A PROJECT REPORT ON UTILIZATION OF WASTE HEAT IN AUTOMOBILES USING THERMO ELECTRIC GENERATOR

INTRODUCTION

Thermo electric generator (TEG) is a highly sophisticated device which converts heat energy into electricity energy by using the Seebeck effect.. One promising idea is to use a solid-state device called a thermoelectric generator (TEG) to convert waste heat directly into electricity. This would reduce the load on the vehicle's alternator and thus vehicle economy can be increased.

OPERATION PRINCIPLES

In TEGs, thermoelectric materials are packed between the hot-side and the cold-side heat exchangers. The thermoelectric materials are made up of p-type and n-type semiconductors.

The temperature difference between the two surfaces of the thermoelectric module(s) generates electricity using the Seebeck Effect. When hot exhaust from the engine passes through an exhaust TEG, the charge carriers of the semiconductors within the generator diffuse from the hot-side heat exchanger to the cold-side exchanger. The build-up of charge carriers results in a net charge, producing an electrostatic potential while the heat transfer drives a current. With exhaust temperatures of 700°C (~1300°F) or more, the temperature difference between exhaust gas on the hot side and coolant on the cold side is several hundred degrees. This temperature difference is capable of generating 500-750 W of electricity.

SEEBECK EFFECT

TEG PRODUCES ELECTRICAL POWER WHEN A TEMPERATURE DIFFERENCE IS

MAINTAINED BETWEEN THE HOT AND COLD JUNCTIONS OF THE

THERMOELECTRIC MATERIALS

A thermocouple is formed by a P type and an N type thermoelectric element joined together electrically by a hot junction electrode. Adjacent thermocouples are joined together electrically by cold junction electrodes.

SYSTEM COMPONENTS OF TEG

A thermoelectric generator requires the following components :

Support structure

Hot Sink

Module

Cold sink (Radiator)

Power Circuit

SUPPORT STRUCTURE

It is the part of the thermoelectric generator where the thermoelectric modules are located. The internal part of this structure normally is modified in order to absorb the most part of the heat accumulated in the exhaust gases.

MODULE SELECTION

A high temperature Bismuth telluride module has been selected due to its high efficiency and high operating temperature.

COLD SINK SELECTION

Cold sink is the second most important component of the system.

Cold sink must dissipate large amount of heat coming through the module and remain at the low temperature.

Fan cooling may be necessary where maximum power or compactness are desired.

COOLANT ARRANGEMENT TO CREATE TEMPERATURE DIFFERENCE IN TEG

(WATER COOLED)

FLOW OF COOLANT IN TEG

3-D DESIGN OF TEG

OUR MODEL DESIGN AND

SPECIFICATION

Specifications

Length -240mm

Breadth -179mm

Height-162mm

Material used for fabrication :

Heat exchanger- stainless steel

Corrosion resistant ,resistant to wear & tear, can withstand high temperature without deformation, cheap as compared to other materials

Insulation - aluminium-backed high-temperature glass fibre

Easy avaibility, thermal conductivity is very good above 500K, electrical insulator, maximum service temperature of about 1500K

Wiring – copper

Good conductor of electricity 401W/mK, high melting point (1358K), can be drawn into fine wire

Thermoelectric module- Si-Ge, Pb-Te

Si-Ge : Operating temperature difference 673K - 1073K Pb-Te :Operating temperature difference 373K- 673K

Pumps- exhaust & coolant pumps

The pump at exhaust outlet is used to overcome the back pressure produced by the sudden restriction at various cross-sections and the pump at coolant side is used to maintain constant flow of water from radiator to TEG heat exchanger

Pipes housings - stainless steel

ASSEMBLED MODEL

FUTURE SCOPE AND APPLICATIONS

The T.E.G setup being able to utilize the waste heat of automobile has a great future ahead. This setup is most advantageous in case of power plants.

In case of an automobile the T.E.G setup could be able to produce enough energy that it can completely replace the alternator. Besides T.E.G setup can also increase the fuel economy (by 5-8%) and finally the overall efficiency of an automobile.

For ships carrying large amount of diesel fuel and operating on diesel power cycle. The T.E.G setup would be quite beneficial. The electricity produced by extracting heat from it’s exhaust can be easily used for onboard electrical supply.

In future if we are able to find some materials which can work more efficiently at low temperature difference, or whose conversion efficiency is very high. Such materials can be easily installed in our design by just increasing the number of whirl leafs and thus more power can be generated which would be enough to replace the alternator.

BMW PROVIDES AN UPDATE ON WASTE HEAT RECOVERY

PROJECTS :THERMOELECTRIC GENERATOR

TEG integrated in the exhaust manifold

TEG integrated into the exhaust gas recirculation system

The two alternative systems developed to date differ in their positioning in the vehicle—one unit is designed for the exhaust system, while the other is intended for the exhaust gas recirculation system. The engineers of the BMW Group basically refined a technology that has been used to power space probes for more than four decades by NASA, the aeronautics and space agency of the United States. The latest generation of TEGs installed in the exhaust are capable of generating 600 watts of electrical power, and it will not be long before the goal of 1,000 watts is reached as research progresses. The current prototype—a BMW X6—was built as part of a development project funded by the US Department of Energy.

VOLKSWAGEN SHOWS THERMOELECTRIC

GENERATOR FOR WASTE HEAT RECOVERY

Volkswagen claims 600W output from the TEG under highway driving condition. The TEG-produced electricity reportedly meets around 30% of the car’s electrical requirements, resulting in a reduced mechanical load (alternator) and a reduction in fuel consumption of more than 5%.

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