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Unformatted text preview: INSTITUTE OF PHYSICS PUBLISHING EUROPEAN JOURNAL OF PHYSICS Eur. J. Phys. 26 (2005) 959–967 doi:10.1088/0143-0807/26/6/003 Simple experiments with a thermoelectric module Yaakov Kraftmakher Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel E-mail: [email protected] Received 8 March 2005, in final form 24 May 2005 Published 8 August 2005 Online at stacks.iop.org/EJP/26/959 Abstract The Seebeck and Peltier effects are explored with a commercially available thermoelectric module and a data-acquisition system. Five topics are presented: (i) thermoelectric heating and cooling, (ii) the Seebeck coefficient, (iii) efficiency of a thermoelectric generator, (iv) the maximum temperature difference provided by a thermoelectric cooler and (v) the Peltier coefficient and the coefficient of performance. Using a data-acquisition system, the measurements are carried out in a reasonably short time. It is shown how to deduce quantities important for the theory and applications of thermoelectric devices. (Some figures in this article are in colour only in the electronic version) 1. Introduction The Seebeck effect consists in the generation of an emf between two junctions of dissimilar metals or alloys when they are kept at different temperatures. For any thermocouple and a given mean temperature, the emf is proportional to the temperature difference between the junctions, 1 T : E = S1T , (1) where the coefficient of proportionality S is called the thermoelectric power, or the Seebeck coefficient. For metals and alloys used for thermocouples, the thermoelectric power is usually in the range 10–60 µ V K − 1 . For semiconductor compounds, this figure may be several times larger. The Seebeck effect is widely used for temperature measurements and for producing electric energy when other sources are inaccessible. A thermopile serves in such cases to increase the generated voltage. The Peltier effect is inverse to the Seebeck effect: when a dc current passes through a junction of two dissimilar materials, a heat additional to that produced by the Joule heating is generated or absorbed in the junction, depending on the direction of the current. The power 0143-0807/05/060959+09$30.00 c ° 2005 IOP Publishing Ltd Printed in the UK 959 960 Y Kraftmakher of the additional heat is proportional to the current: Q = 5 I , where 5 is called the Peltier coefficient. The effect is used for cooling elements of electronics, such as lasers and infrared detectors. Using thermodynamic arguments, Kelvin has deduced a simple equation that relates the Seebeck and Peltier coefficients to one another: 5 = ST , (2) where T is the absolute temperature. Thermoelectric phenomena constitute a part of theoretical and laboratory university courses, and several papers in this field have been published. Gross [ 1 ] considered the efficiency of thermoelectric devices and its dependence on the characteristics of the available thermoelectric materials. Mortlock [ 2 ] described an experiment in which the coefficient of...
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