天然胶乳胶膜干燥过程及交联结构研究

采用失重法、溶胀法及红外光谱,研究了天然胶乳厚胶膜的干燥动力学过程及干燥过程与橡胶分子链交联密度的关系。结果表明,天然胶乳胶膜的干燥温度和厚度显著影响其干燥过程,通过动力学拟合结果,建立了干燥动力学方程;胶膜干燥开始后,橡胶分子交联密度迅速上升,达到最大交联密度后,交联密度随干燥时间的增加而降低,红外光谱的研究结果也证明了这一规律。干燥过程对天然胶膜的交联结构有明显影响。     

Effect of Outer Surface Sealing Treatment on the Reduction of Surface Check Occurrence During the Drying of Center-Bored Round Timber

A significant amount of time and energy is required to dry green timber with a large cross-section. Due to long-lasting internal moisture gradients, internal stress is high during the drying of large cross-sectional timber, and the potential for check occurrence is significant. Although many researchers have aimed to develop a method for drying large pieces of wood without the occurrence of drying defects, a procedure for rapidly drying wood without cracks has not yet been developed. In the present study, an outer surface sealing method and center-boring process (i.e., drilling a hole along the central longitudinal axis) was developed to dry timber with a large cross-section without the occurrence of checks. The proposed center-boring procedure reduces the movement of heat and moisture inside the wood and expedites the drying process by sustaining a small MC gradient. Moreover, the outer surface sealing treatment changes the drying stress direction and controls check occurrence. By kiln drying center-bored (80-mm diameter) and outer-surface-sealed round timber pitch pine (Pinus rigida) with an initial MC of 30% and an outer diameter of 140 mm, a final MC of 6% was obtained within 40 hours without the occurrence of any drying defects.     

Preparation of Silver Nanopowder by Freeze-Drying Procedure

A freeze-drying procedure is developed for manufacturing silver nanopowder with regular shape and uniform diameter. The procedure includes four steps: preparing the precursor solution, freezing the solution, drying the congelation, and calcining the drying product. The starting substances are silver nitrate and caustic soda and the precursor is diammine silver solution. Three freezing styles including direct freezing, vacuum evaporation freezing, and spray freezing are adopted to freeze the precursor solution. In the drying stage, two heating styles for the frozen solution are compared. X-ray diffraction (XRD) and energy disperse spectroscopy (EDS) spectrograms show that the products of freeze drying are pure amorphous silver nanopowder without hard agglomerations. Silver cubic nanocrystals are subsequently obtained by calcination. The chemical fundamentals and the drying curves of freeze drying are given. The processes of preparing silver nanopowder are described in detail. The effect of freezing and heating on characteristics of the powder are discussed. The mechanism of grain forming and growing up is analyzed according to the observation results. The characteristics of powder freeze drying and its feasibility for volume production are presented.     

Vorgehen bei der Trocknerauswahl

Selection Procedure for Dryers. Many different dryers have been developed in the past because of strongly varying drying behavior and widely changing consistency of the drying products. Therefore, a strategy to select the most appropriate dryer for a given problem is needed in order to minimize the cost of process development. A selection procedure consisting of seven steps is presented in this paper. Applying this procedure, a uniform and reproducible selection is obtained.     

Predictive control with multiobjective optimization: Application to a sludge drying operation

The main objective of this study is to develop an offline tuning of the operating input parameters for a sludge drying operation, by using multiobjective optimization techniques combined with a predictive control method. The manipulated variables concerned are the temperature and the relative humidity of the drying air (T_air, RH_air). The optimal time for the reversal operation of the product is also investigated. The optimization procedure is coupled to a one-dimensional numerical model that allows the simulation of moisture content and temperature field evolutions in the product during the drying step. A genetic algorithm is used to identify the two manipulated variables, at each step time, by minimizing simultaneously three objective functions over a finite horizon. These objective functions are linked to penalties concerning the heating and dehumidifying of the outside air used for the drying stage and to a global moisture content gap relative to a drying target. First, the heat and mass transfer model is validated for the drying step of a plate sample of sludge, with a reversal operation. Afterwards, the optimization procedure is carried out, and the results are discussed in terms of an energetic analysis.     

猪源枯草芽孢杆菌喷雾干燥工艺的优化

目的优化猪源枯草芽孢杆菌喷雾干燥工艺,提高菌体喷雾干燥后的存活率。方法应用SAS V 8.0统计分析软件中的二次正交旋转组合设计方案进行试验设计,分析各因素对Y值的效应关系;应用优化的喷雾干燥工艺进行3次重复喷雾干燥试验,验证预测结果的准确性;并检测芽孢率对菌体喷雾干燥存活率的影响。结果优化的喷雾干燥工艺中各条件的最佳参数为:出口温度90℃,入口温度150℃,保护剂浓度20%,入料速度1 200 ml/h;应用优化的喷雾干燥工艺进行3次重复喷雾干燥试验,菌体平均存活率为75.7%,与预测值(77%)基本相符;芽孢率对菌体喷雾干燥存活率影响较大。结论优化了猪源枯草芽孢杆菌的喷雾干燥工艺,为其工业化生产奠定了基础。     

Model‐Based Energy Efficiency Optimization of a Low‐Temperature Adsorption Dryer

Low‐temperature drying is important for heat‐sensitive products, but at these temperatures conventional convective dryers have low energy efficiencies. To overcome this challenge, an energy efficiency optimization procedure is applied to a zeolite adsorption dryer subject to product quality. The procedure finds a trade‐off between the improved drying capacity due to dehumidification and energy expenditure due to regeneration while incorporating product drying properties. By optimizing the regeneration air inlet temperature, drying air, adsorbent, and regeneration air flow rates as well as sensible and latent heat recovery from the regenerator exhausts, the energy efficiency is improved by up to 45 % compared to the state‐of‐the‐art. The high mass transfer effect of high temperatures is utilized in the regenerator to boost dehumidification while isolating the heat‐sensitive dried product from the quality‐degrading effect.     

An effective rate approach to modeling single‐stage spray drying

An effective rate approach (ERA) is proposed to achieve a fast and reliable prediction of dryer outlet conditions for a given single‐stage spray drying system operated under a range of scenarios. This approach is improved from existing methods based on simple mass and energy balances due to the incorporation of a reliable drying rate model, which is the reaction engineering approach for the material of interest. It allows quick solution procedure without the need to solve the partial differential equations that govern the heat and mass transfer in the spray drying process. By following a generic procedure, this technique has been exercised on the experimental results from running a monodisperse droplet spray dryer, that is, a well‐established experimental platform for model validation. The proposed ERA has been shown to be rather promising. It could become a powerful approach for proactive control and optimization for existing spray drying facilities. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4140–4151, 2015     

Experimental Investigation of the Recovery of Soaked Paper Using Evaporative Freeze Drying

The aim of this article is to develop an experiment and a procedure to investigate the restoration of water-damaged paper and archival materials using freeze drying in order to allow a reproducible test and comparison of the influence of different operating conditions on drying time and restored paper quality. Firstly, a reproducible method for the preparation of soaked samples simulating water-damaged paper has been developed. Then, the samples have been freeze-dried in a laboratory-scale apparatus that allowed monitoring the temperature as well as the weight of the samples. The technique of evaporative freezing, which reduces the drying time required, has been used in this case. An innovative procedure for the visualization of the progress of the drying process has been validated, thus allowing the validation of a simple phenomenological model of the time evolution of the ice core volume; in addition, data on the residual moisture of the dried paper sheets in different zones have been given. Finally, optimization of this particular drying process by using simple or more sophisticated approaches has been discussed.     

A Procedure to Measure the Diffusion Coefficient of Water in Brick as a Function of the Water Concentration

A procedure to measure the diffusion coefficient of water in brick as a function of the water concentration has been proposed, based on a method of measuring the mass of a drying brick at both outer ends. In this method, the brick is subjected to one-dimensional drying. The procedure was tested using a simulation with realistic parameter values and experimental inaccuracies. An experiment consisted of 120 s of drying and measuring the masses every 10 s with an accuracy of 10^?6 kg. The sample was first dried to a lower water content and the drying was stopped for some time to allow the concentration profile to approximate a known equilibrium concentration profile, after which another measurement was performed at that lower water content. Minimizing the differences between the masses, as measured and as it follows from the model, gave the value of the diffusion coefficient. The method failed for low water concentrations.     

番茄粉生产的干燥技术

简要介绍了番茄粉生产的工艺流程,系统讨论了番茄酱的三种非常规喷雾干燥技术特点,并对番茄粉生产的几种组合喷雾干燥工艺流程进行了综合评述。     

片状物料滚筒干燥试验研究

针对片状物料玫瑰花瓣滚筒干燥过程中主要干燥介质温度、湿度和滚筒结构及转速等因素的影响,通过试验,结合滚筒干燥过程中物料动力学分析,考察不同干燥温度(60℃、70℃、80℃)下,滚筒内物料含水率、质量、形态、干燥速率、滚筒内部湿度等方面的变化。试验结果表明,片状物料在滚筒干燥过程中,较高的干燥温度不仅有利于缩短干燥时间,而且也有利于提高干燥品质。     

Anforderungen und Möglichkeiten bei der Verfahrensentwicklung in der Trocknungstechnik Ein Vergleich realisierbarer Vorgehensweisen bei unterschiedlichen experimentellen Möglichkeiten

For many products the drying step exerts a great influence on price and application properties. Therefore great effort should be invested in developing and optimizing drying processes. This paper presents a structured procedure for the development of drying processes. In the case of optimal experimental equipment an “ideal” method of proceeding is indicated. Furthermore it is shwon how to develop and optimize drying processes very successfully with little experimental equipment or even if there is no experimental equipment available. Papers published in this field treat only special aspects or presume optimal experimental equipment. This paper is specially interesting for users with limited experimental equipment.     

Ventilated tunnel solar dryers for small-scale farmers communities: Theoretical and practical aspects

The design of so-called “ventilated tunnel solar dryers" is presented in this work under theoretical and practical aspects. These dryers consist in a tunnel with a black floor and a plastic top, ventilated with fans supplied by a photovoltaic module. Along this tunnel, the air first passes through a heating part, which is product free and where the air is heated due to greenhouse effect. It then enters the second part of the dryer, the drying part, where the products to dry are spread. A rational and general design procedure based on the solving of energy and mass balance equations is developed and followed. This procedure allows designing the ventilation system and calculating the lengths of the heating and the drying parts of a dryer according to a scope statement and to design conditions insuring an efficient and homogeneous drying. Two dryers were designed, built and operated, in the frame of two development aid programs, in Cambodia and in Uganda. The fieldwork highlighted the importance of practical building and operating aspects, reported in the present paper, and of including people of the local communities in these programs. Results of field drying experiments are shown and demonstrate the validity of the design procedure. In particular, the validity of the energy balance equations at the basis of the procedure is demonstrated.     

采用远红外加热技术干燥聚酯切片

介绍了采用远红外线加热干燥含水切片的试验过程,分析了此项技术的可行性。通过试验测试了不同的加热温度、料板距离和干燥时间对干燥后切片含水率的影响。试验结果表明,采用远红外线加热干燥后的切片含水率是可以达到螺杆挤压机纺制聚酯短纤维和熔喷非织造布的工艺条件和技术要求的,从而扩大了远红外线的应用范围。     

SIMULATION OF INFRARED DRYING PROCESS

A control volume formulation for the solution of a set of two-way coupled heat and diffusive moisture transfer equations with an infrared source term is presented in three dimensions. The solution procedure developed uses a fully implicit time stepping scheme for the solution of the coupled set of equations and is applied to study the infrared drying of potato using two different drying systems. The maximum deviation between experimental and simulation results were 9.0°C in temperature for potato drying, and 10% (d.b.) for moisture predictions. The overall predictions agreed well with the available experimental data from the two systems and show a good potential for application in infrared drying of food grains and biomaterials.     

Off-Line Determination of the Optimal Command Policies for a Sludge Drying Application

The main objective of this work is to develop, using a predictive control method, an off-line determination of the operating parameters for a sludge drying stage. At each time step, two operating parameters are identified by simultaneously minimizing three objective functions over a finite horizon. A laboratory dryer is briefly presented and used, in order to evaluate the suitability of the direct model employed to simulate sludge drying. Surface temperature, drying kinetics, and evaporated mass flux obtained from experimental measurements are compared to numerical simulations. Afterward, the optimization procedure is carried out and the results are discussed.     

Reduction of a model for single droplet drying and application to CFD of skim milk spray drying

In this work, a novel methodology for the development of a high-accuracy computational fluid dynamics (CFD) model for the spray-drying process is described. Starting point is an own spatially resolving model of droplet/particle drying, which was developed and validated on the basis of a series of single droplet drying (SDD) experiments. This sophisticated model is transformed to a much simpler version: the characteristic drying curve approach, after running the full SDD model in a wide range of operating conditions. Then, the obtained reduced model is implemented into the CFD solver. The CFD spray-drying model takes into account the hydrodynamics of the continuous phase, particle drying kinetics, changes in the particle diameter, and the heat loss from the drying chamber to the environment. Validation of the entire procedure is provided by data obtained from drying experiments performed in a co-current laboratory spray tower. High accuracy of the developed CFD model of skim milk spray drying has been found for both phases, for the mean outlet temperature of the continuous phase (air) and for the change in average particle moisture content along the spray tower (discrete phase).     

Determination of Moisture Diffusivity by Thermo-Gravimetric Analysis under Non-Isothermal Condition

In drying of solids, the diffusion model based on Fick's second law is usually applied to interpret the moisture migration within the solid. Then the temperature dependence of the moisture diffusivity, generally described by an Arrhenius-type equation, is obtained through the drying kinetics. In this article, a nonisothermal (linearly increasing temperature) procedure was used to determine the moisture diffusivity as a function of temperature with the complex optimization method, and the result was accessed by comparison with a classical isothermal procedure. All the experiments were conducted in a thermogravimetric analyzer (TGA) for accurately recording the mass loss from the sample and easily programming the heating profile.     

SIMULATION OF INFRARED DRYING PROCESS

ABSTRACT

A control volume formulation for the solution of a set of two-way coupled heat and diffusive moisture transfer equations with an infrared source term is presented in three dimensions. The solution procedure developed uses a fully implicit time stepping scheme for the solution of the coupled set of equations and is applied to study the infrared drying of potato using two different drying systems. The maximum deviation between experimental and simulation results were 9.0°C in temperature for potato drying, and 10% (d.b.) for moisture predictions. The overall predictions agreed well with the available experimental data from the two systems and show a good potential for application in infrared drying of food grains and biomaterials.