Enhancement of distillate output of double basin solar still with vacuum tubes

The latent heat of condensation is lost to the atmosphere; hence it is not utilized to increase distillate output of single basin solar stills. This difficulty was overcome by attaching an additional basin to the main basin. The performance of the double basin solar still was also increased by attaching vacuum tubes to the lower basin; hence the lower basin possessed a higher temperature throughout the day. The latent heat of condensation of the bottom basin was also utilized to increase distillate. But the distillate output of the top basin was even lower compared with that of the bottom basin. This paper proposed a novel approach to increase the distillate output of the double basin solar still attached with vacuum tubes by introducing different sensible energy storage materials like pebbles, black granite gravel and calcium stones to increase the basin area. Experiments were conducted in climate conditions of Mehsana (23.6000° N, 72.4000° E) Gujarat from April to September 2013 with a constant water depth of 2 cm in the top basin with and without the use of basin materials. The results showed that the distillate output of basin material with calcium stones is greater (74%) compared with that of black granite gravel and pebbles. The integration of vacuum tubes with solar still greatly increases the distillate output of the solar still by providing hot water at the lower basin.     

Effect of energy storage medium (black granite gravel) on the performance of a solar still

In this study, a detailed experiment has been conducted on a single‐basin solar still which is modified with energy storage medium of black granite gravel. An attempt has been made to utilize the maximum amount of solar energy and to reduce the heat loss from the sides and bottom of the still. The conventional still is modified with an energy storage medium of black granite gravel of 6 mm size which is provided in the basin for different (quantity) depths. The black granite gravel functions as energy storage medium and also as an insulation layer to reduce the bottom and side loss coefficients. The black gravel is used for absorbing the excess heat energy from solar radiation during the noon hours. Due to this, the heat accumulated in the space between the water and glass surface is reduced and hence the temperature difference between the water and glass surfaces increases. The depth (quantity) of the gravel layer in the basin will influence the performance of the still and some of the parameters like basin temperature, water temperature, glass temperature and still productivity. This study deals with the effect of aforesaid parameters on the performance of the still. An attempt has been made to optimize the still performance for the above‐mentioned parameters. A mathematical model is developed to estimate the water, gravel, and inside glass temperatures theoretically and to estimate the hourly and daily yield. To show the effectiveness of the modification, its performance is compared with the conventional still under the same climatic condition. It is found that the still yield is increased by 17–20% with almost no cost for this modification as black granite gravel is very cheap. Error analysis was done by comparing the theoretical and experimental results to show the validity of the mathematical model. It is found that the maximum percentage of discrepancy for all the parameters is about ±18%. Theoretical value of yield per day has 8% discrepancy over experimental value. Copyright © 2007 John Wiley & Sons, Ltd.     

Further studies on double solar still

This paper is devoted to the development of a transient model of the performance of a double solar still and its validation by experiments. the dependence of the daily output of the distillate on wind velocity, ambient temperature and daily insolation has been studied analytically. It is seen experimentally that the presence of a black dye in the lower basin increases the distillate output by 10 to 15 per cent.     

Use of waste hot water in double basin solar still

A periodic analysis of a double basin solar still is presented in this paper. In this still waste hot water is fed into the lower basin at a constant rate such as is available from power stations or other industries. The effect of various parameters on the distillate output of the still is also investigated.     

Performance analysis of solar still with cow dung cakes and blue metal stones

The aims of this paper is to investigate the effects of various materials inside the solar still on the increase of the productivity of potable water. Here, blue metal stones and cow dung cakes were used as materials. To investigate their effect, three identical solar stills with an effective area of 1 m square made from locally available materials were tested in climate conditions of Mehsana (23°50′ N 72° 23′). The first and second solar stills were filled with blue metal, stones and cow dung cakes, while the third one was taken as a reference which consisted of only blue paint at the basin. The experiments show that blue metal stones have the highest distillate output at daytime, followed by cow dung cakes solar still and reference solar still. On the other hand, the overall distillate output of blue metal stones and cow dung cakes at daytime as well as at night were 35% and 20% compared with that of reference solar still.     

A hybrid high efficiency single-basin solar still

In this work, an attempt has been made to enhance the distillate output of a single-basin solar still by coupling it with a flat plate solar collector and by coating a thin layer of SnO₂ on one side of the transparent cover plate. The heat transfer fluid was circulated between the still and the collector through a heat exchanger and storage tank by thermosyphonically induced flow. It was observed that good insulation around the storage tank considerably increased the yield at night due to the decrease of ambient temperature. Thermosyphonically induced flow eliminated the need for pumps and control units. A layer of SnO₂ on the transparent cover lowered the thermal radiation loss, one of the major sources of heat energy loss in a solar still. Values for solar radiation, ambient air temperature, salt-water temperature in the basin, temperature of air-vapour mixture within the still, input and output temperatures of the heat exchanger heat transfer fluid, and the distillate yield were collected by a data acquisition system. After making the above modifications, the distillate yield was measured to be 6·745 litres per square metre per day for a September solar radiation of 17820 KJ at Istanbul-Gebze. To compare the distillate yield, a conventional solar still with similar dimensions to those of the improved still was constructed. The overall efficiency of the improved still was found to be 3·26 times the efficiency of the conventional still.     

Transient analysis of double basin solar still with intermittent flow of waste hot water in night

A transient analysis of a double basin solar still has been presented in this paper, incorporating the effect of intermittent flow of waste hot water into the lower basin at a constant rate during off sunshine hours. The waste hot water can be obtained either from a thermal power plant or any other industry. The effect of various parameters, e.g. inlet temperature, flow rate, water mass, etc., on the distillate output of the still has been investigated in detail. It has been found that the yield increases with flow rate if the inlet waste hot water temperature is above its optimum value. If the inlet temperature is below its optimum value, the yield decreases as the flow rate increases. The yield also decreases with an increase of water mass in the lower basin.     

PARAMETRIC STUDIES ON A DOUBLE BASIN SOLAR STILL

Parametric studies on a double basin solar still is presented. Explicit expressions are obtained for the temperatures of various components of the system, distillate output and the efficiency. Effects of the still parameters are also incorporated in the analysis. For appreciation of the analytical results, numerical calculations have been carried out using meteorological parameters of a typical day in Delhi. The parametric investigations reveal some worthinteresting results.     

Simple multiple wick solar still: Analysis and performance

This paper presents the design, analysis and performance of a multiple wick solar still, in which blackened wet jute cloth forms the liquid surface which can be oriented to intercept maximum solar radiation and attain high temperatures on account of low thermal capacity. The wet surface consists of a series of jute cloth pieces of increasing length separated by thin black polythene sheets, resting on foam insulation supported by a net of nylon ribbon; these pieces are arranged along an incline and their upper edges are dipped in a saline water tank. Suction by the cailliary action of the cloth fibre provides a thin sheet of liquid on the cloth; the arrangement ensures that all the surface, irradiated by the sun is wet at all times. The results of an analysis based on Dunkle's relation[16] are in excellent agreement with the observed performance of the still. On a typical cold sunny day in Delhi (viz. 6 February 1980) the distillate output was 2.5 l/m² day, corresponding to an overall efficiency of 34 per cent (as compared to a maximum of 30 per cent for basin type still). The still costs less than half of the cost of a basin type still of same area and provides a higher yield of distillate.     

Transient analysis of double basin solar still

The effect of water flowing over the upper glass cover of a double basin solar still on its transient performance has been presented. A comparative study of the daily distillate production of a double basin solar still with and without water flowing over the upper glass cover has been made, and some interesting conclusions have been drawn. Numerical calculations have been made for a typical hot day (viz 2 May 1980) in Delhi.     

Double basin solar still

This paper presents a periodic analysis and observed performance of a double basin solar still, mounted on a stand. Observations on this type of still are in fair agreement with the results of analysis. The daily distillate production of such a still is on the average 36% higher than that of a single basin still. Some aspects of the operation, design and performance have also been discussed.     

具有内插管的真空管太阳能热水器性能研究

为了提高真空管集热管效率,在相同环境下,对未插内管和插有内管的玻璃真空管太阳能热水器进行了三维数值模拟。分析表明,通过在真空管中插入内管可以改善真空管内冷热水的流动和换热,提高真空管集热器的效率。对插入不同长度内插管的三组实验做了比较,结果表明,应合理选择内插管的长度。     

The progress and prospect of middle/high temperature evacuated tubular solar collector

The all-glass evacuated solar collection tubes, incorporating the dc sputtered double layer metal-aluminium nitride cermet selective surface, have been mass-produced by TurboSun in large quantities under license to the University of Sydney since 1995. A solar absorptance of 0.94–0.95 and emittance of 0.04–0.05 at room temperature has been achieved for the SS-AIN cermet solar coatings. These solar tubes are stable at 330–400°C. These M-AIN cermet tubes have widespread application for solar hot water and steam heaters, as well as the demonstration test units for solar thermal electricity. In China, the production of solar water heaters using all-glass evacuated solar heat collection tubes has rapidly increased since 1995. The experimental results show that the solar selective coatings incorporating dc sputtered tungsten and dc reactively sputtered aluminium nitride components in a cermet should be stable at 500°C in vacuum. It would be possible to produce solar collector tubes for solar thermal electricity application with superior solar performance at a much lower cost.     

Single basin double slope solar still with minimum basin depth and energy storing materials

Solar still is a simple device which can convert available waste or brackish water into potable water using solar energy. A single basin double slope solar still with an inner basin size 2.08 m × 0.84 m × 0.075 m and that of the outer basin size 2.3 m × 1 m × 0.25 m has been fabricated with mild steel plate and tested with a layer of water and different sensible heat storage materials like quartzite rock, red brick pieces, cement concrete pieces, washed stones and iron scraps. It is found that, the still with ¾ in. sized quartzite rock is the effective basin material. The still is theoretically modeled. In previous researcher’s work, variation in transmittance is taken as constant. The variations in solar incidence angle and transmittance of the covers are also considered in this work. The theoretical values are compared with actual values. The theoretical water and glass temperatures and the theoretical production rate are having higher deviation with actual. Hence, another thermal model developed for this still is applied to validate the results accurately. It is found that, the theoretical production rate using thermal model agrees well with experimental.     

Nocturnal distillation in basin-type solar stills

Nocturnal distillation, which dominates the output of deep basin stills, has been studied experimentally. From observations of continuous temperature and distillate measurements, the important factors affecting night-time distillation are identified. A dimensionless analysis of these factors was carried out in an attempt to generalise the night-time behaviour of solar stills. The results indicate that the distillate output is uniquely determined by the stored thermal energy in the still at sunset.     

Theory and experimental investigation of a weir-type inclined solar still

A weir-type solar still is proposed to recover rejected water from the water purifying systems for solar hydrogen production. This consists of an inclined absorber plate formed to make weirs, as well as a top basin and a bottom basin. Water is flowed from the top basin over the weirs to the bottom collection basin. A small pump is used to return the unevaporated water to the top tank. Hourly distillate productivity of the still with double- and single-pane glass covers was measured and the latter showed higher production rates. The average distillate productivities for double- and single-pane glass covers are approximately 2.2 and 5.5 l/m²/day in the months of August and September in Las Vegas, respectively. Mathematical models that can predict the hourly distillate productivity are developed. These compared well with the experimental results. Productivity of the weir-type still with a single-pane glass was also compared with conventional basin types tested at the same location. The productivity of the weir-type still is approximately 20% higher. The quality of distillate from the still is analyzed to verify the ability of the still to meet the standards required by the electrolyzers.     

The use of a thermal energy recycle unit in conjunction with a basin-type solar still for enhanced productivity

A recently developed thermal energy recycling unit operating under forced air circulation was attached to a conventional, basin-type solar still to enhance overall still productivity. In this unit, a relatively large fraction of the latent heat of condensation of the distillate is utilized to preheat and evaporate the feedstock. The system performance was tested in the laboratory using a solar simulator. The solar still was double glazed and no condensation was observed on the inner glazing when operating in the thermal energy recycling mode. The overall system productivity was about three times that of a conventional (single-effect) basin-type solar still. The advantages of the proposed system design are the following: (i) the solar still productivity can be enhanced significantly and at a reasonable cost; (ii) non-wetting glazings (e.g. certain plastic glazings) can be utilized, since in this mode of operation the glazing does not function as a condensation surface; (iii) as a result, the thermal losses from the outer surface of the glazing to the ambient can be reduced significantly by the use of double glazings; (iv) the system is very adaptable to the utilization of an external waste energy source (e.g. wet steam or hot saturated air) for nocturnal distillation, viz. operation in the absence of solar radiation.     

Solar distillation of pond (muddy) water

Solar distillation tests were performed with samples of muddy water in a deep basin type solar still. Results presented show that, on a 24 h basis, the distillate output is independent of the muddiness of the water sample. However, during the daytime, periods between sunrise and sunset, the output increases with the muddiness of the water.     

Performance of an inclined solar still with rectangular grooves and ridges

This work investigates the experimental performance of a new type inclined solar still with rectangular grooves and ridges in absorber plate. The still was fabricated and tested for various inclination angles of 25°, 30° and 35° facing south with absorber plate. Performances of the still were compared with different wick materials (Black cotton cloth, Jute cloth, and Waste cotton pieces) on the absorber plate. The effect of placing porous material (Clay pot) and energy storing material (Mild steel pieces) in the grooves were studied. The results demonstrate that 30° inclination is optimum which yielded 3.77 L/day production. Compared to different wick materials, black cotton cloth helps to achieve maximum productivity of 4.21 L/day. The addition of permeable materials and energy absorbing materials also enhances the distillate output to 4.27 L/day.