模拟含硼废液喷雾干燥试验

研究了三种喷雾干燥方式处理模拟含硼废液试验的性能和影响因素.三种喷雾干燥方式为:旋转式雾化并流喷雾干燥、气流式雾化并流喷雾干燥和气流式雾化混合流动喷雾干燥.对于硼浓度21 000 ppm(10-6)的模拟含硼废液,在供料温度为62～64 ℃,干燥塔进出口温度分别为210～220 ℃和110～120 ℃,压空流量为8.0 m3/h,雾化器转速为73.0 m/s的条件下,三种喷雾干燥方式均得到了流动性良好的粉体,粉体中占总质量95%的粉体粒径在0.356～0.061 mm之间.三种喷雾干燥方式处理模拟含硼废液的减容系数在0.22～0.27之间,气流式雾化并流喷雾干燥方式、气流式雾化混合流动喷雾干燥方式和旋转式雾化并流喷雾干燥方式的废液处理能力依次增大,所得粉体的含水率依次增大.     

粉煤灰、矿粉对水泥浆体变形性能的影响

以高性能混凝土用胶凝材料为研究对象,研究了粉煤灰、矿粉在不同养护湿度和温度下对水泥浆体变形性能的影响规律.结果表明:饱水养护时,粉煤灰的掺入降低了水泥浆体的水养膨胀变形;养护温度升高、粉煤灰掺量增加,水泥浆体水养膨胀变形降低幅度增大,但不同水养温度下掺入矿粉对水泥浆体膨胀变形无明显影响;密封养护时,掺入粉煤灰可有效抑制...     

新型真空关风器的研制

为实现连续真空干燥,开发了一种真空关风器。这种关风器采用弹性密封技术和复合耐磨、自润滑材料来减少关风器的漏气量。漏气率试验证明,该新型真空关风器达到了颗粒物塔式连续真空干燥设备的性能要求。     

Ceramic shell moulds with zircon filler and colloidal silica binder for investment casting of shrouded low-pressure turbine blades

Zircon (ZrO₂·SiO₂) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.     

Evaluation of the Sorption Equilibrium and Effect of Drying Temperature on the Antioxidant Capacity of the Jaboticaba (Myrciaria cauliflora)

In recent years, interest toward berries has increased (e.g., Myrciaria cauliflora or jaboticaba) because of their high phenolic content (phenolic acids, flavonoids, and anthocyanins) that has been associated with positive effects on consumer health and which play an important role in the antioxidant properties of food. This study analyzed the sorption isotherms, thermodynamic properties of sorption (isosteric heat and Gibbs free energy), and the evolution of the antioxidant capacity during the drying process. The effects of drying temperatures of 40°, 50°C, and 60°C on the antioxidant capacity and thermodynamic properties of sorption were evaluated. The gravimetric static method for sorption isotherm determination over a range of relative humidity levels from 0.10 to 0.90 was used. The sorption isotherms exhibited a Type II behavior, typical for many foods. The Guggenheim, Anderson, and Boer (GAB); Oswin; Peleg; and Lewicki models were used to fit the experimental data, and it was determined that the GAB and Peleg models were most appropriate for describing the sorption curves. The isosteric heat and Gibbs free energy were obtained from the experimental sorption equilibrium. The isosteric heat of adsorption decreased when the moisture content increased, while the Gibbs free energy increased. In addition, the phenolic content and antioxidant capacity increased while drying at 50°C and 60°C, whereas these factors decreased at 40°C. Our results provide the food industry with information concerning the best drying conditions to preserve antioxidant properties.     

管式分酸器在硫酸生产中的使用效果

管式分酸器应用于硫铁矿沸腾焙烧制酸装置,效果显著,与原挂钩槽式分酸器相比,干燥塔出口水份含量从０．４ｇ／ｍ＾３降至０．０８ｇ／ｍ＾３。     

Examining the Suitability of the Reaction Engineering Approach (REA) to Modeling Local Evaporation/Condensation Rates of Materials with Various Thicknesses

The reaction engineering approach (REA) is examined here to investigate its suitability as the local evaporation rate to be used in multiphase drying. For this purpose, REA is first implemented to model the convective drying of materials with various thicknesses. The relative activation energy, as the fingerprint of REA, generated from one size of a material is used to model the convective drying of the same material with different thicknesses. Because the results indicate that REA parameters can model the drying of materials with various thicknesses, REA can be scaled down to describe the local evaporation rate (at the microscale as affected by local composition and temperature). The relative activation energy is used to describe the global drying rate in modeling the local evaporation rate. REA is combined with a system of equations of conservation of heat and mass transfer in order to yield the spatial reaction engineering approach (S-REA) as a nonequilibrium multiphase drying model. By using S-REA, the spatial profiles of moisture content, concentration of water vapor, temperature, and local evaporation rate can be generated, which can assist in comprehending the transport phenomena.     

Kiln-, Solar-, and Air-Drying Behavior of Lumber of Tectona grandis and Gmelina arborea from Fast-Grown Plantations: Moisture Content,Wood Color,and Drying Defects

Tectona grandis and Gmelina arborea are common in commercial reforestation in the tropics. However, color variations, moisture content, and drying defects are also present in dried lumber. Moisture content variations, drying defects, and color changes were evaluated in the present work for three drying methods (kiln, solar, and air drying) during three seasons (dry, rainy, and transition season) in Costa Rica. According to the results, kiln drying had the fastest drying times, regardless of the season. On the other hand, air drying had slower drying time and higher final moisture content. With regard to defects, kiln drying produced the highest number and magnitude of defects in both species, whereas air drying showed the lowest quantity and severity of defects. No variations due to the drying methods or the season were observed in check and split, though solar drying presented intermediate values in all drying defects. The seasons of the year did not present any effect on drying defects. Finally, T. grandis dried lumber is darker than green lumber, and dried G. arborea wood is clearer. In addition, there is an increase in red ( a ^* ) and yellow ( L ^* ) tonalities, and color changes (Δ E ^* ) are considered perceptible or very perceptible in both species. No differences were found among the three drying methods in Δ E ^* , although the season of the year affected dif L ^* and dif C ^* significantly.     

A review of “BOOK REVIEW - DRYING OF SOLIDS” Editor A.S. Mujumdar Published by Sarita Prakashan 175 Nauchandi Ground Meerut City,U.P., India

An industrial-scale prototype of spouted bed dryer with a capacity of around 3500 kg/h was constructed and tested. The prototype is shown to have a desirable feature of a spouted bed as well as the capability of continuous drying and offering consistent results throughout the testing period. Experimental results show that the prototype performs well in reducing the moisture content of the paddy and yields high product quality in terms of the milling quality. The high temperatures up to 130–160°C were applied to dry paddy from various initial moisture contents to the range of 14–25%, dry basis without significant change in quality. Thermal energy consumption, in the range of 3.1–3.8 MJ/kg water, is comparable with other commercial dryers.     

Pore-Level Modeling of Isothermal Drying of Pore Networks Accounting for Evaporation,Viscous Flow,and Shrinking

Abstract

Simulation results of pore-level drying of non-hygroscopic, non-rigid, liquid-wet porous media are presented. Two- and three-dimensional pore networks represent pore spaces. Two kinds of mechanisms are considered: evaporation and hydraulic flow. The process is considered under isothermal conditions. Capillary forces thus dominate over viscous forces and the drying is considered as a modified form of invasion percolation. Liquid in pore corners allows for hydraulic connection throughout the network. During drying, liquid is replaced by vapor by two fundamental mechanisms: evaporation and pressure gradient–driven liquid flow. The development of capillary pressure as menisci turn concave induces shrinkage of the matrix, which contributes to the pressure gradient that drives liquid toward the surface of the network. Using Monte Carlo simulation, we find evaporation and drainage times; the shortest calculated indicates the controlling mechanism. Here we report distributions of liquid and vapor as drying time advances. For the calculation of transport properties, details of pore space and displacement are subsumed in pore conductances. Solving for the pressure field in each phase, vapor and liquid, we find a single effective conductance for each phase as a function of liquid saturation. Along with the effective conductance for the liquid-saturated network, the relative permeability of liquid and diffusivity of vapor are calculated.