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.     

OPEN SUN DRYING : AN ANALYTICAL STUDY

This communication presents a simple model of open sun drying to predict the hourly variation of product temperature and moisture constent under constant rate and falling rate regimes of drying. The model is based on the principle of simultaneous heat and mass transfer at the product surface and includes the effects of wind speed, relative humidity, product thickness and the heat conducted to the ground. The computations corresponding to the typical summer (June 1-2,1982) and winter (Dec. 6-8, 1982) days of New Delhi climate, have shown that the highly moistureous fruits/ vegetables having moisture content -80% (wet basis) may be dried to 13% moisture content in 24 and 34 sunshine hours in summer and winter climates respectively. It is also recommended that the layer thickness of the material should not be more than 5 cm for drying under open sun.     

AN EXPERIMENTAL STUDY OF GAS-FIRED INFRARED DRYING OF PAPER

Infrared heating/drying of paper is becoming very common in industry. However, there is a lack of fundamental information explaining the transport phenomena occurring within a paper sheet due to energy supplied by a gas-fired infrared emitter. This experimental study provides basic drying and temperature data for moist paper exposed to gas-fired infrared radiation energy. Two paper types, linerboard and bleached, at three basis weight levels, are used in this study.     

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.     

AN EXPERIMENTAL STUDY OF GAS-FIRED INFRARED DRYING OF PAPER

Infrared heating/drying of paper is becoming very common in industry. However, there is a lack of fundamental information explaining the transport phenomena occurring within a paper sheet due to energy supplied by a gas-fired infrared emitter. This experimental study provides basic drying and temperature data for moist paper exposed to gas-fired infrared radiation energy. Two paper types, linerboard and bleached, at three basis weight levels, are used in this study.     

THE EXPERIMENTAL STUDY OF ROTARY-STREAM FLUIDIZED BED DRYING

Rotary-stream fluidized bed drying is the combination of fluidized bed drying and pneumatic drying. Both non-viscous and viscous materials and even sticky paste can be dried successfully with this technique. The material being processed is turned to powder or granular product of controlled homogeneous in one treatment and no further pulverization is necessary. Correlation of Eu vs Re and Nu vs Re were obtained from hydrodynamic experiment and drying experiment respectively.     

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 %.     

洗过散羊毛干燥特性实验研究

在与工业干燥机基本相同的条件下,实验研究了洗过散羊毛的干燥特性。测得临界湿含量的平均值为x_c=1.1kg/kg;传质系数平均值为K=0.01kg/(m~2·s)。在统计回归的基础上推荐干燥特性曲线用下列幂函数描述:f=Φ~(0.5)。     

A HIGH AIRFLOW DRYING EXPERIMENTAL SET-UP TO STUDY DRYING BEHAVIOR OF POLYMER SOLVENT COATINGS

A High Airflow Drying Experimental Set-up (HADES) has been constructed to simulate conditions encountered in industrial dryers. In this experiment the drying gas flows parallel to the coating in a narrow gap (6 × 10^-3 cm). Measured heat transfer coefficients (HTCs) on HADES range from 7 W/m² K at 0.072 m/s to 26 W/m² K at 0.72 m/s. The range of HTCs could easily be extended by using higher gas flow rates or narrower gap. The drying results obtained in HADES compare well with model predictions for poly (vinyl acetate)/toluene and show expected trends for changes in drying temperature and flow rate. Experimental drying results for poly (methyl methacrylate)/acetone show an anomalous drying behavior where residual solvent content is minimized at intermediate drying gas flow rate. This phenomenon is likely due to formation of a glassy skin at the surface of the drying coating.     

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.     

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.     

A HIGH AIRFLOW DRYING EXPERIMENTAL SET-UP TO STUDY DRYING BEHAVIOR OF POLYMER SOLVENT COATINGS

A High Airflow Drying Experimental Set-up (HADES) has been constructed to simulate conditions encountered in industrial dryers. In this experiment the drying gas flows parallel to the coating in a narrow gap (6 × 10^?3 cm). Measured heat transfer coefficients (HTCs) on HADES range from 7 W/m² K at 0.072 m/s to 26 W/m² K at 0.72 m/s. The range of HTCs could easily be extended by using higher gas flow rates or narrower gap. The drying results obtained in HADES compare well with model predictions for poly (vinyl acetate)/toluene and show expected trends for changes in drying temperature and flow rate. Experimental drying results for poly (methyl methacrylate)/acetone show an anomalous drying behavior where residual solvent content is minimized at intermediate drying gas flow rate. This phenomenon is likely due to formation of a glassy skin at the surface of the drying coating.     

DRYING OF A PAPER COATING : EXPERIMENTAL STUDY AND MODELLING

This research deals with the physical mechanisms that occur during drying of a paper coating. A study at the local scale of the drying of a paper coating coupled with natural binder (starch) migrations is carried out. In this aim, drying experiments have been realized and lead to the determination of drying kinetics, time evolution of moisture content profiles, and starch concentration distribution at the end of drying. The results obtained allow the modelling to be validated. This model, which is based on diffusive liquid transport, takes into account the shrinkage of the coating and the migration of the different solid components during drying. It leads us to suggest that starch migration occurs until the coating is totally consolidated.     

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.     

EXPERIMENTAL STUDY OF THE DRYING OF A THICK LAYER OF NATURAL CRUMB RUBBER

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.     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

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.