STUDY OF LONGAN FLESH DRYING

The objectives of this research were to study the characteristics and quality of longan flesh drying and to develop the models for drying simulations. Finite difference method was applied to solve the drying kinetic equations. Three alternative diffusion models were developed by modifying the Arrhenius factor and/or the energy of activation as a function of moisture content. The results using effective diffusion coefficients obtained from each model were compared. Desorption isotherms were also developed by fitting experimental results to various well-known models. The development and simulation of mathematical drying model of a cabinet dryer were also studied. The effects of drying air temperature and specific air flow rate on specific energy consumption were described. Additionally, the effect of drying air temperature on product quality was investigated by experiment.     

Mathematical Model of Fixed-Bed Drying and Strategies for Crumb Rubber Producing STR20

The objectives of this research were to investigate empirical and diffusion models for thin-layer crumb rubber drying for producing STR20 rubber using hot air temperatures of 110–130°C and to study the effect of drying parameters such as inlet drying temperature, volumetric flow rate, and initial moisture content on the quality of dried rubber. Finally, a mathematical drying model for predicting the drying kinetics of crumb rubber was developed using inlet air flow rates of 300–600 m³/min-m³ of crumb rubber (equivalent to 1.8–5.0 m/s) with the crumb rubber thickness fixed at 0.25 m. The average initial moisture content of samples was in the ranges of 40 and 50% dry basis while the desired final moisture content was below 5% dry basis. The results showed that the drying equation of crumb rubber was highly related to the inlet air temperature, while the drying constant value was not proportional to the initial moisture content. Consequently, the experimental data were formulated using nine empirical models and the analytical solution of moisture ratio equation was developed by Fick's law of diffusion. The result showed that the simulated data best fitted the logarithmic model and was in reasonable agreement to the experimental data. The effective diffusion coefficient of crumb rubber was in the range of 1.0 × 10^?9 to 2.15 × 10^?5 m²/s corresponding to drying temperatures between 40 and 150°C, respectively. The effects of air recirculation, inlet drying temperature, initial moisture contents, air flow rate, and drying strategies on specific energy consumption and quality of samples were reported. The experiments were conducted using two different drying strategies as follows: one-stage and two-stage drying conditions. The results showed that initial moisture content and air flow rates significantly affected the specific energy consumption and quality of rubber, while the volumetric air flow rate acted as dominant effect to the specific energy consumption. The simulated results concluded that the percentage of recycled air between 90 and 95% provided the lowest specific energy consumption as compared to the others.     

OPTIMUM STRATEGY FOR FLUIDIZED BED PADDY DRYING

A feasibility study of paddy drying by fluidization technique was conducted. Operating parameters affecting product quality, drying capacity and energy consumption were investigated. Experimental results showed that drying rate of a paddy kernel was controlled by diffusion. However, drying capacity of a dryer increased with specific air flow rates and drying air temperatures. Energy consumption was reduced when specific air flow rate decreased or when fraction of recycled air increased. Maximum temperature should be limited to 115%C and final moisture content of paddy at 24-25% dry basis if product qualities were maintained. Simulated results obtained from a developed mathematical model indicated that the optimum operating parameters should be as follows : fraction of air recycled of 80%, air velocity of 4.4 m/s, bed thickness of 9.5 cm and specific air flow rate of 0.1 kg/s-kg dry matter. An economic analysis showed that total drying cost was US$ 0.08/kg water evaporated.     

OPTIMUM STRATEGY FOR FLUIDIZED BED PADDY DRYING

Abstract

A feasibility study of paddy drying by fluidization technique was conducted. Operating parameters affecting product quality, drying capacity and energy consumption were investigated. Experimental results showed that drying rate of a paddy kernel was controlled by diffusion. However, drying capacity of a dryer increased with specific air flow rates and drying air temperatures. Energy consumption was reduced when specific air flow rate decreased or when fraction of recycled air increased. Maximum temperature should be limited to 115%C and final moisture content of paddy at 24-25% dry basis if product qualities were maintained. Simulated results obtained from a developed mathematical model indicated that the optimum operating parameters should be as follows : fraction of air recycled of 80%, air velocity of 4.4 m/s, bed thickness of 9.5 cm and specific air flow rate of 0.1 kg/s-kg dry matter. An economic analysis showed that total drying cost was US$ 0.08/kg water evaporated.     

Improvement in the Efficiency and Capacity of Chopped Spring Onion Drying

ABSTRACT

Appropriate strategy for drying chopped spring onion with a batchwise flat bed was investigated. Both experimental and simulated results such as product quality, drying capacity and energy consumption were taken into consideration. For simulation work, equations of drying parameters such as specific heat, equilibrium moisture content and thin layer drying were first developed from the lab-scale experimental results. Then a mathematical model including shrinkage for a batchwix flat bed drying was developed. The model was lested with the results obtained from a food processing plant with an acceptable accuracy. Appropriate drying strategy war then investigated. The approximate conclusion was that the drying should be devided into 3 stages. In the 1^st stage, drying air temperature was 80°C, specific air flow rate was 33.9 m³/min -kg dry matter and drying time was 0.5 h. In the 2nd stage, drying air temperature and drying time were kept unchanged but specific air flow rate was decreased to 13.5 m³/min - kg dry matter. In the final stage, drying air temperature was decreased to 67°C, specific air flow rate was also decreased to 6.8 m³/min - kg dry matter and drying time was approximately 1.7 h. Following the suggested strategy, specific primary energy cornsumption was 6.2 MJ/kg H₂O, drying time was 2.7 h and product quality was maintained. It was proven that energy consumption was approximalcly 70% of that of the present practice in the plant.     

茭白片热风对流干燥模型与传质性能

为了探讨茭白干燥的传递特性,在对流热风干燥实验装置中进行了茭白片薄层干燥实验,研究了干燥温度、片的厚度对干燥过程的影响,将试验的水分比与数学模型进行了拟合,计算了不同温度下的水分扩散系数,并关联了其与干燥温度的关系.结果表明:干燥温度对干燥过程影响显著,薄片有利于水分扩散:用Page模型来描述茭白片热风干燥动力学令人满意;茭白片厚度为0.003m时,随风温升高,水分扩散系数从3.440×10-9 m2·s-1增大到6.357×10-9m2·s-1,并符合阿累尼乌斯方程,活化能为27.86 kj·mol-1.相同温度下,物料中水分的扩散系数基本不受厚度影响.     

Drying and Urease Inactivation Models of Soybean Using Two-dimensional Spouted Bed Technique

The most important factors for examining the quality of soybeans in the animal feed industry are moisture and urease inactivation. Mathematical models for soybean drying and urease inactivation using two-dimensional spouted bed are developed and validated with experimental data. The influences of initial moisture content, inlet air temperature, air recycle on the drying rate, urease inactivation, and energy consumption are also studied. The results revealed that the increase in initial moisture content slightly affected the drying rate and urease inactivation while the inlet air temperature caused a significant effect. To obtain a high drying rate and save energy consumption, the recycle air ratio should be kept in a range of 80–90%.     

Drying and Urease Inactivation Models of Soybean Using Two-dimensional Spouted Bed Technique

The most important factors for examining the quality of soybeans in the animal feed industry are moisture and urease inactivation. Mathematical models for soybean drying and urease inactivation using two-dimensional spouted bed are developed and validated with experimental data. The influences of initial moisture content, inlet air temperature, air recycle on the drying rate, urease inactivation, and energy consumption are also studied. The results revealed that the increase in initial moisture content slightly affected the drying rate and urease inactivation while the inlet air temperature caused a significant effect. To obtain a high drying rate and save energy consumption, the recycle air ratio should be kept in a range of 80-90%.     

DRYING '80 VOLUME 1: DEVELOPMENTS IN DRYING

ABSTRACT

The purpose of this research was to investigate strategies for papaya glacé drying in tunnel. To evaluate the optimum conditions of drying, corresponding mathematical models were also considered. The criteria set for this study included low drying time, low specific energy consumption and acceptable qualities of papaya glace. The results obtained from the model of batch tunnel drying were in good agreement with the experimental ones. From the mathematical models, it was found that the optimum conditions of the first stage of drying of papaya glace (3.1×7.8×1.4 cm) were drying temperature of 70°C, specific air flow rate of 12 kg/h-kg dry papaya glace (velocity of 1.25 m/s) and air recycle ratio of 70%. In the second stage of drying papaya glace (0.98×0.98×0.98 cm), it was found that the optimum drying conditions were: drying air temperature of 55°C, specific air flow rate of 10 kg/h-kg dry papaya glace (velocity of 0.6 m/s) and air recycle ratio of 80%. Ambient air temperature and relative humidity were 30°C and 70% respectively.     

Experimental and Theoretical Investigation of Drying of Carrots in a Fluidized Bed with Energy Carrier

A pilot scale fluidized bed dryer with an inert energy carrier (steel, glass beads ranging from 2.7 to 6.5 mm) was used to investigate the drying of carrots. The effects of sample diameter, inert material type, inert material diameter, amount of inert material, air velocity, and temperature on the rate of drying were studied. A mathematical model was proposed for predicting the drying rate and temperature of drying material. It was found that presence of inert particles enhance the rate of drying. The results of this study also revealed that, although the rate of drying increases with decreasing sample diameter, increasing the inert material thermal conductivity, and increasing air temperature, but the inert material diameter and air velocity have no significant effects on the rate of drying. The independence of rate of drying on air velocity especially in well-fluidized systems indicates that external diffusion is not a controlling step in this process. Also the presence of inert materials causes the drying material to reach more rapidly to its final internal temperature.     

THE EFFECTS OF AIR TEMPERATURE, SPHERE DIAMETER AND PUFFING WITH C02 ON THE DRYING OF POTATO SPHERES

An experimental air dryer was used to investigate the effects of air temperature, sphere diameter and puffing with CO₂ on the drying of potato spheres. Accordingly, the experimental results showed only falling-rate behaviour and hence drying completely controlled by internal mass transfer was interpreted on the basis of Fick's diffusional model for non-steady state diffusion. Drying rate increased with increasing air temperature, and also increased with decreasing diameter of sphere. By considering the diffusion coefficients at different diameters, it was established that the drying occurred by a diffusion mechanism as opposed to a capillary mechanism. It was also found that CO₂ puffing had a positive effect on the drying rate.     

城市污泥与木屑混合薄层干燥实验及动力学分析

角度研究了比,添加木通过对纯污泥和添加木屑的污泥进行薄层干燥对比实验,分别从混合比例、薄层厚度、干燥温度、风速木屑添加对污泥干燥特性的影响,并引入薄层模型对其干燥过程进行模拟。结果表明：与纯污泥干燥相屑后污泥干燥速率明显加快,且木屑添加比例越大、薄层越薄、干燥温度越高干燥速率越快,风速对干燥速率的影响不大;Wang—singh模型能很好的描述两种污泥薄层干燥,利用费克第二扩散定律导出的无限平板公式求出纯污泥和添加木屑的污泥在温度120℃～170℃时的有效扩散系数分别为6．13×10-6m／s～1．11×10-5m／s、1．07×10-5m／s～1．67×10-5m／s;由阿伦尼乌斯方程分别求得活化能为Es=16．67kJ／mol、Es=12．97kJ／mol。     

Constant and Intermittent Drying Characteristics of Olive Cake

The drying kinetics of olive cake, the solid by-product of the olive oil extraction process, has been experimentally investigated in a small-scale tray dryer using both constant and intermittent (on/off) heating schemes. The parameters investigated include inlet air temperature and intermittency of heat input. The drying kinetics was interpreted through two mathematical models, the Page equation and the Lewis equation. The Page equation was most appropriate in describing the drying behavior of olive cake. A diffusion model was used to describe the moisture transfer and the effective diffusion coefficient at each temperature was determined. The dependence of the effective diffusion coefficient on drying temperature can be adequately explained based on an Arrhenius-type relation. The effective diffusion coefficient varied between 7.6 × 10^-8 and 2.5 × 10^-7 m²/min with an activation energy of 38.55 kJ/mol. Comparison of time evolution of material moisture content due to intermittent and constant drying is also made.     

OPTIMIZATION OF OPERATING CONDITIONS IN TUNNEL DRYING OF FOOD

Food drying process in tunnel dryer was modeled from Keey's drying model and experimental drying curve, and optimized in operating conditions consisting of inlet air temperature, air recycle ratio and air flow rate. Radish was chosen as a typical food material to be dried, because it has a typical drying characteristics of food and quality indexes of ascorbic acid destruction and browning in the drying. Stricter quality retention constraint required higher energy consumption in minimizing the objective function of energy consumption under constraints of dried food quality. Optimization results of cocurrent and counter current tunnel drying showed higher inlet air temperature, lower recycle ratio and higher air flow rate with shorter total drying time. Compared with cocurrent operation counter current drying used lower air temperature, lower recycle ratio and lower air flow rate, and appeared to be more efficient in energy usage. Most of consumed energy was analyzed to be used for air heating and then escape from the dryer in form of exhaust air.     

Steady-State Modeling of Multi-Cylinder Dryers in a Corrugating Paper Machine

In this study, a steady-state model was developed to describe the paper drying process and to analyze pocket dryer conditions for a multi-cylinder fluting paper machine in Iran's Mazandaran Wood and Paper Industries. The machine has 35 cylinders grouped in three drying groups and the cylinders are heated from the inside by steam. The model is based on the mass and energy balance relationships written for fiber, air, and water in the drying section. In this research, the heat of sorption and its variations with paper temperature and humidity changes have been taken into account. Temperature and moisture variation of the paper web and cylinder surface temperature in the machine direction were predicted by the proposed model. Also, temperature and humidity of air in the drying pockets and hood exhaust were estimated by the proposed model. Moreover, the model can predict the evaporation rate and specific drying rate with sufficient accuracy in comparison with the TAPPI standard. Finally, the main modeling parameters were compared with the available operating data and the effectiveness of the developed model was verified through validations.     

Application of the reaction engineering approach (REA) for modeling intermittent drying under time-varying humidity and temperature

A ‘good’ drying model is important for the design of dryer, evaluation of dryer performance and prediction of product quality. Among the available models, the reaction engineering approach (REA) is a lumped model, proven to be simple, robust and accurate to model drying of several materials. In this paper, the REA is implemented to model intermittent drying, which is usually practiced for saving energy consumption and maintaining product quality during drying, under time-varying drying air temperature and humidity, which is a challenging drying case to model. For this purpose, the equilibrium activation energy (ΔE_v,b) is defined according to the drying settings in each time period and combined with the relative activation energy (ΔE_v/ΔE_v,b) generated from the convective drying experimental data obtained under constant drying conditions. The mass and heat balances also implement the corresponding drying settings in each time period during the intermittent drying. The results indicate that the REA can describe both the moisture content and temperature profiles of the intermittent drying under time-varying drying air temperature and humidity well. The accuracy, simplicity and robustness of the REA for the intermittent drying under time-varying drying air temperature and humidity are proven here. This has provided a major and significant extension of the REA on modeling challenging drying cases.     

THE EFFECTS OF AIR TEMPERATURE,SPHERE DIAMETER AND PUFFING WITH C02 ON THE DRYING OF POTATO SPHERES

ABSTRACT

An experimental air dryer was used to investigate the effects of air temperature, sphere diameter and puffing with CO₂ on the drying of potato spheres. Accordingly, the experimental results showed only falling-rate behaviour and hence drying completely controlled by internal mass transfer was interpreted on the basis of Fick's diffusional model for non-steady state diffusion. Drying rate increased with increasing air temperature, and also increased with decreasing diameter of sphere. By considering the diffusion coefficients at different diameters, it was established that the drying occurred by a diffusion mechanism as opposed to a capillary mechanism. It was also found that CO₂ puffing had a positive effect on the drying rate.     

PREDICTION OF QUALITY CHANGES DURING OSMO-CONVECTIVE DRYING OF BLUEBERRIES USING NEURAL NETWORK MODELS FOR PROCESS OPTIMIZATION

Artificial neural network (ANN) models were used for predicting quality changes during osmo-convective drying of blueberries for process optimization. Osmotic drying usually involves treatment of fruits in an osmotic solution of predetermined concentration, temperature and time, and generally affects several associated quality factors such as color, texture, rehydration ratio as well as the finish drying time in a subsequent drier (usually air drying). Multi-layer neural network models with 3 inputs (concentration, osmotic temperature and contact time) were developed to predict 5 outputs: air drying time, color, texture, and rehydration ratio as well as a defined comprehensive index. The optimal configuration of neural network model was obtained by varying the main parameters of ANN: transfer function, learning rule, number of neurons and layers, and learning runs. The predictability of ANN models was compared with that of multiple regression models, confirming that ANN models had much better performance than conventional mathematical models. The prediction matrices and corresponding response curves for main processing properties under various osmotic dehydration conditions were used for searching the optimal processing conditions. The results indicated that it is feasible to use ANN for prediction and optimization of osmo-convective drying for blueberries.     

PREDICTION OF QUALITY CHANGES DURING OSMO-CONVECTIVE DRYING OF BLUEBERRIES USING NEURAL NETWORK MODELS FOR PROCESS OPTIMIZATION

Artificial neural network (ANN) models were used for predicting quality changes during osmo-convective drying of blueberries for process optimization. Osmotic drying usually involves treatment of fruits in an osmotic solution of predetermined concentration, temperature and time, and generally affects several associated quality factors such as color, texture, rehydration ratio as well as the finish drying time in a subsequent drier (usually air drying). Multi-layer neural network models with 3 inputs (concentration, osmotic temperature and contact time) were developed to predict 5 outputs: air drying time, color, texture, and rehydration ratio as well as a defined comprehensive index. The optimal configuration of neural network model was obtained by varying the main parameters of ANN: transfer function, learning rule, number of neurons and layers, and learning runs. The predictability of ANN models was compared with that of multiple regression models, confirming that ANN models had much better performance than conventional mathematical models. The prediction matrices and corresponding response curves for main processing properties under various osmotic dehydration conditions were used for searching the optimal processing conditions. The results indicated that it is feasible to use ANN for prediction and optimization of osmo-convective drying for blueberries.