1. Solar Water Distillation In School Laboratories
68.
Solar Water Distillation In School Laboratories
Mkwakwani Secondary School
Maryam Bwanga and Asila Ibrahim
Abstract:
Every 40 minutes, the sun delivers as much energy to the earth’s surface as all the people on the earth use in a year. Yet, although the supply is so vast, people directly use only a fraction of the solar energy that reaches the surface. Tanzania is among the countries which experiences sunshine almost throughout the year. Mostly, Tanzanians tend to complain about the heat and temperature during day and night. But we normally forget that, everything has advantages and disadvantages, and therefore our project seek to make use of this sunlight to solve a major problem in our secondary schools laboratories for science practical's. Students use water for conducting their experiments but it seems that the water used is not pure and contains some impurities such as chlorine and calcium phosphates which most of the times bring wrong results; hence there is a very high need of getting pure distilled water for better results.
Generally, distillation process incurs major expenses such as cost of electricity, instruments and fuel that is used in the process. This makes it harder for schools to afford buying of this modern distillers as well as distilled water since it’s also expensive and not widely available. Hence, our aim is to” make a simple and inexpensive local solar water distiller for secondary school laboratories”.
Method:
For research and collection of data, we visited students and lab technicians of many schools in our region, interviewed them and asked them few questions. The data obtained is represented statistically below.
For making the instrument, we used:
Soft wood to make a rectangular box with specified length of 43.5cm, width of 36.5 cm, height 20cm at the back side and 16cm at front side in order to be at an inclined angle.
Aluminium foil, A black tray.
A transparent glass with high refractive index laid on top of the box for collection of solar radiation, Plastic pipe, Collection vessel
Procedures:
Two experiments were conducted in similar conditions using the same instrument with only difference in glass mirror i.e. the first expt using a low refractive index clear glass and the second expt using a high refractive index clear glass.
Step 1. Half a litre of tap water was poured into the black tray which was kept in the wooden box with glass of low refractive index.
Step 2. The instrument was kept in direct sunlight for an hour for observation.
Step 3. In that hour, readings were taken 4 times, each after every 15 minutes.
The following day the same procedures were repeated in similar weather conditions BUT using a glass with high refractive index.
How it works: The aluminium foil is used as a heat conductor to deliver heat to the black tray inside the box. The black tray is used because black colour absorbs more sunlight than any other colour. Hence, it converts the sunlight to heat and thus warms the water. The clear glass prevents the heat from escaping the tray. The rising hot vapour condenses on the clear glass, and then flows down into a collecting vessel.   
Time(mins) 15 30 45 60
Volume(cm3) 12 63
116
147
In experiment 1, whereby a glass mirror of low refractive index was used, the volume of distilled water taken and recorded as :-
Time(mins) 15 30 45 60
Volume(cm3)
191
346
441
In experiment 2, whereby a glass mirror of high refractive index was used, the volume of distilled water taken and recorded as :-
Results:
After following the procedures mentioned, the following observation was taken and recorded:
In both experiments 1 and 2, the desired results were seen. When the instruments were removed from the sunlight, in both cases distilled water was collected and poured into different measuring cylinders for recording volumes.
Conclusions:
From our results obtained, it shows that the instrument made can be used for the intended purpose of distilling water for science practical's in secondary schools and also at University level. This instrument is very simple to make, inexpensive, made with readily available materials as well as efficient and therefore can also be used in hospitals, beverage factories and even at homes.
We expect this will highly help students and teachers in schools to perform the practical's as required since “pure distilled water will give better and accurate results”. This distilled water can also be used for drinking purposes, since it is free from impurities and bacteria.