高热流密度激光作用下含湿多孔材料的传热传质分析

建立了快速高热流密度激光作用下含湿多孔材料传热传质数学模型,并采用恰当的数值处理方法进行了数值计算.结果表明,快速高热流密度激光作用下含湿多孔材料的传热传质具有经典热质传递理论难以解释的超常效应-非傅立叶与非费克效应,且非费克效应比非傅立叶效应更明显,较高含湿量的材料在高热流密度激光作用下的非费克效应应予以足够重视.     

对流边界条件高强度快速传热传质研究

在考虑非傅立叶效应和非斐克效应的基础上,对所建立的高强度快速传热传质的耦合方程进行了对流边界条件的数值模拟．结果表明：由于超常传热传质的耦合作用会造成多孔介质内部“局部增湿”现象,且温度和湿度的变化会出现滞后现象．     

蒸发相变与界面流动耦合机理研究

本文提出了一种新模型来研究液层在其纯蒸气中的蒸发热动力学特征,尤其是当蒸发界面张力驱动流占主导作用时(如微重力环境中)液层热毛细对流和界面蒸发始终耦合在一起。气-液界面的传热传质规律有待深入研究。本文数值模拟研究了蒸发相变界面热毛细对流与蒸发效应的耦合机质,得到了不同蒸发模式和不同强度热毛细对流蒸发液层的温度分布、蒸发速率以及对流流场分布的数值解。论述了蒸发Biot数和Marangoni数对界面传热传质的影响,发现并解释了蒸发和热毛细耦合的三种模式。     

热脉冲作用下超流氦浴量子涡旋形成准则

在超流氦浴非稳态传热测量的基础上，根据膜沸腾形成时间的实验结果研究了热脉冲作用下超流氦浴量子涡旋形成准则ｔ＝ａｑ＾－３／２，得出了准则数ａ与Ｈｅｌｌ浴温度和压力的关系。有了ａ准则数好可得出Ｈｅｌｌ浴在热负荷ｑ作用下形成量子涡旋所需的时间ｔ，研究表明，Ｈｅｌｌ浴的ａ准则数远小于毛细管内的ａ准则数，其压力效应尤为明显。     

内含质量源的超临界压力水的自然对流传热与传质分析

本文对内含质量源的超临界压力水在竖直加热表面上的层流自然对流传热与传质的耦合问题，在第一类边界条件下进行了数值求解，分析讨论了内部质量源以及超临界压力下水的热物性的剧烈变化对传热与传质的影响，并给出了计算用的准则关系式。     

磁流体热疗中热质传递耦合作用研究

为研究肿瘤磁流体热疗过程中温度梯度与浓度梯度间的耦合效应对磁微粒的弥散及肿瘤内传热的影响,本文根据非平衡热力学唯象定律建立了包含浓度场及温度场的耦合传热传质模型,以常数形式的热扩散系数表征温度梯度对传质过程的影响程度。通过有限元法求解,得到考虑双场耦合作用时肿瘤内的浓度分布和温度分布。模拟结果表明,与不考虑耦合效应的情...     

热扩散效应在热声分离中的作用机理

在充满二元混合气体的声波谐振管中,振荡的气体会在径向上建立振荡的温度梯度,径向的温度梯度会引起两种组分的分子沿着不同方向进行扩散,在这种热扩散效应和热声效应的共同作用下,声波能够把混合气体中的两种组分分别带向谐振腔的速度节点和压力节点,使得混合气体在声波传播方向上逐渐分离。为了研究热声分离过程的机理,本文对一个半波长的声波谐振管进行了二维的建模,并基于可压缩的SIMPLE算法,通过求解He-Ar混合气体的速度场、温度场和一种组分的浓度场,对谐振腔内的传热传质过程进行了详细的数值模拟研究。数值模拟结果与文献的理论计算值进行了比较,结果符合良好。随后,通过研究一个周期内径向上的温度、速度和Ar的摩尔分数分布,揭示了径向上的热扩散过程,以及中间气体与边界层内气体之间的热质交换过程,完整地解释了热声分离过程的发生机理。     

基于质量积耗散的膜法除湿组件结构设计

建立了错流中空纤维膜液体除湿组件的二维传热、传质数学模型,引入研究传质过程质量积耗散的湿阻来衡量溶液除湿过程中水分传递的不可逆性。通过分析膜法除湿组件中除湿与传热耦合的湿空气水分传递过程,得到了热湿传递过程中传质的阻力表达式。通过一个典型设计实例,得出了可以降低中空纤维膜除湿组件不可逆传质损失的管长、根数、管间距、排列方式等设计参数。     

CH_4水合物分解过程的分子动力学模拟:扩散效应和气泡现象

本文在三种系综(NVT、NpT和NVE)、不同温度下进行甲烷水合物分解模拟。NVE体系与外界绝热,传热阻碍较大;NVT和NpT中,分解产生的显热会很快移除,传质作用占主导地位。通过对比,对CH_4水合物分解过程的动力学特征、气泡现象和扩散效应分别进行了解释,并提出了围绕气泡现象的三个分解阶段。考虑到气泡对局部扩散的影响,模拟中将体系划分为8个不同区域,研究局部均方位移和扩散系数,并提出了初步的扩散-气泡动力学模型。     

亚临界与超临界压力水在管内的对流传热与传质

本文对含有金属腐蚀物杂质的亚临界与超临界压力水在竖直加热圆管内的受迫对流与混合对流传热与传质进行了数值模拟，分析了变物性、浮升力以及压力等因素对管内对流传热与传质的影响。结果表明：浮升力使自下而上流过竖直加热圆管的对流传热和传质增强；在不同的温度条件下，超临界压力水的热物性对传热传质的影响有很大不同。     

Significance of Stefan blowing effect on flow and heat transfer of Casson nanofluid over a moving thin needle

The current mathematical model explains the influence of non-linear thermal radiation on the Casson liquid flow over a moving thin needle by considering Buongiorno's nanofluid model.The influences of Stefan blowing, Dufour and Soret effects are also considered in the model. The equations which represent the described flow pattern are reduced to ordinary differential equations(ODEs) by using apt similarity transformations and then they are numerically solved with Runge–Kutta-Fehlberg's fourth fifth-order method(RKF-45) with shooting process. The impacts of pertinent parameters on thermal, mass and velocity curves are deliberated graphically.Skin friction, rate of heat and mass transfer are also discussed graphically. Results reveal that, the increase in values of Brownian motion, thermophoresis, Dufour number, heating and radiative parameters improves the heat transfer. The increasing values of the Schmidt number deteriorates the mass transfer but a converse trend is seen for increasing values of the Soret number. Finally,the escalating values of the radiative parameter decays the rate of heat transfer.     

The influence of cross effects on the characteristics of heat and mass transfer in the conditions of conjugate natural convection

Mathematical modeling of nonstationary conjugate heat and mass transfer is carried out with regard to Soret and Dufour effects in an enclosure with heat-conducting impermeable walls of finite thickness with local heat and mass sources under convective-radiative heat exchange with the environment. The study is based on the two-field method. Temperature, concentration, and stream function distributions in the object analyzed are obtained over a wide range of changes of governing parameters.     

Mixed Convection Heat and Mass Transfer in a Micropolar Fluid with Soret and Dufour Effects

A mathematical model for the steady, mixed convection heat and mass transfer along a semi-infinite vertical plate embedded in a micropolar fluid in the presence of Soret and Dufour effects is presented. The non-linear governing equations and their associated boundary conditions are initially cast into dimensionless forms using local similarity transformations. The resulting system of equations is then solved numerically using the Keller-box method. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The non-dimensional velocity, microrotation, temperature and concentration profiles are displayed graphically for different values of coupling number, Soret and Dufour numbers. In addition, the skin-friction coefficient, the Nusselt number and Sherwood number are shown in a tabular form.     

Influence of magnetic field by free convection flow past an impulsively started vertical cylinder in the presence of Dufour and Soret effects

Numerical modeling of two-dimensional, unsteady, laminar, isothermal heat and mass transfer by MHD free convection flow past an impulsively started vertical cylinder in the presence of Dufour and Soret effects is considered. The governing equations of the flow problems, valid in the free convection regime, are transformed into a nondimensional form using appropriate nondimensional parameters. These equations are solved numerically by an efficient, implicit, iterative, finite-difference scheme of Crank-Nicolson type. A parametric study illustrating the influence of the magnetic field, Grashof number, and the Dufour and Soret numbers on the fluid velocity, temperature, and concentration, as well as the local and average skin friction, Nusselt and Sherwood numbers is conducted. The obtained results are shown graphically and the physical aspects of the problem are discussed.     

Convective and peristaltic viscous fluid flow with variable viscosity

In the present investigation we have analyzed the peristaltic flow when the viscous fluid with variable viscosity is bounded with convective walls. The combined effects of thermaldiffusion (Soret effects) and diffusion-thermo (Dufour effect) are considered. Convective form of the heat and mass transport phenomenon has been given special attention in addition to the effects of magnetic field. Mathematical formulation for the physical systemis derived and simplified using long wavelength and low Reynolds number approximation. Series solutions for the velocity, temperature andmass concentration fields are computed and elaborated for different physical quantities including magnetic parameter, Soret and Dufour effects, Biot numbers, etc. Streamlines analysis is presented showing the effects of bolus movement.     

Onsager Reciprocity in Premelting Solids

The diffusive motion of foreign particles dispersed in a premelting solid is analyzed within the framework of irreversible thermodynamics. We determine the mass diffusion coefficient, thermal diffusion coefficient and Soret coefficient of the particles in the dilute limit, and find good agreement with experimental data. In contrast to liquid suspensions, the unique nature of premelting solids allows us to derive an expression for the Dufour coefficient and independently verify the Onsager reciprocal relation coupling diffusion to the flow of heat.     

Modeling the onset of thermosolutal convective instability in a non-Newtonian nanofluid-saturated porous medium layer

The onset of double-diffusive (thermosolutal) convection in horizontal porous layer saturated with an incompressible couple stress nanofluid saturated is studied with thermal conductivity and viscosity dependent on the nanoparticle volume fraction. To represent the momentum equation for porous media, a modified Darcy-Maxwell nanofluid model incorporating the effects of Brownian motion and thermophoresis has been used. The thermal energy equation includes regular diffusion and cross diffusion (Soret thermo-diffusion and Dufour diffuso-thermal) terms. A linear stability analysis depends on the normal mode technique and the onset criterion for stationary and oscillatory convection is derived analytically. The nonlinear theory based on the representation of the Fourier series method is applied to capture the behavior of heat and mass transfer. It is found that the couple stress parameter enhances the stability of the system in both the stationary and oscillatory convection modes. The viscosity ratio and conductivity ratio both enhance heat and mass transfer. Transient Nusselt number is found to be oscillatory when time is small. However, when time becomes very large, all the three transient Nusselt number values approach to their steady state values.     

考虑Soret和Dufour效应的方腔内双扩散自然对流格子Boltzmann模拟

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.     

Numerical study of magneto-convective heat and mass transfer from inclined surface with Soret diffusion and heat generation effects: A model for ocean magnetic energy generator fluid dynamics

A mathematical model is developed for steady state magnetohydrodynamic (MHD) heat and mass transfer flow along an inclined surface in an ocean MHD energy generator device with heat generation and thermo-diffusive (Soret) effects. The governing equations are transformed into nonlinear ordinary differential equations with appropriate similarity variables. The emerging two-point boundary value problem is shown to depend on six dimensionless thermophysical parameters - magnetic parameter, Grashof number, Prandtl number, modified Prandtl number, heat source parameter and Soret number in addition to plate inclination. Numerical solutions are obtained for the nonlinear coupled ordinary differential equations for momentum, energy and salinity (species) conservation, numerically, using the Nachtsheim–Swigert shooting iteration technique in conjunction with the Runge–Kutta sixth order iteration scheme. Validation is achieved with Nakamura's implicit finite difference method. Further verification is obtained via the semi-numerical Homotopy analysis method (HAM). With an increase in magnetic parameter, skin friction is depressed whereas it generally increases with heat source parameter. Salinity magnitudes are significantly reduced with increasing heat source parameter. Temperature gradient is decreased with Prandtl number and salinity gradient (mass transfer rate) is also reduced with modified Prandtl number. Furthermore, the flow is decelerated with increasing plate inclinations and temperature also depressed with increasing thermal Grashof number.     

Analytical and numerical exploration of oscillatory convection in porous media

This study is part of the research about the influence of the thermal gradient on the composition and the stability of fluids in geological environments. This paper presents modelling results of oscillatory convection in a porous medium using the METSOR code. The model solves the heat and mass transport equations in a porous medium and takes into account the Soret effect (mass transport under thermal gradient). Oscillatory convection may occur in pure fluids and in binary mixtures (as a consequence of the Soret effect). Experimental data confirm the existence of this phenomenon in porous media. Here, the outputs of the METSOR code are verified against existing analytical solutions. A first modelling attempt of oscillatory convection in mixtures is presented (salt aquifer).