Modeling of Banana Convective Drying by the Drying Characteristic Curve (DCC) Method

Experimental convective drying tests of banana have been carried out for different air conditions to show the influence of air temperature, absolute humidity and speed on the drying rate. The analysis of the drying rate evolution as a function of product water content enables the identification of fourth drying phases: temperature rising (phase 1), exponentially decreasing drying rate (phase 2), linearly decreasing drying rate (phase 3) and very low drying rate (phase 4). The temperature rising phase 1 being very short and the last phase 4 being not reached during typical drying, the drying characteristic curve (DCC) has been represented by two different mathematical functions fitting phases 2 and 3. Their parameters have been determined by minimization of the quadratic errors between experimental and theoretical curves. It leads to a unique curve (the DCC) representing all air drying conditions the integration of which enables the calculation of the product water content with a maximum error of 0.09 between experimental and simulated values.     

Drying of seeds through oscillating infrared heating

Oscillating infrared (IR) drying of onion, white mustard, sweet pepper, and wheat seeds as well as the effect of this drying method on the seeds’ stimulation have been studied. It was found that oscillating IR drying was highly advantageous for onion seeds which possess the lowest germination degree and germination energy. The influence of initial moisture content of the onion seeds, the duration of the oscillating IR drying, and the processing temperature on the stimulation effect have been established. The most favorable stimulation temperature was determined. It was shown that this stimulation effect holds unchanged for at least eight months. A mathematical model for drying kinetics based on the solution of the mass conductivity equation was proposed and the method of the process engineering calculation has been developed and validated for onion and mustard seeds. The necessary experimental data on mass conductivity and concentration equilibrium for onions and mustard seeds have been obtained.     

Review of Wood Drying Research in Brazil: 1984-2004

In Brazil, research on wood drying has been more focused on applied aspects than on fundamentals ones, and results have been published almost exclusively in Brazilian journals. The study of lumber deformation under aggressive drying conditions resulted in methods to group species and to define kiln schedules. Relationship between moisture content and electrical resistivity was used to improve quality control of dried lumber as well automatic control of the kiln drying process. Conventional kiln drying is the most common method for industrial drying, but seasoning and solar drying were also studied. The biggest research effort was directed to improve the drying of eucalypt lumber.     

Low Temperature Peanut Drying Using Liquid Desiccant System Climatic Conditions

Field-dried peanuts having 25% average moisture content have been dried by using a liquid dasiccant drying system. This system cansirts of climate simulation subsystem, closed loop air drying subsystem, and regeneration subsystem. The closed loop drying subsystem used in this investigation provides low temperature drying with a little increase in drying air temperature. Regeneration temperature, liquid desiccant concentration, and air flowrate in the drying subsystem have heen kept unchanged during the experiments, but air of different humidity have been used to regenerate the liquid desiccant. Experimental measurements of the system performance have been carried out utilizing a new cost effective desiccant mixrure (CELD) which is composed of equal portions by weight of lithium chloride and calcium chloride. The drying process has been performed using different climatic canditions in the regeneration process. Experimental rasults demonstrate that drying peanuts by the use of a liquid desiccant system is promising.     

On the Analysis of Drying Process

Drying plays an important role in processing agricultural grains/seeds, chemicals, and other materials. In the present work, drying process has been analyzed taking published data on different grains and seeds such as rapeseed, sunflower, soybean, corn, paddy, and wheat. Mathematical expressions have been established for important drying parameters such as critical moisture content, drying rates, time required to reach critical moisture content, total drying time, and diffusivity as function of drying air temperature. The expressions involve a coefficient parameter and an exponential function of drying air temperature, Aexp(- E/RT_g),and interestingly it is shown that the same functional form with same Es can correlate the different relevant drying parameters. The coefficient parameters As and Es are decided by drying materials and drying process, and the values have been derived for different grains/seeds. The correlations are useful in analyzing the drying process.     

Stress Cracking During High-Intensity Drying and its Effect on Grain Quality

Convective and microwave-assisted thin-layer drying of wheat has been studied to identify the relationship between drying parameters and stress cracks affecting the grain quality. Internal cracks developed during drying were visualized by the soft X-ray photography and quantified by a binary index. Definite effects from drying conditions on stress cracks and further on the grain quality categorized in terms of the germination capacity, sprout length and mechanical strength have been found. This confirms suitability of the X-ray method of cracks detection for selection of optimum drying parameters.     

TESTING THE DRYING PROCESS OF SHELLED MAIZE ON ASPECTS OF NUTRITIONAL QUALITY AND THERMAL EFFICIENCY

Interactions between technology parameters of shelled maize drying and the most important characters of drying material were analysed partly on the basis of the results appeared in written literature also on the basis of the authors' test research not published yet. Theorems describing the most important physical limit of drying were published also the change of nutritional values as a function of drying technology parameters were analysed. Most important laws of different ways of energy transfer also their effect on the process of water removal besides the common ways of drying process simulation, especially considering their applicability within agricultural circumstances were discussed. One part of questions mainly not answered yet - which arise because of the specific parameters of the drying material - have been drawn up. Practically applicable results, on the basis of theoretical research activities also experimental measurements have been shortly presented.     

Mathematical models for the drying of rigid porous materials

This paper presents a resume of literature on theories and mathematical models for drying of rigid porous materials. Key work on drying by soil physicists has been neglected in the engineering drying literature. We have included these works here to bring this literature to the attention of engineers. A new and general model for moisture and energy transport in rigid porous media during drying is presented. It is demonstrated that under certain simplifying assumptions, the general model reduces to less general models which have previously been proposed. Experimental and simulation results are given for the drying of Valentine sand. Under the drying conditions studied, the drying rate during the falling rate period is controlled by the capillary flow of water to an evaporation zone in the porous media. The models simulated here are of varying complexity and rigor. The capabilities and limitations of these models are discussed.     

Experimental and theoretical research on agitated contact drying of sewage sludge in a continuous paddle dryer

Sludge drying is an important intermediate process for sewage sludge treatment, usage, and disposal. A series of drying experiments were conducted in a continuous paddle dryer in order to have a better understanding of the sludge drying mechanism. The couple model of penetration model and Markov chain was used to simulate the drying kinetics in a continuous paddle dryer. The drying process has been compared in experimental and theoretical results, which show good agreement. The sewage sludge drying process in a continuous paddle dryer can be divided into three stages: the pasty phase, the sticky phase, and the complete-granular phase. The influences of the drying parameters on the sludge drying kinetics in a continuous paddle dryer were investigated. The sludge flow rate, dryer wall temperature, and dryer slope have remarkable influence on sludge drying in the examined range, but the stirrer speed and steam temperature have little influence on the drying kinetics.     

Mathematical modelling of solvent drying from a static particle bed

Distributed-parameter models of vacuum contact drying of a static particle bed have been formulated and a numerical solution of the resulting set of partial differential equations describing heat and mass transfer in the particle bed has been carried out. Systematic parametric study of the effect of jacket temperature, head-space pressure, bed depth, and gas- and liquid-phase relative permeability has been performed. Trends observed in vacuum contact drying experiments, namely the independence of drying rate on the mode of driving force realisation (by jacket temperature or head-space pressure), linear scaling of heat-transfer rate with bed depth during the constant-rate period, independence of drying rate on particle size above a certain critical size, and disappearance of the constant-rate period below a certain particle size, have been reproduced by the model both qualitatively and quantitatively. A study of the effect of gas-phase permeability on drying kinetics revealed an interesting phenomenon-a reversal of the direction of drying front propagation. The drying front was found to originate from the heat source (heated walls) for large permeability, and from the mass sink (head-space) for low permeability.     

Low Temperature Peanut Drying Using Liquid Desiccant System Climatic Conditions∗

ABSTRACT

Field-dried peanuts having 25% average moisture content have been dried by using a liquid dasiccant drying system. This system cansirts of climate simulation subsystem, closed loop air drying subsystem, and regeneration subsystem. The closed loop drying subsystem used in this investigation provides low temperature drying with a little increase in drying air temperature. Regeneration temperature, liquid desiccant concentration, and air flowrate in the drying subsystem have heen kept unchanged during the experiments, but air of different humidity have been used to regenerate the liquid desiccant. Experimental measurements of the system performance have been carried out utilizing a new cost effective desiccant mixrure (CELD) which is composed of equal portions by weight of lithium chloride and calcium chloride. The drying process has been performed using different climatic canditions in the regeneration process. Experimental rasults demonstrate that drying peanuts by the use of a liquid desiccant system is promising.     

DRYING TECHNOLOGY AND EQUIPMENT IN INDIA

India produces over 200 million tonnes of food grains annually. There is need of postproduction management system to match with the increasing production rate. Drying is the primary need of crop's postproduction system. Sun drying is a popular mode of crops drying in India. The use of mechanical dryers are almost nil at arm level. With ever-growing population, the food grain production will increase to meet the demand of people. However, the agriculture is taking the shape of industry. Therefore, quality maintenance of the food grain is the primary concern. Thus, the crop drying cannot be dependent on sun drying. A good amount of research and development have been carried out on drying technology during the last two decades. So far very little attention have been given on the development of high capacity dryers, which are presently needed. High capacity dryers are also needed in food processing, chemicals and other industries, which are at growing stage in India. Hence, in nut and shell, there is a big demand for high capacity mechanical dryers and advanced drying technology. This paper presents the status of drying equipment and technology in India and its perspectives in future. To overcome the problems of drying and dryer development, the measures taken by the Government have been also mentioned. Potential of drying equipment business in international and domestic market is also highlighted in this paper.     

TESTING THE DRYING PROCESS OF SHELLED MAIZE ON ASPECTS OF NUTRITIONAL QUALITY AND THERMAL EFFICIENCY

ABSTRACT

Interactions between technology parameters of shelled maize drying and the most important characters of drying material were analysed partly on the basis of the results appeared in written literature also on the basis of the authors' test research not published yet. Theorems describing the most important physical limit of drying were published also the change of nutritional values as a function of drying technology parameters were analysed. Most important laws of different ways of energy transfer also their effect on the process of water removal besides the common ways of drying process simulation, especially considering their applicability within agricultural circumstances were discussed. One part of questions mainly not answered yet - which arise because of the specific parameters of the drying material - have been drawn up. Practically applicable results, on the basis of theoretical research activities also experimental measurements have been shortly presented.     

A composite reaction engineering approach to drying of aqueous droplets containing sucrose,maltodextrin (DE6) and their mixtures

Recently, several studies have been published on the spray drying of sucrose and other low‐molecular‐weight sugars which are typically sticky materials. Sticky materials can not be processed under normal drying conditions and may require addition of high‐molecular‐weight carbohydrates such as maltodextrin. Predicting appropriate drying conditions are however difficult due to the unavailability of drying kinetics. In this article, we have formulated the drying kinetics model using the reaction engineering approach (REA) for the drying of aqueous sucrose and aqueous maltodextrin (DE6) droplets. The relative activation energy was empirically obtained based on experimental measurements. To model the drying of droplets containing both solutes (sucrose and maltodextrin), a new “composite” REA has been established and presented here for the first time. Results demonstrated that the composite REA forms a reliable framework to model the drying of aqueous solutions of pure carbohydrates and their mixtures. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Preparation of Highly Oil-Absorbing Resins Consisting of Hollow Nanoparticle Aggregates by Spray Drying

We report on the preparation of a novel poly(styrene-dodecyl methacrylate) (P(St-DMA)) absorbent resin by spray drying. The microstructures of the prepared resins have been examined by scanning electron microscope (SEM), showing that the resins consisted of hollow micrometer-sized spheres that were aggregated by nanoparticles. Meanwhile, the effects of the content of the cross-linker divinybenzene (DVB) on the oil absorption capacity, the desorption efficiency and the resin microstructures have also been studied. The absorption performance and the hydrophobic properties of the resins prepared by spray drying and vacuum drying have been studied and compared.     

COMBINED SUPERHEATED STEAM AND MICROWAVE DRYING OF SINTERED GLASS BEADS: DRYING RATE CURVES

A new drying method of combined superheated steam and microwave drying is being proposed. The drying rates of sintered glass beads in combined superheated steam and microwave drying are experimentally and theoretically investigated. Drying experiments have been carried out in a waveguide where a standing wave is formed to uniformly heat a small sample. Concerning drying rate curves in combined superheated steam and microwave drying, a distinct constant rate period has been observed. For the falling rate period, high drying rates have been observed. For both periods, the drying rates in combined superheated steam and microwave drying are higher than those in superheated steam alone. Also, in comparison with the results of combined nitrogen and microwave drying, the normalized drying rates in combined superheated steam and microwave drying are higher than those at less than the critical moisture content in combined nitrogen and microwave drying. Moreover, theoretical drying rates for the falling rate period (predicted by a modified receding evaporation front model) in combined superheated steam and microwave drying, are in good agreement with the observed drying rates. The combined superheated steam and microwave drying method can attain higher drying rates under mild external conditions.     

用高露点空气干燥小木块时挥发性有机物的释放

Emission of volatile organic compounds (VOCs) during drying of wood particles for particleboard manufacture, or for production of refined biofuels, is a potential environmental problem. The aim of this work is to study the emissions of VOCs during drying, and the influence on the emissions by different drying parameters. The experiments have mainly been done in a batch fluidized bed dryer, but measurements have also been done in a, pilot scale, continuous fluidized bed dryer. The parameters studied are air flow rate through the bed, air temperature, air dewpoint, and bed height. Since the present trend in biofuels and particle drying is towards very high dewpoints during drying, some measurements have been made at dewpoints up to 95℃, corresponding to a water content of 3.2 kg water per kilogram dry air. The emissions have been measured in two different ways, online during drying with a flame ionization detector and through wood analyses of the terpene content in the wood particles before and after dryi     

催干剂对水性醇酸树脂涂料性能的影响

以水性丙烯酸改性的醇酸树脂为基料配制水性木器涂料,探讨了涂料配方中催干剂的用量及催干剂的种类对水性醇酸涂料储存稳定性、干燥性能和涂膜耐水性等性能的影响。从醇酸树脂氧化成膜过程,分析催干剂对干燥性能的影响。初步解决了水性醇酸涂料催干剂在使用中应注意的问题。     

Vacuum Contact Drying Kinetics: An Experimental Parametric Study

Vacuum contact drying kinetics of a model system consisting of nonporous glass beads and water has been experimentally measured on a laboratory scale. A methodology for determination of drying curves from experimental data in a statistically robust way has been developed. The effects of jacket temperature, head-space pressure, particle bed depth, vessel diameter, and particle size on drying rate during constant and falling rate periods have been studied. It was found that in the range of parameters investigated, drying rate does not depend on the means of realization of the driving force (by temperature or pressure); drying rate in the constant-rate period decreases with increasing bed depth while the overall heat-transfer rate increases due to increased surface area. A very strong dependence of drying rate and regime on particle size was observed; the constant-rate period disappeared for small particles.