velocities are calculated by the momentum interpolation. It is proved that this algorithm can be effectively used to simulate fluid flow and heat transfer in complex geometry, by the validation calculation of flow inside branching channel.
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 special device was designed to measure temperature difference in this study of heat transfer of water and oil cross flow inside vertical upward tubes. A new heat transfer correlation was obtained for cross flow. The...
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A special device was designed to measure temperature difference in this study of heat transfer of water and oil cross flow inside vertical upward tubes. A new heat transfer correlation was obtained for cross flow. The experimental results showed that the dependence of heat transfer on Reynolds is much smaller in a narrow space than that in a wide space. It was found that the heat transfer correlation of cross flow in a narrow space is obviously different from that in a wide space, and that the heat transfer correlation obtained in a wide space may not be applicable to the cross-flow heat transfer in a narrow space. Further, the single-phase heat transfer capability of water cross flow was compared with that of oil cross flow. The experimental results showed that the average heat transfer coefficient of water is about 2～3 times that ofoil when they have the same superficial velocity.
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.
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