Analytical expression for thermal efficiency of a passive solar still

Using energy balance equations for the different components of a passive solar still (namely, glass cover, water mass and basin liner), the effect on its thermal efficiency of water flowing over the glass cover with uniform velocity has been studied analytically. The efficiency is found to increase due to the water flow at higher depths of water in the basin. The result is validated by the experimental results of other authors.     

Enhancement of daily yield in a double basin solar still

A straightforward transient analysis of a double basin solar still has been presented, incorporating the effect of water flow over the glass cover and flow of hot water in the lower basin by a flat plate collector. It is concluded that, for higher daily yield, the collector should be disconnected from the still during off-sunshine hours.     

Effect of Water Flow over the Glass on the Performance of a Solar Still Coupled with a Flat Plate Solar Collector†

In this communication a transient analysis of a solar distillation system with water flow over the glass cover is presented. The system comprises of a single basin solar still coupled with a flat plate solar collector. Due to the increased difference between water and glass temperatures the yield of this system is significantly increased. The performance of this system has been compared with that of a simple single basin solar still (SBSS), SBSS with water flow over it and SBSS coupled with a flat plate collector; and it is concluded that a SBSS with water flow over it shows the best performance.     

Numerical study of a passive solar still with separate condenser

A passive solar still with separate condenser has been modeled and its performance evaluated. The system has one basin (basin 1) in the evaporation chamber and two other basins (2 and 3) in the condenser chamber, with a glass cover over the evaporator basin and an opaque condensing cover over basin 3. Basins 1, 2 and 3 yield the first, second and third effects respectively. The top part of the condensing cover is shielded from solar radiation to keep the cover relatively cool. Water vapor from the first effect condenses under the glass cover while the remainder of it flows into the condenser, by purging and diffusion, and condenses under the liner of basin 2. The performance of the system is evaluated and compared with that of a conventional solar still under the same meteorological conditions. Results show that the distillate productivity of the present still is 62% higher than that of the conventional type. Purging is the most significant mode of vapor transfer from the evaporator into the condenser chamber. The first, second and third effects contribute 60, 22 and 18% of the total distillate yield respectively. It is also found that the productivity of the solar still with separate condenser is sensitive to the absorptance of the liner of basin 1, and the mass of water in basins 1 and 2. The mass of water in basin 3 and wind speed have marginal effect on distillate production. Other results are presented and discussed in detail.     

Thermal modelling of high temperature distillation

This communication presents a comparative study of a single basin solar still under various modes of operation. A simple transient analysis of all the modes under the same meteorological conditions has been presented. The water depth in the solar still and the absorptivity of the basin liner along with the water flow over the glass cover of the still has been found to affect the daily distillate production of the system considerably. The thermosyphon mode enhances the daily distillate production. It has also been observed that the evaporative heat transfer coefficient is a very strong function of temperature.     

An investigation of the parameters involved in simple solar still with inclined yute

Desalination of water has been one of the most important technological work undertaken in many countries, in particular Middle East. For this purpose, solar energy is the attractive familiar way in producing such fresh water where the cost of other energy is continuously increased. This paper represents the experimental results carried out with a solar still with inclined evaporating yute to study the effects of air gap, base slope angle and glass cover slope angle on the performance of the still. In order to investigate the parameters involved in the still, three models have been designed, manufactured and tested against some experimental measurements on a still having 1m × 1m basin area. The models have been designed in a way that it can give different base slope angle and glass slope angle. A comparison between the three models has been made for three glass slope angles. The test results show that the model with base slope of 15° and glass slope of 35° gives the best results. It gives a daily desalinated water quantity of 5.6 liter/m².day.     

Analytical thermal modelling of multi-basin solar still

Based on energy balances for different components of a multi-basin solar still, namely, the basin-liner, the water mass and the glass cover, analytical expressions for water and glass temperatures have been derived in terms of climatic and design parameters of the system. It is inferred that the daily yield is a maximum for the least water depth in each basin     

Thermal performance of a solar still coupled with an inexpensive ground water heater

This paper presents the results of investigations carried out over a solar still coupled with an inexpensive solar ground water heater. The explicit expressions for water temperature at the outlet of water heater, glass and water temperatures in the case of a solar still in which the hot water is flowing at a constant rate, have been derived. To appreciate the enhancement in the still productivity, numerical calculations have also been carried out for two typical days at Delhi, India.     

A numerical model and experimental investigation for a solar still in climatic conditions in Abidjan (Côte d''Ivoire)

A solar distillation in a single basin is studied theoretically and experimentally. We present a mathematical model to describe the energy balances for the glass cover, water in the basin and base plate. The model neglects the thermal capacity of the base plate and the temperature gradient through the width of the glass. The energy equations for the glass, water and absorber are simultaneously solved. The effects of water depth, wind speed and glass cover thickness on still productivity are evaluated. The daily total production increases with decreasing water depth. A small increasing of productivity occurs with the increase of wind speed. The thickness of the glass cover has no effect on the production. An experiment has been conducted to validate the mathematical model. The relative difference between experiment and theory is 5% for temperatures, and 15% for productivity.     

Floating vertical solar still for desalination of marsh water

The performance of a floating conical solar still used for producing drinking water in brackish marsh areas has been investigated. The new proposed still consists of a vertical conical-shaped blackened cotton wick installed inside a floating transparent glass cover of similar shape. The base section of the floating cover was properly designed to allow the bottom of the wick to soak directly in the brackish water. Multiple linear regression equations, relating global solar radiation, ambient air temperature, and wind speed with the productivity of the still, have been developed. The regression analysis showed that the daily global solar radiation can be adopted alone to predict still productivity with acceptable accuracy. Results also showed that there is good competition between the proposed conical still and the conventional basin-type solar still concerning productivity and operation requirements. Recommendations have been made to use this type of still for ensuring fresh drinking water in marsh areas where the natural supply of fresh water is inadequate.     

Performance analysis of double basin solar still with evacuated tubes

Solar still is a very simple device, which is used for solar distillation process. In this research work, double basin solar still is made from locally available materials. Double basin solar still is made in such a way that, outer basin is exposed to sun and lower side of inner basin is directly connected with evacuated tubes to increase distillate output and reducing heat losses of a solar still. The overall size of the lower basin is about 1006 × 325 × 380 mm, the outer basin is about 1006 × 536 × 100 mm Black granite gravel is used to increase distillate output by reducing quantity of brackish or saline water in the both basins. Several experiments have conducted to determine the performance of a solar still in climate conditions of Mehsana (latitude of 23°59′ and longitude of 72°38′), Gujarat, like a double basin solar still alone, double basin solar still with different size black granite gravel, double basin solar still with evacuated tubes and double basin solar still with evacuated tubes and different size black granite gravel. Experimental results show that, connecting evacuated tubes with the lower side of the inner basin increases daily distillate output of 56% and is increased by 60, 63 and 67% with average 10, 20 and 30 mm size black granite gravel. Economic analysis of present double basin solar still is 195 days.     

A low cost collector-cum-storage type solar water heater

A low cost collector-cum-storage type solar water heater has been developed. The cost of the heater is reduced by replacing window glass cover with 0.2 mm thick PVC film to avoid glass breakage in transportation and maintenance. In this paper the performances of solar water heaters having double glazing of PVC and glass have been compared. It was found that their performances are similar. Moreover, by providing an insulating cover in the night, the water remains warm till next morning for taking a bath etc. in the early hours when there is no sunshine.     

漂浮黑色海绵吸热－蒸发层太阳能蒸馏装置的实验研究

在普通槽形太阳能蒸馏装置的蒸发面上漂浮一层具有一定厚度且浸润良好的黑色海绵作为吸热层，蒸馏水的产量及蒸馏装置的热效率显著提高。实验研究了海绵厚度和稀疏度，盐水浓度和水层厚度，顶盖倾角以及空腔大小等因素对太阳能蒸馏装置性能的影响。     

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.     

Effect of dye on the performance of a double basin solar still

The use of single basin solar stills for water distillation has been well demonstrated. However, the amount of distilled water produced per unit area is fairly low which makes the single basin solar still unacceptable in situations where space is a limitation. Malik has suggested a new conceptual design of a double basin solar still to overcome the above problem partially. The relative results obtained on a double basin as opposed to a single basin solar still are reported here with reference to (a) its performance, (b) the effect of dye in the lower basin, and (c) the effect of maintaining the raw water level in the basins.     

Analysis of a parallel double glass solar still with separate condenser

A solar still designed and built at Physics department Hacettepe University, Ankara, Turkey (39° 57′N), utilizes direct and reflected (from a reflector) solar radiation incident on a parallel double glass cover, to evaporate sea or brackish water. Water vapor purges from the evaporator and diffuses to an integrated condenser due to pressure difference exists as a result of the volume ratio and temperature difference between the evaporator and condenser. A theoretical analysis based on the energy balance for different components of the unit was performed. Graphical analysis were presented to show the variations of solar radiation, ambient temperature, basin water temperature, vapor temperature and other important temperatures at different locations in the solar still. The productivity was in good agreement with what obtained by other authors and the efficiency was increased from 48% to more than 70% when the condenser cover was cooled down.     

Transient analysis of a winter greenhouse integrated with solar still

The present work deals with a simple transient analysis of a winter greenhouse integrated with a solar still. Explicit expressions for the temperatures of still cover, brine (basin-water), basin of the still/roof of the greenhouse, greenhouse air, plants and floor of the greenhouse have been developed so as to study the transient thermal performance of the system. The effect of several parameters, namely relative humidity, ventilation/infiltration, heat capacity of basin water and plants, etc. has been incorporated in the analysis. On the basis of numerical calculations, some interesting conclusions have been made.     

A multistage solar still with photovoltaic panels and DC water heater using a pyramid glass cover enhanced by external cooling shower and PCM

A novel multistage solar desalination system with a photovoltaic heater was manufactured. The base of the down basin of the solar still had a layer of paraffin wax with a mass of 13 kg as a phase change material. The system has been studied to evaluate the enhancement of freshwater. Saltwater was heated by solar radiation and by a direct current water heater. The surfaces of condensation vapor, such as the pyramid glass cover and lower surface of two stacked trays, were designed. This is to improve the productivity of freshwater by decreasing the resistance of condensation. The high temperature of the glass cover is modified by using a cooling water shower, especially at the highest intensity. The study includes parameters, such as cooling water shower flow rate, down basin water level, and the effect of the heater. It is observed that the novel solar desalination is proportional to solar radiation, paraffin wax, the heat input from a heater, cooling water shower flow rate, and down basin water level. The Multiple Stage Effect Photovoltaic Heater (MSEPVH) can produce 15 L/day of distilled water. The excellent flow rate of cooling water, the total freshwater, and the efficiency of MSEPVH for the optimal day were mathematically and experimentally determined.     

Thermal modeling of solar stills: an experimental validation

Expressions for water and glass temperatures, yield and efficiency of both single and double slope multiwick solar distillation systems in quasi-steady state conditions 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 solar stills. Experimental validation of the thermal model has been carried out by using modified heat transfer coefficients. Internal heat transfer coefficients have been evaluated based on both inner and outer glass cover temperatures for typical days namely January 22, and June 19, 2001 in Delhi. A fair agreement has been observed between theoretical and experimental results by using the modified internal heat transfer coefficients based on inner glass cover temperature.     

Comparative performance investigation of integrated collector‐storage solar water heaters with various heat loss reduction strategies

A detailed comparative assessment is reported on the thermal performance of integrated collector‐storage (ICS) solar water heaters with various strategies for reducing top heat losses. The objective of this investigation is to assess and compare heat loss reduction strategies. The shape of ICS solar water heater considered in present investigation is rectangular. The thermal performance of the solar water heater is evaluated and analyzed for the following cases: (1) single glass cover without night insulation; (2) single glass cover with night insulation; (3) double glass cover without night insulation; (4) transparent insulation with single glass cover; and (5) insulating baffle plate with single glass cover. Energy balances are developed for each case and solved using a finite difference technique. The numerical assessment of the system performance is performed for a typical July day in Toronto. Each strategy is observed to be beneficial, reducing top heat losses, and improving system performance. The greatest performance enhancements are observed for the water heater with a single glass cover and night insulation and for the system with a double glass cover and without night insulation. Copyright © 2010 John Wiley & Sons, Ltd.