An experimental study on single basin double slope simulation solar still with thin layer of water in the basin

Single basin solar still is a popular solar device used for converting available brackish or waste water into potable water. Because of its lower productivity, it is not popularly used. Numbers of works are under taken to improve the productivity of the still. The still productivity depends on parameters like solar radiation intensity, atmospheric temperature, basin water depth, glass cover material, thickness and its inclination, wind velocity and the heat capacity of the still. When compared with other parameters, the basin water depth is the main parameter that affects the performance of the still. For a particular still, the basin water temperature is the function of depth with day variation of solar radiation intensity. In this work a double slope single basin passive type still with basin area of 1.75 m² is fabricated and tested under laboratory conditions for a thin layer of water in the basin. For maintaining thin layer of water basin, it is necessary to spread the water through out the basin by some kinds of wick material or porous materials. In this work, performance of the still is compared by using wick materials like light cotton cloth, light jute cloth and sponge sheet of 2 mm thickness and porous materials like washed natural rock of average size 3/8" × 1/4" and quartzite rock of average size 3/8" as spread materials. The actual solar radiation condition is simulated by 2 kW electrical resistance heater placed below the inner basin. The results show that the still with black light cotton cloth as spread material is found to be more productive. At higher water and glass temperature region, for all basin materials, the production rate increases with the decrease of the difference between the water and glass temperatures for certain period and also the productivity decreases with the increase of water temperature for certain time during this period. Hence the production rate is a complex function of water, glass and the difference between the water and glass temperatures, basin volumetric heat capacity of the material and its porosity.     

Integrated performance of stepped and single basin solar stills with mini solar pond

An attempt is made to enhance the productivity of the solar stills by connecting a mini solar pond, stepped solar still and a single basin solar still in series. Experiment is also carried out by replacing the single basin solar still into a wick type solar still. For further augmentation of the yield, baffle plate, pebble, fins, wicks and sponges are added. Day and night productivity of the solar stills for these modifications is studied. Daily efficiency and percentage increase in productivity for these modifications are also studied. Industrial effluent water is used as feed. Theoretical analysis gives very good agreement with experimental results.     

Augmentation of saline streams in solar stills integrating with a mini solar pond

Industrial effluent was evaporated in a fin type single basin solar still and a stepped solar still separately. To preheat the saline water, a mini solar pond was integrated with these stills. Both the stills were operated with mini solar pond and tested individually. In fin type single basin solar still, maximum productivity is obtained, when it is modified with black rubber, sponge and sand. The stepped solar still was modified with fin, pebble and sponge to enhance their productivities. When mini solar pond, pebble, sponge and fin are used in stepped solar still, maximum productivity was obtained To settle the industrial effluent, a settling tank was also fabricated with five layers namely: tray for raw effluent, pebble layer, coal layer, sand layer and collection tray for settled effluent. Physical and chemical analyses were made for raw effluent, settled effluent and distilled water. Economic analysis was made.     

Modeling and performance analysis of a solar desalination unit with double-glass cover cooling

In this study modeling and performance analysis of a single-basin solar still with the entering brine flowing between a double-glass glazing were investigated. The base area of the solar still is 1 m². The function of this arrangement is to lower the glass temperature and thus increase the water-to-glass temperature difference. This results in improved performance represented by a faster rate of evaporation from the basin. The performance of the still is compared with that of a conventional single-glass cover solar still under identical weather conditions. The results show that the relative performance of the stills depends on the level of insulation used. For perfectly insulated stills the conventional solar still is superior while the double glass is superior when heat loss exceeds a certain value. The hourly and daily productivities of the stills and the temperatures of the water and the glass covers were also predicted under the meteorological conditions of Muscat, Oman.     

Year-round comparative study of three types of solar desalination units

Simulations of three different types of solar stills were performed to compare their productivity using typical meteorological year data of a remote location (Marmul) in Oman. These are the regenerative, conventional, and still with double-glass-cover cooling. Several system parameters were also investigated with respect to their effect on the productivity, namely, water with and without dye in the lower basin, basin heat loss coefficient, mass of water in the basins, and mass flow rate into the double-glass cover. The regenerative still had more than 70% higher productivity in comparison with the conventional still. If the stills are appropriately insulated, the conventional still had higher productivity than the double-glass-cover cooling. Increasing the water in the lower basin moderately reduced the productivity of the three stills. Increasing the water film thickness on top of the lower glass had no effect on the productivity of the still with double-glass-cover cooling, but slightly lowered the productivity of the regenerative still.     

Performance correlations for basin type solar stills

Many experimental and numerical studies have been done on different configurations of solar stills to reach the optimum design by examining the effect of climatic, operational and design parameters on its performance. Some of the most important parameters investigated were solar radiation, cover tilt angle, brine depth, and using dyes with the brine. The majority of the investigators presented their results in scatter diagrams rather than correlations. Four correlations are derived in this work to illustrate the effect of solar radiation, dyes, cover slope and brine depth on the productivity of the basin type solar still using the available data given by the different investigators. The correlations developed illustrate that the still productivity could be influenced by the brine depth alone by up to 33% and by the tilt angle alone by up to 63%. A cover tilt angle of about 30° gives the highest productivity. The still productivity could be enhanced by adding dark soluble dye to the brine by up to 20%. The still productivity increases with the increase of insulation thickness of the still and the solar radiation received.     

Solar stills made with tubes for sea water desalting

The report concerns basic technological features of simple solar stills utilizing tubes for sea water desalting. The evaporation section comprises horizontal transparent thin-walled plastic or glass tubes, of ~0.10–0.25 m inner diameter, half-filled with sea water which absorbs solar radiation. The condensation section is physically separated from the evaporation section, in a shaded space below it, and comprises horizontal plastic or metal tubes of ~0.01 m inner diameter. The wall thickness of condenser plastic tubes is rather small, ~50 μm.

Water vapour released by solar radiation in evaporator tubes flows into condenser tubes to be condensed into produced fresh water by delivering condensation latent heat to atmospheric air. Heat transfer by air convection may be helped by surface winds, often available in coastal areas. Enhanced fresh water productivity is expected with respect to conventional solar stills in which sea water evaporation and water vapour condensation occur in one confined space. Technological features of the proposed solar stills are analysed in some detail and specific experimental work is suggested on prototype solar stills in view of clarifying relevant aspects concerning transparent and opaque construction materials, assembling procedures, and the role of the various operative parameters vis-à-vis energy efficiency and fresh water productivity.     

三效管式海水淡化装置产水性能实验研究

研制了一种三效管式海水淡化装置,对其进行了定功率和太阳能加热运行实验研究,分析了该淡化装置的产水性能及影响因素。定功率实验研究表明,当淡化装置加热功率为300 W时,其性能系数最高达约1.32,提升淡化装置蒸发传热,同时降低热量耗散(辐射耗散和对流耗散),加大装置冷凝温差可以提升淡化装置性能。太阳能加热实验结果表明,淡化装置的产水性能受太阳辐射值、太阳能集热系统效率、热源稳定性、环境温度与风速等多种因素影响,特别是热源稳定性对装置性能有较大影响。     

Experimental and numerical analysis of a tube-type networked solar still for desert technology

A tube-type solar still is proposed to integrate a conventional still and a water distribution network suitable to our concept of desert plantation. This still is directly set up on ground-like pipelines connecting brackish water or seawater ponds. The distilled water is immediately supplied to the plants under the ground by penetration without any extra water pipelines. The still is made of metal-free materials, e.g., plastic as vinyl chloride or PET resin which are inhibited from corrosion by seawater. Experimental data measured in our laboratory using infrared lamps showed the effectiveness of the method for productivity, the design of the basin tray and thermal efficiency up to 12.5%. Numerical simulations with experimental data as the temperature profiles at the tube walls estimated heat convection occurring within the still for modification of the Dunkle's model. Active convection over the basin was predicted in the half-cut tube type of the basin as compared with a conventional flat basin. The secondary convective circulations under the basin in case of the flat basin promote bulk flow from the upper part of the basin to the lower part, which suggests the necessity of insulating the lower part of the still. On the other hand, the tube basin enlarges the evaporative area over the basin and restricts the vapor circulation under the basin. Simulated results show that the performance of this type is not necessary for the insulation of a still and possible for setting up the lower part of the still under the ground. The tube-type solar still is very simple and has been researched, but further research is needed to make it a suitable technology for desert plantations.     

Performance study on solar still with enhanced condensation

Water scarcity and pollution pose critical situation in all walks of life especially in the developing countries. Among the available purification technologies, solar desalination process proves to be a suitable solution for resolving this existing crisis. This renewable energy technology operates on a basic principle of which the solar radiation enters through the glass surface inside a closed chamber touching the black surface generating heat energy, which gets trapped inside. This gradually raises the temperature of the liquid resulting in evaporation process and further condensation, which is drained out for use. In this connection, a basin type solar still (0.5 m²) with improved condensation technique was designed and built, and a performance study was carried out with different samples such as tap water, seawater and dairy industry effluent. The condensation occurs due to the temperature difference not only on the glass surface but also on the four sidewalls, which can be cooled by water circulation through tubes attached on the wall surface for efficiency enhancement. The maximum daily production of the solar still was about 1.4 L/m².d, and its efficiency was about 30%. The condensate water quality was analysed and compared with water quality standards, which was found to be comparable with rainwater and mineral water. Efficiency of the still was calculated for all the samples and compared with each other. The reasons for the findings and their implications for the design of the system are discussed. Some design features that would further enhance the thermal performance of the still were also identified from this present investigation and highlighted.     

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.     

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.     

Active single basin solar still with a sensible storage medium

Transient mathematical models are presented for an active single basin solar still (ASS) with and without a sensible storage material under the basin liner of the still. Sand is used as a storage material due to its availability. The flowing water temperature is assumed to vary with time and space coordinates. Analytical expressions are obtained for various temperatures of the still elements as well as for the temperature of sand. The performance of the still with and without storage is investigated by computer simulation using the climatic conditions of Jeddah (lat. 21° 42′ N, long. 39° 11′ E), Saudi Arabia. Effects of mass flow rate and thickness of the flowing water for different masses of the storage material on the daylight P_dl, overnight P_on and daily productivity P_d and efficiency η_d of the still are studied. The dependence of P_d and η_d on the thickness and thermal conductivity of the basin liner material is also investigated. It is found that P_d and η_d decrease as the mass of the storage material increases, due to the increased heat capacity of the storage material. Furthermore, P_d and η_d are found to decrease with increasing thermal conductivity of the basin linear material. Therefore, it is advisable to fabricate basin liners of ASS from cheap insulating materials such as glass and mica with an optimum thickness of 3 mm. On a summer day, a value of P_d of 4.005 (kg/m² day) with a daily efficiency of 37.8% has been obtained using 10 kg of sand compared to 2.852 (kg/m² day) with a daily efficiency of 27% when the still is used without storage. The annual average of daily productivity of the still with storage is found to be 23.8% higher than that when it is used without storage.     

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.     

Solar stills made from waste materials

Technology for solar desalination has been studied for a long time as a process friendly to the environment and also energy saving. We found a new aspect by diverting attention from industrial mass production systems to the consumer's life-style and resource recycling problems. Thus, desalting solar stills made from waste materials were studied. A type made from a polypropylene tray and polyethylene wrapping sheets was subjected to laboratory tests at steady and unsteady states for heat and mass transfer analysis. The beam strength was substituted by referring to the data the of Meteorological Agency on August 6, 2000 [total solar radiation 26.27MJ/(m²·d)]. The maximum water productivity was delayed 2 h from that of the beam strength. Total productivity of water per day and 1 m² was measured as 3.54 kg and calculated as 2.35 kg. The result indicated the need to improve the performance and the direction of development of the solar still. This concept could be especially worthwhile for producing water without any harm to the environment by utilizing renewable solar energy.     

太阳能海水晒盐强化技术的研究

基于太阳能高效界面蒸发技术,利用活性炭过滤棉、海绵、百洁布和烧结不锈钢形成不同的双层组合,进行优化,以促进太阳能海水晒盐过程.实验结果表明:在光强1 000 W·m-2下,活性炭过滤棉与海绵的双层组合能更有效促进水分的蒸发,光热转化层距水面高度在4 mm左右、仅铺设1层时(厚度为3 mm)会有更好的蒸发效果;在盐聚集的...     

Solar still an appropriate technology for potable water need of remote villages of desert state of India — Rajasthan

Rajasthan, the largest state of the India faces a grim scenario in relation to water availability resources. Rajasthan has two-third of its area as desert and it faces scanty rainfall, recurring droughts in 3–4 years in a cycle of 5 years. It would be seen from the present status of drinking water detailed out of 237 blocks in Rajasthan that only 49 are safe in terms of ground water while 101 are critical and semi critical and 86 are over exploited. It is a hard reality that state dependence on ground water is 91% for drinking water. About 21,190 villages/habitations suffer from the problem of excessive salinity, 23,297 villages/habitations suffer from excess fluoride problem and 20,659 villages/habitations suffer from excess nitrate problem. Based on the WHO guidelines for drinking-water quality about 56% of the water sources are un-potable.

But on other hand Rajasthan is blessed with ample amount of solar radiation. The arid parts of Rajasthan receive average maximum solar radiation of about 7.5 kW h/m² in the month of May and minimum of about 4.6 kW h/m² in the month of Dec & Jan. Part of this energy may be utilized to meet out drinking water need of remote area dwellers of Rajasthan.

Solar distillation and desalination unit is most appropriate for remote area dwellers because it is economical, easy to construct and maintain. Most parts of Rajasthan have enough solar radiation available which is the prime input for the system.

A low cost high efficiency solar still with porous evaporating surface is fabricated for the purpose and cost analysis is done to calculate the cost of water in this paper [Bassam et al., Experimental study of a solar still with sponge cubes in the basin, Energy Conserv. Manage., 44 (9) (2003) 1411–1418; Bouchekima et al., Performance study of the capillary film solar distiller, Desalination, 116 (1999) 185–192; Bassam et al., Water film cooling over the glass cover of a solar still including evaporation effect, Energy, 22 (1) (1997) 43–48].

Water samples are collected from a remote village of state and analyzed to find the quality of drinking water. The working habits and medical history of the villagers is also investigated to work out cost analysis more realistically.     

Design and simulation of a novel solar photovoltaic system assisted single-slope solar still distillation unit

Water is an essential component of our lives. Conventional seawater desalination, based on fossil fuel energy, is primary in meeting freshwater demands. Thus, solar desalination still emerged as an alternative technology that employs environmentally friendly renewable energy. Here, we aim to design and simulate a novel hybrid solar photovoltaic (PV) system coupled with a single-slope solar still unit for freshwater production. Various design techniques were utilized to fine-tune the model towards producing 3–4.6 kg/m² · day of distillate water, thereby calculating the design aspects such as tank size, energy, and cost. The results revealed that a conventional solar desalination system had 22% lower efficiency than the proposed novel still distillation unit assisted with a solar PV system (connected to a heating element). The maximum efficiency of 45% has been recorded at the peak solar insolation due to the combination of the solar PV system. According to our design constraints, only a 3 m² basin area was required to achieve a productivity of ${\mathit{P}}_{\mathit{st}}$ = 1–5 kg/day. Design analysis showed that the total capital cost of a conventional still can be significantly reduced from 2600 to 1500 $/unit with PV system integration at the specified productivity and optimal solar radiation of ~17 MJ/m² · day at peak time (02.00 PM). This work paves the way towards maximizing solar energy utilization from PV integration with solar desalination to achieve high freshwater productivity in single-basin solar still systems.     

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.     

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.