含通电碳纤维复合板电加热过程的数值模拟及优化设计

通过对碳纤维复合板进行模拟仿真发现，其由碳纤维发热丝束与碳纤维布复合得到。利用ABAQUS软件对温度场进行分析，确定了采用复合板通电加热的数学模型和模拟方法。基于影响温度场的部分因素对模型进行了优化设计。结果表明，含通电碳纤维复合板的上表面温度升高至约35℃,最大温度差为1.97℃,测得的上表面温度与实验值能较好的吻合。对模型进行预测发现，当温度为-12℃时，该板的温度升高至0℃以上。另外，在加热功率相同的条件下，随碳纤维发热丝束间距的增加，上表面的平均温度变化较小；随碳纤维发热丝束间距的减小，上表面温度分布的均匀性得到显著提升。在碳纤维发热丝束间距相同的条件下，随碳纤维发热丝束加热功率的增大，上表面温度显著升高，但是，上表面温度分布的不均匀程度增大。当发热丝间距为8或6 mm、通电功率为45 W的条件下，复合板可正常工作。     

基于分区独立温度控制的IMD膜片加热均匀性研究

在通过研究红外辐射加热理论,并结合实验建立红外辐射加热仿真模型的基础上,运用Matlab对模内装饰技术(IMD)膜片温度场分布进行仿真分析,研究了加热板的温度及其与膜片间的高度、加热时间及加热板面积大小对膜片温度场分布的影响。通过分析恒温加热板加热下膜片温度场分布的状况,提出对加热板实施分区独立温度控制,从而改善膜片加热温度的均匀性,扩大其有效成型区域。     

橡胶微波-传统联合加热硫化研究

运用ANSYS有限元分析软件,对圆波导模式下橡胶的微波-传统联合加热硫化过程进行仿真模拟,并与微波加热硫化过程进行对比。结果表明:仅采用微波加热方式,硫化胶内部温度较高,外部温度较低;而采用传统加热与微波加热相结合的方式,加热一定时间后,胶料内外能够同时被加热,胶料内部的温度梯度较小,内部温度分布较均匀。     

频率和功率对轮胎微波加热的影响

在双波导入射功率均为5 k W时,分别对(915±25)MHz频率范围和925 MHz频率时的双波导不同功率分配下的微波加热效率以及轮胎温度场分布进行了模拟。结果表明:微波加热效率随微波频率的变化呈类似于正/余弦曲线波动,在微波作用频率为925 MHz时,微波加热效果最好;双波导功率分配越趋近于一致,微波加热效率越高,轮胎温度场分布越均匀。     

边坡锚固用碳纤维增强复合材料的热固化工艺与性能研究

采用热固化方法制备了边坡锚固用碳纤维增强复合材料。研究了电加热固化、传统微波间接加热固化和优化后微波间接加热固化复合材料的力学及热学性能。结果表明，在电加热固化和微波间接加热固化过程的升温过程中没有出现放热峰，说明碳纤维增强复合材料在电加热固化作用下已经发生完全固化。相较于电加热固化工艺，微波间接加热固化在碳纤维增强复合材料完全固化前提下所消耗的能量仅为前者的24.97%，所需要的时间为前者的60%。微波间接加热固化碳纤维增强复合材料的拉伸性能、压缩性能、弯曲性能和层间剪切性能都高于电加热固化试样，层间剪切性能平均值相较于电加热固化提高了49.71%。     

激光切割陶瓷加工过程的数值模拟研究

激光与材料的相互作用一直是备受人们关注的问题。从工业上的激光热处理技术,到军事上的激光破坏机理研究,均与之密切相关,它在激光加工应用等领域中的诱人前景,激励着这方面的研究工作不断前进。笔者利用有限元理论,对不同模式激光加热Al_2O_3陶瓷的热传导过程及热应力分布进行了数值模拟,得到了Al_2O_3陶瓷的温度场和热应力场分布。根据热传导方程和热应力方程,建立了不同模式的激光辐照下中瞬态温度场和热应力场的物理模型。模拟计算了Al_2O_3陶瓷在不同模式激光照射下的温度场。数值模拟结果表明:吸收的激光能量主要分布在光斑半径以内,因此随着加热时间增加形成的径向温度梯度也越大;陶瓷内部沿轴向不同深度各点的温度随时间增长曲线在加热初始阶段均为S型。笔者的研究结果可为激光切割陶瓷加工过程的数值模拟研究提供参考。     

基于磁-热耦合有限元法的挤出机电磁感应加热温度场模拟研究

通过Ansoft Maxwell和Ansys Mechanical软件对挤出机电磁感应加热的三维有限元模型进行磁-热耦合仿真研究,计算了挤出机机筒与螺杆在电磁感应加热条件下的电流密度分布以及涡流和涡流损耗;并将涡流损耗结果导入Ansys Mechanical热分析模型中,计算得到机筒与螺杆三维模型在电磁感应加热条件下的稳态温度场分布。通过模拟及节电效果估算表明:电磁感应加热方式是一种节能高效的挤出机加热方式。     

微波加热对锰锌铁氧体纳米粉体制备的影响

采用硫酸亚铁、硝酸铁和氢氧化钠为原料，通过微波加热方式与共沉淀法结合制备了四氧化三铁纳米粉体。通过XRD、激光粒度分析和SEM对所得粉体进行了研究，同时研究了表面活性剂加入方式对粉体的影响。结果表明，微波加热可促进四氧化三铁纳米粒子的晶化，在30min加热时间内，可制得平均粒径为13～16nm的四氧化三铁纳米晶粒。通过对微波加热功率和时间的控制，可实现晶粒的可控生长。采用聚乙二醇作为表面活性剂，可明显减弱粉体的团聚现象，在微波辐照前加入活性剂的方式优于在微波辐照后加入活性剂的方式。采用微波加热可以极大地促进粉体的晶化，有利于纳米晶的迅速形成，对于合成纳米晶具有潜在的优势。     

微波加热多层橡胶复合材料的温度场分布及界面特性研究

针对不同波源下微波加热多层橡胶复合材料,建立基于Maxwell方程的一维非稳态有源加热偏微分方程(PDE)模型,以丁苯橡胶材料和丁腈橡胶材料复合为例,采用时域有限差分法进行模拟仿真,研究多层(两层)橡胶复合材料在单/双波源下材料厚度和微波功率对加热温度场和界面特性的影响。结果表明:微波功率变化会影响多层橡胶复合材料加热温度分布;在叠加橡胶材料的交界面处,微波振幅会有微小变化;将介电损耗小的橡胶材料直接暴露于微波源,有利于微波穿过介电损耗小的橡胶材料向深处传播,且各层橡胶材料厚度宜控制在临界穿透深度以下;相对于单波源加热,多波源加热能改善多层橡胶复合材料加热的均匀性。与传统有限元模型的分析结果进行比较,验证了本研究模型的有效性。     

聚合物的微波加热性能

阐述了聚合物微波加热的原理，分析了聚合物的介电性能与作用微波频率和聚合物温度的关系，总结了一些聚合物在不同温度和微波频率作用下的介电性能和微波加热性能，并对比了驻波和行波作用下聚合物的加热效率。比较了固定频率微波和变频微波加热对聚合物的内部温度分布的影响。     

Temperature field simulation of polyolefin-absorber mixture by FDTD-FDM model during microwave heating

This work has performed a numerical simulation of the temperature field during microwave heating of polyolefin-absorber mixture by means of a combined electric and thermal model. A finite difference time domain was used to model the electric field distribution within the cavity, while the finite difference method was used to calculate the temperature field distribution in different reactors. This study has focused only on the process from room temperature to 500 K for reducing heating time and energy consumption. This temperature range is a process with high energy consumption, difficult to control and great influence on the follow-up reaction. Temperature dependence of dielectric properties and thermal properties of heated materials are fully considered and simulated through an iterative process. The simulation results show that input power, the size and location of the heated materials, the position of the waveguide, and the kinds of microwave absorbers are important factors affecting the heating process. As a result, the uniform temperature distribution (the temperature difference T_d < 10 K) can be achieved by choosing the appropriate input power (500–2000 W), the appropriate proportion of microwave absorber (the volume ratio of SiC to HDPE is 30:70), and combining with the moving and rotating of the heated materials. The uniform temperature field obtained without mechanical stirring is very important for reducing energy consumption and subsequent reactions.     

Temperature field simulation of polyolefin-absorber mixture by FDTD-FDM model during microwave heating

This work has performed a numerical simulation of the temperature field during microwave heating of polyolefin-absorber mixture by means of a combined electric and thermal model. A finite difference time domain was used to model the electric field distribution within the cavity, while the finite difference method was used to calculate the temperature field distribution in different reactors. This study has focused only on the process from room temperature to 500 K for reducing heating time and energy consumption. This temperature range is a process with high energy consumption, difficult to control and great influence on the follow-up reaction. Temperature dependence of dielectric properties and thermal properties of heated materials are fully considered and simulated through an iterative process. The simulation results show that input power, the size and location of the heated materials, the position of the waveguide, and the kinds of microwave absorbers are important factors affecting the heating process. As a result, the uniform temperature distribution (the temperature difference T_d < 10 K) can be achieved by choosing the appropriate input power (500-2000 W), the appropriate proportion of microwave absorber (the volume ratio of SiC to HDPE is 30:70), and combining with the moving and rotating of the heated materials. The uniform temperature field obtained without mechanical stirring is very important for reducing energy consumption and subsequent reactions.     

钢渣沥青混合料微波加热自愈合性能研究

为了研究钢渣沥青混合料微波加热自愈合性能,制备了全石型、粗石细钢型、粗钢细石型、全钢型4种沥青混合料,采用热常数分析仪和矢量网络分析仪测试了沥青混合料的热参数和电磁参数,利用热电偶温度传感器和红外测温仪测试了沥青混合料的温度分布,并对比分析了COMSOL软件数值模拟温度场与试验温度分布;最后,采用三点弯曲破坏试验评价了沥青混合料的自愈合性能。结果表明:4种沥青混合料具有不同的微波吸收性能和传热性能,会对沥青混合料的加热速率产生一定影响;钢渣的掺入大大提高了沥青混合料的微波加热性能,且3种钢渣沥青混合料中粗石细钢型表现出较好的加热均匀性;COMSOL软件能够较好地模拟沥青混合料在微波加热下的温度分布;相比于全石型沥青混合料,粗石细钢型、粗钢细石型、全钢型沥青混合料的自愈合性能分别提高了1.11倍、1.14倍、1.11倍,钢渣的掺入较好地提高了沥青混合料的自愈合性能。     

Key Models of Heat and Mass Transfer of Asphalt Mixtures Based on Microwave Heating

Asphalt mixtures are simplified for porous media to study the heat and moisture transportation law based on the multiphysics transfer process of microwave heating. Electromagnetic diffusion and heat transfer models of asphalt mixtures are built. The heat and mass transfer model of moisture is also studied. The models prove capable of predicting the temperature field of recycled asphalt mixtures based on a microwave heating experiment. The pressure gradient increases with the increase in the heating temperature. The center heating region temperature is higher than that of the surrounding region as observed through temperature field simulation. The results can simulate the technical process of hot in-place recycling of asphalt mixtures and provide the theoretical basis for the structural design of heaters.     

碳纤维发热织物的电热性能研究

研究了以碳纤维为基质材料的发热织物的电热性能,通过改变碳纤维的排列以及外界的电学条件,观察发热织物的电阻、温度和发热时间等电热性能的变化情况。经过试验探索得到:碳纤维以交叉的方式排列、电源的功率为5 W时,可在较短的时间内使其织物表面温度达到53.7℃,持续发热6.8 h。通过试验还发现:碳纤维织物的通电时间长短以及断电的次数对碳纤维织物的电阻影响很微弱。     

炼油废水活性炭纤维快速脱附技术研究

对吸附剂吸附平衡状态的分析表明活性炭纤维具有特殊的孔结构和表面性质,这种性质决定可对其进行快速脱附再生。以炼油污水为吸附对象,进行了活性炭纤维的过热蒸汽再生、电流加热再生、电加热再生、微波再生等技术研究,结果表明：电流加热、电加热、微波方法均能达到快速脱附再生的目的,并具有良好的应用前景。     

Temperature control during microwave heating process by sliding mode neural network

In microwave heating applications, Lambert’s law is a common way to calculate power distribution. However, because of the complex application environment, Lambert’s law is not precise for the unknown power distribution on material surfaces. During the microwave heating process, the system process parameters can only be partly known by experience. Therefore, for such situations, to make the entire heating process safe, a sliding mode combined with a neural network algorithm is proposed. The algorithm is designed to calculate the suitable input power at each control period to make the material temperature follow the reference trajectory, which is determined by experience. The simulation and actual application results demonstrate that the proposed algorithm can commendably control the heating process. The difference between the reference trajectory and the material sampling temperature may exceed 1°C initially. However, as time progresses, the difference gradually decreases. Nonetheless, due to the low conduction coefficient, a single microwave heating process may take a long time. Therefore, many actual applications combine convective heat transfer with microwave. This article also discusses the control method of multiple inputs including microwave power and convective heat transfer with unknown model parameters. Another neural network is constructed to identify the unknown parameters. The algorithm is designed to obtain the suitable input power and input convective heat transfer at each control period. The simulation results show that the control algorithm can work well under multiple inputs. The material temperature on both the surfaces and the interior can follow the reference trajectory with a satisfactory difference, and suitable inputs can be obtained with few fluctuations during the learning process.     

Fully coupled electromagnetic‐thermal‐mechanical comparative simulation of direct vs hybrid microwave sintering of 3Y‐ZrO2

Direct and hybrid microwave sintering of 3Y‐ZrO₂ are comparatively studied at frequency of 2.45 GHz. Using the continuum theory of sintering, a fully coupled electromagnetic‐thermal‐mechanical (EMTM) finite element simulation is carried out to predict powder samples deformation during their microwave processing. Direct and hybrid heating configurations are computationally tested using advanced heat transfer simulation tools including the surface to surface thermal radiation boundary conditions and a numeric proportional‐integral‐derivative regulation (PID). The developed modeling framework shows a good agreement of the calculation results with the known experimental data on the microwave sintering of 3Y‐ZrO₂ in terms of the densification kinetics. It is shown that the direct heating configuration renders highly hot spot effects resulting in nonhomogenous densification causing processed specimen's final shape distortions. Compared with the direct heating, the hybrid heating configuration provides a reduction of the thermal inhomogeneity along with a densification homogenization. As a result of the hybrid heating, the total densification of the specimen is attained without specimen distortions. It is also shown that the reduction of the sample size has a stabilization effect on the temperature and relative density spatial distributions.     

微波加热用透波材料的研究进展

微波加热技术因其绿色环保、体积加热、选择性加热等优势,已被广泛应用于化工强化、金属冶炼、陶瓷烧结、食品加工等众多领域,但微波在反应器内普遍存在透波效果差、微波利用率低等问题。随着微波加热技术的不断发展,微波加热设备中透波材料的选用越来越受到大家的关注。本文主要针对透波材料在微波加热领域中的应用现状进行综述,对透波材料的种类进行简要介绍,分别从微波加热用容器和保温材料两方面进行论述。详细介绍了氧化物、氮化物、硅酸盐、磷酸盐等高温透波材料及聚四氟乙烯、玻纤增强树脂基、环氧树脂等中、低温透波材料的研究进展,并具体论述了目前微波加热常用纤维棉、纤维毯和纤维板等各种陶瓷纤维制品的介电特性和透波性能,最后指出了目前微波加热用透波材料普遍存在的问题,并对透波材料的应用和发展作出了展望。     

A review: production of activated carbon from agricultural byproducts via conventional and microwave heating

Production of activated carbon (AC) from agricultural byproducts is a research field that has gained increased interest in recent years because of its potential for the disposal of agro‐residues. At the same time, a beneficial byproduct that can be used in a number of environmental applications is produced. This paper surveys the developments in the production processes of AC from agricultural byproducts in the past 7 years from 2005 to 2012 via conventional and microwave heating. Emphasis is placed on the applied methodology and the influences of activating conditions, such as carbonization temperature, retention time, and impregnation ratio. From the review of AC production processes, agricultural wastes produced by a chemical method with microwave heating can be a source of AC with relatively higher surface area than that produced via conventional heating. © 2013 Society of Chemical Industry