多孔介质内部热质传递的等效耦合扩散模型的推导及其应用

基于Whitaker的体积平均方程，在不附加任何新的假设的基础上，对多孔介质内部热质传递的等效耦合扩散模型进行推导，得出了多孔介质内部热质传递的等效耦合扩散模型。并应用该模型对瓷质砖体干燥过程进行了数值模拟，模拟结果与实验结果十分吻合。     

大面积瓷质砖坯体干燥过程的二维传热传质研究

引用建立于Whitaker的体积平均方程和Darcy定律基础上的多孔介质内部热质传递的等效耦合扩散模型 ,寻出一组关于液体饱和度、温度和气相压力的新支配方程 ,应用该方程组对瓷质砖坯体二维干燥过程进行了数值分析。并将传统干燥器与新型干燥器的模拟数据进行比较 ,以期获得某些定性或定量的结论 ,从而用以指导实际生产过程。     

大规格瓷质砖坯体干燥过程的二维传热传质研究

引用建立于Whitaker的体积平均方程和Darcy定律基础上的多孔介质内部热质传递的等效耦合扩散模型,寻求出一组关于液体饱和度、温度和气相压力的新支配方程,应用该方程组对瓷质砖坯体二维干燥过程进行了数值分析;将传统干燥器与新型干燥器的模拟数据进行比较,以期获得某些定性或定量的结论,用以指导实际生产过程.     

大规格建陶坯体对流干燥热质耦合传递的数值模拟

以Whitaker的体积平均方程为基础,推导出多孔介质内部热质传递的等效耦合扩散模型,并对瓷质砖坯体干燥过程进行了数值分析和实验测定。探讨了干燥介质参数（湿度、温度和流速）和坯体物性参数（有效导热系数和有效扩散系数）对干燥过程的影响。结果表明,温度高、流速快、湿度小的热空气有利于干燥,其中,改变风速对干燥速率的影响很小,介质的温度和湿度对干燥影响较大,但有可能造成干燥缺陷。有效扩散系数对坯体内湿度的分布影响很大,而有效导热系数对坯体内湿度的分布几乎没有影响。     

初始非饱和多孔物料冷冻干燥的数值模拟

为了提高冷冻干燥过程的经济性,本文主要对初始非饱和物料的冷冻干燥过程进行数值模拟。建立了二维含湿多孔介质冷冻干燥数学模型,使用COMSOL Multiphysics 4.3a软件进行求解。液体物料的主要溶质为甘露醇。提出两种新的吸附-解吸平衡关系,并与实验数据进行了对比,分析了其适用条件。结果显示,初始非饱和冷冻物料能够有效减少干燥时间,模拟结果与实验数据吻合良好。通过分析物料内部温度、饱和度分布得知,升华界面随着干燥过程的进行逐渐向物料内部转移,干燥过程也发生在物料冰冻区域。适当提高环境温度有利于强化整个干燥过程。     

基于Fick扩散模型的陶瓷坯体干燥数值模拟

本文使用Fick扩散模型对陶瓷坯体的干燥过程进行了模拟，在实际干燥工艺参数数值范围内，分析了热风速度、温度和相对湿度三个因素对陶瓷坯体内部温度、含水率和干燥速率的影响。结果表明，增加热风速度能够加大坯体表面区域的水分散失速率，但对坯体内部含水率变化影响较小；提高温度能够显著增加坯体内部的干燥速率，当温度从35℃增加至75℃时，最大干燥速率的变化幅度为46.34%;相对湿度对坯体平衡含水率影响较大，当相对湿度从5%增大至85%时，平衡含水率从0.8%增大至5.1%(均为质量分数),提高相对湿度能够改善坯体干燥均匀性，保证坯体干燥质量。模拟和试验数据基本吻合，计算结果将为进一步深入研究陶瓷坯体干燥的传热传质过程，以及后续干燥曲线的优化提供理论依据。     

竹条干燥特性的实验研究

对竹条的热风对流干燥特性进行了系统的实验研究。讨论了干燥方式， 热风速度和温度等因素对干燥过程的影响； 从干燥过程的基本原理出发， 导出了干燥过程的数学模型； 利用此模型对实验结果进行回归整理， 得到了反映竹条干燥特性的实验关系式。     

介电物质对微波冷冻干燥影响的理论研究（二）

用有限差分方法计算的数值求解一个微波冷冻干燥质、热传递数学模型，以考察介电物质对微波冷冻干燥的影响。被干燥物料水溶液的溶质选用乳糖(Lactose)——一种典型的药物赋形荆。介电物质为烧结的碳化硅(SiC)。数值计算结果表明，介电物质能够有效地强化微波冷冻干燥过程，干燥时间大为缩短。在典型操作条件下，干燥时间为179．1min，比普通微波冷冻干燥节省43.4％。通过考察温度、冰饱和度、蒸汽质量浓度和压力分布，分析传质传热机理，确定了干燥速率控制因素。     

考虑结壳现象的液滴干燥过程数值模拟

为更清楚地了解液滴的干燥过程,文中综合考虑溶剂扩散系数与溶液质量分数,溶液质量分数与液滴表面蒸汽压和滴径变化与传热传质之间的耦合关系,建立了包含液滴内部径向热传导方程,液滴内部的传质方程及液滴质量变化方程的液滴蒸发的完整模型。用所建模型对不同操作工况下液滴的挥发过程进行了模拟,描述了干燥过程中液滴质量损失,滴径的变化及液滴表面到中心的溶液组分变化,并对影响液滴干燥速度的重要因素进行了分析。模型模拟结果跟实验结论比较一致。     

低气压环境下硬化水泥浆体的水分传输特性

高原地区的低气压环境对水泥基材料的干燥收缩与抗冻融性能等均有不利影响，该环境下水分传输特性的改变是重要的影响因素。对不同水灰比的硬化水泥浆体开展了不同气压(101、60kPa和20kPa)与相对湿度(43%、98%)环境中270d的等温暴露试验，研究了低气压环境对硬化浆体中含湿量及化学结合水含量的影响，并建立数值模型分析了低气压环境对水分传输特性的影响。结果表明：在等温干燥环境中，低气压环境会促进硬化浆体中水分散失，并导致化学结合水含量的轻微下降；在等温润湿环境中，水分逐渐扩散进入硬化水泥浆体中，使试件质量随暴露龄期呈对数增长，环境气压降低会明显提升早期的质量增长速率与最终质量增加值。水分传输的数值模拟结果说明了低气压环境中水蒸气扩散系数、对流传质系数与硬化浆体的本征渗透率的增大是导致等温干燥和润湿过程水分传输行为的主要原因。     

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.     

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.     

Numerical and experimental study of ion exchange in porcelain tiles

Recently ion exchange, also known as chemical tempering, has been applied to strengthening of porcelain tiles based on the substitution of ions present in the material by larger ones. This paper investigates the chemical tempering in industrial porcelain tiles by the variation of process parameters such as temperature, immersion time, and chemical composition of the porcelain tile. Furthermore, a numerical simulation of the ionic diffusion process was applied. Using a design of experiments approach, the results show that the temperature and the chemical composition primarily affected the flexural strength of the tile. The largest increment obtained was 37% resulting in a porcelain tile with flexural strength of 73 MPa after chemical tempering. Through numerical simulation, it was possible to estimate a diffusion coefficient of potassium ions equal to 1.25 × 10⁻¹⁴ m²·s⁻¹ into the porcelain tile microstructure. This value is about 10 times higher than the diffusion coefficient in glasses.     

MECHANISM OF TWO-DIMENSIONAL HEAT AND MASS TRANSFER DURING CONVECTTVE DRYING OF POROUS MXDIA UNDER DIFFERENT DRYING CONDITIONS

A numerical investigation was conducted to study two-dimensional heat and mass transfer during convective drying of clay brick. The set of macroscopic equations takes into account the effect of gaseous pressure. The established numerical code has allowed us to determine effects of the surrounding air conditions (temperature, pressure and vapor concentration) on drying Kinetic and on space-time evolution of the state variables (temperature, gaseous pressure, and liquid saturation).     

MECHANISM OF TWO-DIMENSIONAL HEAT AND MASS TRANSFER DURING CONVECTTVE DRYING OF POROUS MXDIA UNDER DIFFERENT DRYING CONDITIONS

ABSTRACT

A numerical investigation was conducted to study two-dimensional heat and mass transfer during convective drying of clay brick. The set of macroscopic equations takes into account the effect of gaseous pressure. The established numerical code has allowed us to determine effects of the surrounding air conditions (temperature, pressure and vapor concentration) on drying Kinetic and on space-time evolution of the state variables (temperature, gaseous pressure, and liquid saturation).     

Evaluation of texture distribution during the industrial polishing process of porcelain stoneware tiles

The present work addresses the distribution of texture over the surface of porcelain stoneware tiles due to kinematics imposed by industrial polishing process. The scratching process was simulated using a computational algorithm, which was based on the kinematic equations for the whole myriad of abrasive particles. Different scratching patterns were identified over the polished surface and their corresponding positions were mapped. The experimental results showed that regions in the tile centre present smaller tendencies for exhibiting preferential textures than those of the lateral ones. The final texture was slightly asymmetric and different from those simply left by the last scratches. The definition of three polishing domains was then suggested according to different phenomenological criteria. Results from both experiments and simulations made evident the influence of the kinematic parameters adopted by the industries on the polishing quality of porcelain stoneware tiles.     

具有电介质核圆柱多孔介质微波冷冻干燥过程的双升华界面模型

建立了具有电介质核多孔介质微波冷冻干燥过程的耦合传热传质的数学模型,应用变时间步长的有限体积法对各控制方程进行数值求解.计算结果表明：（1）多孔介质内部存在着两个升华界面;（2）同无核相比,合理选用电介质核可大大缩短干燥时间;（3）在初始饱和度较低时（S₀=0.2）,有、无电介质核两种情况下所需干燥时间相差较大,仍可在物料中加入电介质核来加速干燥.     

Microstructural Variation in Porcelain Stoneware as a Function of Flux System

Fired microstructures of standard porcelain stoneware tile and tile made from mixes containing waste glass as part of the flux system were studied by XRD, SEM, and TEM. The standard porcelain stoneware microstructure consists of 100–1000 μm long mullite needles, feldspar relics, and partially dissolved α-quartz embedded in a glassy matrix. The use of soda–lime–silica (SLS) glass in the flux system led to crystallization of plagioclase, wollastonite, and sodium silicates. CaO-rich areas adjacent to quartz particles, as a result of interactions between SLS glass and silica from the quartz, and eutectic morphologies, revealed that SLS glass accelerated liquid formation and thus sintering and densification. Formation of these additional phases led to lower levels of quartz, mullite, and Na-feldspar in the microstructure although lower firing temperatures could be used to achieve full density due to generation of more fluid liquid. Use of PbO-containing waste glasses had little effect on the microstructure compared with standard composition while use of mixed PbO-containing and SLS glasses led to microstructures containing plagioclase but to lower extent than in tile with higher levels of SLS.