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Experimental Study of Thermoelectric Generators
Ubaidillah a , Suyitno b, Imam Ali c, Eko Prasetya Budiana d and Wibawa Endra Juwana e
1Mechanical Engineering Department, Faculty of Engineering, Universitas Sebelas Maret,
Jalan Ir. Sutami 36A, Kentingan, Surakarta 57126, Central Java, [email protected], [email protected], [email protected],
[email protected], [email protected]
Keywords : thermoelectric generator; measurement; characterization
Abstract. Thermoelectric generator is solid-state device which convert temperature difference, ∆T
into electrical energy based on Seebeck effect phenomenon. The device has been widely used inself-powered system applications. This paper focuses on presentation of methodology forcharacterizing thermoelectric generators. The measurement of its behavior is performed by varyingload resistances. A standard module of thermoelectric generator (TEC1-12710) is used inexamination and an instrument setup consists of controllable heat source, controllable cooler,
personal computer, data logger MCC DAQ USB-1208LS equipped with two sets of K-typethermocouples. The experiment is performed by measuring output voltage and output current in 4values of temperature gradient by applying 10 values of resistive loads connected to thethermoelectric output wires. The common parameters studied in this research are output voltage,current and power. Generally, the relationship between parameters agrees with the basic theory andthe procedure can be adopted for characterizing other type of thermoelectric generator.
Introduction
Nowadays, renewable energy issues have been becoming one of promising research topicsamong researchers since the increase in fossil fuel dependence has much environmental drawbacksand limited sources [1]. Environmental destruction especially greenhouse effect strengthenarguments to leave such fuel [2]. These facts increase the concern in developing potential renewable
power resource and optimizing the existing devices by considering natural sources of each country[2,3]. Renewable energy sources have currently been employing such as solar, wind, ocean, hydro,geothermal, sound, vibration and natural heat. Thermoelectric as shown in Fig. 1 is alternative wayof renewable energy source to optimal heat waste.
Fig. 1: Structure of a thermoelectric [4]
Thermoelectric has two fundamental phenomena namely Seebeck effect and Peltier effect. Anamount of electric current supplied to the thermoelectric will make the device becomes heat pump.This phenomenon is called by Peltier effect. Thermoelectric usually applied for environmental
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friendly cooler [5] such as water dispenser, serum box and mobile refrigerator. Seebeck effectoccurs when thermoelectric converts thermal difference between two surfaces into electricitywithout either any movable parts or fluids [6,7], maintenance free and silent operation. This type ofenergy converter is suitable for standalone wireless devices, which is able for running at long periodof operation time without battery replacement [1].
Several previous researches on thermoelectric generator have been performed and reported.Maneewan et al. [8] has proposed thermoelectric power generator by taking benefits from solarheat. The prototype was applied for roof design and has successfully produces 1 W for 800 W/m 2 ofsolar intensity simulator. The work was then pursued in 2005 [9] by applying the Thermoelectric –Roof Solar Colector (TE-RSC) on a house roof. The TE-RSC could generate about 9 W under972 W/m 2 global solar radiation and 35 oC ambient temperature. Thermoelectric generator calledautomobile exhaust thermoelectric generator (AETG) has also been applied for truck exhaust byThacher et al. [10]. The AETG employing 16 pieces of HZ-20 was designed to produce 300 Welectric power. Lertsatitthanakorn et al. [11] reported performance and economic analysis ofthermoelectric generator in a solar water heater. At atemperature difference of 27.1 oC, thethermoelectric generator could achieve a power output of 3.6 W and the efficiency of electrical-
power generation is about 0.87 percents. Thermoelectric generator based liquid heat exchanger hasalso applied by [12] for industrial heat waste recovery.
The thermoelectric power conversion effect was firstly discovered by Seebeckin 1822 [13].Seebeck found an electric flowwhen one junction of two dissimilar metals bounded at two places,was heated while theother junction was kept at a lower temperature [14]. An artistic illustration ofthermoelectricpower module shown in Fig. 1 shows an interconnected n-type and p-type heavilydoped semiconductor thermoelementsin series by highly-conducting metal strips.If two junctions ofsemiconductor pair is subjected to different temperature, an electron will be appeared at the hot sideand absorb heat in the process. The pairs recombine and reject heat at the cold side. This will resultvoltage potential which drives the electron flows [1,2]. In this work, TEC1-12710 was used asmeasurement object. Both n and p types of semiconductor are made of bismuth tin (BiSn) while theceramic covers are made of alumina (Al 2O3).
The performance of thermoelectric device can be determined by figure-of-merit of the materialsused [1]. The figure-of-merit is dimensionless parameter, ZT, which is expressed by Eq. 1 below:
= (1)
where α is Seebeck coefficient in VK -1, T is temperature in K, ρ is electrical resistivity in Ωm and is thermal conductivity in Wm -1K -1. Other parameter represents performance of thermoelectricknown as power factor. The power factor can be written in Eq. 2 [1]:
= (2)
This research focuses on the methodology for measuring thermoelectric converter performances.The paper reports examination results of commercial thermoelectric module TEC1-12710 havingeffective surface area of 40 mm by 40 mm which can work until peak temperature of 470 K.
Measurement Setup
Schematic diagram shown in Fig. 2 is complete configuration in thermoelectric performancemeasurement.A piece of thermoelectric is placed coincide two aluminum fins. One side facescontrollable heat source and the other side touching controllable cooling unit. A thermal paste isused to increase the thermal contact surfaces between thermoelectric and aluminum plate. This
arrangement will make the heat flow with lower thermal resistivity.Two thermocouples K-type are mounted in each side to measure hot side and cold side
temperatures. The thermometer connected to the data acquisition via bridge amplifier to ensure the precise measurement of temperature. Measurement computing MCC DAQ USB-1208LS is used as
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data logger in which this data logger is low-cost with reasonable technical specification for theapplication proposed in this paper. The data are stored and displayed in personal computer viaTracerDAQ software. The USB interface is preferable since its fast data transfer with resolution of12 bits and sampling rate of 1.2 kS/s. The thermoelectric generator is loaded by variable resistor orrheostat having maximum resistance of 100 ohm. The measurement of output voltage and current
uses 4 digits digital multimeter in parallel and series, respectively.The procedures applied for thermoelectric generator characterization are described as follows:
the hot side and cold side temperatures are set to be constant heat flow for several resistive loadsconnected to the thermoelectric generator output. These are performed by controlling heat sourceand cooling radiator pump using dependent analog control. Both cooler and heater have ability inmaintaining operation in certain set point. Having temperature gradient adjustment, the rheostatwhich has been set in certain load resistant before is the connected to the thermoelectric output.This step will change the value of current and the temperature gradient has to be adjusted to reachthe previous value. The temperature gradients of 7 oC, 27 oC, 42 oC, 61 oC were selected in thisexperiment. The set temperature gradients are not fixed values and they depend on both heater andcooler abilities. When taking voltage and current data of each temperature gradient, several loadresistances of 10 ohm, 20 ohm, 30 ohm, 40 ohm, 50 ohm, 60, ohm 70 ohm, 80 ohm, 90 ohm, 100ohm were set in the rheostat. So that, each certain value of temperature gradient obtained 10 sets ofoutput voltage V out and output current I out . From the data, several relationships could be figured outand analyzed.
Fig. 2: Experimental configuration
Result and Discussion
Characterization results of the bismuth telluride based single module thermoelectric generatorare displayed in Fig. 3 and 4. As expected, output voltage data displayed in Fig. 3(a) increases alongwith the increasing temperature gradient ( ∆T=T h -T c ) in various applied resistive load. The increaseof output voltage in equal temperature gradient is also occurred in various rheostat values.In otherwords, the value of voltage increases in the same resistant as the influence of increasing temperaturegradient.The peak value of output voltage of the device is 2.3 V at ∆T =61 oC. This relationship isvalid theoretically.
The characteristic of current output as shown in Fig. 3(b) has different trend with outputvoltage.The figure informs that the increase of temperature gradient results in decrease of outputcurrent as the increase of resistive load in logarithmic curves.This trend agrees with the theoretical
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relationship between current and resistant. In the same value of resistant, the output current increasein resultant of temperature gradient.
Relationship between output powers in variation of resistive load is shown in Fig. 4(a). Thedecrease of power does not form logarithmic curve. The values of power are obtained frommultiplication between output voltage and output current measured parallel at shunt resistant andseries to the rheostat. The peak power achieved in this experiment is about 113 mWat thetemperature gradient of ∆T =61 oC and resistive load of 20 ohm. In the same value of load, the valueof power increases as the increase of temperature gradient.
Furthermore, the relationship between output current and output voltage is shown in Fig. 4(b).The figure shows linearity between output current and output voltage. The higher value of outputcurrent corresponds to the lower value of output voltage. It can also be seen from the figure that thegradient of each curve is negative and almost the same gradient value. The internal resistant ofthermoelectric generator can further be calculated from the relationship between generated currentand voltage at the present treatment .
(a) (b)(b)
Fig. 3: (a) Output voltage in various load, (b) output current in various load
(a) (b)
Fig. 4: (a) Current versus Voltage, (b) power in various load
ConclusionCharacterization of bismuth telluride based single module thermoelectric generator TEC1-12710has been performed and briefly reported. The measurement device has been set up by elaboratingcommon device and simple configuration. The method is based on measuring output current and
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voltage as the response to variations of resistive load. The procedure has also been provenexperimentally resulting in valid relationship between parameters compared to the basic theory.This characterization procedure can be applied to other types of thermoelectric generator that useSeebeck effect.
Acknowledgement
The present project was supported by Directorate of High Education, Republic of Indonesia,through DIPA LPPM-UNS 2013 under contract number of 2342/UN27.16/PN/2012
References
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DOI References
[1] J.P. Carmo, J. Antunes, M.F. Silva, J.F. Ribeiro, L.M. Goncalves, J.H. Correia, Characterization of thermoelectric generators by measuring the load dependence behavior, Measurement. 44 (2011) 2194-2199.http://dx.doi.org/10.1016/j.measurement.2011.07.015 [5] N.F. Guler, R. Ahiska, Design and testing of a microprocessor-controlledportable thermoelectric medicalcooling kit, Applied Thermal Engineering. 22 (2002) 1271-1276.http://dx.doi.org/10.1016/S1359-4311(02)00039-X
[7] C.B. Vining, Semiconductors are cool, Nature. 413 (2001) 577-578.http://dx.doi.org/10.1038/35098159 [8] S. Maneewan, J. Khedari, B. Zeghmati, J. Hirunlabh,J. Eakburanawat, Investigation on generated power ofthermoelectric roof solar collector, Renewable Energy. 29 (2004) 743-752.http://dx.doi.org/10.1016/j.renene.2003.10.005 [9] S. Maneewan, J. Hirunlabh, J. Khedari, B. Zeghmati, S. Teekasap, Heat gain reduction by means of thermoelectric roofsolar collector, Solar Energy. 78 (2005) 95-503.http://dx.doi.org/10.1016/j.solener.2004.08.003 [10] E.F. Thacher, B.T. Helenbrook, M.A. Karri, C.J. Richter, Testing of an automobile exhaust
thermoelectric generator in a light truck, Proceedings of the Institution of Mechanical Engineers, Part D:Journal of Automobile Engineering. 221 (2007) 95.http://dx.doi.org/10.1243/09544070JAUTO51 [12] D. Dai, Y. Zhou, J. Liu, Liquid metal based thermoelectric generation system for waste heat recovery,Renewable Energy. 36 (2011) 3530-3536.http://dx.doi.org/10.1016/j.renene.2011.06.012 [13] J. Eakburanawat, I. Boonyaroonate, Development of a thermoelectric battery-chargerwithmicrocontroller-based maximum powerpoint tracking technique, Applied Energy. 83 (2006) 687704.http://dx.doi.org/10.1016/j.apenergy.2005.06.004
