Design of a small solar-powered desalination system

A design is presented for a solar/thermal system configured to power a reverse osmosis (RO) desalination unit to produce 7000 gallons of fresh water in an eight hour period. A field of line-focus tracking solar collectors is used to heat a high pressure liquid-vapor water storage tank supplying two compound reciprocating steam engines, one direct-connected to the RO high-pressure pump and the other to an electric generator for auxiliary power. An auxiliary heating loop with an oil-fired boiler is also used to supply the steam engines.The system operates in either all-solar, all-oil, or mixed solar/oil modes. Primary operating mode is assumed to be a mixed solar/oil mode in which the oil-fired boiler is used only to prevent shutdown of the RO system during the course of a partly sunny day. In this mode, the RO system does not come on line in the morning until the solar collector field has brought the high-pressure storage tank to a point near maximum operating pressure. Thereafter, the oil-fired boiler comes on automatically whenever the storage tank is drawn down to a pressure near minimum full-power operation (due to inadequate or intermittent insolation) and remains on, supplying the steam engines, until the solar collectors have again brought the storage tank to the high-pressure cutoff.In the all-solar mode, the system continues to operate at reduced power as storage tank pressure drops below the point at which the oil-fired boiler would otherwise come on. A portion of the RO system is shut down to maintain pressure in the remainder.The all-oil mode is used whenever fresh water is required during non-sunny periods, or to increase fresh water production in sunny periods.     

Analysis of a solar-powered membrane distillation system

Nowadays, in dry and rural areas, solar-powered membrane distillation (SPMD) technology is considered a feasiblemeans for the production of pure water from brackish water. Prior to the design and construction of a SPMD pilot plant, there is a need to predict its performance theoretically by means of a computational simulation program. Unlike previous approaches followed by other investigators to develop a mathematical model that can describe the components of a SPMD pilot plant, the developed mathematical model in this study is based on the fact that the SPMD process by nature is unsteady. The performance of a proposed SPMD pilot plant is then obtained by means of a numerical solution of the model with the aid of a simulation computer program. The results reveal that the proposed SPMD pilot plant has some unique features, which differ from a similar MD process operated at steady-state conditions in a laboratory. The analysis of the system has shown that heat recovery via an external heat exchanger is not only possible, but even effective, and an economical way to intensify the SPMD process. The plant productivity can be improved by increasing the heat-exchanger capacity (KA), decreasing the flow rates of both feed and permeate or otherwise by increasing the effective surface area of the membrane. The achieved enhancements in the SPMD pilot plant productivity are directly related to an improved heat recovery rate in the heat exchanger. However, further analysis reported in this paper shows that the increase in KA and membrane area should be optimized for any planned capacity in the design of a SPMD pilot plant.     

A neural network-based optimizing control system for a seawater-desalination solar-powered membrane distillation unit

Several schemes have been proposed so far for coupling desalination processes with the use of renewable energy. One of their main drawbacks, however, is the nature of the energy source that requires a discontinuous and non-stationary operation, with some control and optimization problems. In the present work, a solar powered membrane distillation system has been used for developing an optimizing control strategy. A neural network (NN) model of the system has been trained and tested using experimental data purposely collected. Afterwards, the NN model has been used for the analysis of the process performance under various operating conditions, namely distillate production versus feed flow rate, solar radiation and cold feed temperature. On this basis, a control system that optimizes the distillate production under variable operating conditions has been developed, implemented and tested.     

Exergy analysis of desalination by solar-powered membrane distillation units

There has been an increasing interest in using exergy as a potential tool for analysis and performance evaluation of desalination processes where the optimal use of energy is considered an important issue. Unlike energy, exergy is consumed or destroyed due to irreversibilies in any real process and thus provides deeper insight into process analysis. Exergy analysis method was employed to evaluate the exergy efficiency of the “compact” and “large” solardriven MD desalination units. The exergy efficiency of the compact and large units with reference to the exergy collected by the solar collector was about 0.3% and 0.5% but was 0.01% and 0.05%, respectively, when referenced to the exergy of solar irradiance. The exergy efficiency of the flat plate solar collectors in both units varied diurnally and the maxima was 6.5% ad 3% for the compact and large units, respectively. The highest exergy destruction was found to occur within the membrane distillation module.     

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。     

Design and operation of a commercial soybean-oil refining plant,using acetic anhydride as a degumming reagent

Summary The 50 oil process has been demonstrated on a commercial scale to be physically possible and economically attractive to refiners of soybean oil. The flavor and stability characteristics of the finished oil are identical to the conventional caustic-refined product.     

Economic evaluation of desalination by small-scale autonomous solar-powered membrane distillation units

Solar-powered desalination is an attractive and viable method for the production of fresh water in remote arid areas. One of the most important factors determining desalination decisions is economics. This paper presents an economic assessment performed to estimate the expected water cost, which is the ultimate measure of the feasibility of the stand-alone system. Based on the calculations, the estimated cost of potable water produced by the compact unit is $15/m³, and $18/m³ for water produced by the large unit. Membrane lifetime and plant lifetime are key factors in determining the water production cost. The cost decreases with increasing the membrane and/or the plant lifetime.     

Optimization of solar-powered reverse osmosis desalination pilot plant using response surface methodology

A solar thermal and photovoltaic-powered reverse osmosis (RO) desalination plant has been constructed and optimized for brackish water desalination. The central composite experimental design of orthogonal type and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of different responses such as the salt rejection coefficient, the specific permeate flux and the RO specific performance index that takes into consideration the salt rejection coefficient, the permeate flux, the energy consumption and the conversion factor. The considered input variables were the feed temperature, the feed flow-rate and the feed pressure. Analysis of variance (ANOVA) has been employed to test the significance of the RSM polynomial models. The optimum operating conditions have been determined using the step adjusting gradient method. An optimum RO specific performance index has been achieved experimentally under the obtained optimal conditions. The RO optimized plant guarantees a potable water production of 0.2 m³/day with energy consumption lower than 1.3 kWh/m³.     

太阳能吸附式空调固化复合吸附剂性能

测试了氯化钡-膨胀石墨固化复合吸附剂的吸附性能,并对采用该吸附剂的太阳能吸附式空调系统性能进行了分析。实验结果表明,固化复合技术有利于提高吸附剂的传热传质性能,实验中复合吸附剂循环吸附量可高达0.61 kg·kg^-1;同时,加热流体温度、冷却温度、蒸发温度以及反应约束压力对吸附剂性能都有着不同程度的影响。对于采用该复合吸附剂的太阳能空调系统,在加热温度80℃,冷却温度30℃,蒸发温度分别为5、10、15℃时,系统COP 和SCP均随蒸发温度的升高而增大,在15℃时可分别高达0.5和192 W·kg^-1。     

工业用多级离心压缩机设计及变工况计算方法

本文提出了一种工程实用的多级离心压缩机设计工况及变工况性能的预估方法，据此法编制的计算程序具有很好的通用性，特别适合整机的初步设计。     

Optimization of a commercial brake pad formulation

A brake pad material used in a popular, commercially available vehicle that consisted of steel wool, iron powder, graphite, coke, styrene–butadiene rubber, MgO, BaSO₄, and phenolic resin was tested with the friction assessment and screening test. The average friction coefficient (0.357) and total wear (19.75 wt %) were measured. An alternative friction material formulated with identical constituents but optimized with the golden section principle and relational grade analysis was produced in a laboratory environment. This material exhibited an average friction coefficient of 0.419 and a low total wear of 6.25 wt %. An analysis of component costs indicated that the large volume price of the commercial material, $1.01/kg, was less than that of the laboratory material, $1.21/kg. However, the performance/cost ratio of the new material was appreciably greater. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2498–2504, 2002     

Binary blends containing a commercial polyarylate

A commercial polyarylate (PAr), a copolyester of Bisphenol-A with 50 percent terephthalate-50 percent isophthalate, has been characterized by means of a combination of gel permeation chromatography and viscometry. It has been studied as first component of a series of polymer blends. The presence of either one glass transition temperature (T_g) or two has been used as a criterion to determine the miscibility of each blend. In some cases, the possible incidence of transesterification reactions has been considered.     

不同驱动温度下间歇性太阳能吸附制冰机的实验研究

设计并搭建了太阳能吸附制冰系统,主要包括制冰机、槽式太阳能集热器及恒温油槽等。通过油槽中的电加热模拟不同太阳能辐射量的工况,得到吸附制冰机在不同驱动热源条件下的运行特性。吸附制冰机采用氯化钙/活性炭复合吸附剂,氨作为制冷工质。实验通过电加热模拟的太阳能驱动温度在110～155℃变化,对应的每天制冰量为10～28kg,计算得到太阳能COP为0.09～0.14。     

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.     

Dielectric dispersions in a commercial acrylonitrile-butadiene-styrene polymer

Observations of dielectric constant and loss from ?120°C to +140°C over the frequency range 30 Hz to 3MHz are presented for a low rubber content acrylonitrile-butadiene-styrene (ABS) polymer of commercial origin. Seven dielectric dispersions are distinguished in the tan δ contour map and constant-frequency plots together with evidence for an eighth at the lowest temperatures. Possible sources for each dispersion are proposed in relation to the miscibility and morphology of the individual phases present in this multicomponent polymeric material.     

Mixtures of soap and a commercial alkyl aryl sulfonate

Summary This middle ground between the soaps and synthetics has not been actively exploited in spite of the intense current interest in the straight products. It has been a no man's land where the manufacturers of synthetic detergents have carefully avoided soap, which they regard as outside of their field, while many manufacturers of soap have been indifferent to the effect of the synthetic detergents. In spite of this general indifference work has been done on both sides of the fence with a continually increasing use of the mixtures. Where mixtures have been ready-made, the soap manufacturers have been largely responsible for their manufacture. Commercial mixtures of soaps and synthetics have been sold where synthetic detergents have been found to improve soap for specific uses. This trend is certain to expand. The present success should encourage further research and development commensurate with the increasing commercial importance of the products. Presented at the annual fall meeting, American Oil Chemists' Society, Oct. 31, Nov. 1–3, 1949, Chicago, Ill.