Chapter Ii: Review of Related Literature

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Chapter 2
Review of Related Literatures and Studies
This chapter mainly focuses on the related concepts, principles and studies about the operation of converting waste thermal energy into a usable electric signal. Information was cited in various sources and references including books, newspapers, magazines, journals and internet. Foreign Literature

The basis of the studies about thermocouples was first established by Thomas Johann Seebeck in 1821 when he discovered that a conductor generates a voltage when subjected to a temperature gradient (Cavicchi, Thomas, 1993). A circuit made from two dissimilar metals with junctions exposed at different temperature was able to deflect a compass magnet. Due to that phenomenon, he first concluded that the outcome was due to magnetism induced by the temperature difference. However, after further studies, it has been proven that it was the current which made the compass be deflected with respect to the change in temperature (Cook, N.1997) According to Robert G Seippel in his book Fundamentals of Electricity (1974), this phenomenon was in line with the Law of Conservation of Mass created by a French chemist Antoine Laurent Lavoiser. According to him, “Energy cannot be created nor destroyed; it can only be transferred from one form to another”. In relation with this, waste heat can also be converted to a usable microvoltage output through the principle of thermocoupling. To measure this voltage, one must use a second conductor material which generates a different voltage under the same temperature level. Otherwise, if the same material was used for the measurement, the voltage generated by the two materials can then be measured and related to the corresponding temperature gradient. It is thus clear that, based on Seebeck's principle; thermocouples can only measure temperature differences and need a known reference temperature to yield the absolute readings. (Cook, 1997) Grolier Encyclopedia of Knowledge (1995) explained the three major effects involved in a thermocouple circuit namely Seebeck, Peltier and Thomson Effect. If a homogenous material having charges has temperature T1 at one end and T2 at the other end while it is in an open circuit, then a difference in electric voltage will occur between the two ends. This voltage is directly proportional to the temperature difference (T1 – T2). If the material is homogenous, the voltage will depend only on T1 and T2 and will be independent on the detailed temperature conditions between the two ends. This existence of a voltage difference was called Seebeck Effect and was first reported to the Prussian Academy of Sciences by Thomas Seebeck in 1822.

Unlike the Seebeck effect, which occurs in a single material in the presence of a temperature difference without an electric current, the Peltier effect only occurs at the junction of two dissimilar materials when electric current flows. Heat, called the Peltier heat, is either emitted or absorbed at the junction, depending on the direction of current flow. This effect was discovered by the French Physicist Jean C. A. Peltier in 1834. Meanwhile, in 1854, William Thomson used thermodynamic arguments to relate the Peltier and Seebeck effects. In the process he predicted a third effect – namely, that an electric current flowing through a homogenous material that also has a temperature difference will cause the emission or absorption of heat in the body of the material. The direction of the electric current relative to the sense of the temperature difference (that is, flowing toward a higher or lower temperature) determines whether heat is emitted or absorbed. This effect was subsequently discovered and called the Thomson effect. ThomasNet.com published last February 8, 2012 that because different combinations of metals will produce different temperatures, and these different metals have different durability and strength levels, researchers have produced standardized combinations to...
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