Modeling of baking of thin layer of cake using the lumped reaction engineering approach (L-REA)

Baking is a simultaneous heat and mass transfer process commonly applied in the food industry. It is desirable to have a simple, accurate and robust model in order to assist efficient process design and evaluation of product quality. The reaction engineering approach which was proven to be accurate to model several challenging drying cases, was implemented in this study to model the baking of thin layer of cake. The equilibrium activation energy (ΔE_v,b) was evaluated according to the baking oven temperature and corresponding humidity. It was then combined with the relative activation energy (ΔE_v/ΔE_v,b) to produce a unique relationship. Results of the modeling indicate that the L-REA can describe the profiles of moisture content and temperature very well. While the results are accurate, the model itself remains simple. Another significant application of the REA for modeling the processing of food products has been made by this research.     

The Relative Activation Energy of Food Materials: Important Parameters to Describe Drying Kinetics

An effective drying model should be accurate and require a small number of experiments to generate the parameters. The relative activation energy of various food materials, important drying kinetic properties used in the reaction engineering approach, is evaluated and summarized. The reaction engineering approach is then implemented to model the global and local drying rates of food materials. By using the relative activation energy, the reaction engineering approach describes the (R² higher than 0.99) global drying rate of food materials well. The reaction engineering approach can be coupled with a set of equations of conservation of heat and mass transfer to model the local drying rate of food materials. The relative activation energy is indeed proven to be accurate to model the local drying rate. While the predictions are accurate, the reaction engineering approach is very effective in generating the drying parameters since the relative activation energy can be generated from one accurate drying run. Different drying conditions of the same material with similar initial moisture content would result in the similar relative activation energies. The drying kinetics parameters generated here are readily used for design of new equipment, evaluating the performance of existing dryers, and monitoring the product quality.     

An accurate account of mass loss during cheese ripening described using the reaction engineering approach (REA)‐based model

Cheese ripening is an important step in cheese making for modifying surface and curd properties. Due to physical, chemical and biological changes, mass loss usually occurs during the process. Although these changes are essential for developing the texture and flavour of cheese, mass loss decreases product yields. A reliable mathematical model is used to quantify mass loss during cheese ripening so that the processing conditions can be fine‐tuned to achieve the desirable throughput. In this study, for the first time, the reaction engineering approach (REA)‐based model is applied to model the cheese ripening. The study shows that the REA‐based model is accurate to model cheese ripening of Camembert and French smear cheese. In addition, the REA is able to model the cheese ripening under time‐varying environmental conditions. For this purpose, the equilibrium activation energy is evaluated according to the corresponding humidity and temperature in each period, while the same relative activation energy for ripening under constant environmental conditions is implemented. The REA is a simple yet effective approach to model the simultaneous heat and mass transfer process accompanied by chemical and biological reactions. Considering its effectiveness, the REA can be applied in industrial settings for predicting mass loss during cheese ripening.     

DRYING of COFFEE BERRIES IN A VIBRATED TRAY DRYER OPERATED WITH SOLIDS RECYCLE and SINGLE‐STAGE1

A vibrated tray dryer was tested for drying coffee berries. It consists of a vertical chamber (0.33 m × 0.18 m × 1.30 m) provided with four trays. the trays are supported by a vibrated shaft. Experimental tests were carried out at a vibration amplitude of 1 mm and at a variable frequency. the process itself consisted of feeding the vibrated tray dryer with an initial mass of coffee berries: after leaving the dryer through the discharge channel, the berries were fed again to the top of the dryer by a bucket elevator (intermittent operation with recycle of the coffee berries). Drying tests were carried out with drying air velocity of 2.4 m/s. the drying air control temperature was related with the temperature of the coffee berries at the discharge (under 45C). the drying time required for coffee berries to reach 12.6% (wb) moisture was 28 h, initial mass (moisture of 67% wb) was 5.54 kg. In this work the influence of vibration in single‐stage drying is also shown. the single‐stage operation shows that vibration (besides promoting the conveyance of coffee berries) also reduces the time of drying.     

PREDICTION OF SPRAY-DRIED PRODUCT QUALITY USING TWO SIMPLE DRYING KINETICS MODELS

Increasing attention has been given to spray drying because of its popularity in the manufacturing of various powders with prerequisite quality. A large number of theoretical and experimental studies have been published during the last five decades to study spray‐drying operations. Despite this progress, there is still lack of information on the selection of an accurate and simple drying kinetics model to characterize the droplet drying process. This article has particularly focused on the comparison of two simple and effective drying kinetics models: the characteristic drying‐rate curve and reaction‐engineering approach (REA) models. This article reported mathematical models that can be used to design the spray‐drying operation and to predict the particle's characteristics for realistic dryer‐wide situations. Both the physical and biochemical quality attributes were investigated regarding their sensitivity to the model parameters used in the two drying kinetics models. The REA model was found to deliver more realistic predictions during the modeling of the droplet drying process for all the sets of conditions tested.     

Effect of continuous and intermittent ultrasound on drying time and effective diffusivity during convective drying of apple and red bell pepper

A new approach of ultrasound-assisted convective drying was tested in this study using a screen as product support and sound transmitting surface. Red bell pepper and apple cubes were dried at 70 °C in a laboratory scale hot-air drying oven. In addition to continuous ultrasound used for both products, intermittent ultrasound was applied for apple drying reducing net sonication time to 50% and 10%. Significant improvements of drying characteristics were observed for continuous sonication and intermittent ultrasound at 50% net sonication time. Experimental data were fitted with eight models, among which the Midilli model resulted in the best fit with R² > 0.9988 and reduced χ² ? 0.0002. The influence of ultrasound on drying time to reach 20% and 30% residual moisture content as well as on effective moisture diffusivities and drying periods is discussed.     

Dehydration characteristics of Maesaengi (Capsosiphon fulvescens) in hot-air drying

Maesaengi (Capsosiphon fulvescens) was dehydrated in a single layer at drying air temperatures ranging from 50–80°C in a laboratory scale convective dryer with an air velocity of 0.26 m/s. The effect of drying air temperature on the drying kinetic characteristics was determined. Maesaengi was dried to equilibrium moisture content within 200–600 min under these drying conditions. Drying rate curves of maesaengi showed an initial short period of a constant drying rate, followed by a falling drying rate period. The moisture decrease in the sample during dehydration was well described by the zero-order kinetic model. An Arrhenius-type equation was used to test the effect of temperature on drying rate according to an activation energy value of 29.36 kJ/mol.     

Experimental investigation of drying behaviour and conditions of pumpkin slices via a cyclone‐type dryer

This paper describes an experimental investigation of the drying behaviour and conditions of pumpkin slices via a convective cyclone‐type dryer. Drying experiments were conducted at air inlet temperatures of 60, 70 and 80 °C and air velocities of 1 and 1.5 m s^?1. Samples of 200 g of cylindrical pumpkin slices (thickness 5 mm × diameter 35 mm) were arranged in a single layer on each of two trays. The least squares method was applied to derive the drying curve equation of samples. During the experiments the following parameters were measured: weight loss, temperature, relative moisture and velocity. From these parameters, dimensionless mass loss, moisture content, mass shrinkage and drying rate of samples were calculated and are discussed in detail. Additionally, the transport of water during dehydration was described by the diffusion mechanism, and Fick's equation was used for evaluation of the experimental data. The linear sections of drying curves were analysed by linear regression to obtain the moisture diffusivities. It was found that pumpkin slices would dry perfectly within 340–720 min under these drying conditions. The convective cyclone dryer could also be used to dry other products. Thus it is expected that this new dryer will help farmers and producers to reduce the cost of drying. Copyright © 2003 Society of Chemical Industry     

5HDH35多级混流式谷物烘干机的设计与应用

详细介绍了５ＨＤＨ３５多级混流式大型谷物烘干机的设计计算，并对应用效果进行了总结分析，该机烘干玉米的一些性降水幅度可达１８％以上，日出干粮为２００ｔ以上，烘干水稻的爆腰率增值为２．７％，能够较好的保证烘后粮食的品质。     

Application of simulation in determining suitable operating parameters for industrial scale fluidized bed dryer during drying of high impurity moist paddy

A systematic approach has been developed for selecting the suitable drying parameters to be used for drying of high moisture and high impurity paddy with an industrial fluidized bed paddy dryer (10–20 t h⁻¹ capacity) based on targeted specific air flow rate and residence time during two typical paddy drying seasons. A mathematical model was developed by modifying an existing model and was simulated and validated with observed industrial drying data as well as data reported in the literature. Comparison between the observed and simulated results showed that the mathematical model is capable of predicting outlet paddy moisture content and air temperature well. Suitable operating parameters were determined for reducing any initial paddy moisture content (mc) down to 24–25% dry basis (db), the safe mc level after fluidized bed drying to maintain rice quality, to achieve maximum possible throughput capacity of the dryer with corresponding energy consumption. Based on these criteria, bed thickness at 10 cm, specific air flow rate of 0.05 kg kg⁻¹ s⁻¹ (for corresponding bed air velocity of 2.3 m s⁻¹), air temperature of 150 °C and residence time of 1.0 min were found to be suitable drying conditions for reducing paddy mc from 30 to 24.30% (db) in one season while the maximum throughput capacity of 15.7 tonne per hour (t h⁻¹) might be achieved. The specific electrical and thermal energy were 0.48 and 6.15 MJ kg⁻¹ water evaporated, respectively. On the other hand, the dryer capacity was found to be limited to 7.4 t h⁻¹ during drying paddy of higher initial mc (35% db). This approach might provide easy and comprehensive guidelines for selecting suitable sets of operating parameters for any industrial fluidized bed dryer at its possible maximum throughput capacity for drying of freshly harvested high moist paddy with a high level of impurities.     

Monte Carlo simulation of the collective behavior of food particles in pneumatic drying operation

Although most of the time drying operation aims at controlling the mean batch behavior, the quality of the final product is often related to the individual behavior of the supplied materials in a batch. The mean batch models provide limited information for quality evaluation studies. Since the initial physical and thermal properties of rice powder in a batch influence the final condition of product dried with a pneumatic dryer, a Monte Carlo simulation with initial random parameters is useful to investigate the individual behavior of rice particle during pneumatic drying. In this study, we analyzed the influence of initial moisture content and particle diameter of rice powder on the conditions of the final product in pneumatic drying process. Samples of initial moisture content and particle diameter distributions were generated by means of the covariance decomposition algorithm and Monte Carlo simulations with 5000 runs based on momentum, energy and mass balances between drying air and rice particles were performed to obtain the profiles of the response variables, rice powder temperature, moisture content and particle diameter, in a pneumatic dryer. The developed pneumatic conveying drying (PCD) model could describe the complex behavior of rice particles in a batch.     

基于工艺流程的纸机干燥部建模与模拟

基于三段通汽式干燥部工艺流程,在“输入已知、输出未知”和“先烘缸、再通风、后纸张”的原则指导下,以烘缸组为最小建模单元,根据序贯模块法的基本思路,构建了纸机干燥部的静态模型。以某新闻纸机干燥部为对象进行模拟,给出了进出各模块的物流和能流信息,模拟结果与该纸机实际运行情况基本一致。该模型符合纸机干燥部工艺流程,可以用来模拟各模块之间的物流和能流信息,便于为干燥部用能分析提供依据。     

Industrial paddy drying and energy saving options

Paddy drying is an energy-intensive process and influences rice quality. In this study, the energy consumption of paddy drying in a large-scale milling plant was investigated. Furthermore, some drying experiments were conducted in a laboratory. The aims were to gain practical information and to propose more economical drying options to the industry. The results indicated that the current drying in the plant consumed specific primary energy of between 3.874 and 4.421 MJ/kg of water evaporated. The experimental results showed that two-stage drying with tempering by using a fluidised bed dryer at 100–110 °C in the first stage and drying with ambient air using a solar dryer for the second stage provided rice quality that was comparable to that of the plant. Also, from the calculation, the energy cost of the plant could be reduced if an in-store dryer was used after the first-stage drying by LSU dryer.     

Modeling and minimizing process time of combined convective and vacuum drying of mushrooms and parsley

The aim of this work was to obtain a technological and economic alternative for mushroom and parsley dehydration combining convective and vacuum drying. Depending of product, this combination of technologies allows minimization of total drying time and avoids negative effects on quality of thermo-sensitive products during drying. Experimental drying curves were determined in a cross-flow convective dryer and in a cabinet vacuum dryer at 35, 45 and 55 °C. The most appropriate theoretical models were obtained and applied for combined processes in order to minimize the overall drying time and avoid final product damage. For parsley at the highest temperature (45 °C), reductions of 63% and 16% in drying time were observed with the combined drying process compared to the sole convective and sole vacuum drying, respectively. This reduction in process time was obtained when dryer change was done at the intermediate moisture condition that determines the highest drying rate during the whole combined process of convective and vacuum drying. For mushrooms, convective drying throughout the process, at the highest temperature (55 °C) compatible with product visual quality, minimized drying time.     

Comparison of performances of pulsed and conventional fluidised-bed dryers

Consumption of energy, outlet moisture content and quality of the dried commodity are important parameters of paddy-dryer performance. The fluidised-bed paddy-dryer has been commercialised for several years and in this paper, paddy drying by pulsed and conventional fluidised-bed dryers are compared. Experimental results have shown that the variation of moisture content at the exits of both dryer types in test runs was very small. Heat utilisation was more effective when such dryers were used to dry paddy at moisture contents above 24% dry basis and up to 50% of the thermal energy was saved by recycling 70–80% of the air. Paddy qualities i.e. head-rice yield and colour of the dried white rice were similar with both dryers and almost the same as the original undried values, or slightly higher in the case of head-rice yield, depending upon the drying conditions. Below 28% dry basis, it is recommended that inlet-air temperature should be lower than 145 °C in order to maintain white colour. The cooked rice obtained from paddy dried at a temperature of 145 °C was harder than naturally dried control samples. A mathematical model based on energy and mass balance predicted values in good agreement with experimental results for both the pulsed and conventional fluidised-bed dryers. Calculated thermal and electrical energy consumptions indicated that the pulsed flow dryer was more economical than the conventional dryer.     

稻谷薄层热风干燥工艺优化及数学模型拟合

对稻谷进行薄层热风干燥,采用正交试验方法研究稻谷在不同热风温度、初始含水率和热风风速条件下的热风干燥特性,比较10种数学模型在稻谷热风干燥中的适用性。结果表明:稻谷在热风干燥过程中没有出现明显的恒速干燥阶段,且干燥主要发生在降速干燥阶段;热风温度是影响稻谷热风干燥的最主要因素,其次是初始含水率;取初始含水率20%、热风温度50℃、热风风速1.4 m/s的方案为稻谷的最优热风干燥工艺,此时的最佳数学模型为Page模型;缓苏可有效抑制稻谷的爆腰率,缓苏温度越高,缓苏时间越长,缓苏效果越好;当初始含水率24%、热风温度40℃时,实验值和模型值的相对平均误差分别为1.563%和1.474%,表明模型预测的干燥曲线和实验所得的干燥曲线一致性较好;随着热风温度的升高,稻谷的有效水分扩散系数变大,经热风温度从40℃升高到60℃,其有效水分扩散系数由9.69×10~(-10) m~2/s增加到10.77×10~(-10) m~2/s,稻谷的干燥活化能为47.1 k J/mol。     

稻谷薄层红外干燥特性及数学模型

采用正交实验对稻谷进行红外干燥,研究了稻谷在不同含水率、干燥温度和装载量干燥条件下的红外干燥特性,确定了稻谷最优红外干燥工艺方案,匹配了稻谷红外干燥在10种干燥数学模型中的应用情况,找出了稻谷最优红外干燥数学模型,结果表明：稻谷在干燥前期失水率变化较大,水分比下降较快,而干燥后期,失水率变化趋于平缓。对稻谷红外干燥工艺影响的3个主要因子排列顺序为：干燥温度B>装载量C>含水率A,且稻谷最优红外干燥方案为含水率36%、干燥温度60℃、装载量50 g,此时的稻谷最优干燥数学模型为Wang and Singh模型。当装载量和温度分别为50 g和70℃时,实验值和模型值的相对平均误差分别为0.901%和1.119%,进一步验证数据的实验值和模型值拟合度较好。随着干燥温度的升高,稻谷的有效水分扩散系数升高,当干燥温度从50℃提升到70℃时,稻谷有效水分扩散系数从10.72×10^-10 m²/s增加至13.87×10^-10 m²/s,此时稻谷的活化能为11.9 kJ/mol。     

Determination of convective heat transfer coefficient and specific energy consumption of potato using an ingenious self tracking solar dryer

In the present work, an attempt has been made to experimentally determine the heat transfer properties of potato in terms of convective heat transfer coefficient, specific energy consumption and specific heating rate. Drying experiments with potato cylinders have been performed in an in-house fabricated laboratory scale natural convection indirect solar dryer with self tracking mechanism. The convective heat transfer coefficient of cylindrical potato samples was evaluated by considering the combined effects of heat capacities of food product as well as radiative heat transfer from drying chamber to the food product. This study revealed that the convective heat transfer coefficient for potato cylinders was varying from 11.73 to 16.23 W/m² °C with an experimental error of 7.86 %. The specific energy consumption was decreasing exponentially with drying time, and the average value was estimated to be 3,491 kJ/kg. It was also observed that the specific heating rate for potato cylinders decrease with dimensionless moisture content.     

MODELING and EXPERIMENTAL STUDY ON DRYING of APPLE SLICES IN A CONVECTIVE CYCLONE DRYER

The main objective pursued in this paper is to experimentally investigate the single layer drying behavior of apple slices in a convective type cyclone dryer and also to perform the mathematical modeling by using single layer drying models in literature. the experiments were conducted at drying air temperatures of 60, 70 and 80C in drying air velocities of 1 and 1.5 m/s. It was concluded that apple slices with the thickness of 12.5 mm would perfectly dry in the ranges of 280–540 mm while those with the thickness of 8 mm would dry in the ranges of 180–320 min in these drying conditions by using convective type cyclone dryer. Additionally, the mathematical model describing the single layer drying curves was determined by nonlinear regression analysis, and the logarithmic model was selected as the most suitable model to obtain the drying curve equation of apple slices. Considering the parameters such as drying time, drying rate, moisture transfer, velocity and drying air temperature it is suggested that the apple slices be dried at the above optimum processing conditions.     

Development of Mobile Dryer for Freshly Harvested Paddy

Presently, due to an increase in usage of large scale mechanical threshers and combine harvesters, moisture content of freshly harvested paddy is being high as much as 18-24%. The mechanical threshers or combine harvesters with elevated capacity enable for both harvesting and threshing at once. Thus the paddy harvested all over persists with high moisture content that affects adversely in unit operations of paddy processing such as cleaning, storing, and milling. The research was conducted to overcome this problem by developing a mobile paddy dryer that can be used at field level for freshly harvested paddy. A mobile dryer, one ton capacity, was developed and tested for drying freshly harvested paddy. The performance of the mobile dryer was evaluated in terms of overall thermal efficiency, heat utilization factor, coefficient of performance, total heat efficiency and head rice yields. The overall thermal efficiency of this dryer was 46.83%. The average heating efficiencies namely heat utilization factor and total heat efficiency were 0.82 and 0.72 respectively. The coefficient of performance of the developed dryer was 0.18. The head rice yields of freshly harvested paddy after drying at 60 °C air temperature was of 73.78%. The overall drying performance of the dryer was found to be good.