微波加热过程的温度模拟研究进展

因为微波作用于物体具有一些特殊性,微波技术在化工行业中得到了较为广泛的应用。作者简述了微波加热的温度分布模拟在化工中的用途,总结了微波加热温度分布模拟的一些方法的发展和应用,并对目前存在于温度分布模拟研究中的问题提出一些讨论。     

化工工艺计算二则：间歇式反应釜加热和冷却时间的预算

间歇式带夹套反应釜的操作需要控制其加热和冷却速率。为此,我们必须要确定夹套内传热流体的温度,一般可以由累试法实验来解决,但利用取决于时间的传热方程式更快,更直观。该方法仅需做一次加热试验,就可将试验结果代入该方程式,得到温     

热管搅拌反应釜内综合性能的数值模拟

将热管技术应用于高放热搅拌反应釜,用椭圆截面热管代替矩形挡板。以糖精钠生产中酰胺化工序中的反应为依托,设计出新型热管搅拌釜。基于ANSYS中Fluent模块,编写热量源项用户自定义函数（UDF）,以表征搅拌过程中釜内液体实际散热状况,采用数值模拟的方法,综合考察3个结构参数和搅拌转速对釜内最优温度持续时间、搅拌混合均匀时间等性能参数的影响。搅拌转速对釜内性能影响的权重远大于3个结构参数,就最优温度持续时间而言,搅拌器安装角度>热管中心线到釜壁距离>搅拌器下层桨到釜底距离;就搅拌混合均匀时间而言,搅拌器下层桨到釜底距离>搅拌器安装角度>热管中心线到釜壁距离。同时模拟出单个因素对搅拌釜性能的影响,并分别优选出热管中心线到釜壁距离为85mm,搅拌器下层桨到釜底距离为340mm,搅拌器安装角为0°,搅拌转速为240r/min。     

加热温度对GOI法生长蓝宝石晶体影响的数值模拟

利用数值模拟分析方法,模拟了通过调节加热温度促进GOI法蓝宝石晶体生长的过程。分析了加热温度变化对晶体生长的固液界面凸出率、晶体内温度分布、温度梯度的影响;热交换器散热参数与加热温度之间的关系。结果表明,在GOI法蓝宝石晶体生长中,合适的降温控制程序有利于提高晶体生长质量,晶体生长速率会随着加热温度的降低而快速增加。在相同降温程序下,较大的热交换器散热能力具有较快的晶体生长速率;低的热交换器散热能力和加热温度有利于降低晶体生长的界面凸出率。     

垂直列管加热的搅拌槽中温度场的测量与数值模拟

在装有 4组对称垂直加热列管、直径为 5 0 0mm的搅拌槽中使用PBT桨进行搅拌 ,以甘油为工作物料 ,采用液晶测温技术测量搅拌槽内温度的分布 .实验研究了温度随时间的变化以及搅拌转速对温度分布的影响 .采用计算流体力学软件CFX - 4对槽内轴向、径向温度分布进行数值模拟 ,并将模拟结果与实验结果进行了比较 ,发现二者基本符合.     

激光与微波协同加热碳纤维的温度与热应力分布规律

利用仿真软件建立微波加热-激光加热-热辐射-流动传热-固体力学多物理场模型,研究了激光加热直径1mm碳纤维丝束的温度场分布与热应力大小,以及不同激光功率对于温度场与热应力的影响。同时,首次提出激光加热与微波加热结合的方式调节温度场分布与热应力大小的方法,仿真结果显示激光加热与微波加热结合的方式可以改善碳纤维丝束温度场的分布,有效降低丝束加热过程中的热应力。     

外夹套反应釜与外半管反应釜热交换形式的对比分析

反应釜对传热能力要求较高.探讨外夹套反应釜和外半管反应釜换热方式的优劣,结合实例进行分析,目的在于方便用户对反应釜外壁换热方式进行选择.     

橡胶微波加热硫化的有限元分析

运用有限单元法求解Maxwell方程和传热方程,并采用ANSYS有限元软件计算和分析橡胶传统的热量由外向内传递的加热过程和微波加热过程。结果表明:微波加热硫化橡胶加热时间短,效率高;橡胶内的电场强度分布、焦耳热密度分布和温度分布都不均匀;随着微波加热时间的延长,胶料内的温度提高,但处于较高硫化温度的胶料范围几乎无变化。     

Numerical simulation of the temperature distribution in a planetary MOCVD reactor

In this study, a planetary MOCVD reactor was thermally analyzed and a numerical model was proposed to predict an actual thermal distribution, comparing the results between the numerical simulation and experiment. Numerical simulations were performed for various modifications, namely, the ceiling design and heat shield layout, to improve the heating efficiency. The reactors comprising the ceiling design and modified heat shield layout conserved 15% and 5% of the heating energy, respectively. This study provides a method for predicting the temperature distribution inside MOCVD chambers and evaluating the heating efficiency yielded by design modifications. These results could be used to expand and consolidate the design engineering knowledge database.     

外循环喷雾式乙氧基化反应器的数学模型与模拟

对半间歇操作外循环喷雾式乙氧基化反应器的数学模型与模拟进行了研究,分析了反应器的特性,建立了同时考虑气液传质、动力学、汽液平衡、反应体积变化和惰性气氮气影响的反应器的数学模型和数值模拟算法。以合成聚乙二醇为例,模拟得到反应器中温度、压力、环氧乙烷浓度及乙氧基化产物随时间和空间位置的分布。模拟结果同工业操作数据进行了比较,结果表明了模型的可靠性。     

Modelling the particle contact influence on the Joule heating and temperature distribution during FLASH sintering

FLASH sintering is a field-assisted technique that allows the densification of ceramics in a few seconds at temperatures significantly lower than those of conventional cycles. There is still discussion among the scientific community about the mechanism behind this sintering process, that has been typically attributed to Joule heating, defect creation and movement or liquid phase assisted sintering. Computational modelling can be a powerful tool in helping to explain and predict this process. Using potassium sodium niobate (KNN) as a case study, a lead-free piezoelectric, this work explores Finite Element Modelling to evaluate the dependence of Joule heating generation and temperature distribution as a function of the cubic particle orientation.     

Computation of the near-optimal temperature and initiator policies for a batch polymerization reactor

Optimal control theory is applied to a batch polymerization reactor for PMMA to calculate the near-optimal temperature and initiator policies that are required to produce a polymer with a desired final conversion, and desired number average and weight average molecular weights. The two-point boundary value problem that results from the application of the Pontryagin minimum principle to the mathematical model of the reactor is solved by the discretization control method. According to this, the total reaction time is divided into N equal subintervals. It is assumed that the control variables remain constant in each interval and the Hamiltonian is minimized by a first-order gradient technique. It is shown that the introduction of the “target set” concept, which is well suited to industrial practice, simplifies the numerical solution of the TPBV problem. Results of the simulations demonstrate the potential gains possible from the application of the optimal control theory to the batch polymerization of PMMA.     

Refined simulation of temperature distribution in molds during autoclave process

Since the production of advanced composites, they have gained popularity in many industrial applications because of their unique performances. The advantages of these materials are very important, especially in the area of aviation. Among all the molding methods adopted in their production, the autoclave stands out as distinct method. Considering the temperature distribution in molds, it is one of the crucial aspects to impart quality to composite components during the process of autoclave molding, and it is necessary to do research and analysis on temperature distribution in molds, especially those of large frame-type molds. In previous studies, many authors improved the simulation accuracy simply by changing the grids or boundary conditions. A few of them took boundary layer grids into consideration for further precision. With the aid of computer softwares, this paper conducts simulation on large frame type of molds. Given that the boundary layer grids will largely determine the simulation precision, this study attempts to give emphasis on the study of boundary layer grids to make the simulation results more accurate, and finally make a comparison with the experimental data. The error between simulation and experiment results was within 5 %. This indicated that the boundary layer grids had great influence on the accuracy of simulation of the paper conducted, and should be given more attention. Therefore, the method of simulation in this study can be further used to accurately simulate the temperature distribution in molds.     

Mapping of temperature distribution in pharmaceutical microwave vacuum drying

Microwave vacuum drying is getting more and more popular—thanks to its known advantageous features. In spite of its uniqueness, there is a rightful resistance and mistrust because of the nonhomogeneous electric field that may cause nonhomogeneous temperature distribution in the workload. In practice the best uniformity of power density and the shortest drying time are sought simultaneously, thus the drying method is close to its secure limit. Control and monitoring of a running process remains unsolved but even experimental mapping is rather circuitous. The dielectric and thermal properties of a complex pharmaceutical composition are rarely known, and moreover, they change during a drying process, which makes accurate mathematical modelling rather uncertain. For that very reason preliminary tests can never be neglected. The aim of our study is to experimentally map and evaluate the heat distribution quantitatively. To get a 3D overview of a free-flowing bulk, the workload was divided with Teflon layers to form cross-sectional surfaces. After dissipation of microwave energy, IR thermocartograms were taken and the temperature distribution was evaluated quantitatively. The “3D layered thermography” method offers reliable and workload-specific information, via a simple executable technique, for optimization of a microwave assisted drying process.     

High temperature fluidized bed reactor: measurements,hydrodynamics and simulation

This paper was made possible through the development of a novel high temperature optical fiber probe to study the hydrodynamics of a high temperature fluidized bed reactor. The experimental results show that the hydrodynamic parameters considerably change with bed temperature when fluidizing FCC particles. For a given superficial gas velocity, the average local particle concentration, the dense phase fraction and the particle concentration in the dense phase decrease with increasing bed temperature. As a result of an increase in temperature, the fluidized behavior of the FCC particles progressively shifts from typical Geldart A towards B. Consequently, a modified two-phase model, based on the simple two-phase model, integrating the effects of temperature and superficial gas velocity on the hydrodynamics, is proposed. Simulation of a reactive catalytic system using a conventional simple two-phase model and the modified model is achieved. The predicted reactor performances strongly differ for each model. In the present case, the simple two-phase model underestimates the reactor performance by inadequately accounting for the solid fractions in the bubble and dense phases and their dependence on temperature and superficial gas velocity. This suggests that the hydrodynamic models should take into account the effects of temperature and superficial gas velocity when simulating the performance of a high temperature fluidized bed reactor.     

延迟焦化炉内湍流燃烧和炉管表面温度、热流分布

准确描述出炉膛内湍流燃烧过程,进而获得炉管表面温度和热流的分布情况,对焦化炉结构优化和防止管内结焦具有重要意叉.本文采用数值模拟方法,实现了对工业焦化炉包括燃烧器群、炉膛、炉管整体的,流动,燃烧和传热全部工艺过程的全尺寸耦合计算.计算得到了炉内温度以及炉管表面温度、热流分布的详细信息,揭示了焦化炉内燃烧和传热过程的基本特性.     

多物理场耦合模拟微波蒸馏反应器：升温和沸腾过程

使用COMSOL Multiphysics软件建立了耦合电磁场、流体流动、传热以及物质传输的多物理场模型用于模拟蒸馏型反应器的微波能量利用过程,探究了蒸馏反应器中水负载在微波能辐射作用下从升温至沸腾过程,阐明了在升温阶段,样品温度呈上下层分布,上层温度较高,最大温差达20 K,自然对流的产生改善了温度分布的不均匀性;在沸腾阶段,由于下层温度较低,沸腾现象有延迟,气泡的产生消除了部分过热,其中表面蒸发量更大,最大时约为内部蒸发量的3倍,与此同时湍流现象明显改善了温度均匀性。探究了馈入功率对全沸腾状态的影响,揭示了全沸腾状态的最终温度取决于馈入功率和蒸发损耗功率的相对大小。研究结果可为微波辅助分离、反应等化工过程及装备设计提供理论基础与借鉴。