Introduction: (Initial Observation)
In winter we use electric heater to create heat. Electric heater converts electric energy to heat energy. Converting energy from one form to the other can help us to have the right type of energy for our needs. For example in a cold winter, we do not need high winds!, so we can use wind turbines to convert wind energy to mechanical energy and then use the mechanical energy to run an electric generator and make electrical energy. Finally we can use electrical energy to create light or heat as we need. Converting electrical energy to heat is a very simple procedure. Almost any piece of wire can act as a heat element if we have the right amount of electricity.
A simple experiment for that is connecting the poles of a D cell battery to each other with a very thin wire. Wire will get very hot and may even burn.
The reverse of this process also can be very useful. Heat from the sun, heat from active volcanoes and many other sources of heat are easily available. Converting such heat to the electrical energy can be a good step toward energy conservation.
Adult supervision and help is required in this project.
Industrial conversion of heat to energy is usually a multi-step process. First heat is used to create steam. Steam spins turbines that in turn run an electric generator.
Heat can also be converted to electricity directly.
Direct conversion of heat into electric energy, or vice versa is called thermoelectric. This term is generally restricted to the irreversible conversion of electricity into heat described by the English physicist James P. Joule. According to Joule’s law, a conductor carrying a current generates heat at a rate proportional to the product of the resistance (R) of the conductor and the square of the current (I). The German physicist Thomas J. Seebeck discovered in the 1820s that if a closed loop is formed by joining the ends of two strips of dissimilar metals and the two junctions of the metals are at different temperatures, an electromotive force, or voltage, arises that is proportional to the temperature difference between the junctions. A circuit of this type is called a thermocouple; a number of thermocouples connected in series is called a thermopile. In 1834 the French physicist Jean C. A. Peltier discovered an effect inverse to the Seebeck effect: If a current passes through a thermocouple, the temperature of one junction increases and the temperature of the other decreases, so that heat is transferred from one junction to the other. The rate of heat transfer is proportional to the current and the direction of transfer is reversed if the current is reversed. http://www.encyclopedia.com/searchpool.asp?target=@DOCTITLE%20thermoelectricity
Heat can be converted to electricity using a thermocouple. This is a device that consists of two unlike metal pairs at different temperatures. This produces electricity due to the Seebeck effect. Just as in a battery, when two unlike metals are in contact, their outer electrons are at two different energy levels. This energy difference depends on the temperature at which these two metals reside. The thermocouple uses a second pair of the exact two metals at a different temperature to create a potential difference between the two. Interestingly enough, thermocouples are used on the Voyager spacecraft to supply power. As a hot source, they use the heat from the decay of radioactive elements (They are too far away from the sun to use it.).
Can heat produce electricity? The purpose of this project is to research and discover the possibility of mass producing electricity, directly from heat.
Also determine how does the temperature affect the produced voltage in a specific thermocouple made of two different metals. Draw a graph to show the changes of voltage for different temperatures.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable (also known as manipulated variable) is the heating temperature.
Dependent variable (also known as responding variable) is the voltage.
Controlled variables are the type of metals used in thermocouple and their contact area.
Based on the collected information I think we are able to produce electricity by making a thermocouple using a strip of iron and a strip of copper. We should also be able to make a series of such connections to create more electricity.
Following is a sample hypothesis.
I hypothesize that as we increase the temperature, the voltage will increase.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Introduction: In this experiment you will test combination of different metals in order to determine which pairs are the best for making thermocouples. (You will identify the pairs that produce the most voltage, because they are the pairs that are more suitable.)
Material: You will need the following materials for this experiment:
- Different strips or wires of iron, copper, aluminum , and possibly other metals
- A sensitive voltmeter that can show millivolts
- Wire leads (Contact Wires with alligator clips on both ends)
- An ice bath (A cup of ice-water)
- Plastic bag (used to cover the cold joint)
- Heat source (flame, hot plate, etc.) to heat up the hot joint
1. Cut wires to about 20 cm long each.
2. Join one copper wire to one iron wire to build a pair. You can do this by twisting one end of copper wire to one end of iron wire. Call it Hot Joint.
3. Repeat the above procedures to build a second pair. Call it cold joint.
4. Attach two of the same type metals from each pair together. (For example you may connect copper to copper. You may do this by connecting the ends or using a connection wire. Or you could initially use a longer copper wire as shown in the diagram bellow)
5. Attach the other two same type metals to the voltmeter. (So you may connect the ends of iron wires to the voltmeter. Connect one iron wire to the positive or red probe of the voltmeter and connect the other iron wire to the negative or black probe of the voltmeter.)
6. Make sure your voltmeter is set to the lowest range so that it can read millivolts.
7. Cover the pair (named cold joint) by a plastic bag and insert it into the ice bath.
8. Heat up the other pair (Hot Joint) using any strong heat source.
9. Read the voltmeter and record the reading in the chart below.
Note: Although Iron and copper are two easily accessible metals, thermocouples made from combination of other metals may be able to produce more electricity.
When using copper and Iron as shown in this diagram, the iron wire from the hot joint connects to positive probe of the voltmeter. Otherwise the indicator needle may move backward.
Repeat the above procedures for all possible pairs. Which pair gave the highest voltage?
|Metal Combination||Produced Voltage|
|Iron – Copper|
|Iron – Aluminum|
|Copper – Aluminum|
|Titanium – copper|
Evaluation: This experiment only worked due to the sensitivity of the voltmeters used. The effect would not have shown up too well on the standard voltmeters found in middle grade and high schools
In this photo we are using one copper strip in the middle and two aluminum strips attached to two ends of the copper strip. So from left to right we have one aluminum-copper joint and one copper-aluminum joint. We connected the probes of a precision multi-meter to open ends of aluminum strips and set the meter to DC voltage. It initially showed zero, but after we started to heat up one joint (copper-aluminum), it started to show 1 millivolt, then two and finally 3 millivolts.
Procedure: In this experiment we connect a series of thermocouples that we made in experiment one to see if the produced voltage will be more. To do this we can use strips or wires of two different metals (such as Iron and copper) about one foot long and connect them to build a thermopile.
One side of thermopile will be in cold place and the other side will be in heat. Measure the amount of electricity and record it in the following table. Repeat the experiment with different number of thermocouples in your thermopile.
Procedure: Join one copper strip to one iron strip to build a pair like experiment number 1. You can do this by twisting one end of copper strip to one end of iron strip. Repeat the above procedures to build a second pair. Attach two of the same type metals from each pair together. Attach the other two same type metals to the voltmeter. Place one pair into the ice bath while placing the other into the oil bath. Place a thermometer in the oil bath and use a hotplate to heat up the oil slowly. (Hot oil is very dangerous and flammable. Goggles and protective clothing are required)
Read the voltmeter and thermometer and record your readings in the chart below.
|Oil temperature||Produced Voltage (millivolts)|
1. The temperatures in the above table are examples. You do not need to record the temperature and voltage in certain intervals.
2. You may use your results table to draw a graph.
3. A sensitive digital volt meter (able to show millivolts) is required.
4. Thermometer can be a cooking thermometer or any other thermometer that shows a wide range of temperatures.
Materials and Equipment:
List of materials can be extracted from the experiment section. For oil, you may use mineral oil or corn oil. For this project you will need a voltmeter that can measure millivolts.
When using a desktop multimeter model 360 set the knob at 0.1 DCV.
DC = Direct Current
V = Volt
Ready made thermocouples are a good alternative to the metal strips or wires you may find locally.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
No calculation is required for this project.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Although producing electricity from heat is possible, it is not very efficient. However this technology can have many other applications such as thermometers that can measure high temperatures in furnaces and heaters.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Search the Internet for the term “Thermocouple” to see samples and applications of producing electricity using heat.
Visit your local library and search physics books for thermocouple and its scientific fundamentals.