Development of Solar Drying

ABSTRACT

Importance of Solar Drying is increasing worldwide, especially in areas where the use of the abundant, renewable and clean solar energy is essentially advantageous. In the developing countries and in rural areas the traditional open-air drying methods should be substituted by the more effective and more economic solar drying technologies.

R&D needs should be considered in the basic research and experimental fields; in performance measurement; in the modelling-simulation-design and testing. The international co-operation of experts should be improved and more efforts would be needed in the policy and in the public information.     

太阳能-除湿-常规分段组合木材干燥工艺优化

为降低木材干燥能耗,通过对杨木进行太阳能-除湿-常规分段组合干燥,即含水率40%以上采用太阳能进行预干,25%—40%采用除湿干燥,25%以下采用常规干燥,并与常规干燥进行干燥能耗和木材质量的对比。结果表明,分段组合干燥比常规干燥节能19%左右,而且干燥质量和常规干燥基本一致。分段组合干燥充分利用了三者各自的优势,从而达到节能的目的。     

Optimization of Solar Kiln for Drying Wood

Abstract

Theoretical investigation of the physical process of solar drying of timber based on conventional heat and mass transfer equations is presented. The governing equations and boundary conditions of the mass diffusion through the wood timbers are derived; also the governing equations of the components of the solar kiln are presented. The finite difference technique is used to solve the set of these equations by means of a simulation program that is based on object-oriented approach. The simulation program is used to investigate the effect of several design parameters on the drying rate and duration of the wood timbers in order to accomplish the drying process with minimal drying defects. These parameters include the ventilation conditions that control the drying schedule inside the solar kiln, wood volume as a ratio to the solar kiln absorber area, wood timber thickness, season of drying, the drying air velocity, and the stresses that formed on the timber boards due to drying with these several parameters, leading to derive the limit of damage for a selected local wood type. The selected local wood type is Casuarina, which is common in Egypt, and it is commonly used in many simple industries.     

Optimization of Solar Kiln for Drying Wood

Theoretical investigation of the physical process of solar drying of timber based on conventional heat and mass transfer equations is presented. The governing equations and boundary conditions of the mass diffusion through the wood timbers are derived; also the governing equations of the components of the solar kiln are presented. The finite difference technique is used to solve the set of these equations by means of a simulation program that is based on object-oriented approach. The simulation program is used to investigate the effect of several design parameters on the drying rate and duration of the wood timbers in order to accomplish the drying process with minimal drying defects. These parameters include the ventilation conditions that control the drying schedule inside the solar kiln, wood volume as a ratio to the solar kiln absorber area, wood timber thickness, season of drying, the drying air velocity, and the stresses that formed on the timber boards due to drying with these several parameters, leading to derive the limit of damage for a selected local wood type. The selected local wood type is Casuarina, which is common in Egypt, and it is commonly used in many simple industries.     

落叶松太阳能热泵干燥特性研究

本文介绍了一种木材太阳能热泵干燥装置及其三种不同的运行方式,并以落叶松为试材,通过两组对比实验,分析干燥介质与干燥箱内的温度变化以及木材含水率变化之间的关系。结果表明太阳能水源热泵联合干燥的优化比传统干燥节能约76．7％,太阳能水源热泵联合干燥比传统干燥节能约66．2％,优化模式比只用太阳能水源热泵联合干燥木材时耗能更低,且干燥质量更好。     

太阳能干燥集热器的农业应用

提出了太阳能进行农产品干燥应用的可行性,对太阳能集热器干燥注意的问题进行了总结,完成了典型物料太阳能干燥计算,为不同类别的农产品太阳能干燥提供了依据。     

Experimental Evaluation of Solar Kiln for Drying Wood

Semi-greenhouse solar dryer was designed and constructed in the Solar Energy Department, National Research Center, Cairo, Egypt. It consists of steel frame structure and all the sides were insulated and covered by galvanized iron sheet. The roof faces south with a tilt angle of 30° and covered by glass sheets. Corrugated iron sheets, painted black on the top, were fixed beneath the glass roof as an absorber. The humidity inside the solar kiln is controlled by inlet vent at south wall and two outlet vents at north wall. Data Capture System was designed to ease the measurements and to capture the measured data automatically and continuously for 24 h a day. The selected local wood type is Casuarina, which is common in Egypt, and it is commonly used in many simple industries. The experimental results with this type of wood show considerable agreements with the simulated ones. A comparison was made between experimental results of solar wood drying and traditional air-drying. The results show that timber boards were dried inside solar kiln to moisture content of 12% within 17 days, where air dying moisture content was limited to 20% for the same period.     

Drying Kinetics of Tomato Slices in Vacuum Assisted Solar and Open Sun Drying Methods

A lab model vacuum-assisted solar dryer was developed to study the drying kinetics of tomato slices (4, 6, and 8 mm thicknesses) compared with open sun drying under the weather conditions of Montreal, Canada. The drying study showed that the time taken for drying of tomato slices of 4, 6, and 8 mm thicknesses from the initial moisture content of 94.0% to the final moisture content of around 11.5 ± 0.5% (w.b.) was 360, 480, and 600 min in vacuum-assisted solar dryer and 450, 600, and 750 min in open sun drying, respectively. During drying, it was observed that the temperature inside the vacuum chamber was increased to 48°C when the maximum ambient temperature was only 30°C. The quality of tomato slices dried under vacuum-assisted solar dryer was of superior quality in terms of color retention and rehydration ratio. The drying kinetics using thin-layer drying models and the influence of weather parameters such as ambient air temperature, relative humidity, solar insolation, and wind velocity on drying of tomato slices were evaluated.     

Elimination of Cyabogebic Compounds of Cassava During Solar Drying

ABSTRACT

Cassava, a crop originated from central and south america, is now being cultivated in all tropical countries of the world. This was possible because of its adaptative capacity to all types of soil and its resistance to dry weather.The most widely used method for the transformation of fresh cassava roots is solar drying. We have studied the evolution of the cyanogenic compounds of cassava during solar drying begining at 9 h or 18 h. Three cassava varieties were dried (MBRA 195, CG 165-7 and CG 915-1) using loads of 12.5 kg/m² of chips having a dimension of 3x3x5-10 mm. Results showed that The loss of total and bound cyanides observed varied between 84-89% and 80-100% respectively, with respect to the initial content of cyanogenic compounds. In all cases, the concentration of cyanide residue was less than 40 ppm (dry basis). The rate of cyagenic compounds elimination was better in the experiments begining at 18 h than those began at 9 h. Our results also show that water diffuaion into the interior of the chips has a great influence on the elimination of cyanogenic compounds of cassava.     

Elimination of Cyabogebic Compounds of Cassava During Solar Drying

Cassava, a crop originated from central and south america, is now being cultivated in all tropical countries of the world. This was possible because of its adaptative capacity to all types of soil and its resistance to dry weather.The most widely used method for the transformation of fresh cassava roots is solar drying. We have studied the evolution of the cyanogenic compounds of cassava during solar drying begining at 9 h or 18 h. Three cassava varieties were dried (MBRA 195, CG 165-7 and CG 915-1) using loads of 12.5 kg/m² of chips having a dimension of 3x3x5-10 mm. Results showed that The loss of total and bound cyanides observed varied between 84-89% and 80-100% respectively, with respect to the initial content of cyanogenic compounds. In all cases, the concentration of cyanide residue was less than 40 ppm (dry basis). The rate of cyagenic compounds elimination was better in the experiments begining at 18 h than those began at 9 h. Our results also show that water diffuaion into the interior of the chips has a great influence on the elimination of cyanogenic compounds of cassava.     

基于太阳能的工业物料干燥技术研究

以工业废料(铬渣)为干燥对象,研究探索利用太阳能干燥工业物料的方法和技术。在研究物料的物理特性与传统的干燥工艺的基础上确定了基于太阳能的物料干燥工艺;对空气集热器模型进行试验、优化,得出空气集热器的主要技术参数;利用计算机三维造型,设计了适于铬矿渣烘干的隧道式烘干窑和干燥架;最终设计出由太阳能空气集热器、常用的热风炉和隧道式烘干窑组合而成的混合型干燥系统。经理论计算与虚拟实验,用于工业物料的干燥是可行的。     

Drying of Porous Materials in the Presence of Solar Radiation

We present a combined heat and moisture transfer model for predicting the drying characteristics of porous building materials exposed to solar radiation. The model has been validated for convective drying using published data and for radiative drying using results of an experimental study carried out using a solar lamp to simulate solar radiation conditions. Actual and predicted moisture content profiles and the drying rates when compared give favourable results.     

Drying of Porous Materials in the Presence of Solar Radiation

ABSTRACT

We present a combined heat and moisture transfer model for predicting the drying characteristics of porous building materials exposed to solar radiation. The model has been validated for convective drying using published data and for radiative drying using results of an experimental study carried out using a solar lamp to simulate solar radiation conditions. Actual and predicted moisture content profiles and the drying rates when compared give favourable results.     

The Effect of Adding Straw on Natural Solar Sludge Drying

The effect of straw on natural solar sludge drying was investigated. As the thickness of the stack increased, the rate of water removal per unit area slightly increased and the rate of water removal per unit volume rapidly decreased. The rate of water removal increased as the accumulation of solar energy increased but decreased as the relative humidity increased. On the 23rd day, the moisture content of the dewatered sludge and the chopped straw mixture decreased from 75.2 to 45.1% at a thickness of stack of 30 cm, with an average water evaporation rate of 7.2 kg/m²d.     

Drying Of Vanilla Pods Using A Greenhouse Effect Solar Dryer

ABSTRACT

This paper describes the basic design of the GHE solar dryer and evaluates the performance of the dryer when used to dry vanilla pods. From laboratory test results it was indicated that the average drying time for vanilla pods was between 49 to 53, 5 hrs, for the case of heating augmentation using coal briquette stoves. The total amount of coal briquettes used to produce drying air temperature between 33 C to 65 C and RH of about 34% during day time was 61 kg equivalent to 6.1 kW heating rate and the average electric energy usage of 36.5 kWh, respectively. Quality test results indicated that the dried products were of grade IA of the export quality standard with vaniline content of 2.36%.     

Evaluating a Solar Dryer for In-Shell Drying of Split Pistachio Nuts

Abstract

A thin-layer forced air solar dryer was designed to study the feasibility of drying pistachio nuts. The dryer was tested during the 2001 and 2002 drying seasons. The maximum temperature in the solar collector reached 56°C, which was 20°C above the ambient temperature. The required drying time was 36 h. During the first day of drying (0800 to 1700 h) the moisture content dropped to about 21% (wb). The final moisture content of the dried nuts was 6% wb, which was 1% below the recommended storage moisture. The drying constant of the pistachio nuts during solar drying was determined using two mathematical models, a one-term series solution of Fick's diffusion equation and an exponential decaying model. There was no significant difference between the two models (α = 0.05). In general, the quality of solar dried nuts was better than the conventional heated air due to slower drying rates.     

集热式太阳能污泥干化系统能效评估与适应性分析

污泥集热式太阳能干化技术改变了太阳能利用形式,采用恒定的加热温度,相对于温室型太阳能干化技术能够提高干燥效率,保证系统稳定运行。文章通过对该系统的物料和热量衡算得出,在不采用辅助能源时,干化时间、单位面积处理能力、干化床占地面积均与太阳能辐射强度成反比例函数关系,集热器占地面积随着污泥处理量增加而增大,且均大于干化床的占地面积。结合系统投资与运行成本分析,随着干化时间延长处理费用增加,当干化时间为10~15天时,可使污泥日处理费用达到最低。因此,考虑到干化床和集热器的占地面积,该系统适用于处理规模小且所在地区太阳能辐射强度大的污水处理厂。     

Influence of Factors on the Drying of Cassava in a Solar Simulator

ABSTRACT

In tropical countries, sun drying is still the most popular method used for processing root and tuber crops like cassava and yam. Relatively very little has been done on studying the kinetics of sun drying a bed of chips of cassava and similar crops, but this information is invaluable in finding options for reducing drying time and costs, and increasing tonnage produced. This project studied some factors that have an effect on the sun drying rate of cassava chips. The factors were ambient temperature, relative humidity, radiation intensity, air velocity, and loading density.

A solar simulation chamber was constructed so that drying could be achieved under controllable conditions similar to those obtained in sun drying. Experiments carried out in the simulator revealed that temperature had the most significant effect on drying rate, followed by air velocity, and radiation intensity. Regression equations were developed relating the drying rate with the factors studied.     

太阳能相变储热在木材干燥中应用的初步研究

针对木材太阳能干燥间歇性的不足,在原有太阳能干燥装置的基础上,增设了多管道叉排石蜡相变储热系统。研究结果表明,随着储热系统管排数的增加（5、7、9、11排）,其放热时间逐渐缩短,换热系数呈现增加趋势,平均值分别为17．8、22．1、24．7、26．4W／（m^2·℃）;在其它参数相同的条件下,当管排数不大于5时,储热温度对换热系数的影响不大,但当管排数大于11,储热系统显热储存的热量就不能够忽略;在其它参数相同的条件下,随着风速的增加,换热系数呈现增长趋势,风速为1．0、1．5和2．0m／s时,放热速率的比值为0．89：0．94：1。     

太阳能流化干燥的数值模拟与试验研究

设计了太阳能流化床干燥的试验装置,通过试验的方法研究了流化干燥特性和太阳能利用的效益。对冷热态,不同流量,不同物料层高等参数变化,进行了测试,对比进行了多次试验,得到了不同参数的试验结果。分析总结了各参数对物料干燥的影响,表明空气流量,料层高度和冷热态均会影响物料干燥程度,且热管传递的热量只有部分传递给了物料。应用Fluent商用计算软件,对热管换热开展了数值模拟,获得了换热效率的变化,研究结果说明数值计算与试验结果符合较好。