Making a Miniature Solar Water Distiller

Transcription

1 Making a Miniature Solar Water Distiller This science workshop calls for students to make a miniature solar water distiller, also known as a still, using easy-to-get supplies. When complete, the activity will teach them about the water cycle (evaporation and condensation processes), how distillation works and the ability of some materials to absorb water. It can be used to do a number of experiments, such as what happens if seawater, simple syrup or freshly cut grass is distilled. This activity connects sustainable development, science and technology. What is a solar water distiller? Solar water distillers use the sun s rays to extract the particles dissolved in a liquid. They can therefore desalinate seawater and remove heavy metals or microorganisms in a solution. Goals > Make a small device to produce clear water from recycled materials. > Use the distiller to perform different experiments to explore its possible uses. Examples include a mini seawater desalination station, recovering morning dew and purifying dirty water. Supplies for a Miniature Solar Water Distiller An empty metal can (like a tuna can) A plastic bottle cap Thick cellophane wrap A stone the size of an olive Two wide rubber bands Glue pads (Patafix) A liquid or a damp solid to distill, such as seawater, colored water, muddy water, damp moss, fresh peelings or cut grass. Acrylic paint or stickers, to decorate the can 1

2 Instructions 1 2 1) Decorate the outside of the can with acrylic paint or stickers. 2) Using a piece of glue pad, glue the cap to the inside of the container (in the middle) ) Prepare your choice of contaminated liquid (seawater, water + dye, muddy water) or solid to sweat (wet moss, apple peelings, etc.). 4) Pour the liquid into the can, being careful to keep its level below the cap. If you re using a damp solid, just place it in the can around the cap. 5 5) Cover the can with clear cellophane wrap, held in place with a rubber band. We recommend not to stretch the cellophane too tight, for the next step. 2

3 6 6) Attach the remaining rubber band to the one holding the cellophane wrap in place using a hitch knot. This creates a small loop and lets you attach it to the distiller so that you can move it around between two experiments. 7 7) Place the stone in the middle of the cellophane wrap, to create a downward slope in the direction of the cap ) Place the distiller in full sunlight, preferably on a warm surface (asphalt or bricks, for example). 9) Wait a few hours, then remove the rubber band and the cellophane wrap to observe the result. 3

4 Observe and Draw Conclusions > Photocopy an Observations sheet (page 6) for each student. Then ask them to draw two annotated diagrams for each experiment conducted: a first observation diagram at the start of the experiment and a second diagram when observation is complete. > Ask the students to look at their classmates drawings and share their experiments. Are some things the same and others different? Which experiments were successful? What conclusions can they draw from them? > To Build on the Lesson Understanding How the Miniature Solar Water Distiller Works A liquid was poured into the bottom of the can. When the sun s rays hit the distiller, the temperature rises in the can, creating a greenhouse effect. The air in the can heats up and fills with water: it gets more and more moist. This creates vapor that condenses on the underside of the cellophane wrap. The temperature difference between the air in the can and the outside air causes condensation, in other words, the vapor becomes liquid. The weight of the stone placed on the cellophane wrap creates a slope. So the condensation droplets start to run down the cellophane wrap, then fall into the cap placed under the stone. This is the distillate (distilled water). When all the water in the bottom of the can has evaporated, only the solid particles (salt crystals, bits of dirt, sugar, etc.) and the distillate remain. This process is called distillation. You can also use damp solids in place of the liquid. For example, freshly cut vegetation contains water. The plant matter will sweat, or secrete droplets of water that will run into the cap. This is called guttation. This distillation process is used on various scales in the world. There are solar wells, cans and pyramids that can produce several hundred liters of distilled water a day. These installations can produce clean water from dirty water, for example for bathing. Distilled water is used in chemistry, but also in irons and car batteries. Something to point out to students: The minerals stayed in the can. They didn t evaporate. Only the liquid dripped into the cap. 4

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6 My Miniature Solar Water Distiller Observation Sheet Experiment 1 Date Last name First name Class End of the experiment End of the experiment Start of the experiment Metal cans 1. Draw the experiment you re performing, in the metal cans sketched below. 2. Describe your diagram using notes. 6 Experiment 2 Date Start of the experiment