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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 Td < 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. 相似文献
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将相变储能技术应用于电热水器,并通过添加石墨纳米颗粒改善相变材料的导热特性,对其储能过程进行调节,可以起到“移峰填谷”的作用。建立了四种不同结构的电热水器三维模型,模拟了电热水器内部速度场与温度场分布特性。考察了进出口水管结构、电加热管布置方式、保温层结构等因素对热水器内部流场及传热特性的影响,研究了不同储能层厚度对电热水器储能的影响。结果表明,水平加热管与垂直加热管相比,加热过程中加热效率提高了2.2%;进水管管径增大1.5倍,热水输出率提升了17.9%;加入相变材料可在相同保温时间内(36 h)使水温最大提高10.6%。 相似文献
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Non-uniform heating is a major issue in microwave applications, mainly due to inherently uneven distribution of electromagnetic energy in the microwave applicator. In this work, our aim is to improve electric field distribution uniformity by utilizing microwave reflection from electrically conductive beads placed in the microwave oven. The effects of position, size, and number of electrically conductive beads on the electric field distribution were numerically investigated, and validated through water-load experiments in the cavity. It is found that uniform electric field distribution was realized to some extent by appropriate placement of electrically conductive beads; meanwhile, average electric field intensity in the microwave oven was increased. 相似文献
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Microwave heated materials often reach a quasi-stable temperature resulting in thermal runaway. To control steady state in microwave processing, it is important to predict the quasi-stable temperature of the steady state. We demonstrated that the microwave heating behavior of hematite varies significantly with its initial temperature. In microwave heating, hematite samples could not be heated from room temperature, whereas hematite samples preheated to 410 °C or higher was heated to a temperature of 1020 °C. The microwave heating behavior can be accurately predicted by considering the steady-state energy balance. 相似文献
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Tristan Garnault Didier Bouvard Jean-Marc Chaix Sylvain Marinel Christelle Harnois 《Ceramics International》2021,47(12):16716-16729
This paper presents a thorough analysis of direct microwave heating as a sintering process of ceramic materials. It questions why susceptor-assisted microwave heating is used in most experimental works, although direct microwave coupling is preferable for taking advantage of the possible beneficial effects of the microwave field on the sintering phenomena. This issue was investigated by conducting both experiments and numerical simulations. The experiments consisted of sintering alumina and yttria doped zirconia powder samples in a 2.45 GHz resonant cavity with automatic thermal monitoring, whereas the numerical simulations coupled electromagnetics, thermal transfer and sample deformation. Alumina and yttria doped zirconia are widely used materials and they exhibit different microwave field behaviours (transparent and absorbent, respectively), which are representative of most ceramic materials. The influence of the insulating material was discussed by considering different sintering cell designs. The very low coupling capacity of alumina made its direct heating very difficult. It was therefore necessary to apply a strong electric field to heat it. This situation promoted the absorption of microwave energy by other elements such as the insulating material, leading to heating instabilities and degradation of the insulation cell. In the case of zirconia, its coupling properties change abruptly with increasing temperature. It is poorly absorbent at low temperature, highly absorbent at intermediate temperature and it finally becomes reflective at the end of the sintering process. The consequences of this behaviour are (i) a very difficult control of direct heating (ii) a propensity to form damaging hot spots and (iii) the impossibility to reach high temperatures without forming plasma. Therefore, this experimental and numerical study showed that direct microwave heating is not suitable for conducting reliable and homogeneous sintering of classical ceramics. This explains why susceptor-assisted heating is most of time preferred. 相似文献
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微波加热薄膜蒸发技术在促进极性/非极性混合物分离领域潜力巨大,但仍面临着能源利用效率低和加热不均的挑战,而电场分布不均是其根本原因,但影响电场分布的因素十分复杂且不可控,因此,从蒸发器结构及流体流动形式视角出发可为解决微波能高效利用的瓶颈提供新思路。为此本文提出了液桥式螺旋降膜蒸发器,通过COMSOL建立三维模型并模拟计算了微波能强化蒸发器上的螺旋降膜流动与蒸发过程,以蒸发率和温度变异系数作为评价指标,探究液膜厚度、螺距、蒸发器直径、流量以及时间对微波能利用效率的影响规律,研究结果表明该种结构在一定微波入射功率下,液膜蒸发率可达29.26%,温度变异系数降至0.0867,为微波能强化蒸发分离装置的设计提供了依据。 相似文献
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This paper demonstrates that microwave enhanced thermal decontamination of oil contaminated waste is a potentially important and highly efficiency approach to achieving the required environmental discharge limit. Numerical simulation of microwave thermal decontamination of oil contaminated wastes within an applicator known to support high electric field strengths was used to assess the influence of electric field and power loss density distributions on oil removal from the waste materials. It was found during this study that the water content plays the most important role in oil removal. As the microwave receptors within the material matrix, water molecules absorbed the bulk of the applied microwave energy. This energy was subsequently transferred to the oil in the form of heat, and was shown to cause thermal desorption. The boiling point of oil can also be reduced when it is mixed with water, since free water is beneficial to uniform heating, whilst bound water has a significant effect on the latter stages of oil removal. The experimental and simulation results suggest that the lowest residual oil levels were achieved when the sample material had a high dielectric loss factor and was placed in the position of maximum electric field strength. The cost of using a microwave technique for the remediation of oily waste can be up to 20 times lower than conventional heating. 相似文献
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Zn-based MCM-41 supporter sorbents were prepared using the microwave in-situ oxidation method. Other sorbents were heated using a conventional heating method to contrast the performance for H2S removal. The sorbents were tested at 500°C in fixed reactor and dried simulated Texaco coal gas was employed for the sulphurized atmosphere. The results show that sorbents prepared by microwave oxidation had a better toleration for the adsorption of H2S. A 13.2% improvement occurred in the sulphur capacity of the sorbents heated by the microwave method. XRD, SEM with EDS-element mapping, TEM, N2 adsorption, and XPS were used to characterize the properties of the sorbents. Due to the selective heating of the microwave and the superiority of the in-situ oxidation method, the sorbents heated by microwave exhibited more appropriate structures for sulphurization. Meanwhile, the even heating environment supplied by the microwave resulted in a more uniform distribution of the active component. The microwave also had an effect on the chemical bond and reduced the binding energy of the active component, which enhanced the reactivity between the H2S and the sorbents. The preferable features generated by microwave in-situ oxidation accelerate the replacement of S to O, and therefore the Zn-based MCM-41 sorbents prepared by the microwave method have an increased capability for H2S removal in high temperature coal gas. 相似文献
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通过实验测量了直接电加热的滚塑模具在加热阶段的表面温度和模内温度以及所消耗的电能。然后根据实验数据对该滚塑工艺的加热阶段进行了传热分析,计算了有效热能和无效热能,并提出了评估该滚塑工艺的3个指标参数——热能利用率、加热每单位质量粉料所消耗的电能、加热每单位质量粉料所需的时间。结果表明,该滚塑模具的表面温度具有一定的不均匀性,不同位置处的最大温差为8 ℃。3种实验情形下的最高热能利用率为37.5 %,另外在相同的模内加热温度下,热能利用率随模内粉料质量的增大而减小。 相似文献
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This paper reports the state of the art of the microwave super‐heated boiling phenomenon. When a liquid is heated by microwaves, the temperature increases rapidly to reach a steady temperature while refluxing. It happens that this steady state temperature can be up to 40 K higher than the boiling point of the liquid. With the same reactor, overheating is not observed under conventional heating. The bulk temperature of a microwaved solvent under boiling depends on many factors: physical properties of the solvent, reactor geometry, mass flow, heat flow, and electric field distribution. The influence of these factors is studied and discussed. The kinetics of homogeneous organic reactions shows an extension of Arrhenius behaviour into the super‐heated temperature region. Reaction rate enhancement of order 10–100 can thus be achieved, which is normally only possible under pressure. Finally, we present a model predicting reaction kinetics and yields under classical and microwave heating, based on predicted temperature profiles in agreement with experimental data. 相似文献
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Charles Manière Christelle Harnois Guillaume Riquet Thomas Grippi Stéphanie Behar-Lafenetre Sylvain Marinel 《Journal of the American Ceramic Society》2023,106(2):848-859
Microwave sintering is a method presenting the following advantages for flash sintering: contactless/volumetric heating, and the possibility to control the heating cycle of the microwave power. In this study, the transition from a typical 100 K/min to an ultra-rapid heating rate of 500 K/min is studied. The heating homogeneity of the typical hybrid configuration using silicon carbide susceptors is tested up to the stability limit of the system. We show that zirconia specimens as thick as 10 mm can be heated and sintered up to 500 K/min heating rate at which thermal cracks appear. However, the centimetric size of the specimens seems to favor coarsening implying an important remaining porosity in the end. A comprehensive simulation including microwave heating and convection has allowed the determination of the heating regime transition during the flash process and the quantification of each specimen's cooling fluxes. 相似文献
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Yeqing Ling Qiannan Li Hewen Zheng Mamdouh Omran Lei Gao Jin Chen Guo Chen 《Ceramics International》2021,47(6):8067-8074
Partially stabilised zirconia has advantages for the applications in the metallurgical processes which have special requirements in corrosion resistance and high-temperature performance. In the present work, controllable microwave heating was used for the uniform thermal field and consequent microstructure improvement to further improve the stability of partially stabilised zirconia, which was 88.14% prepared by electric arc melting. Analyses including X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman) were used to study the effect of temperature change on the phase composition and structure of the samples. After heating at temperatures of 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C for 1h, the stabilities of the heated product were 88.51%, 95.02%, 95.17%, 96.31% and 97.64%, respectively. From the phase transformations based on the experimental results, the discussion indicates that the martensitic transformation temperature of zirconia from m-ZrO2 to t-ZrO2 during the heating stage was reduced under the radiation of microwave energy. 相似文献
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陶瓷微波加热过程模型研究 总被引:2,自引:0,他引:2
建立了TF10N单模微波烧结腔中陶瓷同波烧结加热过程的有限元数学模型,并对小尺寸圆柱形和长方柱形氧化铝陶瓷试体分别用二维轴对和二维模型进行了加热过程的数值模拟,所得结果能基本准确地反映实际过程,文中还讨论了材料物性参数,介电损耗因子、热导率等对加热过程的影响作用。 相似文献
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基于加热均匀性的微波干燥研究进展 总被引:1,自引:0,他引:1
微波干燥通过电磁场辐射物体而在其内部产生热量,促进物体内部水分向外部迁移,是一种先进的干燥技术。但是,微波干燥存在加热不均匀的问题。本文针对该问题,分析了导致微波加热/干燥不均匀的影响因素,综述了通过提高微波干燥室内电磁场分布均匀性及改变被处理物料位置,以改进微波加热均匀性的可行措施,最后指出进一步实现微波均匀干燥的研究发展趋势。 相似文献
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Amikam Birnboim David Gershon Jeffery Calame Amnon Birman Yuval Carmel John Rodgers Baruch Levush Yurii V. Bykov A. G. Eremeev V. V. Holoptsev Vladimir E. Semenov David Dadon Peter L. Martin Moshe Rosen Ron Hutcheon 《Journal of the American Ceramic Society》1998,81(6):1493-1501
Temperature gradients that develop in ceramic materials during microwave heating are known to be strongly dependent on the applied microwave frequency. To gain a better understanding of this dependence, identical samples of ZnO powder compacts were microwave heated at three distinct widely separated frequencies of 2.45, 30, and 83 GHz and the core and surface temperatures were simultaneously monitored. At 2.45 GHz, the approximately uniform "volumetric" heating tends to raise the temperature of the sample as a whole, but the interior becomes hotter than the exterior because of heat loss from the surface. At 30 and 83 GHz, this interior to exterior temperature difference was found to be reversed, especially for high heating rates. This reversal resulted from increased energy deposition close to the sample's surface associated with reduced skin depth. A model for solving Maxwell's equations was incorporated into a newly developed two-dimensional (2-D) heat transport simulation code. The numerical simulations are in agreement with the experimental results. Simultaneous application of two or more widely separated frequencies is expected to allow electronic tailoring of the temperature profile during sintering. 相似文献