Simulation of fresh water production using a humidification-dehumidification seawater greenhouse

A thermodynamic simulation study was performed on the influence of greenhouse-related parameters on a desalination process that combines fresh water production using humidification-dehumidification with the growth of crops in a greenhouse. With the system under study, surface seawater trickles down a porous front wall evaporator through which air is drawn into the greenhouse. The saturated air passes through a condenser, which is cooled using cold deep seawater or cool seawater coming out of the evaporators. Thermodynamic modeling of the seawater greenhouse system in our laboratory has shown that the dimension of the greenhouse had the greatest overall effect on water production and energy consumption. A wide shallow greenhouse, 200 m wide by 50 m deep gave 125 m³.d⁻¹ of fresh water. This was greater than a factor oftwo compared to the worst-case scenario with the same area (50 m wide by 200 m deep), which gave 58 m³.d⁻¹. Low power consumption went hand-in-hand with high efficiency. The wide shallow greenhouse consumed 1.16 kWh.m⁻³, while the narrow deep structure consumed 5.02 kWh.m⁻³ . The benefits of the development of the seawater greenhouse for arid regions are discussed.     

Micro-climatic environmental conditions inside a greenhousewith a built-in solar distillation system

A numerical study was carried out to investigate the micro-climatic environmental conditions inside a greenhouse-distillation system, self-sufficient for irrigating water. The greenhouse consists of the planting cavity, circulating air channels and roof solar distiller for the production of a rather modest rate of irrigating water. A turbulent, steady-state flow, energy and humidity concentration equations were solved using the numerical code FLUENT 6.1. Velocity vectors, steam function, isotherms and temperature and humidity distribution inside the greenhouse present the resultant: micro-climatic environmental conditions. The results are presented for hot days where cold and humid air (from the evaporative cooler) enters the greenhouse from one side and is circulated through the partially porous cavity (representing the plants) and flows through air flow channels and leaves from a vertical thermal chimney. The results show that, with the selected inlet flow conditions, the flow velocity, temperature, and relative humidity can be within the comfort values for plant growth. The effect of some important environmental, design, and operational parameters on greenhouse micro-climatic conditions has also been highlighted.     

Artificial neural network simulation of the condenser of seawater greenhouse in Oman

The prediction of freshwater production from the condenser of an agricultural seawater greenhouse is important for designing the greenhouse process. Two models, namely, Artificial Neural Network and multilinear regression (denoted as ANN and RA, respectively), were developed and tested to predict the freshwater production rate considering ambient solar intensity, condenser inlet moist-air temperature, humidity ratio and mass flowrate, and inlet coolant temperature. Statistical analysis indicated that all parameters significantly affected the prediction (p?<?0.05). The accuracy of the ANN and RA models was then compared to two models previously developed by Yetilmezsoy and Abdul-Wahab and Al-Ismaili et al. (denoted as Yetilmezsoy model and Al-Ismaili model, respectively). The ANN model showed the best prediction when seven statistical criteria were considered. The Pearson correlations for ANN, RA, Yetilmezsoy, and Al-Ismaili models were observed as 1.00, 0.98, 0.88, and 0.96, respectively, while mean absolute percentage errors (MAPE) were 17.84, 79.72, 63.24, and 80.50%, respectively. Hence it could be recommended to use ANN model for the prediction of freshwater production rate, however other three simple models could also be used with lower accuracy in the cases of unavailability of the ANN model.     

Modeling and simulation of the drying of thin sheets in a continuous infrared dryer

The model gives the temperature and moisture distributions of the air, and of the moist sheet, as a function of time and distance in the dryer. The influence of the sheet's velocity and that of the radiant energy on the dryer performance as well as the effect of the moisture content of the entering sheet have been studied. A set of 27 experiments was carried out using the infrared dryer in order to calibrate the model. In these, the following three variables each had three operational levels: web velocity, initial web moisture and heating power. The model predictions agreed very well with the experimental data. Model predictions using arithmetic averages for the parameters, and parameters correlated with operational variables, are also presented and discussed.     

An experiment with a plastic solar still

A solar still is a device which allows obtaining fresh water from seawater or brackish water. It utilizes the greenhouse effect by using solar energy. In a conventional solar still the production of fresh water in bright sunny weather and with warm air temperature is about 5-5.5 L m⁻² d⁻¹, according to the depth of the water in the solar still. In some devices it is possible to obtain efficiencies of up to 0.50 and 0.60. The aim of this research is to increase distillation productivity by utilizing the latent heat released by the condensing water steam. For this purpose the author built a solar still characterized by two basins (B₁ and B₂) superimposed upon each other. The building materials were a sheet of black Plexiglas for the bottom of the solar still, a sheet of transparent Plexiglas for all boxes, and a sheet of expanded polystyrene, used as insulating material. The solar still was hermetically sealed to reduce the leakage of vapor to the surroundings. The greatest quantity of fresh water obtained by the tested solar still was 1.7-1.8 L m⁻² d⁻¹. This result was achieved in the third week of July when solar radiation was 27-28 MJ m⁻² d⁻¹. The efficiency of the tested solar still was about 0.16. This low efficiency is probably due to the low temperature of the water contained in the still (about 50°C). The solar still has only been used in experiments for some months, during which it has not been possible to study the deterioration of the material (Plexiglas). These results show that an elaborate design and the increased costs for such design and construction do not always improve the water yield.     

船用海水淡化装置的产水水质特性及经济性分析

船用海水淡化装置是远洋船泊的必备设备之一,对产水水质特性及经济性进行研究具有重要的意义。本文设计搭建了一套板式蒸馏造水机性能测试平台,对系统产水pH和电导率随真空度变化规律以及进料水盐度和真空度对产水溶解性固体总量（TDS）的影响进行了研究,同时建立淡水成本数学模型探讨真空度和进料水流量引起的淡水产量变化对造水成本的影响,并进一步分析了油价、水价和渔船航行距离对淡水成本的敏感性问题。结果表明：真空度一定的情况下,进料水盐度升高,系统产水的TDS增大;真空度变化对系统产水pH影响不大,而对系统产水电导率、TDS和淡化水成本影响较大,且随着真空度的升高呈减小趋势。进料水流量为150L/h时,系统产水率最优造水成本最低,造水成本差价对油价的敏感性最高并且造水成本始终低于渔船运输淡水成本。     

A mixed integer optimisation approach for integrated water resources management

In areas lacking substantial freshwater resources, the utilisation of alternative water sources, such as desalinated seawater and reclaimed water, is a sustainable alternative option. This paper presents an optimisation approach for the integrated management of water resources, including desalinated seawater, wastewater and reclaimed water, for insular water deficient areas. The proposed mixed integer linear programming (MILP) model takes into account the subdivided regions on the island, the subsequent localised needs for water use (including water quality) and wastewater production, as well as geographical aspects. In addition, the integration of potable and non-potable water systems is considered. The optimal water management decisions, including the location of desalination, wastewater treatment, and reclamation plants, as well as the conveyance infrastructure for desalinated water, wastewater and reclaimed water, are obtained by minimising the annualised total capital and operating costs. Finally, the proposed approach is applied to two Greek islands: Syros and Paros-Antiparos, for case study and scenario analysis.     

Dynamic optimization of the methylmethacrylate cell‐cast process for plastic sheet production

Traditionally, the methylmethacrylate (MMA) polymerization reaction process for plastic sheet production has been carried out using warming baths. However, it has been observed that the manufactured polymer tends to feature poor homogeneity characteristics measured in terms of properties like molecular weight distribution. Nonhomogeneous polymer properties should be avoided because they give rise to a product with undesired wide quality characteristics. To improve homogeneity properties force‐circulated warm air reactors have been proposed, such reactors are normally operated under isothermal air temperature conditions. However, we demonstrate that dynamic optimal warming temperature profiles lead to a polymer sheet with better homogeneity characteristics, especially when compared against simple isothermal operating policies. In this work, the dynamic optimization of a heating and polymerization reaction process for plastic sheet production in a force‐circulated warm air reactor is addressed. The optimization formulation is based on the dynamic representation of the two‐directional heating and reaction process taking place within the system, and includes kinetic equations for the bulk free radical polymerization reactions of MMA. The mathematical model is cast as a time dependent partial differential equation (PDE) system, the optimal heating profile calculation turns out to be a dynamic optimization problem embedded in a distributed parameter system. A simultaneous optimization approach is selected to solve the dynamic optimization problem. Trough full discretization of all decision variables, a nonlinear programming (NLP) model is obtained and solved by using the IPOPT optimization solver. The results are presented about the dynamic optimization for two plastic sheets of different thickness and compared them against simple operating policies. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Some investigations on the possibility of using ocean thermal gradient (OTG) for seawater desalination

In tropical areas, there exists a constant temperature gradient of about 20° C throughout the year between warm surface seawater and cold deep water.The use of that temperature difference for electrical energy production has been widely investigated and is well known as OTEC (Ocean Thermal Energy Conversion).Although Open Cycle OTEC plants may produce fresh water as a by-product, when steam is condensed on surface condensers, one may conceive a purely thermal use of Ocean Thermal Gradient (OTG) for seawater desalination, the electrical energy needed for plant operation being produced by conventional means.Plants of 250 to 1 000 cubic meters per day capacity might be designed around desalination modules derived from those proposed for the utilization of low temperature heat rejects. Cold water might be delivered through polyethylene pipes of commercially available diameters.At first main features of OTG desalination are reviewed. Then some technical solutions for desalination modules and cold water pipe are briefly described and preliminary economical evaluations are given.     

Concentrating solar power for seawater desalination in the Middle East and North Africa

The paper presents a long-term scenario for the demand of freshwater in the Middle East and North Africa (MENA) and shows how it may be covered by a better use of the existing renewable water sources and by sea water desalination powered with solar energy. Growth of population and economy, increasing urbanization and industrialization, and the rather limited natural resources of potable water in MENA are leading to serious deficits of freshwater in many parts of MENA. Modern infrastructure for water distribution, enhanced efficiency of use and better water management are to be established as soon as possible. However, even the change to best practice would leave considerable deficits, which are poorly covered by over-exploiting groundwater resources. Increased use of desalted seawater is therefore unavoidable in order to maintain a reasonable level of water supply. The desalination of seawater based on fossil fuels is neither sustainable nor economically feasible in a long-term perspective, as fuels are increasingly becoming expensive and scarce. Concentrating solar power (CSP) offers a sustainable alternative to fossil fuels for large scale seawater desalination. CSP can help to solve the problem, but market introduction must start immediately in order to achieve the necessary freshwater production rates in time.     

Potential of heat pipe technology in nuclear seawater desalination

Heat pipe technology may play a decisive role in improving the overall economics, and public perception on nuclear desalination, specifically on seawater desalination. When coupled to the Low-Temperature Multi-Effect Distillation process, heat pipes could effectively harness most of the waste heat generated in various types of nuclear power reactors. Indeed, the potential application of heat pipes could be seen as a viable option to nuclear seawater desalination where the efficiency to harness waste heat might not only be enhanced to produce larger quantities of potable water, but also to reduce the environmental impact of nuclear desalination process. Furthermore, the use of heat pipe-based heat recovery systems in desalination plant may improve the overall thermodynamics of the desalination process, as well as help to ensure that the product water is free from any contamination which occur under normal process, thus preventing operational failure occurrences as this would add an extra loop preventing direct contact between radiation and the produced water. In this paper, a new concept for nuclear desalination system based on heat pipe technology is introduced and the anticipated reduction in the tritium level resulting from the use of heat pipe systems is discussed.     

Large scale dew collection as a source of fresh water supply

A scheme for large scale dew collection as a source of freshwater supply is outlined in the present paper. The scheme envisages bringing cold seawater (5°C) from about 500 meters depth and about 5 km from the shore, in 4, 1.22 m diameter plastic pipes. It then passes through a heat exchanger field with an area of 1.29 × 10⁵ m² (1.39 × 10⁶ ft²) where it condenses 643m³ of dew over the 24 hour period. The pumping of seawater from the sea and through the field is accomplished by three 200 kW wind machines. Technical and economical feasibility of the scheme is analysed and the possibility of marine culture as a source of food is explored. The present scheme is economically not feasible as compared to a reverse osmosis facility of equivalent capacity.     

Improved mathematical modeling for the sheet reheat phase during thermoforming

In any thermoforming process, plastic sheet heating is the most important phase as it is responsible for final part quality as well as overall process efficiency and productivity. The goal of the study reported here was to improve existing mathematical models to accurately predict the temperature profile inside a heated sheet, where the model could be used to better control the overall thermoforming process. A mathematical model with temperature dependent, variable sheet material properties including density, thermal diffusivity, specific heat, and thermal conductivity was developed and validated against experimental data. Models with constant and variable plastic sheet properties were created, simulated, and compared in Matlab. The models were validated by experiments which obtained temperature profiles at different depths within a plastic sheet by inserting thermocouples and recording temperatures. Further, the effect of sheet color on heating was investigated by considering two extreme cases: white (transparent) and black (opaque) colored sheets, and the effect of oven air temperature and velocity on sheet heating was also investigated. Results indicated that a variable properties model was needed to control sheet reheating especially with narrow forming windows, and that the heating profiles required for colored and noncolored sheets were very different. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

蒸发式冷凝器应用于海水淡化系统的试验

将蒸发式冷凝器应用于海水淡化装置中,并作为热源对海水进行加热加湿,将蒸发器作为冷源对海水降温除湿,通过建立试验台,测试海水淡化装置的性能,研究海水入口温度和空气入口湿球温度对海水淡化装置性能的影响因素。试验表明:在喷淋水量为125kg/h,空气入口湿球温度为19.3℃,海水入口温度为32℃时,系统淡水产量可以稳定达到2.5kg/h。这种海水淡化装置的电耗率最小可以达到0.18kW·h/kg,是一种高效、节能并适合家庭用的小型海水淡化系统。     

聚乙烯给水管道的生产及应用现状

简述了聚乙烯材料作为压力管道的优势,以及聚乙烯给水管道及管道材料在国内外的生产现状及发展趋势。列举了几种塑料管道的不同使用范围,最后针对国内聚乙烯管道应用方面存在的问题提出了相关的建议。     

Characterization of uncertainties in the operation and economics of the proposed seawater desalination plant in the Gaza Strip

In the Gaza Strip, the available freshwater sources are severely polluted and overused. Desalination of seawater through reverse osmosis (RO) has become the most realistic option to meet a rapidly growing water demand. It is estimated that the Gaza Strip will need to develop a seawater desalination capacity of about 120,000 m³/d by the year 2008, and an additional 30,000 m³/d by the year 2016 in order to maintain a fresh water balance in the coastal aquifer and to fulfill the water demand for different uses in a sustainable manner. Cost and reliability of a large RO facility are still subject to much uncertainty. The cost of seawater desalination by RO systems varies with facility size and lifetime, financing conditions, intake type and pre-treatment requirements, power requirements, recovery rate, chemicals cost, spare parts cost, and membrane replacement cost. The permeate salinity is a function of feed water temperature, recovery rate, and permeate flux. The quantity of water produced depends mainly on plant size, recovery rate, and operating load factor. Many of these parameters are subject to a great deal of uncertainty. The objective of this work is to develop a probabilistic model for the simulation of seawater reverse osmosis processes using a Bayesian belief network (BBN) approach. This model represents a new application of probabilistic modeling tools to a large-scale complex system. The model is used to: (1) characterize the different uncertainties involved in the RO process; (2) optimize the RO process reliability and cost; and (3) study how uncertainty in unit capital cost, unit operation and maintenance (O&M) cost, and permeate quality is related to different input variables. The model utilizes information from journal articles, books, expert opinions, and technical reports related to the study area, and can be used to support operators and decision makers in the design of RO systems and formulation of operational policies. The structure of the model is not specific to the Gaza Strip and can be easily populated with data from any large-scale RO plant in any part of the world.     

聚乙烯塑料管的设计选择

概略介绍了聚乙烯塑料管的材料性能规格、作为压力管线的设计选择,以及管子安装的要求。     

European GRP industry records ‘slight improvement’

THE FEARED return of a slump in European glass reinforced plastic (GRP) production in 2002 failed to materialise, reported Dr. Uwe Bültjer, managing director of German association AVK-TV at the 6th International AVK-TV Confer-ence on 7-8 October in Baden-Baden. In fact, an increase of 0.8% was seen overall — mainly a result of high demand for GRP pipes and a slight increase in sheet moulding compound (SMC) production.This is a short news story only. Visit www.reinforcedplastics.com for the latest plastics industry news.     

塑料管材在水利工程中的具体应用及质量检测

通过分析水利工程中常用塑料管材的种类与特点,了解塑料管材在农田水利、建筑给水、建筑排水中的具体应用,并对水利工程中塑料管材的具体质量检测方法进行阐述,为城市、乡村水利工程建设提供参考.     

Thermoforming conditions in transparent/opaque coextruded sheet

Processors have encountered processing problems in dealing with thermoforming co-extruded sheet where one layer is semitransparent to incident radiant energy of the heater banks and the other is opaque. An analysis of the radiant heating process shows that significant volumetric absorption of radiant energy takes place within the semitransparent sheet. From the model, it is shown that to minimize temperature excursions within laminated sheets (and thus reduce the tendency for delamination and blistering), heater banks should be programmed to cycle in an on-off mode with a rather short cycle period.