Dynamic Modeling and a Parametric Study of an Indirect Solar Cabinet Dryer

A dynamic mathematical model for drying of agricultural products in an indirect cabinet solar dryer is presented. This model describes the heat and mass transfer in the drying chamber and also considers the heat transfer and temperature distribution in a solar collector under transient conditions. For this purpose, using conservation laws of heat and mass transfer and considering the physical phenomena occurring in a solar dryer, the governing equations are derived and solved numerically. The model solution provides an effective tool to study the variation of temperature and humidity of the drying air, drying material temperature, and its moisture content on each tray. The predicted results are compared with available experimental data. It is shown that the model can predict the performance of the cabinet solar dryer in unsteady-state operating conditions well. Furthermore, the effect of some operating parameters on the performance and efficiency of dryer is investigated and compared with selected published data.     

Solar Dryer for Powder Drying

A natural circulation solar dryer for drying products in the form of powder has been developed. It is of modular design and aperture area of one module is 3.34 m². A new concept of moveable glazing has been introduced for ease in loading and unloading. Air entering the dryer moves in a zig-zag path as it flows over the product and under each tray before leaving from the top. There is a provision to dry the product under shade. Also, the dryer can be dismantled and stored in a room during off-season. The dryer was tested to dry Di-calcium phosphate (DCP) at Ludhiana (31°N). The average drying efficiency for a batch was found to be 54.0%. The cost of drying DCP using this solar dryer was 0.56 Rupees per kg of dried DCP as compared to 1.94 Rupees per kg of dried DCP for a wood-fueled industrial dryer. In comparison to a solar tunnel dryer for DCP drying, the initial investment per kilogram of the dried DCP, floor area per kilogram of wet DCP, and cost of drying per kilogram of dried DCP for this dryer was reduced by 7.1%, 67.2%, and 16.4% respectively.     

A Comparative Study on Exergetic Performance Assessment for Drying of Broccoli Florets in Three Different Drying Systems

This article deals with the exergy analysis and evaluation of broccoli in three different drying systems. The effects of drying air temperature on the exergy destruction, exergy efficiency, and exergetic improvement potential of the drying process were investigated. The exergy destruction rate for the drying chamber increased with the rise in the drying air temperature at 1.5 m/s, both in the tray and the heat pump dryer. The highest exergy efficiency value was obtained as 90.86% in the fluid bed dryer in comparison to the other two drying systems and the improvement potential rate was the highest in the heat pump dryer during drying of broccoli at the drying air temperature of 45°C and the drying air velocity of 1.0 m/s.     

太阳能光伏产业的热场材料

单晶硅、多晶硅等硅材料是实现光电转换的主要材料之一.生产高纯度的多晶硅和单晶硅不仅需用大量的石墨材料,而且耗能量也非常大.随着产量的提高和生产设备的大型化,碳/碳复合材料坩埚和加热元件以及石墨纤维保温筒将是发展方向.高纯度和大尺寸热场材料具有显著的社会和经济效益.     

Comparison Between Drying of Timber in a Solar Dryer and in an Electrically-Heated Kiln

ABSTRACT

Solar dryers have been considered for timber drying in a number of countries because of the expected savings in drying costs. From a review of past works on solar, natural, and conventional drying it was observed that while solar dryers were able to dry timber faster compared to natural drying, the difference was only marginal in some instances. The drying rates are expected to be dependent upon ambient conditions in which the dryera are operated. Solar dryers would operate more efficiently in countries with low humidity than in tropical regions. Thus the thermal performance and also the economics of solar dryer is country dependent. In the present paper, a comparison of the drying rates obtained with a solar dryer is made with that obtained with an electrically operated drying kiln.     

An Experimental Study of Wheat Drying in Thin Layer and Mathematical Simulation of a Fixed-Bed Convective Dryer

Drying of wheat (Algerian cultivar: Hadba03) in thin layers was studied and mass flux phenomenon was used to characterize the thin-layer drying process. Thin-layer drying of wheat was determined for drying air temperature range of 40–60°C, relative humidity of drying air from 10 to 30%, air velocity of 0.7 m/s, and initial grain moisture from 26 to 31% (dry basis). Equilibrium moisture content of wheat was determined using desorption isotherms obtained from the thin-layer drying data. An equilibrium model for a stationary deep bed with drying air moving vertically upward was developed using mass and energy balance between grain and drying air in the bed and drying air characteristics obtained from thin-layer drying experiments. The developed model was validated by drying wheat in a laboratory dryer using different drying air temperatures and initial moisture contents.     

Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO₂) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H₃PO₄) etching, nitrogen (N₂) gas anneal and forming gas (Ar: H₂) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.     

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 of the Photovoltaic Solar Electro-Oxidation (PSEO) process for wastewater treatment

The Photovoltaic Solar Electro-Oxidation (PSEO) process combines the effectiveness of the electrochemical oxidation based on boron-doped anodes to mineralize organic matter, with the autonomy and environmentally friendly characteristics of photovoltaic solar energy. The PSEO process constitutes an attractive technology for the treatment of urban wastewaters of isolated communities where standard solutions cannot be applied. The aim of this work is the design of this process, which implies the sizing of the electrochemical reactor and the photovoltaic modules. The input variables for the design are the characteristics of the effluent, the wastewater flow rate (which depends on the number of equivalent inhabitants for whom the plant operates), the required yield and the solar irradiance. The solar irradiance depends on the location in which the PSEO process is applied, since differences in the required PV module area higher than 170% are obtained in several locations in Spain. Moreover, the residence time distribution in the reactor also significantly affects the dimensions of the electrode (A_a) and solar module (NA_PV) areas.     

组合干燥系统在浆料干燥中的应用

介绍了应用于浆料干燥的两种桨叶组合干燥系统,重点阐述了工艺流程及关键设备,分析了两种组合形式的特点及经济性,并列出了两种具有代表性浆料的工业应用参数。     

干燥系统的设计分析模拟软件

对现有的干燥过程模拟商业软件做了简要回顾。这些软件在用于设计、分析、故障排除以及控制与优化干燥系统中可大大降低成本。推荐并分析了一款新的干燥分析软件（Simprosys）。讨论了该软件产品成功的关键因素,并介绍了该软件开发的动机和原理及其应用。     

Drying of a Root Crop in Vibro-Fluidized Beds

ABSTRACT

Drying of sliced corm of Moyu which represents a group of hard-to-dry herbaceous plants was carried out in a batch laboratory vibrated fluid bed to determine drying kinetics and identify operating parameters for required product quality. Results from laboratory studies were verified in a pilot-scale continuous VFB dryer. Field trials performed over the Moyu harvest season confirmed the resulls extrapolated from laboratory data.     

Drying and Testing of Mint (Mentha piperita) by a Hybrid Photovoltaic-Thermal (PVT)-Based Greenhouse Dryer

Mint has been used as a medicinal and aromatic plant since ancient times. Its leaves are used for flavoring, spicing, and mint oil, which is used to treat several diseases. In order to preserve this seasonal plant for consumers during the year, it undergoes various technological treatments, such as drying. The economy of medicinal plant production is burdened considerably by the energy costs of drying. To substitute high-cost fossil energy, a hybrid photovoltaic-thermal (PVT) ultraviolet (UV)-stabilized polyethylene greenhouse dryer was developed to lower the initial costs. The drying process from an initial moisture content of 80% wb to a final moisture content of 11% wb takes 21 h. Testing was done for different samples of dried mint powder and comparison was made to fresh samples. The results show that nutritional and calorific values are retained along with a major degree of its original color, which, coupled with a significant reduction in moisture content, resulted in longer shelf life of the dried product. Further, the results show that the efficiency of the dryer and net CO₂ mitigation over the lifetime was 34.2% and 140.97 tons, respectively. The carbon credit earned ranges from a minimum of $704.85 per ton of C to a maximum of $2,819.40 per ton of C.     

Modeling of Fertilizer Drying in Roto-Aerated and Conventional Rotary Dryers

Conventional rotary dryers are equipped with flights placed parallel along the length of the shell to promote a rain of solids across the dryer section. In the roto-aerated dryer the hot air flows through the particles that run on the bottom of the drum through a series of mini-pipes and there is no cascading. This study analyzed heat and mass transfer modeling between the air and the fertilizer particles in conventional rotary and roto-aerated dryers, as well as the simulation results with the experimental data. A good agreement between the simulated and experimental results was obtained for the two rotary dryer configurations analyzed.     

利用太阳能和高温热泵的城市污泥热干化系统技术研究

太阳能是取之不尽的能源，高温双热源热泵也是节能型产品，节能率比普通热泵高70％。所以将太阳能与热泵组合作为热源对城市污泥进行热干化，热干化的污泥可以作为燃料进行焚烧，具有极大的应用潜力。介绍了利用太阳能和热泵作为热源，利用干燥机对城市污泥进行热干化的系统结构、工作原理和实验研究。该系统也可应用于干燥其它物料，如食品、药材等。     

造纸制浆污泥由蚯蚓处理或是干化处理的探讨

从蚯蚓处理制浆污泥的流程和空心桨叶干燥机处理流程进行探讨对比,蚯蚓处理污泥既节能又环保,但占地面积大;空心桨叶干燥机处理污泥不节能,但占地面积小.通过讨论,对大规模处理污泥,建议采用蚯蚓处理污泥,处理后的蚯蚓粪用作有机肥.     

组合干燥系统在染料工业中的应用

本文介绍了应用于染料工业干燥的双桨叶-盘式连续干燥系统，重点阐述了工艺流程及主要设备，分析了这种组合形式的优势及应用领域，并与另外一种组合干燥器浆叶-浆叶连续干燥器进行了比较。     

Solar Drying of Peeled Longan Using a Side Loading Type Solar Tunnel Dryer: Experimental and Simulated Performance

This article presents experimental and simulated results of drying of peeled longan in a side-loading solar tunnel dryer. This new type of solar tunnel dryer consists of a flat-plate solar air heater and a drying unit with a provision for loading and unloading from windows at one side of the dryer. These are connected in series and covered with glass plates. A DC fan driven by a 15-W solar cell module supplies hot air in the drying system. To investigate the experimental performance, five full-scale experimental runs were conducted and 100 kg of peeled longan was dried in each experimental run. The drying air temperature varied from 32 to 76°C. The drying time in the solar tunnel dryer was 16 h to dry peeled longan from an initial moisture content of 84% (w.b.) to a final moisture content of 12% (w.b.), whereas it required 16 h of natural sun drying under similar conditions to reach a moisture content of 40% (w.b.). The quality of solar-dried product was also good in comparison to the high-quality product in markets in terms of color, taste, and flavor. A system of partial differential equations describing heat and moisture transfer during drying of peeled longan in this solar tunnel dryer was developed and this system of nonlinear partial differential equations was solved numerically by the finite difference method. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5. The simulated results agreed well with the experimental data for solar drying. This model can be used to provide the design data and it is essential for optimal design of the dryer.     

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。     

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m² pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.