Analysis of Drying Kinetics of Iron Ores using Irreversible Thermodynamics and Transport Phenomena Principles

Drying kinetics of iron ores, the primary raw material for the iron and the steel industry, has been studied in this work. Experimental drying kinetics and equilibrium moisture content data have been obtained using thermogravimetric techniques at controlled conditions of humidity, temperature and gas flow. A theoretical model based on the principles of irreversible thermodynamics and transport phenomena, and a computer program for the simulation of drying process has been developed (SimDry 1.0 for Windows). The results of simulation have been compared with the experimental results and there has been reasonable agreement between them.     

Modeling of Diffusion in Capillary Porous Materials During the Drying Process

ABSTRACT

This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.     

Modeling of Diffusion in Capillary Porous Materials During the Drying Process

This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.     

Shrinkage of Recycled Paper Sheet During Drying

The properties of recycled paper are strongly affected by shrinking during drying, which depends on the drying conditions. An experimental study of the shrinkage phenomenon during drying of paper is presented. Drying experiments were conducted in a drying oven with controlled temperature. The temperature influence on shrinkage extent, porosity, and apparent density of the paper was evaluated. Structural changes on the paper surface after drying were analyzed by scanning electronic microscopy. Thickness contraction, surface, and volumetric shrinkage were correlated as a function of the moisture content. Lower apparent density values and more porous paper samples were obtained for higher temperatures.     

多孔介质内部传热传质规律的研究进展

多孔介质中的热质交换理论及其实验研究是一个涉及面广、研究难度大而又颇具工程应用价值的课题。本文对多孔介质内部传热传质规律的研究从理论和实验两方面作了简要的综述及展望,并对一些描述热质传递过程的数学模型及方程作了介绍。     

高初始含湿多孔介质喷雾干燥过程的热质耦合传递

多孔介质是大量干燥过程的主体,由于实际多孔介质干燥过程的复杂性,建立通用的干燥过程传热传质模型十分困难。通过分析喷雾干燥过程中高初始含湿多孔介质与干燥介质之间的传热传质机理以及各因素对传热传质的影响,根据马歇尔方程探讨了干燥介质与料雾之间的水蒸汽分压差在干燥过程中的变化情况,反映了多孔湿介质在喷雾干燥操作中的传热传质过程的几种特性,为确定实际生产中喷雾干燥器的操作条件指明了新的出路。     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

ABSTRACT

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally obtained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

ABSTRACT

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally obtained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

固定床内石灰石煅烧与传递过程的数值模拟

将固态颗粒填料床视为由规则颗粒堆积而成的松散多孔介质,在推导出传热控制机制下微元体综合速率的基础上,采用局部热不平衡假设建立了一维固定床中石灰石热分解反应与传热、传质耦合的数学模型,运用有效容积法对其离散求解,并采用文献中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. 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.     

Numerical Simulation of the Drying of a Deformable Material : Evaluation of the Diffusion Coefficient

ABSTRACT

We are interested in the simulation of heat and mass transfer processes accompanying the drying of a deformable agricultural product. We have used an implicit method with classical finite differences to resolve the set of equations. The identification of the diffusion coefficient within a thin carrot layer is carried by trial and error on two analytical forms. These two forms take into account moisture content, temperature and shrinkage of the product.

The drying rates of thin layer of carrot pieces are measured in a laboratory tunnel dryer. These drying curves are established by varying some airflow parameters such as velocity, temperature and relative humidity. The internal and surface temperature of the slab were recorded by means of therrnosensors. The simulated solutions are in agreement with the experimental results.     

化工原理课程中三传相似性教学要点分析

单元操作从本质上讲可以分解为动量传递、热量传递、质量传递这三种传递过程或者它们的结合。学习和掌握三传相似性在加强学生对化工原理知识的深入认识、融会贯通方面有着重要的意义。文章就三传相似性的一些教学要点进行了深入剖析,并对教学方法进行了简要探讨。     

A Multiphase Model to Analyze Transport Phenomena in Food Drying Processes

The aim of the present work is the development of a theoretical model describing the transport phenomena involved in food drying. A fundamental multiphase approach was utilized to account for the simultaneous presence of both liquid water and vapor within the sample undergoing drying. The transport equations referred to the food were coupled, by a proper set of boundary conditions, to momentum and heat and mass transfer equations referred to the drying air, thus obtaining a general model that did not rely on the specification of any heat and mass transfer coefficient at the food/air interfaces.     

Impingement Drying of Paper

The complete drying history of paper dried under an array of multiple round jets of air was determined. The drying rate - paper moisture content relations, determined as a continuous function by on-line measurements for about 80 sheets, permitted examination of the following parameters: basis weight 20 to 50 g/m2, which covers the tissue to communication paper range; initial moisture content 1.5 to 3 kg water/kg fibre; nozzle to paper spacing of 5, 7.6 & 8.5 nozzle diameters: nozzle plate open area ratio from 1.4 to 3.1%; jet Reynolds number in the range of 450 to 11.100.

Three methods of quantifying the complete drying rate curves were tested. Use of the common assumption of drying rate linear with moisture content over the falling rate period gave inadequate representation. Secondly, the general method of Churchill for any transport process that has a transition between two asymptotic relations was applied for the fmt time to the drymg of paper. This approach gives     

Impingement Drying of Paper

ABSTRACT

The complete drying history of paper dried under an array of multiple round jets of air was determined. The drying rate – paper moisture content relations, determined as a continuous function by on–line measurements for about 80 sheets, permitted examination of the following parameters: basis weight 20 to 50 g/m2, which covers the tissue to communication paper range; initial moisture content 1.5 to 3 kg water/kg fibre; nozzle to paper spacing of 5, 7.6 & 8.5 nozzle diameters: nozzle plate open area ratio from 1.4 to 3.1%; jet Reynolds number in the range of 450 to 11.100.

Three methods of quantifying the complete drying rate curves were tested. Use of the common assumption of drying rate linear with moisture content over the falling rate period gave inadequate representation. Secondly, the general method of Churchill for any transport process that has a transition between two asymptotic relations was applied for the fmt time to the drymg of paper. This approach gives