Abstract. This paper investigates experimentally the thermal performance of conventional solar water still with enhanced solar heating system. A number of variables have been considered including the water depth inside the still and the inlet saline water temperature to the solar still from the preheater solar collector system and the still basin geometry. The still is modified to include preheating solar system, to preheat saline water before entering the solar still, in order to enhance its hourly or daily yield of pure water. A single slope conventional solar still with solar preheating unit was constructed and experimentally tested under different weather conditions. Different quantities of water in the solar still basin were tested to find the effect of water quantity on the hourly yield and still&apos;s thermal efficiency. It was found that 1 cm depth and finned still basin gives the best performance in terms of fresh water yield and thermal efficiency. The addition of the solar water preheater to the system has significantly increases the inlet basin saline water temperature to almost saturated temperature and saline water in the basin needed only small heat to be vaporized and hence increases the production of fresh water and enhances the solar still thermal efficiency

Abdullah M Al

M Tahat

Shabibi

CiteSeerX

 
International Conference on Renewable Energies and Power Quality (ICREPQ’15) 
La Coruña (Spain), 25th to 27th March, 2015 
exÇxãtuÄx XÇxÜzç tÇw cÉãxÜ dâtÄ|àç ]ÉâÜÇtÄ (RE&PQJ) 
 ISSN 2172-038 X, No.13, April 2015 
 
 
 
 
Thermal Performance of a Single Slope Solar Water Still with Enhanced Solar 
Heating System 
 
Abdullah M. Al Shabibi and M. Tahat 
Department of Mechanical and Industrial Engineering 
Sultan Qaboos University – P.O. Box 33, Al Khoud123 (Oman) 
Fax number:+968 24141316, e-mail:  ashabibi@squ.edu.om 
 
 
 
 
Abstract. This paper investigates experimentally the thermal 
performance of conventional solar water still with enhanced solar 
heating system. A number of variables have been considered 
including the water depth inside the still and the inlet saline water 
temperature to the solar still from the preheater solar collector 
system and the still basin geometry. The still is modified to 
include preheating solar system, to preheat saline water before 
entering the solar still, in order to enhance its hourly or daily 
yield of pure water. A single slope conventional solar still with 
solar preheating unit was constructed and experimentally tested 
under different weather conditions. Different quantities of water 
in the solar still basin were tested to find the effect of water 
quantity on the hourly yield and still’s thermal efficiency. 
It was found that 1 cm depth and finned still basin gives the best 
performance in terms of fresh water yield and thermal efficiency. 
The addition of the solar water preheater to the system has 
significantly increases the inlet basin saline water temperature to 
almost saturated temperature and saline water in the basin needed 
only small heat to be vaporized and hence increases the 
production of fresh water and enhances the solar still thermal 
efficiency. 
 
Key words 
 
Solar energy, solar desalination, single slope solar water 
still. 
 
1. Introduction 
 
Single slope water still simply consists of a thermally 
insulated box with a glass cover. The solar energy 
penetrates the glass and causes a greenhouse effect inside 
the box. The water inside the box heats up and evaporates 
leaving behind any impurities such as the salt. The water 
vapour then condensate when it contacts the inside glass 
cover. The condensated pure water can then be collected. 
Single slope still was studied both theoretically and 
experimentally by a number of researchers. Nafey at al. [1] 
investigated the effect of the solar radiation, wind speed, 
brine depth and glass tilting angle on still productivity. It 
was found that the solar radiation is the most affecting 
parameter on the productivity. The productivity decreases 
with the increase of the wind speed increases due to the 
decrease in the fractional energy of evaporation. 
Furthermore, when the brine depth was increased the 
productivity decreased. Moreover, it was found that in 
summer the tilt angle of the glass cover should be 
maintained as small as possible because the horizontal 
plane receive more radiation than the inclined plane does, 
while in winter the productivity increases when the 
inclination is increased. Solar still was tested in different 
climate conditions and in many places around the world. 
Singh and Tiwari [2] studied the monthly performance of 
passive and active solar stills for different Indian climate 
conditions. Medugu and Ndatuwong [3] designed and 
tested a solar still under actual environmental condition 
of Mubi, Nigeria. They developed theoretical analysis of 
heat and mass transfer mechanisms inside the still. They 
did experimental and theoretical investigation on the 
distillation performance of the solar still. They found that 
the instantaneous efficiency increases with the increase 
of the solar radiation and the feed water temperature. 
Hassanain and Abu-Zied [4] conducted a study about 
single slope solar still for sea water distillation. The 
investigation was carried out under the open 
environmental conditions of Egypt on a single slope still 
inclined by 20%. The investigation addressed the 
following: The still productivity, distilled water salinity 
and still performance in term of the still efficiency and 
the coefficient of performance. They found that the still 
productivity and efficiency increases by increasing the 
solar radiation. The highest productivity was 0.226 L/2 
obtained during the month of July. Also, they found that 
the still performance increases gradually from the sunrise 
time till it reaches certain maximum value at noon and 
afternoon by about an hour respectively and then 
decreases until it reaches minimum value at sunrise time. 
Arjunan et al. [5] conducted an experimental study on 
solar still with sponge liner. Two types of measurements 
were performed for the same climatic conditions: one 
with the sponge sheet placed on the inner wall surfaces 
(the back and the side wall) and one without the sponge 
sheet. It was found that the productivity of the solar still 
was 15% higher than the conventional still. They also 
found that decreasing the water depth increases the 
productivity of the still. Afrand et al. [6] carried out a 
theoretical study of solar distillation in a single basin 
under the open environmental condition of Chabahar – 
Iran. In this research, they were investigating the still 
https://doi.org/10.24084/repqj13.417 585 RE&PQJ, Vol.1, No.13, April 2015
productivity, distilled water salinity and still performance 
in term of the still efficiency. They found that the 
maximum efficiency of the solar still was at noon due to 
the high radiation. Another study about single solar still 
was conducted in India by Prasad et al. [7]. The still was 
modified with graphite powder to maximize the 
absorptivity. In this study, the effect of four parameters 
was investigated; the amount of silicate, amount of acid, 
amount of graphite powder and water depth. The 
maximum productivity of the still was 1.6 L/m2. It was 
found that the productivity of the solar still decreases as 
the amount of water is increased. When the amount of 
sodium silicate is increased the productivity increases, but 
when more than 150g was added the productivity 
decreased. The same result was obtained when increasing 
the amount of graphite and acid. The peak performance 
was obtained by 150g of sodium silicate, 100ml of 2NHCl, 
and 50g of graphite.  
 
The main aim of the present work is to design and test a 
single slope water still with pre-solar water heating system 
in order to investigate the effect of the amount of water in 
the basin, the inlet water temperature to the basin from the 
pre-solar water heater on the amount of fresh water yield 
and on its thermal performance, and the still basin 
geometry (flat, finned and corrugated surface).  
 
2.  Test Rig 
 
A single slope solar water still with solar preheater system 
was designed and fabricated. The still consisted mainly of 
a base unit, made from galvanized steel, and a glass cover. 
The surface area of the still is 1 square meter. The bottom 
inner surface of the base unit is painted black and the inner 
side walls are painted white. The side walls of the base 
unit are insulated from outside with Styrofoam. At the 
bottom end of the inclined surface of the base unit, a 
passage is made to collect the fresh water coming down of 
the cover glass. Three floating valves are attached to the 
back side of the still to allow the adjustment of the water 
depth inside the basin of the still (see figure 2). A simple 
solar collector was constructed and made of a single glass 
cover with water loop to preheat the salinity water before 
entering the still. The whole system, the still; the collector 
and the supply tank, was assembled as shown in figure 1. 
 
3. Experimental Procedure 
The experiments conducted to study the effect of water 
level in the basin and the effect of using solar preheater on 
the yielded fresh water and on the solar still thermal 
performance. Thermocouples were positioned at different 
locations in the still to measure the temperatures 
throughout the day. The thermocouples were connected to 
a data logger to record and save the temperatures readings 
every 15 minutes.  
First, the solar collector was connected to the inlet of the 
solar still basin and the correct amount of salinity water 
was introduced into the basin. The basin inlet and the solar 
collector outlet temperatures were measured by 
thermocouples and recorded every 15 minutes in order to 
find the mean average hourly temperatures. The same 
procedure was followed for measuring the still water, the 
cover glass, the vapor and the ambient temperatures. The 
fresh water yield was collected and recorded using sealed 
graduated glass container on an hourly basis.  
 
 
 
Fig. 1 Experimental set up of single slope solar water still 
with solar energy heating system 
 
4. Thermal Efficiency of the Water Still 
 
To assess the performance of the still, it is important to 
identify its thermal efficiency. The still efficiency can be 
calculated using the following formula 
 
in
evp
Q
Q
energysolarinputtotal
heatnevaporatio
&
&
==
   
 η  
 
The heat of vaporization can be calculated using the 
following formula 
 
fgevp hmQ && =  
 
Where m&  is the mass flow rate and fgh  is the latent heat 
of vaporization. The energy input due to solar radiation 
can be calculated as 
 
IAQ pin ατ=&  
 
Where α, τ, pA , and I are absorptivity coefficient, 
transmission coefficient of the glass cover,  area of the 
absorbing plate and solar intensity on horizontal surface 
respectively. 
 
5. RESULTS 
The result of the experimental tests shows that the 
production rate of fresh water is directly related to the 
water level height in the basin and to the solar radiation. 
As the water level in the basin decreases and solar 
radiation increases the production rate increases. For 
finned bottom surface, the hourly accumulated fresh 
water for three different water depths are shown by figure 
https://doi.org/10.24084/repqj13.417 586 RE&PQJ, Vol.1, No.13, April 2015
2 and it shows that the depth of 1cm depth outperform the 
2cm and 3cm of water depth in the solar still basin. This is 
due to the small heat capacitance of the water at 1cm depth 
compared with the other two depths and because it needs 
less energy to be vaporized. The maximum hourly amount 
of fresh water yield is at noon and the total hourly 
accumulated is about 1800 ml per meter squared for water 
depth of 1 cm. 
The average efficiency is calculated over the testing time 
which lasted between 7 am and 5 pm and it was found to 
be 61.9% for finned basin surface. The addition of the 
solar water preheater to the system has significantly 
increased the inlet basin saline water temperature to almost 
saturated temperature and saline water in the basin needed 
only small heat to be vaporized as shown in figure 3. An 
increase of about 20% is noticed in the fresh water yield 
when finned surface was used in the still basin. Figure 4 
shows the temperature readings obtained inside the still for 
flat and finned surface. Figure 5 shows the fresh water 
yield with and without using a solar preheater. An increase 
of about 50% in the yielded fresh water was found. 
 
 
 Fig. 2 Fresh water commulative yield for finned surface 
 
 
Fig3. temperature readings at the solar collector inlet and 
outlet 
 
Fig. 4 Comparison of temperature readings inside the still 
for flat and finned surface 
 
 
Fig. 5 Comparison of yielded fresh water hourly rate for 
still with and without solar preheating 
 
6.  Conclusion 
 
This paper investigates the thermal performance of solar 
water still with enhanced solar heating system. A number 
of variables have been considered including the water 
depth inside the still and the inlet saline water 
temperature to the solar still from the preheater solar 
collector system. It was found that 1 cm depth gives the 
best performance in terms of fresh water yield and 
thermal efficiency. The addition of the solar water 
preheater to the system has significantly increased the 
inlet basin saline water temperature to almost saturated 
temperature and saline water in the basin needed only 
small heat to be vaporized and hence increases the 
production of fresh water and enhances the solar still 
thermal efficiency. Three types of still basin bottom 
surface were tested: flat, finned and corrugated. The 
finned surface was found to give the best performance. 
Using finned surface can increase the fresh water 
production by 20%. The effect of using a solar heating 
system was also investigated and found to enhance the 
still performance significantly 
 
References 
 
[1] A.S. Nafey, M. Abdelkader, A. Abdelmotalib and A.A. 
Mabrouk, “Parameters affecting solar still productivity”, 
Energy Conversion & Management, 41, pp. 1797-1809. 
[2] H.N. Singh and G.N. Tiwari; “Monthly performance of 
passive and active solar stills for different Indian climatic 
conditions”, Desalination, 168, pp. 145-150. 
[3] D.W. Medugu  and L.G. Ndatuwong, “Theoretical analysis  
of water distillation using solar still”, International Journal 
of Physical Sciences, 4(11), pp. 705-712.  
[4] S.M. Radwan, A.A. Hassanin and M.A. Abu-zeid, “Single 
slope   solar still for sea water distillation”, World Applied 
Sciences Journal, 7(4), pp. 485-497. 
[5] T.V. Arjuna1, H.Ş. Aybar and N. Nedunchezhian, “A study 
on effects of water capacity on the performance of a simple 
solar still”, International Journal of Applied Engineering 
Research, 4(11), pp. 2223–2234. 
[6] Masoud Afrand, Amin Behzadmehr, Arash Karimipour, “A 
Numerical simulation of solar distillation for installation in 
Chabahar-Iran”, World Academy of Science, Engineering 
and Technology, 47, pp. 469-474. 
[7] P. Rajendra Prasad, Padma Pujitha, B., G. Venkata Rajeev 
and K.Vikky, “Energy efficient solar water still”, 
International Journal of ChemTech Research, 3(4), pp. 
1781-1787. 
https://doi.org/10.24084/repqj13.417 587 RE&PQJ, Vol.1, No.13, April 2015


Thermal Performance of a Single Slope Solar Water Still with Enhanced Solar Heating System

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=E06B6DEC7CC3A9C6D06B4629D0A8EA1A?doi=10.1.1.1054.6379&rep=rep1&type=pdf

Thermal Performance of a Single Slope Solar Water Still with Enhanced Solar Heating System

Abstract

Similar works

Full text

Available Versions

CiteSeerX