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本文使用Fick扩散模型对陶瓷坯体的干燥过程进行了模拟,在实际干燥工艺参数数值范围内,分析了热风速度、温度和相对湿度三个因素对陶瓷坯体内部温度、含水率和干燥速率的影响。结果表明,增加热风速度能够加大坯体表面区域的水分散失速率,但对坯体内部含水率变化影响较小;提高温度能够显著增加坯体内部的干燥速率,当温度从35℃增加至75℃时,最大干燥速率的变化幅度为46.34%;相对湿度对坯体平衡含水率影响较大,当相对湿度从5%增大至85%时,平衡含水率从0.8%增大至5.1%(均为质量分数),提高相对湿度能够改善坯体干燥均匀性,保证坯体干燥质量。模拟和试验数据基本吻合,计算结果将为进一步深入研究陶瓷坯体干燥的传热传质过程,以及后续干燥曲线的优化提供理论依据。 相似文献
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微波干燥有别于热风干燥和远红外线干燥,具有提高水分活性,加快坯体内部水分扩散的特性。对于器形复杂,坯体厚薄不一的卫生陶瓷、日用陶瓷坯体是比较理想的干燥方式。 相似文献
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《化学工程》2017,(2):26-32
以柳树河油页岩为原料,分别在100℃热风温度和不同的微波功率的干燥条件下进行试验;用Weibull分布函数对油页岩的干燥曲线进行拟合分析,结合尺度参数估算水分有效扩散系数。结果表明:加速干燥阶段脱除的是油页岩颗粒的表面水;前期存在预热过程,温度升高,水分析出很少;随后干燥速率显著增大。恒速阶段析出的也是表面水,受物理脱附作用的影响;功率越大,恒速段时间越短。降速第一阶段主要是大孔隙中水分的脱除,降速第二阶段主要是中孔和微孔中水分的汽化。临界水分比随功率的增加而升高。Weibull分布函数准确模拟了油页岩微波干燥曲线;尺度参数α值随功率增加而减小,功率大于550 W后减小幅度降低;微波干燥的形状参数β1,即升速段出现在干燥前期;估算的水分有效扩散系数随功率增加而增大。微波干燥和热风干燥时相比,油页岩颗粒形态并没有发生显著变化。 相似文献
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为了提高卫生陶瓷生产时干燥品质,将分段式变温变湿干燥与传统定温定湿干燥进行仿真对比,以热风温、湿度为工艺参数,坯体内部含水率分布不均匀系数作为评价指标,采用三维扩散模型,应用COMSOL Multiphysics软件对陶瓷湿坯在不同温湿度热风条件下进行干燥模拟仿真研究。仿真结果表明:随干燥时间坯体含水率不均匀度整体趋势是先升高后下降。含水率不均匀度随着热风相对湿度降低和温度的升高而增大,最大值出现时间提前。当干燥初始温度过高时,会在干燥前期产生较大的干燥不均匀,使用升温降湿干燥工艺,能有效降低坯体干燥过程含水率不均匀度,降低产生干燥缺陷的风险。 相似文献
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本文利用微波干燥法进行卫生陶瓷坯体干燥试验,探究微波可以实现对卫生陶瓷快速干燥的原因。在此基础上,对围绕着微波设备大型化、连续化中面临的关键技术及微波干燥电耗相对较高等技术进行攻关,开发了卫生陶瓷微波干燥辊道窑,并在实际工厂使用。结果表明:微波干燥过程实现了沿坯体纵向与沿坯体局部区域横向的均匀干燥及微波干燥能显著提高干燥的内扩散速率,最终实现对卫生陶瓷的快速干燥;采用微波、热风耦合加热技术能显著降低微波干燥电耗;开发的卫生陶瓷微波干燥辊道窑,可极大缩短干燥周期,降低场地占地面积,提高干燥合格率。 相似文献
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为降低生物质型煤干燥成本,提高干燥效率,研究热风干燥风速和温度对热风干燥特性的影响,拟合了生物质型煤在不同热风干燥条件下水分随时间变化的模拟曲线。结果表明:生物质型煤与多数多孔介质类似,干燥过程可分为加速干燥、恒速干燥、降速干燥3个阶段,其中恒速干燥阶段的干燥时间约25 min;热风温度越高,风速越大,生物质型煤的干燥速率越大,干燥时间越短,干燥时的裂纹率也越高。当干燥温度180℃,风速1.2 m/s时,生物质型煤热风干燥效果较好,干燥热效率最高为48.34%。通过对不同温度、风速条件下的生物质型煤干燥试验数据与常用干燥模型进行拟合分析,发现Sabbet干燥模型拟合度最好,当干燥温度180℃,风速1.2 m/s时相关性系数为0.997,二者相关性显著,因此Sabbet干燥模型可较好地反映生物质型煤在不同温度、风速下的干燥特性。 相似文献
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随着我国日用陶瓷工业的发展,链式干燥机已在日用瓷坯体干燥中大量应用。本文介绍一种采用隧道窑冷却带余热作热源,用于日用瓷干燥的链干机,供从事陶机设计的工程技术人员和有链干机设备的厂家参考。一、干燥速度的确定陶瓷坯体的干燥工艺,已从缓慢的自然干燥发展到快速的复合干燥,其周期已经有了数量级的缩短,而且有继续缩短的趋势,主要是因为干燥手段越来越先进,使干燥速度越来越快。国外已成功地采用了微波干燥、远红外热风复合干燥等多种快速干燥技术。英国Casburt有限公司已将干燥时间缩 相似文献
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陶瓷坯体水分的测量有烘箱法,电阻法、电容法、红外线法、微波吸收法等。本文主要探讨微波干燥法快速测定薄型砖素坯含水率,研究表明将功率调至130w,样品5g加热时间13分钟,所测坯体中水分与烘箱干燥法所绘得的水分完全一致。 相似文献
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During combined microwave–hot-air drying, the surface and the core temperatures of the sample have great influence on the process. To investigate the influence systematically, drying system with feedback control strategy of the two temperatures was proposed. Then various pairs of the two temperatures were applied in the drying mode 1. However, it was found difficulty to achieve both short drying time and high product quality with fixed temperature pair, because the interaction between microwave and the sample changes as the moisture content decreases in the drying process. Different temperature pairs were applied during the three drying stages in drying mode 2, so that better product can be obtained in shorter drying time. To further improve the product quality, the drying rate was controlled by a feedback loop within a desired range in drying mode 3. The change of drying rate was realized by adjusting the two temperatures continuously. To omit the weighing scale, a feedforward control strategy for the drying rate was put forward in drying mode 4, where the temperatures were controlled along with preset lines. The results showed that the product quality and the drying time were similar to those in drying mode 3. 相似文献
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Effect of Microwave-Vacuum Drying on the Carotenoids Retention of Carrot Slices and Chlorophyll Retention of Chinese Chive Leaves 总被引:3,自引:0,他引:3
Microwave-vacuum drying, and combined microwave-vacuum with air or vacuum drying were investigated as potential methods for drying green and high-carotenoid vegetables of Chinese chive leaves and carrot slices. The samples were dried by microwave-vacuum until the moisture content reached about 20% (wet basis), and then by conventional air drying at the temperature of 45-50°C or conventional vacuum drying at the temperature of 55-60°C or by continued microwave-vacuum drying at lower power level to final moisture content about 6% (wet basis). The carotenoid retention of carrot slices and chlorophyll retention of Chinese chive leaves, dried by these methods, was evaluated and compared with those dried by freeze-drying and conventional hot-air drying. The comparison showed that the carotenoid retention of carrot slices and chlorophyll retention of chive leaves, dried by the current methods, was very close to or even as much as those dried by freeze-drying and much better than those dried by conventional hot-air. Blanching was not necessary when using microwave-vacuum drying or combined microwave-vacuum with conventional hot-air drying or vacuum drying, because the activity of enzymes which were responsible for the degradation of color was greatly reduced with extremely rapid decreasing of moisture, and because oxygen was absent in microwave-vacuum drying. 相似文献
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AbstractThe aim of this study was to improve the drying uniformity and quality of Pleurotus eryngii by using the combination of microwave drying and hot-air flow rolling drying. The moisture content, drying uniformity, and water migration of P. eryngii during microwave hot-air flow rolling drying (MARD) were analyzed in detail. The temperature distribution images were obtained via infrared thermal imaging techniques and the relationship between relaxation time and signal amplitude were obtained via low-field nuclear magnetic resonance analysis and imaging (LF-NMR/MRI). The curves of signal amplitude with moisture content changes were fitted by a linear model with good linearity correlation. It was found that the hot-air and rolling bed could improve the drying uniformity of microwave drying. And the free water was found to transform into immobilized water and bound water during the drying process. Only a small amount of water was left in the dried P. eryngii in the final stage. The results could provide supportive information for improving the uniformity and quality of the drying processes of the edible fungi. 相似文献
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2种方式干燥的天然橡胶干燥特性之研究 总被引:2,自引:0,他引:2
为探讨微波干燥天然橡胶新技术,分别在温度115℃下,采用电热烘箱产生热空气和微波干燥装置干燥湿天然橡胶胶粒,对二者的干燥特性及硫化胶性能进行对比分析研究。结果表明,微波干燥只需13.467min就可使胶料含水量降至0.791%,热空气干燥则需211min。天然橡胶微波干燥和热空气干燥主要包含失水率加速期、失水率减速期、失水率相对恒速期3个失水阶段。整个干燥过程中,微波干燥失水率较大,而热空气干燥失水率比较小。微波干燥天然橡胶硫化胶的耐热氧老化性能得到显著提高:其老化前后拉断伸长率变化率(-35%)和拉伸强度变化率(-59%)明显高于热风干燥天然橡胶硫化胶的拉断伸长率变化率(-62%)和拉伸强度变化率(-89%)。 相似文献
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A combined conventional and microwave drying process for Ximeng lignite was investigated in this paper. Samples were firstly dehydrated by hot air to achieve a conversion moisture content, and then were managed to final moisture content by microwave drying. Results showed that the drying rate was significantly improved in the decreasing rate period by microwave drying, approximately 3–5 times faster than that of conventional drying. Finally, the orthogonal test was used to clarify the effects of each factor on the energy consumption, and the magnitude ranking order was conversion moisture content?>?microwave power?>?hot air temperature. 相似文献
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Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying 总被引:10,自引:0,他引:10
Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors. 相似文献
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《Drying Technology》2013,31(7):1173-1184
Abstract Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors. 相似文献
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The effects of three different drying methods (e.g., intermediate infrared-assisted convection drying, low-frequency (915 MHz) microwave drying, and hot-air drying) on the quality of squid cubes were investigated. The quality parameters used to evaluate the drying efficiency were color, shrinkage, rehydration ratio, and hardness of the final dried products. The results showed that intermediate infrared-assisted convection drying and low-frequency microwave drying have the advantages over hot-air drying in terms of drying rate, shrinkage percentage, and rehydration ratio. Low-frequency microwave-dried samples displayed a puffed structure and their hardness was the highest. The intermediate-wave infrared-assisted convection drying, at 60°C, was identified as the best method for squid-cube drying in this study. 相似文献