EXPERIMENTAL STUDY OF CASSAVA SUN DRYING

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.     

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

ABSTRACT

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.     

THIN LAYER SOLAR DRYING OF SOME VEGETABLES

In this study, a solar cabinet dryer consisting of a solar air heater and a drying cabinet, was used in drying experiments. Pumpkin, green pepper, stuffed pepper, green bean, and onion were dried in thin layers. Three different drying air velocities were applied to the process of drying to determine their effects on drying time. Fresh materials were dried by a natural sun drying method. In order to explain drying curves of these products different moisture ratio models were performed and evaluated based on their determination coefficients (R²). Our results revealed that drying air temperature could increase up to about 46°C. Drying air velocity had an important effect on drying process. Drying time changed between 30.29 and 90.43 hours for different vegetables by the solar drying. This drying time was between 48.59 and 121.81 hours for the natural sun drying. Drying curves could be explained by determined thin layer drying models satisfactorily with very high determination coeffcients.     

THIN LAYER SOLAR DRYING OF SOME VEGETABLES

In this study, a solar cabinet dryer consisting of a solar air heater and a drying cabinet, was used in drying experiments. Pumpkin, green pepper, stuffed pepper, green bean, and onion were dried in thin layers. Three different drying air velocities were applied to the process of drying to determine their effects on drying time. Fresh materials were dried by a natural sun drying method. In order to explain drying curves of these products different moisture ratio models were performed and evaluated based on their determination coefficients (R²). Our results revealed that drying air temperature could increase up to about 46°C. Drying air velocity had an important effect on drying process. Drying time changed between 30.29 and 90.43 hours for different vegetables by the solar drying. This drying time was between 48.59 and 121.81 hours for the natural sun drying. Drying curves could be explained by determined thin layer drying models satisfactorily with very high determination coeffcients.     

EXPERIMENTAL STUDY OF SORPTION ISOTHERMS AND DRYING KINETICS OF MOROCCAN EUCALYPTUS GLOBULUS

ABSTRACT

The paper deals with sorption isotherms and drying kinetics of Eucalyptus globulus. The sorption isotherms have been determined using a static gravimetric method and then fitted by GAB equation at T = 30, 40, and 50°C over a range of relative humidity from 0.05 to 0.9. The drying kinetics in a solar dryer with an auxiliary heating system are determined. The results show with good reproducibility that temperature is the main factor in controlling the drying rate. The drying rate equation is determined empirically from the characteristic curve of drying.     

EXPERIMENTAL STUDY OF SORPTION ISOTHERMS AND DRYING KINETICS OF MOROCCAN EUCALYPTUS GLOBULUS

The paper deals with sorption isotherms and drying kinetics of Eucalyptus globulus. The sorption isotherms have been determined using a static gravimetric method and then fitted by GAB equation at T = 30, 40, and 50°C over a range of relative humidity from 0.05 to 0.9. The drying kinetics in a solar dryer with an auxiliary heating system are determined. The results show with good reproducibility that temperature is the main factor in controlling the drying rate. The drying rate equation is determined empirically from the characteristic curve of drying.     

ANALYSIS OF OPEN SUN DRYING EXPERIMENTS

Open sun drying has lost its previous importance due to the fact that different factors affect its reliability and the quality of the products obtained.

One of the set-backs for the analysis of solar drying exoeriments is their deoendence on a non-controlled source of energy, i.e. solar radiation depends on climatic conditions and experiments are difficult to compare. It is thus necessary to investigate the advantages of a particular set up as well as the climatic influences. Open sun drying could constitute the natural reference, allowing the comparison of different drying strategies.

A new way of standardizing drying times, based on solar radiation inout, is proposed, to allow better evaluation of the experiments. An equivalent time is defined, allowing comparison of experiments carried out under different circumstances. Carrots and potatoes were used in these experiments.

The use of the average daily solar radiation 15.28 MJ m^-2.d^-1 in Palma de Mallorca (39.33°N, 2.37°E), is proposed for comparison purposes. An improvement of more than 12 % in the explained variance was observed, the unexplained variance being lower than 1 %.     

ANALYSIS OF OPEN SUN DRYING EXPERIMENTS

ABSTRACT

Open sun drying has lost its previous importance due to the fact that different factors affect its reliability and the quality of the products obtained.

One of the set–backs for the analysis of solar drying exoeriments is their deoendence on a non–controlled source of energy, i.e. solar radiation depends on climatic conditions and experiments are difficult to compare. It is thus necessary to investigate the advantages of a particular set up as well as the climatic influences. Open sun drying could constitute the natural reference, allowing the comparison of different drying strategies.

A new way of standardizing drying times, based on solar radiation inout, is proposed, to allow better evaluation of the experiments. An equivalent time is defined, allowing comparison of experiments carried out under different circumstances. Carrots and potatoes were used in these experiments.

The use of the average daily solar radiation 15.28 MJ m^-2.d^-1 in Palma de Mallorca (39.33°N, 2.37°E), is proposed for comparison purposes. An improvement of more than 12 % in the explained variance was observed, the unexplained variance being lower than 1 %.     

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 THERMO-IMAGE EXPERIMENTAL STUDY FOR THE OPTIMIZATION OF SEEDS DRYING

Abstract

Using the method of combining the two subjects of engineering thermophysics and physiology, this paper carried out the thermo-image experiments of drying Chinese cabbage seeds at both dynamic and static states in the infrared radiation vibrofluidized dryer that was made by us. Meanwhile the seed physiology experiments were also conducted. The results show that the critical drying temperature of seeds is the function of their drying time and moisture content. It is higher when the initial moisture is lower, or the drying time is shorter. This provided the theoretical basis for the optimization of heat and mass transfer of seeds drying.     

THE THERMO-IMAGE EXPERIMENTAL STUDY FOR THE OPTIMIZATION OF SEEDS DRYING

Using the method of combining the two subjects of engineering thermophysics and physiology, this paper carried out the thermo-image experiments of drying Chinese cabbage seeds at both dynamic and static states in the infrared radiation vibrofluidized dryer that was made by us. Meanwhile the seed physiology experiments were also conducted. The results show that the critical drying temperature of seeds is the function of their drying time and moisture content. It is higher when the initial moisture is lower, or the drying time is shorter. This provided the theoretical basis for the optimization of heat and mass transfer of seeds drying.     

蒙东褐煤干燥特性实验研究

研究了蒙东地区两种不同煤化程度褐煤的干燥过程,并对干燥至不同程度的褐煤进行分析.在干燥过程中不同煤化程度褐煤干燥速率变化趋势较为一致,煤化程度对干燥速率有一定的影响.煤化程度较低的乌拉盖褐煤其平均干燥速率较高,达到最大干燥速率的时间点较早.干燥过程改变了褐煤的微观结构,干燥后水分较低的褐煤其比表面积与原煤相比有所增加.随着干燥后水分的不断降低,褐煤中的含氧官能团表现为先减少后增加的趋势.与宝日希勒褐煤相比,乌拉盖褐煤中含氧官能团开始增加的时间点较早,更容易被氧化.     

喷雾干燥节能技术研究

通过从喷雾干燥所涉及的操作工艺参数和喷雾干燥工艺流程调整等方面进行探索 ,深入研究了影响喷雾干燥能耗的主要因素和相应的结果 ,并提出了针对性的解决喷雾干燥能耗高的方法 ,使得采用喷雾干燥达到理想的效果     

微波干燥对炼焦煤煤质影响的实验研究

通过选取不同炼焦煤的特征指标,对微波干燥前后这些特征指标的分析比较,探索微波干燥技术对炼焦煤煤质的影响.结果表明,微波干燥技术在去除炼焦煤水分的同时,对炼焦煤的工业分析和黏结指数无明显影响;对基氏流动度和奥亚膨胀度存在正影响,但不明显;对胶质体影响较大,特别是其过程行为.因此微波干燥技术对炼焦煤煤质无较大影响,如果存在影响,也是有利于改善炼焦煤煤质的.     

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 THE DRYING OF A THICK LAYER OF NATURAL CRUMB RUBBER

ABSTRACT

An experimental study describing the mechanisms of drying of a thick layer of natural crumb rubber is presented. The evolution of the ternventure profiles of the crumb and profiles of temperature and relative humidity of intergranular air and water content of crumb arc presented. These evolutions enable understanding of the internal mechanisms involved and lead to practical recommendations for the management of industrial driers.     

STUDY OF THIN-LAYER DRYING OF GRAPE WASTES

The effect of drying temperature on grape wastes, the solid wastes of the wine and raki production processes, was investigated in a cabinet dryer. Drying experiments were performed three air temperatures of 70°, 90,° and 110°C, at constant air velocity of 1.2 m/s, and initial thickness of 1.8 cm for grape marc and 2.0 cm for grape pulp. Experimental data were fitted to Henderson and Pabis, Page, and logarithmic models, respectively. The performance of these models is evaluated by comparing coefficient of determination and reduced chi-square between the observed and predicted moisture ratios. The statistical analysis concluded that the best model was the logarithmic model. The effective moisture diffusivity varied from 8.55 × 10^?10 to 3.32 × 10^?9 m²/s over the temperature range. Temperature dependence of the diffusivity was well documented by an Arrhenius-type relationship. The activation energies for grape marc and grape pulp were calculated as 25.41 and 13.74 kJ/mol, respectively.     

干燥对褐煤爆炸危险性的实验研究

为探究干燥前后褐煤的爆炸危险性,基于粉尘爆炸机理,通过粒度分析和爆炸性测定实验,分析了干燥前后褐煤粒径分布变化、扬尘特性及爆炸危险性变化.结果表明,干燥褐煤大粒径颗粒频数减小,小粒径颗粒频数增加,粒径变小,扬尘量增加;干燥褐煤最小点燃能量、粉尘云/层最低着火温度较干燥前褐煤都有所降低.干燥褐煤较原煤更易扬尘达到爆炸极限浓度,且更易发生着火燃烧爆炸,干燥褐煤爆炸敏感性和危险性都增加.     

单颗粒褐煤高温烟气干燥过程实验研究

针对10mm~25mm粒径的大唐五间房褐煤,通过单颗粒高温烟气干燥实验,得到了600℃~900℃烟气温度下的干燥特性曲线,研究了干燥介质温度和粒径对褐煤高温脱水效果的影响,发现干燥过程主要处于降速干燥阶段;高温条件下,温度对干燥速率的影响并不显著;针对褐煤水分在干燥过程中的迁移特点以及大唐五间房褐煤的孔隙特征,基于努森扩散定律,建立了水分蒸发为蒸汽再扩散出煤粒的缩核干燥动力学模型;得到了不同温度下的有效水分扩散系数,并利用Arrhenius公式求出了10mm~25mm粒径下的干燥活化能.     

EXPERIMENTAL RESEARCH ON DRYING CHARACTERISTICS OF LITCHI

Abstract

The changes of inner temperature and drying characteristics of rind, membrane, flesh and stone of Litchi were investigated under constant relative humidity of drying medium at different temperatures at atmospheric and decompression conditions. Results show that the membrane resists moisture from moving the flesh or stone to rind. Decompression drying is helpful to the moisture evaporation of the fruit; when the moisture content lowers to a certain critical point, the drying rate is higher than that of atmospheric drying. Drying curves are very different from those of seeds drying or particle drying. In the drying process, temperature of Litchi whole fruit rises quickly at the beginning to a maximum region, then falls to a minimum before rising again slowly. All the phenomena are due to the composite structure of Litchi.