Mingde’s Science Corner 2: Science Fair!

Hello everyone,

As I’ve already said in the first edition of Mingde’s Science Corner, I attended a science fair.

For it, I made a project along with a couple of friends, used to make dirty water drinkable. We made a solar still, which uses the power of the sun’s light to evaporate water purify it.

The Problem:

Water shortages are a key problem for a significant portion of the modern world. It is said that 1 in 10 people, even in our time, lack access to clean water. While efforts have been made to give clean water to those who need it, a lot of the ways that we get water are hard to sustain, and cost a lot of money.

Water pollution is global issue, assumed to be the largest leading cause of deaths and diseases, accounting for approximately 16000 people every week, with an estimated 580 dying in India everyday (211700 deaths yearly) due to the fact that the water they have access to is of poor quality. Diseases caused from dirty water are said to cause more deaths than war and all other forms of violence combined.

Furthermore, 90% of water in the cities of China is polluted and as of 2007 half a billion people in china did not have access to clean drinking water.

In Africa, women have to spend a cumulative total of 40 billion hours annually just getting water. This stops them from developing their community and the ability to break free from the cycle of poverty.

The problem is also spreading. It is said that by 2025, half of the world’s population will be living in water-stressed areas.

What is our Solution?

Our goal is to create a cheap, portable and easy to use system in order to provide access to clean water for people in Africa and Southern Asia. Many people in these regions suffer from water shortage and often die of dehydration. Due to the fact that these locations receive plenty of sunlight, we have decided to use a distillation system involving sunlight – a solar still.

What is a Solar Still?

Solar stills are devices that distill (purify) water via evaporation and subsequent condensation into a collection chamber. Dirty or contaminated water is heated by sunlight, to the point of evaporation. The clean vapour is condensed and ready for consumption.

Subpoint: Safety

Traditional water purification devices consists of filtration systems. While these can remove particulate contaminants as well as organic matter (including viruses and harmful bacteria), filters cannot easily remove harmful dissolved compounds. For instance, seawater cannot be rendered drinkable by filtration, nor can chemically contaminated water. Solar stills, on the other hand, completely eliminate this disadvantage and allow only pure water vapour to pass. They are thus one of the safest methods of removing harmful contaminants from water, which is one of the most needed resources for survival.

Subpoint: Simplicity

Whereas the design of a well-functioning filter can become extremely complicated, a well-functioning solar still is very simple in concept, and in practice. The lack of moving parts in the most basic designs as well as a lack of requirement for complicated design makes solar stills easy to produce and easy to maintain.

Our Design:

Most solar stills are heavy and complex, but our design aims to eliminate the primary drawbacks of solar stills for water purification.

  1. Solar still are heavy.
  2. Solar stills are difficult to transport and use.

We believe that there is great refinement to be made in solar still design, hence our model.1xN-IFGCMl0IjotxASwHj3XbSo16uiIxU4ya51zQ.jpg

Our answer to the downsides of a solar still is The Superb Stowable Solar Still. We have designed it keeping in mind the downfalls of conventional solar stills.

The design uses a lightweight wood construction to make it easy to carry. It features two hinging trapezoidal wings, which fold out to make 4 reflective trapezoidal surfaces. The wings are locked in place using strings, which can be twisted around mounting points.

The entire reflector assembly fully deployed measures 58 by 46 centimetres. The centre frame measures 16 by 16 cm, netting a total reflective surface of approximately 2528 cm^2 or 0.02528 m^2.  The reflector is angled to allow sunlight of many angles to strike the water. Even under sub-optimal conditions, the reflector will still be able to focus sunlight into the water.

Stowed, the assembly measures 58 by 16 cm, making easy to store or carry in one hand. The mounting strings can be tied together to make a carrying handle, making our solar still portable. While the majority of solar stills have to be constructed in one location, unable to move with the user, the Superb Stowable Solar Still can move depending on where it is needed.

Material Choice:

Our reflectors use mylar, which is a plastic film blast coated with a thin layer of aluminum. It is considered to be a fair reflector, with an albedo of approximately 0.7, and comes close to the reflectivity of a mirror. The highest albedo on the list is magnesium oxide, but it offers diffuse reflection. The reason we cannot use diffuse reflection is due to the fact that is produces a soft, unfocused reflection, useless for a solar still. Mirrors are far too heavy for our design and silver far too expensive. Our optimal material is thus mylar. It is not only adequately reflective, but also lightweight, strong, and inexpensive with respect to other materials on the list.

A primary chamber is used for containing dirty water. This water is evaporated by the sunlight, and the vapour travels up a tube at the top of the container. The vapour condenses in a relocatable collection container, which can be separated from the entire assembly for direct consumption. The intermediate vapour tube screws onto both containers at each end. The tube is long enough to allow the water to condense, and the collection container can be placed in shade or directly under the reflectors to mitigate subsequent evaporation.

One significant drawback of the design is the vapour collection system. The vapour must travel a long distance to reach the collection chamber, and much of the condensed water my return to the original chamber, thus decreasing the efficiency. Our next step for the design would be to make the vapour collection system more efficient.

Materials and Costs:

As seen in the calculations, our total materials cost is less than that of a foot-long (source needed) submarine sandwich.

¼ Sheet of $3.00 mylar $0.75
3 Wooden Sticks @ $1.00 each $3.00
4 Brass Hinges @ $2.00 for 4 $2.00
Miscellaneous screws and staples Approximately $0.50
Plastic Tubing, Retention Ring and Containers Approximately $0.50

Total Cost: Approximately $6.75

The brass hinges could be replaced with a cheaper plastic system, thus reducing the cost even more. The frame construction could also be replaced with plastic. Given that even our proposed model is as cheap as it is, there are many possibilities for bringing the product to foreign countries for access to water, and even opportunities for selling the product commercially as a camping utility.

Performance:

Our solar still is designed to hold up to 600 ml of water in the clean water chamber, but has more space in the primary chamber.

Given that 1 gram of water takes 1 calorie to heat by 1°C, and the average density of water is 1g/ml, 600 ml of water will take 600 calories to heat by 1°C. In our testing and use cases, the ambient temperature and starting temperature of the water should be at least 20°C. This leaves 80°C to the boiling temperature of water at sea level. This changes with altitude, with the boiling temperature decreasing as altitude increases.

If a user decides to use the solar still while on a mountain, the efficiency would be increased, provided that the ambient temperature is the same. Realistically, the ambient temperature would likely nullify any benefits gained from the reduction in air pressure.

However, we intend for the Superb Stowable Solar Still to be used mainly near the surface, close to sea level, as ambient temperatures are higher and direct sunlight would not be inhibited by precipitation at higher altitudes.

The theoretical minimum time for 600 ml of water to be refined in our solar still is approximately 416 seconds, which is comparable to a conventional stove!

Under optimal conditions, the entire quantity of water can be boiled in less than 7 minutes. These conditions will most likely be observed in equatorial locations like Africa, rather than Canada. However, this is excellent for our cause, as this suggests that the solar still will function well in Africa.

Testing:

Our testing conditions for the solar still were sub-optimal. The solar still was placed indoors at an ambient temperature of 21.5° C (according to a thermostat), and 600 ml of cold tap water was loaded into the main chamber. The still was placed next to a window, receiving direct sunlight at an angle of approximately 30 degrees to the horizon.

After 2 hours of testing, approximately 5 ml of water was accrued. This pitiful result was due to the lack of adequate sunlight and highly sub-optimal conditions.

1xN-IFGCMl0IjotxASwHj3XbSo16uiIxU4ya51zQ.jpg18tqv3WHUY0OVweRZQ8AEdnlLweXHuTpPZkr2uJM.jpg

Vapour accumulation can be seen on the sides of the bottle, indicating a proof of concept.
Under more realistic usage scenarios, we believe that efficiencies will be close to the calculated theoretical values.

Conclusion:

We got a fairly good result in the fair from our efforts, but we were told one important thing: to continue on with the project. I envision this solar still being used for humanitarian aid in the future and maybe even as a store-bought product, once we refine the design. If any of you reading this are interested, please speak up and message me here. Otherwise, thanks for reading!

Stay tuned and stay sciency,

Mingde

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