Solar thermal desalination technologies

The use of solar energy in thermal desalination processes is one of the most promising applications of the renewable energies. Solar desalination can either be direct; use solar energy to produce distillate directly in the solar collector, or indirect; combining conventional desalination techniques, such as multistage flash desalination (MSF), vapor compression (VC), reverse osmosis (RO), membrane distillation (MD) and electrodialysis, with solar collectors for heat generation. Direct solar desalination compared with the indirect technologies requires large land areas and has a relatively low productivity. It is however competitive to the indirect desalination plants in small-scale production due to its relatively low cost and simplicity. This paper describes several desalination technologies in commercial and pilot stages of development. The primary focus is on those technologies suitable for use in remote areas, especially those which could be integrated into solar thermal energy systems.     

Solar desalination using humidification—dehumidification technology

A numerical study has been carried out to investigate the performance of a simple solar desalination system using humidification—dehumidification processes. The desalination system consists of a solar air heater, humidifier, dehumidifier and a circulating air-driving component. The study covers the influence of different environmental, design, and operational parameters on the desalination system productivity. Environmental parameters include solar intensity, ambient temperature and wind speed. Design parameters include the solar heater base insulation, the humidifier and the dehumidifier effectiveness. Operational parameters include air circulation flow rate, feed water rate and temperature. The results indicated that the solar air heater (energy source) efficiency significantly influences system productivity. Increasing the solar intensity and ambient temperature and decreased wind velocity increases system productivity. Increasing the air flow rate up to 0.6 kg/s increases the productivity, after which it has no significant effect. The feed water flow rate has an insignificant influence on system productivity. The surprising result is that the dehumidifier effectiveness has an insignificant influence on system productivity, which has a very important implication for the system's economy. The physical explanation of this finding is given.     

Thermal modeling of a controlled environment greenhouse cum solar distillation for composite and warm humid climates of India

The present study is concerned with the analysis of solar desalination system combined with a greenhouse for both composite and warm humid climate of India. Analytical expressions for water temperature, greenhouse room air temperature, glass cover temperature, flowing water mass over the glass cover, hourly yield of fresh water and thermal efficiency have been derived in terms of design and climatic parameters for a typical day of summer and winter period. Temperature rise of flowing water mass with respect to distance and time in solar still unit has also been incorporated in the mathematical modeling. The effects of various still and design parameters on its performances have been discussed in detail. The yield of fresh water was found to be higher in warm humid climate than composite climate.     

Industrial Water Desalination by Vacuum Multi‐Effect Membrane Distillation

Water shortage and a rising water demand are prevalent issues on the political agenda worldwide. Available water resources must not only be provided to ensure a domestic and drinking water supply for a steadily increasing population but also for the growing industrial and agricultural sectors. This work outlines how the use of the innovative vacuum multi‐effect membrane distillation contributes to improve the water management efficiency in the following key industry sectors: desalination, drinking water and beverage industry, pharmaceutical, agro and chemical as well as oil and gas industry.     

太阳能光热发电中熔盐蓄热储能循环系统的设计开发

分析了熔盐蓄热储能技术,讨论了光热发电中使用的熔盐混合物特性,介绍了采用熔盐蓄热储能技术的太阳能光热发电站的结构和型式。开发了熔盐蓄热储能循环系统的工艺流程,并对熔盐的流量与流速、熔盐膜壁温度、熔盐分解物、熔盐结垢堵塞等问题及其相互之间的关系进行了研究,给出了熔盐管路预热与保温、熔盐贮罐内防固化、惰性气体密封装置和安全保护措施等的设计原则。     

太阳能综述

在能源频频告急,环境问题不时亮起红灯的今天,人们开始努力寻求新能源。风能、太阳能、生物能等可再生能源引起研究者们竞相追捧,而其中的太阳能更是首当其冲。对当今世界各国太阳能研究和使用情况以及一些前沿进展作了调查与举证。罗列了从技术含量稍低的太阳能热水器到技术含量稍高的太阳能电池,从太阳能空调再到太阳能光伏发电,以及现已完成的一些太阳能建筑。还介绍了对太阳能的经济性、可行性所作的分析,以及一些国家采取的相应的鼓励政策和措施。对光伏发电以及对整个太阳能前景作了展望。     

Theoretical study on multi-effect solar distillation system driven by tidal energy

Based on an analysis of the characteristics of solar and tidal energy, an innovative, multi-effect solar distillation unit for seawater desalination utilizing solar and tidal energy has been developed. The uniqueness of the system is that without being transferred to electricity, tidal energy is utilized to supply power for water supply and drainage, and vacuum extraction instead of pumps powered by electricity. So the cost can be greatly reduced. The system is based on multi-effect evaporation-condensation processes and operates under vacuum condition, so low grade solar heat can be used with a high thermal efficiency. Hydrodynamic and thermal analysis is carried out for the water supply and drainage system driven by tidal energy. The operating mechanism of the vacuum extraction system driven by tidal energy is presented. A parametric study of the behavior of the solar desalination unit has been performed.     

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.     

Thermal performance of a single-sloped basin still with an inherent built-in additional condenser

This paper presents a theoretical study of the thermal performance of a single-sloped basin still with enhanced evaporation and a built-in additional condenser. The still was built so that one of its cover sides (the condenser) is tilted to be parallel to the sun rays and, therefore, be in the shaded area. The condenser heat capacity and surface area (finned) could be increased so that it will always be cooler than the other glass cover sides and act as a more effective heat and mass sink. Enhancing evaporation is carried out by adding black dyes in the still basin to improve basin absorbitivity and increase evaporation surface area. The proposed still design is simple and is not more complex than the conventional design. The effect of different design, operational, and environmental parameters on still performance are studied. The most influencing parameters are found to be solar intensity, base insulation effectiveness, basin mass, evaporation surface area and condenser inner reflectivity. Other parameters such as condenser material, mass, outer emissivity and surface area, cover angle, and wind speed were found to be of less importance. The effect of glass cover frequent instantaneous cooling (up to once every hour) was also investigated as one of the operational parameters and was found to have insignificant effect. Factors having the most influence were combined together and found to produce a yield of about 55% over the base case.     

纳米材料对太阳能集热器应用的影响

以碳纳米管为分散相材料,乙二醇水溶液为分散介质,可制备出用于直接吸收式太阳集热器的新型吸热与传热循环工质～碳纳米管悬浮吸热黑液流体。该黑液流体的分散稳定性主要受到分散介质的组成、碳纳米管粒子的含量、分散剂的属性和含量、分散方式以及分散时间等因素的影响。分散稳定性好的碳纳米管黑液流体的对太阳辐射具有全波段强吸收特性,可以提高集热效率,加入分散剂可使光热转化效率提高12％～15％。     

锂离子电池集流体的研究进展

集流体是锂离子电池的重要组成部件之一,它不仅能承载电极活性物质,而且还可以将电极活性物质产生的电流汇集起来,形成较大的电流输出,提高锂离子电池充/放电效率.本文综述了当前文献中单一或复合集流体材料如铜、铝、镍、不锈钢、碳、覆碳铝箔等在锂离子电池中的最新研究进展.     

Experimental Investigation of a Photovoltaic-Powered Solar Cassava Dryer

This communication describes the design and experimental performance evaluation of a photovoltaic (PV)-powered solar drying system suitable for processing of export-grade cassava developed at the National Centre for Energy Research and Development, University of Nigeria, Nsukka. The drying system, which is capable of handling about 50 kg of fresh crop per batch, comprises an 8.40 m² roof-type solar collector; a drying unit with five trays, each with a cross-sectional area of 0.60 m²; and a PV-powered 90 WAC blower. The experience gained with the solar drying system described here indicates that, in essence, the unit is structurally and functionally operative. The experimental results suggest that, even under unfavorable weather conditions, the unit is able to produce good quality products. Although the active dryer is more expensive than a passive drying system of comparable capacity, it is nonetheless suitable for application in rural, off-grid agricultural settlements in Nigeria.     

Sun tracking system for productivity enhancement of solar still

A sun tracking system was deployed for enhancing the solar still productivity. A computerized sun tracking device was used for rotating the solar still with the movement of the sun. A comparison between fixed and sun tracked solar stills showed that the use of sun tracking increased the productivity for around 22%, due to the increase of overall efficiency by 2%. It can be concluded that the sun tracking is more effective than fixed system and it is capable of enhancing the productivity.     

纳米材料对太阳能集热器应用的影响

以碳纳米管为分散相材料,乙二醇水溶液为分散介质,可制备出用于直接吸收式太阳集热器的新型吸热与传热循环工质-碳纳米管悬浮吸热黑液流体。该黑液流体的分散稳定性主要受到分散介质的组成、碳纳米管粒子的含量、分散剂的属性和含量、分散方式以及分散时间等因素的影响。分散稳定性好的碳纳米管黑液流体的对太阳辐射具有全波段强吸收特性,可以提高集热效率,加入分散剂可使光热转化效率提高12%～15%。     

Experimental study of basin-type, multiple-effect, diffusion-coupled solar still

Basin-type, multiple-effect, diffusion-coupled solar stills consisting of a tilted double glass cover, a horizontal basin liner and a number of closely spaced vertical partitions in contact with saline-soaked wicks were constructed and then examined in an outdoor experiment in fall and winter at Okinawa, Japan. This new type of still is greatly improved by narrowing diffusion gaps between the partitions, increasing the number of partitions, sandwiching small spacers between partitions and insulating the frame of the glass cover. The daily performances of the improved still are in good agreement with predictions calculated from the theoretical model developed by Tanaka et al. [1]. The still with 5-mm diffusion gaps between 11 partitions produces 14.8-18.7 kg/d distillate per unit effective area of the glass cover at 20.9-22.4 MJ m⁻² d⁻¹ solar radiations incident on the glass cover and 19-30°C ambient air temperatures and is highly productive in comparison with the 7-effect diffusion-type still with 8-mm gaps developed by Okamura et al. [2] and the 3-effect diffusion-type still with 19-mm gaps of Cooper and Appleyard [3].     

新型太阳能海水淡化技术研究进展

总结了微纳尺度下毛细驱动的局域热法太阳能海水淡化的相关机制,包括毛细驱动水分传输、太阳能热量传递机理。叙述了界面太阳能局域热法光蒸汽系统最近发展,并归纳了在1个太阳辐照下突破单级产水量理论极限的新型研究思路,指出了太阳能局域热法海水淡化的当前挑战,包含盐分结晶和蒸汽冷凝效率低等问题。认为界面太阳能局域热法海水淡化技术在效率和成本上都具有极大的优势,系统材料制备简单、结构紧凑、系统创新明显,特别适用于偏远山区和海岛地区电力缺乏的家庭生活淡水制备。随着研究者更多地转向保证蒸汽高效凝结和收集、水蒸汽潜热回收利用,预计这种新型海水淡化技术的未来应用范围将不断扩大。     

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%.     

Water disinfection by solar photocatalysis using compound parabolic collectors

TiO₂ solar photocatalysis has been proven to be a degradation process for aqueous organic contaminant leading to total mineralisation of a large number of compounds. Furthermore, the interest in using this technique for water disinfection has grown in the last decade. Recent publications have reported photokilling of bacteria and viruses by TiO₂ photocatalysis. Therefore, solar photocatalysis disinfection seems to be a very promising process, which could help to improve public health in rural areas of developing countries.

The objective of this work was to assess the feasibility of using TiO₂ solar photocatalysis to disinfect water supplies for future applications in developing countries. This article reviews the viability of solar photocatalysis for disinfection in low cost compound parabolic collectors, using sunlight and titanium dioxide semiconductor, both applied as slurry and supported. We report on the bactericidal action of TiO₂ on a pure culture of Escherichia coli with a low cost photoreactor based on compound parabolic collectors. The influence of different experimental set-ups and parameters are also analysed.

The results and potential application of the solar photocatalysis technology to water disinfection are studied within the frame of two research EU projects whose objective consist on the development of a fully autonomous solar reactor system to purify drinking water in remote locations of developing countries.     

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 Comparison of Various Solid Desiccants for Regeneration by Evacuated Solar Air Collector and Air Dehumidification

In this article, the regeneration and adsorption of different desiccants such as silica gel, activated alumina, and activated charcoal for producing dry air is proposed. The air needed for regeneration was heated in an evacuated tube solar collector with a surface area of 4.44 m². The desiccants were regenerated at temperatures in the range of 54.3–68.3°C. The regeneration performance was greatly affected by the regeneration temperature but depended on the initial moisture content, temperature of the desiccants, and flow rate of regeneration air. Comparison of the performances showed that at high hot air flow rate the regeneration time and adsorption time were shorter for these desiccants than that at low flow rate. Silica gel was observed to perform better at high as well as low flow rates for regeneration and adsorption than activated alumina and activated charcoal.