Experimental investigation on atomizing characteristics of coal-water paste for pressurized fluidized bed

According to the properties of coal-water paste (CWP), a series of experimental nozzles were developed for a detailed study of the effect of nozzle design on CWPs behavior in a pressurized fluidized bed. The particle size and its distribution of atomized CWP using several types of nozzles are measured by PIV instrument and newly developed image processing software, and the effect of a number of factors on the atomizing properties are analyzed. The atomizing experimental results show that the atomization quality of CWP was found by correlating with the characteristics of CWP, gas to CWP mass ratio, atomization air motion, coal particle size distribution and the structure of nozzle etc. Mass median diameter (MMD) of atomized particles decreases with the increase of gas to CWP mass ratio. The proper type of nozzle type and proper parameters for engineering application are suggested.     

The effect of coal properties on the viscosity of coal-water slurries

Studies on coal-water slurries (CWSs) have been conducted for many years to replace fuel oil. In this research project, the effect of coal properties on CWSs have been investigated using two Turkish coals of different ranks and a Siberian bituminous coal. Physical, chemical and surface properties of coal samples were determined. Furthermore, adsorption tests were carried out in order to put forward the effect of additive adsorption on the viscosity of CWSs. Viscosity measurements were realized for CWSs of various solid ratios by weight that were prepared using coal samples having mean particle sizes of 19, 35 and 50 μm.     

CFD simulation of coal-water slurry flowing in horizontal pipelines

An Eulerian multiphase approach based on kinetic theory of granular flow was used to simulate flow of coal-water slurries (CWS) in horizontal pipelines. The RNG k-ɛ turbulent model was incorporated in the governing equation to model turbulent two-phase flow with strong particle-particle interactions. In this model, the coal particles with bimodal distribution were considered as two solid-phase components, and the moment exchange between solid and liquid as well as that between solid and solid were accounted for. The model was firstly validated with pressure gradient and concentration profile data from the open literature, and then validated with pressure gradient data of the authors’ experiments. The effects of influx velocity, total influx concentration and grain composition were numerically investigated, and the results have displayed some important slurry flow characteristics, such as constituent particle concentration distribution and velocity distribution as well as pressure gradients, which are very difficult to display in the experiments. The results suggest that both gravity difference between large and small particles and strong particle-particle interaction had significant effects on concentration distribution as well as velocity distribution. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, China, July 25–28, 2008.     

Local resistance characteristics of highly concentrated coal-water slurry flow through fittings

The local resistance characteristics of high concentration coal-water slurry (CWS) flowing through three types of local fittings, namely the gradual contractions, sudden contractions and 90° horizontal elbows, were investigated at a transportation test facility. Results show that the local resistance loss of gradual contractions decreases as the contraction angle increases. When pipe diameter ratio varies little, local resistance loss of sudden contractions changes insignificantly. There is an optimal value of bend diameter ratio, at which the local resistance loss of horizontal elbows is the least. As Reynolds number increases, the resistance coefficients of all the three fittings first reduce and then stabilize, while the three pipes have different ratio of equivalent length to pipe diameter L _e /D behaviors, that is, L _e /D of the gradual contractions decreases gradually and then keeps stable; that of the sudden contractions diminishes at first and then increases, and that of the horizontal elbows increases linearly. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

研磨对EPVC糊性能的影响

介绍了研磨前后EPVC糊黏度的变化情况,结果表明:研磨可增大EPVC糊黏度,随着研磨比例的增大糊黏度逐渐增大,但随着放置时间的延长,研磨前后糊黏度趋于一致。     

十二烷基硫酸钠碳链分布对PVC糊树脂特性的影响

采用不同种类的市售十二烷基硫酸钠作为乳化剂生产PVC糊树脂,研究了十二烷基硫酸钠的碳链分布对PVC糊树脂粒度分布、糊黏度(B式)、72 h增稠率以及标准糊S流动性的影响,设计出适合PVC糊状树脂生产的配方。     

Effect of blockage on heat transfer from a cylinder to power law liquids

The influence of planar confining walls on the steady forced convection heat transfer from a cylinder to power-law fluids has been investigated numerically by solving the field equations using FLUENT (version 6.2). Extensive results highlighting the effects of the Reynolds number (1?Re?40), power-law index (0.2?n?1.8), Prandtl number (1?Pr?100) and the blockage ratio (β=4 and 1.6) on the average Nusselt number have been presented. For a fixed value of the blockage ratio, the heat transfer is enhanced with the increasing degree of shear-thinning behaviour of the fluid, while an opposite trend was observed in shear-thickening fluids. Due to the modifications of the flow and temperature fields close to the cylinder, the closely placed walls (i.e., decreasing value of the blockage ratio) further enhance the rate of heat transfer as the fluid behaviour changes from Newtonian to shear-thickening fluids (n>1), the opposite influence is seen with the decreasing value of the flow behaviour index (n) in shear-thinning (n<1) fluids. Finally, the functional dependence of the present numerical results on the relevant dimensionless parameters has been presented in the form of closure relationships for their easy use in a new application.     

Experimental study of gas diffusion in cement paste

This paper presents an experimental study of gas diffusion in binary mixtures of hydrogen-nitrogen and xenon-nitrogen through cement pastes (CEM I and CEM V) of different water/cement ratios (0.35 and 0.45). First, the impact of water saturation on gas diffusion is investigated by performing tests on samples pre-conditioned in specific atmospheric conditions (dry, 55, 70, 82, 93 and 100% RH) by means of saline solutions. The comparison of the results obtained for the CEM I and the CEM V samples (w/c ratio of 0.45) demonstrate the importance of pore size distribution/connectivity on gas diffusion. Second, diffusion tests at different total pressures and using two different mixtures (hydrogen-nitrogen, xenon-nitrogen) are performed to study the nature of gas diffusion in cement paste. Results demonstrate that gas diffusion in cement paste is controlled by Knudsen and ordinary diffusion at pressures greater than 100 kPa and mainly by Knudsen diffusion at pressures less than 100 kPa.     

Effect of the high-power electromagnetic pulses on the reactivity of the coal-water slurry in hot environment

An effect of the high-power electromagnetic pulses onto the droplet of coal-water slurry inside the furnace was investigated. In contrary to the previously investigated laser-induced fuel atomization that occurs at the room temperature, the pre-heated (to 400 K) slurry becomes dry enough to prevent the explosion-like steam formation. Thus, fuel does not atomize and the ignition does not accelerate. Furthermore, the absorption of several laser pulses leads to evident sintering of irradiated surface with following increase of the ignition delay time for up to 24%. Variation of the pulse energy in range 48–118 mJ (corresponding intensity up to 2.4 J·cm⁻²) leads to certain variation of the increase of ignition delay. The strong pulsed overheating of the coal water slurry which does not initiate the fine atomization of the fuel generally makes its ignition longer.     

抛光膏中磨料的解析

利用SEM，EDS分析了抛光膏中磨料的形状，尺寸和成分。结果表明，进口抛光膏中采有的磨料是直径为2－5μm的柱状氧化铝。     

Rheological properties of cement paste: Thixotropic behavior and structural breakdown

In this work, a new material model is presented to simulate rheological behavior of cement paste. This material model is among others based on combined concepts by Hattori and Izumi and by Tattersall and Banfill. More precisely, coagulation, dispersion and re-coagulation of the cement particles (giving a true thixotropic behavior) in combination with the breaking of certain chemically formed linkages between the particles (giving a so-called structural breakdown behavior) are assumed to play an important role in generating the overall time-dependent behavior of the cement paste. The model evaluation is done by comparing experimental data with model prediction.     

Origin of the thermoelectric behavior of steel fiber cement paste

Carrier scattering dominates the origin of the Seebeck effect in steel fiber cement. The scattering sites include the fiber-matrix interface, which is like a pn junction, since the fiber and cement paste have opposite signs of the absolute thermoelectric power. The scattering results in positive and negative values of the absolute thermoelectric power, depending on the fiber content.     

Slip in Flow through Assemblages of Spherical Particles at Low to Moderate Reynolds Numbers

Effects of slip velocity and volume fraction of slip spheres on the momentum transfer characteristics of assemblages of slip spheres are numerically investigated. The fluid slip along the surface of the sphere is considered by Navier's linear slip model. The dimensionless governing continuity and momentum equations are solved using a semi‐implicit marker and cell method implemented on a staggered grid arrangement in spherical coordinates. The convection and viscous terms of momentum equations are discretized by means of the QUICK scheme and a second‐order central differencing scheme, respectively. The present numerical solver is benchmarked via grid independence and comparisons with the existing literature values. Results were obtained over a wide range of pertinent dimensionless numbers such as the Reynolds number, volume fraction of the dispersed phase, and dimensionless slip parameter.     

The influence of aminosilanes on macroscopic properties of cement paste

In this work the authors present the results obtained by studying the influence of γ-aminopropyltriethoxysilane or (CH₃CH₂O)₃Si(CH₂)₃NH₂, (APTES), and N-β-aminoethyl-γ-aminopropyltrimethoxylsilane or (CH₃O)₃Si(CH₂)₃NH(CH₂)₂NH₂, (AEAPTES), on macroscopic properties of fresh and hardened cement pastes and mortars prepared from ordinary Portland cement. The mixing ability of aminosilane substances with water is an advantage in comparison to other types of organofunctional silanes when used as an admixture to the cement system. This enables direct blending with water and cement and homogeneous distribution of aminosilane molecules through the bulk of the cement material. The highly polar amine and alkoxide groups of aminosilane molecules exhibit strong chemical interactions with cement matrix which are reflected in modified macroscopic properties of the cement system. The effect of APTES and AEAPTES on (a) properties of fresh cement paste and mortar as workability, setting time, water/cement ratio, air content and density, and on (b) properties of hardened cement paste and mortar as compressive and flexural strength, was studied.     

Severs流变仪测定聚氯乙烯糊的流变性

用Severs流变仪测定聚氯乙烯糊的流动特性参数,探讨利用所得数据计算其表观黏度,确定聚氯乙烯糊的流变行为.     

Damage monitoring of cement paste by electrical resistance measurement

Electrical resistance measurement is effective for monitoring damage (due to damage infliction and subsequent microcrack opening) and healing (due to microcrack closing) of cement pastes (plain, with silica-fume, and with latex) in real time during repeated compressive loading. Damage causes the resistance to increase; healing causes the resistance to decrease.     

Performance of new viscosity modifying admixtures in enhancing the rheological properties of cement paste

The use of viscosity modifying admixtures (VMA) has proved to be very effective in stabilizing the rheological properties and consistency of self-compacting concrete (SCC). SCC is known for its excellent deformability, high resistance to segregation and use, without applying vibration, in congested reinforced concrete structures characterized by difficult casting conditions. Most of the commercial VMAs currently available in the market are costly and increase the price of such a concrete. Identification or production of new low-cost VMA is then essential. This paper presents the performance of four new polysaccharide-based VMAs in enhancing the rheological and consistency properties of cement paste. The study of the rheological properties and consistency of cement paste to screen the dosage and type of new VMA to be used in SCC is a promising approach. Investigation was carried out on cement pastes with combinations of various dosages of new VMAs and of a superplasticizer (SP) to study the influence on rheology, consistency and washout mass loss. A commercial VMA designated in this paper as “COM” was tested for comparison. The study on new VMAs is encouraging and confirms that pastes with satisfactory rheological and consistency properties comparable with or even better than commercial VMA can be developed. The combined use of proper dosages of VMA and SP is shown to clearly contribute to securing high-performance cement pastes that is highly fluid yet cohesive enough to reduce water dilution and enhance water retention. Attempt has also been made to correlate rheological properties (yield stress) to consistency (slump) of pastes.     

Microstructure-based micromechanical prediction of elastic properties in hydrating cement paste

Elastic properties of hydrating cement paste can be successfully predicted by combination of the hydration model, percolation theory and micromechanical analysis. Reconstruction of hydrating microstructure is based on the 3D digital NIST model of cement hydration, which is enhanced for the prediction of two C-S-H types. Chemical phases in a percolated microstructure served as an input in a two-level analytical or one-level 3D FEM or FFT elastic homogenization. Special mesh generation for the percolated microstructure is discussed as well as its numerical implementation. Good results from FEM and FFT were found for the size of the representative volume element of 50 × 50 × 50 μm, considering water-to-cement ratio in the range from 0.25 to 0.5. While good predictions in well-hydrated cement pastes were obtained for both analytical and numerical approaches, numerical homogenization was found more accurate and versatile for the whole hydration time.     

水基石墨烯-铜复合导电浆料的制备及性能

采用水基载体替代有机载体,以粒径为5和15μm的混合铜粉作为主导电相,添加少量石墨烯为导电增强相,按一定的质量配比制备水基石墨烯-铜复合导电浆料。用四探针测试仪、SEM等分析测试手段研究水基载体对浆料性能的影响,分析其导电机理并建立导电相连接模型。结果表明,在m(去离子水)∶m〔羧甲基纤维素钠(CMC)〕∶m〔聚乙二醇(PEG)〕∶m(消泡剂)=96.9∶1.5∶1.5∶0.1的条件下制备的水基载体性能较好;水基载体含量为30%(质量分数)时,制备的水基石墨烯-铜复合导电浆料具有优良的印刷性能,且电阻率较小,为1.65 mΩ·cm;添加石墨烯的水基复合浆料较纯铜浆料电阻率降低了97.1%,较有机载体制备的石墨烯-铜复合浆料电阻率降低了75.78%。制得的导电膜更平坦、致密,导电相间的接触更紧密,大量的石墨烯在铜粉间隙之间或横向搭接,或径向填充,与铜粉形成并联或串联的导电通道,从而形成致密的导电网络,改善复合浆料的导电性能。     

流体阻力摩擦系数关联式的比较与改进

着眼于流体阻力摩擦系数的计算关联式。在众多基础教材中,选取常用的三本进行比较。在通用工具莫迪图上,用三本教材中的关联式对图中七条不同相对粗糙度的曲线,进行特定雷诺数范围内的流体阻力摩擦系数的计算。并应用Excel的函数库和图表向导功能作出大量的图表,以便对这些关联式进行定量的误差分析。进而又运用数形结合的方法,将计算值与实验值的相对误差,同摩擦系数的相互作用参数-雷诺数结合在一起,并给出校正关联式的拟合公式。使得计算精度在很大程度上得到提高。