Concentrating PV systems usually use Fresnel lens as radiation concentrator. In this paper, in order to study the concentrating performance of the Fresnel lens, modular Fresnel lens mode was developed and its optical ...
Concentrating PV systems usually use Fresnel lens as radiation concentrator. In this paper, in order to study the concentrating performance of the Fresnel lens, modular Fresnel lens mode was developed and its optical performance was analyzed by the ray tracing method. The imaging characteristic of Fresnel was studied and the optimal imaging location and the size of dispersion spot with different inlet angle were figured out. Flux distribution of the different imaging plane were also examined and compared. The results show that the dispersion spot deviates from the focus and the size of the dispersion spot is enlarged as the incidence angle increase, especially at the high geometric concentration ratio. Then in order to solve the problem, a flat light pipe was applied to reflect sun light onto the absorber plane. The simulation results show that with the new design, sun lights with large inlet angle could also be casted on the absorber.
A simple line interface calculation-volume of fluid(SLIC-VOF) interface reconstruction technology was developed on the basis of the triangular unstructured grid. For a cell containing the interface, a straight line se...
详细信息
A simple line interface calculation-volume of fluid(SLIC-VOF) interface reconstruction technology was developed on the basis of the triangular unstructured grid. For a cell containing the interface, a straight line segment parallel with one side of the triangle cell was set on the interface according to the volume fractions in the three neighbor cells. The volume flux of the fluid with the assigned phase was determined by the geometry relation between the interface line and the volume flux on each side. Three tests were performed to verify the feasibility of the present unstructured SLIC-VOF interface reconstruction method, including an advection test of a right-angled triangle, the Zalesak slotted disk rotation test, and a single-vortex shearing flow test. The results show that the accuracy of the present method for the unstructured grid with 7600 cells is comparative with that of the conventional SLIC-VOF method for the structured grid with 6400 cells after the interface restoration in the reversed velocity field.
Bubbly mixing layer with polymer additives is investigated by PIV. The void fraction is 0.5%. The comparison between single-phase and bubbly mixing layer shows that the dynamic development of mixing layer is greatly i...
详细信息
Bubbly mixing layer with polymer additives is investigated by PIV. The void fraction is 0.5%. The comparison between single-phase and bubbly mixing layer shows that the dynamic development of mixing layer is greatly influenced by the bubble injection. Similar with single phase, the Reynolds stress and vorticity still concentrate in a coniform area of central mixing flow field and the width increases with increasing the Reynolds number. Mean Reynolds stress decreases with bubble injection at high Reynolds numbers and the decreasing of Reynolds stress with polymer additives is much more than that in a pure water case. There is an obvious decreasing to the peak value of vorticity when bubbles are injected into the fluid, and the influence on the viscoelastic fluid is smaller than that on the pure water.
This paper considers an epidemic model of a vector-borne disease which has the vectormediated transmission only. The incidence term is of the bilinear mass-action form. It is shown that the global dynamics is complete...
详细信息
This paper considers an epidemic model of a vector-borne disease which has the vectormediated transmission only. The incidence term is of the bilinear mass-action form. It is shown that the global dynamics is completely determined by the basic reproduction number Ro. If Ro ≤ 1, the diseasefree equilibrium is globally stable and the disease dies out. If Ro 〉 1, a unique endemic equilibrium is globally stable in the interior of the feasible region and the disease persists at the endemic equilibrium. Numerical simulations are presented to illustrate the results.
A finite volume solver for Casson fluid flow based on SIMPLE algorithm of Newtonian fluid on unstructured collocated grid is developed to simulate haemodynamics in complex vessel. The discretization of convective flux...
详细信息
A finite volume solver for Casson fluid flow based on SIMPLE algorithm of Newtonian fluid on unstructured collocated grid is developed to simulate haemodynamics in complex vessel. The discretization of convective flux and source term are similar with Newtonian fluid. For the discretization of diffusion flux, viscosity will take the value calculated from the flow field of previous iteration so as to avoid the complexity caused by the complicated viscosity expression as a function of shear rate. Then the discretization of momentum equation is similar with that of Newtonian fluid with variable viscosity and SIMPLE algorithm can be used to resolve the pressure-velocity coupling. With this algorithm, blood flows in a T-typed bifurcation are simulated. The simulation results of Casson fluid are more consistent with experimental data than that of Newtonian fluid, which indicates that using Casson model to simulate non-Newtonian characteristics of blood flow is successful and necessary.
Turbulent mixing layer flow was simulated by the discrete vortex method, and viscosity was modeled by the random walk method and the solid wall was represented by the vortex sheet in the simulation. The predictions of...
详细信息
Turbulent mixing layer flow was simulated by the discrete vortex method, and viscosity was modeled by the random walk method and the solid wall was represented by the vortex sheet in the simulation. The predictions of the profiles of mean velocity and turbulent flow parameters agree well with experimental data. The results show that the peak value of Reynolds shear stress increases but the fluctuations of the peak value occur because of vortex-pairing, and vorticity peak value increases in the downstream direction. Then the effect of Reynolds number on the distribution of the turbulent flow parameters at the same velocity ratio was explored. It seems that the peak values of Reynolds shear stress under different Reynolds numbers will increase at the similar slope in the downstream direction. The average vorticity peak value will decrease in the downstream direction, and the decrease rate will increase with Reynolds number. In addition, the vorticity peak value in each section will increase nearly linearly with Reynolds number.
In order to show the effects of different diameter combinations on crude oil temperature when a crude oil pipeline and a products pipeline are laid in one trench, four typical diameter combinations are selected to con...
详细信息
In order to show the effects of different diameter combinations on crude oil temperature when a crude oil pipeline and a products pipeline are laid in one trench, four typical diameter combinations are selected to conduct numerical simulation. After a series of calculations, the minimum mean temperature difference and the maximum temperature difference of the crude oil along the pipelines are obtained. In real pipeline constructions, the effects of other diameter combinations on crude oil temperature can be predicted by the method of linear interpolation to calculate results of the four diameter combinations obtained in this study.
The dimension of erythrocyte is close to capillary diameter and in microcirculation blood should be treated as a two-phase flow system, i.e., erythrocytes suspended in plasma. The rheological property of erythrocytes ...
详细信息
The dimension of erythrocyte is close to capillary diameter and in microcirculation blood should be treated as a two-phase flow system, i.e., erythrocytes suspended in plasma. The rheological property of erythrocytes will significantly influence the hemodynamics. In our experiment, the motion and deformation of erythrocytes in a microfluidic chip with rectangular cross-section microchannel was captured by optical microscope and high speed CCD camera. The aggregation, deformation and common movement forms of erythrocytes were observed under different viscosity, hematocrit and velocity. It was found that erythrocytes behaved a regular biconcave disc shape at low velocity and low-to-medium viscosity, and always rolled and rotated themselves in their movement. At high velocity and medium viscosity, RBCs elongated obviously along the flow direction and presented a flat oval shape together with a tank-treading motion (TTM).
multiphaseflow induced CO2 corrosion has resulted in serious losses in oil and gas production. In this paper, gas‐liquid two‐phase vertical upward slug flow has been analyzed from aspects containing flow structure,...
multiphaseflow induced CO2 corrosion has resulted in serious losses in oil and gas production. In this paper, gas‐liquid two‐phase vertical upward slug flow has been analyzed from aspects containing flow structure, hydrodynamic characteristics, mass transfer characteristics and their effects on pipe wall and corrosion product film, and it is found that slug flow has a distinct effect on transports of corroding species to and of corrosion products from the wall, momentum interchange between fluid and wall and the formation and damage of corrosion product film. In addition, the transports of corrosive species and corrosion product are also an important step in CO2 corrosion process. It is assumed that the slug flow induced CO2 corrosion of pipeline is dependent on the non‐linear coupling of the characteristics including the shear stress, the normal stress, the mass transfer coefficient, and the electrochemical reaction.
This paper proposes an improved lattice Boltzmann scheme for incompressible axisymmetric flows. The scheme has the following features. First, it is still within the framework of the standard lattice Boltzmann method u...
详细信息
This paper proposes an improved lattice Boltzmann scheme for incompressible axisymmetric flows. The scheme has the following features. First, it is still within the framework of the standard lattice Boltzmann method using the single-particle density distribution function and consistent with the philosophy of the lattice Boltzmann method. Second, the source term of the scheme is simple and contains no velocity gradient terms. Owing to this feature, the scheme is easy to implement. In addition, the singularity problem at the axis can be appropriately handled without affecting an important advantage of the lattice Boltzmann method: the easy treatment of boundary conditions. The scheme is tested by simulating Hagen-Poiseuille flow, three-dimensional Womersley flow, Wheeler benchmark problem in crystal growth, and lid-driven rotational flow in cylindrical cavities. It is found that the numerical results agree well with the analytical solutions and/or the results reported in previous studies.
暂无评论