Fluidization Characteristics of Silicon Particles with a Wide Size Distribution

Fluidization characteristics of silicon particle system are studied by the pressure fluctuation method. The existence of fine particles in the system can improve fluidization. Silicon particles with a wide size distribution, preferably with some fines, behave as Group A particles according to Geldart classification, although the system belongs to Group B actually. The system is also approved to be suitable for organochlorosilane monomer production using a fluidized bed reactor. Experimental data obtained in this work are important for the design and operation of commercial fluidized bed reactors for the production of organochlorosilane monomers.     

Influence of Particle Size on Vacuum–Fluidized Bed Drying

The effect of particle size on the vacuum–fluidized bed drying process was experimentally studied using pepper seed particles with two distinct diameters. In the constant drying rate period, the small particles demonstrated stronger drying rates resulting from higher mass transfer coefficient values and larger contact area for per unit particle humidity.

The experimental results also showed that the falling drying rate period was controlled in the beginning by the particle diameter and later by the effective porosity of the particle. Consequently, in the beginning of the falling drying rate period the small particles presented higher drying rates, whereas toward the end of the period, the large particles, with higher effective porosity, produced stronger drying rates than the small ones.

The effects of the vacuum pressure and the superficial gas velocity throughout the process were only observed in the constant drying rate period, whereas the higher operating temperatures enriched the drying rates in both periods.     

Atmospheric Freeze Drying—Modeling and Simulation of a Tunnel Dryer

Drying is an important unit operation in processing of foods and other biotechnological products. Vacuum freeze drying is said to be the best drying technology regarding product quality of the end product, but the disadvantages are, among others, expensive operational costs and batch drying. Atmospheric freeze drying was introduced to lower the production costs of high-quality dried foods, and the need of simulation tools became important in estimations of the industrial drying processes.

A simplified mathematical model (AFDsim) is developed based on uniformly retreating ice front (URIF) considerations. The model is used to calculate theoretical drying curves of atmospheric freeze dried foods in a tunnel dryer. Studies of thermal and mass transfer properties during drying are essential for understanding the changes in product quality and for designing and dimensioning the drying process. The model can be used to simulate industrial atmospheric freeze drying of different foodstuff in a tunnel. The results from AFDsim modeling are in good accordance with the experimental results.     

Drying of Liquid Dispersions—A Unified Approach to Kinetics and Modeling

Abstract

The article presents a unified approach to interpretation of drying kinetics and modeling of the drying process for suspensions, solutions, emulsions and pastes. The approach is based on phenomenological analysis of temperature-moisture relationships T(X) with account for temperature plateaux that actually show-up, or could exist under certain drying conditions. In addition, a unified mathematical model is proposed that includes the differential equations for mass and heat diffusion along with their analytical solutions for a multi-layer plate, cylinder and sphere. Interconnections in the simultaneous heat-mass transfer, cross-effects and any other details of a real process are taken into account separately, by semi-empirical temperature-moisture function T(X). The principles of piece-wise multizone approximation of these temperature-moisture curves are presented. The hyperbolic and two-arc approximations for each separate zone are described. The set of 12 organic and inorganic materials either synthetic or of animal and plant origin such as meat processing sludge, heavy corn steep water, gelatin, starch, sugar, salt, combined latex emulsion, P-salt, gamma acid, dispersing and bleaching agents was taken as example for the development and validation of this approach.     

The Ejffect of Vertical Internal Baffles on Fluidization Hydrodynamics and Grain Drying Characteristics

The effect of vertical internal baffles on the particle mixing and grain drying characteristics in a batch fluidized bed column is investigated. Experimental work was carried out in a 3m high rectangular fluidized bed dryer of cross sectional area of 0.15 m×0.61 m at different operating conditions using paddy, a group D particle, as the fluidizing material. The results of the study showed that the fluidized bed dryer system with vertical internal baffles gave better particle mixing effect in the bed of particles than that without vertical internal baffles. This is due to the fact that the vertical internal baffle act as gas bubble breakers by breaking up the large gas bubbles into smaller ones. The smaller bubbles cause a more vigorous mixing in the bed of particles before finally erupting at the bed surface. This improves the contacting efficiency and enhanced the heat and mass transfer of the fluidized bed system. Thus a higher drying rate was obtained in the falling rate period because the higher con     

The Effect of Graphite Particle Size on Properties of Low Carbon MgO-C Composite Materials

The effects of graphite granularity on the properties of low carbon MgO-C based materials have been investigated in the work. Large crystal fused magnesia, natural flake graphite with different particle sizes and anti-oxidant were adopted as raw material for preparation of specimens. However, the results show that the physical properties oxidation resistance and thermal shock resistance of low carbon MgO-C materials with content of 4.0 wt% graphite are improved obviously through the use of special and suitable size graphite. The excellent performance achieved was considered as a result of microstructure modification of MgO-C materials. Therefore, it is suggested that both fine and micro grade natural flake graphite used for production of low carbon MgO-C bricks.     

Study on the Characteristics of SiO2 Distribution and Silicate Phases in MgO—ZrO2 Composites

This work studied the characteristics of SiO2 distribution and structure of silicate phases in MgO-ZrO2 composites synthesizedby raw materials of light fired magnesite nd zircon,The results indicate that 30 wt%-40wt% SiO2 content in the system is existed in the form of crystalline of forsterite (M2S),the remaindering of SiO content (60wt%0-70wt%) is existed in the glass phase,The chemical composition of glass phase is well agreed with the chemical composition of monticellite(CMS).     

Spray Evaporation of Different Liquids in a Drying Chamber——Effect on Flow,Heat and Mass Transfer Performances

Almost without exception literature data and modeling effort are understandably devoted to water as the sprayed liquid since it constitutes the most common liquid used in spray drying applications. In selected applications, however, the liquid making up the solution or suspension may not be water. The objective of this work is to examine the differences in flow patterns, thermal behavior and drying rates caused by different liquids having different thermo-physical properties spray into a spray dryer using a computational fluid dynamic model. Numerical experiments were carried out for water (base case), ethyl alcohol and isopropyi alcohol-the latter two as model non-aqueous liquids. The chamber geometry was cylinder type with a co-current axial pressure nozzle and also an axial central exit so that the configuration is two dimensional and axi-symmetric. It is shown that the liquid properties can have major influence on the thermal field, droplet trajectories, residence times and overall evaporation capaci     

Effect of the Fuel Type on the Characteristics of Air‐Breathing Engines

Experimental studies of airbreathing engines operating on gaseous and liquid fuels are analyzed. It is shown that, for flight conditions with a Mach number 5 at the ground level, the results on operation and thrust–economic characteristics, which were obtained for hydrogenpowered engines, may be used directly in development of the ducts of hypersonic airbreathing engines operating on liquid organoborn fuels.     

Spray Drying of Aqueous Salbutamol Sulfate Solutions Using the Nano Spray Dryer B-90—The Impact of Process Parameters on Particle Size

In order to prepare spherical salbutamol sulfate particles of adjustable size, a Nano Spray Dryer B-90 was employed. A 3³ full-factorial design was used to investigate the influence of process parameters (mesh size, feed concentration, and drying air temperature) on particle size (median size and width of the particle size distribution), amount of product produced per time, and product yield. The median particle size was significantly influenced by all three factors of the statistical design. Within the design space studied, particle sizes of 1.0 to 6.4 µm were obtained. The width of the particle size distribution (span) increased with increasing mesh sizes. All particles with a particle size greater than 2.4 µm showed a bimodal particle size distribution. Generally, larger mesh sizes as well as higher concentrations led to an increase in the amount of product prepared per time. The corresponding values observed were from 0.4 to 75.8 mg/min. The product yield was independent of the process parameters studied. All products were amorphous after spray drying and were stable up to a relative humidity of 60% at a temperature of 25°C.     

Drying Characteristics and Kinetics of Vacuum Microwave–Dried Potato Slices

Vacuum microwave dehydration characteristics and drying kinetics of potato slices were evaluated using a laboratory-scale dryer. The test materials were placed on a rotating tray to allow uniform exposure to the microwave field. The effect of drying conditions on the drying characteristics was investigated. As expected, higher drying rates were obtained with higher microwave power and lower vacuum levels. The effect of vacuum pressure on drying rate was not as significant as that of microwave power. The Henderson & Pabis model provided better simulation of the drying curves for potato slices. Empirical models are presented for the drying rate constant as a function of the microwave power and vacuum pressure for potato slices under the range of operating conditions tested.     

Effect of Processing Variables on the Solution Characteristics of γ-Glycidoxypropyltrimethoxysilane (γ-GPS)

The effects of the hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy and FT-Raman spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. The production of methanol and loss of methoxy groups in 25% solutions of γ-GPS in water was characterized using Raman spectroscopy. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was complete in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Raman spectroscopy also showed hydrolysis to be rapid and complete in a 25% solution of γ-GPS in water after 1 hour. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In the Raman spectra, condensation was characterized by the disappearance of the SiOH band near 725 cm^?1 and the development of an SiOSi band near 600 cm^?1. In addition to the proton NMR, Si-29 NMR was used to characterize the silane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time. The oligomer growth was correlated with mechanical test results.     

Study on Drying Organic Sludges by Thermal Jet Dryer—Part 1: Drying Performance of Thermal Jet Dryer

The authors are developing a thermal jet dryer (TJD), with a vertical disc-shaped drying tank, for the purpose of weight and volume reduction of solid wastes with high water content, such as organic sludges. In order to obtain the drying performance of TJD, drying experiments using three kinds of solid wastes were carried out. The following results were obtained: (1) Drying performance depended most on the disintegration characteristics of sample. (2) There was little influence of the samples' properties on the gas–solid multiphase flow in the tank. (3) There was a critical feed rate at which the drying performance changed drastically.     

Study on Drying Organic Sludges by Thermal Jet Dryer—Part 2: Characteristics of Air-Particle Multiphase Flow in Thermal Jet Dryer

The authors are developing a thermal jet dryer (TJD) with a vertical disc-shaped drying tank for the purpose of reducing the volume of solid wastes with high water content, such as organic sludges. In order to obtain the characteristics of air-particle multiphase flow in a TJD, cold model experiments and computational fluid dynamics (CFD) simulations were conducted. The following results were obtained: (1) A combined eddy was generated in the tank, such as in a cyclone separator. (2) “Cascading” phenomena occurred in the particle discharging mechanism. (3) In the TJD, particles maintained consistent drying conditions throughout the drying process.     

Effect of Industrial Alumina Powder Particle Size on Preparation of Active α-Al2O3 Micropowder

To study the effect of the particle size of industrial alumina powder on the properties of active alumina micropowder(α-Al2O3 micropowder),the fine powders with...     

Microwave Freeze–Drying Characteristics and Sensory Quality of Instant Vegetable Soup

Instant vegetable soup mix was dehydrated in a microwave freeze dryer to study the drying characteristics and sensory properties of the dried product. The mix was dried at different microwave power levels, material thicknesses, and material loads. As expected, microwave power significantly influenced the total drying time and sensory quality of the final product. The total drying time increased with the increase of material thickness and load. A material layer that is too thin causes the product quality to deteriorate.     

The Effect of Glass Transition Temperature on the Procedure of Microwave–Freeze Drying of Mushrooms (Agaricus bisporus)

Freeze drying (FD) yields the best quality of dried mushroom but at the cost of a long drying time and high overall cost. Air drying (AD) gives an unacceptably poor quality product. To achieve faster drying along with a high-quality product, a microwave–freeze drying (MFD) technique was developed to dry mushrooms. The relationship between dried mushroom quality and the glass transition temperature during the MFD process was studied to optimize the MFD process. According to the change tendency of the glass transition temperature of mushroom during MFD, a step-down microwave loading scheme for the MFD process was developed to obtain good product quality.     

Characteristics of vertical sharp-edged orifice discharge（Ⅲ）Effect of geometry on orifice discharge coefficient

通过实验,分别考察了相同流通截面积下,圆形、椭圆形、正方形、矩形和三角形等不同几何形状的垂直锐边典型“大孔”和“小孔”的自由出流特性。所得孔流系数曲线形态基本相同,孔流系数值略有差异,圆孔最高,三角形最低,说明孔几何形状对孔流能量损失有一定影响,但不是关键结构参数,不会从根本上改变孔流机理。其能量损失差异可根据孔口的水力半径、锐角界面张力以及非圆形孔射流的穿透现象加以解释,藉此对前期的圆孔流动机理进行了补充。此后,为了详细考察孔形状对孔流速度分布和能量损失的影响,采用计算流体力学软件Fluent 6.2对其进行了模拟,模拟流场说明孔形状对孔前流动影响区的主体范围和速度分布基本没有影响,孔前流动的机械能损失仍可采用半球形模型研究,进一步说明不同孔形状的孔流机械能损失差异是入孔以后造成的。