卫生陶瓷坯体干燥含水率不均匀度模拟研究

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。     

改善木材干燥室内空气流动特性的初步研究

木材干燥室内部温度场、湿度场的均匀性是评价干燥设备和确保木材干燥质量的重要指标之一。在原有顶风式和长方体型端风式干燥室的基础之上，通过合理地设置导风挡板采改善干燥室内空气的流动均匀性。首先运用气体流动的伯努利方程，从理论上确定了干燥室内导风挡板的尺寸和安装位置；之后，通过实测验证了合理设置导风挡板对于提高干燥室内气流速度和均匀程度的有效性。研究结果表明：在不改变其他条件下，通过合理设置导风挡板可使干燥室内气体流动均匀性提高10％。长方体型端风式干燥室完全可通过合理设置导风挡板。达到斜壁型端风式干燥室相同的干燥效果，且具有更大的灵活性和土建优势。     

基于气流均匀分配的下进风袋式除尘器灰斗结构优化

采用计算流体动力学软件Fluent对袋式除尘器内部流场进行三维数值模拟,提出3种优化灰斗结构模型,得到除尘器灰斗内部的气流流场分布特征,将其与原灰斗结构的气流分配效果对比.结果表明,原灰斗结构气流进入灰斗后形成一股冲击射流,在选取的监测面上速度最大为8.3 m/s,最小仅为0.5 m/s,速度分布均方根值高达0.99,速度在监测面上分布极不均匀;3种优化结构中袋室内气流均匀性均比原灰斗结构显著改善,在灰斗内添加导流装置可提高气流分配的均匀性;3种优化结构中,添加竖直导流板的灰斗结构对改善气流分配均匀性最明显,比原灰斗结构流动均匀性提高了41.41%,而考虑射流偏转添加倾斜导流板或翼板的优化结构与竖直导流板相比流动均匀性无显著变化,灰斗内部射流偏转对流场分布的影响可忽略.     

加热风前后湿法脱硫直排烟囱二次脱水流场的模拟计算

在安装有二次脱水装置的湿法脱硫直排烟囱内引入热风,可进一步降低烟囱出口含水率,有效解决烟囱飘雨问题。为考察热风对气流流动特性影响,进而优化脱水装置结构,使脱水效果与运行阻力达到最佳匹配,基于CFD方法,采用离散相模型、RNG k-ε双方程湍流模型和组分输运模型组合建立了描述直排烟囱内部流场的流体动力学模型,对其进行了数值模拟,获得了加热风前后烟囱内温度、速度、压强和含水率的变化规律。结果表明,加热风后,烟囱出口处温度上升3 K,速度增加0.6 m·s^-1,压强降低55 Pa,含水率减小29 mg·m^-3,旋流板最佳叶片角度是45°。模拟结果均处于工程实际监测数据波动范围内,验证了模拟合理性和可行性,为优化直排烟囱内部结构和指导工程实际现场取样点提供了理论依据。     

热风循环隧道烘箱的流场模拟及结构优化

采用CFD数值模拟方法研究热风循环隧道烘箱的内部温度及流场分布,提出了6种结构优化方案,考察了不同方案下的气流分布特性。结果表明,烘箱出口面局部温差在1 K以内,温度分布较均匀;气流速度分布是影响烘干品质的主要因素,原始结构下出口气流分布极不均匀,出口面角落位置出现局部高速区,最大速度达3.48 m/s,平均速度为0.94 m/s,相对均方根值为0.73;相比原始结构,6种改进方案中,弯头三隔板结构出口面的相对均方根值最低,最大速度降低51.4%,最佳风速区域占比提升至75.17%,整流效果最明显;弯头内设置三块隔板后,风罩内再设置隔板对气流均匀性的改进作用不大。     

盐泥颗粒热风干燥特性及动力学模型

为优化盐泥颗粒干燥设备及结构参数，搭建热风干燥实验装置对盐泥颗粒进行热风干燥实验，研究不同风温、风速和堆积厚度对盐泥颗粒热风干燥特性的影响。对不同条件下的干燥特性曲线，通过比较决定系数R²、卡方x²和标准误差ESME等指标，评价5种常用干燥动力学模型对干燥曲线的拟合结果。结果表明：Midilli模型可以预测盐泥颗粒热风干燥过程水分的变化规律，模型预测的干燥曲线与实验干燥曲线有较高的拟合度。盐泥颗粒热风干燥过程中干燥速率逐渐下降，热风干燥特性与风温和堆积厚度密切相关。当温度从50℃增加到80℃时，有效水分扩散系数由2.038 39×10^-9 m²·s^-1增加到8.137 643×10^-9 m²·s^-1。     

气流旋转干燥器

1 旋风气流干燥器 旋风气流干燥器的干燥室结构以圆筒形居多,但也有锥形结构,锥形干燥室可使物料颗粒旋转速度由小到大,能达到强化干燥的目的. 旋风气流干燥器由内筒和外筒组成.外筒呈上大下小的锥形,物料从上部切线进入干燥器后,随热风向下部进行旋转运动,在干燥室内物料被干燥.到达底部后受气流夹带,粉体从内筒向上运动,经出料口排出.旋风气流干燥器的优点是使物料及热空气在干燥器内形成的转向降低了设备的高度,延长了物料在干燥器内的停留时间.     

基于Fick扩散模型的陶瓷坯体干燥数值模拟

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。     

旋流干燥器流场模拟研究

旋流干燥器(SMTD)作为一种新型的干燥装置,其结构简单、干燥效率高、处理量大,成为气固二相流干燥研究的新方向.文中用流体力学软件Fluent对旋流干燥器内部的流场进行了数值模拟研究,采用雷诺应力模型(RSM)模拟气相流动,模拟结果表明:旋流干燥器各干燥事内气流主要做旋转运动,穿过旋流板时,主要做返混运动;切向速度分布...     

基于气流均匀分配的大型袋式除尘器布风风道的几何特性

以大型袋式除尘器为对象,研究其布风风道的气流分配不均匀性,以解决由此导致的除尘效率低、压降偏高及运行成本上升等问题;分析了表征布风风道内流体流动特性的不可压缩恒定流能量方程的相关参数,重点研究了布风风道流动摩擦阻力系数λ、局部阻力系数ζ的影响因素及量化方法,确定了风道的几何结构;采用数值模拟方法分析了布风风道内气流分配均匀性.结果表明,该风道内气体流动处于紊流第IV区,可用阿里特苏里公式确定风道摩擦阻力系数λ;当布风风道结构参数ψ一定时,局部阻力系数ζ与风速比C相关,C2.155时ζ的变化呈指数规律增大,C2.155时ζ的变化区间为1.51～1.57,逐渐趋于稳定;改进前后布风风道内流体流动分配的不均匀系数U分别为0.70和0.93,表明改进后布风风道内流体流动分配均匀性显著提高.     

Infrared assisted dry-blanching and hybrid drying of carrot

Infrared (IR) blanching and IR assisted hot air (hybrid) drying of carrot slices were attempted and their performance (processing time, retention of vitamin C and rehydration characteristics) was compared with conventional blanching and drying techniques. Intermittent heating of carrot slices using IR radiation (chamber maintained at 180–240 °C) for 8–15 min resulted in desired level of enzyme inactivation. The time required for blanching of carrot slices (10 mm thick) using hot water, steam and IR radiation was 5, 3 and 15 min, respectively. Retention of water soluble vitamin C was higher (62%) in IR blanched carrot as compared to water (43%) and steam (49%) blanching. IR blanching reduced the moisture content by 13–23% (absolute). IR blanched samples dried by hybrid mode took ～45% lesser time compared to water blanched–hot air dried samples. Higher rehydration moisture of dried samples indicated the retention of cell structure during IR blanching. Vitamin C retention was ～39% higher in IR blanched–hybrid dried slices compared to water blanched–hot air dried. The study shows the potential application of dry-blanching and IR assisted hybrid drying in food processing for improving product quality.     

EXPERIMENTAL INVESTIGATION ON SOLAR DRYING OF FISH USING SOLAR TUNNEL DRYER

This paper presents field level performance of the solar tunnel dryer for drying of fish. The dryer consists of a transparent plastic covered flat plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using four d.c. fans, operated by two 40 watt solar modules. This dryer can be used to dry upto 150 kg of fish and three sets of full scale field level drying runs for drying silver jew (Johnius argentatus) fish were conducted in February-March, 1999. The temperature of the drying air at the collector outlet varied from 35.1 ° C to 52.2 ° C during drying. The fish was initially treated with dry salt and stacked for about 16 hours before drying. The salt treated fish was dried to a moisture content of 16.78% (w.b.) from 67% (w.b.) in 5 days of drying in solar tunnel dryer as compared to 5 days of drying in the traditional method for comparable samples to a final moisture content of 32.84%. In addtion, the fish dried in the solar tunnel dryer was completely protected from rain, insects and dust, and the dried fish was a high quality product.     

Optimal Operating Conditions to Produce Nutritious Partially Parboiled Brown Rice in a Humidified Hot Air Fluidized Bed Dryer

V-type amylose–lipid complexes present in partially parboiled rice can decrease starch digestibility. Formation of such complexes can be accomplished using high-temperature fluidized bed drying; the degree of the complexes depends on the thermal condition. The effects of drying media (hot air and humidified hot air), operating conditions (drying air temperature and relative humidity [RH]), and the initial moisture content on the degree of V-type crystallinity and subsequent starch digestibility (or glycemic index, GI) and brown rice texture were examined experimentally. The results showed that paddy drying with humidified hot air (HHA) requires a longer time than hot air (HA). Higher drying air temperature, RH, and initial moisture content of paddy yield higher degrees of starch gelatinization and V-type amylose–lipid complexes. The brown rice dried by HA or HHA had lower starch digestibility and a harder texture than the reference sample. Within the range of parameters studied, to obtain the lowest GI for the dried brown rice, paddy at an initial moisture content of 33% (db) should be dried by HHA at 150°C and 6.4% RH.     

Analysis of Drying Kinetics and Moisture Distribution in Convective Textile Fabric Drying

The drying process of crude cotton fabric is analyzed under two main aspects: analysis of moisture distribution inside the textile sheet, and analysis of certain operational convective drying process variables. Experimental apparatus consisted of a drying chamber in which samples of pure cotton textile were suspended inside the drying chamber and exposed to a convective hot air flow. The influence of the operational variables on the drying process behavior was studied by two different ways with generalized drying curves. The behavior of moisture distribution profiles was compared to average moisture content of the textile fabric verifying whether average values were able to represent the textile moisture content during the drying process.     

Mathematical Model of Fixed-Bed Drying and Strategies for Crumb Rubber Producing STR20

The objectives of this research were to investigate empirical and diffusion models for thin-layer crumb rubber drying for producing STR20 rubber using hot air temperatures of 110–130°C and to study the effect of drying parameters such as inlet drying temperature, volumetric flow rate, and initial moisture content on the quality of dried rubber. Finally, a mathematical drying model for predicting the drying kinetics of crumb rubber was developed using inlet air flow rates of 300–600 m³/min-m³ of crumb rubber (equivalent to 1.8–5.0 m/s) with the crumb rubber thickness fixed at 0.25 m. The average initial moisture content of samples was in the ranges of 40 and 50% dry basis while the desired final moisture content was below 5% dry basis. The results showed that the drying equation of crumb rubber was highly related to the inlet air temperature, while the drying constant value was not proportional to the initial moisture content. Consequently, the experimental data were formulated using nine empirical models and the analytical solution of moisture ratio equation was developed by Fick's law of diffusion. The result showed that the simulated data best fitted the logarithmic model and was in reasonable agreement to the experimental data. The effective diffusion coefficient of crumb rubber was in the range of 1.0 × 10^?9 to 2.15 × 10^?5 m²/s corresponding to drying temperatures between 40 and 150°C, respectively. The effects of air recirculation, inlet drying temperature, initial moisture contents, air flow rate, and drying strategies on specific energy consumption and quality of samples were reported. The experiments were conducted using two different drying strategies as follows: one-stage and two-stage drying conditions. The results showed that initial moisture content and air flow rates significantly affected the specific energy consumption and quality of rubber, while the volumetric air flow rate acted as dominant effect to the specific energy consumption. The simulated results concluded that the percentage of recycled air between 90 and 95% provided the lowest specific energy consumption as compared to the others.     

DRYING RATE AND TEMPERATURE PROFILE FOR SUPERHEATED STEAM VACUUM DRYING AND MOIST AIR DRYING OF SOFTWOOD LUMBER

Two charges of green radiata pine sapwood lumber were dried, either using superheated steam under vacuum (90°C, 0.2 bar abs.) or conventionally using hot moist air (90/60°C). Due to low density of the drying medium under vacuum, the circulation velocity used was 10 m/s for superheated steam drying and 5.0 m/s for moist air drying, and in both cases, the flow was unidirectional. In drying, stack drying rate and wood temperatures were measured to examine the differences between the superheated steam drying and drying using hot moist air.

The experimental results have shown that the stack edge board in superheated steam drying dried faster than in the hot moist air drying. Once again due to the low density of the steam under vacuum, a prolonged maximum temperature drop across load (TDAL) was observed in the superheated steam drying, however, the whole stack dried slower and the final moisture content distribution was more variable than for conventional hot moist air drying. Wood temperatures in superheated steam drying were lower.     

Effect of Four Drying Methods on the Quality of Osmotically Dehydrated Cranberries

Partially dehydrated cranberries (osmotically dehydrated) were dried to low water contents using one of following four methods: hot air drying; microwave-assisted convective drying; freeze-drying; and vacuum drying. Quality evaluation was performed on all samples, including sensory evaluation (appearance and taste), texture, color, water activity, and rehydration ratio. Hot air drying produced dried cranberries with the best visual appearance while freeze-dried cranberries had the highest rehydration ratio. The other methods presented similar rehydration ratios. There was no significant difference in color measurements and water activity. Few differences in texture were found, except for freeze-dried cranberries, which had a lower toughness compared to the other drying methods including commercially available dried cranberries. Microwave-assisted to hot air drying rate ratios increased as the moisture content decreased.     

榴莲蜜变温间歇干燥

新鲜的榴莲蜜舍糖量高,水分多,是一种很容易腐烂的水果。为了能够延长贮存时间必须降低含水量。由于舍糖量高,当用传统的热风干燥进行干燥时,榴莲蜜表面会出现焦糖化。为了克服这个问题,在干燥的开始阶段应用间歇热泵干燥机,在干燥中期应用低温的除湿空气。结果表明：利用循环温度和递升温度干燥的样品湿含量可降低到0．081—0．110（g水／g干物质k此研究中用有限差分法来估算有效扩散系数值,较好地模拟了干燥动力学数据。就产品质量而雷,在循环温度干燥中减少热风干燥时间可生产柔软的干燥产品。而且,低温除湿空气的缓苏作用能减少干燥样品的总体颜色变化。     

Thin-Layer Drying Characteristics and Quality Evaluation of Air-Dried Ganoderma Tsugae Murrill

Ganoderma is normally dried to extend its shelf life without using chemical preservative and to concentrate the medicinal value in the fruiting body. Convective hot air drying characteristics of Ganoderma tsugae Murrill were evaluated in hot air circulated oven at different drying temperatures, sizes, and air flow rates. The drying kinetics of Ganoderma tsugae in kidney shape and slices were investigated and compared at different drying conditions. The variation of effective moisture diffusivity values at decreasing moisture contents during drying was determined from the drying data. Four well-known thin-layer drying models were fitted to the experimental data and the Midilli model was found to satisfactory describe the drying characteristics of kidney-shaped Ganoderma tsugae. Ganoderma tsugae dried at 50°C with air velocity of 1.401 ms^?1 showed the highest retention of crude ganoderic acid content compared to other drying conditions.