Self-Similar Solution of Heat and Mass Transfer of Unsteady Mixed Convection Flow on a Rotating Cone Embedded in a Porous Medium Saturated with a Rotating Fluid

A self-similar solution of unsteady mixed convection flow on a rotating cone embedded in a porous medium saturated with a rotating fluid in the presence of the first and second orders resistances has been obtained. It has been shown that a self-similar solution is possible when the free stream angular velocity and the angular velocity of the cone vary inversely as a linear function of time. The system of ordinary differential equations governing the flow has been solved numerically using an implicit finite difference scheme in combination with the quasi-linearization technique. Both prescribe wall temperature and prescribed heat flux conditions are considered. Numerical results are reported for the skin friction coefficients, Nusselt number and Sherwood number. The effect of various parameters on the velocity, temperature and concentration profiles are also presented here.

CONJUGATE MODEL FOR HEAT AND MASS TRANSFER OF POROUS WALL IN THE HIGH TEMPERATURE GAS FLOW

Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow. The main attention is given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.

Numerical Study of Heat Transfer and Contaminant Transport in an Unsaturated Porous Soil

Penetration of chemicals in the soil ground through irrigation water or rainfall induces important risks for the environment. These risks are badly known and may lead to direct contamination of the environment (atmosphere or ground water) or harmful effects on organisms living at ground level, indirectly affecting men. It is thus necessary to estimate these potential chemical risks on the environment. For that reason, the gradual change of these products (fertilizers, solutions, pollutants, ...) in the ground has been the subject of a lot of recent research works, based in particular on the study of non-saturated porous media in a theoretical, numerical or experimental way. Most of these works are incomplete and, in order to simplify the problem, they don’t take into accounts some process, which may be of prime importance under particular natural conditions. Complexity of such studies results from their multidisciplinary nature. In this communication, we study simultaneous transport of pollutant, the water that provides transport and the heat transfer in a 200 cm long cylindrical column full of sand taken as a non-saturated porous medium. We consider two kinds of conditions on the temperature at the column surface: the case of constant temperature and the case of sinusoidal temperature. We evaluate the influence of this temperature on the transfers. This study is purely numerical. We use the control volume method to determine hydrous, thermal and pollutant concentration profiles.

New Analytical Study of the Effects Thermo-Diffusion, Diffusion-Thermo and Chemical Reaction of Viscous Fluid on Magneto Hydrodynamics Flow in Divergent and Convergent Channels

In this paper, the magneto hydrodynamic (MHD) flow of viscous fluid in a channel with non-parallel plates is studied. The governing partial differential equation was transformed into a system of dimensionless non-similar coupled ordinary differential equation. The transformed conservations equations were solved by using new algorithm. Basically, this new algorithm depends mainly on the Taylor expansion application with the coefficients of power series resulting from integrating the order differential equation. Results obtained from new algorithm are compared with the results of numerical Range-Kutta fourth-order algorithm with help of the shooting algorithm. The comparison revealed that the resulting solutions were excellent agreement. Thermo-diffusion and diffusion-thermo effects were investigated to analyze the behavior of temperature and concentration profile. Also the influences of the first order chemical reaction and the rate of mass and heat transfer were studied. The computed analytical solution result for the velocity, temperature and concentration distribution with the effect of various important dimensionless parameters was analyzed and discussed graphically.

Soret and Dufour effects on mixed convection unsteady MHD boundary layer flow over stretching sheet in porous medium with chemically reactive species

This paper studies the thermal-diffusion and diffusion thermo-effects in the hydro-magnetic unsteady flow by a mixed convection boundary layer past an imperme- able vertical stretching sheet in a porous medium in the presence of chemical reaction. The velocity of t^he stretching surface, the surface temperature, and the concentration are assumed to vary linearly with the distance along the surface. The governing partial differential equations are transformed into self-similar unsteady equations using similarity transformations .and solved numerically by the Runge-Kutta fourth order scheme in as- sociation with the shooting method for the whole transient domain from the initial state to the final steady state flow. Numerical results for the velocity, the temperature, the concentration, the skin friction, and the Nusselt and Sherwood numbers are shown graph- ically for various flow parameters. The results reveal that there is a smooth transition of flow from unsteady state to the final steady state. A special case of our results is in good agreement with an earlier published work.

A MATHEMATICAL MODEL FOR HEAT AND MASS TRANSFER IN UNSATURATED WET POROUS MEDIA CONSIDERING EFFECT OF CAPILLARY HYSTERESIS

Based on the transport mechanism of heat and mass transfer and by using the minimum gradient theory for unsaturated flow in capillary porous media, a mathematical model is developed for heat and mass transfer in unsaturated wet porous media considering the effect of capillary hysteresis. The heat and mass transport properties in the derived differential equations are analyzed in detail. which opens new way to further develop practical methods for determining heat and mass transport properties in wet porous media.

Analysis of 2D Flow and Heat Transfer Modeling in Fracture of Porous Media

Heat and mass transfer between porous media and fluid is a complex coupling process, which is widely used in various fields of engineering applications, especially for natural and artificial fractures in oil and gas extraction. In this study, a new method is proposed to deal with the flow and heat transfer problem of steady flow in a fracture. The fluid flow in a fracture was described using the same method as Mohais, who considered a fracture as a channel with porous wall, and the perturbation method was used to solve the mathematical model. Unlike previous studies, the shear jump boundary condition proposed by Ochoa-Tapia and Whitaker was used at the interface between the fluid and porous media. The main methods were perturbation analysis and the application of shear jump boundary conditions. The influence of permeability, channel width, shear jump degree and effective dynamic viscosity on the flow and heat transfer in the channel was studied by analysing the analytical solution. The distribution of axial velocity in the channel with the change of the typical parameters and the sensitivity of the heat transfer was obtained.

NATURAL CONVECTIVE HEAT AND MASS TRANSFER BY THE COUPLING OF TEMPERATURE CRADIENT AND CONCENTRATION GRADIENT IN A POROUS MEDIUM

The coupling of temperature gradient and concentration gradient and it's effects on heat and mass transfer are considered for natural convection in a porous enclosure. By use of the penalty finite element method, the distributions of flow, temperature and concentration fields are numerically simulated in four kinds of boundary condition. The profiles of heat and mass transfer coefficients along with the vertical wall are shown in the peper.

Analytical Solution of Coupled Laminar Heat-Mass Transfer in a Tube with Uniform Heat Flux

Analytical solution is obtained of coupled laminar heat-mass transfer in a tube with uniform heat flux.This corresponds to the case when a layer of sublimable material is coated on the inner surface of a tube with its outer surface heated by uniform heat flux and this coated material will sublime as gas flows throught the tube.

填料式液体除湿系统传递过程理论解及验证

通过将交叉流填料式液体除湿系统的热质传递过程抽象为空气和溶液均可以横向混合的 ,并且可将两流体的传递过程分别化为一维来分析的问题进行处理 ,建立了描述该过程的数学模型 .经合理简化 ,推导出该数学模型的一种近似解析解 。

逆流填料式液体除湿系统传热传质过程解析解

在建立逆流填料式液体除湿系统传热传质过程的数学模型基础上 ,通过合理的简化处理 ,导出了描述这一热质传递过程的常微分方程组 ,得到了相应的解析解 ;并与精确数学模型的数值解进行了对比 ,二者具有良好的吻合性 ;利用解析解分析了各参数对除湿性能的影响 ;

含湿毛细多孔介质传热与传质基本方程的一组代数显式解析解

对含湿毛细多孔介质传热与传质过程的基本主控方程,以建议使用的加法分离变量法导出了一套代数显式解析特解。它仅由时间的线性项与几何坐标的二次项组成,比较简单明了,具有一定的物理意义。这个特解尤其适合作为标准解发展计算传热传质学。

逆流填料式液体除湿系统传热传质过程的分析解法及应用

通过对逆流填料式液体除湿系统传热传质过程数学模型的合理简化 ,推导出描述这一热质传递过程的常微分方程组的分析解 ,并与未简化数学模型的数值解作对比 ,二者具有良好的吻合性。所得分析解可用于分析填料高度上各参数的分布情况及各参量的变化对除湿性能的影响 ,并可用于除湿系统的设计校核计算等 。

板式蒸发冷却器传热传质模型与解析解

对热湿交换过程进行质量与能量衡算,建立逆流板式蒸发冷却器传递过程的微分方程组。借鉴Braun的方法,引入空气湿球比热与湿球换热系数,对湿空气饱和线作线性化假设,推导得到了基于空气湿球温度的数学模型和控制微分方程组的解析解,实测结果验证了解析解对流体出口温度预测值的准确合理性。分析循环热水温度、喷淋水温度、空气干湿球温度的变化规律,以及空气进口干湿球温度对冷却器性能的影响。该分析模型与解析解可用于预测板式蒸发冷却器的性能。

坝体廊道通风换热性能的解析研究

随着我国水电事业的飞速发展,各类水电站相继建成,改善水电站厂房环境已经成为一个重要课题。本文以云南景洪水电站为背景,推导了空气流经坝体廊道时换热性能的解析计算式,并用MATLAB语言编制了程序,求得了各种工况下坝体廊道换热性能的解析解;分析了室外空气温度、空气流速、隧道洞长等因素对坝体廊道换热效果的影响,获得了坝体廊道内空气物性变化的一般规律。结果显示,廊道本身的蓄能作用对引入空气具有良好的加热或降温效果,对节能降耗、改善水电站厂房环境和提高发电效率具有指导意义。

闭式冷却塔热力计算方法研讨(上)

提出不忽略蒸发水量热焓的逆流闭式塔与顺流闭式塔的微分方程组,对解析解法进行改进,导出沿程水温与空气焓值分布的计算公式;根据IFC公式建立湿空气状态参数方程,以及塔内水与空气绝热平衡温度计算公式配合微分方程求解。实例计算表明:不忽略蒸发水量热焓方程解得的盘管填料面积要比忽略的少约40%;顺流塔要比逆流塔多约27%。最后提出用解析解的关系式整理试验数据的方法。

Drying characteristics of biological porous media during convective drying

Experiments with potatoes were carried out in order to analyze the variation of the temperature and the mean dry basis moisture content over time,the effect of the drying conditions on the drying rate,and the relationship between deformation and dry basis moisture content.A two-way sequentially coupled thermo-hydro-mechanical math model was developed on the basis of Fickian diffusion theory,Fourier’s law of heat conduction and thermoelasticity mechanics in order to analyze the spatio-temporal distributions of moisture,temperature and drying stresses in the potatoes.The transient mathematical model,composed of a system of partial differential equations,was solved by finite difference methods.The numerical results obtained by using the mathematical model were in good agreement with the experimental data.The variations in temperature and moisture distributions,drying curves and stresses within potatoes over time were simulated,and the ways in which these are affected by the drying conditions were discussed.This work could help in developing an understanding of the relationship between mass and heat transfer,shrinkage,stress,and physical degradation of biological materials.

A NEW INSTRUMENT FOR MEASURING LOCAL MOISTURE CONTENTS IN MOIST POROUS MEDIA

A new instrument was developed for measuring the local moisture content in moist porous media based on the needle-type capacitance sensor and single-chip microprocessor technique. The working principle, the structure and characteristics of the hardware and software of the instrument were presented. The dynamic response characteristics and reliability of the instrument were experimentally determined. As an example, the instrument was employed to measure the heat and mass transport properties of a moist porous material. The experimental results show that the instrument can be used for measuring the local moisture content in moist porous media and would be an effective tool for determining the heat and mass transport properties in moist porous media.

热风干燥过程固壁水膜蒸发特性分析

本文对热风干燥过程固体壁面上水膜蒸发过程进行了研究,视干燥过程为传热传质耦合传递过程。结合分离变量法得到了特定边界条件下水膜内部的温度分布解析解,并以此研究了水膜厚度、水膜表面对流换热系数等因素对水膜蒸发特性的影响。结果表明水膜越厚,水膜内温度分布非线性越显著,水膜表面达到湿球温度所需时间越长。随着蒸发过程的进行,水膜内导热热流逐渐减小,水膜表面蒸发潜热逐渐增加,最终完全等于对流换热热流。