A Model for Drying of an Aqueous Lactose Droplet Using the Reaction Engineering Approach

Spray drying is the primary method for manufacturing of food powders from liquids. Optimal design and optimization of spray drying operations at the fundamental level require both modeling of the drying characteristics of a single droplet and dryer wide simulations using computational fluid dynamics (CFD). An accurate yet simple model for drying of a single droplet, which does not require solution of partial differential equation, is ideal input for CFD simulations. The reaction engineering approach (REA) is shown to be appropriate in this regard. It has been successfully used for prediction of skim and whole milk droplet drying behavior under various drying conditions. In this study, an aqueous lactose solution was dried in droplet form and the appropriate REA model parameters obtained. The change of diameter of the droplet during drying was measured experimentally and compared with the model results.     

A Model for Drying of an Aqueous Lactose Droplet Using the Reaction Engineering Approach

Spray drying is the primary method for manufacturing of food powders from liquids. Optimal design and optimization of spray drying operations at the fundamental level require both modeling of the drying characteristics of a single droplet and dryer wide simulations using computational fluid dynamics (CFD). An accurate yet simple model for drying of a single droplet, which does not require solution of partial differential equation, is ideal input for CFD simulations. The reaction engineering approach (REA) is shown to be appropriate in this regard. It has been successfully used for prediction of skim and whole milk droplet drying behavior under various drying conditions. In this study, an aqueous lactose solution was dried in droplet form and the appropriate REA model parameters obtained. The change of diameter of the droplet during drying was measured experimentally and compared with the model results.     

Reaction Engineering Approach (REA) to model the drying kinetics of droplets with different initial sizes—experiments and analyses

Droplets with different initial sizes, which are typical in conventional liquid atomization for spray drying applications, will result in varying drying and crust formation histories. It is essential for any droplet drying model to accurately capture such fundamental phenomena. This study used a newly constructed glass-filament single droplet rig to evaluate the applicability of the Reaction Engineering Approach (REA) in describing such effect. For the three initial sizes (1, 2 and 3 μL) tested, the glass filament gravimetric method clearly distinguished the different drying kinetics and the crust formation phenomenon, delineated by the drying behavior. Analysis from the drying kinetics revealed that the main premise of the REA, which utilizes a material-specific master activation energy curve, is applicable to droplets of different initial sizes at all the three air temperatures tested. This allowed the REA to accurately predict the different temperature and moisture histories given by droplets with different initial sizes. The result supports the REA as a good modeling approach for a wide range of initial droplet conditions. A new master curve approach was proposed to predict the diameter change of droplets with different initial concentrations. Validation with the current and past experimental data revealed that this approach has strong potential to account for the different feed concentrations typically found in spray drying applications.     

Simulating Industrial Spray-Drying Operations Using a Reaction Engineering Approach and a Modified Desorption Method

A predictive tool using a thermodynamic approach has recently been developed to determine several important gas-feed parameters for industrial spray-drying processes. In this approach, a desorption behavior of materials was evaluated and the behavior was linked with overall heat and mass balances over the dryer. Using the desorption behavior of materials and the overall heat and mass balances, a spray-drying software SD²P® was designed at the Institut National de la Recherche Agronomique (INRA) in France. The SD²P® software allows the prediction of optimal inlet drying air temperatures with acceptable accuracy (95–99% accuracy) for spray drying of dairy products. In order to predict detailed quality parameters and stickiness behavior of a product during processing, the reaction engineering approach (REA) was combined with a modified desorption method. A traditional experimental setup is replaced with a new setup, which is described in this article. Drying kinetics parameters were predicted using this new setup. Important gas-feed parameters were predicted using the 1D simulation-based software and compared with SD²P® predictions and are reported here.     

Single Droplet Drying Technique to Study Drying Kinetics Measurement and Particle Functionality: A Review

Advances in the study of the rate processes in spray drying have helped improve product quality. Single droplet drying (SDD) is an established method for monitoring the drying kinetics and morphological changes of an isolated droplet under a controlled drying environment, mimicking the droplet convective drying process in spray drying. To enhance particle quality requires understanding of both the particle formation process and knowledge of how different particle properties are affected by the drying conditions used. The latest development in the SDD technique enables evaluation of these aspects by incorporating a dissolution test in the drying experiment. The experiment is realized by attaching a solvent droplet to a dried/semi-dried single particle in situ and then video-recording the resultant morphological changes. Some of the particle (e.g., crystallinity) properties obtained under different drying conditions can be modelled using the measured droplet drying kinetics. This paper reviews the applications of SDD experiments in measuring the drying kinetics and monitoring the droplet morphological changes during drying. Some examples of extending the glass filament SDD technique to examine particle functionalities are discussed. SDD experiments are shown to be a powerful tool for particle engineering due to its ability to study both the external convective transport process of a single droplet and to understand the different particle functionalities of the resultant single dried particle.     

Sensitivity Analysis of the Reaction Engineering Approach to Modeling Spray Drying of Whey Proteins Concentrate

Whey proteins concentrate (WPC) powder is an important protein source for humans and is commonly produced from whey using a spray-drying technique. Predicting several drying parameters as well as the parameters that govern the quality of the product is essential before manufacturing WPC in industries. Drying kinetics is an essential tool for predicting the drying rate and various parameters that are rate dependent. However, there have been only a few studies published previously on both modeling WPC drying and dryer-wide simulations using different computational tools. In this article we review the application of a reaction engineering approach (REA) to model the droplet drying process. Results based on dryer-wide simulations using the REA are presented. More importantly, a sensitivity analysis of the REA using drying of WPC and skim milk droplets is reported. This analysis will be helpful to select an appropriate drying kinetics model and forms a benchmark for the future WPC drying modeling work.     

Modeling of Drying of Food Materials with Thickness of Several Centimeters by the Reaction Engineering Approach (REA)

Food materials are highly perishable. Drying is necessary to restrict biological and chemical activity to extend shelf life. A good drying model is useful for design of a better dryer, evaluation of dryer performance, prediction of product quality, and optimization. The reaction engineering approach (REA) is a simple-lumped parameter model revealed to be accurate and robust to model drying of various thin layers or small objects. Modeling drying behavior of different sizes is essential for a good drying model, yet it is still very challenging, even for a traditional diffusion-based model, which requires several sets of experiments to generate the diffusivity function. The REA is implemented in this study, for the first time, to model drying of rather thick samples of food materials. An approximate spatial distribution of sample temperature is introduced and combined with the REA to model drying kinetics. Results have indicated that the REA can model both moisture content and temperature profiles. The accuracy and effectiveness of the REA to model drying of thick samples of food materials are revealed in this study. This has extended the application of REA substantially. The application of the REA is currently not restricted for thin layesr or small objects but also for thick samples.     

Three-Dimensional Numerical Investigation of a Mono-Disperse Droplet Spray Dryer: Validation Aspects and Multi-Physics Exploration

Many studies have been carried out on using computational fluid dynamics (CFD) to explore spray-drying phenomena. However, due to the complexity of the drying process in a conventional spray dryer, including the wide droplet size distribution, complicated particle trajectory, and difficulty in taking online measurements, validation of the computational codes or the models remains a challenging task. In this study, experimental conditions employed in a more defined spray-drying condition, published recently on the spray drying of mono-disperse skim milk droplets in a vertical cylindrical chamber, are simulated using ANSYS FLUENT. We have examined the effects of droplet-dispersion patterns on the drying results and found ways to incorporate more practical shrinkage models into the code to make simulations more realistic. Through a comparison with the relevant experimental results on 10～50 wt% skim milk published recently by the same group, we have identified a few areas that urgently need more detailed research. Using the revised sets of codes established here, we simulated skim milk droplets (with a uniform size between 180 μm to 220 μm) spray dried by 90°C to 180°C hot-air streams. The quantitative drying history data predicted by our new model would help ensure better understanding of the system.     

Unraveling the droplet drying characteristics of crystallization‐prone mannitol – experiments and modeling

Spray‐dried mannitol is a potential lactose replacement in pharmaceutical formulations, yet the drying behavior of individual mannitol droplets within the spray chamber has not been fully understood. This work explored the drying characteristics of mannitol by employing the reaction engineering approach (REA) in data analysis. A glass filament single droplet drying technique was used to monitor the changes in droplet temperature, mass, and diameter. The drying kinetics data obtained clearly demonstrated the droplet “wet‐bulb” period, the crust formation, and the crystallization phenomena. The master activation‐energy curves developed from REA modeling responded sensitively to varying drying temperatures, which could have led to different crystallization events. The deviation of these plots from the expected norms that do not encounter a phase change was used effectively to discern the physics involved. A REA kinetic model was proposed to assist in process optimization of large‐scale spray‐drying operations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1839–1852, 2017     

Modeling Intermittent Drying of Wood under Rapidly Varying Temperature and Humidity Conditions with the Lumped Reaction Engineering Approach (L-REA)

For improving product quality and minimizing energy consumption during drying, intermittent drying is often recommended. The mathematical models that are used to describe intermittent drying are usually transport phenomena based, complex models. In this study, the lumped reaction engineering approach (L-REA) is implemented to model wood drying under rapid periodically changed drying air temperature and humidity with high number of cycles of intermittency. The equilibrium activation energy (ΔE _v,b ), an important parameter for REA approach, is evaluated according to the corresponding drying air temperature and humidity in each drying section. The results of modeling suggest the L-REA works well with the experimental data. The simplicity of the L-REA is obvious and is hoped to be used in an industrial setting more readily. The L-REA can be used for sustainable processing in industries to assist in energy audit and management.     

反应动力学贯串的化学反应工程教学思路及教学案例

化学反应工程是一门工程学科.学生在掌握基本概念的同时,需要与实验研究、工程实践相结合,培养分析、解决工程问题的能力.我们基于化学反应工程课程教学,提出了以反应动力学作为主线,贯串化学反应工程的教学思路,同时结合自身科研实践及工程实例,使学生能直观、系统地掌握知识点,为工程实践打下坚实的基础.     

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.     

Roasting of Barley and Coffee Modeled Using the Lumped-Reaction Engineering Approach (L-REA)

Roasting is a complex process of simultaneous heat and mass transfer involving water removal as well as color and flavor changes. In this study, the lumped-reaction engineering approach (L-REA) was implemented to model roasting of barley and coffee. The approach was able to capture the details of the process kinetics and the predictions matched the experimental data well. Benchmarks against the diffusion-based model indicated that the L-REA yielded comparable or even better results. As such, the L-REA approach can be adopted for simulation of the roasting process and optimization or model-based control strategies.     

水污染控制工程生物处理部分教学思路的探讨

本文着眼于环境工程学科的发展历程,本着基本理论与工程实践相结合的原则,立足于传统知识与前沿知识并重的考虑,通过调整"水污染控制工程"生物处理部分的教学思路,改善了知识结构系统性,更新与补充了内容设置,经过教学实践的检验,效果良好.     

Modeling of Drying Curves of Silica Nanofluid Droplets Dried in an Acoustic Levitator Using the Reaction Engineering Approach (REA) Model

The use of nanoparticles has become of great interest in different industrial applications. The spray drying of nanofluids forms nanostructured grains, preserving the nanoparticle properties. In this work, individual droplets of silica nanofluids were dried in an acoustic levitator. Tests were carried out under different experimental conditions to study the influence of the variables on the drying process. The drying curves were experimentally obtained and an REA model was used to obtain the theoretical curves and the correlations for the activation energy. The critical moisture content theoretically obtained was used to predict the grain diameter.     

基于专业群建设缓解高职高专化工专业招生困境的途径

随着社会经济体制改革的不断深入,对化工各种人才需求也日益增加。近些年,苏北高职高专的化工专业面临招生困境,培养学生的数量远远不能满足化工企业对各类化工人才的需求,各高校通过各种途径解决招生困境。本文是基于专业群建设人才培养中的课程改革、社会实践能力的创新、产学研与工学结合的升级、毕业生就业水平的提高等途径来缓解化工专业所面临的招生困境。