What is Thermoelectricity?
We know that electricity can be generated employing various methods. Electricity can be generated from wind, with the help of windmills, from water at hydroelectric power plants. Similarly, electricity can be generated from heat energy as well. So thermoelectricity as the name itself suggests is the electric current generated from heat energy. The conversion of heat energy into electrical energy with the help of a thermocouple generates thermoelectricity.
The thermocouple combines two dissimilar metals (conductors) to develop a potential difference at the junction of the conductors. At the junction of two dissimilar metals (i.e., at the junction of a thermocouple) or within a single conductor, when the temperature difference exists an emf will be generated, resulting in the flow of electricity in a given circuit. The emf so generated is called thermo emf and the electricity is known as thermoelectricity or thermoelectric current. This effect is known as the thermoelectric effect.
Peltier Effect
The ability to cool air or exchange heat is important in many situations. From computer chips that require to stay from overheating to spacecraft that require to face up to temperature extremes the planning of cooling systems may be a business.
The Peltier effect is one of the most interesting phenomena. A potential difference applied across a thermocouple generates a temperature difference between the junctions of the various materials within the thermocouple. This in turn results in the generation of thermoelectricity. Peltier module consists of two dissimilar materials fused together and maintained at room temperature.
The Peltier effect is the opposite of the Seebeck effect (it is named after the scientist who discovered it in 1821). Seebeck Effect suggests that, if two dissimilar metals (conductors) are connected in two separate places, and the intersections are kept at two different temperatures (usually one at zero and another at room temperature), then a potential difference (emf) between the junctions (the intersections) will be generated. This generation of emf when a thermocouple maintained at two different temperatures is known as the Seebeck effect.
Later, in the year 1834, Jean Peltier found that even the opposite (reverse) of the Seebeck effect is also true, which says that, a potential difference (or emf) and thus a current can also result in a temperature difference, regardless of what the desired amount of temperature is. The Peltier module is also the same as the Seebeck construction or the Seebeck module, and the only difference is the result. Hence it was concluded and was in good agreement with the result is that the Peltier effect is the opposite of the Seebeck effect.
The Peltier effect is the reverse phenomenon of the Seebeck effect. The electric current flowing through the junction of two conductors will emit or absorb heat per unit time at the junction to balance the temperature difference in the chemical potential of the two conductors.
One of the important applications of the Peltier effect is an electronic refrigerator that can be constructed with the help of a Peltier module known as the Peltier cooler. The Peltier cooler has been applied to many types of electrical equipment such as infrared detectors, CPU coolers, wine cellars, etc. because the cooling power of the Peltier cooler is lower than that of compressor-based refrigerators.
Peltier Cooler
Theory
Peltier found there was an opposite phenomenon to the Seebeck Effect, whereby thermal energy might be absorbed in one dissimilar metal junction and discharged at the opposite junction when an electric current flows within the closed circuit.
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In the above figure, the circuit is modified to obtain a different configuration that illustrates the Peltier Effect. If a voltage (V) is applied to terminals T\[_{1}\] and T\[_{2}\], an electrical current (I) will flow in the given circuit. As a result of the flow of electric charges or the electric current, a slight cooling effect (Q\[_{cool}\]) will occur at thermocouple junction A (where heat is being absorbed), and a heating effect (Q\[_{heating}\]) will occur at junction B (where heat is dissipated). We have to note that this effect may be reversed whereby a change in the direction of the flow of electric current will reverse the direction of heat flow.
Joule heating, having a magnitude of I\[^{2}\]R (where R is the electrical resistance used), also occurs in the conductors as a result of the flow of electric current. This Joule heating effect acts in opposition or contradiction to the Peltier Effect and hence it results in a net reduction of the available cooling. The Peltier effect can be expressed mathematically as:
⇒ Q\[_{cool}\] = β x I
⇒ Q\[_{cool}\] = αT x I
Where,
β - The differential coefficient between the two materials
I - The electric current flowing in the given circuit
Working of Peltier Cooler
In the world of thermoelectric technology and thermoelectric generation, semiconductors (usually the materials such as Bismuth Telluride) are the material of choice for producing the Peltier effect because they are efficient enough and can be more easily optimized for pumping heat. Using this type of semiconducting material, a Peltier module (i.e., thermo electric module) can be constructed in its simplest form around a single semiconductor pellet which is soldered to the electrically conductive material on each end (usually plated copper). In this configuration, the second dissimilar material required for the Peltier effect is really the copper connection paths to the facility supply.
It is important to note that heat will be transformed in the direction of charge carrier motion throughout the given circuit (in fact, it is the charge carriers that transfer the heat). While performing thermoelectric experiments, Peltier found there was an opposite phenomenon to the Seebeck Effect, in which thermal energy can also get absorbed in one dissimilar metal junction and dissipated at the other junction when an electric current flowed within the closed circuit.
By arranging n-type and p-type pellets in the form of a single pair or a couple (as demonstrated in the given figure below) and forming a junction between them with the help of plated copper tab, it is possible to construct a series circuit that can keep all of the heat moving in the same direction. As represented in the given illustration, the free or in other words bottom end of the p-type pellet connected to the positive terminal of the source, and the free (bottom) end of the n-type pellet similarly connected to the negative terminal of the source.
At the same time, we know that for n-type of semiconductor, heat is absorbed from the junction near to the negative terminal of the source and heat is released at the junction near the positive terminal of the source. For the p-type semiconductor, heat is absorbed from the junction near to positive terminal of the source and released at the junction near the negative terminal of the source.
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By arranging the given circuit as shown in the above figure, it is possible to expel heat to one part and absorb it from another end. Using these salient features and special properties of the TE couple, it is possible to team many such pellets all together in rectangular arrays to create practical thermoelectric modules and many thermoelectric devices.
Did You Know?
All the Peltier modules and the Peltier thermoelectric coolers are very useful cooling devices, but they are far from perfect. One of the biggest issue or drawback with a Peltier module is its inefficiency. A Peltier cooler is found to be comparatively less efficient than a conventional coolant-based device. Even though they can be used to create minute air conditioning units it would be impractical to use them to cool down an entire building.
Another drawback of the Peltier cooler is its lifespan. The Peltier module or the Peltier cooler will not last forever, all thermoelectric coolers or just thermo cooler will experience declined efficiency as they age. technically, even some conventional air conditioning systems also suffer the same drawback.
FAQs on Thermoelectricity
1. What exactly is thermoelectricity?
Thermoelectricity is a fascinating area of physics that describes how a temperature difference can be directly converted into electric voltage, and also how an electric voltage can be used to create a temperature difference. It's based on three main principles: the Seebeck effect, the Peltier effect, and the Thomson effect.
2. How does the thermoelectric effect actually work to create electricity?
It works because of the Seebeck effect. When you join two different conductive materials (like two types of metal) to form a loop with two junctions, and you keep one junction hot and the other cold, the heat energy causes charge carriers (electrons) to move from the hot junction to the cold one. This movement of charges creates a small but measurable voltage in the circuit.
3. What is the Peltier effect and how is it used in cooling?
The Peltier effect is essentially the reverse of the Seebeck effect. When you pass an electric current through a junction of two different materials, heat is either absorbed or released at that junction. By controlling the direction of the current, you can make one junction get cold while the other gets hot. This is the principle behind thermoelectric coolers, which are used in devices like portable car fridges and for cooling electronic components.
4. What is the main difference between the Seebeck and Peltier effects?
The main difference lies in the cause and the result. In the Seebeck effect, a difference in temperature is the cause, and it produces an electric voltage. In the Peltier effect, an electric current is the cause, and it produces a temperature difference (heating or cooling). They are two sides of the same fundamental thermoelectric phenomenon.
5. What are some real-world examples of thermoelectricity in action?
Thermoelectricity has several practical applications in both power generation and temperature control. Some common examples include:
- Thermocouples: These are simple, robust sensors used to measure temperature in everything from industrial ovens to car engines. They work using the Seebeck effect.
- Thermoelectric Generators (TEGs): These devices convert waste heat directly into useful electricity. They have been used to power space probes like Voyager and are being developed for capturing heat from car exhausts.
- Peltier Coolers: These solid-state devices use the Peltier effect for cooling and are found in portable mini-fridges, car seat coolers, and for precise temperature control of sensitive electronics.
6. Is the Thomson effect related to the Seebeck and Peltier effects?
Yes, the Thomson effect is the third key thermoelectric effect. It describes the absorption or release of heat within a single current-carrying conductor that has a temperature difference along its length. While the Seebeck and Peltier effects happen at the junction between two different materials, the Thomson effect happens within a single material.
7. Why are semiconductors better than metals for thermoelectric devices?
Semiconductors are much more efficient for thermoelectric applications. This is because they can be designed to have a high Seebeck coefficient (producing more voltage for a given temperature difference) while also having low thermal conductivity (they are good insulators of heat). This combination allows a device to maintain a large temperature difference and convert energy more effectively than typical metals.
8. Is the cooling from the Peltier effect the same as how a regular refrigerator works?
No, they work on completely different principles. A regular refrigerator uses a compressor and a refrigerant gas that goes through a cycle of compression and expansion to move heat out. A Peltier cooler, on the other hand, is a solid-state device with no moving parts or gases. It uses an electric current to directly create a temperature difference at a junction of two materials.
