共查询到11条相似文献,搜索用时 62 毫秒
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《Particuology》2014
A computational fluid dynamics (CFD) modeling of the gas–solids two-phase flow in a circulating fluidized bed (CFB) riser is carried out. The Eularian–Eularian method with the kinetic theory of granular flow is used to solve the gas–solids two-phase flow in the CFB riser. The wall boundary condition of the riser is defined based on the Johnson and Jackson wall boundary theory (Johnson & Jackson, 1987) with specularity coefficient and particle–wall restitution coefficient. The numerical results show that these two coefficients in the wall boundary condition play a major role in the predicted solids lateral velocity, which affects the solid particle distribution in the CFB riser. And the effect of each of the two coefficients on the solids distribution also depends on the other one. The generality of the CFD model is further validated under different operating conditions of the CFB riser. 相似文献
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Mechanisms of Particle Transport Acceleration in Porous Media 总被引:2,自引:0,他引:2
Experimental data show that the groundwater transport of radionuclides in porous media is frequently facilitated when accompanied
with colloid particles. This is usually explained by the size exclusion mechanism which implies that the particles move through
the largest pores where the flow velocity is higher. We call attention to three other mechanisms which influence the colloid
particle motion, while determining both the probable transport facilitation and retardation. First of all, it is shown that
the transport facilitation may be significantly reduced and even transformed into a retardation due to the growth of the effective
suspension viscosity (a friction-limited facilitation). Secondly, we will show that the transport of particles through the
largest pores can be retarded due to a reduced connectivity of the large-pore cluster (a percolation-breakup retardation).
Thirdly, we highlight the Fermi mechanism of acceleration known in statistical physics which is based on the elastic collisions
between particles. All three effects are analyzed in terms of the velocity enhancement factor, by using statistical models
of porous media in the form of a capillary bundle and a 3D capillary network. Optimal and critical regimes of velocity enhancement
are quantified. Estimations show that for realistic parameters, the maximal facilitation of colloid transport is close to
the experimentally observed data. 相似文献
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An experimental investigation was performed to compare the boiling heat transfer coefficients and two-phase pressure drops from a square inline and a staggered tube bundle having the same tube pitch-to-diameter ratio (P/D = 1.30) and from two square inline tube bundles having different pitch-to-diameter ratios (P/D = 1.30 and 1.70). Except at the highest heat fluxes the heat transfer coefficients generally were higher in the staggered tube bundle than in the inline tube bundle and higher in the larger P/D tube bundle than in the smaller. As the heat flux increased, the differences decreased. The differences were attributed to the tradeoff between nucleation and convection. The staggered tube bundle had higher pressure drops than the inline bundle except at low mass velocities; the larger pressure drop in the staggered bundle was attributed to the combination of a larger void fraction and a larger friction multiplier, with the frictional component dominating at higher mass velocities. Comparing the inline tube bundle pressure drops, it was concluded that the larger P/D bundle had a larger void fraction than the smaller P/D tube bundle; no conclusions could be drawn regarding the relative magnitude of the two-phase fraction multiplier. 相似文献
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Tadeusz Tomczak Katarzyna Zadarnowska Zbigniew Koza Maciej Matyka Łukasz Mirosław 《International Journal of Computational Fluid Dynamics》2013,27(4-5):201-209
While new power-efficient computer architectures exhibit spectacular theoretical peak performance, they require specific conditions to operate efficiently, which makes porting complex algorithms a challenge. Here, we report results of the semi-implicit method for pressure linked equations (SIMPLE) and the pressure implicit with operator splitting (PISO) methods implemented on the graphics processing unit (GPU). We examine the advantages and disadvantages of the full porting over a partial acceleration of these algorithms run on unstructured meshes. We found that the full-port strategy requires adjusting the internal data structures to the new hardware and proposed a convenient format for storing internal data structures on GPUs. Our implementation is validated on standard steady and unsteady problems and its computational efficiency is checked by comparing its results and run times with those of some standard software (OpenFOAM) run on central processing unit (CPU). The results show that a server-class GPU outperforms a server-class dual-socket multi-core CPU system running essentially the same algorithm by up to a factor of 4. 相似文献
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V. N. Vetlutskii V. L. Ganimedov M. I. Muchnaya 《Journal of Applied Mechanics and Technical Physics》2005,46(6):824-834
A two-phase flow with high Reynolds numbers in the subsonic, transonic, and supersonic parts of the nozzle is considered within
the framework of the Prandtl model, i.e., the flow is divided into an inviscid core and a thin boundary layer. Mutual influence
of the gas and solid particles is taken into account. The Euler equations are solved for the gas in the flow core, and the
boundary-layer equations are used in the near-wall region. The particle motion in the inviscid region is described by the
Lagrangian approach, and trajectories and temperatures of particle packets are tracked. The behavior of particles in the boundary
layer is described by the Euler equations for volume-averaged parameters of particles. The computed particle-velocity distributions
are compared with experiments in a plane nozzle. It is noted that particles inserted in the subsonic part of the nozzle are
focused at the nozzle centerline, which leads to substantial flow deceleration in the supersonic part of the nozzle. The effect
of various boundary conditions for the flow of particles in the inviscid region is considered. For an axisymmetric nozzle,
the influence of the contour of the subsonic part of the nozzle, the loading ratio, and the particle diameter on the particle-flow
parameters in the inviscid region and in the boundary layer is studied.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 65–77, November–December, 2005. 相似文献
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柱体形状对气液两相涡街的影响 总被引:4,自引:0,他引:4
本文试验研究了柱体形状对气液两相涡街的影响,得出了在气液两相流中的最佳涡街发生体和发生两相涡街时,两相斯托拉赫数,来流截面含气率,水流量三者之间的关系。试验工质为水和空气,混合物流动方向垂直向上。参数范围:相对压强0.0-0.2MPa;来流截面含气率0.0-0.35;水流量0.0-26m3/h。 相似文献
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Flow patterns, void fraction and friction pressure drop measurements were made for an adiabatic, vertical up-and-down, two-phase flow of air–water mixtures across a horizontal in-line, 5×20 tube bundle with a pitch-to-diameter ratio of 1.28. The flow patterns in the cross-flow zones were obtained and flow pattern maps were constructed. The data of average void fraction were less than the values predicted by a homogenous flow model and showed a strong mass velocity effect, but were well-correlated in terms of the Martinelli parameter Xtt and liquid-only Froude number FrLO. The two-phase friction multiplier data could be well-correlated with the Martinelli parameter. 相似文献
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In this work, the drag coefficient and the void fraction around a tube subjected to two-phase cross flow were studied for a single tube and for a tube placed in an array. The drag coefficients were determined by measuring the pressure distribution around the perimeter of the tube. Single tube drag data were taken when the tube was held both rigidly and flexibly. The test tube was made of acrylic and was 2.2 cm in diameter and 20 cm in length. In the experiments, liquid Reynolds number ranged from 430 to 21,900 for the single tube and liquid gap Reynolds number ranged from 32,900 and 61,600 for the tube placed in a triangular array. Free stream void fraction was varied from 0 to 0.4. At low Reynolds numbers, the ratio of two-phase to single-phase drag coefficient is found to be a strong function of εGr/Re2. However, at high Reynolds numbers only void fraction is the important parameter. Empirical correlations have been developed for the ratio of two-phase drag on a single tube and on a tube placed in an array. 相似文献