Drying-Induced Cracking of Abrasive Rings:Risk Prediction and Process Optimisation by Numerical Simulation

The dependence of the mechanical stresses distribution on the water content and temperature profiles has been numerically investigated in a porous unsaturated hygroscopic abrasive agglomerate of annular shape. The thermophysical, kinetic and mechanical properties of the abrasive agglomerate were determined experimentally. The simulations have been applied to unfired abrasive rings convective drying optimisation by fitting operating conditions in order to avoid cracks formation.     

Residual stress trend in thermal barrier coatings in through thickness direction measured by photoluminescence piezospectroscopy

Abstract

Photoluminescence piezospectroscopy (PLPS) has been used to determine residual stresses in sapphire, alumina in the yttria stablised zirconia (YSZ)/Al₂O₃ composite and alumina in thermal barrier coatings (TBCs). The TBC of YSZ containing 0·5?wt-% alumina has been produced using electron beam physical vapour deposition. The stress profile through the TBC thickness was measured using a depth sensing method. Reasonable residual stress profiles have been obtained using PLPS with the confocal system for all three material systems. Measurements of TBCs suggest that stress distribution in a TBC system is not uniform in general. However, uniform stress distribution has been found in some positions where damage in TBCs might occur.     

棉秆塑木复合材料的制备及性能研究

以棉秆粉和回收聚乙烯为原料、钛酸酯为偶联剂,采用热压法制备了棉秆塑木复合材料,利用正交试验法探讨了棉秆粉含量、热压温度和保温时间对塑木复合材料性能的影响,并通过物理力学性能测试单独考察了棉秆粉含量对塑木复合材料性能的影响。正交试验法的结果表明:棉秆粉含量对复合材料的弯曲强度、弹性模量和吸水率影响最大,热压温度和保温时间对复合材料的弯曲强度和弹性模量影响较大,对吸水率影响不大;当棉秆粉含量为40%、热压温度为160℃、保温时间为10 min时,塑木复合材料具有最优的综合性能。物理力学性能测试结果表明:复合材料的弯曲强度和弹性模量随棉秆粉含量的增加均呈现先增大后减小的趋势,在棉秆粉含量为40%时均达到最大值;吸水率随棉秆粉含量的增加而增大。     

CONVECTIVE DRYING OF PAPER CALCULATED WITH A NEW MODEL OF THE PAPER STRUCTURE

Paper drying models are based on the assumption of a rigid solid matrix. Because of the interaction of water molecules and paper fibre the dimensions of the sheet are changing, especially the thickness. These changes influence the moisture transport within the material. A model of the paper structure has been developed taking into account different kinds of pores in the paper.

By the assistance of this model the dependence between water content and thickness or transport parameters as permeability and thermal conductivity can be predicted. The only informations which are needed are sorption isotherms, apparent paper density and permeability of the single phase flow. Further informations as the pore size distribution are useful but not necessary.

The transport parameters are generated in the suggested way for wood pulp. It is shown that in the case of convective drying, the agreement between experimental results and model simulations is good.     

Seawater integrated desalination plant without brine discharge and powered by renewable energy systems

Environmental effects are one of the main concerns of massive desalination facilities. To reach the objective of no brine discharge the salt from seawater must be completely separated and obtained as a secondary and valuable product. If no CO₂ emission increase is desired, the power source must be a combination of renewable energy systems (RES). This paper presents an analysis of an integrated desalination scheme consisting of two sequential systems: a multi-effect distillation (MED) plant and a mechanical vapour compression (MVC) system based on evaporator equipment. The energy is obtained by several wind turbines (WT) and a thermal solar collector (TSC) field. Separation of salt and water is achieved in a coupled multi-effect distillation-mechanical vapour compression (MED+MVC) two step process. The MED stage is driven by thermal solar collectors, whereas the energy consuming mechanical compression of the vapour (MVC) is fuelled by wind-powered turbines. Interestingly, the final products of this process are dry salt and fresh water. Such a system has been designed and dimensioned for a throughput of 100 m³/h of desalted water A preliminary study of the investment, amortization and exploitation costs of a combined MED+MVC+WT+TSC installation with these dimensions has been done. The price of desalted water, after considering the profits due to the sale of salt and electricity has been estimated at 0.59 ?/m³. If the initial investment has a 35% subsidy, a final price of 0.41 ?/m³ could be ensured, which is near the price associated to conventional energy sources. An outline of the solar collector system and the technical requirements of the wind turbines in needed to meet the energy demand of the MED+MVC system are also included.     

Thermal,Mechanical and Morphological Characterization of Jute/Gelatin Composites

Jute fabrics/gelatin biocomposites were fabricated using compression molding. The fiber content in the composite varied from 20–60 wt%. Composites were subjected to mechanical, thermal, water uptake and scanning electron microscopic (SEM) analysis. Composite contained 50 wt% jute showed the best mechanical properties. Tensile strength, tensile modulus, bending strength, bending modulus and impact strength of the 50% jute content composites were found to be 85 MPa, 1.25 GPa, 140 MPa and 9 GPa and 9.5 kJ/m², respectively. Water uptake properties at room temperature were evaluated and found that the composites had lower water uptake compared to virgin matrix.     

Directional control of physico-chemical and mechanical properties of epoxide composites by the addition of graphite-graphene structures

ABSTRACT

As a result of the research, the possibility of directional control of the operational properties of epoxy composites by the use of small additives of thermally expanded graphite-graphene structures has been proved, providing the bending failure stress increases by 32% and the bending elastic modulus increases by 44%, the compression strength increases by 49%, the tensile strength increases by 74% and the tensile elastic modulus increases by 34%, impact resilience increases by 78%. The addition of thermally expanded graphite increases thermal, fire and heat resistance as well as the coefficient of heat-conducting epoxy composite.     

Mechanical and thermal characterization of <Emphasis Type="Italic">cis</Emphasis>-polyisoprene and <Emphasis Type="Italic">trans</Emphasis>-polyisoprene blends

Measurements of mechanical and thermal transport properties have been made on the blends of cis-polyisoprene (CPI) and trans-polyisoprene (TPI) prepared by a solution casting method. Characterization of these blends has been done using wide angle X-ray scattering. Thermo-mechanical, mechanical, and thermal transport properties have been determined employing dynamic mechanical analyzer (DMA) and transient plane source. Storage modulus and tan δ as determined from DMA have been found to increase and decrease with the increase in TPI content, respectively. Mechanical properties such as Young’s modulus and tensile strength, as determined from strain–stress behavior of CPI/TPI blends, have been found to increase with increasing TPI content. This increase in properties has been explained on the basis of the crosslink density, calculated using theory of rubber elasticity. Thermal transport properties such as thermal conductivity, thermal diffusivity, and volumetric heat capacity are higher for all the three blends as compared to their pure components.     

Structural and mechanical properties of polybutadiene-containing polyurethanes

A series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure-property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment T_g at ?74°C for the unsaturated polyurethanes and at ?69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The low T_g, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90-95 percent of the urethane N-H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene-containing polyurethanes the extent of H-bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segment T_g and stress-strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σ_b), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.     

2-D Hydro-Viscoelastic Model for Convective Drying of Highly Deformable Saturated Product

The aim of this work was to simulate in two-dimensions the spatio-temporal evolution of the moisture content, the temperature, and the mechanical stress within a highly deformable and water saturated product during convective drying. The material under study was an elongated potato sample with a square section placed in hot air flow. A comprehensive hydro-thermal model had been merged with a mechanical model, assuming a viscoelastic material, a plane deformation, and an isotropic linear hydric-shrinkage of the sample. This model was validated on the basis of the average water content and core temperature curves for drying trials under different operating conditions. The material viscoelastic properties were measured by means of stress relaxation tests at different water contents. The viscoelastic behavior was described by a generalized Maxwell model whose parameters were correlated to water content. The simulations of the spatio-temporal distributions of mechanical stress were performed and interpreted in terms of product potential damage. The sample shape was also predicted all aver the drying process with reasonable accuracy.     

TWO DIMENSIONAL SIMULATION OF DEHYDRATION OF A HIGHLY DEFORMABLEGEL : MOISTURE CONTENT,STRESS AND STRAW FIELDS

Abstract

A model taking into account the simultaneous influence of mechanical and hygrometric actions (Mrani and al., 1995a, 1995b) was applied to study of the dehydration of a cylinder of highly deformable biphase gel (agar gel) (Mrani and al., 1995b). Numerical solution of the water transport equation and the mechanical equilibrium equation provided access to the water content and stresses and strains in the cylinder. The numerical results were validated for water content and overall deformation of gel cylinders. The model clearly shows the inversion of the curve of the faces of the cylinder observed experimentally. Three deformation phases were observed. In the first phase, when the concaveness of the faces of the cylinder was turned inwards, tractive stress appeared at the surface of the sample. More uniform distribution of the water content became established in a second phase and the cylinder recovered its initial shape corresponding to the relaxation of the stress state. In the third phase, the concaveness of the faces of the cylinder was turned outwards, the surface became rigid with compression at the surface and traction in the centre.     

Drying Potential Of Humid Air - A Thermodynamical Anlysis

ABSTRACT

Theoretical analysis of thermodynamical potentials relevant for water vapour transfer processes in the system: wet material - moist air, pertormed in the paper. leads to the conclusion that masimal possible isothermal decrease of chemical potential of water vapour in the moist air might be considered as the measure of humid air afinity to unbound water vapour. The concept developed provides better estimation of the drying ability of humid air of different states, as well as tracing Lines of equal values of humid air drying potential into psychrometric charts and constructing several new types of diagrams for convective drying processes in which air is used as the drying medium.     

Synthesis, characterization, and platinum-catalyzed hydrosilation cross-linking of copoly(methylsilylene/1,4-phenylene/methylvinylsilylene): Properties of aromatic carbosilane thermosets

Low molecular weight copoly(methylsilylene/1,4-phenylene/methylvinylsilylene) (I) has been prepared by the reaction of a mixture of methyldichlorosilane and methylvinyldichlorosilane with the di-Grignard reagent prepared fromp-dibromobenzene.I has been characterized by¹H,¹³C, and²⁹Si NMR as well as FT-IR spectroscopy. Its molecular weight distribution has been determined by gel permeation chromatography (GPC), its thermal stability in nitrogen evaluated by thermogravimetric analysis (TGA), and its glass transition temperature (T _g) measured by differential scanning calorimetry (DSC). Platinum-catalyzed hydrosilation cross-linking ofI yields a thermoset material. The bending modulus (logE), tan·, andT _g of these cross-linked materials have been measured by dynamic mechanical thermal analysis (DMTA). Carbon fabric treated with catalytic amounts of platinum has been coated withI. Multilayers of coated carbon fabric have been consolidated (cured) to yield aromatic carbosilane/carbon composite materials. The interlaminar shear strength of these materials has been determined by short beam shear. Flexure strength and modulus of elasticity of these composite samples have been measured. The ultimate compressive strength and compression modulus as well as the tensile strength and elastic modulus of these have been determined.Presented at the XXVIth Silicon Symposium, Indiana University-Purdue University of Indianapolis, March 26–27, 1993.     

A Theoretical Model for the Nongray Radiation Drying of Polyvinylalcohol/Water Solutions

Abstract

A theoretical analysis of heat transfer and moisture variation was performed while a PVA solution was exposed to high-intensity nongray irradiation and/or air flow convection. Effective absorption coefficients were incorporated in the radiative transfer analysis. The influence of various radiation and convection parameters on the transfer of heat and moisture variation in the coated layers on an optically thick substrate was investigated. The effects of radiation and convection parameters on the transfer process were presented in terms of the rate of water content removal, heat transfer, and moisture distribution. Results were compared to those of drying when using convective heat. It is evident that the use of thermal radiation combined with convective heat will help in improving the drying rate. Numerical results show that both the radiative energy absorbed by the solution and the substrate and the distribution of water mass fraction in the solution are closely related to the rate of water removal from the solution during the process.     

RELATIVE IMPORTANCE OF VAPOUR DIFFUSION AND CONVECTTVE FLOW IN MODELLING OF SOFTWOOD DRYING

ABSTRACT

The influence of vapour diffusion on the drying rate of a softwood board has been examined for drying temperatures varying from 60°C to 140°C. It is found that for very low temperature drying a model which considers both vapour convective and diffusion in wood predicts dry-rate curves matching the experimental data closely. For high temperature drying, both of the above drying model and a drying model which considers only vapour convective flow give predictions in agreement with the observed data. This illustrates that the diffusion of vapour and air is important in low temperature drying panicularly during the late stages of drying. However, for high temperature drying, the convective flow of moisture vapour is dominant and the diffusion component is negligible. The observation provides evidence for simplifying a drying model for high temperature drying without reducing its credibility in predicting drying rate curves.     

Influence of firing temperature on correlation between thermal shock and mechanical impact resistance of refractory castables

Abstract

Three refractory castables used in the aluminium industry were investigated to establish correlations, which can be applied in practice, among the relevant properties important for performance in service. To determine the influence of firing temperature on the correlations, samples were fired at 1200 and 1450°C followed by mechanical impact (at 900°C) and thermal shock tests (quenched from 950°C into water). The relevant properties were evaluated including modulus of rupture, elastic modulus, work of fracture, and thermal expansion coefficient. The results show that there is a positive correlation between thermal shock and the mechanical impact resistance as well as with the σ_o R_st parameter at 1200°C. Two other positive correlations were established at 1450°C, the first involving mechanical impact resistance, modulus of rupture, and σ_o R_st , and the second between thermal shock resistance and the R′′′′ and R_st parameters.     

Physical and Mechanical Behavior of Polyamide-6 Containing Oxyaromatic Compounds

Abstract

The distribution of oxyaromatic compound in PA-6 amorphous regions between two structural forms, which are characterized by different energy of interaction with polymer matrix, was studied. Physical and mechanical properties (glass transition temperature, water sorption, elastic modulus) of PA-6 containing oxyaromatic compound were shown to be controlled not only by the net content of oxyaromatic compound in polymer, but by its distribution between these structural forms. This distribution appears to govern the mechanical properties of the polymer in the region of its relaxation transition from glassy to rubbery state, whatever this state was achieved by increasing the concentration of plasticizer (water) or by increasing the temperature. The experimental evidence obtained was discussed with the account for structural heterogeneity of the amorphous regions of semicrystalline PA-6.     

Oilseed Meal Based Plastics from Plasticized, Hot Pressed Crambe abyssinica and Brassica carinata Residuals

With the increased use of plant oils as sustainable feedstocks, industrial oilseed meal from Crambe abyssinica (crambe) and Brassica carinata (carinata) can become a potential source for oilseed meal based plastics. In this study, crambe and carinata oilseed meal plastics were produced with 10–30 % glycerol and compression molding at 100–180 °C. Size exclusion HPLC was used to relate tensile properties to changes in protein solubility and molecular weight distribution. By combining glycerol and thermal processing, increased flexibility has been observed compared to previous work on unplasticized oilseed meal. Tensile results varied from a brittle crambe based material (10 % glycerol, 130 °C), Young’s modulus 240 MPa, strain at maximum stress of 2 %, to a soft and flexible carinata based material (30 % glycerol, 100 °C), Young’s modulus 6.5 MPa, strain at maximum stress of 13 %. Strength and stiffness development with increasing molding temperature is in agreement with the protein profiles obtained. Thus, the highest mechanical parameters were obtained at the protein solubility minimum at 140 °C. Higher temperatures caused protein degradation, increasing the level of low molecular weight extractable proteins. In carinata based materials the strain at maximum stress decreased as the protein aggregation developed. Results presented indicate that both crambe and carinata oilseed meal based materials can have their properties modulated through thermal treatment and the addition of plasticizers.     

Stress–strain behavior in uniaxial compression of polymer gel beads

A method for carrying out mechanical testing on spherical microparticles (Versabeads?) has been evaluated using an incompressible viscoelastic finite element model. The mechanical test is based on the compression of a single bead from which stress–strain data are obtained. Simulations based on the finite element model are used to investigate whether or not an apparent elastic modulus found as the slope of the initial close to linear stress–strain curve can be related to the real elastic modulus. The numerical results indicate that the apparent modulus is in fact related to the elastic shear modulus and that the relation E_app ≈ 4G can be used to obtain the shear modulus from the mechanical test. These results, however, only apply for purely elastic beads. The finite element solution has also been compared to the Hertz's expression relating axial displacement and compression force. Good agreement with the Hertz's expression is obtained at axial displacements below 10% and fit of the Hertz's expression to simulated force–displacement curves leads to a Hertz's modulus that is equal to 4G. This is expected for incompressible materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3037–3047, 2006     

DETERMINATION OF MOIST AIR DRYING ABILITY USING CHEMICAL POTENTIAL OF WATER VAPOUR

ABSTRACT

A thermodynamically simple method for calculation of chemical potential of water vapour, contained in the unsaturated moist air used as a drying medium in convective dryers, is developed. The introduced concept enables determination of the moist air drying potential for different patterns of air state change in convective drying processes and tracing new lines in psychrometric and similar diagrams that enables prediction of the optimal drying process. The proposed method also facilitates the evaluation of air consumption and efficiency of the specific drying process.