INFLUENCE OF PROCESS CONDITIONS ON THE DRYING RATE OF CASSAVA CHIPS IN A SOLAR SIMULATOR

Experiments were carried out in a solar simulator to study the influence of air temperature (25-40°C), air relative humidity (40-80%), air velocity (0.95-2.2 m/s), radiation intensity (0-916 W/m²), and loading density (10-30 kg/m²) on the drying rate of a bed of cassava chips (2×2×2 cm). Well-known thin-layer drying equations were fitted to the experimental data, and the empirical constants were used in a statistical analysis of the influence of process conditions on the drying rate. The air temperature, air velocity, radiation intensity, and loading density influenced the drying rate significantly (p=0.05). The effects of the air temperature and the radiation intensity were attributed to the temperature-dependent diffusion of moisture within the chips, while the effect of the air velocity was ascribed to the resistance to mass transfer at the air-chip interface. Equations were presented to express the empirical constants as functions of the process variables.     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

ABSTRACT

Drying kinetic curves and modelling for cassava chips were determined using a pilot-size air dryer. Operating conditions involved temperatures ranging from 35 to 90 ° C, air flow velocities from 0.5 to 2.0 m/ s, and air moisture content from 0.005 to 0.060 kg water/ kg dry air. Sorption isotherms at temperatures of 23, 45 and 60 ° C were obtained. Results for the drying experiments can be used to calculate the optimal drying conditions for dehydration of cassava roots in multilayers     

EXPERIMENTAL STUDY OF CASSAVA SUN DRYING

ABSTRACT

Experiments were carried out in Davis, California, USA to compare sun drying of a bed of cassava chips placed in wire mesh trays with those placed in trays made of sheet metal. The wire mesh permitted wind to blow easily through the bed of chips, while the sheet metal constrained the wind to flow across the top of the bed, Drying was faster in the wire mesh trays; the chips reached a moisture content for safe storage after 27 hours of drying, while those in the sheet metal trays took 35 hours. The uniformity of drying was also markedly better in the wire mesh trays. Higher temperatures were attained in the chips contained in the sheet metal trays due to contact heat transfer between the trays and the chips. However the restricted air flow around the chips in the sheet metal trays led them to dry slower than those in the wire mesh trays.     

THE INFLUENCE OF THE DRYING MEDIUM ON HIGH TEMPERATURE CONVECTIVE DRYING OF SINGLE WOOD CHIPS

High temperature convective drying of single wood chips with air and superheated steam respectively is studied theoretically. The two-dimensional model presented describes the coupled transport of water, vapour, air and heat. Transport mechanisms included are the convection of gas and liquid, intergas as well as bound water diffusion. In the initial part of the drying process, moisture is transported to the surface mainly due to capillary forces in the transversal direction where evaporation occurs, As the surface becomes dry, the drying front moves towards the centre of the particle and an overpressure is simultaneously built up which affects the drying process

The differences between drying in air and steam respectively can be assigned to the physical properties of the drying medium. The period of constant drying rate which does not exist (or is very short) in air drying becomes more significant with decreasing amounts of air in the drying medium and is clearly visible in Dure superheated steam drying. The maximal drying rate is larger in air drying, and shorter drying times are obtained since the heat flux to the wood chip particle increases with increasing amounts of air in the drying medium. The period of falling drying rate can be divided into two parts: in the first, the drying rate is dependent upon the humidity of the drying medium whereas in the second, there is no such correlation.     

THE INFLUENCE OF THE DRYING MEDIUM ON HIGH TEMPERATURE CONVECTIVE DRYING OF SINGLE WOOD CHIPS

ABSTRACT

High temperature convective drying of single wood chips with air and superheated steam respectively is studied theoretically. The two-dimensional model presented describes the coupled transport of water, vapour, air and heat. Transport mechanisms included are the convection of gas and liquid, intergas as well as bound water diffusion. In the initial part of the drying process, moisture is transported to the surface mainly due to capillary forces in the transversal direction where evaporation occurs, As the surface becomes dry, the drying front moves towards the centre of the particle and an overpressure is simultaneously built up which affects the drying process

The differences between drying in air and steam respectively can be assigned to the physical properties of the drying medium. The period of constant drying rate which does not exist (or is very short) in air drying becomes more significant with decreasing amounts of air in the drying medium and is clearly visible in Dure superheated steam drying. The maximal drying rate is larger in air drying, and shorter drying times are obtained since the heat flux to the wood chip particle increases with increasing amounts of air in the drying medium. The period of falling drying rate can be divided into two parts: in the first, the drying rate is dependent upon the humidity of the drying medium whereas in the second, there is no such correlation.     

KINETICS OF DRYING AND HYDRATION OF THE SCLEROGLUCAN POLYMER. A COMPARATIVE STUDY OF TWO CONVENTIONAL DRYING METHODS WITH A NEW DRYING PROCESS: DEHYDRATION BY SUCCESSIVE PRESSURE DROPS

The scleroglucan polysaccharides are mainly used in the petroleum industry but also have applications in the food, cosmetics and pharmaceutical industries. For most of these applications, the dissolution rate of hydrocolloïds is an important qualitative criterion. In this study, the kinetics of scleroglucan drying was investigated with the aim of improving the hydration capacity and the dissolution rate of the polymer. Two conventional methods (hot air and vacuum drying) were compared with a new drying process: dehydration by successive pressure drops, or DDS (Déshydratation par Détentes Successives). This process involves processing the polymer in a series of cycles that consist in placing it in desiccated air then subjecting it to an instantaneous (200 msec) decompression to a vacuum (50 mbar). Two parameters were varied: pressure (P: 4.5–7.5 bars) and processing time at this pressure (t = 5–10 sec). During each decompression, a certain quantity of water is eliminated by vaporisation, improving the diffusion of water by capillary action during hydration. Our results showed that processing time at high-pressure (P) has a significant effect on the drying kinetics. In contrast, processing pressure was not a critical parameter. The results showed that hot air and vacuum drying of scleroglucan are less effective techniques.     

THE INFLUENCE OF COMPRESSION WOOD ON THE DRYING CURVES OF PINUS RADIATA DRIED IN DEHUMIDIFIER CONDITIONS

Measurements of drying rate of Pinus radiata at 55°C and 30% RH are presented. The data, which has been used to establish empirical models for P. radiata under dehumidifier drying conditions, was obtained in four drying runs in a drying tunnel, each yielding detailed drying curves for twelve sample sapwood boards of size 350 × 100 × 50 mm. Compression wood was found to have a significant effect on the drying rate curve, giving lower drying rates at 40-100% MC. This effect is interpreted through the use of a numerical multiple-mechanism two-zone model and quantified by using best-fit diffusion parameters from an isothermal diffusion model. A positive correlation was discovered between the moisture diffusion coefficient and initial moisture content, a strong indicator for the presence of compression wood. In the two-zone model, the compression wood effect was replicated by using a tenfold decrease in permeability to liquid flow. Attributes of compression wood that could cause reduced permeability include an increased proportion of latewood, narrower lumen, and a scarcity of bordered pits on the radial walls of longitudinal tracheids.     

EFFECTS OF OPERATIONAL CONDITIONS ON DRYING CHARACTERISTICS IN CLOSED SUPERHEATED STEAM DRYING

The effects of operational conditions on the drying performance in closed superheated steam drying were examined theoretically and experimentally. The vapor generated from the sample was circulated in the drying chamber. In the theoretical analysis, the replacement of air with vapor in drying chamber and the convective vapor transfer in sample were considered. At the start of drying, the drying chamber was filled with air. As the drying proceeded, the air was replaced with the vapor generated from sample. The calculated results explained the characteristics of experimental data. The pore diameter of sample had little effect on the drying characteristics. During the internal evaporation period, the evaporation occurred in the narrow zone, which moved from the surface to the bottom of sample. The convective vapor transfer in sample had a significant influence on the drying performance. The excess increments in temperature and velocity of drying gas hardly contributed to shortening the drying time.     

EFFECTS OF OPERATIONAL CONDITIONS ON DRYING CHARACTERISTICS IN CLOSED SUPERHEATED STEAM DRYING

The effects of operational conditions on the drying performance in closed superheated steam drying were examined theoretically and experimentally. The vapor generated from the sample was circulated in the drying chamber. In the theoretical analysis, the replacement of air with vapor in drying chamber and the convective vapor transfer in sample were considered. At the start of drying, the drying chamber was filled with air. As the drying proceeded, the air was replaced with the vapor generated from sample. The calculated results explained the characteristics of experimental data. The pore diameter of sample had little effect on the drying characteristics. During the internal evaporation period, the evaporation occurred in the narrow zone, which moved from the surface to the bottom of sample. The convective vapor transfer in sample had a significant influence on the drying performance. The excess increments in temperature and velocity of drying gas hardly contributed to shortening the drying time.     

THE INFLUENCE OF COMPRESSION WOOD ON THE DRYING CURVES OF PINUS RADIATA DRIED IN DEHUMIDIFIER CONDITIONS

ABSTRACT

Measurements of drying rate of Pinus radiata at 55°C and 30% RH are presented. The data, which has been used to establish empirical models for P. radiata under dehumidifier drying conditions, was obtained in four drying runs in a drying tunnel, each yielding detailed drying curves for twelve sample sapwood boards of size 350 × 100 × 50 mm. Compression wood was found to have a significant effect on the drying rate curve, giving lower drying rates at 40–100% MC. This effect is interpreted through the use of a numerical multiple-mechanism two-zone model and quantified by using best-fit diffusion parameters from an isothermal diffusion model. A positive correlation was discovered between the moisture diffusion coefficient and initial moisture content, a strong indicator for the presence of compression wood. In the two-zone model, the compression wood effect was replicated by using a tenfold decrease in permeability to liquid flow. Attributes of compression wood that could cause reduced permeability include an increased proportion of latewood, narrower lumen, and a scarcity of bordered pits on the radial walls of longitudinal tracheids.     

THE INFLUENCE OF DRYING MEDIUM,TEMPERATURE, AND TIME ON THE RELEASE OF MONOTERPENES DURING CONVECTIVE DRYING OF WOOD CHIPS

ABSTRACT

The release of volatile organic components (VOC) during the drying of wood chips was studied experimentally. The drying medium was hot dry air with a pressure of 1 bar and velocity of 1 m/s. Four different temperature levels of the drying medium, i.e., 120, 140, 160 and 180°C, and two different materials, Scots Pine and Norway Spruce, were investigated. It was found that the main components released consist of various types of monoterpenes, with α-pinene dominating in each of the two materials. The amount released is time-dependent, showing a maximum at shorter times. The release rate is more intensive at higher drying temperatures. The mass-balance for α-pinene was checked by comparing the amount present in the wood chip before and after drying with the amount obtained by integrating the release curve. A good agreement was obtained. Environmental Scanning Electron Microscope pictures were taken of both the spruce and pine chip in order to investigate differences in the wood structure before and after drying with air at 160°C. No obvious structural change could, however, be observed. The influence of the drying medium on the release rate of monoterpenes (air and superheated steam) was also studied. The results showed that the release rate was faster when drying with superheated steam.     

STACK-WIDE EFFECTS IN THE MODELING OF SOLAR KILNS FOR DRYING TIMBER

This study examines the stack-wide effects due to the humidification and cooling of air as it passes through a 6 m wide stack of Australian ironbark timber for conditions that are representative of those for solar drying (dry and wet-bulb temperatures of 60 and 50°C, respectively). A solar kiln model for a greenhouse-type design has been modified to account for the drying of timber boards and the possibility of stack-wide effects, in terms of moisture-content differences in the streamwise direction of air flow through the stack. The maximum difference between the moisture contents of the leading and trailing boards is predicted to be 0.011 kg kg^-1 for these conditions, compared with timber moisture contents of 0.15-0.35 kg kg^-1. Hence, the stack-wide effect is insignificant for these conditions in this greenhouse kiln design and may be ignored, reducing the simulation time by over 50%. In addition, 14 elements within a finite-difference model for the drying of the timber boards (25 mm thick) gives predictions of the drying time that are acceptably accurate, while minimizing the computational time.     

THE INFLUENCE OF CONSTANT AND VARIABLE CONDITIONS ON THE DRYING KINETICS OF APPLES

Abstract

The purpose of this work was to examine the influence of constant and variable temperatures or velocities on apples' drying kinetics. The step changes of temperature influenced forcefully on apples1 temperature in all situations. The drying curves -6f apples showed the influence of air's temperature as well velocity on the water content. The largest difference between the apple drying curves and absolute value of drying rate are obtained after introducing step changes or rectangle impulses of air's temperature or velocity at the beginning of the process.     

AN ANALYTICAL SOLUTION OF THE GRANULAR PRODUCT IN DEEP-BED FALLING RATE DRYING PROCESS

Abstract

According to analysis of drying characteristics of granular product, the paper describes analytical solutions on a single grain with two falling rale drying stages during corresponding period of deep-bed drying process. Changes of drying and physical parameters and their correlation were discussed. A mathematical model was developed and solved numerically. The application of this analytical solution is also given.     

食品冷冻干燥过程的模型及影响因素

在合理简化的基础上,得到了只需较少参数的冷冻干燥过程一维数学模型。通过对胡萝卜和土豆食品的冷冻干燥实验,研究了加热方式、加热搁板温度和干燥室真空度对干燥时间的影响,模型的数值解与实验值吻合良好。     

DEVELOPMENT AND VALIDATION OF A PROCESS SIMULATOR FOR DRYING SUBBITUMINOUS COAL

Drying subbituminous coal has never been practiced commercially. The commercial dryers built to date have been designed for drying surface moisture in conjunction with upstream coal preparation facilities. This type of drying is mainly controlled by input energy and the basis of the design is an energy balance. In drying inherent moisture from subbituminous coal, the thermal conductivity of the coal and the diffusion of molecular water within coal particles impose limitations on the process conditions. Energy input and solids residence time in the dryer have to be controlled properly for simultaneously balancing the heat and mass transfer within the coal particles. Improper control of either parameter can cause fires and explosions during the key steps of the drying process—drying and cooling

In parallel to the Anaconda coal drying pilot plant program, a cross-flow, fluid-bed coal drying/cooling process simulator was developed for: (1) understanding the drying phenomena on an individual particle basis; (2) analyzing potential risks and safety limits, and (3) designing the Anaconda pilot plant program

The development of the process simulator was based on both first principles and laboratory data and can be divided into two phases:

1 Development of a semi-mechanistic drying model for Powder River Basin subbituminous coal employing an analytical solution of the diffusion equation

2.Formulation of a fluid-bed cross-bed cross-flow dryer/cooler simulator employing simultaneous heat and mass transfer

This model was validated against process variables data taken on a 4 tph pilot plant. An operable range, or process envelope, has been developed through the pilot plant experience and the process simulation study. Based on the model predictions, an uncertainly range was defined in the design recommendations of a pioneer coal drying plant in scale-up.     

SINGLE-LAYER DRYING BEHAVIOR OF MEXICAN TEA LEAVES (CHENOPODIUM AMBROSIOIDES) IN A CONVECTIVE SOLAR DRYER AND MATHEMATICAL MODELING

Single-layer solar drying experiments were conducted for Mexican tea leaves (Chenopodium ambrosioides) grown in Marrakech. An indirect forced convection solar dryer was used in drying the Mexican tea leaves at different conditions such as ambient air temperature (21° to 35°C), drying air temperature (45° to 60°C) with relative humidity (29 to 53%), airflow rate (0.0277 to 0.0556 m ³/s), and solar radiation (150–920 W/m²). The experimental drying curves showed only a falling rate period. In order to select the suitable form of drying curves, 14 mathematical models were applied to the experimental data and compared according to their statistical parameters. The main factor in controlling the drying rate was found to be the temperature. The drying rate equation was determined empirically from the characteristic drying curve. The diffusion coefficient of the Chenopodium ambrosioides leaves was estimated and varied between 1.0209 × 10^?9 and 1.0440 × 10^?8 m ²·s^?1.The activation energy was found to be 89.1486 kJ·mol^?1.     

THE RELATIVE INFLUENCE OF DIELECTRIC AND OTHER DRYING TECHNIQUES ON THE PHYSICO - MECHANICAL PROPERTIES OF A PHARMACEUTICAL TABLET EXCIPIENT. PARTI: COMPACTION CHARACTERISTICS.

The relative Influence of nine techniques for drying wet granulated microcrystal-lline cellulose (MCC) on the subsequent compaction characteristics was studied In terms of the tensile strength and corrected work of failure of the tablets. Wet granulation resulted in a substantial decrease in compatibility. However, the drying technique used was found to affect the degree of loss in compatibility. In general, microwave-vacuum drying using the “high” process type resulted in the production of granules with the highest compatibility followed by freeze drying and fluidized bed drying. Granules dried under ambient conditions, and granules tray dried to “just dry” or “over dried” conditions resulted In tablets possessing approximately comparable compatibilites, with the poorest compaction characteristics being exhibited by vacuum dried granules, in addition It was found that use of a “low” drying process type during microwave- vacuum drying yielded granules with inferior compaction characteristics to those dried by the “high” process type. Radio frequency drying was found to yield granules which produced tablets having slightly inferior tensile strength to tray dried material, although the tablet work of failure values were comparable. The effect of drying technique on the subsequent compaction characteristics was not found to be directly related to the moisture content of the granules.     

RELATIONSHIP BETWEEN A SOLAR DRYING MODEL OF RED PEPPER AND THE KINETICS OF PURE WATER EVAPORATION (I)

ABSTRACT

Drying of red pepper under solar radiation was investigated, and a simple model related to water evaporation was developed. Drying experiments at constant laboratory conditions were undertaken where solar radiation was simulated by a 1000 W lamp.

In this first part of the work, water evaporation under radiation is studied and laboratory experiments are presented with two objectives: to verify Penman's model of evaporation under radiation, and to validate the laboratory experiments. Modifying Penman's model of evaporation by introducing two drying conductances as a function of water content, allows the development of a drying model under Eolar radiation.

In the second part of this paper, the model is validated by applying it to red pepper open air solar drying experiments.     

型煤干燥过程的研究

对型煤的干燥过程进行了分析, 通过实验对型煤水分和干燥时间的关系进行了探讨, 并建立了干燥数学模型, 以期对实际生产提供帮助。