Mean Residence Time and Residence Time Distribution When Sawdust Is Dried in Continuous Dryers

Information on the mean residence time and the residence time distribution is of importance when optimizing a continuous dryer. In this study, an industrial method for determining the mean residence time is developed. The produced method is benchmarked on a laboratory scale against the stop-and-empty method. The method, which uses LiCl as the tracer does not cause any disturbances in the biofuel drying or pelleting processe.     

Characterization of Residence Time Distribution in a Plug Flow Reactor

One of the biggest advantages of plug flow reactors lies in their narrow residence time distribution. The pulse experiment, as a common method on acquiring that distribution, relies on the tracer injection being a perfect pulse. A deviation from a perfect pulse leads to erroneous results if not taken into account. With a numerical analysis of experimental data, this effect is quantified in turbulent and laminar flow regime and the results are compared to an analytical method. Significant deviations occur mostly in the turbulent regime, which has the greatest technical relevance.     

Residence Time Distribution in Granulation Drums on the Example of Industrial Carbon Black

The present work describes systematic investigations into dry granulation of industrial carbon black with special regard to the residence time characteristics, using a continuously operated semitechnical bead‐forming drum. A novel experimental method and a model for the determination of residence time distribution of carbon black in the bead‐forming drum have been developed and very good agreement of model and experiment has been demonstrated.     

玻璃窑内玻璃液停留时间分布的研究

在玻璃熔窑中引入停留时间分布的概念，阐述了停留时间分布研究对提高玻璃液熔制质量的重要性和可行性。     

带固体循环系统气流干燥器停留时间分布的计算

本文就具有固体循环系统的气流干燥器停留时间分布规律进行了研究,提出了停留时间分布密度的计算公式。通过计算,得出了在不同的循环比下停留时间分布的计算结果。     

气化炉停留时间分布的数学模型

本文给出了高径比、筒体出口通道面积各异的模型气化炉在不同射流速度时的冷态停留时间分布测试结果,提出了无因次停留时间分布密度函数的数学模型及参数估计值。     

强制反循环制盐蒸发器内流体的停留时间分布

给出了不同液位,不同流量下强制反循环斜进料蒸发器内流体仪时间分布的测定结果;运用组合模型,分析了蒸发器内流体的流动特点,得到了模型参数,为工业生产应用提供了理论依据。     

循环流化床提升管中固体颗粒停留时间的分布

在内径１４０ｍｍ，高１０ｍ的循环流化床提升管中，采用磷光颗粒示踪法对床内固体颗粒的停留时间分布进行了测定。在气速１．５～９．０ｍ／ｓ，固体循环量１０～１４０ｋｇ／ｍ２ｓ的范围内，实验测得的停留时间分布曲线均有明显的双峰分布。这种双峰分布是由于提升管中弥散颗粒和颗粒团共同作用的结果。本文提出的一维两组分扩散叠加模型可较好地描述提升管中固体的混合行为。考察了在实验条件下，操作条件对固体混合行为的影响。发现：气速及固含对颗粒的轴向Ｐｅｃｌｅｔ数影响不大，提升管中颗粒的返混主要是由于颗粒团引起的。将研究结果与近期文献报道的其他研究进行了对比     

数值积分法在停留时间分布统计特征值教学中的应用

计算停留时间分布统计特征值常采用数值积分的方法。教学过程中发现大部分学生对数值积分的数学过程存在一些困惑。为了帮助学生理解和掌握数值积分方法在停留时间分布统计特征值计算中的应用,本文详细地介绍了矩形法、梯形法和抛物线法（Simpson公式）三种常用的数值积分方法,并对其准确性进行了对比。     

Residence Time Distribution in Tubular Joule Effect Heaters with and without Geometric Modifications

In the food industry, heat treatment of highly viscous fluids in continuous processes is becoming more and more common, and the process should perform as a homogenous thermal treatment, in order to ensure quality and safety of the final product. To improve treatment homogeneity, geometric modifications can be used even in the laminar regime, to induce flow perturbation and mixing. The objectives of this work include: (i) Investigation of the residence time distribution (RTD) for industrial indirect Joule effect heaters (JEH), with smooth (ST) and modified (MT) tubes, (ii) Demonstration and quantification of the efficiency of the geometrical modifications, and (iii) Proposition of a single semi‐empirical model including the flow regime (10 < Re < 2000) and tube diameters (18 and 23 mm). The results obtained confirm that the simple Dispersed Plug Flow (DPF) model is not adaptable to small Reynolds numbers. Further analysis demonstrates that certain geometrical modifications improve the treatment homogeneity by increasing the plug flow contribution and reducing the value of the reduced variance. These beneficial effects increase when the Reynolds number is increased, the nominal diameter is reduced, and modified tubes are used. The proposed model enables the prediction of the RTD in JEH with an accurate degree of confidence.     

Application of Residence Time Distribution for Measuring the Fluid Velocity and Dispersion Coefficient

Most studies on residence time distribution (RTD) have focused on the tail of the RTD curve, and very little attention has been paid to the effect of white noise on the measured results. The aim of this work is to study the effect of white noise on the calculated parameters with different data processing methods. The anti‐disturbance abilities of the moment method and the least squares method are compared. The results show that the anti‐disturbance ability of the least squares method was better than that of the moment method. As a result of peak overlapping in the RTD curve of a loop reactor, the moment method cannot be used to calculate the fluid velocity and dispersion coefficient. Experiments show that the least squares method is still applicable in a loop reactor.     

Inline Measurement of the Residence Time Distribution in High-Pressure Extraction Columns

Axial backmixing lowers the efficiency of packed countercurrent high-pressure extraction columns. To quantify backmixing, a method of measuring the residence time distribution and calculating the axial dispersion coefficient in high-pressure extraction columns is introduced. Using a design of experiments, the effect of supercritical and liquid mass flow rates as well as the pressure at a constant temperature on the mean residence time and the axial dispersion coefficient are evaluated for the system water/supercritical CO₂. The experimental data is correlated to the Reynolds and Schmidt number.     

循环流化床气体返混及停留时间的分布

本文采用脉冲示踪技术,研究了直径140 mm循环流化床内气体的返混特性及其停留时间分布规律,并通过一维轴向扩散模型,得到了气体轴向扩散系数。实验结果表明,在循环流态化条件下,气体轴向流动明显偏离于平推流,并且随操作气速增大或颗粒循环速率的减小,气体轴向返混程度减小。     

Residence Time Distribution of a Capillary Microreactor Used for Pharmaceutical Synthesis

The main drivers for application of small-scale reactors in the pharmaceutical industry are the possibility of rapid synthesis and screening of novel drugs as well as the readiness of the scale-up. The characterization of fluid flow pattern was performed through step-up and step-down residence time distribution experiments using a tracer at six different flow rates. Four single-parameter models were considered for representing deviations from ideal plug flow and ideal laminar flow in tubes. The model that provided the best results was the axial dispersion model and the Peclet and Reynolds numbers could be well correlated. Obtained Peclet values from 44 to 244 were close to Pe > 100, in which axial dispersion can be neglected and the reactor can be considered as plug flow reactor.     

喷雾干燥法烟气脱硫过程的数学模拟

影响喷雾干燥法烟气脱硫过程的因素很多，如液滴初始粒径、液滴初始速度、烟气入口温度、烟气入口速度和SO2入口浓度等。在分析喷雾干燥塔内气液两相流动及单个粒子与气相之间传热传质过程的基础上，建立了喷雾干燥法烟气脱硫过程的数学模型，模拟分析并讨论了上述各因素对脱硫效率的影响，并通过实验对模型进行了验证。     

振荡流反应器的物料停留时间分布模型研究

提出了一个基于马尔柯夫链（Markov chains）的考虑腔室间返混的振荡流反应器物料停留时间分布模型。通过对在内径50mm,长1．95m的振荡流反应器进行的理想脉冲示踪试验数据的统计分析,给出了模型的唯一参数回流比R的经验计算公式。发现在试验条件下,存在一个与最小回流比R相对应的振荡条件。这振荡条件可表示为振荡流雷诺数（Reo）与净流雷诺数（Ren）的比值ζ,其范围为1．6〈ζ〈2．5。     

Stochastic Modeling of the Particle Residence Time Distribution in an Opposed Multi‐Burner Gasifier

The gasification technology of impinging streams has been extensively applied to chemical production and power generation. Particle residence time distribution (RTD) is an important parameter required for modeling, designing and optimization of an impinging stream gasifier. A stochastic mathematical model based on the Markov chains model is developed for the opposed multi‐burner gasifier (OMBG), which closely describes the behavior of the flow pattern and particle RTD in the gasification system. The model simulates the motion of single particle moving in the gasifier using the Markov chains. The predicted results give a reasonable fit to the experimental data. This shows that the flow process of particles in the gasifier has recirculation eddies, which have a downward flow direction near the downflow core and an upward flow direction near the wall, but no short‐circuit. Finally, the effect of particle flux rate on the RTD is predicted, and the contrast between gas and particles RTDs at a laboratory scale and in an industrial gasifier are presented.     

New Engineered Particles from Spray Dryers: Research Needs in Spray Drying

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.