An experimental study on an inclined solar water distillation system

An inclined solar water distillation system was designed and tested under actual environmental conditions of northern Cyprus. Unlike solar still systems, the feed water falls down on the solar absorber plate, and the system produces fresh water and hot water simultaneously. It was suspected that the longer the flowing water is held on the absorber plate, the greater the rate of evaporation, leading to an increase in the amount of distilled water. Therefore, the system was tested with three variants: bare plate, black-cloth wick, and black-fleece wick. As was expected, the wicks increased the fresh water generation by two or three times of a bare plate. The hot water temperature was good enough for domestic usage.     

The effect of using different designs of solar stills on water distillation

Solar distillation is one of the important methods of utilizing the solar energy for the supply of potable water to small communities where the natural supply of fresh water is inadequate or of poor quality, and where sunshine is abundant. Solar energy utilization in two different types of solar stills is considered, and factors that influence the productivity of solar stills are discussed. The present investigation showed that the productivity of asymmetric greenhouse type still (ASGHT) having mirrors on its inside walls was higher than that of the symmetric greenhouse type still (SGHT) and more efficient. It was found that the distilled water output of the asymmetrical greenhouse type was 20% higher than that of symmetric greenhouse type. Performance characteristics of the two stills showed that the temperature at the water surface is closely related to the incident solar radiation, and the productivity of the stills can be increased with decreasing water depth, and by the addition of dye.     

Effect of water depth on internal heat and mass transfer for active solar distillation

In this communication, an attempt has been made to find out the convective heat transfer coefficient for active solar distillation system. It is a well-known fact that the distillate output (the yield) decreases significantly with the increase of water depth in the basin of the solar still. It is also known that more yield is obtained in case of active solar distillation system as compared to passive solar still due to higher temperature difference between the water and inner glass cover temperatures in the active mode. For the present study, experiments have been conducted for 24 hours during winter months for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. The objective of the present paper is to study the effect of different water depths in the basin on the heat and mass transfer coefficients. It is inferred that the convective heat transfer coefficient between water and inner condensing cover depends significantly on the water depth in the basin. It is also observed that more yield is obtained during the off shine hours as compared to daytime for higher water depths in solar still (0.10 m and 0.15 m) due to storage effect.     

Theoretical study on multi-effect solar distillation system driven by tidal energy

Based on an analysis of the characteristics of solar and tidal energy, an innovative, multi-effect solar distillation unit for seawater desalination utilizing solar and tidal energy has been developed. The uniqueness of the system is that without being transferred to electricity, tidal energy is utilized to supply power for water supply and drainage, and vacuum extraction instead of pumps powered by electricity. So the cost can be greatly reduced. The system is based on multi-effect evaporation-condensation processes and operates under vacuum condition, so low grade solar heat can be used with a high thermal efficiency. Hydrodynamic and thermal analysis is carried out for the water supply and drainage system driven by tidal energy. The operating mechanism of the vacuum extraction system driven by tidal energy is presented. A parametric study of the behavior of the solar desalination unit has been performed.     

Enhancement of solar water distillation process by surfactant additives

The presence of surfactant additives in water is found to enhance the boiling heat transfer significantly. The effect of using a surfactant as sodium lauryl sulfate (SLS) in relatively small dosages of concentration with a small size unit of solar water distillation process is investigated. Sun simulator (electric heater and variac transformer) is used to quantify the same input power for each experiment for the system instead of the sun. The experimental results show that a small amount of surfactant additive makes the top brine temperature (TBT) considerably higher, hence the freshwater product. Temperature curves for various surfactant concentrations are obtained and compared. The percentage of the increase in the system productivity is 0.7%, 2.5%, 4.7% and 7% at additive concentration equal to 50, 100, 200 and 300 ppm respectively. It is found that increasing the surfactant concentration more than 300 ppm not affecting the system daily productivity (DP) and TBT. Using surfactant concentration more than 400 ppm will decrease the DP by 6%.     

Design of an autonomous solar desalination plant using vacuum membrane distillation,the MEDINA project

The unit presented in this paper is designed to provide a high quality of potable water in remote coastal areas with bad infrastructure and without a network connection. The installation is designed completely autonomous; indeed the only source of energy is the sun.     

Computer modeling of passive/active solar stills by using inner glass temperature

Expressions for water and glass temperatures, hourly yield and instantaneous efficiency for both passive and active solar distillation systems have been derived. The analysis is based on the basic energy balance for both the systems. A computer model has been developed to predict the performance of the stills based on both the inner and the outer glass temperatures of the solar stills. In the present work two sets of values of C and n(C_inner, n_inner and C_outer, n_outer), obtained from the experimental data of January 19, 2001 and June 16, 2001 under Delhi climatic conditions, have been used. It is concluded that (i) there is a significant effect of operating temperature range on the internal heat transfer coefficients and (ii) by considering the inner glass cover temperature there is reasonable agreement between the experimental and predicted theoretical results.     

First experimental results of a new hybrid solar/gas multi-effect distillation system: the AQUASOL project

From 2002 to 2006, a combined R&D project named AQUASOL has been carried out at the facilities of the Plataforma Solar de Almería (Spain). Main objective of this project has been the development of a hybrid solargas desalination system based on multi-effect distillation process that meets at the same time the requirements of low-cost, high efficiency and zero discharge.

The final AQUASOL plant, implemented at the Plataforma Solar de Almería for its evaluation under real meteorological conditions, is composed of: (i) a 14-cell forward-feed vertically-stacked MED unit, (ii) a 500m2 stationary CPC (compound parabolic concentrator) solar collector field, (iii) a 24 m3 thermal storage system based on water, (iv) a new advanced prototype of double-effect absorption (LiBr-H2O) heat pump, (v) a smoketube gas boiler to guarantee 24-h operation

This paper shows the first experimental results obtained during the test campaign of the project. The performance ratio reached by the distillation plant in different operational modes is evaluated, as well as the issues related with the operation of the subsystems that compose the AQUASOL desalination system.     

分子蒸馏过程数学建模及模拟验证

建立了分子蒸馏过程径向和轴向的二维数学模型,采用CFD方法对DBP-DBS混合物系的分离过程进行模拟计算,分析了蒸馏温度和进料速率等操作条件对蒸馏过程的影响。将模拟结果与文献中采用BGK模型计算得到的结果进行对比,两者具有较好的吻合性,验证了模型的合理性。     

Performance evaluation of a solar still by using the concept of solar fractionation

In this communication an attempt has been made to find out distribution of solar radiation, using the concept of solar fraction inside a conventional (single slope) solar still by using AUTOCAD 2000 for a given solar azimuth and altitude angle and latitude, longitude of the place. Further the experimental validation of the model developed earlier has been carried out for design and climatic parameters. Numerical computations have been carried out for New Delhi climatic conditions (latitude 28°35′ N, longitude 77°12′E). It has been observed that for given parameters, solar fraction can play a very important role at a lower value of the solar altitude angle.     

A theoretical model of a free flow solution over an inclined long flat plate solar still

This analysis is used to investigate a free flow inclined flat plate solar still.To study the effect of significant parameters on a laminar falling liquid solution over an inclined long flat plate solar still, a mathematical two dimensional flow analysis is carried out based on continuity, momentum and energy equations for liquid and vapor phases together with the interface. As far as the liquid film is concerned, the velocity, film thickness, pressure, temperature and the hourly evaporated water volume profiles are found. It is shown that the significant parameters which affect the solar still are the initial film thickness (i.e, the initial mass flow rate), the plate inclination, the still length and the absorber heat flux (i.e., the solar radiation reaching the plate). It is also shown that the variation in liquid film thickness down the still has a significant effect on the evaporation rate (i.e., the condensed water) and should not be neglected particularly in the case of a long inclined solar still.     

Performance study on an acrylic mirror boosted solar distillation unit utilizing seawater

A solar still is a simple desalination unit, but typical configuration is a sealed box with an angled glass top. Sunlight shining into the box heats water or liquid, causing it to evaporate. The moisture condenses on the relatively cool glass cover and runs down the sloped surface for collection. In this paper, the performance of solar still in terms of collection of distilled water have been analyzed and a booster mirror (acrylic) is attached with just above the glass cover of solar still, which will reflect solar radiation in excess to water and it is possible to adjust the booster mirror for perfect reflection depending upon the sun moving angle. Low rates of distillation have been observed with the existing unit. A notable result has been observed with a boosted distillation unit (4.2 L/m²/d at 890 W/m² max.). The arrangements have been made by commercial Al sheet material and insulated with a thermocol sheet.     

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.     

膜蒸馏技术在水处理中的应用

从膜蒸馏技术的膜分离过程、原理、分类、优缺点以及应用领域尤其是在水处理行业中的广泛应用进行了叙述,并指出膜蒸馏技术的应用前景和发展趋势。     

Experimental assessment of connection of an absorption heat pump to a multi-effect distillation unit

Theoretical analysis of integrating an absorption heat pump cycle in a multi-effect distillation (MED) process has shown better performance than with other types of heat pumps conventionally used as thermocompressors. However, to date, only two pilot facilities have been implemented worldwide. Both of them have been developed and tested in the framework of two different research and demonstration projects carried out at the Plataforma Solar de Almería (Spain). Two different double-effect absorption (LiBr-H₂O) heat pump (DEAHP) prototypes were coupled to an existing 14-effect MED unit. This paper reports the results of the experimental assessment of integrating the second prototype in the process. Although the initial design of the DEAHP prototype was based on fitting it to the MED unit power demand and their direct connection, the prototype was unable to achieve steady operation in this configuration. However, the indirect connection of both units by means of two auxiliary tanks was successful. An overall performance ratio of 20 was measured; therefore, integration of the DEAHP doubles the performance ratio of the MED unit alone, although the temperature of the external heat input required is increased from 70 °C to 180 °C.     

Performance of packings for water distillation

Distillation of water has been investigated in packed columns of 300, 500 and 750 mm diameter. Both ordered packings (Goodloe, Mellapak and Sulzer CY) and random packings (Hy-Pak, Mini-ring and Pall-ring) were studied and performance compared. It was found that, with surface treatments, phosphor bronze packings show good performance and insignificant scale-up factors. Plastic materials are not suitable for water distillation because of their poor wetting characteristics.     

A vertical multiple-effect diffusion-type solar still coupled with a heat-pipe solar collector

We proposed a newly designed, compact multiple-effect diffusion-type solar still consisting of a heat-pipe solar collector and a number of vertical parallel partitions in contact with saline-soaked wicks. The solar collector and the vertical multiple-effect diffusion-type solar still can be folded or separated when it is carried, so that the still would be easy to carry and shipping cost would be very cheap. The solar energy absorbed on the solar collector is transported as latent heat of working fluid to the vertical multiple-effect diffusion-type still where the energy is recycled to increase the productivity of distillate. The performance of the proposed still is analyzed theoretically, and the still is predicted to produce 21.8 kg/m²d distilled water on a sunny autumn equinox day of 22.4 MJ/m²d solar radiation, and the productivity is greater than that of a vertical multiple-effect diffusion-type still coupled with bulky basin type still.     

Solar barometric distillation for seawater desalting Part II: Analyses of one-stage and two-stage distillation technologies

The report concerns design aspects for the recently proposed solar barometric distillation technology for seawater desalting (SW–SBD) with an underground barometric layout. Two types of SW–SBD desalting plants are analysed. The first plant utilizes a single-stage distillation process with one distillation heat exchanger (operative condensation temperature 50°C). The second plant utilizes a two-stage distillation process with two distillation heat exchangers connected in series (operative condensation temperatures 40 and 60°C). Vacuum solar collectors of simple design and construction, utilizing glass or suitable glass/polymer blends as transparent material, are proposed for the SW–SBD plants. The present analyses suggest that SW–SBD desalting technology may have a promising technico-economic potential. Field research on SW–SBD prototype plants is necessary to bring SW–SBD desalting technology to its full technological development.     

Parametric investigation of a basin-type-multiple-effect coupled solar still

Parametric analysis was performed for the basin-type multiple-effect coupled solar still with a triangle cross-section consisting of a horizontal basin liner and a number of vertical parallel partitions in contact with saline-soaked wicks with narrow gaps between the partitions, under dry weather conditions at 26.1 °N latitude. The productivity of the still increased in winter with an increase in the angle between the glass cover and the basin and decreased in summer. In the spring and autumn seasons productivity had a gentle peak between a 40° and 45° angle. Increasing supply rates of saline water to the wicks and increasing initial mass of the basin water decreased productivity. With a decrease in diffusion gaps between partitions, productivity exponentially increased, and it also showed exponential increases with an increase in the number of distillation cells between the partitions. The productivity of the still of 13 partitions with 5-mm gaps and a 40° angle of the glass cover was four times more than the basin-type stills, and the still was more productive than the conventional multiple-effect stills by about 40% or more.