多孔物料微波冷风对流干燥Re自模区研究

针对多孔物料在微波冷风时而干燥过程中出现流速变化对干燥速率无影响区间或称为Ｒｅ自模化区这一现象，采用集总参数分析法，从理论上对多孔物料的微波对流干燥过程进行量化分析，找出Ｒｅ自模化区的范围。结合实验结果，对这一现象的成因作出解释，从而获得一些有益的结论。     

胶体毛细管多孔薄层物料的干燥静力学

针对胶体毛细管多孔薄层物料干燥静力学问题,用非平衡热力学关联了多层吸附和毛细管凝聚现象,提出了新的数学模型,可在较宽的相对湿度范围内描述吸着等温线.当相对湿度较低时,本模型转化为BET公式.     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

耐火浇注料对流与微波干燥的实验研究

进行了耐火浇注料热重分析,热风和微波干燥实验研究,得到了浇注料热风和微波干燥特性曲线。实验结果表明,与热风干燥比较,微波加热极大地降低了耐火浇注料干燥时间、提高了干燥效率和能源效率高,在耐火浇注料干燥过程中有着广阔的应用前景。     

多孔介质对流干燥机理及其模型

在对现有的多孔介质对流干燥传热、传质模型归类分析的基础上,从介质内部热湿迁移机制出发,建立了能较完善、较准确地描述多孔介质在恒速段及降速段热质传递规律的“三耦合-六场量”混合理论模型.同时针对干燥问题数值模拟中的移动边界问题,提出了一种迭代修正的思想,并发展了相应的数值计算方法.对砖的干燥模拟计算结果表明,本文的模型较其他模型具有更好的精确性.     

微波干燥过程中功率密度对多孔陶瓷干燥品质的影响及应用研究

本文主要针对具有三维网络结构的多孔陶瓷在制备过程中挂浆后,采用微波干燥工艺,通过控制微波功率密度,对比分析了不同微波功率密度干燥后产品含水率及对产品性能的影响.结果表明,微波功率密度越高,产品最终含水率越低,但是产品的性能降低,当功率密度超过26W/g时,产品干燥后显微镜下可见明显裂纹,当功率密度低于26W/g时,产品...     

膏糊状物料气流对流干燥试验研究

以分子筛滤饼作被干燥物料,模拟带式干燥机进行了干燥试验研究。考察了气流速度、温度以及干燥时间对物料干燥效果的影响,并与烘箱干燥试验数据进行对比。结果表明:气流速度越高,干燥温度越高,干燥后物料的水分含量越低;带式气流干燥机干燥时间短,处理量大,可以连续操作,干燥效果明显优于箱式干燥器,可以作为膏糊状物料的干燥设备。     

热泵干燥装置在生物物料干燥中的应用分析

干燥是食品、药品及生物活性制品生产的基本环节之一。就热泵与生物物料干燥装置相结合 ,提高干燥过程的热效率 ,降低生物物料在干燥过程中的质量损失进行了较深入的分析 ,同时也对热泵干燥装置应用与推广需进一步解决的问题及其应用策略进行了剖析。     

微波真空干燥技术的探讨

干燥是高能耗行业,我国干燥能耗约占全部工业能耗的12％。“节能减排”是保障我国能源安全、发展经济和保护环境的基本国策。根据不同的生产条件,科学选用烘干工艺和设备,对节约能源、减少原材料消耗、降低生产成本、提高经济效益、增强企业市场竞争力具有重要的意义。     

Criterion for crack initiation during drying: Alumina porous ceramic strength improvement

Improvement in the mechanical strength of the supports of porous catalysts is increasingly needed by the refining industry because of the high stresses induced by the exploitation of catalysts. Drying is known to be a critical process for mechanical strength during the preparation of supports, leading to micro-cracks in the case of hard drying conditions.In order to predict failure during drying, a crack initiation criterion, combined with a drying induced elastic stress simulation is proposed. Model parameters are the thermo-hydro-mechanical properties of the gel and the criterion is based on the tensile strength of an alumina gel at various moisture contents. The developed tool gives good results and can be easily adapted to several gel formulations as only effective properties of the gel are required.     

A kinetic study of microwave and fluidized-bed drying of a Chinese lignite

The drying kinetics of Chinese lignite in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave were investigated. The changes in the mass as a function of drying time were measured under various drying conditions. The variations of moisture ratio with time were used to test ten different thin-layer empirical drying models given in the literature. In studying the consistency of all the models, some statistical tests, such as χ², residual sum of squares (RSS) and F-value were also used as well as coefficient of determination R². In nitrogen fluidized-bed and superheated steam fluidized-bed, the Midilli–Kucuk model best described the lignite drying process. Drying data in microwave were best described by the Page model, indicative of a difference in kinetics between the two drying methods. This difference was attributed to different heat transfer mechanisms under conventional and microwave drying conditions. The effects of drying parameters in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying on the constants and coefficients of the selected models were studied by multiple regression analysis. The apparent diffusion coefficient of moisture in samples was obtained from the kinetics data and the apparent activation energies under nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying were found to be rather similar.     

Convective drying of porous material containing a partially miscible mixture

Non-hygroscopic capillary porous bodies were dried by convection to investigate the influence of a two-phase moisture on the drying characteristics. The samples were wetted with the ternary liquid mixture 2-propanol/water/1-butanol. This system forms two liquid phases at low propanol concentrations. The drying rate is not significantly influenced by a two-phase moisture. Selectivity is influenced by the drying conditions as well as the characteristics of the capillary porous body. In the two-phase region selectivity can be shifted most effectively by the temperature of the drying air and by the pore size of the porous body. Selectivity can even inverted if the initial moisture composition is close to the boundary line. In the porous body a moisture profile, as well as a concentration profile, was measured.     

Experimental study on microwave drying of Chinese and Indonesian low-rank coals

Drying characteristics of low rank coals in a local microwave oven operating at 2.45 GHz were investigated. Effects of coal particle size, microwave power level, and coal sample size on drying characteristics were studied. Weight losses and temperature history of the samples were measured during drying. Drying rates were then obtained vs. drying time and moisture content. It was found that drying rate was increased with increasing coal particle size showing different trends from conventional drying methods reported in the literature. It was also observed that drying rate increased with increasing power output of the microwave oven or with decreasing coal sample weight. Effects of coal ash content and coal type were also investigated by comparing Chinese and Indonesian low rank coals. Ash content seems to be the governing factor in determining the drying characteristics for coal samples with small particle sizes. Drying mechanism of coals under microwave drying conditions was also discussed.     

Combustion synthesis of porous Fe3-xZnxO4 powders for high-performance microwave absorbers

Fe_3-xZn_xO₄ (x = 0.1, 0.2, and 0.3) powders were synthesized by facile combustion method using metal nitrates as oxidants and glycine as fuel. The structural, microstructural, magnetic, and microwave absorption properties are characterized as a function of Zn²⁺ substitution. With the increase of Zn²⁺ contents, some hematite (α-Fe₂O₃) phases appeared together with the magnetite (Fe₃O₄) phase. The transmission and scanning electron microscopy observations showed that the particle size was decreased from 120 to 70 nm, while the amount and size of pores increased with adding Zn²⁺ cations. The as-synthesized Fe_2.9Zn_0.1O₄ powders had the highest saturation magnetization of 92 emu/g, which decreased to 72 emu/g for the Fe_2.7Zn_0.3O₄ sample. The Fe_2.8Zn_0.2O₄ sample exhibited an intense reflection loss of ?53 dB in the K_u band at the matching thickness of 2 mm. Despite the reduction of reflection loss, the effective bandwidth increased up to 5.5 GHz with the Zn content, which is attributed to the better impedance matching and higher contribution of magnetic and dielectric loss mechanisms.     

Bimetallic sulfides embedded into porous carbon composites with tunable magneto-dielectric properties for lightweight biomass- reinforced microwave absorber

Currently, biomass-derived porous carbon materials have great potential for the development of advanced microwave absorbing materials (MAMs) with lightweight, high performance, wide effective bandwidth (EAB), and thin matching thickness. Herein, we reported low-cost, high-performance MAMs for the successful anchoring of Cu-based bimetallic sulfides CuCo₂S₄@CoS₂ on biomass porous carbon (BPC) derived from pistachio shells using a simple carbonization, hydrothermal, and electrostatic self-assembly method. The results demonstrate that the prepared BPC@CuCo₂S₄@CoS₂ composite exhibits excellent microwave absorption due to its balanced impedance matching and the combined effect of conductive loss, dipole polarization, interfacial polarization, dielectric loss, and magnetic loss. To be precise, the minimum reflection loss (RL_min) of BPC@CuCo₂S₄@CoS₂ reaches −64.2 dB at a packing load of 20 wt%, with an EAB of 6.6 GHz and a thickness of 2.3 mm. This work provides new insights into the study of copper-based bimetallic sulfide and BPC composites in MAMs.     

Fabrication and microwave absorbing property of WO3@WC with a core-shell porous structure

Special microstructure can significantly improve the microwave absorption property of rare materials. In this paper, porous WC powders were successfully synthesized by spray granulation method. Then, WO₃@WC materials with core-shell porous structure can be prepared after 410 °C heating treatment at different time to form the outer WO₃ oxidation layer. In addition, the microstructure, morphology, phase analysis and electromagnetic property were fully studied by investigating the WC-based materials in different structures. For WO₃@WC core-shell porous materials, when the coating thickness was 2.1 mm, the maximum reflection loss can reach ?19.4 dB at 12.6 GHz, which shows quite good microwave absorbing effects. The core-shell porous structure enhances the original microwave absorption performance due to the multiple reflection reflections and polarizations.     

Modeling drying in thin porous media after coupling pore-level drying dynamics with external flow field

This article uses a novel, fully coupled method to solve the isothermal slow drying of porous media in laminar flow. The film effect is included and a novel logistic equation is used to relate the pore network variables with the external field variables. The model is used to simulate the drying of several thin porous media with different aspect ratios in a flow. One, two, or all sides of the pore network are opened to the flow. The studies show that the higher exposed area vs. total volume ratio leads to faster drying while the orientation of the porous media is immaterial.     

微波技术在鲜花干制中的应用

介绍微波干制的机理，探讨了微波技术在鲜花干制中的应用，主要包括杀菌作用，对色泽、营养成分的影响及其定形效果。