Turbulence in the freeboard of a gas-fluidised bed: The significance of ghost bubbles

The turbulence in the upward gas flow above a gas-fluidised bed was measured by hot wire anemometry. In this region above the bed—defined as the free is the fluidising velocity. The irregularity of the motion is caused by bursting bubbles at the surface of the bed. It appears that the gas within a bu are termed “ghost bubbles”.Ghost bubble mechanics were studied by releasing single bubbles from: (i) stagnant liquid; and (ii) an incipiently fluidised bed. Tle velocity field wa The velocity of a ghost bubble diminishes as it rises, due to fluid entrainment caused by turbulent circulatory flow within the bubble.From the freeboard turbulence measurements for a continuously bubbling fluidised bed, it is clear that the turbulence is due to ghost bubbles, but the ghost bubble.     

Formulation of a physically motivated specific breakage rate parameter for ball milling via the discrete element method

A physically based specific breakage rate parameter of the population balance model for batch dry‐milling is formulated, which explicitly accounts for the impact energy distribution calculated by the discrete element method (DEM). Preliminary DEM simulations of particle impact tests were first performed, which concluded that dissipation energy should be used in contrast to collision energy to accurately define the impact energy distribution. Subsequently, DEM simulations of the motion of spheres representing silica glass beads in a ball mill were performed to determine the specific breakage rate parameter, which was in good agreement with those found experimentally. An analysis of the impact energy distribution, which was only possible within context of the physically motivated specific breakage rate parameter, emphasized the importance of accounting for a threshold impact energy. Without proper assessment of the impact energy distribution, DEM simulations may lead to an erroneous evaluation of milling experiments. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2404–2415, 2014     

Two-stage procedures for the bounded risk point estimation of the parameter and hazard rate in two families of distributions

Two families of distributions are considered that cover a large number of probability distributions useful in investigations involving reliability studies and survival analyses. The problem of bounded risk point estimation of the parameter and hazard rate function of the two families of distribution is handled. Motivated by Mukhopadhyay and Pepe (2006 Mukhopadhyay, N. and Pepe, W. (2006). Exact Bounded Risk Estimation When the Terminal Sample Size and Estimator Are Dependent: The Exponential Case, Sequential Analysis 25: 85–101.[Taylor &; Francis Online] , [Google Scholar]), Roughani and Mahmoudi (2015 Roughani, G. and Mahmoudi, E. (2015). Exact Risk Evaluation of the Two-Stage Estimation of the Gamma Scale Parameter under Bounded Risk Constraint, Sequential Analysis 34: 387–405.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]), and Mahmoudi and Lalehzari (2017 Mahmoudi, E. and Lalehzari, R. (2017). Bounded Risk Estimation of the Hazard Rate Function of the Exponential Distribution: Two-Stage Procedure, Sequential Analysis 36: 38–54.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]), two-stage procedures are developed based on the maximum likelihood estimator (MLE) as well as uniformly minimum variance unbiased estimator (UMVUE). The estimation problem based on the minimum mean square estimator (MMSE) is also considered. We establish that the MMSE of the parameter and hazard rate provides a smaller risk.     

沟槽对湍流流动影响研究

设备内部气体可能存在湍流流动状态,设备壁面形成沟槽形式可能会对原流动状态产生影响从而影响设备性能。以前相关研究很少,但设备内部气体是否存在湍流流动状态,流动状态改变是否会对设备性能产生影响还需要进一步研究。为研究壁面形成沟槽形式对原湍流流动产生的影响,对流动状态变化前后沿壁面温度分布进行了计算,采用脉动温度符合一定概率分布的方法计算了脉动温度,对流动状态变化时温度场变化情况进行了分析。     

旋风管内气相的湍流运动特性

利用二维激光多普勒测速仪(LDV)测量了旋风管内湍流运动的时均速度、脉动速度、能谱函数、微分尺度及湍流耗散等参数，对湍流特性参数分布进行了详细的描述，并初步分析了旋风管内湍流运动特性对颗粒分离的影响.     

Turbulence of a non-Newtonian fluid

This paper presents a simple theory for a non-Newtonian fluid, especially the corotational Jeffreys model. Particular attention is paid to the frequency spectrum of the strain fluctuations, and through this article it is found that the Jeffreys fluid will exhibit an “onset” Reynolds number, above which the effects of the non-Newtonian nature of this fluid are felt. Because time dependent behavior of the strain-strain correlation is emphasized, this study is complementary to the molecular theory.     

双组分扩散过程界面湍动现象观察

利用激光纹影仪对静止、水平流动以及降膜流动的乙醇水溶液双组分扩散过程中传质导致的界面对流结构进行了观察,同时考察了温度、液层厚度、流体运动状态等因素对界面对流结构的影响.研究结果有助于寻求增进传质的有效途径,并且为传质界面湍动现象的理论分析提供实验依据.     

The significance of defect chemistry for the rate of gas–solid reactions: three examples

Three examples are revisited in which the reaction rate could be reliably correlated with point defect chemistry highlighting the role of point defects as acid–base active centers. In the case of dehydrohalogenation of tertiary butyl chloride, AgCl becomes increasingly active as heterogeneous catalyst, if AgCl is homogeneously or heterogeneously doped. By such a procedure the silver vacancy concentration is adequately increased. The oxygen incorporation into SrTiO₃ offers an example in which the surface mechanism in terms of adsorbed species, oxygen vacancies and electronic centers has been elucidated. Appropriate surface coatings give rise to significant catalytic effects. Increasing iron (acceptor) doping not only changes the point defect chemistry but also the nature of the rate determining step. Lastly, the electrocatalytic function of Sr-doped LaMnO₃ is considered as regards oxygen reduction reaction and O²⁻ incorporation into Y-doped ZrO₂ in the context of solid oxide fuel cells. Again the defect chemistry is of prime importance for the reaction rate.     

The significance of heating rate on char yield and char properties in the pyrolysis of cellulose

The carbonization of powdered cellulose was investigated in the temperature range 200–950°C by measuring weight loss, carbon and hydrogen content, BET-adsorption of nitrogen and carbon dioxide, mercury penetration and particle-size distribution. Evidence is presented in support of a kinetic model according to which cellulose decomposition is controlled by dehydration at low temperature and by cleavage/scission at high temperature. Increased char yield and lower $\text{O}\text{C}$ ratio at low heating rate, as well as kinetic investigations into the effect of potential catalysts, support this model. The difference in reaction mechanism according to the heating rate appeared to influence the char properties considerably. Yield in micropore volume and surface area of slowly carbonized cellulose is up to four times larger than that of rapidly heated cellulose. Mercury pore volume, density and particle diameter depend on the heating rate, also. By adsorption of various gases, differences in relative size of the pore openings of different chars can be discerned. Micropore volumes measured with carbon dioxide were as much as seventy times larger than the corresponding volume measured with nitrogen. Thus, it is possible to obtain chars with molecular sieve properties by simple pyrolysis heating schemes.     

Analysis of microbial adaptation at enzyme level for enhancing biodegradation rate of BTX

Catechol was found to be a common intermediate in the degradation of benzene and toluene byAlcaligenes xyhsoxidans Y234, and the ring cleavage of the catechol mediated by catechol 1,2-dioxygenase was a rate-determining step. Since benzene induced higher level of catechol 1,2-dioxygenase than toluene, the cells pre-adapted to benzene showed higher degradation rate of benzene and toluene. The degradation rate ofm-xylene was also increased significantly when benzene-adapted cells were inoculated.m-Xylene was metabolized via 3-methyl catechol which was effectively cleaved by catechol 1,2-dioxygenase.     

Some Observations of Diatoms Under Turbulence

The effect of turbulence on several freshwater diatom taxa was investigated and our findings are described herein. We have compared diatom morphology in shallow natural systems that experience turbulence due to wind and in river/waterfall systems where turbulence is due to high flow rates. We have also introduced turbulence into diatom laboratory cultures by mechanical shaking and by forcing air into the media. In particular, we have studied diatoms in five independent environments or cultures: the freshwater diatoms Tabellaria and Eunotia in equatorial lakes experiencing extreme seasonal variability in depth; two freshwater diatom monocultures of Aulacoseira granulata var angustissima and Melosira varians in the laboratory; and a freshwater diatom community possessing equal amounts (by number) of elongated and non-elongated diatoms (mostly Nitzschia and mostly Cyclotella, respectively) in the laboratory. We have demonstrated the effect of turbulence on freshwater diatom frustule morphologies and, perhaps more importantly, the effect of turbulence on freshwater diatom species population after controlled perturbation of the organisms’ environment. It has been widely reported that symmetry is often preferred in biological evolution, however here we have observed a preference towards asymmetry for the survival of diatoms in the presence of environmental stress (in particular, turbulence). We also note that to date there have been no systematic attempts to manipulate diatom frustules using external stimuli. We therefore present a proof-of-concept study in order to demonstrate: (i) that diatom morphologies can be manipulated by controlled simple external triggers (chemical and physical) (ii) that population balance (i.e. natural selection) can be controlled via simple external triggers (chemical and physical). This approach could open up an entire new field of future studies wherein controlled environmental perturbations are used to manipulate the structure, form, growth and reproduction of biological species.     

Effect of Turbulence of the Freeboard on Fluidized-Bed Biomass Combustion

Fluidized-bed combustion is a very popular technology used to convert solid biomass into thermal energy, which has many advantages over other conversion technologies. However, these advantages strongly depend on the freeboard combustion. This study focuses on the effect of turbulence of the freeboard via developing a comprehensive mathematical model including four-way coupling, biomass thermal decomposition, and turbulent combustion by means of an Eulerian-Lagrangian framework. The validated model predicts with significant accuracy for all gas species when turbulence modeling is improved. The optimum amount of the secondary air ratio and the optimum excess air ratio were determined, which give a higher freeboard temperature while maintaining minimum emission.     

An investigation into the effects of gravity level on rate of heat release and time to ignition

Two experiments were performed on board an aircraft flying repeated parabolic trajectories to generate free-fal conditions. The first experiment investigates the way in which rate of heat release (RHR) varies with gravity for a candle flame under an imposed low-speed flow. In line with previous studies of flame spread rate it has been shown that rate of heat release drops significantly in imcrogravity. The heat loss due to radiation decreases by a larger proportion than that due to non-radiative processes indicating a lower flame temperature. The RHR from a microgravity flame is flow rate dependent, increasing for increased flow rate at air speeds under 0.03 ms^?1. For the geometry used in this experiment hypergravity caused only a small increase in RHR. The second experiment studied the ignitability of thermoplastics under an imposed radiant heat flux. The ignition test apparatus consists of a conical spiral heating element positioned horizontally above the sample, a continuous spark ignition source and a removable heat shield. Experiments were conducted in a sealed pressure chamber on samples of either PMMA or POM, 1.5 mm thick, with a ceramic backing. There is some indication that gravity influences the time to ignition for some materials.     

液位控制系统干预下小孔全过程泄漏速率模型

泄漏速率是计算泄漏量、确定泄漏持续时间及评估泄漏风险的前提和基础,通过搭建液相储罐小孔泄漏实验系统,构建不同泄漏场景,对比液位控制系统干预下的泄漏速率变化情况,并结合泄漏速率模型计算值进行分析。结果表明：液位控制系统响应后,泄漏速率下降速度变缓,并随时间推移逐渐开始回升,最后稳定在某值处达到稳态泄漏,进出流量对储罐小孔泄漏速率的影响基本可忽略。通过改进储罐泄漏经典公式,建立基于实际液位控制系统干预条件下的储罐小孔泄漏速率模型,提出泄漏孔口高压修正系数计算方法和模型,通过验证分析证明该模型可有效提高液位控制系统干预下泄漏速率计算精度。     

Nucleation parameter and size distribution of critical nuclei for nonisothermal polymer crystallization: The influence of the cooling rate and filler

The nucleation parameter K_g of filled PP, HDPE, and PA6 is determined through nonisothermal DSC measurements. A novel method is proposed for the determination of the size distribution of critical nuclei, where the most commonly found fraction was obtained as a peak value. The models are tested at different cooling rates and different filler loadings. K_g varies up to a certain cooling rate and afterwards remains constant. The introduction of talc in PP and HDPE facilitates nucleation and thus reduces K_g. An opposite trend occurs upon the addition of bentonite in PA6. The changes of K_g and are reflected on sample morphology, as confirmed with SAXS. The ratio between the final crystal thickness and amounts to approx. 2 and thus agrees well with the one listed in literature. The simple linear correlations of the obtained K_g are established with Young's modulus and yield stress. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41433.     

SMX型静态混合器湍流特的数值模拟

以SMX型静态混合器为研究对象,运用计算流体力学软件Fluent对3种结构静态混合器管内湍流流场进行数值模拟.结果表明:SMX型静态混合器的混合元件对流体有切割和分散作用,可使径向速度与周向速度的最大值达到轴向平均表观流速的2～2.5倍;流体流经3、4个混合元件后流动基本达到稳定;混合器前3个混合元件对流体湍动强化作用...     

气液传质过程的界面湍动

界面湍动对相际传质具有重要影响。利用显微激光全息干涉技术研究了 CO2 在乙醇 -水溶液中吸收过程的界面湍动情况 ,实验观察了界面湍动强度与溶液浓度的关系 ,结果表明 ,乙醇浓度越高 ,界面湍动强度越大 ,文中对此进行了分析和讨论。     

单组分扩散过程中界面湍动对流结构的观察

利用激光纹影仪从垂直和平行于界面两个方向对静止和流动乙醇吸收、解吸C02的传质对流结构进行了观察，发现在液相主体中明显存在传质导致的液体对流现象，同时发现对流结构在液相流动方向取向具有优先性。研究界面对流对增大传质速率，探索微观传质机理和寻求强化传质途径具有理论和实际意义。     

紊流双套管气力输灰技术及其设计要点

紊流双套管密相气力输送技术与其它气力输送技术明显不同是干灰不需要悬浮输送，因而其系统的设计、运行方式有其鲜明的特点：输送能力大，需要的输灰管道很少，输送速度低对系统的磨损轻。该技术在水泥余热利用中得到了成功的应用。