Study on a multi-effects regeneration and integral-type solar desalination unit with falling film evaporation and condensation processes

Based on the analysis of the mechanism of falling film evaporation and condensation, a new solar desalination unit with three effects regeneration was designed. The performance of the unit was tested through in-door experiments, using an electric heater as heat source. The results indicate that the unit has relatively high performance ratio because of a considerable fraction of the latent heat of condensation and the sensible heat of the warm condensate being successfully utilized three times to preheat and evaporate the feedstock. The unit has also excellent transient-state performance because of using the thin layer evaporation and falling film condensation which are the most effective processes for heat and mass transfer. When the operation temperature is over 90 °C and the inner pressure is below 15 kPa, the performance ratio of the unit can reach about 2.35 and its yield ratio can reach about 135 kg/h. The main factors influencing the performance of the unit were researched and analyzed. The reasonable ranges of some parameters were presented.     

Experimental study on a horizontal tube falling film evaporation and closed circulation solar desalination system

A specifically designed solar desalinization system with a solar collector (about 2.01 m² in area) has been developed and tested under practical weather conditions. In this system, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a condensation cavity and heat exchangers. The thermal performance of the system is greatly improved because of the falling film evaporation technology used. As a result, the yield is about two to three times more than that of a conventional single basin type solar still under the same conditions. The transient-state performance of the system, the relationships with the solar radiation, the operating temperature, the feedstock flow rate and the productivity are presented. Other factors influencing the freshwater are also discussed.     

Steady-state experimental study of a closed recycle solar still with enhanced falling film evaporation and regeneration

An active regenerative solar still with an area of 1.03 m², enabling one to reuse the latent heat of condensation and sensible heat of brine, is constructed and tested indoors, using a solar simulator for irradiation. In this still, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a falling film evaporator–condenser. The forced thin layer evaporation and film condensation, which are the efficient enhanced processes for heat transfer, are applied in this unit. As a result, the performance ratio of the unit is about two to three times greater than that of a conventional basin-type solar still (single-effect).     

一种新型太阳能、风能联合海水淡化装置

淡水资源短缺已成为一个世界性问题,我国也不例外.为了加大淡水供应,一条现实的途径就是充分利用我国丰富的海水资源,以及西北内陆地区的苦咸水(统称海水)进行淡化.提出了一种海水淡化装置,该装置利用温室效应原理和风能致热原理,可充分利用太阳能与风能进行海水淡化.与现有海水淡化装置相比该装置具有利用清洁能源、对环境无污染、适应性强、性价比高等特点.理论计算结果表明,该装置每小时产水量约为普通盘式太阳能海水淡化装置在晴天工作时的2倍.     

海水淡化中降膜蒸发过程的实验研究

由于横管降膜蒸发具有传热系数高、热耗低、可利用低品位能源等优点,横管降膜蒸发技术成为低温多效海水淡化技术中应用最广泛的方法.搭建了单管横管降膜试验台,观测了横管降膜蒸发的流动过程,研究了横管降膜蒸发过程中的流动特性和传热特性,归纳了管间距、喷淋密度对横管降膜蒸发过程中流动特性和传热特性的影响.实验结果表明:喷淋密度的增...     

小型太阳能海水淡化装置

基于空气增湿-除湿海水淡化技术,采用热海水与空气逆流对喷的空气加湿器,设计了结合太阳能集热器的小型太阳能海水淡化系统。试验结果表明,该结构的空气加湿器具有很好的加湿效果,出口空气相对湿度可达到98%以上。当喷水温度为60℃、空气流量为11.8 L/s时,该小型海水淡化装置产水率可达3.42 kg/h。     

三效管式太阳能海水淡化装置性能分析

设计制造了一种三效管式太阳能海水淡化装置,对该装置进行了产水性能试验,给出了产水率、累计产水量随时间变化的曲线。试验结果表明,在全天累计辐照量为22.09 MJ/(m2·d)的情况下,装置全天累计产水量为2.48 kg。文章重点研究了系统的传热传质机理,构建了理论模型,利用数值计算软件Matlab对装置进行了性能分析,得到了装置的各级产水率、总产水量等数据。比较计算结果和试验结果表明,两者最大误差只有11%,说明所建立的理论模型是比较准确的。     

Brackish water desalination by a stand alone reverse osmosis desalination unit powered by photovoltaic solar energy

Desalination of brackish water as a viable option to cope with water scarcity and to overcome water deficit in Jordan is assessed. A stand alone reverse osmosis (RO) desalination unit powered by photovoltaic (PV) solar energy is proposed, and a computer code in C++ was generated in order to simulate the process, and to predict the water production at 10 selected sites based on the available solar radiation data, sunshine hours and salinity of the feed water (TDS of 3000, 5000, 7000, and 10,000 mg/L). It was found that most of the selected sites showed favorable application of the proposed system in Jordan. Tafila, Queira, Ras Muneef, H-4, and H-5 are the most favorable sites. With TDS of 7000 mg/L, the highest annual water production of 1679 m³/year was observed in Tafila, followed by Queira with production of 1473 m³/year. Ras Muneef, H-4, and H-5 showed close to each other production of 1363, 1345, and 1340 m³/year, respectively. Among the most favorable sites (Tafila, Queira, Ras Muneef, H-4, and H-5), Ras Muneef was found to be the best site in terms of the daily amount of water produced during the driest months of the year (May–September). Its production during these months forms about 65% of its total daily water production during a 1-year cycle, while for each of the other most favorable sites namely Tafila, Queira, H-4, and H-5, a 61% of production was observed during the same period.     

横管降膜低温多效蒸发海水淡化系统的优化设计

随着横管降膜蒸发技术在低温多效蒸发海水淡化系统中的应用和推广,低温多效蒸发海水淡化技术以其传热系数高、热耗量小、要求供热的温位低等优点成为未来第二代海水淡化技术的主流技术.本文开展了横管降膜低温多效蒸发海水淡化系统的优化设计,比较了不同流程下低温多效蒸发海水淡化系统的热力特性,串并结合流程以其传热面积小、设备制造成本低...     

功能表面降膜蒸发传热特性的实验研究

研究了处理表面镀铬铝管、PTFE铜管和纯铝氧化管水平管降膜蒸发传热，研究了喷淋密度、热流密度、管内蒸汽速度和管表面处理对降膜蒸发传热特性的影响。实验结果表明：在表面蒸发区，水平管降膜蒸发传热系数随热流密度的增加而提高，随喷淋密度增大先降低后升高，冷凝例传热系数基本保持不变。总传热系数对操作条件变化很不明显，表面阳极氧化膜使传热系数略有下降，但由于其优良的抗垢时蚀性能，非常有必要再进行深入地研究。     

Modeling and experimental validation of a humidification–dehumidification desalination unit solar part

This paper presents the modeling and the experimental validation of air and water solar collectors used in humidification-dehumidification (HDH) solar desalination unit. The solar desalination process is currently operating under the climatological conditions of Sfax (34 N, 10 E), Tunisia. To numerically simulate the air and water solar collectors, we have developed dynamic mathematical models of the solar collectors. The resulting distributed parametric systems of equations are transformed into a system of ordinary differential equations (ODEs) using the orthogonal collocation method (OCM). A comparison between numerical and experimental data was conducted. It was found that the two-temperature mathematical model describes more precisely the real behaviour of the water solar collector than the one-temperature mathematical model. It was also shown that the developed mathematical models are able to predict accurately the trends of the thermal characteristic of the water and air solar collectors. As a result, the proposed models can be used to size and test the behaviour of such a type of water and air solar collectors.     

大型水平管降膜蒸发器管外热力参数分布计算分析

将分布参数方法与三维有限容积数值计算方法相结合,对大型水平管降膜蒸发海水淡化装置内的海水蒸发过程进行了模拟计算,获得了海水温度、海水盐度、二次蒸汽流速等参数的三维空间分布。详述了传热系数、海水沸点升高、传热温差等参数的空间分布特征。为低温多效蒸发海水淡化装置的工作特征理论提供了支持,为海水淡化装置的大型水平管降膜蒸发器分析与设计提供了理论基础。     

Impact of solar energy cost on water production cost of seawater desalination plants in Egypt

Many countries in North Africa and the Middle East are experiencing localized water shortages and are now using desalination technologies with either reverse osmosis (RO) or thermal desalination to overcome part of this shortage. Desalination is performed using electricity, mostly generated from fossil fuels with associated greenhouse gas emissions. Increased fuel prices and concern over climate change are causing a push to shift to alternative sources of energy, such as solar energy, since solar radiation is abundant in this region all year round.     

Sustainably integrating desalination with solar power to overcome future freshwater scarcity in China

Freshwater resources and energy are the two material foundations of human survival and the two challenges for human sustainable development. China’s huge population needs a large amount of freshwater for basic necessities. Desalination is an intelligent and promising technology for increasing water resources to realize a sustainable supply of freshwater. However, high levels of energy consumption and greenhouse gas emissions have restricted the development of desalination. Solar energy has the unique advantage that it can be harnessed in different forms. This paper discusses the water resources and solar energy utilization status in China and presents a comprehensive review on a possible solution: coupling desalination technologies with sustainable energy. China’s desalination market is reviewed, and the energy consumption for several desalination processes is summarized to present a brief outlook of desalination techniques in China. Potential coupled methods for solar-powered desalination are compared. This study will facilitate understanding of the latent water crisis in China and help China’s desalination market transition from conventional energy sources to choose an appropriate solar-powered desalination process.     

Status of solar desalination in India

The work was motivated by the increasing awareness of the need for enhancing water supplies schemes in arid lands featuring an appropriate technology for solar energy use in the desalination field in India. The fresh water crisis is already evident in many parts of India, varying in scale and intensity at different times of the year. India's rapidly rising population and changing lifestyles also increases the need for fresh water. Fresh water is increasingly taking centre stage on the economic and political agenda, as more and more disputes between and within states, districts, regions, and even at the community level arises. The conventional desalination technologies like multi stage flash, multiple effect, vapor compression, iron exchange, reverse osmosis, electro dialysis are expensive for the production of small amount of fresh water, also use of conventional energy sources has a negative impact on the environment. Solar distillation represents a most attractive and simple technique among other distillation processes, and it is especially suited to small-scale units at locations where solar energy is considerable. India, being a tropical country is blessed with plenty of sunshine. The average daily solar radiation varies between 4 and 7 kWh per square meter for different parts of the country. There are on an average 250–300 clear sunny days in a year, thus it receives about 5000 trillion kWh of solar energy in a year. In spite of the limitations of being a dilute source and intermittent in nature, solar energy has the potential for meeting and supplementing various energy requirements. Solar energy systems being modular in nature could be installed in any capacity as per the requirement. This paper consists of an overall review and technical assessments of various passive and active solar distillation developments in India. This review also recommended some research areas in this field leading to high efficiency are highlighted.     

Desalinated water and hydrogen generation from seawater via a desalination unit and a low temperature electrolysis using a novel solar-based setup

This study investigates the proficiency of employing solar energy in a novel setup geared towards simultaneous production of desalinated water and hydrogen wielding parabolic trough solar collectors (prime mover) in three solar radiation approaches; low radiation, high irradiation and no radiation. Targeted for coastal areas, this setup generates electricity using an organic Rankine cycle; utilizing its waste heat, a desalination unit applying humidification and dehumidification processes, yields desalinated water. Subsequently, hydrogen is produced through exploiting a proton exchange membrane electrolyser as a low temperature electrolyser fed by electricity and water. One of the cardinal points of this system is the production of hydrogen by means of electricity and desalinated water obtained from previous stages. With the purpose of determining the efficiency of this setup, a parametric study has been conducted grounded on the effect of important parameters on production rates and different efficiencies. Ensuing, multi-objective optimization is set forth by implementing a genetic algorithm in order to effectuate the optimal design state. The results indicated that the desalination rate in the three solar radiation approaches mentioned are 1.76 kg/s, 1.07 kg/s and 1.36 kg/s, respectively, and the hydrogen production rate are 4.33 g/s, 2.62 g/s and 3.54 g/s, correspondingly.     

Economic analysis of a solar assisted desalination system

This paper deals with an economic analysis of a solar assisted desalination system. The analysis is carried out for four types of applications, two domestic, a hotel and a village. It is shown that solar desalination is viable for the two bigger installations (hotel and village) with water prices below C£0.89/m³. It is also shown that the water cost is insensitive to the changes in method of payment or to small variations in direct costs. It is not worth operating the desalination system solely on solar energy due to the high cost of the desalination system and the diurnal nature of the solar input which implies high percentage of inactive time.     

基于海洋温差能的海水淡化小试系统的建立及试验研究

介绍了利用海洋温差能进行海水淡化的基本原理,建立了设计规模为每小时淡水产量5 kg、模拟表层海水温度29 ℃、深层海水温度10 ℃的小试系统并进行了实验测试,得到了表层海水、深层海水流量与淡水产量的关系.实测结果表明,额定工况下最佳闪蒸温度为23.5 ℃,单位能耗为3.79 kWh.     

一种连续式冷冻法海水淡化方法及其特性分析

给出了一种基于界面渐进原理的连续式冷冻法海水淡化新方法,该方法具有易于大规模连续生产、淡化水中的含盐量易于控制、制取淡化水的能源消耗低等特点。在对其工作过程进行简要介绍的基础上,计算分析了该方法的主要特性指标吨水能耗比,并对下一步需开展的工作进行了探讨。