共查询到19条相似文献,搜索用时 203 毫秒
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采用局部热不平衡假设,对发生强吸热化学反应的多孔介质体系建立了反应与传热、传质耦合问题的数学模型,采用Ergun-Forchheimer-Brinkman方程描述多孔介质中的流体流动.运用交替方向隐式(ADI)方法对模型离散求解,并采用文献中的实验数据对模型进行验证.计算了不同条件下颗粒物料层内气体和固体骨架的温度场、产物气体浓度场以及固体转化率分布,以得到多孔介质体系内固有化学反应时的传热、传质规律.结果表明,不能忽略固体骨架与流体间的温度差.入口渗流速度、入口气体温度以及固体颗粒尺寸是影响系统反应特性的重要参数.研究结果对具有强吸热反应的固定床反应器的设计和运行具有一定的参考作用. 相似文献
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青藏高原冻土区储存着大量的天然气水合物资源,CO2置换开采冻土区的天然气水合物可实现天然气水合物的安全开采和温室气体CO2的地层封存。冰点以下多孔介质中气体水合物的生成动力学,是冻土区天然气水合物置换开采研究领域的难点和热点问题。本文全面综述了冰点以下多孔介质中气体水合物的生成动力学研究进展,讨论了不同体系冰点以下多孔介质中气体水合物的形成机理及其生成特性;详述了冰生成水合物机理及其冰粉/多孔介质体系中气体水合物的生成特性,分析了冰点以下多孔介质中气体水合物生成动力学研究尚待完善和改进的地方。最后本文指出冰点以下多孔介质中水合物的生成过程是由传热、传质等多种因素所控制,揭示不同过程的主导因素及其影响规律是今后研究的重点方向。目前对冰点以下多孔介质中水合物的生成特性及机理的认识尚未成熟,仍需深入研究。 相似文献
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多孔介质内的气泡熟化行为广泛存在于CO2封存等领域,为探究多孔介质内气泡的熟化特性,本文采用空气作为模拟气体,通过可视化实验和数值计算,对双孔隙和四孔隙气泡熟化过程进行了研究,阐释了多孔介质非均质性对熟化过程的影响规律。结果表明:在双孔隙气体饱和度较小情况下,虽然也发生正向熟化,但是孔隙结构的存在使熟化速率明显低于自由流体情况;四孔隙研究显示多孔介质非均质性对气泡熟化过程影响显著,由于孔隙的几何限制,气泡在某些情况下会发生逆Ostwald熟化,即生长的气泡在充满当前孔隙空间后会停止生长并反向熟化导致尺寸缩小;在非均质多孔介质中,由于熟化作用,气泡有传质到大孔隙区域趋势,导致大孔隙区域富集大气泡,存在泄漏风险,从而影响封存。 相似文献
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设计了两种横向和纵向喉道宽度比值(wh∶wz)分别为1.48∶1和1∶1的各向异性和各向同性多孔介质微流体芯片,以CO2为气体,二甲基硅油为液体,采用可视化实验,系统地研究了升温条件下多孔介质结构对气泡生长和聚并规律的影响。结果表明,温度升高引起的传质生长是气泡突破喉道的动力。单个气泡在多孔介质内生长方向的选择依赖于喉道的门阙压力,气泡倾向于突破门阙压力小的喉道。随着温度的升高,气泡侵入和突破喉道速度加快。在各向异性多孔介质中,气泡倾向于在横向生长时与其他气泡发生聚并,而在各向同性多孔介质中,气泡更易发生纵向聚并。当多个气泡存在于各向异性多孔介质内时,气泡的初始分布会显著影响气泡间的生长和聚并过程;在各向同性多孔介质内时,影响则较小。各向异性多孔介质在实际工程应用过程中更易实现气泡流型调控。 相似文献
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利用随机泡沫数目守恒模型,针对具有收缩进口及收缩出口的均质多孔介质二维模型,对泡沫流体驱替突破前的动态过程开展了数值模拟研究。采用IMPES方法对二维两相泡沫动态驱替过程的控制方程组进行求解,通过液相压力、液相饱和度、气泡数目等参数在多孔介质内的分布结果对泡沫动态驱替特性进行了分析研究。数值模拟结果表明,泡沫驱替过程显示出明显的入口效应,其压力分布、液相饱和度及泡沫数目分布随气体与活化剂溶液在缩小入口的注入呈现明显的发展过程。在泡沫液未完成驱替突破的情况下,缩小出口未显示出对泡沫液驱替特性的影响。数值计算结果与相应实验结果趋势一致,表明所采用的随机泡沫数目守恒模型能够正确表征多孔介质中泡沫的生成及湮灭机理,进而对泡沫液在均质多孔介质内的动态驱替特性进行准确模拟和预测。 相似文献
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天然气水合物因其储量巨大、清洁无污染而成为未来最具潜力的清洁能源之一,CO2置换法可实现天然气水合物的安全开采和温室气体的地层封存。然而,多孔介质中CO2-CH4水合物的置换过程存在反应周期长、速率慢、效率低等特点,已成为制约天然气水合物高效开采的瓶颈问题。本文全面综述了多孔介质体系中CO2-CH4水合物的置换特性,分析了CO2-CH4水合物的置换机理及其动力学过程。在此基础上,详述了不同因素对多孔介质中CO2-CH4水合物置换效率的影响规律及强化机理,包括热刺激、置换压力、小分子气体、化学添加剂等的作用机理及其规律。最后指出了多孔介质体系中CO2-CH4水合物置换过程强化技术存在的不足和未来的发展方向。对多孔介质体系中CO2-CH4水合物置换过程的强化机理及其动力学机制的认识仍需进一步研究。 相似文献
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通过建立包含动量、质量传递以及化学反应动力学方程的多物理场耦合数值模型,对以Ni为催化剂的甲烷二氧化碳重整制合成气过程中的积炭效应展开了计算。计算结果阐明了包含多孔介质催化剂段的反应通道中的速度场及压力分布,以及在通道中随气体流动以及沉积在催化剂表面的碳颗粒的浓度分布,分析了积炭对 催化剂孔隙率和渗透率的影响,并进一步讨论了甲烷浓度以及温度对积炭产生的影响,最后提出了消减积炭的方法。本文的结论对于进一步研究Ni基催化剂在CH4-CO2重整制合成气反应中积炭效应的消减有一定的指导意义。 相似文献
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To study the influence of the Soret and Dufour effects on the reactive characteristics of a porous packed bed with endothermic reactions and forced convection, a two-dimensional mathematical model cons... 相似文献
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The 2-D unsteady magnetohydrodynamic free-forced convective boundary layer flow of a viscous incompressible fluid is studied numerically taking into account heat and mass transfer. The fluid is subjected to uniform heat and mass fluxes embedded in a porous medium by the presence of coupled Dufour and Soret effects. A new class of similarity equations has been obtained by introducing a time-dependent length scale and a corresponding similarity variable. The resulting equations are then integrated numerically using the Nachtsheim-Swigert shooting iteration technique along with the sixth-order Runge-Kutta integration scheme. By developing locally similar solutions of the fluid flow, the behavior of the velocity, temperature, and concentration fields as well as the rate of heat transfer, wall temperature gradient, rate of mass transfer, and skin friction coefficient have been investigated. The effects of Grashof number (Gr), modified Grashof number (Gm), combined effects of the porous and magnetic parameter (S), suction/injection parameter Fw, Brinkman number (Br), Soret number (Sr), and Dufour number (Df) have been observed on the flow field and discussed. 相似文献
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This study investigates the unsteady mixed convection flow past a vertical porous flat plate moving through a binary mixture in the presence of radiative heat transfer and nth-order Arrhenius type of irreversible chemical reaction by taking into account the diffusion-thermal (Dufour) and thermo-diffusion (Soret) effects. Assuming an optically thin radiating fluid and using a local similarity variable, the governing nonlinear partial differential equations have been transformed into a set of coupled nonlinear ordinary differential equations, which are solved numerically by applying shooting iteration technique together with fourth-order Runge-Kutta integration scheme. Graphical results for the dimensionless velocity, temperature, and concentration distributions are shown for various values of the thermophysical parameters controlling the flow regime. Finally, numerical values of physical quantities, such as the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are presented in tabular form. 相似文献
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This work is focused on the numerical solution of steady boundary-layer stagnation-point flow of a polar fluid towards a stretching surface embedded in porous media in the presence of the effects of Soret and Dufour numbers and first-order homogeneous chemical reaction. The governing boundary-layer equations of the problem are formulated and transformed into a self-similar form. The obtained equations are solved numerically by an efficient, iterative, tri-diagonal, implicit finite-difference method. Both assisting and opposing flow conditions are considered. Comparisons of the present numerical results with previously published work under limiting cases are performed and found to be in excellent agreement. Representative results for the fluid velocity, angular velocity, temperature, and solute concentration profiles as well as the local heat and mass transfer rates for various values of the physical parameters are displayed in both graphical and tabular forms. 相似文献
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G. M. Abdel‐Rahman 《化学工程与技术》2008,31(4):554-559
The problem of thermal diffusion and magnetic field effects on combined free‐forced convection and mass transfer flow past a vertical porous flat plate, in the presence of heat generation is studied numerically. The governing momentum, energy and concentration equations are converted into a system of nonlinear ordinary differential equations by means of similarity transformations. The resulting system of coupled nonlinear ordinary differential equations is solved numerically by using the Shooting method. Numerical results are presented for velocity, temperature and concentration profiles within the boundary layer for different parameters of the problem including suction parameter, heat generation parameter, Soret number, Dufour number, magnetic parameter, etc. In addition, the effects of the pertinent parameters on the skin friction and the rates of heat and mass transfer are discussed numerically and illustrated graphically. 相似文献
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An investigation was performed to study the influence of thermo-diffusion and diffusion-thermo effects in the transient, free convective flow of a viscous, incompressible, and doubly stratified fluid past an isothermal vertical plate in the presence of first-order chemical reaction. The governing boundary layer equations were solved numerically using an implicit finite difference scheme of the Crank-Nicolson type. The effects of the Soret number, Dufour number, thermal stratification parameter, mass stratification parameter, and chemical reaction parameter are analyzed and presented graphically. Also, the influence of the parameters on local as well the average skin-friction coefficient and the rate of heat and mass transfer are analyzed and discussed. The results are compared with particular solutions available in the literature. The present results are found to be in good agreement with the existing solution. 相似文献
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Numerical simulation of asymmetric flow of coupled heat and mass transfer in a square cavity 下载免费PDF全文
The heat and mass transfer of fluid in a square cavity with a solutal and thermal source is numerically investigated. For different Rayleigh numbers, buoyancy ratio, Soret and Dufour numbers, the bifurcation characteristics of heat and mass transfer in a symmetrical square cavity are studied systematically. The results show that there is a critical Rac for onset of bifurcation that changes the fluid flow pattern. When Ra < Rac, the streamline, temperature and concentration are symmetrically distributed; when Ra > Rac, the transition from a symmetrical state to a stable asymmetric state is observed. The fluid is more prone to bifurcation with increasing of buoyancy. An increment to the Soret and Dufour effects enhances heat transfer symmetry and increases the critical Rayleigh number for breaking symmetry. 相似文献
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The Dufour and Soret effects on the unsteady laminar free convective flow with mass transfer flow past a semi-infinite isothermal
vertical cylinder were studied numerically. The governing partial differential equations were converted into a non-dimensional
form and solved numerically by applying a Crank-Nicolson type of implicit finite-difference method with a tri-diagonal matrix
manipulation and an iterative procedure. For the hydrogen-air mixture, which is a non-chemical reacting fluid, the profiles
of the unsteady dimensionless velocity, temperature and concentration are shown graphically for the different values of thermal
and mass Grashof numbers, thermal diffusion parameters (Soret numbers) and diffusion-thermo parameters (Dufour numbers). Finally,
the simulated values of the average skin-friction coefficient, the average Nusselt number and the average Sherwood number
are presented. The numerical results reveal that for an increasing Soret number or decreasing Dufour number, the time to reach
the temporal maximum and the steady-state decreases for the flow variables. As the Soret number increases or the Dufour number
decreases, both the skin friction and the Sherwood number increase, whereas the Nusselt number decreases. 相似文献