课程文献中心 更多>>

关键词： Binary mixture   Biomass   Fast pyrolysis   Fluidization   Mixing   Separation  

摘要： To guarantee the uniform mixing of biomass and inert particles in the fluidized bed reactor for the full and complete reaction during the biomass fast pyrolysis process, a visualized cold fluidized bed experimental apparatus was set up to investigate the effects of static bed height, moisture content and particle diameter on the fluidization quality of single component particles, and the mixed volume ratio on the fluidization characteristics of binary mixtures. The results showed that the appropriate static bed height was significant for the stability of the fluidized bed. As the moisture content increased, the minimum fluidization velocity increased rapidly while the fluidization index continued to decrease. In addition, the fluidization performed on binary mixtures of larch/quartz sand-2 indicated that the same minimum fluidization velocity was the key parameter for the two kinds of particles to be fully fluidized simultaneously, avoiding the semi-fluidization phenomenon. The mixed volume ratio of larch (M = 10.3%)/quartz sand-2 and superficial gas velocity range were also the important factors affecting fluidization and mixing quality, and the optimal value were 1: 3 and 3-5 u(mf), respectively.

关键词： Turbo air classifier   Rotor cage's outer and inner radii   The width of annular region   Numerical simulation of flow field   Classification performance  

摘要： The effects of rotor cage's outer and inner radii on flow field of the turbo air classifier are comparatively analyzed by numerical simulation using ANSYS-FLUENT. The results of quantitative analysis show when the rotor cage's outer and inner radii are increased, the tangential velocity, radial velocity and upward axial velocity decrease in the annular region and near the entrance of the rotor cage. However, when the rotor cage's outer and inner radii are too large or too small, the tangential velocity and radial velocity will be fluctuated greatly. Moreover, the rotor cage's outer and inner radii directly influence the radial velocity distribution in the rotor cage channel. The rotor cage's outer and inner radii should not be too large or too small. Therefore, in the seven contrast rotor cage models, model 100-70 and 90-60 are selected to carry out the calcium carbonate classification experiments due to their small tangential velocity and radial velocity fluctuations and well-distribution in the rotor cage channel. The experimental results reflect the characteristics of the numerically simulated flow field in the classifier.

关键词： coarse wood   fluidized bed   grindability   semi-biochar   thermogravimetric characteristics  

摘要： For the utilization of leftover materials from furniture factory, a two-step pyrolysis, an initial treatment at mild temperature followed by a fast pyrolysis step, in a fluidized bed reactor was proposed in this study. The grindability of semi-biochar samples after the mild temperature pyrolysis was studied. The fast pyrolysis characteristics and kinetics parameters of the semi-biochar samples were also investigated by thermogravimetric analysis. Results showed that an improvement in the grindability characteristics was observed. The grinding of semi-biochars that do not completely devolatilize mainly produces a mixture of fine particles and small fragments, whereas the semi-biochars that completely devolatilize have good grinding characteristic, and the main ground products are short and round particles. Most differential thermogravimetric (DTG) curves of the semi-biochar samples presented two peaks and four common stages. With increase of the temperature or residence time in mild temperature treatment process, the decomposition intensity of hemicellulose and cellulose in grinding residues decreased gradually, while the decomposition intensity of lignin changed little. Peak DTG value ranging from 4%/min to 6%/min can be adopted to estimate the optimal operation condition for mild temperature pyrolysis. Three-dimensional diffusion model can accurately describe the fast pyrolysis of semi-biochar.

关键词： Liquid-containing gas-solid fluidized bed reactor (LC-GSFBR)   Liquid content   Surface tension   Fluidization characteristics   Stagnation zone  

摘要： The fluidization process within gas-solid fluidized bed reactor can be intensified by adding liquid, as it can enhance mass and heat transfer between gas phase and solid phase. With the help of computational fluid dynamics(CFD) and discrete element methods(DEM), fluidization characteristics are investigated at different liquid contents((V) over cap) and surface tension(Bo(g)). To be specific, the bed expansion ratio, particle concentration and particle velocity profiles are compared and analyzed. Numerical simulations show that Bo(g) should be less than 5 at (V) over cap = 0.013. At this recommended range, liquid addition makes interparticle force increase and has little effect on fluidization performance. From transient particle agglomeration behavior, the Bo(g) increase is more likely to enhance interparticle force, resulting in obvious particle agglomerations during fluidization process. The variation of stagnation zone height can be reflected from the abrupt increase of particle velocity in annulus region. It can be found that (V) over cap increase reduces particle velocity at critical height but Bo(g) increase is more likely to cause larger stagnation region. By analyzing the distribution of spout, annulus and fountain regions at different (V) over cap and Bo(g), the annulus region expands with (V) over cap increase below the initial bed height while the spout region expands with Bo(g) increase.

关键词： Compressor cascade   Blade-end treatment   Flow loss   Topological analysis   Vortex dynamic mechanism  

摘要： Elucidating the underlying mechanism of the vortex dynamics in compressors is essential for determining the sources of the flow losses in compressor cascades. Hence, the effects of blade-end treatments on a linear compressor cascade should be analyzed at the microscale. In this study, the design parameters for various blade-end treatment methods were determined based on the topological structure of the saddle and spiral points on the blade surface. Then, based on the results, the underlying mechanism of the corresponding vortex dynamics was determined. The results showed that the total flow loss is primarily determined by the passage and concerted shedding vortices and the profile losses. The positive effect of the blade-end treatment is that it weakens the vortex structures, while its negative effect is that it causes the low-energy fluid clusters to converge into a separation bubble. However, the negative effects are compensated for by the positive, resulting in a significant reduction in the total flow loss. Furthermore, the changes induced in the pressure gradients by the treatments were also analyzed in this study. Thus, the microscale relationship between the vortex structure and the flow loss was clarified and the suitability of various blade-end treatment for preventing cascaded flow losses was analyzed in this study. (C) 2020 Elsevier Masson SAS. All rights reserved.

关键词： Oil and Gas well leakage   Primary cementing   Herschel-Bulkley fluid   Displacement flow  

摘要： We develop a simplified approach to predicting the displacement front behaviour of two Herschel-Bulkley fluids displacing one another along a narrow eccentric annulus in turbulent and mixed regimes. The approach involves the use of scaling arguments to reduce the full system of equations to a single hyperbolic equation that models the displacement front evolution. Analysis of the flux function is sufficient to predict whether or not the front will elongate along the annulus. Predictions of the simplified model are compared with a two-dimensional annular displacement model, showing good predictive abilities. The underlying eccentric annular flow is important in the industrial process of primary cementing. More specifically, the proposed method is aimed to provide a quick and reliable computational framework for analyzing primary cementing flows, leading to more successful cementing designs. (C) 2020 Elsevier Ltd. All rights reserved.

摘要： The thesis aims to address two main questions regarding certain features of liquidity-based asset classification. A first question is about the validity of such a classification: Does liquidity-based asset classification pick out a natural kind? I use the case of the category 'liquid assets' to show that liquidity is a functional property that can be realized in two genuinely different ways: monetary trades and credit trades. Accordingly, 'liquid assets' can be regarded as a functional kind with multiple realizations. I also argue that the kind 'liquid assets' earns its credential of natural kind by playing an epistemic role in explanatory economic models. I finally point out that mind-dependence does not threaten realism about the kind 'liquid assets'. The second question is about the extension of the categories resulting from liquidity-based asset classification: Is there a sharp boundary between categories of assets that are classified based on their liquidity? I use the case of 'money' to discuss if it is possible to find an unambiguous distinction between the categories 'money' and 'non-money.' I argue that such a view can be successful only, if following traditional essentialism, there is a set of intrinsic properties that are necessary and sufficient for membership in the natural kind designated by the term 'money.' However, based on what is currently known by monetary economists, there is neither set of intrinsic properties nor necessary and sufficient characteristics that one could use to separate 'money' unambiguously from 'non-money.'

关键词： WXT520超声波风速传感器   风洞   皮托管   SolidWorks   Fluent  

摘要： 针对目前铁路上广泛使用的WXT520超声波风速传感器存在检定及校准效率低、精度低、时间长等一系列问题,基于皮托管测量风速的原理,结合风洞设计理论,设计了一种能够快速、准确地提供均匀和稳定风源的低成本可移动微型低速风洞。通过将皮托管风速的测量值与被检定传感器风速的测量值进行对比,实现在现场完成对风速传感器的校准。利用Solid Works建立了WXT520风速传感器和低速风洞的三维模型,并导入Fluent中进行仿真计算。仿真结果表明,该风洞满足传感器的校准要求,并通过实验进行了验证。

关键词： 钼矿   包裹体特征   成矿条件   浅成   随枣北部  

摘要： 随枣北部处在东秦岭钼矿聚集区和西大别钼矿聚集区之间的桐柏造山带,具有良好的钼矿成矿环境条件及找成矿前景。随枣北部钼矿流体包裹体类型、均一温度及盐度、密度反映成矿流体属岩浆热液与大气降水混合的产物,发生过沸腾和分离作用,钼的富集与流体的沸腾作用关系密切,主要成矿温度在290~390℃之间,属高温成矿环境,成矿压力为9.06~72 MPa,成矿深度为0.91~6.83 km,属浅成环境。