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。     

竖壁自储水式太阳能蒸馏装置运行特性分析

设计一台三效回热竖壁自储水式太阳能海水淡化装置。对其在实际天气下的运行参数进行测试,得到装置全天温度、产水率及累计产水量变化曲线,实验测试中装置性能系数为1.35。构建装置的传热传质计算模型,通过与实验数据对比验证模型的准确性并进一步对装置特性进行研究。利用所构建模型分析系统的能量流动情况,结果发现无效热能散失过大是装置在实际天气运行时性能系数偏低的主要原因。最后,对该类太阳能海水淡化系统经优化后的实地运行性能进行预测和评估,为工程应用提供指导。     

漂浮式聚光升膜多效太阳能蒸馏器的性能研究

提出一种漂浮在海面上进行淡化产水的聚光升膜多效太阳能蒸馏器，该淡化装置包含一个抛物面聚光镜和多个垂直布置的蒸发-冷凝单元。采用吸水芯作为蒸发器，利用毛细吸力使海水形成上升的液膜，有效减少了加热损失。建立理论模型分析装置内部的传热传质过程。通过实验研究不同运行参数对装置温度、产水量和比能耗的影响。室内稳态研究结果表明，当太阳辐照度为900 W/m²时，蒸馏器内部温差为56.9℃，产水率可达到2.64 kg/(m²·h)。在户外平均太阳辐照度为603.7 W/m²的条件下，装置一天产水量为5.3 kg/(m²·d)，日平均比能耗为1591.6 kJ/kg。     

一种竖管降膜蒸发太阳能海水淡化装置的实验研究

设计了一种竖管降膜—横管冷凝的太阳能海水淡化装置。以电加热作为供热热源,在不同的运行参数下进行了实验研究,分析了影响装置性能的各种因素。分析表明:在供能相同的情况下,闭式循环的单位能耗产水率比开式循环提高了约1.0~1.5倍;提高循环热水进口温度有利于提高产水率和单位能耗产水率;海水流率有一个理想取值范围。     

具有折皱底面的多级迭盘式太阳能蒸馏器的模拟实验研究

设计制作了一台蒸发面积为0．2025m^2，各盘具有折皱底面的多级迭盘式太阳能蒸馏器，用普通电热器作为热源对之进行了模拟实验研究。对装置的瞬态和稳态性能进行了测试，给出了在不同迭盘数的情况下，蒸馏器的运行温度、能耗与产水量的关系，并计算了在不同运行温度下装置的性能系数。结果表明，当温度大于70℃时，内强化传热多级迭盘式太阳能蒸馏器有良好的产水性能．对影响产水率的其它因素也作了讨论。     

海水淡化中水平管降膜蒸发器传热传质的研究现状

水平管降膜蒸发器广泛应用于制冷、食品和海水淡化领域,其传热传质过程直接影响到整个蒸发器的性能,因而受到各国研究者的重视。介绍了水平管降膜蒸发器的传热传质过程及影响因素,通过对传热温差、蒸发温度、热通量、喷淋密度、管束布置方式等对液膜厚度、液膜流动状态、热阻、液体黏度、表面张力等的影响分析进而得出其对传热传质过程的影响。     

回热对竖管式太阳能海水淡化装置性能的影响

针对管式太阳能海水淡化装置淡水产量较低的问题,提出一种新的具有回热功能的竖管式太阳能海水淡化装置,通过建立装置内部传热传质关系,得到竖管式太阳能海水淡化装置理论淡水产量预测计算方法,分别对单效和两效淡化装置在回热和非回热运行条件下,定温运行工况时的淡水产量、进料海水温度等进行试验研究。结果表明,运行温度为80℃,两效淡化装置在回热运行条件下,淡水产量比非回热运行条件时增加13.32%,单效淡化装置在回热运行条件下,淡水产量比非回热运行条件时增加32.83%,进料海水温度明显升高,装置淡水产量试验测试值与理论计算值趋势一致,吻合度较好。     

横管降膜蒸发内回热式太阳能海水淡化装置的实验研究

设计建造了一台利用太阳能或其它余热驱动的横管降膜蒸发内回热式海水淡化装置，并利用模拟热源对该装置进行了实验研究，由于在系统的蒸发及冷凝过程中，大部分水蒸汽的凝结潜热被重复利用于海水的预热及蒸发过程，因而系统具有较高的产水率，同时，由于在气流的闭式环过程中，蒸发腔中处于负压状态，冷凝腔中处于正压状态，强化了系统的产水性能，使系统的产水效率比传统的盘式太阳能蒸馏器提高了3倍左右，介绍了系统的瞬态特性及运行温度，供海水流率与产水量的相互关系，对影响系统产水率的其它因素进行了讨论。     

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。     

不同特征尺寸管式降膜太阳能海水蒸馏器热性能分析

为提高小型太阳能海水蒸馏器热能利用效率和产水速率,设计一种管式降膜太阳能海水蒸馏器,基于小高径比环形封闭空间水蒸气传热传质特性,分析特征尺寸和运行温度对装置单位冷凝面积产水速率的影响机理,研究不同特征尺寸管式降膜太阳能海水蒸馏器蒸发冷凝温差、竖直方向冷凝温度梯度等变化规律。结果表明,运行温度为85℃时,特征尺寸为0.015 m的管式降膜太阳能海水蒸馏器单位冷凝面积产水速率为0.696 kg/(h·m~2),比特征尺寸为0.035 m的蒸馏器增加10.48%,冷凝温度T_4为81.94℃,比特征尺寸为0.035 m的蒸馏器高3.83℃,在测试范围内蒸发冷凝温差最小为1.9℃,该研究可为强化管式太阳能海水淡化装置热质传递过程提供技术参考。     

多级降膜式太阳能蒸馏器的模拟实验研究

用热水作为供热热源,对一台小型多级降膜式蒸馏器进行模拟实验研究。介绍了实验装置,给出了不同条件下的产水量。研究了蒸发－凝结板偏离铅垂线的角度θ与产水量同蒸馏器单级和四级时的比产水率曲线。     

A novel integrated solar desalination system with multi-stage evaporation/heat recovery processes

A novel small-sized integrated solar desalination system with multi-stage evaporation/heat recovery processes is designed and tested in this study. The system consists of four linked collecting units and operates under barotropic and atmospheric pressure. Each of the four units contains a seawater tank and at least one solar collecting/desalination panel mainly comprising a simplified CPC (Compound Parabolic Concentrator) and an all-glass evacuated tube collector. In the last three units, heat exchangers made of copper tubes are inserted concentrically into the all-glass evacuated tubes to recover heat. In each unit, an independent desalination process including solar collecting, heat recovery (no heat recovered in the first unit) and seawater evaporation can be carried out completely. The experimental results show that the freshwater field of the designed system can reach as high as 1.25 kg/(h m²) in the autumn and the system total efficiency is close to 0.9. Both experimental results provide a striking demonstration that the designed solar desalination system has outstanding performance in solar collecting, heat recovery and seawater evaporation.     

Application of the concept of a renewable energy based-polygeneration system for sustainable thermal desalination process—A thermodynamics' perspective

Fossil fuel-powered thermal desalination processes have many harmful environmental effects including greenhouse gas (GHG) emissions and high-salinity brine discharge resulting in biological damages, in addition to energy losses because of the high temperatures of the streams leaving the desalination unit. In this study, a solar energy-based polygeneration approach has been proposed to address these issues. In the proposed system, concentrated solar parabolic trough technology is used to drive a multi-stage flash (MSF) desalination unit for production of fresh water. To recover the waste heat carried by the produced clean water, an organic Rankine cycle is integrated to produce electricity. In addition, to recover the waste heat carried by brine, an absorption cooling system is employed to provide cooling. In order to mitigate the effects of high-salinity brine, a pressure retarded osmosis (PRO) unit is installed, which reduces the salinity of the discharge and produces additional electrical energy. To ensure stable nighttime operations, a thermal energy storage (TES) system is also added to the system. A comprehensive thermodynamic analysis is conducted through mass, energy, and entropy, as well as exergy balances along with energetic and exergetic efficiencies to assess the overall performance of the system. The attained results show that at reference conditions with an overall parabolic trough collectors (PTCs) area of 100 000 m², the system produces 583.3 kW of electricity, approximately 4284 kW of cooling, and 1140 m³ of freshwater daily. Furthermore, the effects of changing operational conditions on the overall performance of the system are investigated. At design conditions, the overall energetic and exergetic efficiencies of the system are found to be 34.54% and 14.55%, respectively.     

A study on membrane distillation by a solar thermal‐driven system

Membrane distillation (MD) is a membrane separation process that has long been investigated in small scale laboratory studies and has the potential to become a viable tool for water desalination. MD is a separation process that combines simultaneous mass and heat transfer through a hydrophobic microporous membrane. A solar collector is used in direct contact membrane distillation (DCMD) to heat seawater as a temperature driving force in heat transfer to establish seawater desalting systems. The effect of the temperature difference makes the brine vaporize in the hot fluid side and condense in the cold fluid side. The optimal operating parameters on the pure water production rate will also be examined in this study. The purposes of this study are to develop the theoretical heat and mass transfer formulations, simulate heat transfer rate of solar collector with internal fins in membrane distillation, and investigate the mass‐transfer efficiency improvement in membrane distillation with the brine flow rate, solar collector efficiency, and temperature difference between both sides of membrane as parameters. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 417–428, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20172     

Derivation of heat transfer equations for a closed solar desalination pond to predict the produced mass of potable water

In many developing countries, access to clean and drinkable water is a major necessity. The sweetening of saline water in these areas is used to provide water for different requirements. The solar distillation is based on solar technology. The aim of this study is to calculate the efficiency of a solar desalination pond to produce freshwater. To achieve the purpose of research and validation of the obtained mathematical results, the experimental measurements are used. The conservation law of energy is considered and mathematics is applied to predict the required heat for the evaporation process. Finally, a new mass transfer equation on the basis of experimental data is introduced to predict the efficiency of solar desalination pond performance. The obtained results show the maximum deviation between the experimental and theoretical condensation rates. In October, the deviation is 4.93%, approximately, whereas, this deviation for June is 1.75%, approximately. So, the mathematical equation can predict the efficiency of a solar desalination pond precisely.     

Experimental study of a solar desalination pond as second stage in proposed zero discharge desalination process

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20 wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also, evaporation rates are calculated theoretically and are verified by experimental data. Theoretical values predict evaporation rate accurately. Results show good agreement with experimental data. According to results, maximum evaporation rate is 5 l/m² day when the insolation rate is about 24,602 kJ/m² day Solar energy absorption factor on June is max. Also, experimental results show the best proposed time to gain highest thermal energy is on spring therefore performance efficiency of solar desalination pond promote on spring comparing with the other months. Extracted data for specific gravity prove the bottom of solar desalination pond, layer 1, is best zone for energy saving and energy utilization.Also, theoretical values of evaporation rate are calculated according to measured temperatures and related mass conservation equation. Comparison between theoretical and experimental values shows dusty weather, humidity and wind velocity affects on heat transfer coefficients approximately. So, deviations between theoretical data and measured values can be explained. Results show good agreements with experimental data.     

Design and simulation of water-cooled dehumidifier for HDH desalination plant

Condensers are widely used in thermal applications to transfer the maximum heat between the working fluids and change the phase of vapor. In basic thermal-based humidification–dehumidification (HDH) desalination, a condenser is used as a water-cooled dehumidifier for improving freshwater production within the minimum area. In this thermal-based HDH system, desalinated water production is the major output. The simulation tool is used to analyze the thermohydraulic performance of a water-cooled dehumidifier. In this thermohydraulic analysis, variables, like, airflow rate, tube diameter, and longitudinal pitch are thoroughly investigated to identify the optimum parameters for improving the performance of the water-cooled dehumidifier. The obtained results indicate that the heat transfer area and performance index are increased when the airflow rate and tube diameter change. But at 8 and 10 mm tube diameter, the surface area and performance index are contradictory in nature while longitudinal pitch varies from 30 to 45 mm. At 12.5 mm tube diameter, surface area and performance index decrease gradually but the certain period of pitch limit performance increases markedly. In addition, the yield of HDH desalination has been investigated. When the mass flow rate changed from 100 to 500 kg/h, it was 0.667–3.32 L/h.     

降膜蒸发—凝结型闭式循环太阳能蒸馏系统的模拟实验研究

建立了一套采光面积为1．07m∧2、主动回收蒸汽潜热及浓海不余热降膜蒸发－凝结型闭式循环太阳能蒸馏系统,4盏卤素灯作为太阳能模拟器，对该系统进行了模拟实验研究。实验结果表明，由于在本蒸馏系统中采用了强迫降膜蒸发及降膜凝结技术，使其中大部分的蒸汽潜热以及浓盐水的显热都得到了重复利用，单位采光面积的产量相对于传统的盘式（单级）太阳能蒸馏器提高了2－3倍。     

复合抛物面聚光太阳能加湿除湿脱盐系统研究

为提高装置热利用效率,减少外部换热环节减少热损失、减少盐垢、提高集热器使用寿命,研究一种利用复合抛物面聚光器（CPC）为系统供能,建造小型太阳能海水淡化系统。实验研究发现：在系统稳态条件下,系统产水量一天可达7908 g,最高小时产水量在12:00达861 g/h,脱盐率达99.9%以上,瞬时系统装置性能GOR（gained output ratio）最高为1.14,最高瞬时有用能为1114.9 W,在太阳辐照度达到最高1072 W/m²时,此时加湿箱湿度达到最大湿度为97%,11:30—16:00加湿箱湿度一直在90%以上。     

Experimental analysis and exergy efficiency of a conventional solar still with Fresnel lens and energy storage material

This study focuses on the experimental investigation and exergy analysis of a modified solar still (MSS) with convex lenses on glass cover to collect the solar radiation at the focus on surface water. A comparative analysis of the performance and yield of the MSS with convex lenses and the conventional single slope SS were carried out for the same climatic condition of Tanta (Egypt). Similarly, the effect of modification in the SS using convex lenses, with or without black stones, on the freshwater yield is experimentally investigated. The results indicated that the lenses focus the solar radiation to the water placed in the basin and increase the water‐glass temperature difference (T _w – T _g). The yield of freshwater from the MSS with the convex lenses is comparatively higher than that of the conventional SS (26.64%). In addition to convex lenses in the inner cover surface, freshwater yield improved by 35.55% by adding blue stones as energy material inside the basin under constant water mass of 30 kg. The maximum exergy efficiency of the SS with lenses and blue stones was 11.7%, while the SS with lenses alone was 4%. The quality of freshwater produced after desalination was well within the World Health Organization standards. The total dissolved solids and pH after desalination were 22 mg/L and 8.08, respectively.