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。     

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 grape pomace with a double pass solar collector

This study aims to analyze the performance of a novel design of the double pass solar air collector (DPSAC)-assisted drying system and investigate the drying kinetics of grape pomace which is an agricultural by-product. The samples were dried to a moisture content of 0.01?g water/g dry matter between 100 and 250?min depending on the weather conditions. The average thermal efficiencies of DPSAC were calculated as 79.77, 79.85, and 69.46%. Average values of the coefficient of performance of DPSAC were determined as 5.32, 5.13, and 4.32. The highest specific moisture extraction rate value was achieved as 617.18?g water/kWh. Whereas the mass transfer coefficient (h_m) values ranged from 9.15E?11 to 1.04E?7?m/s, the effective moisture diffusivity (D_e) values were obtained between 3.04E?13 and 1.02E?10?m²/s. The qualitative analysis showed that the drying using DPSAC may be an alternative for drying applications in terms of short drying time and energy usage. Nevertheless, these results clearly suggest a complex and effective interplay between thermal performance and drying kinetics.     

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.     

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。     

太阳能与热泵联合干燥木材特性的实验研究

介绍了国内外利用太阳能干燥木材的概况、太阳能与热泵联合干燥系统的组成与工作原理、太阳能与热泵联合干燥木材的特性和干燥木材的工艺实验。实验结果显示。太阳能与热泵联合供热可以弥补太阳能或热泵单独供热的缺点。太阳能比联合干燥节能3．8％,而联合干燥比热泵干燥节能11．8％;联合干燥比太阳能干燥时间缩短了14．9％。从能耗及生产效率综合考虑。太阳能与热泵联合干燥是值得推荐的一种干燥方法。     

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.     

DESIGN AND CONTINUOUS OPERATION OF A SOLAR CONVECTION DRIER WITH AN AUXILIARY HEATING SYSTEM

A solar drier of the through-draft type (4 trays at 0.5 m² surface area) with natural air convection and an auxiliary gas heating system was constructed. General relationships between the climatic conditions of the ambient air, product load and drying characteristics were established. Test runs with the drier as continuous equipment were carried out over a period of 24 h, using carrot dice as experimental material. Air flow rates through the dryer between 100 and 140 kg/h and overall drying rates between 1.5 and 2 kg/h were reached. The overall energy efficiency coefficient for the hybrid heating system amounted to 27 % as compared to 31 to 37 % for the solar energy heating alone and to 22 to 27 % for gas heating energy alone. A combination of continuous drying in the first stage with subsequent batch-wise finish drying in the same or a supplementary drier seems to be advantageous.     

DESIGN AND CONTINUOUS OPERATION OF A SOLAR CONVECTION DRIER WITH AN AUXILIARY HEATING SYSTEM

A solar drier of the through-draft type (4 trays at 0.5 m² surface area) with natural air convection and an auxiliary gas heating system was constructed. General relationships between the climatic conditions of the ambient air, product load and drying characteristics were established. Test runs with the drier as continuous equipment were carried out over a period of 24 h, using carrot dice as experimental material. Air flow rates through the dryer between 100 and 140 kg/h and overall drying rates between 1.5 and 2 kg/h were reached. The overall energy efficiency coefficient for the hybrid heating system amounted to 27 % as compared to 31 to 37 % for the solar energy heating alone and to 22 to 27 % for gas heating energy alone. A combination of continuous drying in the first stage with subsequent batch-wise finish drying in the same or a supplementary drier seems to be advantageous.     

Sun Drying of Sultana Grapes

ABSTRACT

In this paper, an experimental investigation is presented on natural sun drying of Sulruna grapes. in drying experiments, a new pretreatment solution was employed to decrease the drying time and to obtain better quality products. In addition to this solution, grape drying experiments in the pretreated form with potasa solution -the most common mixture in Turkey for grape drying- and in the untreated form were carried out. The measurements of weight loss and dry matter (and brix) during drying experiments, and the color, pH and total acidity measurements at the end of drying experiments were carried out. The results show that the total drying period for grapes pretreated with the present solution was 128 hr while the drying periods for the cases, e.g., pretreated with potasa solution and untreated were 176 hr and 436 hr. This means that the drying rate for pretreated grapes with the present solution was 1.375 times faster than the pretreated case with potwa and 3.4 times faster than the untreated case. In light of the results obtained here. it is clear that the present solution is a very good alternative for grape drying applications and will be beneficial to the relevant industry and people.     

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.     

微波真空干燥技术的探讨

干燥是高能耗行业,我国干燥能耗约占全部工业能耗的12％。“节能减排”是保障我国能源安全、发展经济和保护环境的基本国策。根据不同的生产条件,科学选用烘干工艺和设备,对节约能源、减少原材料消耗、降低生产成本、提高经济效益、增强企业市场竞争力具有重要的意义。     

SOLAR DRYING. FOR REAL APPLICATIONS

The techniques of professional drying can be utilized in solar drying with the view to satisfy the real needs of large agricultural productions and secure product quality and standardization. A solar batch convection dryer designed along this line is presented and its performance for drying fruits and vegetables is discussed together with the techniques used to dry these products.     

压缩空气干燥方式应用研讨

从理论和经济的角度出发,研讨了如何确定压缩空气的干燥方式及怎样进行设备选型,并讨论了压缩空气干燥系统的配置。     

Through Drying of Paper

Through drying of paper of basis weight 25 to 50 g/m² was studied through 89 experiments with 22 to 90°C air at mass flow rates from 0.125 to 1.45 kg/m²s. The complete drying rate curves are represented with five quantitative parameters:moisture contents at the end of the increasing and constant rate periods, the constant drying rate, and exponents for the increasing and falling rate period relations. The constant drying rate period disappears at higher drying intensities leaving the increasing rate period accounting for as much as 37% of the drying. The constant drying rate may be controlled by thermodynamics or by transport phenomena. The critical moisture content depends on effects from the intrinsic local nonuniformity of through drying as well as on sheet average conditions. A universal set of relations was obtained for representation of the complete drying rate curve and was verified for prediction of drying rate and drying time. Through drying rates cannot be increased significantly by providing the drying air as an impingement flow.     

Experimental Study on Energy Consumption of Combined Conventional and Dehumidification Drying

Conventional drying, dehumidification drying, and combined conventional-dehumidification drying of wood were experimentally studied in this article. The results showed that the energy consumption in the dehumidification drying is the least but its drying time is the longest. The energy consumption in the combined drying is more than that in the dehumidification drying but less than that in the conventional drying, and the drying time is half of that in the dehumidification drying. The advantages of the combined conventional and dehumidification drying are discussed from the experiments results.     

SOLAR DRYING. FOR REAL APPLICATIONS

The techniques of professional drying can be utilized in solar drying with the view to satisfy the real needs of large agricultural productions and secure product quality and standardization. A solar batch convection dryer designed along this line is presented and its performance for drying fruits and vegetables is discussed together with the techniques used to dry these products.     

Experimental Study on Energy Consumption of Combined Conventional and Dehumidification Drying

Conventional drying, dehumidification drying, and combined conventional-dehumidification drying of wood were experimentally studied in this article. The results showed that the energy consumption in the dehumidification drying is the least but its drying time is the longest. The energy consumption in the combined drying is more than that in the dehumidification drying but less than that in the conventional drying, and the drying time is half of that in the dehumidification drying. The advantages of the combined conventional and dehumidification drying are discussed from the experiments results.     

流化床干燥聚碳酸酯小试实验研究

使用流化床小试装置对聚碳酸酯粉料进行干燥,绘制聚碳酸酯干燥速率曲线,初步证明了卧式流化床干燥聚碳酸酯具有一定的可行性。     

Effect of Pulsed Electric Field and Osmotic Dehydration Pretreatment on the Convective Drying of Carrot Tissue

The influence of pulsed electric field (PEF) and subsequent centrifugal osmotic dehydration (OD) on the convective drying behavior of carrot is investigated. The PEF was carried out at an intensity of E = 0.60 kV/cm and a treatment duration of t_PEF = 50 ms. The following centrifugal OD was performed in a sucrose solution of 65% (w/w) at 40°C for 0, 1, 2, or 4 h under 2400 × g. The drying was performed after the centrifugal OD for temperatures 40-60°C and at constant air rate (6 m³/h).

With the increase of OD duration the air drying time is reduced spectacularly. The dimensionless moisture ratio Xr = 0.1 is reached for PEF-untreated carrots after 370 min of air drying at 60°C in absence of centrifugal OD against 90 min of air drying after the 240 min of centrifugal OD. The PEF treatment reduces additionally the air drying time. The total time of dehydration operations can be shortened when OD time is optimized. For instance, the minimal time required to dehydrate untreated carrots until Xr = 0.1 is 260 min (120 min of OD at 40°C and 140 min of drying at 60°C). It is reduced to 230 min with PEF-treated carrots.

The moisture effective diffusivity D_eff is calculated for the convective air drying based on Fick's law. The centrifugal OD pretreatment increases drastically the value of D_eff. For instance, 4 h of centrifugal OD permitted increasing the value of D_eff from 0.93 · 10^-9 to 3.85 · 10^-9 m²/s for untreated carrots and from 1.17 · 10^-9 to 5.10 · 10^-9 m²/s for PEF-treated carrots.