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1.
Packed beds of fuel wood chips are commonly found in thermal conversion processes such as combustion or gasification. Wood chips in particular are mostly used as fuel for small-scale domestic heating boilers but also for commercial-scale combustion units. The characterization of spatial voidage distribution inside the wood chip beds is of great importance for flow and reactor modelling. This study focuses on the radial porosity variations of cylindrical beds of three different types of commercially available wood chips including chips classified as G30 size class. The conventional technique of consolidating packed beds with a resin was chosen as the experimental procedure. The radial voidage distribution in different cylindrical beds is determined by image analysis of sections of the solidified packings. Additionally, a packing of monosized spheres was investigated in order to assess the selected procedure in comparison with widely available literature data for spheres. The results are discussed and summarized in a mathematical expression correlating the radial voidage distribution depending on average wood chip size, packing core porosity and dimensionless distance from the tube wall. 相似文献
2.
T. Renganathan 《Chemical engineering science》2005,60(10):2545-2555
Studies on voidage fluctuations, axial voidage profile and bed expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid-solid inverse fluidized bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the bed except for particles with size distribution. All the literature and present experimental data on bed expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The bed expansion data are also predicted using the drift flux model. 相似文献
3.
Unsteady gas-liquid flows in bubble columns are comprised of various flow processes occurring with varying length and time scales and govern mixing and transport processes. In the present work, we have characterized dynamic and time-averaged properties of gas-liquid flows in rectangular bubble columns using conductivity probes. The development of a single-tip conductivity probe, data processing methodology, and photographic validation procedure is discussed in detail. The effect of superficial gas velocity and aerated liquid height-to-width (H/W) ratio on voidage fluctuations and time-averaged gas holdup was investigated. The experimental data presented here can help in understanding the dynamics of various flow processes and validating computational fluid dynamics based models. 相似文献
4.
X-ray computed tomography (CT) is used to explore the differences in gas dispersion in a stirred-tank reactor (STR) for different operating conditions by varying the impeller speed and gas flow rate. X-ray imaging has been carried out in a 0.21 m ID acrylic STR equipped with a nylon Rushton-type impeller. From the CT images, major differences in local gas holdup are observed for different operating conditions. Completely dispersed conditions have a relatively uniform holdup profile while flooded conditions show a high gas holdup near the impeller shaft. The high resolution of the X-ray system allowed fine details such as recirculation regions behind the baffles to be visualized. 相似文献
5.
本文对UPR合成中掺合技术的应用与FRP制造中正确认识材料、正确使用材料及FRP制品 中空洞率与质量的关系进行了论述。 相似文献
6.
Xuefeng Su 《Chemical engineering science》2006,61(10):3098-3104
Three bubble column diameters (D=10.2, 15.2, and 32.1 cm) are employed to study the scale-up effect on gas holdup in air-water and air-water-cellulose fiber (hardwood, softwood, and BCTMP) systems. The effect of column diameter depends on flow regime and fiber mass fraction. When , gas holdup decreases with increasing column diameter for the transitional and heterogeneous flow regime, and column diameter effects are negligible in the homogeneous flow regime. When , gas holdup is only affected by column diameter in the transitional flow regime for an air-water system and low fiber mass fraction suspensions (C?0.25%); column diameter effects disappear at medium fiber mass fractions (e.g., C=0.8%) but are significant at high fiber mass fractions (e.g., C=1.4%). 相似文献
7.
Junxian Yun 《Chemical engineering science》2004,59(24):5873-5881
Based on the previous work (Yun et al., Chem. Eng. Sci. 59 (2004) 449-457), after the analysis of adsorbent structure, bed expansion and in-bed fluid hydrodynamics, a model was developed to describe the axial variations of the mean particle size and local bed voidage for adsorbents with a broad size distribution and different densities in expanded bed. In the model, the different-size particles were assumed to have different densities while the equal-size particles have the same density. Particle densities were described by a function that considered two parts of each particle: the resin-core part consisting of resin and inert core-particulates, and the thin resin film part without inert core-particulates. With UpFront FastLine SP adsorbents as interest test particles, the particle size and local voidage changes with bed height were measured in a 20 mm I.D. column and then predicted by the model. It was shown that the mean particle size decreased, while the local bed voidage increased with increase of bed height. These trends are similar to those for particles with a broad normal size distribution and nearly uniform density. More obvious increase trends of voidage with increase of bed height exist in expanded beds with UpFront FastLine SP particles compared with those of Streamline particles. The present model gave a good prediction of bed expansion, the mean particle sizes and local voidages in most parts of bed compared with experimental data. 相似文献
8.
FCC细颗粒湍流流化床流体力学性能研究李俊,张蕴璧,闫遂宁(西安石油学院,西安710061)(西北大学)(洛阳石化公司)关键词:流化床,湍流,气泡,空隙率1前言湍流流化床有着广泛的工业背景。湍流流化床反应器存在着物质空间分布的不均匀现象,这种分布对湍... 相似文献
9.
Junxian Yun Dong-Qiang Lin Miao-Hua Lu Wen-Ting Zhao 《Chemical engineering science》2004,59(2):449-457
Axial distribution of adsorbent particle as well as local voidage variation is very important and fundamental for the predicting and understanding of adsorptive performance in expanded bed adsorption. Based on the analysis of bed expansion and fluid hydrodynamic behaviors, a model was developed to predict the mean particle size and local voidage variations with the axial bed height under various operation conditions in expanded bed. Experimental measurements of particle size and local voidage changes with bed height were conducted in a modified glass column of inner diameter with sampling ports. Experimental data obtained in this work and in the literature with Streamline SP, Streamline Phenyl and Streamline quartz base matrix particles in the columns of inner diameters 20-, were used to verify the model prediction. The results were in good agreement with the experimental data. 相似文献
10.
Chengzhi Tang 《Chemical engineering science》2007,62(5):1408-1417
An experimental investigation is reported on the effect of fiber length distribution on gas holdup in a cocurrent air-water-fiber bubble column. Different combinations of 1 and 3 mm Rayon fibers are used to simulate different fiber length distributions. At a constant total fiber mass fraction, gas holdup generally decreases with increasing mass fraction of the 3 mm Rayon fiber while other conditions remain constant. Crowding factors estimated using four different methods (Nc=Nc,A, , Nc,L, and Nc,M) and the parameters and are tested on their performance to quantify the overall effects of fiber mass fraction and fiber length and its distribution on gas holdup. and provide the best characterization of the fiber effects on gas holdup in the cocurrent air-water-fiber bubble column. The crowding factor estimated using the model-based average fiber length (Nc,M) also provides a good characterization and is better than the other crowding factor definitions. 相似文献