Simulation of Temperature Distribution in Stored Wheat without Aeration

A neural-deterministic simulation model applied for calculating distributions of temperatures and moisture content in a bed of wheat stored in a steel silo without aeration is presented in the article. The model consists of differential equations of heat and moisture transfer, initial and boundary conditions, and three artificial neural networks used during simulated ambient air conditions. Experiments and computer simulations were carried out in order to determine temperature fields in wheat grain stored in a steel silo for two months. The computer simulations were carried using MATLAB and FEMLAB software. The difference between measured and simulated temperature in grain near the silo wall at a height of 2.5 m from the bottom was less than 3.0°C. On the basis of the analysis performed it was concluded that the temperature distributions obtained with the model were consistent with the measured results obtained for grain stored in a steel silo without aeration.     

Stresses in bulk solids in wedge hoppers: A flexible formulation of the co-ordinate specific, Lame-Maxwell equations for circular arc, principal stress systems

A 2-D model of stress distribution within bulk solids, with circular arc principal stress orientation, in a wedge hopper was developed in a previous paper [Matchett, O'Neill, & Shaw, Stress distributions in 2-dimensional, wedge hoppers with circular arc stress orientation — a co-ordinate-specific Lamé-Maxwell model, Powder Technology, 187(2008) 298-306]. This model worked in an orthogonal, curvilinear co-ordinate system co-incident with the principal stress trajectories: (x − ψ_o) space.This paper presents an equivalent model in (x − ε) space. This allows backward numerical integration of the force balance equations, enabling surface and wall boundary conditions to be modelled. This was not possible in the original model.The equations are first-order, and boundary conditions can only be specified at single surfaces. Thus, if a stable, cohesive arch is proposed, the surface overpressure is determined by the model. Calculated overpressures have reasonable physical values.The present model was integrated backwards from the surface downwards and it was found that the integration was very sensitive to the surface overpressure stresses.Likewise, wall boundary conditions were specified with backwards integration in ε.The minimum outlet for flow was calculated from the model and compared with the experimental data of Berry et al. Wall normal stresses in a wedge hopper from Schulze and Schwedes were also compared to model predictions. In both cases there was reasonable agreement between measurements and model predictions.     

An Experimental Study of Wheat Drying in Thin Layer and Mathematical Simulation of a Fixed-Bed Convective Dryer

Drying of wheat (Algerian cultivar: Hadba03) in thin layers was studied and mass flux phenomenon was used to characterize the thin-layer drying process. Thin-layer drying of wheat was determined for drying air temperature range of 40–60°C, relative humidity of drying air from 10 to 30%, air velocity of 0.7 m/s, and initial grain moisture from 26 to 31% (dry basis). Equilibrium moisture content of wheat was determined using desorption isotherms obtained from the thin-layer drying data. An equilibrium model for a stationary deep bed with drying air moving vertically upward was developed using mass and energy balance between grain and drying air in the bed and drying air characteristics obtained from thin-layer drying experiments. The developed model was validated by drying wheat in a laboratory dryer using different drying air temperatures and initial moisture contents.     

Numerical Simulation for Particle Penetration Depth Distribution in Deep Bed Filtration

A two‐dimensional model has been developed to simulate particle penetration through porous media. The particle penetration depends on many parameters including the Reynolds number, particle drag coefficient, the ratio of the diameter of injected to filtered particles, fluid velocity, and pore size, etc. The numerical model for separation efficiency in periodic porous media was studied. Previous work has described the effects of injected particle size, Reynolds number and particle drag coefficient. In this study, the porous media flow is modeled (solution of the Navier‐Stokes equations) by using the finite element method, and the analysis is restricted to the case of two‐dimensional periodic porous media. The effects of these factors and particle depth distribution in porous media are investigated. It is noted that the results for the three Reynolds numbers 1, 16.56, and 100, are qualitatively similar, and about 40 % of particles are trapped in the top part of the filter.     

Simulation of autohydrolysis effect on adsorptivity of wheat straw in the case of oil spill cleaning

This work deals with the use of chemically modified wheat straw as efficient low-cost adsorbent for combating oil-spills in aquatic environment. The autohydrolyzed wheat straw was produced from the corresponding raw material by autohydrolysis in a PARR batch reactor (autoclave) at 160–240 °C for 0–50 min isothermal reaction time (following a non-isothermal preheating period). Oil adsorbency tests were performed, using diesel and crude oil spills in freshwater and seawater. Diesel and crude oil adsorbency values were found to increase up to a maximum by intensifying the autohydrolysis conditions, i.e., time and temperature. The adsorbency values were estimated by a proposed novel model incorporating the autohydrolysis severity factor R₀. Optimal modification conditions were found for log R₀ = 5.15 (i.e., 200 °C, 10 min isothermal time period) giving diesel adsorbency up to 6.65 g g⁻¹ and crude oil adsorbency up to 6.91 g g⁻¹. The maximum adsorbency values were comparable to those of the commonly used commercial adsorbents.     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.     

Modeling of Moisture and Temperature Changes of Wheat during Drying in a Triangular Spouted Bed Dryer

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction.     

梭式窑温度场影响因素的数值模拟

为深入了解梭式窑内温度场分布情况,利用ANSYS软件,采用湍流标准动能———动能耗散率(K-ε)方程,对影响梭式窑温度均匀性的因素用正交试验法进行了有限元数值模拟研究。得出了温度场的分布特征。分析了影响温度不均匀分布的成因。     

小麦施用粉煤灰磁化肥数学模型及农艺措施研究

采用三因素二次通用旋转组合设计 ,对豫东潮土区影响小麦产量的农艺措施、施灰量、小麦种植密度及灌水量进行定量研究 ,建立了小麦目标产量函数模型。通过模型解析选优 ,确定了每亩目标产量≥ 475kg、≥ 45 0kg、≥42 0kg及最大经济效益的综合农艺措施     

基于实测的复杂结构模拟瞬态温度场仿真重建技术研究

从有限的实测数据出发,以某直升飞机降落平台的现场测试数据为例,进行了温度场重建技术研究。在所建立的几何模型基础上,探讨了对实测温度数据的分析扩展原则,利用软件进行插值得到边界温度场分布的方法,探讨了在ANSYS软件中将三维数据表读入软件并实施各个瞬时传热边界上的表参数加载方法,最终得到了复杂边界在时变温度场下的瞬态热分析结果,重现了测试过程中直升飞机平台的瞬态温度场演变过程。     

反应精馏过程模拟优化的研究进展

反应精馏过程的数学模拟是反应精馏塔设计、放大、控制的基础。对反应精馏过程模拟模型、求解方法以及优化的研究进展进行了综述。     

螺旋板式换热器数值模拟计算的研究

为对螺旋板式换热器进行模拟计算,使用等角度间隔的方式将换热器中的流动通道及传热面分为多个流动单元和面单元,分析及建立了流动单元与传热面单元的对应关系,应用传热学原理建立了螺旋板式换热器的数学模型。应用Visual Bisic 6.0进行程序设计,自动生成方程组,并使用高斯消去法进行求解。模拟计算得到了换热器内的温度分布、总传热系数及总流动阻力。利用这一模型,本文对实际的螺旋板换热器进行了模拟计算,数学模型求解所得的结果与实验数据吻合较好。应用此数学模型还研究了圈数及板间距等对换热器参数的影响。     

秸杆/聚丙烯复合材料

秸杆与聚丙烯复合制备了能替代木材使用的复合材料。考察了秸秆含量、界面处理剂用量对复合材料力学性能、流动性及形态的影响。结果表明：复合材料的拉伸强度和冲击强度随秸杆含量增加而下降,但下降幅度较小;而热性随秸杆含量增加而升高。处理剂效果较好,最佳用量为８ＰＨＲ。未经处理的复合材料随秸杆含量增加,其流动性先增加后逐渐降低;经处理过的复合材料流动性受秸杆含量影响不大。秸杆含量较少时,分散均匀;较多时有敛集     

Simulation Model for Digital Twins of Pneumatic Vacuum Ejectors

Increasing productivity, as well as flexibility, is required for the industrial production sector. To meet these challenges, concepts in the field of “Industry 4.0” are arising, such as the concept of Digital Twins. Vacuum handling systems are a widespread technology for material handling in industry and face the same challenges and opportunities. In this field, a key issue is the lack of Digital Twins containing behavior models for vacuum handling systems and their components in different applications and use cases. A novel concept for modeling and simulating the fluidic behavior of pneumatic vacuum ejectors as key components of vacuum handling systems is proposed. In order to increase the simulation accuracy, the concept can access instance-specific data of the used asset instead of object-specific data. The model and the data are part of the Digital Twins of pneumatic vacuum ejectors, which shall be able to be combined with other components to represent a Digital Twin of entire vacuum handling systems. The proposed model is validated in an experimental test setup and in an industrial application delivering sufficiently accurate results.     

片材机头中物料温度分布的模拟分析

本文利用ANSYS和MATLAB软件,对衣架型和T型片材机头中熔体的温度分布进行三维有限元模拟和分析。通过对机头流道内温度分布的模拟,得出了衣架型机头流道的温度分布优于T型机头。     

Simulation of condensation flow in a rectangular microchannel

The condensation flow of the refrigerant FC-72 in a rectangular microchannel with a 1-mm hydraulic diameter is numerically studied using the volume of fluid (VOF) model. The heat transfer related to the condensation is taken into account by a thermal equilibrium model assuming the interface temperature is at saturation. The numerical method is validated against experiments from the literature and well predicts the flow patterns along the microchannel. The vapor phase in the microchannel forms a continuous column with a decreasing diameter from upstream to downstream. Slugs are periodically generated at the head of the column. Decreasing the wall cooling heat flux or increasing the flow mass flux increases the vapor column length. Waves along the interface cause necks in the column and locally increase the vapor velocity and decrease the pressure, facilitating breakage of the vapor column into slugs. The liquid temperature is close to saturation near the interface and lower downstream and in the thin liquid layer close to the cooling surface. The initial bubble size increases with increasing flow mass flux or decreasing cooling heat flux.     

The effective diffusivities in porous media with and without nonlinear reactions

The question of whether effective diffusivities in porous materials under reactive and nonreactive conditions are equal is addressed. Previous studies had considered the problem with first-order reactions. We study the issue with two nonlinear reactions—a second-order reaction and one governed by the Michaelis-Menten kinetics. Pore network and continuum models of porous media are utilized to estimate the effective diffusivities under reactive and nonreactive conditions. We show that the two effective diffusivities are significantly different. The difference is due to the heterogeneities of the porous material, and the fluctuations that they cause in the spatially varying local concentrations and diffusivities, and can be as large as a few orders of magnitude. Theoretical analysis of diffusion and reactions in porous media is also presented that supports the results of the simulations. In particular, it is shown that the results of pore network simulations cannot be fitted to the classical continuum equation of diffusion and reaction, and that a more complex continuum equation should be used for this purpose.     

加氢反应器气液分配盘数值模拟

以加氢反应器UOC(Union Oil Company)型气液分配盘为对象,利用计算流体力学(CFD)方法对分配盘内的气液两相流动进行了研究。根据某工厂数据确定了分配盘的几何尺寸,应用原油和氢气为介质,使用群体平衡模型(PBM)等多种计算模型进行计算。计算结果表明,UOC型气液分配盘是依据分配盘上单个分配器的内外压力差作为动力,氢气与原油在分配器内外进行充分的碰撞,达到混合及分配效果。原油通过分配盘后以多个点状峰值状态存在,分配器存在中心聚集现象,消除分配器的中心汇聚现象为其结构改进的主要方向。     

数值研究液-液水力旋流器内颗粒浓度分布特性

根据计算流体力学(CFD)的原理和方法,应用Fluent软件对液-淡水力旋流器内部颗粒浓度分布进行数值模拟,得到了不同进口流量和不同进料浓度下旋流器内各个截面上浓度分布情况.结果表明:旋流器内各截面上浓度变化曲线呈现抛物线型;进口流量越大,在管壁处浓度值越小,油滴不断向管芯聚集;进料浓度越大,在旋流器的大部分区域中,浓...