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。     

Mathematical Model Based on DSMC Method for Particulate Drying in a Coaxial Impinging Stream Dryer

An impinging stream dryer (ISD) belongs to a unique class of dryers that has proved to be an excellent alternative to flash dryers for removing surface moisture of particulate materials due to the collision of streams and particles in the dryer. However, the performance analysis of such devices, from a viewpoint of mathematical modeling, has not been investigated extensively. In this study, a mathematical model based on the direct simulation Monte Carlo (DSMC) method is proposed to describe the drying process of particulate materials in a coaxial ISD. The collisions between particles and the heat exchange between impacting particles are included in the present mathematical model. The predicted results were in good agreement with the experimental data, which indicates the validity of the present model. The drying process and the effects of various parameters, including the feeding mode and impinging distance, on the drying performance of the dryer were then numerically investigated and discussed.     

运用马尔科夫链模拟气化炉停留时间分布

将连续时间马尔科夫链与多级全混流串联模型结合建立停留时间分布数学模型。通过对气化炉流场的认识,将气化炉划分为几个区域状态,组成马尔科夫链状态转移图,用多级全混流模型表示该各个区域的混合程度。通过对两种气化炉停留时间分布的模拟和实验值进行对比,结果比较吻合,表明该模型模拟气化炉停留时间分布是可行的。     

Simulation of Drying Characteristics of Evaporation from a Wet Particle in a Turbulent Pulsed Opposing Jet Contactor

The motion and drying characteristics of a single particle in a novel two-dimensional pulsed opposing jet contactor (POJC) are modeled and discussed. Hot air is used as the drying medium. To simulate particle drying, the gas phase and dispersed phase conservation equations are considered in the Eulerian reference frame and the Lagrangian reference frame, respectively. The RNG turbulence model is used to determine the turbulent characteristics of the gas phase. The particle motion is described by the BBO (Basset-Boussinesq-Oseen) equation. The effects of the key parameters, such as the jet Reynolds number, amplitude of pulsation, frequency of pulsation, particle diameter, location of release of particle from one jet as well as velocity profile on residence time (RT) and particle penetration depth (PN) into the opposite jet, are examined. Results show that POJC has strong potential for particulate heat transfer as well as drying; it can improve evaporation rate relative to the corresponding steady OJC by up to 30% as a result of increased residence time in the impingement zone within the parameter ranges simulated.     

Modeling of the Residence Time Distribution and Application of the Continuous Two Impinging Streams Reactor in Liquid‐Liquid Reactions

The two‐phase monosulfonation of toluene, as an example of liquid‐liquid reactions, has been conducted in a continuous two impinging stream reactor (TISR). The extent of reaction under different operating conditions has been determined. A comparison has been made between the performance capability of the TISR and that of continuous stirred tank reactors (CSTR). Under identical conditions, including mean residence time, temperature, feed compositions and phase ratio, the impinging stream reactor has shown a higher efficiency. Finally, a stochastic model, based on Markov chain processes has been developed for the TISR, which describes the flow pattern and the residence time distribution (RTD) within the reaction system. The RTD model, combined with the kinetic expression, has been applied to calculate the conversion of toluene in the reactor. The predicted values for toluene conversion have been compared with those determined experimentally.     

Numerical Analysis of Gas-Particle Flow in Vertical Impinging Stream Chamber

For impingement stream drying, it is important to understand the complex gas-particle flow field in order to control the quality of dried products accurately. Hence a numerical analysis of three-dimensional gas-particle flow field was carried out including momentum, heat and mass transfers between the two phases. Simulation results for millet drying in a vertical impingement chamber were obtained and discussed. There is a great difference between gas phase and particle phase flow fields. The impingement planes of gas phase and particle phase are not coincident along the axial direction. Not all the millet particles can be taken away by the gas flow leaving some wet particles in impingement chamber for a prolonged drying. The temperature of millet rises up quickly approaching the value of drying medium in some zones. Consequently, it is important to regulate the inlet gas temperature for drying of thermal sensitive materials.     

Numerical Analysis of Gas-Particle Flow in Vertical Impinging Stream Chamber

Abstract

For impingement stream drying, it is important to understand the complex gas-particle flow field in order to control the quality of dried products accurately. Hence a numerical analysis of three-dimensional gas-particle flow field was carried out including momentum, heat and mass transfers between the two phases. Simulation results for millet drying in a vertical impingement chamber were obtained and discussed. There is a great difference between gas phase and particle phase flow fields. The impingement planes of gas phase and particle phase are not coincident along the axial direction. Not all the millet particles can be taken away by the gas flow leaving some wet particles in impingement chamber for a prolonged drying. The temperature of millet rises up quickly approaching the value of drying medium in some zones. Consequently, it is important to regulate the inlet gas temperature for drying of thermal sensitive materials.     

Modeling of Sewage Sludge Flow in a Continuous Paddle Dryer

A model based on the theory of Markov chains has been developed to represent the residence time distribution (RTD) of municipal sewage sludge in a continuous paddle dryer. The flow of dry solids is described by a chain of n perfectly mixed cells, n corresponding to the number of paddles attached to the shaft. The transition probabilities between the cells are governed by two parameters: the parameter of internal recirculation, R, and the solids hold-up, Hu. In the absence of available correlation, both parameters are identified by fitting the model to experimental RTD data. The model demonstrates its ability to describe the sludge flow in a continuous lab-scale paddle dryer. A sensitivity analysis highlights that R is critical for the treatment uniformity while Hu controls the mean residence time and thus the final moisture content.     

Modeling of Sludge Behavior in a Steam Dryer

Steam dryers are in widespread use for sewage sludge treatment. The effectiveness of the steam dryer could be improved by increasing the drying rate, which is influenced by the movement of the sludge in the dryer. Therefore, it is necessary to understand the movement of sludge and water evaporation in the dryer. In this study, tracers were used to elucidate the behavior of sludge in the dryer. The experiment confirmed that sludge did not simply flow in one direction; instead, part of the sludge flowed in the reverse direction (back-mixing). A tanks-in-series model analysis was performed to analyze the back-mixing phenomenon. This analysis provided insight into the behavior of sludge in the dryer, and the drying rate of each segment was determined.     

Chaotic Analysis of the Concentration Field in a Submerged Impinging Stream Mixer

The concentration field was measured with various nozzle diameters, nozzle distances, and inlet flow rates in a submerged impinging stream mixer (SISM) using planar laser‐induced fluorescence to obtain characteristic parameters such as correlation dimension, Kolmogorov entropy, and Lyapunov exponents that describe the chaos phenomenon and reflect the microcosmic mixture effect of a SISM by mean of the chaos theory. The chaotic characteristic parameters were influenced significantly by different nozzles distances, nozzle diameters, and inlet flow rates and their distributions followed a similar changing regularity by which all parameters decreased with larger nozzle diameter and increased with higher inlet flow rate.     

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.     

Characterization of the Residence Time Distribution in Spray Dryers

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.     

Reversible Jump Markov Chain Monte Carlo Strategies for Bayesian Model Selection in Autoregressive Processes

Abstract.  This paper addresses the problem of Bayesian inference in autoregressive (AR) processes in the case where the correct model order is unknown. Original hierarchical prior models that allow the stationarity of the model to be enforced are proposed. Obtaining the quantities of interest, such as parameter estimates, predictions of future values of the time series, posterior model-order probabilities, etc., requires integration with respect to the full posterior distribution, an operation which is analytically intractable. Reversible jump Markov chain Monte Carlo (MCMC) algorithms are developed to perform the required integration implicitly by simulating from the posterior distribution. The methods developed are evaluated in simulation studies on a number of synthetic and real data sets.     

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。     

Mathematical Modeling and Simulation of Drying Using Two Industrial Concurrent and Countercurrent Rotary Dryers for Ammonium Nitrate

Drying of ammonium nitrate (AN) is accomplished in the Shiraz Petrochemical Complex (SPC) using a concurrent rotary dryer following a countercurrent rotary dryer. A mathematical model for these rotary dryers including heat and mass transfer was developed. The model was checked against industrial-scale data, which showed a good agreement. The average absolute deviation of the simulation results compared to the industrial data for the concurrent dryer was 4.0% for solids moisture, 1.3% for solids temperature, and 1.8% for air temperature and for the countercurrent dryer it was 9.0% for the solids moisture, 2.0% for solids temperature, and 4.6% for air temperature. These simulation results reveal that for outlet solid moisture, inlet AN moisture, and air temperature as well as the outlet temperature of product, the inlet solid and air temperature have major effects for both concurrent and countercurrent flow.     

Studies on the Behaviour and Application of the Continuous Two Impinging Streams Reactors in Gas–Liquid Reactions

A stochastic model was developed to predict the residence time distribution in continuous two impinging streams reactors with spray nozzles (CISR). The reaction between carbon dioxide and monoethanolamine was chosen as an example of gas–liquid reactions to demonstrate the performance capability of the CISR in chemical absorption operations. © 1997 SCI.     

Mathematical Modeling of Kiln Drying of Softwood Timber: Model Development, Validation, and Practical Application

Mathematical modeling of wood drying is a powerful tool to better understand and quantify the effects of wood properties as well as the effects of drying and post-drying treatment conditions on drying and thus the wood drying models can be used to improve drying quality. The models that have been developed can be divided into three categories: models for drying a single board, models for drying a kiln-wide stack, and models for drying stress and deformation. The single-board drying model employs comprehensive heat and moisture mass transfer equations and can be used to investigate the influence of wood variability. The kiln-wide drying model, which is based on the transfer processes between wood and the drying medium, is able to examine the influence of drying schedules and wood properties. The stress model can predict stress development in drying and stress relief in final steam conditioning and post-kiln treatment. An integrated model can be used to optimize drying schedules and develop strategies for high-quality dried timber.     

Superheated Steam Drying of a Single Particle in an Impinging Stream Dryer

ABSTRACT

Impinging stream contactors provide a novel configuration for drying and/or chemical reactions of particulates, pastes or suspensions which can be dispersed in a flowing gas stream. Essentially they consist of one or more highly turbulent “impingement” zones formed by collision of two opposing jets (OJ) in a confied channel or duct. The objective of this paper is to present computational fluid dynamic predictions for two-dimensional turbulent opposing jets over a range of nozzle-to-nozzle separations and jet Reynolds numbers for the simulation of single particle drying in these systems using superheated steam. A number of different turbulence models were tested ( e.g. high Reynolds, Lam-Bremhorst, Launder and Sharma models etc.). Predictions are performed in two distinct parts. In the first part a power law, finite volume method based on the “SIMPLEC” algorithm is used to solve the momentum and energy conservation equations for air in OJ systems in order to gain insight into their     

浸没循环撞击流反应器极具应用潜力的液相和液固相反应装置

理论分析和实验研究结果表明, 浸没循环撞击流反应器（ＳＣＩＳＲ） 与传统的搅拌槽反应器（ＳＴＲ） 相比,虽然在可测量尺度上的混合特性并不占优;但由于撞击区中流体元间剪切速率更高,因而微观混合更强烈。这对于在分子尺度上进行的化学反应具有重要意义。制取“超细”白炭黑研究的结果佐证了ＳＣＩＳＲ强化微观混合的特性。除此以外, ＳＣＩＳＲ在结构方面还具有多项胜过ＳＴＲ的优点, 极具开发应用的潜力。     

Dynamic Characteristics of Solids Transportation in Rotary Dryers

Abstract

An original method was proposed for the determination of the mean residence time in a continuous dryer, based on the step-change in the solids feed rate. The method has been validated through experiments performed in a pilot-scale rotary dryer. The effect of the solids flow rate, gas flow rate, dryer rotation speed, and dryer slope was quantified. Several design correlations to predict the residence time in rotary dryers were critically evaluated, and a new, more accurate correlation was derived.