Effects of Four Different Drying Methods on the Quality Characteristics of Peeled Litchis (Litchi chinensis Sonn.)

Four different drying methods, namely, air drying (AD), microwave-assisted vacuum drying (MWVD), coupled microwave–hot air drying (MWAD), and freeze drying (FD), were studied, in terms of drying time, color, reducing sugar content, shrinkage, microstructure, and sensory evaluation. The drying rate of MWVD and MWAD were notably faster than that of AD and FD. The highest reducing sugar content was observed in MWAD, followed by MWVD. No significant differences were observed in reducing sugar between air-dried and freeze-dried products. FD had the best color and shrinkage among the other drying methods. The color and shrinkage of MWVD drying is close to the fresh litchis and much better than hot air and MWAD. Scanning electron microscopy (SEM) images showed that the MWVD and FD litchis have a porous structure, whereas AD and MWAD litchis have a compact structure. The sensory evaluation suggests that peeled litchis dried by the four studied drying methods are of a quality that is accepted by consumers.     

Modeling and Numerical Simulation of Clays Cracking During Drying

During drying or desiccation of clay-type materials, some stresses appear. Usually they are compressional inside of the material and tensional close to the surface. If the tensional stresses exceed the material strength, the clay cracks. This article is devoted to the modeling and numerical simulation of this phenomenon. The proposed model consists of two parts. The mass transfer is described by a simple diffusion equation together with convective boundary conditions. In the mechanical part it is assumed that the clay is composed of small particles linked together by cohesive forces. These forces are described with the use of mesh models. Two models are proposed: elastic (mesh consists of springs) and viscoelastic one (mesh consists of Maxwell elements). Four types of clays were tested experimentally to obtain the model parameters. The tested materials were selected with respect to different mineralogical compositions that determine the water-bonding ability. Simulations of the convective drying of bricks made of these clays were performed. It was shown that the degree of cracking depends on the quartz content of the clay. The obtained results were compared with experimental ones and good agreement between simulations and experiment was obtained. Additionally, the inner forces caused by drying are analyzed and discussed in this work.     

ESTIMATION OF THE EFFECT OF PRODUCT SHRINKAGE ON THE DRYING TIMES,HEAT INPUT AND CONDENSER LOAD OF THE PRIMARY AND SECONDARY DRYING STAGES OF THE LYOPHILIZATION PROCESS IN VIALS

ABSTRACT

The effects of cake shrinkage on the drying times and energy requirements of the primary and secondary drying stages of the freeze drying process involving the drying of a material in a vial, are estimated through the construction and solution of an extended unsteady state and spatially multidimensional model that accounts for the changes introduced by cake shrinkage on the internal and external mass and heat transfer mechanisms of the freeze drying     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

ABSTRACT

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D _e ) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X _o ). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

精密塑料齿轮收缩率对模具型腔尺寸设计的影响

利用Moldflow软件Flow-Shrink模块,研究了精密塑料齿轮不同位置的收缩率,得到指导塑料齿轮模具型腔设计依据。     

14英寸显像管玻壳锥凸模铸造工艺的优化设计

计算机模拟技术为铸造工艺的设计提供了一种能大幅度地节约时间和降低费用生产铸件的途径,也为预测铸造缺陷提供了手段。详细介绍了通过铸造ＣＡＤ技术预测玻壳模具铸造缺陷进而优化工艺方案的方法,提出了运用Ｇ／ＶＣ判据与临界固相率法相结合的方法对缩孔及缩松进行预测。确定了相应的判据临界值。     

熔模铸钢件缩孔(松)的防止

结合生产实例，系统阐述了防止熔模铸钢件缩孔（松）的主要措施：其一是转移，即将缩孔由铸件中转移到浇注补缩系统中；其二是分散，即将缩孔分散成许多细微的缩松。     

球墨铸铁缩孔缩松的铁液冶金因素影响探析

梳理了国内外关于冶金因素对球铁缩孔缩松影响的认知,并列述了一些具有共识的看法和一些具有争议的观点.对球铁碳当量的选择、过冷度的控制,炉料选择等给出了自己的看法,同时阐明了需加强通过提高冶金质量及浇注过程中气体排放等措施来改善球铁的缩孔缩松倾向.     

Effect of pretreatment on surface topographical features of vegetables during drying

It is well recognized that many adverse changes occur to a food product during drying. Various pretreatment methods have thus been introduced to maintain the quality of the product. Among the various qualities, or properties, of a food product surface characteristics are one of the most important as these affect directly the consumer acceptance of the product. In terms of food safety surface characteristics may also be related to the attachment and hence thermal resistance of pathogenic microorganisms on the product surface. In this study attempt was made to investigate changes of the surface topographical features of vegetables as affected by pretreatment (blanching in hot water or soaking in 0.5-1.5% v/v acetic acid solution) and hot air drying (60 °C); cabbage and spring onion were selected as model vegetables to represent different natural topographical features of vegetables. An image analysis technique was used to monitor the changes of vegetable surfaces after pretreatment and during drying. The surface characteristic changes of vegetables were described quantitatively in terms of the relative roughness factor (R). It was observed that the surface characteristic changes, as affected by both pretreatment and drying processes, could be well monitored by the evolution of the R value.     

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Abstract

This work proposes a hypothesis for the interpretation of shrinkage anisotropy during sintering of an Fe–Cu–C alloy based on the effect of the structural modifications of the powder, due to the prior compaction, on the mass transport phenomena. Dislocations are introduced by cold compaction in the contact regions between particles, with different densities along the compaction direction and the transversal one. Therefore, the mass transport by volume diffusion is strongly activated in both directions, and a prevailing effect in the compaction direction is shown. The volume diffusion coefficients derived from the kinetic model correspond to the dislocation pipe diffusion mechanism.