A Simple Data Processing Approach for Drying Kinetics Experiments

A simple mathematical approach is proposed to be applied to drying kinetics raw data processing. The data collected in a drying experiment of powder cork under constant air drying conditions served as case study to present the methodology. Two functions (linear and third-degree polynomial) were used to fit solid moisture content in the constant drying rate and the falling rate periods. The drying rate curve was obtained by differentiation and the time at which the drying rate period's transition occurs was determined iteratively until virtually continuous functions were achieved. The critical moisture content was easily identified and two falling drying rate periods were detected.

The powder cork moisture decrease was also used to test several semiempirical models available in the literature. The Logarithmic, Midilli, and Page Modified I models were the ones that revealed the best correlations performance. When the methodology proposed was applied using these models, the critical moisture content was underpredicted.

The effective moisture diffusivity and the activation energy were also obtained for powder cork after the proposed mathematical approach has been applied on the raw data obtained in experiments performed at different air drying temperatures.     

Hygrothermal aging of an adhesive reinforced with microparticles of cork

In the present study, natural microparticles of cork are used with the objective to increase the toughness of a brittle epoxy adhesive. The cork particles act as a crack stopper, leading to more energy absorption. This fact occurs because cork presents a remarkable combination of properties (low density, low cost and sustainability of the raw material). Adhesives are susceptible to the presence of moisture in the environment. There are several studies that refer that moisture can degrade the molecular structure of the adhesive, and, therefore, its mechanical properties. The main objective of this research is to investigate the effect of moisture on the degradation of an adhesive reinforced with micro cork particles, knowing that cork presents a great capability to absorb water. The water absorption and desorption characteristics have been studied, for specimens without cork and with 1% cork, 125–250 μm. The moisture uptake behaviour in the adhesive was studied to obtain the coefficient of moisture diffusion. The effect of water exposure on the mechanical properties and glass transition temperature was also investigated. It was observed that the presence of water alters the mechanical properties of the adhesive (with and without cork), but these changes are not permanent.     

Analysis of the drying process of a biopolymer (poly-hydroxybutyrate) in rotating-pulsed fluidized bed

A rotating-pulsed fluidized bed (RPFB) dryer was employed to conduct the drying of poly-hydroxybutyrate (PHB) cohesive granules. Along the experiments, it was possible to identify, visually, 3 different dynamic regimes that were related with the temperature profile, the drying kinetics and the fluid dynamic behavior. The drying kinetics of PHB showed a short constant drying rate period followed by a decreasing drying rate period. The constant drying rate (N_c) and final moisture content (dry basis) were related to the rotation frequency (responsible for the pulsation effect), temperature and velocity of the inlet air. Furthermore, measurements of molecular mass (gel permeation chromatography analysis) and Carr Index (flowability test) on PHB samples were done before and after the drying. The RPFB dryer showed to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamic behavior that provided uniform drying of the solid. The best conditions of drying were identified at 7 Hz of rotation frequency, 90 °C and 0.55 m/s of inlet air temperature and velocity. At these conditions the dried PHB reached final moisture content of 0.56% (wet basis) after 2 h of drying.     

PROBABILISTIC ANALYSIS AND DESIGN OF THE INDUSTRIAL TIMBER DRYING PROCESS

The distribution in the moisture content of dried planks is an important parameter for kiln operators. The evolution of variability in the moisture content of timber boards during a batch drying process is investigated. This random variability in moisture content arises from a distribution in plank initial moisture content and dispersion in plank drying rate. A simple deterministic model of timber drying is outlined. Theoretical probabilistic analysis is applied to this model to predict the mean and standard deviation in board moisture content as a function of time. The solution is assessed with representative industrial kiln drying data. The utility of the approach in suggesting strategies to promote uniformity in final moisture content is outlined using some design studies. These strategies include sorting of the timber by moisture content and adjusting the drying rate and equilibrium moisture content to reduce variability. It is also demonstrated that the probabilistic approach can yield a better estimation of kiln average moisture content.     

Spouted bed drying of cork stoppers

The spouted bed is commonly used to dry granular particles as it displays some special characteristics which render it capable of performing cyclic operations, with particles that are very difficult to fluidize under a different type of bed.Information on the characteristic drying rates of cork stoppers is still very limited in the technical and scientific literature, and until now no published data was found on the spouted bed drying of cork stoppers.The characterization of the drying performance of Port wine cork stoppers was carried out in a laboratory scale spouted bed. Characteristic drying curves were determined with 29 mm × 21 mm cork stoppers under several operating conditions. Values for the effective diffusivity were obtained in the range of 1.36 × 10⁻⁹ to 4.44 × 10⁻⁹ m²/s, with the temperature dependence represented by an Arrhenius-type relationship. The activation energy obtained was 28.72 kJ/mol.     

Experimental and theoretical investigation of shelled corn drying in a microwave-assisted fluidized bed dryer using Artificial Neural Network

Drying characteristics of shelled corn (Zea mays L) with an initial moisture content of 26% dry basis (db) was studied in a fluidized bed dryer assisted by microwave heating. Four air temperatures (30, 40, 50 and 60 °C) and five microwave powers (180, 360, 540, 720 and 900 W) were studied. Several experiments were conducted to obtain data for sample moisture content versus drying time. The results showed that increasing the drying air temperature resulted in up to 5% decrease in drying time while in the microwave-assisted fluidized bed system, the drying time decreased dramatically up to 50% at a given and corresponding drying air temperature at each microwave energy level. As a result, addition of microwave energy to the fluidized bed drying is recommended to enhance the drying rate of shelled corn. Furthermore, in the present study, the application of Artificial Neural Network (ANN) for predicting the drying time (output parameter for ANN modeling) was investigated. Microwave power, drying air temperature and grain moisture content were considered as input parameters for the model. An ANN model with 170 neurons was selected for studying the influence of transfer functions and training algorithms. The results revealed that a network with the Tansig (hyperbolic tangent sigmoid) transfer function and trainrp (Resilient back propagation) back propagation algorithm made the most accurate predictions for the shelled corn drying system. The effects of uncertainties in output experimental data and ANN prediction values on root mean square error (RMSE) were studied by introducing small random errors within a range of ±5%.     

Optimization of pelletisation and combustion in a boiler of 17.5 kWth for vine shoots and industrial cork residue

Wood pellets have become an important renewable energy fuel. Nowadays the main raw materials used for their production are wood wastes from wood industries. However, these wood wastes have other uses in Spain and it is necessary to look for other possible raw materials. In this work, vine shoots and industrial cork residue were studied as raw materials. The results showed that pelletisation of vine shoots presented a high energy demand. This energy requirement was reduced with the addition of industrial cork residue. Moreover, industrial cork residue decreased the ash content of pellets and increased their heating value, although it decreased their physical properties at the same time. Regarding combustion, the addition of industrial cork residue decreased the accumulation of ash in the pellet burner and its sintering tendency. The major conclusion of the work is that the most appropriate blend to improve pelletisation and combustion processes is 30% wt. of vine shoots and 70% wt. of industrial cork residue.     

Change of mechanical properties related to starch gelatinization and moisture content of rice kernel during fluidized bed drying

Rice fissuring during the drying process is a major problem affecting rice quality. To alleviate this critical issue, it is necessary to understand the change of mechanical properties and the drying kinetics of paddy during drying. The objective of this work is therefore to study the drying characteristics and changes of mechanical properties, i.e., breaking force (F), ultimate tensile strength (UTS), and apparent modulus of elasticity (AMOE) during fluidized bed drying. Suphanburi 1 paddy variety with three initial moisture contents (Mi) of 29.5, 30.2, and 42.8% dry basis was used as the raw material, which was dried at drying air temperatures (Ta) of 110, 130, and 150?°C. A three-point bending method was used for testing the mechanical properties with a texture analyzer. The experimental results showed that the breaking force and the ultimate tensile strength of paddy during drying were more strengthened with higher drying temperatures and higher initial moisture content while its apparent modulus of elasticity was changed only with the moisture content. However, both operating parameters positively affected the apparent modulus of elasticity when evaluated at a 16% dry basis. The maximum changes in F, UTS, and AMOE concerning the initial moisture content were 25.1, 25.2, and 19.5%, respectively. Besides, the maximum changes in F, UTS, and AMOE concerning drying temperatures during drying were 14.2, 14.3, and 13.5%, respectively. The improvement of the mechanical properties could be attributed to the starch gelatinization of which the degree was higher in cases of higher initial moisture content and higher drying temperatures. The empirical models of ultimate tensile strength and apparent modulus of elasticity were developed and related to intermediate moisture content and the degree of starch gelatinization.     

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.     

黑加仑真空冷冻干燥工艺研究

以黑加仑为原料，对其真空冷冻干燥特性和工艺进行了试验研究。结果表明：黑加仑的共晶温度为-24℃，共融温度为-21℃；其合理的工艺参数为：升华温度为50℃，保持4．5h；解吸温度为60℃，保持2h。冻干后的黑加仑含水量为5％左右，能很好保持黑加仑的品质，Vc的保留率为82．6％，花青苷的保留率为57．5％。     

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.     

Soybean Drying by Two-Dimensional Spouted Bed

Urease activity, cracking, and breakage are important factors in considering the quality of raw soybean for feed meal industries. A two-dimensional spouted bed dryer was investigated to determine its capability for thermally inactivating the urease enzyme and maintaining its other qualities. The experimental results have shown that the drying kinetics of soybean in a two-dimensional spouted bed dryer are of the form described in the thin layer drying. The expression for the model parameter in Newton's law of cooling equation accounting for the moisture contents and inlet air temperatures was developed. The initial moisture content and inlet air temperature conditions cause cracks in the kernels. The strong collision between kernels and deflector because of high superficial velocity leads to high percentage of broken soybeans in the spout region. However, the velocity of 15.9 m/s can reduce the breakage below 5%. The inactivation of urease at low-to-moderate moisture content is suitably described by the first order kinetics. The modified Monod equation is applied when the moisture content is higher than 26% dry basis due to the inhibitory effect of water content on the inactivation rate. To complete urease inactivation and maintain protein quality, the temperatures of 150°C should be used.     

Engineering methods to reduce aflatoxin contamination of corn in on-farm bin drying and storage systems

On-farm, in-bin drying of corn is weather dependent process that requires a careful selection of drying strategy in a locality to prevent reduction in the grain quality. This study simulated drying and storage of corn using different fan control methods and assessed the impact of infrared heat treatments to decontaminate corn of harmful molds spores. Fan operation considered included running the fan continuously, only at night (NANO), only during the day (NADO), at a set window of equilibrium moisture content of natural air, and when supplemented with heating of ambient air. The drying was investigated at various initial moisture contents (16 to 22%, wet basis), air flow rates (1.11 to 4.46?m³?min^?1[air] t^?1 [corn]) and corn harvesting start dates (August 15–November 15). To prevent aflatoxin contamination, freshly-harvested corn should be dried within 10 days to MC below 15% if prevailing relative humidity exceeds 86%.     

THIN-LAYER DRYING CHARACTERISTICS OF ROUGH RICE AT LOW AND HIGH TEMPERATURES

Thin-layer drying characteristics of rough rice were determined at temperature ranging from 11.8 to 51 °C and for relative humidities ranging from 37.1% to 91.3%, with initial moisture contents in the range of 24.7 to 41.6% dry basis. An oven, a self contain air conditioning unit, recently developed in Japan, was used for this experiments. With this apparatus, very smooth drying curves were obtained. The data of sample weight, and dry and wet bulb temperatures of the drying air were recorded continuously throughout the drying period for each test. The drying process was terminated when the moisture content change in 24 h was less than 0.2 % d.b. (weight change was less than 0.05 g). The final points were recorded as the dynamic equilibrium moisture contents.

The drying data were than fitted to the Page model. The model gave a very good fit for the moisture content with an average standard error of 0.294 % d.b¨ Both the drying parameters, K and N, are function of drying air temperature and relative humidity. The effect of variable initial moisture content was also described effectively by the empirical Page model. The drying time employed had a large effect on the K and N values. The results presented here, over typically 5 day drying, will be useful in the long term moisture transfer process occurring during ventilated storage.     

Soybean Drying by Two-Dimensional Spouted Bed

Abstract

Urease activity, cracking, and breakage are important factors in considering the quality of raw soybean for feed meal industries. A two-dimensional spouted bed dryer was investigated to determine its capability for thermally inactivating the urease enzyme and maintaining its other qualities. The experimental results have shown that the drying kinetics of soybean in a two-dimensional spouted bed dryer are of the form described in the thin layer drying. The expression for the model parameter in Newton's law of cooling equation accounting for the moisture contents and inlet air temperatures was developed. The initial moisture content and inlet air temperature conditions cause cracks in the kernels. The strong collision between kernels and deflector because of high superficial velocity leads to high percentage of broken soybeans in the spout region. However, the velocity of 15.9 m/s can reduce the breakage below 5%. The inactivation of urease at low-to-moderate moisture content is suitably described by the first order kinetics. The modified Monod equation is applied when the moisture content is higher than 26% dry basis due to the inhibitory effect of water content on the inactivation rate. To complete urease inactivation and maintain protein quality, the temperatures of 150°C should be used.     

COMPARISON OF TIMBER DRYING USING SOLAR ENERGY,ELECTRICAL HEATING AND DEHUMIDIFIER.

ABSTRACT

The performance of three different types of dryers for the hot air drying of sawn-limber planks are compared. These were the electric resistance dryer, solar dryer, and the dehumidifier dryer. Whilst the electric and solar dryers depended only upon hot air for drying, the dehumidifier dryer relied on hot dehumidified air. The results of investigations carried out on timber drying employing these three types of dryers in the Engineering Faculty are compiled and compared here in this paper. The results showed that the electric dryer produced the fastest drying lime and lowest moisture content, followed by dehumidifier drying. The solar dryer achieved a lower moisture content and a faster drying rate compared to natural drying, although the difference in drying times was marginal.     

Germinated Brown Rice Drying by Hot Air Fluidization Technique

Germinated brown rice containing moisture content of 52% dry basis (db) needs to be dried in a reasonable time in order to prevent the growth of microorganisms. Fluidized bed drying is a possible method because this drying technique provides a high mass and heat transfer rate and high-temperature drying can be used. However, such a high-performance dryer may affect the quality of the finished product. The effect of fluidized bed drying temperatures (90, 110, 130, and 150°C) on the quality of germinated brown rice, that is, cooked rice textural property, γ-aminobutyric acid (GABA) level, fissured grain, and microorganisms was therefore investigated. The germinated brown rice was dried to the moisture contents of 18–20% (db), tempered for 30 min, and ventilated by ambient air until the sample moisture content reached 13–15% (db). The experimental results showed that the drying rate increased with increasing drying temperature. The high drying rate, in particular drying at 130°C or higher, caused severe fissuring on the kernel and this fissuring subsequently affected the cooked rice shape and textural property of rice; that is, hardness. The GABA contents of germinated brown rice insignificantly changed with drying temperatures and did not depend on the rice varieties. The populations of attached bacteria, yeast, and mold on the surface of the dried samples were less than 10⁴ colony-forming units (CFU)/g, which is safe for food.     

AN ANALYSIS OF MASS TRANSFER IN AIR-DRYING OF FOODS

A theoretical model for the convective drying of food materials was developed. These materials shrink considerably, as moisture content decreases; for this reason, the proposed model takes shrinkage into account as a fundamental part of the drying operation. This is accomplished by modeling the movement of dry solids and the consequent movement of bound substance during drying. The resulting system of three non-linear partial differential equations is solved numerically and the predicted values of moisture content and temperature are compared with experimental data for the drying of Sultana grapes. The effective moisture diffusivity in the mass of grapes was described by an Arrhenius-type equation. A sensitivity analysis of the predicted values and the examination of the confidence regions of the estimated parameters showed that the activation energy for mass transfer was estimated with a high degree of precision. The agreement between the calculated results and the experimental measurements, using various criteria, was very satisfactory.     

THIN-LAYER DRYING CHARACTERISTICS OF ROUGH RICE AT LOW AND HIGH TEMPERATURES

Abstract

Thin-layer drying characteristics of rough rice were determined at temperature ranging from 11.8 to 51 °C and for relative humidities ranging from 37.1% to 91.3%, with initial moisture contents in the range of 24.7 to 41.6% dry basis. An oven, a self contain air conditioning unit, recently developed in Japan, was used for this experiments. With this apparatus, very smooth drying curves were obtained. The data of sample weight, and dry and wet bulb temperatures of the drying air were recorded continuously throughout the drying period for each test. The drying process was terminated when the moisture content change in 24 h was less than 0.2 % d.b. (weight change was less than 0.05 g). The final points were recorded as the dynamic equilibrium moisture contents.

The drying data were than fitted to the Page model. The model gave a very good fit for the moisture content with an average standard error of 0.294 % d.b? Both the drying parameters, K and N, are function of drying air temperature and relative humidity. The effect of variable initial moisture content was also described effectively by the empirical Page model. The drying time employed had a large effect on the K and N values. The results presented here, over typically 5 day drying, will be useful in the long term moisture transfer process occurring during ventilated storage.     

An Experimental Study of Wheat Drying in Thin Layer and Mathematical Simulation of a Fixed-Bed Convective Dryer

Drying of wheat (Algerian cultivar: Hadba03) in thin layers was studied and mass flux phenomenon was used to characterize the thin-layer drying process. Thin-layer drying of wheat was determined for drying air temperature range of 40–60°C, relative humidity of drying air from 10 to 30%, air velocity of 0.7 m/s, and initial grain moisture from 26 to 31% (dry basis). Equilibrium moisture content of wheat was determined using desorption isotherms obtained from the thin-layer drying data. An equilibrium model for a stationary deep bed with drying air moving vertically upward was developed using mass and energy balance between grain and drying air in the bed and drying air characteristics obtained from thin-layer drying experiments. The developed model was validated by drying wheat in a laboratory dryer using different drying air temperatures and initial moisture contents.