Solar desalination using the vacuum freezing ejector absorption (VFEA) process

This paper consists of design analysis and economic evaluation of a solar-assisted vacuum freezing ejector absorption (VFEA) desalination plant with a capacity of 1 mgd and located in Abu Dhabi, UAE adjacent to the coast of the Gulf. The effect on the design and plant cost of variations in several of the operating parameters was investigated. These parameters are: the sea water salinity, the sea water temperature, and solar collector outlet temperature. Two collector outlet temperatures were used, namely 90°C and 120°C typical of flat plate and evacuated tube collectors, respectively. The absorber loop of the VFEA system uses a sodium hydroxide solution with concentration ranging from 0.5 (dilute stream) to 0.6 (concentrated stream).The results indicate that the capital cost of the VFEA system increases by increasing the sea water salinity and sea water temperature. The capital cost of the system decreases when using the higher value of collector outlet temperature (120°C) typical of evacuated tube collectors. The thermal load on the concentrator is also affected by the sea water salinity and collector outlet temperature with the load increasing with increasing the sea water salinity. The load drops substantially for the collector outlet temperature of 120°C as compared to 90°C.Life cycle savings in fuel costs of the solar-assisted VFEA plant were also estimated using a set of economic ground rules with the objective of specifying the optimum collector area which yields the maximum life cycle savings. It was observed that the optimum area increases with increasing the sea water salinity.     

Desalination using ambient air: simulation and energy optimization

This work applies to process design, simulation, analysis, and optimization to minimize the energy requirements for producing desalinated water using ambient air (humidification and dehumidification process). The only operating cost is for the use of air blower to supply air flowrate of 65-70 kmol/h. The production rate is 1 gpm of desalinated water per 2.25 gpm of saline water. By using process simulation and applying energy optimization concepts, the process parameters were manipulated and analyzed so that the feed saline water to the column is used to cool the exit air stream. The proposed approach reduced the solar energy requirement by 65%, and the cooling energy is eliminated. A case study is pursued to show the effectiveness of using process simulation and energy optimization concepts.     

环周进汽型喷射器的火用效率分析

对环周进汽型喷射器的工作原理进行了深入分析,从可用能角度出发,建立了分析喷射器运行经济性的火用分析模型,计算得到了不同结构参数和运行参数下喷射器的火用效率,对喷射器火用效率的影响因素进行了分析,并将计算值与实验结果进行了对比。研究结果表明,喷射器的火用效率随入口水温、引射系数和升压比的升高而增大,随蒸汽压力的变化存在最小值,计算和实验得到的各参数对喷射器火用效率的影响规律基本一致,为环周进汽型喷射器的设计和应用提供了理论基础。     

Experimental investigation of a two-stage solar humidification–dehumidification desalination process

This paper experimentally evaluates a two-stage technique to improve the humidification–dehumidification process in fresh water production from brackish water. According to modeling results of multi-stage process and on the basis of construction cost estimation, using a two-stage process is the most suitable choice that can improve important parameters such as specific energy consumption, productivity and daily production per solar collector area and thus, investment cost. A pilot plant was designed and constructed in an arid area with 80 m² solar collector area to evaluate the two-stage process. This unit was tested on cold and hot days. The effect of main parameters on fresh water production of the unit is studied. Experimental results show that two-stage HD desalination unit can increase heat recovery in condensers and hence, reduce thermal energy consumption and investment cost of the unit. Moreover, productivity can be increased by 20% compared with the single-stage unit.     

Energy Analysis and Air Entrainment in an Ejector Induced Downflow Bubble Column with Non‐Newtonian Motive Fluid

In an ejector induced downflow bubble column energy supplied as a high velocity liquid jet is utilized in different sections of the ejector‐contactor system, which leads to air entrainment at the secondary entrance of the ejector. The energy losses in the different sections, viz. ejector, mixing zone and gas‐liquid bubbly flow zone have been evaluated theoretically. Experimental results show that the total energy losses calculated on the basis of theoretical expression are almost the same as energy supplied by the liquid jet. A simple correlation was developed for the air entrainment rate in terms of operating and design parameters of the system.     

Economics of small solar-assisted multiple-effect stack distillation plants

The objective of this paper is to compare the economics of using solar energy to operate small, multiple-effect seawater distillation systems in remote areas with the conventional method of using fossil fuels. The particular multiple-effect system used is an advanced horizontal-tube, falling-film system called “multiple-effect stack” (MES) in which the pumping energy requirement is relatively low compared with the horizontal in-line system. Three system configurations were investigated: (1) a conventional system using a steam generator to provide steam for the MES evaporator and a diesel generator to provide pumping power, (2) a solar-assisted system which uses solar thermal collectors to provide hot water (instead of steam) for the evaporator and a diesel generator for pumping power, and (3) a solar stand-alone system which uses solar thermal collectors for the evaporator heat requirement and a solar PV array to provide electrical energy for pumping. At the present time, solar energy cannot compete favorably with fossil energy, particularly under the present international market prices of crude oil. However, in many remote sunny areas of the world where the real cost of fossil energy can be very high, the use of solar energy can be an attractive alternative. Two important cost parameters affect the relative economics of solar energy vis-à-vis conventional (fossil) energy: the collector cost in dollars per square meter and the cost of diesel oil in dollars per giga Joule. Solar energy becomes more competitive as the local cost of procuring conventional fuel increases and as the collector cost decreases. The water cost from a solar thermal-diesel-MES system (configuration #2) can be seen to approach the water cost from a steam generator-diesel-MES system (configuration #1) when the collector cost drops to $200/m² and diesel oil cost at the remote site reaches $50/GJ. Using a 100% solar system (configuration #3) with solar thermal and solar PV collectors, the economics was seen to improve in favor of the solar system. Even when diesel fuel can be procured at $10/GJ at the remote site, the cost of water from the solar system can be seen to approach that from a conventional plant when thermal collectors costing $200/m² are used. The cost of water from the solar system was shown to be always less than that from a conventional system which uses diesel oil procured at the high price of $50/GJ, but always higher than water produced from a conventional system using diesel oil at the low price of $10/GJ.     

太阳能喷射制冷系统临界冷凝特性实验研究

为了了解太阳能喷射制冷系统的系统性能随冷凝温度的变化规律,进而提出合理的系统运行控制策略,文中设计并搭建了太阳能喷射制冷实验研究平台,以HFC134a为制冷剂,对太阳能喷射制冷系统的临界冷凝特性进行了实验研究.研究表明:太阳能喷射制冷系统工作时,系统性能系数(COP)、制冷量和能效比(EER)等参数随着冷凝温度的升高呈...     

Applicability of flashing desalination technique for small scale needs using a novel integrated system coupled with nanofluid-based solar collector

The present study introduces an attempt for the application of flash desalination technique for small scale needs. An integrated system uses a flashing desalination technique coupled with nano-fluid-based solar collector as a heat source has been made to investigate both the effect of different operating modes and that of the variation of functioning parameters and weather conditions on the fresh water production. The flashing unit is performed by similar construction design technique of commercial multi-stage flashing (MSF) plant. The thermal properties of working fluid in the solar collector have been improved by using different concentrated nano-particles. Cu nano-particle is used in the modeling to determine the proper nano-fluid volume fraction that gives higher fresh water productivity. An economic analysis was conducted, since it affects the final cost of produced water, to determine the cost of fresh water production. Although a system may be technically very efficient, it may not be economical. The effect of different feed water and inlet cooling water temperatures on the system performance was studied. The mathematical model is developed to calculate the productivity of the system under different operating conditions. The proposed system gives a reasonable production of fresh water up to 7.7 l/m²/day under the operation conditions. Based on the cost of energy in Egypt, the estimated cost of the generated potable water was 11.68 US$/m³. The efficiency of the system is measured by the gained output ratio (GOR) with day time. The gained output ratio (GOR) of the system reaches 1.058. The current study showed that the solar water heater collecting area is considered a significant factor for reducing the water production cost. Also, the produced water costs decrease with increasing the collecting area of the solar water heater. The volume fractions of nano-particle in solar collector working fluid have a significant impact on increasing the fresh water production and decreasing cost.     

The exchange crystallization freeze desalination process

The Exchange Crystallization (E-C) freeze desalination process is a unique and innovative approach to the problem of sea water desalting. Utilizing solid-liquid phase transformations to accomplish the freezing, the E-C plant avoids both costly corrosion problems and the mechanical intricacy of vapor handling. The use of exchange engines as energy recovery devices permits the E-C process to compare favorably with other freezing processes and to be substantially lower than evaporation processes in the area of energy consumption. On both an energy and capital cost basis, the E-C process is one of the most attractive desalination processes presently available.The operational problems encountered in the E-C process should be solvable by utilizing existing technology. Development work is presently under way to eliminate the problems which have been identified. In the near future, the E-C process will prove its potential for economic sea water desalination.     

Parametric investigation of a double-effect solar still in comparison with a single-effect solar still

This paper reports the use of two mathematical models to compare the productivity of single-effect and double-effect solar stills under different climatic, design and operational parameters in Oman. The shallow water basin, 23° cover tilt angle, 0.1 m insulation thickness, and asphalt coating of the solar still were found to be the optimum design parameters that produced an average annual solar still yield of 4.15 kg/m²/d and 6 kg/m²/d for single and double effect solar stills, respectively. A cost analysis is carried out to shed some light on the potential of utilizing an array of single-effect solar stills or double-effect solar stills for the production of drinking water in remote areas in Oman. It has been found that the unit cost for distilled water using an array of single-effect solar stills is $74/1000 gal (16.3 $/m³) or $62.4/1000 gal (13.7 $/m³) when using a double-effect solar still. The cost saving is 15.7%.     

A naturally circulated humidifying/dehumidifying solar still with a built-in passive condenser

A numerical study has been carried out to investigate the transient thermal performance of a naturally circulated humidifying/dehumidifiying solar still. A comparison of forced circulation performance and the influence of different environmental, design, and operational parameters on the still productivity and efficiency were investigated. The naturally circulated still shows very similar results to that of forced circulation. This finding is of significant technical and economic importance. Different attempts have been considered to investigate the effect of partial storage of basin energy and partial recovery of condensation energy. The results show insignificant changes on still performance. An economic assessment of water production cost was also highlighted and showed that solar stills can challenge other technologies for special applications.     

新型闭式太阳能海水淡化装置及其性能模拟

本文提出了一种闭式海水淡化装置,阐述了系统的工作原理,建立了相应的数学模型。就冷却水流量、海水喷淋量、集热器面积、蒸发器尺寸等因素对系统淡水产量的影响情况进行了计算机模拟,根据实验测得的气象数据对一天内系统淡水产量随时间变化情况进行了模拟,并根据典型的月平均日气象数据对系统一年内每个月的系统性能进行了分析。分析表明,不计系统夜间运行时的淡水产量,在西安地区系统淡水产量可以达到4.6kg/d.m2。     

自然工质风冷太阳能双级喷射中低温空调制冷系统的设计及性能分析

依据中低温空调温度要求,分别以水、氨、R290和R600a为工质,设计了额定制冷量为10kW的风冷太阳能双级喷射制冷系统并对其进行变工况性能分析。在获得相同制冷量和室内温度的条件下,水系统最省材料,其次是氨和R290系统,且二者相当,R600a系统最耗材。4种工质系统均具有较强的变工况性能;综合考虑环境温度和太阳辐照度的影响,各系统制冷能力相当。水系统的COP较其他系统的高,且在低太阳辐照度时更明显;其余3个系统COP从高到低依次为氨、R290、R600a。在太阳辐照度较弱地区,使用水喷射制冷系统更合理。     

Development of a marine osmotic solar still for sea water desalination

This paper describes the principals of an approach to desalt sea water via exploitation of solar energy and membrane technology. The approach has been under test aimed at commercialization of the process in the near future. The process is a combination of diffusion across a salinity gradient established by evaporation and distillation in the form of a solar still-type arrangement. An osmotic membrane is used to separate the liquids of different solid concentration. In other words, the desalination devise is a hybrid of a solar still and osmosis unit which could operate in an economical and efficient utilization of solar energy.The marine osmotic solar still does not have the complexity of a solar powered reverse osmosis that draws power from an active solar collection system. Solar collectors and associated energy delivery systems, if used with an RO unit, will be rather expensive, and will occupy a large space. Conventional solar stills occupy large space and are rather inefficient in water production. The marine osmotic solar still is a stand alone solar energy system which is capable of providing distilled water of high purity. It can also be constructed offshore or on land near the seashore.The offshore scheme involves floating units in contact with the sea water. Each is capable of producing 150 gallons of water containing less than 50 ppm of dissolved solid. A conceptual design has been developed and described here of a pilot plant that produces 6,000 gpd.Material tests have been conducted in Singapore and Malysia to assure proper selection of structural material that are suitable for the highly corrosive environment. Measurements on flow rate have shown values of 15 to 20 gallones per square foot per day. The measurements have been conducted in Long Island Sound off Southport, Connecticut.In this paper, the actual design of the plant is described and results of material tests and simulation system analysis are reported. A comparison is made with conventional solar stills and solar powered membrane desalination processes. Results of an extensive marketing research are reported for various applications of the process.     

Optimization of Solar Kiln for Drying Wood

Theoretical investigation of the physical process of solar drying of timber based on conventional heat and mass transfer equations is presented. The governing equations and boundary conditions of the mass diffusion through the wood timbers are derived; also the governing equations of the components of the solar kiln are presented. The finite difference technique is used to solve the set of these equations by means of a simulation program that is based on object-oriented approach. The simulation program is used to investigate the effect of several design parameters on the drying rate and duration of the wood timbers in order to accomplish the drying process with minimal drying defects. These parameters include the ventilation conditions that control the drying schedule inside the solar kiln, wood volume as a ratio to the solar kiln absorber area, wood timber thickness, season of drying, the drying air velocity, and the stresses that formed on the timber boards due to drying with these several parameters, leading to derive the limit of damage for a selected local wood type. The selected local wood type is Casuarina, which is common in Egypt, and it is commonly used in many simple industries.     

下喷式环流反应器环隙气含率影响因素

下喷式环流反应器是一种用于强化气-液两相反应过程的新型装置，虽然已在工业上有了较广泛的应用，但对其理论研究远未成熟，其工业装置的设计仍依赖于实验和经验。本文借助实验室自制实验装置，对下喷式环流反应器环隙气含率的影响规律进行了研究。首先，对喷射器的吸气量进行了测量，获得了不同条件下喷射器最大吸气量的性能曲线；在此基础上，分别研究了气相流量、液相流量以及喷射器安装位置对环隙气含率的影响规律。结果表明：气相流量和液相流量对气含率具有重要的影响，随着气相流量和液相流量的增大，气含率快速提高，而喷嘴位置对气含率的影响相对较小；考虑到增加气相流量和液相流量所需要的能耗和设备代价，通过增加液相流量来达到提高气含率的目的是优选方案。     

太阳能直热式多效蒸馏淡化系统热力分析

本文设计了一种太阳能直热式多效蒸馏淡化系统,它将太阳能直热式系统和多效蒸馏系统相结合来淡化苦成水。文中对这一系统进行产水量和蒸发器的热力分析并进行了模拟计算,结果表明当太阳能直热式系统出水温度达到60℃,系统一天的产水量可达40Kg,当多效蒸馏的效数为4时,淡水的成本在5—7元。在太阳能资源丰富而淡水缺乏的地区,使用太阳能直热式多效蒸馏系统是可行的。     

准二级压缩-喷射热泵的设计与实验研究

为回收利用普通准二级压缩热泵系统中补气回路的有用能,提出了准二级压缩-喷射热泵系统。文中对其设计方法进行了介绍,搭建了蒸发温度-20℃样机实验台。测试结果表明,在保证制热量的情况下,能效比较普通补气系统增加3%—5%,设计方法能为其他工质、其他容量的涡旋压缩机准二级压缩-喷射复合热泵系统的设计提供参考。     

Optimization of Solar Kiln for Drying Wood

Abstract

Theoretical investigation of the physical process of solar drying of timber based on conventional heat and mass transfer equations is presented. The governing equations and boundary conditions of the mass diffusion through the wood timbers are derived; also the governing equations of the components of the solar kiln are presented. The finite difference technique is used to solve the set of these equations by means of a simulation program that is based on object-oriented approach. The simulation program is used to investigate the effect of several design parameters on the drying rate and duration of the wood timbers in order to accomplish the drying process with minimal drying defects. These parameters include the ventilation conditions that control the drying schedule inside the solar kiln, wood volume as a ratio to the solar kiln absorber area, wood timber thickness, season of drying, the drying air velocity, and the stresses that formed on the timber boards due to drying with these several parameters, leading to derive the limit of damage for a selected local wood type. The selected local wood type is Casuarina, which is common in Egypt, and it is commonly used in many simple industries.