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Abstract Imagine a refrigerator with no moving parts that would fit in your pocket. Cool, huh? In this science fair project, you will explore just such an object—a thermoelectric device that uses voltage to create a temperature gradient, and that temperature gradient to create an electric voltage, which can be used to heat or cool an object.Objective In this science fair project, you will explore the thermoelectric effect. Investigate how temperature changes can be used to create an electric voltage, and how an applied voltage can be used to cool or heat an object. Introduction The thermoelectric effect is the direct conversion of temperature differences to electric voltage, and vice versa. The basic concept behind thermoelectric technology is the Peltier effect—a phenomenon first discovered in the early nineteenth century. The Peltier effect occurs whenever electrical current flows through two dissimilar conductors; depending on the direction of current flow, the junction of the two conductors will either absorb or release heat. The Peltier effect is used to rapidly cool and heat a block of metal in polymerase chain reaction machines, to cool central processing units in computers, and in many other applications.
Most modern Peltier coolers use solid-state components consisting of n-type semiconductors and p-type semiconductors. Figure 2 shows how a Peltier device can be used as a cooler when a voltage is applied (panel A) and as a voltage source when a temperature gradient is applied (panel B). The websites listed in the Bibliography have good detailed explanations of the thermoelectric effect and its use in consumer products.
In this science fair project, you will explore how a voltage can be used to cool or heat an object, using a thermoelectric cooler. Also called Peltier coolers, these devices can serve as solid-state heaters or coolers, depending on the direction of the applied voltage. Since heaters can be made using simpler technologies, Peltier devices are most often used as coolers rather than as heaters in consumer products. Their applications are best for small cooling needs. Because of their low efficiency, they cannot replace the standard kitchen refrigerator. Thermoelectric coolers are available at many retail stores. They are designed for high portability and plug into the 12-V DC power socket found in most automobiles. They have different designs, depending on the manufacturer, but share certain features: 1) a thin plate that contains the electronic components; when a voltage is applied, one side gets hot and the other side gets cold; 2) metal heat sinks that transfer heat or cold away from the Peltier cooler; 3) a fan to carry away heat from the heat sink; and 4) a power cord to connect the unit to the 12-V power source. You will be able to perform this experiment without removing the Peltier device from the cooler if you use the cooler listed in the Materials and Equipment section. By removing a single plastic plate, you will have access to both surfaces of the Peltier cooler. You will determine how the temperatures of the hot and cold surfaces vary with time, using an infrared thermometer. You will also measure the voltage created by a temperature gradient across the device. To measure the voltage, you will simply attach the leads from a digital multimeter to the positive and negative terminals on the plug. Terms, Concepts, and Questions to Start Background Research
Questions
Bibliography
Materials and Equipment This science fair project is based on use of a thermoelectric device with a power source. The easiest way to work with such a device is to purchase a thermoelectric cooler that has easy access to both the hot and cold surfaces, such as the Black and Decker cooler listed below. Other coolers are available, but tend to be more expensive.
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Section 1: Testing the Thermoelectric CoolerHow cold and hot can the device get? In this first section, you will test the thermoelectric cooler and get some practice using the infrared (IR) thermometer. The goal here is to determine the device's range of temperatures, and the rate at which the electrical power supplied by the 12-V battery is converted into a temperature change. In this section, you will measure the temperature of the metal plate in the food storage area. Later, you will remove an access panel so that you can measure the temperature on the other side of the Peltier device.
Section 2: Measuring the Temperature Gradient and the VoltageWhat is the actual temperature difference between the hot and cold sides of the Peltier device, and how does the size of this temperature difference relate to the magnitude of the voltage created by the Peltier device? In this section, you will compare the temperature of the two sides of the thermoelectric cooler, and graph the temperature difference vs. the voltage. In the previous section, the applied voltage created a temperature gradient. In this section, you reverse the process and measure the voltage produced by the temperature gradient across the Peltier device. When you unplug the thermoelectric cooler from the power source, the two leads on the plug are attached to the two sides of the Peltier device (the thermoelectric cooler). The difference in temperature between the two sides creates a voltage difference, which you can measure by attaching the leads of the multimeter to the two leads on the plug. One lead on the plug is the circular knob on the tip of the plug. When it is time to measure the voltage, attach the red lead from the multimeter to this knob. The other lead on the plug is connected to the metal strips on the sides of the plug. Attach the black lead from the multimeter to either of these. If you'd like more information about how to measure voltage, visit the Science Buddies page Using a Multimeter.
Section 3: Generating Voltage with IceCan you generate a voltage by creating a temperature gradient using ice? Think about it: is it really possible to generate useful energy in the form of a voltage difference just by adding ice? In this section, you will measure the voltage at the plug and you will not plug the unit into the 12-V socket.
Variations
Credits David B. Whyte, PhD, Science Buddies
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If you like this project, you might enjoy exploring related careers.
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Physicist Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy. |
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Electrical & Electronics Engineer Just as a potter forms clay, or a steel worker molds molten steel, electrical and electronics engineers gather and shape electricity and use it to make products that transmit power or transmit information. Electrical and electronics engineers may specialize in one of the millions of products that make or use electricity, like cell phones, electric motors, microwaves, medical instruments, airline navigation system, or handheld games. | |
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Semiconductor Processor What do traffic lights, lasers, and microchips have in common? They are made from special materials called semiconductors. Semiconductors have helped revolutionize technology. If you enjoy hands-on work and are interested in participating in cutting-edge semiconductor technology, then a career as a semiconductor processor maybe of interest to you! | |||
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