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.     

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.     

Single basin solar still coupled with flat plate collector

This paper presents the transient performance of a single basin solar still coupled with a flat plate collector. The average daily production of distilled water has been found to be 24% higher than for a simple single basin solar still     

Effect of Temperature Dependent Internal Heat Transfers on the Performance of a Solar Still

In this paper, an effect of the temperature dependence of internal heat transfer coefficients on the performance of a single basin solar still has been studied by incorporating the change of water mass in the basin with time, initial basin water temperature etc. On the basis of numerical calculations based on simple transient analysis, the following conclusions have been drawn:

i) the evaporative heat transfer coefficient is a strong function of brine temperature, and

ii) the change of brine mass with time has insignificant effect on the performance of the still in nocturnal production which is in accordance with the assumption made by Malik and Tran (1973). This is true for other cases also.

These have also been validated by experimental results.     

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.     

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.     

A step basin type solar water heater-cum-solar still

This communication reports the design details, performance and testing of a step basin type solar water heater-cum-solar still. The combined efficiency of the system is 64.5 per cent.     

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.     

EFFECT OF ADDING A PASSIVE CONDENSER ON SOLAR STILL PERFORMANCE

A theoretical and experimental study was carried out to investigate the effect of adding a passive condenser on the performance of the single slope, basin type solar still. A theoretical model based on Dunkle [1] mass transfer (evaporation) rate was developed. The model assumes that the transfer of water vapour from the still to the condenser is due to one or more of the following mass transfer modes; (i) diffusion, (ii) purging and (iii) natural circulation. The theoretical results indicate that diffusion contribution is relatively small. The contribution through purging represents the fraction [V(cond)/(V(cond) + V(s))] of the still yield, while it represents 75% of the still yield through natural circulation. An experimental study that simulates the purging mass transfer mode was investigated. The experimental results show good agreement with the theoretical predictions and an increase of 45% in solar still efficiency was obtained.     

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.     

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.     

Experimental evaluation of a single-basin solar still using different absorbing materials

Single-basin solar stills can be used for water desalination. Probably, they are considered the best solution for water production in remote, arid to semi-arid, small communities, where fresh water is unavailable. However, the amount of distilled water produced per unit area is somewhat low which makes the single-basin solar still unacceptable in some instances. The purpose of this paper is to study the effect of using different absorbing materials in a solar still, and thus enhance the productivity of water. Experimental results show that the productivity of distilled water was enhanced for some materials. For example, using an absorbing black rubber mat increased the daily water productivity by 38%. Using black ink increased it by 45%. Black dye was the best absorbing material used in terms of water productivity. It resulted in an enhancement of about 60%. The still used in the study was a single-basin solar still with double slopes and an effective insolation area of 3 m².     

Cavity geometry influence on mass flow rate for single and double slope solar stills

An experimental setup was built in order to evaluate the distillate yield for a double slope laboratory still under controlled conditions for basin water and collector temperatures within typical operating ranges. Additionally, experimental data previously gathered are correlated to propose a new empirical model to estimate mass flow rates in single slope solar stills. This model is compared with those from other published relations and with the double slope still experimental data. It was found that the proposed model reproduces in good agreement shallow stills experimental data and that there is not significant difference in productions between single and double slope cases subject to the same water and cover temperature. Dunkle’s model [R.V. Dunkle, Solar water distillation: the roof type still and a multiple effect diffusion still, International Development in Heat Transfer (Part 5) (1961) 895–902] is found to slightly underestimate production in shallow solar stills.     

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.     

Periodic theory of a greenhouse

This work presents a simple mathematical model of a greenhouse system whose top surface is covered by a solar still. The effect of various parameters such as relative humidity, ventilation/infiltration, heat capacity of basin water and plants, thickness of roof and water distillate output on the performance of the greenhouse system has been studied. It is found that the proposed system provides fresh water to cater to the needs of plants inside the greenhouse.     

Experimental Validation of Thermal Analysis of Solar Still with Dye

A simple straight forward transient analysis of a single basin solar still has been presented by incorporating the effect of presence of dye and attenuation of solar flux with depth in the water mass of the basin. An explicit expression for water and glass temperature, hourly yield and efficiency of solar still have been derived. Effect of various parameters viz temperature dependence of internal heat transfer coefficients, water depth, absorptivity of water mass and basin liner have been discussed in detail. An experiment has been conducted to validate the theoretical results obtained by present theory. It is concluded that

(i) there is a good agreement between theoretical results and experimental observation for 0.02 m water depth.

(ii) there is a significant effect of dye at larger depth which is in accordance with the experimental observation obtained by Sodha et al.(1.)     

Thermal modeling of passive and active solar stills for different depths of water by using the concept of solar fraction

This communication presents the thermal analysis of passive and active solar distillation system by using the concept of solar fraction inside the solar still with the help of AUTOCAD 2000 for given solar azimuth and altitude angle and latitude, longitude of the place. Experiments have been conducted for 24 h (9 am to 8 am) for New Delhi climatic conditions (latitude 28°35′N, longitude 77°12′E) during the months of November and December for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. Analytical expressions for water and glass cover temperatures and yield have been derived in terms of design and climatic parameters. It is observed that

(i) the solar fraction plays a very important role at lower values of solar altitude angle;

(ii) the internal convective heat transfer coefficient decreases with the increase of water depth in the basin due to decrease in water temperature;

(iii) there is a fair agreement between the experimental observation and theoretical prediction during daytime as compared to that during the night.

Performance assessment of a solar still using blackened surface and thermocol insulation

Fluoride contaminated drinking water is a severe problem in many parts of the world because of fluoride-related health hazards, which are considered to be a major environmental problem today. The present work is aimed at utilizing solar energy for removal of fluoride from drinking water by using a “solar still”. Also tests have been conducted with the “solar still” to find out hourly output rate and “still efficiencies” with various test matrixes. It is observed that the distillate from “solar still” showed a fluoride reduction of 92–96%. Further, the efficiency of “solar still” got increased by 11% when capacity of water in the solar basin was raised from 10 to 20 L. Upon suitable modification of the solar basin with appropriate base liner and insulation, this efficiency of the “solar still” is found to be further increased by 6% with a 20 L basin capacity.     

Exploitation of solar energy collected by solar stills for desalination by membrane distillation

The aim of this work was to evaluate the technical feasibility of producing potable water from simulated seawater by integrating a membrane distillation module with a solar still. The relatively hot brine in the solar still was used as a feed to the membrane module. The synergistic action of the solar still and the membrane module in the production of potable water was quantified. For this purpose, two types of experiment were conducted, indoor experiments and outdoor experiments. The sensitivity of the permeate flux to the brine temperature, flow rate, salt concentration and solar irradiation were all investigated. Overall, the flux of water from the solar still was no more than 20% of the total flux. The brine temperature significantly affected the flux of both the solar still and the membrane module, while the effect of salt concentration was marginal. The effect of these process parameters was more noticeable in the membrane module than in the solar still.     

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.