微波干燥过程中氯化钠电磁特性数值模拟研究

多模微波腔体是最为常见的加热腔体,然而在加热过程中待加热的物料常会表现出选择性加热的特点,这是由于微波加热的效果与物料的电磁特性参数密切相关。针对氯化钠在微波腔体中加热效果呈现出的差异性造成腔体内电磁场分布以及加热不均匀等问题,建立电磁热模型对氯化钠在加热过程中的电磁敏感性对温度变化的影响进行研究。通过时域有限差分法(Finite Difference Time Domain ,FDTD)耦合求解电磁场及热场方程,对微波加热氯化钠的升温速率随着电磁特性参数以及氯化钠含水率变化的规律进行实时的仿真计算。结果表明:随着氯化钠相对介电常数的增大,其腔体内的电场分布越均匀,介质对电磁波的吸附作用越明显。随着氯化钠损耗角和含水率的增大,腔体内氯化钠的升温速率以及稳态温度增大。     

垂直腔面发射激光器的热学特性

通过求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法，计算了垂直腔面发射激光器（VCSEL）的电势分布，进而求解热传导方程，得到VCSEL的温度分布．详细分析了注入电流密度小于或等于阈值电流密度时，晶片键合结构垂直腔面发射激光器的键合界面阻抗、氧化层限制孔径、外加电压以及分布布拉格反射镜的热导率的大小对VCSEL内部温度分布的影响．     

微波辅助油炸的加热均匀性研究

为了实现高均匀性的微波和油炸的联合加热，本文设计了一种延展的微波单模腔，扩大了微波加热区域，通过调节矩形加热区域在极化方向的尺寸可获得均匀的电场分布，同时建立了微波加热的多物理场仿真模型来计算腔体内的电磁场分布以及土豆的温度分布。仿真结果表明，在设计的腔体内模拟微波油炸初步实现对土豆油炸效率的提升，模拟土豆在矩形加热腔内做匀速平移运动以及调节上下两个端口之间的相位差随时间不断变化能够进一步提高油炸均匀性，并建立实验系统，验证了所提方法的准确性。还讨论了不同厚度、不同含水量的土豆片对油炸均匀性的影响。     

微波加热效应的多物理场仿真与实验

微波对物质的加热涉及电磁、热、加热物的物理参数随温度变化等多种物理过程的综合作用。研究耦合电磁场、热传导和被加热物质物理参数方程构建多物理场方程组,数值求解获得微波加热过程的温度变化。给出多物理场算法公式和计算流程,以2.45 GHz微波加热水为例,多物理场仿真了该加热过程的微波功率分布、热量累积和温度上升,设计和加工制作了微波加热实验装置。在工作频点2.45 GHz处,测试装置的回波损耗为16.2 dB,同时测试了输入功率40 W时4个指定点处60 s内的温升,多物理场仿真结果与测试结果吻合良好,验证了多物理场仿真的正确性。     

加热低电阻率硅带和硅片用的行波谐振器

研究了加热低电阻率硅片用的行波谐振腔和微波加热器。微波电路的性能与理论预计是一致的。描述了150毫米(6英寸)直径硅片用微波加热器。对温度的分布进行了理论计算并测量了某些温度分布。     

热疗用微波辐射器长度对其性能影响的理论分析

本文分析了一种带冷却水的用于人体体腔内部热疗的绝缘偶极子微波辐射器的特性。利用辐射器上的电流分布导出辐射阻抗和驻波经与辐射器长度的关系式，探讨了体腔周围被加热生物组织中分布的比吸收率，进而根据热平衡方程得到辐射器长度对温度场分布的影响，为体腔内部热疗用微波辐射器的设计提供了理论依据。     

垂直腔面发射激光器的热学特性

通过求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法,计算了垂直腔面发射激光器(VCSEL)的电势分布,进而求解热传导方程,得到VCSEL的温度分布.详细分析了注入电流密度小于或等于阈值电流密度时,晶片键合结构垂直腔面发射激光器的键合界面阻抗、氧化层限制孔径、外加电压以及分布布拉格反射镜的热导率的大小对VCSEL内部温度分布的影响.     

一种双圆柱腔微波加热系统的仿真研究

本文提出并设计了一种工作频率为2．45GHz的双圆柱腔微波加热系统。该加热系统是在矩形波导宽边中央开孔,用两支铜棒将矩形波导中传输的微波耦合到双圆柱腔内并对圆柱腔内的化学反应罐进行加热。仿真研究表明,通过调节短路活塞、耦合铜棒和调配螺钉,在主要工作频带内输入端反射系数小于-10dB,耦合进两个圆柱腔内的功率相等,两个圆柱腔内场分布大致相同。此双圆柱腔微波加热系统具有效率高、加热均匀等特点,在微波化学分析中具有较好的应用前景。     

微波对固体培养基灭菌的研究

自新冠肺炎疫情爆发以来,各行各业对消毒灭菌的要求越来越高,因此开展微波灭菌技术的研究意义重大。传统的微波灭菌技术中由于固体培养基存在受热不均匀的问题,导致出现灭菌“冷点”,灭菌时间过长。文章首先对微波辐射腔的电场分布特性和固体培养基的温度分布特性进行了仿真研究。研究结果表明:微波辐射腔内的电场分布呈现馈源较近区域内场强大于较远区域内场强的特点,固体培养基的温度呈现出四周高于中心位置的特征。然后采用在辐射腔内添加搅拌器的措施,有效改善了腔体内部的电场分布和培养基的温度分布特性。最后通过微波灭菌试验证明了搅拌器能显著改善微波灭菌中的受热不均匀问题,提高了灭菌率。自新冠肺炎疫情爆发以来,各行各业对消毒灭菌的要求越来越高,因此开展微波灭菌技术的研究意     

基于双通道固态源的腔内三分区加热研究

微波加热在医疗、食品加工等特殊领域应用广泛,但是很难工程上实现对任意方向的定向加热的控制。本文基于线性相控阵天线理论,设计了一个双通道固态源的腔内三分区指向加热系统,该系统通过调节固态源各通道间的相位差以实现腔体内的微波指向从而达到三分区定向加热的效果。同时,本文通过耦合电磁场和热传递方程建立了微波加热的多物理场模型,以模拟腔内的微波分区加热,进一步的搭建了相应的实验系统验证分区加热的效果。     

微波多模腔体对水性聚氨酯涂膜加热仿真分析

水性聚氨酯为水与高分子聚酯材料的混合材料,工业上采用热风和红外干燥方式对水性聚氨酯材料进行干燥存在干燥效率低同时时间长等问题。为解决在传统干燥过程中存在的问题,本文通过使用有限元方法对水性聚氨酯涂膜在多模微波腔体内进行建模,通过测试并拟合水性高分子聚氨酯乳液介电常数随温度的变化曲线;仿真了微波干燥方式下涂膜的温度分布,获得了涂膜整体平均温度随微波功率的变化仿真结果,确定了在相同的时间内有利于水性聚氨酯涂膜干燥的微波功率,仿真了在该微波功率下涂膜整体温度随时间的动态变化过程。     

管道式固体材料微波加热装置的仿真设计*

为了解决工业上固体材料在微波加热过程中普遍存在的能量不集中、效率低、加热不均匀的问题,提 出了一种管道式固体材料微波加热装置的设计方案。利用多物理场仿真对固体材料微波加热均匀性影响因素进行 分析,并优化了微波馈入装置的分布和管道结构,仿真表明该装置具有较好的加热均匀性和较高的效率。基于优化 后的设计,计算了褐煤在微波加热时的温度分布情况,其温度场的变异系数COV 值达到0.166,表明温度分布具有 良好的均匀性。该装置实现了对褐煤的微波均匀加热,对固体材料微波加热的工业应用具有指导意义。     

TLM simulation of microwave sintering of ceramics using SiC stimulus.

Microwave heating technology is becoming a successful technique used for sintering ceramic materials. However, various aspects of sintering experiments, such as the use of process stimulus and the preparation of sample arrangements, depend mainly on human expertise. The Transmission Line Matrix (TLM) method is first used to solve the combined electromagnetic and thermal equations modeling microwave heating of dielectric materials. It is then used to simulate microwave sintering of a low-loss ceramic material in a multimode microwave cavity. To enhance the microwave sintering process, Silicon Carbid (SiC) was first used as a susceptor and in a picket fence arrangement. As multiple samples may be processed in a microwave oven, the TLM was used to model such a process, and the introduction of SiC as a stimulus was also examined. Results show the importance of the stimulus thickness and configuration on the uniformity and density of the electromagnetic field distribution and, therefore, on the power dissipation within the ceramic load.     

基于数值仿真的多馈微波加热温度控制系统

针对常用多模腔加热的不均匀性,对多馈口微波加热进行了研究,提出了一种基于数值仿真分析来设计微波加热系统的方法。通过建立1/2 全尺寸有限元模型进行仿真计算,分析了馈口数量对微波加热的影响,在此基础上采用Bang-Bang 控制策略设计了加热系统。其中,圆柱形谐振腔模型的高度为800 mm,半径为395 mm。腔体周围环形布置10个微波源,通过德拜模型仿真温度变化和测量值进行对比,验证了仿真模型的正确性。不同馈口数的COMSOL仿真结果表明,馈口数为4时,温度变异系数(COV)为0.0897,相比于一个馈口的情况,温度的均匀性提高了10.5%。通过实验测试了微波加热系统性能,实验结果表明,媒质温度能得到合理控制。     

Microwave radiometry for continuous non-contact temperature measurements during microwave heating.

Temperature measurement during microwave heating in industrial and commercial processes can improve quality, throughput, and energy conservation. Conventional ways of measuring temperature inside a microwave oven cavity are costly, inconvenient, or unsuitable for high-volume industrial applications. In this paper, we describe the theory of microwave radiometry as applied to the measurement of temperature during microwave heating. By extending the theory of radiative transfer to the case of thermal microwave radiation inside a cavity, we show that the same characteristics which make a microwave cavity suitable for heating materials also assist in obtaining meaningful temperature data with microwave radiometry. We present experimental data from the heating of liquid and solid materials which confirm the essential features of the theory, and show agreement between this method and more conventional methods of +/-4 degrees C.     

基于多物理场计算的微波加热能量转换分析

近年来,微波能的应用在食品、化工、医疗等方面越来越广泛,特别是微波加热技术在日常生活中充当着重要角色,得到了学者们的广泛关注。然而,关于微波加热机理的基础研究并不多,而且相对较为深奥,难于理解掌握。因此,通过COMSOL multiphysics建立简易微波加热模型,以水为被加热对象,研究了其在微波作用下的电场及温度分布情况,并通过计算分析了其中的能量转换关系,使得对微波加热机理的阐释通俗易懂。     

Modeling of intraluminal heating of biological tissue: implicationsfor treatment of benign prostatic hyperplasia

A computer model for predicting the thermal response of a biological tissue to different intraluminal heating modalities is presented. A practical application of the model is to calculate the temperature distributions during thermal coagulation of prostate by contact heating and radiative heating. The model uses a two-dimensional axisymmetric diffusion approximation method to calculate the light distribution during radiative heating. The traditional Pennes' bio-heat equation is used to calculate the temperatures in the presence of blood flow. An implicit finite difference scheme with nonuniform grid spacings is used to solve the diffusion equation for light distribution and the bio-heat equation. Model results indicate that the radiative heating of prostate by Nd:YAG (1,064 mm) and diode (810 mm) lasers can be a more effective and efficient means of coagulating a large volume of prostate, as compared to contact heating of the tissue. Blood perfusion is shown to provide a considerable heat sink as the laser exposure time is increased. Surface cooling by irrigation during the laser irradiation of tissue is shown to be an effective method for delaying tissue explosion and obtaining a large volume of coagulated tissue. The model also shows that the volume of the coagulated tissue is appreciably altered by a change in the rate of energy deposition     

Quantification of the 3-D electromagnetic power absorption rate intissue during transurethral prostatic microwave thermotherapy using heattransfer model

Experiments were performed in a tissue microwave-equivalent phantom gel to quantitatively examine the volumetric heating produced by a microwave antenna with a peripheral cooling system for the transurethral prostatic thermotherapy. Based on previous research, expression for the specific absorption rate (SAR) of microwave energy in the gel was extended to three dimensions, which includes its dependence on radial, angular, and axial direction. A theoretical heat transfer model was developed to study the temperature distribution in the gel by introducing this proposed SAR expression. The parameters in this expression and the convection coefficient due to the chilled water running around the antenna were determined using a least-square residual fit of the theoretical temperature predictions to the experimentally measured steady-state temperature field within the gel. The analytical expression of the three-dimensional SAR distribution obtained in this study will help provide a better understanding of the microwave heating pattern in the prostatic tissue and, thus, to aid in designing improved applicators. It can also be used in the future as an accurate input to heat transfer models which predict temperature distributions during the transurethral microwave thermotherapy