Drying and Hydration of Cement Based Self-Leveling Flooring Compounds

Water in building materials not only influences important physical properties and chemical processes but is also related to the well-being of the occupants of a building. The drying of cementitious materials is complex, involving several different drying processes. The conditions for each drying process change as the material changes its properties as it goes from a particle suspension in the fresh state to a fine porous material in the hardened state. The present article describes and quantifies the drying processes of cement-based self-leveling flooring compounds (SLCs) and relates them to the extent of reaction, which here is quantified by isothermal calorimetry. The relative importance of the different drying processes is discussed and a model for the drying of the SLCs is proposed.     

Development of a porosity prediction model based on shrinkage velocity and glass transition temperature

Abstract

Pore formation and evolution is a common physical phenomenon observed in food materials during different dehydration processes. This change affects heat and mass transfer process and many quality attributes of dried product. Many mathematical models ranging from emperical to classical models proposed in the literature for predicting porosity during drying of food materials. Classical model is in its infancy as the required materials properties during drying are not avaiable for the material charecterisation. Empirical and semi-empirical models are reasonably well developed in establishing relationships between pore evolution and moisture content and determining experimental based coefficients. However, there are no simplistic models that considered process conditions and material properties together to predict the porosity. The purpose of this work is to develop a simplistic theoretical model for pore formation taking both process parameters and changing material properties during drying into consideration. A new “shrinkage velocity” approach has been introduced and the model has been developed based on this shrinkage velocity taking into account the main factors that influence the porosity including the glass transition temperature. Experimental results show good agreement with simulated results and thus validated the model. This study is expected to enhance the current understanding of pore formation of deformable materials during drying.     

SHRINKAGE OF POROUS MATERIALS DURING MICROWAVE DRYING

The dissipation of electromagnetic energy inside a material creates a thermal imbalance state producing some reactions different from those observed through slow classic drying processes. Important drying rates obtained by microwave application can be understood by taking into account induced pressure gradients which greatly accelerate the thermomigration mechanism and thereby modify the physical properties of the product. The shrinkage of porous materials during the drying stage is very sensitive to the internal vapour pressure.The quality of such products depends on the shrinkage behaviour, and it is therefore interesting to study this phenomenon in order to control the characteristics of the product. This study is an experimental approach leading to a theoretical model describing the shrinkage mechanism. This model is developed from results obtained by a computer controlled measurement system allowing to regulate the drying kinetics.     

SHRINKAGE OF POROUS MATERIALS DURING MICROWAVE DRYING

The dissipation of electromagnetic energy inside a material creates a thermal imbalance state producing some reactions different from those observed through slow classic drying processes. Important drying rates obtained by microwave application can be understood by taking into account induced pressure gradients which greatly accelerate the thermomigration mechanism and thereby modify the physical properties of the product. The shrinkage of porous materials during the drying stage is very sensitive to the internal vapour pressure.The quality of such products depends on the shrinkage behaviour, and it is therefore interesting to study this phenomenon in order to control the characteristics of the product. This study is an experimental approach leading to a theoretical model describing the shrinkage mechanism. This model is developed from results obtained by a computer controlled measurement system allowing to regulate the drying kinetics.     

COMBINED DRYING OF CRYSTALLOCOLLOIDAL MATERIALS

Principles of a new high-effective technique of granulating and drying some materials are discussed. The material properties are shown to affect the granulation and drying processes. Methods to describe falling and fluidized bed drying are suggested.     

COMBINED DRYING OF CRYSTALLOCOLLOIDAL MATERIALS

ABSTRACT

Principles of a new high-effective technique of granulating and drying some materials are discussed. The material properties are shown to affect the granulation and drying processes. Methods to describe falling and fluidized bed drying are suggested.     

RATE OF DRYING AND STRESSES IN THE FIRST PERIOD OF DRYING

The paper presents a computer simulated processes and illustrate how the drying induced stresses are influenced by the rate of drying. It is shown that the moisture transport coefficient, and thus the rate of drying, depends on the thermal state of the drying material, defined by the wet-bulb temperature. Through these simulated processes one can observe the evolution of the moisture content and stress distributions during drying at constant, but in each process different, wet-bulb temperatures. A convective drying process of a bar with rectangular cross-section is considered as example, and a two-dimensional initial-boundary value problem is solved numerically with the use of the finite element method. The numerical results are visualised in spatial diagrams.     

Heat of Desorption of Water From Cellulosic Materials at High Temperature

ABSTRACT

During the falling rate period of drying the heat requirements for drying hygroscopic materials may be increased substantially ahove the normal latent heat by the heat of desorption of water. In various new high intensity drying processes which are of increasing interest industrially, the drying material may reach quite high temperatures for periods of time sufficiently short that there is no degradation of the properties of the dried material. However the limited stability of many materials at high temperatures precludes determination of heals of desorption by direct measurements because of the long experimental times required for thermodynamic techniques. The present study develops a thermodymically valid method whereby heats of desorption determined at low lemperatures may be extrapolated reliably to the high temperatures where such information is needed but cannot be measured. A relation between isosteric heat of desorption and latent heat of water is derived in order to compare the new     

Preparation of porous ceramic materials based on wollastonite using silicon-containing components

Results are provided for evaluation of the possibility of preparing porous ceramic materials using synthetic wollastonite and silicon-containing components by chemical pore formation. The mechanism of pore formation, and also chemical processes during material drying and firing are studied. The physicochemical properties and microstructure of the material obtained are studied.     

微波-对流干燥技术在聚丙烯酰胺生产中的应用

采用微波－对流干燥技术对高含水、粘度较大、过热表面易结壳的热敏性物料进行烘干试验,取得了较好的效果,解决了干燥领域的一大难题,并给出了烘干曲线及微波－对流干燥原理图,可供设计参考。     

Dr. Carl W. Hall,Founding Editor

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.     

Effect of Wall Surface Properties at Different Drying Kinetics on the Deposition Problem in Spray Drying

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.     

新型耐水石膏基墙体材料制备及性能研究

就石膏墙体材料的轻质化目的,运用两种不同的EPS颗粒的加入工艺,对两种工艺的耐水石膏材料的吸水率、强度等多种系数及性能开展对比研究,最终经过试验验证可知,EPS掺入最优值是1.3%,基于此石膏表观密度是839.06 kg/m~3。干燥时的抗压及抗折度是4.05和2.06 MPa,两者软化系数是0.517和0.650,对比未加EPS颗粒时提升百分比分别为20.8%和11.5%。虽然掺入ESP颗粒后要比未掺入的强度要大,但石膏耐水性获得了显著的提高,并且符合《石膏砌块》以及《建筑隔墙用轻质板条》对于石膏材料的性能要求。     

高镍三元正极材料表面碱性物质研究进展

高镍三元正极材料表面形成的碱性物质容易导致电池容量衰减加快、寿命缩短,因而调控三元材料表面碱性物质对于提高锂离子二次电池的功能和安全性至关重要。综述了高镍锂离子电池三元正极材料表面碱性物质的形成机理及处理手段,从不同角度阐述了环境中的水、二氧化碳对表面碱性物质形成的影响。探讨了表面碱性物质形成过程中,由于锂离子和过渡金属的迁移与固化引发的表面结构的相变现象,造成了三元正极材料的加工储存性能的恶化。还对降碱工艺中的洗涤、干燥、低温烧结等过程进行了重点说明,阐述了洗涤工艺对三元材料表面碱性物质降低及对材料性质的影响,指出需选择合适的洗涤、干燥条件,减小材料表面发生的变异。最后结合目前降碱工艺对后续研究方向提出了建议。     

Radiowellenunterstützte thermische Behandlung als neue Technologie zur Trocknung und Dekontamination von Bauteilen

Direct dielectric heating using radio waves, i. e., electromagnetic waves in the high‐frequency range, was successfully tested for the application in the field of building redevelopment. It could be shown that this method can be utilized to homogeneously and efficiently heat various materials such as sandstone and fibre concrete in a controlled manner. Final temperatures of more than 100 °C can be achieved. This allows drying of building materials without disturbance of the structure. By placing formed structures in a packed bed of an appropriate material, this method can also be applied for the preservation of cultural goods, for example for drying sculptures.     

Transport in deformable food materials: A poromechanics approach

A comprehensive poromechanics-based modeling framework that can be used to model transport and deformation in food materials under a variety of processing conditions and states (rubbery or glassy) has been developed. Simplifications to the model equations have been developed, based on driving forces for deformation (moisture change and gas pressure development) and on the state of food material for transport. The framework is applied to two completely different food processes (contact heating of hamburger patties and drying of potatoes). The modeling framework is implemented using total Lagrangian mesh for solid momentum balance and Eulerian mesh for transport equations, and validated using experimental data. Transport in liquid phase dominates for both the processes, with hamburger patty shrinking with moisture loss for all moisture contents, while shrinkage in potato stops below a critical moisture content.     

Investigation of the Effects of Microwave Treatment on the Optical Properties of Apple Slices During Drying

The objective of this work was to study the changes of optical properties of apple (Golden Delicious) slices during drying. The optical parameters compared on the basis of Hunter values (L, a, b) changes as well as total color difference (Δ E) and browning index (BI). The effect of coating materials including carboxymethylcellulose (CMC), starch, and pectin as well as microwave treatment on optical properties and microstructure of dried samples were investigated. To analyze the effects of these processes on microstructure, scanning electron microscopy (SEM) was employed. Results showed that optical properties as well as microstructure of apple were affected by coating material and drying condition. Coated samples by CMC had a lower L and higher BI, but different results in the presence of starch were obtained. Microwave treatment in the presence of appropriate coating materials could improve the optical properties of dried apple slices.     

Drying in active hydrodynamic regimes

It is shown that the activation of hydrodynamic regimes is one way of solving the problem of increasing the efficiency of drying processes, which includes solving the problems of the process intensity and cost effectiveness, as well as the quality of the final product. A method for estimating the degree of the activity of a hydrodynamic regime is recommended. A strategy for choosing the optimal apparatus-technological design of the drying process is developed that includes the complex analysis of the materials to be dried and the classification of wet disperse materials according to sorption-structural characteristics taking into account adhesion-autohesion properties. Standard apparatuses for each class of materials are recommended. The problem of drying materials with increased adhesion-autohesion properties is chosen. Drying in vortex apparatuses with simultaneous size reduction is considered as an example.     

Kinetics of Drying of Fibre Materials and Fibre-Forming Polymers with Warming

Drying with heating of fibres, fibre materials, and fibre-forming polymers takes place with low-intensity energy feed, with an increase in the thickness of the material dried, or with a high moisture content of the drying agent. Heating of the material in the initial drying period is analyzed and the corresponding equation for the drying kinetics is obtained. The dependences for describing the kinetics of drying with heating are obtained for different materials and conditions. The general kinetic curve describes periods of heating and a constant and diminishing drying rate. Drying with first and second periods (instantaneous heating of the material) is obtained from the overall dependence as a special case. The dependences obtained are compared with the experimental data for different types of drying of fibres, fabrics, and fibre-forming polymers. The calculated drying parameters are found. The calculated curves are in good agreement with the experimental data in the working range. A method for calculating drying using the dependences obtained is described.