盘式连续干燥器的传质传热模型

建立了盘式连续干燥器内加热盘面物料的传质模型,给出了干燥器内料环高度、盘面积料量及干燥时间的计算方法.应用颗粒传热理论和扩散理论,导出了每道料环的传热计算公式,由该迭代公式可逐步计算出每道料环的出料温度、出料湿含量及干燥速率.扩散理论中的惟一经验参数——搅拌参数N_mix,在本模型中可由不同进料工况下的多组实验数据加以确定.最后给出了应用该模型进行计算的实例,结果表明,理论计算值与实测值吻合较好,误差一般在20%以内.     

MASS TRANSFER FROM FLAT PLATES TO POWER-LAW FLUIDS IN LAMINAR FLOW

Mass transfer from vertical flat plates to water and 0.5 to 1.5% aqueous CMC solutions is measured in the Reynolds number range of 10^{- 2}to 6.0 x 10₃. Blasius analysis has been found to be valid only up to a Reynolds number of 100, below which Graetz-Leveque solution is more appropriate.     

A MATHEMATICAL MODEL FOR OXYGEN TRANSFER IN FLAT PLATE MEMBRANE OXYGENATOR

Mass transfer in a flat plate membrane oxygenator was studied and a convective mass transfer modelfor instantaeous reversible oxygenation of Cassonian fluid was presented. Numerical solution of the model canbe obtained with finite difference method. When a     

INTENSIFICATION OF HEAT AND MASS TRANSFER IN CHANNELS OF PLATE CONDENSERS

An analysis is presented for the main factors which control the intensity of vapor condensation in plate condenser channels, such as heat transfer both in single-phase stream of the coolant and in the condensate film, heat and mass transfer in gas-vapor phase, thermal resistance of fouling at heat transfer surface and pressure drop in condensing stream. On the basis of a relationship between the heat transfer and the wall shear stress, an approximate equation is obtained for calculating heat transfer from the pressure drop data. For calculation of heat transfer in condensate film during the condensation of high speed vapor, an analogy between heat and momentum transport has been used. An analysis of fouling deposition on heat transfer surface has been performed and an equation is presented for calculating the reduction of the fouling thermal resistance as compared with shell and lube heat exchangers. Experimental data are in good agreement with theoretical results. These data have shown the improvement of all the mentioned factors, which determine the intensity of the whole condensation process compared to the same factors in shell and tube condensers. Under the equal conditions, the required area of the heat transfer surface is reduced by 1.6 to 3 limes for the plate condenser, as compared with conventional shell and tube units.     

INTENSIFICATION OF HEAT AND MASS TRANSFER IN CHANNELS OF PLATE CONDENSERS

An analysis is presented for the main factors which control the intensity of vapor condensation in plate condenser channels, such as heat transfer both in single-phase stream of the coolant and in the condensate film, heat and mass transfer in gas-vapor phase, thermal resistance of fouling at heat transfer surface and pressure drop in condensing stream. On the basis of a relationship between the heat transfer and the wall shear stress, an approximate equation is obtained for calculating heat transfer from the pressure drop data. For calculation of heat transfer in condensate film during the condensation of high speed vapor, an analogy between heat and momentum transport has been used. An analysis of fouling deposition on heat transfer surface has been performed and an equation is presented for calculating the reduction of the fouling thermal resistance as compared with shell and lube heat exchangers. Experimental data are in good agreement with theoretical results. These data have shown the improvement of all the mentioned factors, which determine the intensity of the whole condensation process compared to the same factors in shell and tube condensers. Under the equal conditions, the required area of the heat transfer surface is reduced by 1.6 to 3 limes for the plate condenser, as compared with conventional shell and tube units.     

自由降膜传热传质数值模拟技术应用进展

自由降膜过程在许多工业领域，特别是在石油化工工业中有着非常广泛的应用。近年来，随着计算机技术的发展，研究人员采用理论分析、数值模拟和实验相结合的技术手段，对降膜传热传质过程进行了深入的研究，为优化降膜传热传质过程和新型设备的开发提供了理论基础。     

石墨化电炉传热学模型研究

在分析了炉子电热特性的基础上建立了石墨化炉传热数学模型。应用传热学知识，得到炉内导热方程式，并利用数理方程和傅立叶级数代换，推导出炉内温度分布方程式，并借助于计算机绘制出相关要素的变化曲线。通过分析该变化曲线，对石墨化炉供电制度提出了合理建议。     

EFFECT OF THE VARIABILITY OF HEAT AND MASS TRANSFER COEFFICIENTS ON CONVECTIVE AND CONVECTIVE-RADIATIVE DRYING OF POROUS MEDIA

A numerical investigation was conducted to study two-dimensional heat and mass transfer during convective drying of a clay brick. The established numerical code has allowed us to determine the effect of heat and mass transfer coefficients variability on state variables and on the drying kinetic.     

干燥过程热质传递的简化模型

对多孔介质体积平均理论进行简化,得到简化的热质传递干燥模型,用一个理论式表达模型中有效扩散系数。对香蕉片千燥的研究表明,模型的预测值与实验结果相     

CARBON MASS TRANSFER INTO COMPOSITE SLABS UNDER THE EFFECT OF NON-FICKIAN DIFFUSION MODEL

Mechanisms of mass transfer into composite thin slabs consisting of two thin metal layers in perfect contact using the hyperbolic mass conduction model have been studied. The non-Fickian phenomena are analyzed by comparison of the solutions between Fickian and non-Fickian equations. The effects of diffusion ratio of carbon, density ratio, and thermal relaxation time on the spatial and transient behavior of the composite slabs are investigated semi-analytically using the Laplace transformation technique.     

错流降膜液体干燥剂除湿/再生传热传质数学模型及分析

分析了错流降膜液体干燥剂除湿及再生传热传质过程 ,建立了基于实际除湿系统的描述再生和除湿过程的数学模型 ,考虑到除湿过程中产生的热效应 ,以氯化钙溶液为除湿剂时 ,对气侧和液侧的传热传质系数进行了理论和数值求解 .计算结果表明 ,传热传质系数与气流流动状态、除湿剂的热物理性质等因素有关     

DIMENSIONAL ANALYSIS OF HEAT AND MASS TRANSFER CORRELATIONS USING MICRO- AND MACRO-SCALES

A new kind of dimensional analysis, which uses two kinds of scales, provides a powerful tool for analyzing heat and mass transfer correlations as has been demonstrated by Ruckenstein (1986) in the case of forced convection of Newtonian fluids. In this work, the approach based on micro- and macro-scales is extended to free convection of Newtonian fluids, as well as to forced and free convection of power-law fluids.

As the micro-participation and macro-participation dominate in laminar and turbulent flow respectively, bounds on the exponents of the Reynolds number Re and the Grashof number Gr can be established in the case of forced and free convection respectively. An upper bound is obtained for laminar flow and a lower bound for turbulent flow. Thus, for free convection in Newtonian fluids, it is demonstrated that the bounds on the exponent of Gr for laminar and turbulent flow are 0.25 and 0.375 respectively.     

多孔介质对流干燥机理及其模型

在对现有的多孔介质对流干燥传热、传质模型归类分析的基础上,从介质内部热湿迁移机制出发,建立了能较完善、较准确地描述多孔介质在恒速段及降速段热质传递规律的“三耦合-六场量”混合理论模型.同时针对干燥问题数值模拟中的移动边界问题,提出了一种迭代修正的思想,并发展了相应的数值计算方法.对砖的干燥模拟计算结果表明,本文的模型较其他模型具有更好的精确性.     

HEAT AND MASS TRANSFER IN THE ADSORBENT BED OF AN ADSORPTION HEAT PUMP

The heat and mass transfer equations governing an adsorbent bed in an adsorption heat pump and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes.     

PRESSURE DROP AND MASS TRANSFER COEFFICIENTS IN CONCURRENT SCREEN PLATE BUBBLE COLUMN

Pressure drop and oxygen desorption from water and four other aqueous CMC solutions were determined in a 5 cm diameter multistage bubble column with and without plate reciprocation. The plates were made from stainless steel wire screens of porosities greater than 0.62. The column pressure loss was found to increase with plate agitation, phase velocities and screen mesh number. A modified Reynolds number was proposed to permit a reasonable prediction of the pressure loss, based on the model of Noh and Baird (1984). At a specific power consumption, the present volumetric mass transfer coefficients arc considerably larger than those reported in earlier studies with sieve plates. The coefficients were correlated with specific power input, phase flow velocities and system physical properties.     

A MODEL FOR PREDICTING HEAT TRANSFER TO A TURBULENT FALLING FILM

A modified form of Carey'ls method for predicting the heat transfer to a turbulent falling film is presented. The new model is successfully tested against experimental data as well as other models. This method utilizes an optimization technique along with the Rombcrg integration to determine two universal constants for the modified turbulent diffusivisity model. The results show that in spite of its relative simplicity, the new model is a fairly accurate one, having an overall average error of less than 9%.     

NATURAL CONVECTION HEAT AND MASS TRANSFER FROM A VERTICAL FLAT PLATE WITH VARIABLE WALL TEMPERATURE AND CONCENTRATION TO POWER-LAW FLUIDS WITH YIELD STRESS IN A POROUS MEDIUM

The problem of natural convection coupled heat and mass transfer of non-Newtonian power law fluids with yield stress from a vertical flat plate in a fluid-saturated porous medium is analyzed under boundary layer approximations. Similarity solutions are obtained for the general case of power law variations of the wall temperature and concentration. Velocity, temperature, and concentration profiles as well as local heat and mass transfer rates are presented and discussed for different values of the rheological parameters of a power-law fluid, the Lewis number, and the thermal and concentration buoyancy ratio.     

COMBINED HEAT AND MASS TRANSFER IN FREE CONVECTION ALONG A ROTATING PLATE UNDER UNIFORM HEAT AND UNIFORM MASS FLUXES

The problem of combined heat and mass transfer in laminar free convection along a vertically rotating plate subjected to a uniform heat flux and/or a uniform mass flux is studied analytically. The governing non-dimensional nonlinear coupled partial differential equations are solved by local similarity and local nonsimilarity approach. Numerical results for the local Nusselt number, the local Sherwood number and the local wall shear stress for the convective-diffusion of hydrogen, water vapor and naphthalene into the air are presented in tabular forms. The analysis extends the range both when the concentration buoyancy force assists as well as opposes the thermal buoyancy force.     

COMBINED HEAT AND MASS TRANSFER IN FREE CONVECTION ALONG A ROTATING PLATE UNDER UNIFORM HEAT AND UNIFORM MASS FLUXES

The problem of combined heat and mass transfer in laminar free convection along a vertically rotating plate subjected to a uniform heat flux and/or a uniform mass flux is studied analytically. The governing non-dimensional nonlinear coupled partial differential equations are solved by local similarity and local nonsimilarity approach. Numerical results for the local Nusselt number, the local Sherwood number and the local wall shear stress for the convective-diffusion of hydrogen, water vapor and naphthalene into the air are presented in tabular forms. The analysis extends the range both when the concentration buoyancy force assists as well as opposes the thermal buoyancy force.     

DRYING MODEL WITH NON-ISOTROPIC SHRINKAGE DEFORMATION UNDERGOING SIMULTANEOUS HEAT AND MASS TRANSFER

A model of simultaneous heat and moisture transfer in a cylindrical sample was coupled with the virtual work principle applicable to a body undergoing shrinkage deformation in two dimensions. Non-constant physical and thermal properties were also incorporated in the model. Governing equations and boundary conditions were solved numerically using Galerkin's finite element method. To check the mathematical model drying experiments were carried out. A cylindrical potato was used as a drying sample. Experimental conditions were as follows: a drying temperature of 333 K, relative humidity of 5.4%, and air velocity of 1.6 m/s. We obtained the central temperature of the sample, average moisture content, and the shrinkage change in the axial and radial directions during drying. It was observed that the shrinkage coefficients in the axial and the radial directions were significantly different during air-drying. Comparison between predicted and experimental results provides satisfactory agreement.