"The focus on the hot topic of renewable energy . . . makes this a timely resource." —Booklist
Doable Renewables: 16 Alternative Energy Projects for Young Scientistsby Mike Rigsby
Humankind needs to find and develop alternative forms of energy. As the world’s population continues to grow, more people will need access to lighting, communication, transit, and computing. Fossil fuels are being used up at an alarming pace, but other energy sources--solar, wind, waves, “waste” heat, and even human power--are both renewable and
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Humankind needs to find and develop alternative forms of energy. As the world’s population continues to grow, more people will need access to lighting, communication, transit, and computing. Fossil fuels are being used up at an alarming pace, but other energy sources--solar, wind, waves, “waste” heat, and even human power--are both renewable and environmentally friendly. The projects in this book will help any budding scientist construct and explore working models that generate renewable, alternative energy.
In Doable Renewables, readers will learn how to build a Kelvin water drop generator out of six recycled cans and alligator clip jumpers, a solar-powered seesaw from a large dial thermometer and a magnifying glass, and a windmill from eight yardsticks, PVC pipe, cardboard, and converter generator. Children will investigate the energy-generating properties of a solar cell, a radiometer, a Nitinol heat engine, and a Peltier cell. They’ll even build a human-powered desk lamp.
Each project includes a materials and tools list, as well as online information on where to find specialized components. And for young scientists, author Mike Rigsby demonstrates how to use an infrared thermometer, a digital multimeter, and an electrical usage monitor to test their designs. Armed with this collection of technological possibilities, can the solution to the earth’s energy crisis be far off?
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16 Alternative Energy Projects for Young Scientists
By Mike Rigsby, Scott Rattray
Chicago Review Press IncorporatedCopyright © 2010 Mike Rigsby
All rights reserved.
SIMPLE HEAT ENGINE
In this chapter you learn to create a device that will turn heat into motion.
MATERIALS AND TOOLS
Corrugated cardboard, 1/8 inch thick
Sewing needle, 1 5/8 inches long 4 rubber bands, 7 inches long and 1/16 inch wide 60-watt incandescent desk lamp (or heat source) Aluminum foil (optional)
Cut one Rotor (1A), three Base pieces (1B), and four Sides (1C), two with holes and two without (refer to template). The cut pieces, along with the needle and rubber bands, should look like the photo here.
The needle should be 1 5/8 inches long. If your needle is a different length, adjust the width of the base. The base should be 1/4 inch shorter than the length of the needle. The rubber bands I used are 7 inches long (cut apart and measured without stretching) and 1/16 inch wide. You can experiment with this, but a band that is too strong or short may bend the needle. But if the band is too loose, it may not contract properly when heated.
Glue the three base pieces together in a stack.
The complete base assembly should appear as shown here.
Glue the side pieces together in two pairs. Each pair should have one piece with a hole and one piece without a hole. Flip one of the assemblies around so that one hole is on the left side while the other assembly has the hole on the right side.
The completed side assemblies should appear as shown here.
Glue one side assembly to the base assembly as shown. Note that the hole faces up, toward the base piece.
After the glue is dry from the previous step, glue the other side assembly to the base with the holes facing each other.
Now use the rubber bands to suspend the needle in the center of the rotor. One at a time, wrap the four rubber bands around the rotor and loop them over the needle as follows: place one end of a rubber band over an end of the needle, bring the rubber band around the rotor and loop the other end of the rubber band over the opposite end of the needle. Repeat this with the remaining three rubber bands, forming an X, as shown here.
Once the rubber bands are in place, the needle should be in the center of the rotor. Adjust the rubber bands to make them even by sliding them along the outside edge of the rotor. The tension on the rubber bands must be adjusted so that the needle is perpendicular to the rotor. Notice how the upper part of the needle is slanted (incorrectly) toward the left in this photo:
To correct this, pull the thumb (on the lower part of a rubber band) to the left while pushing the finger (on the upper portion of the rubber band) to the right. The goal is to get the needle — the axle on the motor — perpendicular to the rotor, as shown here.
Once the glue is dry on the base, gently pull the sides outward and slide the needle into the holes. The rotor should spin freely.
Place a heat source (a 60-watt desk lamp, for example) next to the rotor. Turn the lamp on and the wheel will rotate at a few revolutions per minute.
Do not use an open flame as your heat source. (Burning cardboard emits carbon dioxide — you don't want to spoil the atmosphere.) To keep the cardboard cool, particularly if you are going to run the Simple Heat Engine for a long time, you may want to attach aluminum foil to the outer side wall adjacent to the heat source.
How does this engine work? Most materials expand when heat is applied, but stretched rubber contracts (shrinks) as it warms.
With that in mind, consider the rotor at rest with no heat applied, as drawn below.
The rotor is balanced and is content to stay where it is. But when you add heat to the rubber band between A and O (which we'll call AO), rubber band AO shrinks.
When rubber band AO is contracted, the rotor is unbalanced, which causes the right side to start rotating downward. Because there is more cardboard on the right side of O than the left, the right side is heavier. It will settle as shown here.
Now rubber band AO is away from the heat source, and as it cools it will stretch back to its original position.
The rotor is now stable, but it has rotated ¼ turn clockwise. Rubber band DO is now in front of the heat source, and it will start to contract. This cycle will repeat, causing the rotor to continue its rotation.
This project works, but many questions are left unanswered. How long will the rubber bands last? How much stretch is optimum? What benefit can be obtained by adding more bands? How much heat can be added before problems occur? Where is the best place to add heat? Devise your own experiments to answer these questions.
More to Think About
Will more rubber bands make the wheel turn faster?
Will a larger wheel turn more smoothly?
What happens if you use a heat lamp rather than an incandescent bulb?
What happens if you use a fluorescent bulb instead of an incandescent bulb?CHAPTER 2
NITINOL SPRING WHEEL
In this chapter you learn how to build a durable heat engine using nitinol springs. Nitinol can be costly — check your budget before you commit to this project.
MATERIALS AND TOOLS
Steel rod, 1/8 inch diameter, 2½ inches long
Steel ring, 3½ inch diameter (craft store or old embroidery hoop)
4 nitinol springs (www.jameco.com, Part # 357835)
Magnet wire (#26), 10 inches long
Square aluminum tubing, ¼ inch square, 8 inches long
Wood base, 6 × 3½ inches, ½ inch thick Metal sheet, aluminum or stainless steel, 6 × 4 inches 2 wood screws Heat lamp
Nitinol is a metal alloy composed of nickel and titanium. You can stretch or bend a nitinol spring until it appears to be damaged beyond repair.
However, when you apply heat (120ºF or more), the spring returns to its original shape.
This Nitinol Spring Wheel will turn very slowly, about one revolution every two minutes. Yet because the springs can be stretched and compressed thousands of times, this machine is very reliable and could potentially operate for years without repair.
Start the construction by connecting the 2½ inch length of steel rod (? inch diameter), the axle for the engine, to the 3½ inch diameter ring with one of the springs. I used part of an old holiday decoration for the ring, though an embroidery hoop will work just as well. Slip one end of the spring over the rod and the other end over the ring.
Repeat using three other nitinol springs until you have a spring-loaded wheel with the springs located evenly around the ring.
Using magnet wire, secure the four spring ends to the steel rod. I anchored this point about ¾ inch away from one end of the steel rod.
Next, make two supports for the steel rod. Using ¼ inch square aluminum tubing, cut two pieces, each 4 inches long. At a distance of ½ inch from one end of each tube, drill a 9/64 inch hole through one side of the tube. Do not drill through both sides of the tube, since the back wall of the tube will hold the steel rod in alignment.
Use the Base template (2A) to cut a ½ inch thick wooden base, then drill two 5/16 inch holes as indicated. Insert one of the tubes into one of the holes, as shown. The hole in the aluminum tube should be at the top facing in toward the base.
Place the axle from the ring/spring assembly into the 9/64 inch hole in the aluminum tube. Fit the free end of the axle into the hole in the other piece of aluminum tubing as you push it into the other hole in the base.
Make a heat shield by fastening a stainless steel or aluminum sheet, 6 inches by 4 inches, onto the base using two wood screws, as shown.
Place a heat lamp near the engine.
Viewed from the side of the heat lamp, the spring on the left will get warm and contract, much as the rubber bands in the previous project did. The contracting spring will stretch the spring opposite it (on the right), causing the wheel to become unbalanced. The wheel will rotate clockwise, bringing a new stretched spring into the heat where the cycle will be repeated.
In chapters 10 and 11, you will find two other versions of nitinol heat engines.
More to Think About
Does the wheel move more smoothly with more springs?
Does a larger wheel (stretching the springs more) help or hurt the engine's movement?
Can you focus sunlight on a spring to make the wheel turn?
What is the lowest temperature needed to achieve movement?CHAPTER 3
SOLAR DRINKING BIRD
The Solar Drinking Bird toy is a type of heat engine.
MATERIALS AND TOOLS
Drinking Bird (novelty shop or http://scientificsonline.com, Part # 3053617)
Black enamel paint (such as Krylon SCB-028 Flat Black) and paintbrush
Corrugated cardboard, 1/8 inch thick
Colored paint or crayons (optional)
To make the Drinking Bird drink, you usually place a cup of water in front of it. When you place the bird's beak into the water, its fuzzy head gets wet. Water on the wet head evaporates (unless the humidity is very high) as it bobs back and forth, cooling the head. The head, being cooler than the body, causes the liquid inside — a special liquid that boils at a low temperature — to rise up the neck, higher into the bird. The rising liquid causes the bird to become top-heavy and tip forward. When it tips forward, the head falls back into the glass and gets more water, while the liquid inside is allowed to return to the body. The cycle then repeats.
This is not perpetual motion or magic. The transfer of heat from the bird's warmer body to its cooler head creates the movement.
To create a Solar Drinking Bird, you also need to make its body warmer than the head. If you paint its lower body black and expose it to the sun, it will get warmer faster than its head. And if you shade the head to keep it cool, you will create the temperature difference needed to cause the bird to bob.
To start, pull the feather off the bird's tail.
Next, paint the lower body of the bird black.
Cut a Shade (3A) out of cardboard.
Bend the shade on the dashed line, then cut out a 2 inch square cardboard Support (3B).
Glue the shade and the support together as shown.
After the glue is dry, place the shade assembly between the bird and the sun. The sun should shine on the bird's lower body, but not on its head. In a few moments, the Solar Drinking Bird should bob back and forth, and continue until the sun goes down.
You can paint and color the cardboard shade to make the project more attractive.
More to Think About
Will a different color paint work better on the bird's body?
Will a large hat on the bird work as well as the cardboard sun shade?
Does the bird dip faster if the sun is brighter?
Can you use a light to make the bird dip?CHAPTER 4
THE WAY THE WORLD WORKS
You can't get something for nothing. This is an important rule of physics, the main part of the Laws of Thermodynamics.
Yet it's tricky. Just because you "can't get something for nothing" doesn't mean you can't get something for free. On a chilly autumn day you can step into the sun and it will warm your body. You don't pay money for the sun, yet it will provide you with free energy.
To change heat into movement, as the Solar Drinking Bird or the Nitinol Spring Wheel do, there must be a temperature difference, a hot side and a cold side. If there is no temperature difference, there will be no movement.
Typically, when you take heat and change it into movement, most of the heat is wasted rather than being converted into motion. When an automobile burns gasoline, more than half of the energy is converted to heat. Only a small portion is actually used to make the car go. Unfortunately, the same is true of electric power plants. Usually more than half the energy goes toward creating heat, the rest being converted to electricity.
The amount of work you get out of a system compared to the amount of energy put in is called efficiency. The conversion of heat to motion is very poor, usually 15 to 30 percent, with 70 percent or more of the energy being thrown away as extra heat.
Why? There is another pesky "rule" from the Laws of Thermodynamics. Efficiency is related to the difference in temperature between the hot side and cold side of a heat engine. The hotter the hot side and the colder the cold side, the greater the efficiency. You can't get 100 percent efficiency because to do so a heat engine would have to lose all of it's heat. The temperature of the cold side would have to be about –460° Fahrenheit, the temperature at which there is no heat.
In 1824 Nicolas Carnot, a French physicist, described the Carnot cycle, which determines the maximum possible efficiency of a heat engine. Because real engines have friction and are made from imperfect, real materials, it is not possible to achieve Carnot efficiency. A precision Stirling heat engine (see Chapter 5: Stirling Engine) operating from the heat of your hand, is about one percent efficient — 99 percent of the heat is thrown away. The same engine with sun shining on its black surface (about 150°F) is about 10 percent efficient (90 percent of the heat is thrown away).
The good news is that anywhere you can find a temperature difference, you can harness it to do work. The bad news is that the efficiency will be poor if the temperature difference is small.
If you are curious as to exactly how the temperature differences between the hot and cold sides of a heat engine affect efficiency, a little math is needed. I will try to explain the Carnot efficiency formula as simply as possible.
To make the calculation, all temperatures need to be measured in degrees Kelvin. To change from degrees Fahrenheit (°F) to degrees Kelvin (°K), first convert degrees Fahrenheit to degrees Celsius (°C) using the following formula:
°C = (°F - 32) × 5/9
Then change from degrees Celsius (°C) to Kelvin using the following formula:
°K = °C + 273.15
Efficiency (E), as a percentage, is determined by the following formula where Thigh (in degrees Kelvin) is the hot side of your heat engine and Tlow is the cool side of the heat engine.
E = ((Thigh - Tlow)/Thigh) × 100
To get an idea of how efficient a Stirling engine would be in practice, plug in some numbers. What would a Stirling engine's maximum possible efficiency be when the temperature difference between the hot side and cold side is 7° Fahrenheit?
Assume the room temperature (on the cold side) is 72°F and the hot side (your hand temperature) is 79°F. First change 72°F into degrees Kelvin:
°C = (72 - 32) × 5/9
°C = 22.22
°K = °C + 273.15
°K = 22.22 + 273.15
°K = 295.37
Using the same method, change 79°F into degrees Kelvin:
°C = (79 - 32) × 5/9
°C = 26.11
°K = °C + 273.15
°K = 26.11 + 273.15
°K = 299.26
Now plug the high and low temperature values into the efficiency formula:
E = ((Thigh - Tlow)/Thigh) × 100
E = ((299.26 - 295.37)/299.26) × 100
E = 0.0129 × 100
E = 1.29
The maximum efficiency of this engine is almost 1.5 percent. Over 98 percent of the heat energy cannot be converted into mechanical motion.
This formula tells us that the hotter the hot side and the colder the cold side, the better the potential efficiency in converting heat into movement.
Excerpted from Doable Renewables by Mike Rigsby, Scott Rattray. Copyright © 2010 Mike Rigsby. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Meet the Author
Mike Rigsby is a professional electrical engineer and author of Amazing Rubber Band Cars and Haywired. He has written for Popular Science, Robotics Age, Modern Electronics, Circuit Cellar, Byte, and other magazines.
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