A review on Thermoelectric Generator by using Flexpde SummaryIn this project different systems related to TEG with their potential application, pros, cons and researches associated with TEG are elaborated. The main purpose of using TEG is to produce electrical power from unused heat to reduce the amount of pollution from the environment. By using seebeck effect principle, voltage is produced across two junctions namely n and p type. Higher the temperature difference between cold and hot junction, more amount of efficiency and power can be produced. TEG consists of total four components such as copper electrode, TEG module, TEG shield and Thermal fin. More commonly bismuth telluride and antimony telluride are used as a material for Thermoelectric module. Mostly TEG is used in space applications, automobile sectors and power plant. Design of TEG module creates direct influence on efficiency of the TEG system. Heat exchangers are used in TEG module to provide heating and cooling. Cooling on one side is done by using air or water. TEG is the best alternative in this challenging world to control the pollution from the environment. Due to this, more amount of investment is ongoing in the field of TEG. Keywords: Thermoelectric generator, Trapezoidal Geometry, Flexpde, Seebeck coefficient, Pollution, Thermocouple, Figure of merit NomenclatureV            Voltage produced across two junctions, (volt)?             Seebeck Coefficient, (V/K)?T            Temperature difference between hot and cold junction, (K)Z              Figure of Merit, (dimensionless)?              Electrical Resistivity, (?*m)k              Thermal conductivity, (W/m*K)P              Output Power, (W)I               Electrical Current, (A)RL            Load Resistance, (?)Qh            Heat at Hot junction, (W)Qc            Heat at Cold junction, (W)Greek Symbols?              Seebeck Coefficient?              Efficiency of TEG?              Resistivity?              Resistance Full form of some termsTEG          Thermoelectric GeneratorPV             PhotovoltaicSTEG        Solar Thermoelectric Generator   TE             Thermoelectric        Table of ContentsSr noTitlePage no1Summary12Keywords13Nomenclature24Introduction and Application45Literature Review66Results and Discussions97Conclusion128References12List of FiguresFigure noTitlePage no1Thermoelectric generator working apparatus62Graph of output power vs hot side temperature in TEG83Graph of Efficiency vs hot side temperature in TEG94Temperature distribution of TEG with Trapezoidal Geometry95Electrical Potential of TEG with Trapezoidal Geometry106Distribution of current density in TEG with Trapezoidal Geometry107Distribution of Heat in TEG with Trapezoidal Shape118Summary of the output values for TEG by using Flexpde11 Introduction and ApplicationThermoelectric Generator is an ultimate device to generate energy from waste heat. Function of TEG is almost similar to heat engine. It consists thermoelectric module which is nothing but the circuit with thermoelectric material which helps to produce power from unusable heat. Thermoelectric module comprises of two distinct thermoelectric materials. They both are connected at their end points namely as n- type and p- type semiconductor. n type and p type semiconductor have negative and positive charge respectively. Because of temperature difference, current flows through entire circuit which ultimately produce power. Thermoelectric Generator works on seebeck effect principle [1]. In case of internal combustion engine, from the total energy generated by the combustion of petrol, only 30 percent heat is utilized to drive the vehicle while remaining 70 percent heat is wasted in terms of exhaust gas and coolant with 40 percent and 30 percent in proportion respectively [2]. But in case of TEG, this waste from exhaust gas and coolant are converted into thermal power which finally gives pollution free environment to the world. Seeback, peltier and Thompson effects are associated with TEG system. Because of two different semiconductors, seeback effect comes into effect. Due to this, it creates temperature difference and finally voltage is produced in between two materials. If voltage is applied to TEG, then it produces temperature gradient. Due to this temperature gradient, particles in the material are forced to move from hot side to cold side. This is called Peltier effect. In this system, electrons are used as a working fluid [1]. Nowadays, Pollution is becoming major trouble for the entire globe. TEG system is best alternative to reduce pollution from environment. Many researchers are working on this green technology alternative. Thermoelectric power generation is also called as thermoelectricity [3]. TEG was used in North Sweden to give little amount power to some of the Sweden’s isolated areas [4]. It was the best option compared to costly gasoline. Cost of entire TEG is summation of cost of device and working cost. Main purpose of using TEG in replacement to any other power producing devices is its economic competency in market [paper 3]. Selection of thermoelectric material depends on mainly three parameters namely thermal conductivity, electrical conductivity and seebeck coefficient [paper 4]. If the temperature difference increases between hot and cold side of thermoelectric module, efficiency and power generation also increases with it [paper 5]. TEG contains total four components such as TEG module, TEG shield, thermal fin and copper electrode. Mostly Bi2Te3, PbTe, Sb2Te3 are used as a thermoelectric module semiconductor.Thermoelectric shield provides protection to the modules from high temperature. Ceramics such as Al2O3 are used as a material to make TEG shield. Thermal fin is used to augment the value of thermal grade. Normally it is made from Aluminium. It helps to increase overall efficiency of the system [paper 9]. From the survey it has found that, around 70% of world energy production is wasted in atmosphere through heat rejection by different media, which is prime reason for global warming. TEG helps to reduce this problem in addition to this it contributes to save energy and environment [5].There are certain advantages of using TEG such as there is no maintenance needed for this device because of no moving parts associated with it [6]. It is not producing any noise. It is a reliable instrument. It is simple, safe and efficient device. It consumes very less space and light in weight. It is a portable device. It can be used for small and mobile applications. It is an eco friendly technology to produce electricity [6-9]. It helps to achieve high overall efficiency. It is a cheaper alternative compared to other system. It has lower operating cost. Heat is used as an input source instead of light, so it can be used in day as well as night time [paper 9]. It has long lifespan. It saves time because normal heat engine converts thermal energy into mechanical energy and then further converts it into electricity while TEG converts thermal energy directly into electrical energy. It has some drawbacks as well like high generator output resistance, low thermal conductivity and continuously heat removal from cold side by using air to create difference in temperature between to sides [1]. TEG is used in various applications such as wireless sensors, jet engine parts, hot water tubes, computer/refrigerator body heat, IC engine parts, furnace cover, aerospace, military, medical, industrial instruments, automobile, marine applications, etc.Working of TEG is simple and straightforward. Working of TEG is shown in below figure. Basic unit of TEG module is thermocouple. Thermocouple has two main parts namely n-type and p-type semiconductor pallets. They both are attached with hot side where heat is supplied at one end and cold side where heat is constantly rejected by some source. Both semiconductors are sandwiched between two ceramic plates which act as a TEG shield. One circuit is attached with this system. Electric current flows through the circuit due to temperature difference between the ends which ultimately helps to produce voltage [1].Fig 1. Thermoelectric generator working apparatus [1] Literature ReviewHsu et al. proposed that performance of the TEG module can be improved by increasing pressure on it [10]. Andrea et al. did investigation to determine loss of power due to dissimilarity in temperature in TEG module arrangement. It has found that series interconnection of TEG modules gives better result compared to parallel interconnection [11]. Most of researches happened with the aim to augment seebeck coefficient and to diminish thermal conductivity by introducing nanostructure concept in thermoelectric material. From the research it has found that by changing shape of TEG directly affects efficiency of the system. Yadav et al. developed a flexible and cheaper TEG with thin film thermoelectric on fibrous material [12]. Yodovard et al. evaluated the effect of waste heat power generation for diesel cycle and gas turbine cogeneration in Thailand [13]. A little while back, Taguchi discovered an exhaust gas-based TEG for automobile applications.Wang et al. generated one mathematical model of TEG. In this system, exhaust gas of the vehicle was used as an input source [14]. Demir and Dincer examined a water-electric cogeneration system with TEG with 21.8MW power generating capacity [15]. Niu et al. created one cheaper with simple design TEG by using Bi2Te3 material with capacity of 150-200W [16]. Crane and Jackson combined thermoelectric module with cross flow heat exchanger to make the entire TEG system more efficient [17]. Yu and Zhao proposed a numerical model of TEG with parallel-plate heat exchanger with focus to analyze the temperature difference across the Thermoelectric modules [18].Luo et al. found application of TEG in cement manufacturing in Portland [19]. Xie at al. established a TEG that use hydrothermal energy as an input source from which heat is extracted and converted into electrical energy [20].Voltage produced through seebeck effect is given by following equation_V=??T   —-(1)Where ? is seebeck coefficient and ?T is temperature difference between hot and cold junction.Thermoelectric materials of n and p type semiconductors are distinguished by a parameter called figure of merit Z, which is evaluation of the ability of thermoelectric materials to convert heat into electricity. The figure of merit is given by_Z=?2/?k   —-(2)Where ?, ?, k are seebeck coefficient, electrical resistivity and thermal conductivity respectively.Output power is given by_P= I2RL=Qh-Qc —-(3)Where I, RL,Qh,Qc are input current,load resistance,heat at hot and cold junction respectively.Efficiency of the TEG is given by:?=P/Qh    —-(4)where p is the output power and Qh is input heat provided to the system [21].Hayashi et al. launched mutual layer of TEG with TE ceramic oxide layers which was attached with combine layer technology [22]. Belanger et al. developed one stage model of TEG in a cross-flow heat exchanger to determine the impact of internal structure on performance of the system [23]. Lee et al. determined the design of TEG including output power and efficiency with respect to external load and geometry of the thermoelement [24]. Gou et al. studied the effects of performance on low temperature TEG [25]. Choi et al. developed tellurium-based film with nanotubes as a thermoelectric material [26]. Weber et al. examined thin polymer layer with TEG which is ideal for small electronic device such as wristwatch. In case of wristwatch, heat which is released from human body is the prime thing for running this miniature device [27]. Niu joined 56 BiTe based TEG modules in series to show the progressive nature of TEG in terms of good conversion efficiency at low temperature [28]. Amatya and Ram outlined efficiency of 3% by using Bi2Te3 based TEG [29].                                                                     Fig 2. Graph of output power vs hot side temperature in TEG [21]From the fig 2. it can be seen that cold side temperature is keeping constant at 373K and constantly increasing hot side temperature which creates temperature difference between them and produces more power. Higher the temperature difference produces more power in TEG system.                                                                                                Fig 3. Graph of Efficiency vs hot side temperature in TEG [21]From the fig 3. it can be said that with increase in temperature difference, output power can be increased. From equation (4), output power is directly proportional to the efficiency. So by increasing output power, Efficiency can be augmented. It can be said that there is a direct relation between efficiency and hot side temperature.Results and DiscussionsTemperature distribution                          Fig 4. temperature distribution of TEG with trapezoidal geometry                           Fig 5. Electrical Potential of TEG with Trapezoidal Geometry                            Fig 6. Distribution of current density in TEG with Trapezoidal Geometry                       Fig 7. Distribution of Heat in TEG with Trapezoidal Shape                     Fig 8. Summary of the output values for TEG by using Flexpde ConclusionWorking of TEG is shown in fig 1. Through research it has found that for competitiveness of TEG with other power producing methods, value of figure of merit should be more than 3. Because of its effectiveness, it is being used in almost every sector to produce electricity. Normally TEG with fin is used because fin helps to increase rate of heat transfer from the system which ultimately contributes to enhance the efficiency and performance of TEG system. Fig 2 and 3 display the variation in power and efficiency with hot side temperature by keeping cold junction temperature as a constant. From fig 4 to 8, it can be said that by changing shape of the TEG module, different parameters such as input heat, output heat, current density, electrical potential and temperature can be changed which directly affects output power and overall efficiency of the TEG system. 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