Abstract of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The report is about the “design of the TEG by automotive heat recovery”. The waste of the heat recovery used the TEG which is the promising approach for the various vehicle and the manufactures equipment’s which is also reduced the consumption of fuel. The system of TEG could also convert the wasted of the Thermal energy from the engines to the electricity which is directly used for the vehicle systems. The focused of the paper is on the design of the TEG and also determined the heat losses and efficiency of TEG.

In this research report there are the different section which should be discussed as shown in the below discussion. There are five chapter discussed in this research. The first chapter of the research study is introduction in which the ideas are generated to perform the research on the particular topics. In this section of the research study the brief back ground of TEG and the working principle of the TEG. The 2^nd chapter is the literature review that is describes about the theories of the several authors who have worked to analyzing the challenges TEG for automatic waste of heat recovery. This section of the research study discusses the related work of previous18 years from 2002-2019.The 3^rd chapter is about the description of the system in which heat losses and the efficiency of the TEG is discussed. And the chapter 4^th is about the discussion and result in this the temperature distribution is discussed. The last chapter concludes the research report and gives recommendations about the TEG.

Chapter1 Introduction of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The substantial thermal energy is always available for the exhaust gases in the automotive modern engines. From the combustion of the vehicles there are two third of energy in the vehicle is the loss of the waste heat and that is the 40% is form of the exhaust gas. By using the potential of thermoelectric generator (TEG) to recover the various waste of energy for the exhaust stream and it is the potentially improving of the fuel economy through the great 5%. The detailed theoretical study which is concluded the TEG powered through the exhaust heat and it could also meet the electrical requirements for the medium sized vehicles.  TEGs are employed for the specialized military along with the space application. The converter of thermoelectric is also used for the power deep space due to the ease of simplicity and scalability which is also compared by the different approaches (Stabler, 2002).

TEG Modeling of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The analysis of steady is the hot exhaust gas flow with the length of TEG and it is also performed for the current study. The change in the fluid properties along with the properties of moelectric by the temperature is supposed in the flow direction. The TEG is the symmetric by the respect of height and its only half domain is simulated. The domain of TEG is also discretized for the small control volume and the length. The rectangular modeling of the TEG is also shown in the below figure. A thermoelectric generator is one of best suitable applications for light duty passenger vehicles. In thermoelectric generator the temperate between cold side and hot side of TEG is directly converted into electrical energy. Thermoelectric generators have been shows to improve the fuel economy by as much as 5%.

Figure 1: Schematic of TEG

Even the best combustion engines do not have very good efficiency. At the very best, they can convert 35-40% of the fuel energy into the mechanical energy. The exhaust gas which leaves the combustion chamber of the engine has very high temperature which translates to about 33% of the total fuel energy which is wasted into the environment. Not only this does waste the fuel energy but it also raises the carbon emission in the environment which is very serious environmental issue. With the increase in the total number of vehicles in the last decade or so which adds to this fuel consumption, recovering heat wasted from vehicles is becoming more and more important with each passing day. There are several approaches which have been in effect to resolve this issue and these includes the Rankine cycle mode, turbocharging and the thermoelectric generator etc.

Working principle of thermoelectric generator (TEG)

Thermoelectric generator is solid-state semiconductor devices which utilizes the temperature difference between its cold side and hot side and convert this heat flow into useful DC power. Thermoelectric generators use the “Seedback” effect to generate the voltage. Consequently, this generated voltage causes electric current and subsequently useful power. At the very core of a thermoelectric generator is a thermocouple. A thermocouple consists of a one n-type and one p-type semiconductor. These semiconductors are connected to each in a series connection with a metal strip.

These semiconductors are known as pellets, thermoelements or dice. The Seedback effect is known be the direct conversion of heat energy into a voltage potential. The movements of charge carriers inside the semiconductor are the cause for the Seedback effect. Holes are the charge carriers in a doped p-type semiconductor while electrons happen to be the charge carries in a doped n-type semiconductor. Charge carries diffusion occurs from the hot side of the semiconductor which in turn builds up the charge carriers at one end of the semiconductor.

 This buildup becomes the cause of the potential difference which is directly proportional to the difference of temperature across the semiconductor. Most commonly used materials in thermoelectric generators are lead telluride (PbTe), silicon germanium (SiGe) and bismuth (Bi2Te¬3). The use of the correct material depends on many factors which include the characteristics of cold sink being used, characteristics of heat source plus the design of thermoelectric generator.

In a thermoelectric generator module, many n-type and p-type semiconductor couples are connected with each other either in series or in parallel combination to create the required current and voltage. There ceramic places between couples which provided the required structural rigidity and also prevents electrical short circuits as it is an insulator (Alfred, 2020).

In this article it has been suggested by Jaziri, Ayda and Jens (2019) that some of the designs have been presented which is related with thermoelectric generators which have been based on decrease temperature along with co-fired ceramic technology. In this it has been mentioned that carbon dioxide emission and cost of fuel has been enhanced in most of the automotive organization started which mainly pay emphasis on the investigations and change power source to decrease power cost and better the performance of engine. (Jaziri, Ayda , & Müller, 2019)Despite from tis it has also been stated that the introduction which is related with LTTC on the basis of TEGs as consume waste heat recovery system.

 Furthermore, engendering high power which as been based on the thickness of film on the basis of TEG which is quite complex task. Mainly in the passenger’s automobile under the consistent driving situations, they deplete system which can be originate almost 10KW of thermal energy which gives the output of 700-800 in order to attain almost 10% of energy alteration effectiveness. As well as the most cited emplacement of TEGs in the literature had on consume heat exchanger surface due to high temperature which has been originated.

As it has been mentioned by Lan, Zhijia and Richard (2018) that some of the waste heat recovery while utilizing thermoelectric generator has the talented aspect for the automobile real instrument which has been developed to decrease the consumption and also reduce the exhaustion of CO2. Despite from this TEG could be transferred other than this wasted thermal energy from engines to the electricity mainly for its usage in the system of Vehicle. Moreover, the study also pay emphasis on growth of diverse model of TEG system which has been designed for automobile waste heat recovery which has been developed form counter flow heat exchanger and national thermoelectric modules. (Lan, Yang, & Stobart, 2018)This model as been designed form the elements of thermoelectric with in the TEMs and then in the system. as well as it has also been mentioned that this model has been installed within the upstream after having the treatment system which is presented in the model of heavy-duty truck and has been taken to evaluate the power and temperature output with in the divers driving cycle. In this regard the outcome has been attaining as in the form of temperature that shows the model which has been utilized and based on the development of control system for dynamic operation system.

According to Nicholas, Yanliang (2016) it has been suggested that automotive fuel effectiveness has been enhanced by having thermoelectric power generation utilizing exhaust waste heat. In this article it has been presented that increased temperature of thermoelectric generator which transfers the waste heat which has been exhausted into the electricity replicated on the basis of light-weight duty passengers’ automobile which holds four gasoline cylinder engines. In this regard various strategies have been developed to arrange the conformation of and the design of heat exchanger for the appropriate (Kempf & Zhang, 2016) effectiveness and betterment of fuel has been given.

Although in this assessment of stainless steel and also the silicon carbide which is also the heat changer and it has been initiate form both ideal design of TEG and this will mainly expand the effectiveness and consumption of fuel which is depend on the thermal conductivity of heat exchanging elements. Moreover, the study also pay emphasis on growth of diverse model of TEG system which has been designed for automobile waste heat recovery which has been developed form counter flow heat exchanger and national thermoelectric modules.

Chapter3: Description of the system
Automotive unit for TEG of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The system of the TEG is shown in the below figure which is also consist on the series of the repeat units which is segregated and  exhaust stream as well as shaped by the practical exhaust pipe. A repeat unit is also created by the concentric thermoelectric modules, cooling and hot plates and twelve pipes in the every plate are highlighted by the red and blue (Huang,et al , 2018).

Figure: Schematic of the concentric cylindrical TEG system

For the investigations of and influence of the coolant flow direction and the coolant flow rate along with the cooling unit arrangement in automatic exhaust of thermoelectric generators , and the model of thermoelectric generators is also related with the test bench which are constructed . The uniformity of temperature is also improving the cooling units (Su,et al , 2106).

Heat losses (temperature measurements)

The performance of the TEG is also determined through the equation of the heat fluxes and it’s across the surface of heat exchanger to the heat fluxes for the cold and warm junction of the thermoelectric generators;

A heat fluxes by the cold and warm sides for the heat exchangers is also calculated and it is also connected through the thermal conduction of the coefficient. A heat fluxes for the thermoelectric junctions are complicated where these entire junction for the heat flux is the sum of the thermal conduction and the joule heating and the peltier effects.

Using the relationship among temperature;

The expression for the total resistance along with the TEG current

Heat losses of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

In this report the heat losses in the TEG is done by the convection, conduction, radiation where the simultaneously and the singlehandedly is by the heat losses mechanism for the TEG (Bjørk,et al , 2014).

Engine type	Shaft power	Cooling	Exhaust	Other
Petrol	20-25%	20-25%	35-45%	10-15 %
Diesel	30 – 35 %	15 - 35%	20 - 30%	3 – 10 %

 Drawings, Material, Manufacturing of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The author purpose is to provide the thermoelectric device which has the very low cost and thus the processing by the high thermoelectric efficiency. All these devices are called thermoelectric generators which are also used to generate the electricity from the waste of the automatic exhaust through the conversion of the temperature gradient into the electric energy.

The material of thermoelectric which is also providing the voltage  and the temperatyure gradient  which is present regarding to the seebeck effect;

Where s is representing the seebeck coefficient and the conversion efficiency for the thermoelectric material which is also denoted by the dimensional figure of the ZT merit and it is also defined as;

The drawing of the thermoelectric is shown in the below figure (Besganz, et al , 2014);

Figure: Drawing of thermoelectric generator

Manufacturing of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

The thermoelectric device manufacturing is also changes and it is based on the various type of the material of thermoelectric which is also employed. The provided overview is applied and the bulk of the materials along with the traditional manufacturing process. For all of types TEG which is not comprehensive and it is also provided the references of enhance which is understanding the engineering challenges by the materials (LeBlanc, et al , 2014). The schematic of the thermoelectric devices along with the manufacturing process is also shown in the below figure;

Figure: Manufacturing of thermoelectric module

Chapter4: Results and discussion

Assumptions about temperature

The temperature assumptions are lies in different ranges when effect of temperature   of cold and heat sources is researched by performance of the two stages TEG at 500.800K which is also the range of the exhaust temperature and there are different aspects if researched (Dunham, et al, 2019);

The approximation is maximum by the use of the power solution;

 Temperature distribution in the source

To resolve the temperature distribution for the TEG systems which could also examined through the thermal imaging. To enables the measurement for vertical and lateral temperature distribution of the thermoelectric modules along with the determining of the electrical and the thermal ties of the TEG systems.  By the infrared thermography which is also helps to evaluate the distribution of temperature distribution of the TEG system.

LHC	Engine speed	Load (relative)	Exhaust mass	Temperature	Mass flow	EGR temperature
1	1000	25	400	250	125	320
2	1150	20	420	260	200	330
3	1300	75	950	350	200	490
4	1300	50	800	300	250	220
5	1300	100	1400	400	220	560

Calculate change in voltage as a function of temperature difference

The material of thermoelectric which is also providing the voltage  and the temperatyure gradient  which is present regarding to the seebeck effect;

Where s is representing the seebeck coefficient and the conversion efficiency for the thermoelectric material which is also denoted by the dimensional figure of the ZT merit and it is also defined as;

Calculate efficiency of TEG system

The efficiency for the TEG system of for the automotive waste of heat recovery is given as below;

TEM	TEG height	Fin height	No of sub TEG	Number of modules
264-1.5	440	6	15	250
264-1.5	420	9	13	220
264-1.5	440	15	14	250

Chapter 5: Conclusions and Recommendations
Conclusion of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

Summing up all the discussion it is concluded that the report is about the design of the TEG of automotive exhaust heat recovery. The waste of heat recovery along with the increasing of the energy efficiency which is also creates the waste heat recovery by the thermoelectric generator and it is the promising technology.   All the requirements of this report are fulfilled.

Recommendation of Design of Thermoelectric Generator (TEG) for Automotive Waste Heat Recovery

Through the fabrication of thermoelectric module the effect of leg length plus the ceramic plate material is prove.

The dimensionless method for the TEG module is verified through experimental by the fabricated module and it is also based on the optimization.

By using the optimum design the effect of cold and hot side of heat exchangers is validated.