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Effect of Thermal Convection on Density Segregation in Binary Granular Gases with Dissipative Lateral Walls 下载免费PDF全文
《中国物理快报》2017,(11)
Molecular dynamics simulations are employed to investigate the effect of thermal convection induced only by dissipative lateral walls on density segregation of the strongly driven binary granular gases under low gravity conditions. It is found that the thermal convection due to dissipative lateral walls has significant influence on the segregation intensity of the system. The dominant factor in determining the degree of segregation achieved by the system is found to be the relative convection rate between differing species. Moreover, a qualitative explanation is proposed for the relationship between the thermal convection due to dissipative lateral walls and the observed segregation intensity profiles. 相似文献
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采用格子Boltzmann方法对可变形腔体内自然对流问题进行数值研究,给出平均努赛尔数的经验关系式.腔体左壁加热长度分为左壁面的整个区域(H)和左壁面的中间区域(0.5H)两种情况,右壁向外界环境开放,上下边界绝热且可以上下移动,以此调节右出口尺寸.主要研究瑞利数(104 ≤ Ra ≤ 106),右出口尺寸(1.0H ≤ L ≤ 2.0H),左壁加热尺寸(Lh=0.5H或Lh=H)对腔体内等温线、流线、局部努塞尔数和平均努赛尔数的影响.结果表明:腔体内换热随着瑞利数的增大越来越强烈,表现为椭圆形准静止区域更加靠近上绝热壁,且热分层厚度逐渐变小,平均努赛尔数增加.而右出口尺寸的增加,对于两种加热尺寸下腔内的换热效果有不同程度影响,其中与加热尺寸为左壁面的全部区域Lh=H相比,加热尺寸为左壁面的中间情况Lh=0.5H时,右侧开口尺寸的增加对换热效果的影响不显著.此外,左壁加热尺寸为0.5H时显示出比加热尺寸为H时更高的平均传热效率.最后,针对不同的加热尺寸,提出加热面平均努赛尔数与Ra数及右壁面开口尺寸L*之间函数关系的经验预测,拟合效果满足工程实践与设计需要. 相似文献
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H. Saleh & I. Hashim 《advances in applied mathematics and mechanics.》2016,8(2):279-292
Magnetohydrodynamic natural convection heat transfer in a rotating, differentially
heated enclosure is studied numerically in this article. The governing equations
are in velocity, pressure and temperature formulation and solved using the
staggered grid arrangement together with MAC method. The governing parameters
considered are the Hartmann number, 0≤$Ha$≤70, the inclination angle of the magnetic
field, 0$^◦$≤$θ$≤90$^◦$, the Taylor number, 8.9×10$^4$≤$Ta$≤1.1×10$^6$ and the centrifugal force
is smaller than the Coriolis force and the both forces were kept below the buoyancy
force. It is found that a sufficiently large Lorentz force neutralizes the effect of buoyancy,
inertial and Coriolis forces. Horizontal or vertical direction of the magnetic field
is the most effective in reducing the global heat transfer. 相似文献
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建立自然对流作用下融化的格子Boltzmann双分布函数模型,根据非线性对流扩散方程的格子Boltzmann模型理论提出一个新的表征融化温度场的分布函数演化方程,并通过变松弛时间方法处理固液两相变热物性传热问题.应用模型对热传导融化及自然对流融化特别固液变热物的融化过程进行模拟.模拟结果与分析解、经典的关联式结果吻合较好,模型的正确性得到了验证.模拟结果表明,自然对流对融化传热过程有着重要的影响,此外固相热传导也对融化传热、融化速率及固液两相温度分布都有一定影响. 相似文献
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采用SIMPLE算法,QUICK差分格式,对底部加热三维长方体腔内空气的自然对流进行了数值模拟。根据模拟结果,探讨了方腔内流体流动与换热的静态分岔与振荡等非线性现象。数值结果显示,在固定的几何尺寸和不同Ra的情况下,当初始场不同时,会出现若干不同的解,即存在解的静态分岔;在固定的几何尺寸和相同的初始场情况下,低Ra时流动和换热处于稳态,当Ra超过某一临界值时,流动和换热就会随时间振荡,并通过倍周期分岔过渡到混沌;当方腔的几何尺寸不同时,分岔点的特征值Ra也发生变化。 相似文献
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为提升高热流密度下LED灯具的自然对流散热性能,以一款基于热电制冷(TEC)的单颗LED小型灯具模组为研究对象,在采用实验测量和回归拟合准确获得TEC性能参数的基础上,建立了有无TEC参与散热的等效热路模型,并选择合理的数学公式对其进行性能描述,进而遵循本文设计的计算流程快速得到各种散热性能数据。LED模组的散热分析表明:在恒定的LED热功率下,施加最佳的TEC电流可获得最高的散热性能;LED热功率越低,安装TEC的散热性能越比常规方法优异。经遗传算法优化前后的性能对比分析表明:优化后结构中TEC的合理工作区明显增大,能满足LED更高功率的散热需求;当LED为0.493 W时,优化后结构的最佳结温仅为15.66℃,远低于30℃的环境温度。基于TEC实验数据建立的等效热路模型,能为装配TEC的LED模组提供快速完整的散热设计分析与结构优化的合理方案。 相似文献
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使用热格子Boltzmann方法针对圆内开缝圆自然对流的流动与换热进行数值模拟,通过相空间、功率谱等进行非线性动力学特性分析,研究其流动与换热的稳定性.结果表明:随着瑞利数Ra的增加,流场的相图从开始稳定的平衡点经历Hopf分岔后转变为极限环,表明流场进入一个倍周期性振荡状态;随着瑞利数进一步增加,稳定的极限环分岔为二维环面,系统相空间结构复杂化;当瑞利数Ra大于某一临界值时,二维环面分岔突变进入混沌状态,系统在相空间中出现非常复杂的轨线结构.总体上,通过系统不同瑞利数所对应的非线性动力学特性的表现形式,表明系统经过Ruelle-Takens道路到达混沌,展现出自然对流从稳定的流动和换热发展到非线性运动特征的混沌历程. 相似文献
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Valentin Roussellet Xiaodong Niu Hiroshi Yamaguchi & Fré dé ric Magoulé s 《advances in applied mathematics and mechanics.》2011,3(1):121-130
In this article, natural convection of a temperature-sensitive magnetic fluid
in a porous media is studied numerically by using lattice Boltzmann method. Results
show that the heat transfer decreases when the ball numbers increase. When the
magnetic field is increased, the heat transfer is enhanced; however, the average
wall Nusselt number increases at small ball numbers but decreases at large ball
numbers due to the induced flow being more likely confined near the bottom walls
with a high number of obstacles. 相似文献
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Abstract The laminar natural convection in an air-filled square cavity with a partition on the heated vertical wall was experimentally investigated. Temperature measurements and flow visualizations were performed for cases with heated and cooled vertical walls (corresponding to a global Grashof number Gr H of approximately 1.4 × 108) and non dimensional top wall temperatures θ T of 0.57 (insulated) to 2.3. Experiments were performed with an aluminum partition with non dimensional height H P /H of 0.0625 and 0.125 attached to the heated vertical wall at y/H = 0.65 and 0.95. The blockage effect and/or the thermal effect of the partition resulted in changes to the temperature and flow fields but were mainly limited to the vicinity of the partition. For the cases with the heated top wall, the change in the height of the partition at y/H = 0.95 resulted in changes to the ambient temperature outside the boundary layer due to the reduction of the size of the recirculating flow in the corner region. The changes in the partition height and the top wall temperature affected the blockage effect of the partition, resulting in the local Nusselt number near the corner region to be affected. The local Nusselt number over most of the heated vertical wall of the partitioned cavity (y/H < 0.7) was correlated to the local Rayleigh number in the form Nu = C · Ra n . 相似文献
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In this paper, we consider the stationary double-diffusive natural convection model, which can model heat and mass transfer phenomena. Based on the fixed point theorem, the existence and uniqueness of the considered model are proved. Moreover, we design three finite element iterative methods for the considered problem. Under the uniqueness condition of a weak solution, iterative method I is stable. Compared with iterative method I, iterative method II is stable with a stronger condition. Moreover, iterative method III is stable with the strongest condition. From the perspective of viscosity, iterative method I displays well in the case of a low viscosity number, iterative method II runs well with slightly low viscosity, and iterative method III can deal with high viscosity. Finally, some numerical experiments are presented for testing the correctness of the theoretic analysis. 相似文献
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In this paper, we propose an adaptive defect-correction method for natural convection (NC) equations. A defect-correction method (DCM) is proposed for solving NC equations to overcome the convection dominance problem caused by a high Rayleigh number. To solve the large amount of computation and the discontinuity of the gradient of the numerical solution, we combine a new recovery-type posteriori estimator in view of the gradient recovery and superconvergent theory. The presented reliability and efficiency analysis shows that the true error can be effectively bounded by the recovery-based error estimator. Finally, the stability, accuracy and efficiency of the proposed method are confirmed by several numerical investigations. 相似文献
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A. A. Sen Indrajit Chakrabarty T. R. Seshadri 《General Relativity and Gravitation》2002,34(4):477-490
We have investigated cosmological models with a self-interacting scalar field and a dissipative matter fluid as the sources of matter. Different variables are expressed in terms of a generating function. Exact solutions are obtained for one particular choice of the generating function. The potential corresponding to this generating function is a standard tree-level potential arising in the perturbative regime in quantum field theory. With suitable choice of parameters, the scale factor in our model exhibits both decelerating behaviour in the early time as well as an accelerating phase at late times. For certain choices of the parameter the solution also exhibits an attractor nature towards an asymptotic de-Sitter universe. 相似文献
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采用格子Boltzmann方法,考虑Soret和Dufour效应,对内置高浓度发热圆的方腔内部双扩散自然对流现象进行数值模拟.高浓度发热圆位于方腔中心,四周壁面均为低温低浓度.在该模型中,用三个独立的LBGK方程分别模拟速度场、温度场和浓度场,并通过Boussinesq近似将它们耦合起来.分析Soret数和Dufour数对方腔内部双扩散自然对流的影响,得到流线图、等温线图、等浓度线图、发热圆表面平均Nusselt数和平均Sherwood数.结果表明:Soret和Dufour效应对方腔内双扩散自然对流影响明显,不能忽略. 相似文献
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The goal of this article is to study numerically the mixed convection in a differentially heated lid-driven cavity with non-uniform heating of the bottom wall. The velocity field is solved by a hybrid scheme with multiple relaxation time Lattice Boltzmann(MRT-LBM) model, while the temperature field is obtained by resolution of the energy balance equation using the finite difference method(FDM). First, the model is checked and validated using data from the literature. Validation of the present results with those available in the literature shows a good agreement.A good efficiency in time simulation is confirmed. Thereafter, the model has been applied to mixed convection in a driven cavity with non-uniform heating wall at the fixed Grashof number Gr = 106. It is found that, the heat transfer is weakened as the Richardson number is augmented. For Gr = 106, we note the appearance of secondary vortices at different positions of the cavity corners. 相似文献