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排序方式: 共有1097条查询结果,搜索用时 31 毫秒
1.
大掺量粉煤灰轻质墙体砌块是以粉煤灰为主要原材料 ,普通硅酸盐水泥为胶凝材料 ,配以各种外加剂 ,经发泡剂发泡 ,在常温、常压条件下养护而成。具有重量轻、导热系数小、抗冻性高以及粉煤灰掺量大、成型方便、工艺简单、投资小、见效快等优点。 相似文献
2.
Meng Wai Woo 《Drying Technology》2008,26(1):15-26
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. 相似文献
3.
《Drying Technology》2007,25(6):971-983
This article reviews developments in the simulations of spray dryer behavior, including the challenges in modeling the complex flow patterns inside the equipment, which are often highly transient and three-dimensional in nature. There appears to be considerable scope for using CFD simulations for investigating methods to reduce the rates of wall deposition and of thermal degradation for particles by modifying the air flow patterns in the chamber through small changes in the air inlet geometry. Challenges include building particle drying kinetics and reaction processes, as well as agglomeration behavior, into these simulations. The numerical simulations should be valuable supplements to pilot-scale testing, enabling more extensive and accurate optimization to be carried out than hitherto possible. New understanding of reaction processes and materials science, in combination with recent knowledge of the application of CFD to these problems, may enable new engineered powder products to be developed from the one-step spray-drying process. 相似文献
4.
HerlinaAdrian Wing-Keung Law 《International Journal of Heat and Mass Transfer》2002,45(24):4899-4905
The results of a laboratory investigation on the turbulence characteristics of a circular three-dimensional turbulent wall jet are presented. Measurements were taken up to 50 nozzle diameters using combined particle image velocimetry and planar laser induced fluorescence. The results showed that the induced turbulence was still evolving in the present range and had not achieved similarity. While the turbulent intensity for both velocity and concentration increased downstream, the turbulent mass transport showed a decline over distance for both the streamwise and spanwise directions, implying weakening dispersion from the jet core. 相似文献
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为提高包钢钢联股份有限公司Ф400mm自动轧管机轧制的钢管壁厚精度.进行了轧卡试验及有限元模拟分析,获得了钢管在孔型中的应变分布状况,经过优化孔型参数和改进轧辊孔型,使轧制的钢管横向和纵向壁厚偏差大大减小。 相似文献
8.
Anthony G. Dixon 《Chemical Engineering Communications》1988,71(1):217-237
The effective radial thermal conductivity and apparent heat transfer coefficient for a packed bed were experimentally determined for beds of spheres, full cylinders and hollow cylinders, for flow rates giving particle Reynolds numbers in the range 100-1000, and for tube to particle diameter ratios of 5-12. Over these ranges the radial Peclet number Per showed significant dependence on solid conductivity, gas flow rate and particle shape, while the wall Biot number Bi showed significant dependence on tube to particle diameter ratio, gas flow rate and particle shape. These dependencies were predicted well by equations incorporating the effects of these variables into individual gas and solid phase parameters, which were then combined to give the effective or lumped parameters 相似文献
9.
Jan Tobi? 《Chemical engineering science》2006,61(8):2447-2456
The pressure drop and the fluid velocity profiles were investigated experimentally and numerically in the model packings of complex geometry. The numerical estimations were performed by means of the hybrid method involving the use of structural macro-correlations. In this paper it has been demonstrated on several examples that the structural macro-correlations allow to predict the macro-scale flow behaviour in non-homogeneous packings. Finally, the recent mechanistic approaches to flow modelling in packed tubes of low tube-to-particle diameter ratio have been discussed. 相似文献
10.
Decay characteristics of ozone concentration in oxygen in a chamber with three types of wall material (stainless steel, copper, and aluminum) are measured using the 254 nm photoabsorption method. Effective lifetimes of ozone are estimated from decay curves of ozone concentration. These values depend on the wall material: They are largest for stainless steel and smallest for aluminum. The relationship between effective lifetime and gas pressure is investigated precisely to determine three values. The equivalent diffusion coefficient of ozone in oxygen and the reflection coefficient of ozone at the wall correspond to the loss rate of ozone at the wall. The collisional loss (quenching) rate coefficient of ozone in oxygen is also determined. 相似文献