User:Rnagfn/sandbox

Diesel generator is generally used as a backup power source for different kind of application. But about one third of its fuel energy is wasted in the form heat directly from the exhaust of the diesel engine and this heat is generally not captured for utilization in any application. This project deals with the feasibility and design of the recovery of waste exhaust heat with the help of heat exchanger and this heat is used to maintain the temperature difference which causes power generation using Seebeck power generator module. Exhaust flow rate and temperature are the parameter on which heat recovery system design and amount of heat recoverable depends.

Introduction
During the process of producing electrical power, there is unused heat from the diesel engines. If the waste heat could be used, there would be a significant fuel savings. Energy utilization of fuel is shown in the given pie chart.



From above data it can be observed that about 30 percent of fuel energy is wasted in the form of exhaust heat. In this project we will try to utilize this 30 percent heat in the generation of small amount of power using SP1848 27145 module .Schematic diagram of the system which utilize this heat is shown below:



Basic block of the system consists of heat exchanger, heat sink, heating block, water reservoir, pump and heart of the system i.e. thermo-electric generator module. Arrangement of these blocks is shown in the above figure. This system can be divided into two section viz thermo-electric generator section and heat transfer section. Thermo-electric section will consists of heat sink, heating block and TEG module and heat transfer section will consists of heat exchanger and the water circuit of the system.

Component Required

 * 1) Copper Tube
 * 2) Water Heating Aluminum Block
 * 3) Heat Sink
 * 4) Thermoelectric Generator Module(SP1848 27145)(40mmx40mmx3.4mm)
 * 5) Fountain Pump(6 volt, 2watt)
 * 6) Water Reservoir
 * 7) Thermal Paste
 * 8) Connecting pipes and other hardware components

Copper Tube Coil
This copper tube coil used to exchange heat from hot exhaust gas to the water flowing through the tube and this hot water feed to the heating block with the help of feed tube.

Heating Block
This block is used to maintain high temperature on one side of the thermo-electric generator module by taking heat from hot water fed by the heat exchanging copper coil.

Heat Sink
This is also a kind of heat exchanger which transfer heat generated by an electronic device to a medium by increasing surface area of cooling with the help of fins and fan can also be used in conjunction with this device to increase the rate of cooling. And thus this helps to maintain low temperature at one side of thermo-electric module.

Thermal Paste
It is a very high heat conductive paste that is used between heat sink and thermoelectric module and also between heating block and thermoelectric module to get a better heat conduction.

Thermo-electric Generator Module
It is also called a seebeck generator, is a solid state device that convert heat flux (temperature difference) directly into electrical energy through a phenomenon called the seebeck effect. This can also be called as the heart of this project. One side is pasted with heat sink and another side is pasted with heating aluminum block with the help of thermal paste to maintain the temperature difference between two sides of the module. Dimension of the block is 40mmX40mmX3.8mm

Water Pump (3 volt, 2watt)
This is used to circulate water throughout the water circuit by maintaining pressure difference. Inlet is connected to the water reservoir and outlet is fed to the copper tube coil.

Heat Transfer and Water Circuit
Heat exchanger block consists of copper tube coil enclosed in an enclosure for the transfer of heat from hot flue gas to the water flowing through the copper tube. The transfer of heat depends upon the coefficient of heat transfer and area exposed of copper tube in the chamber. Coefficient of heat transfer for a particular material depends upon the characteristics and geometry of material. Copper has very good thermal conductivity of 386 w/mK at 20° C that is generally more than aluminum i.e. 200 w/mK and less than silver which has 405 w/mK. This makes it suitable for the purpose we required here.



Area of expose of copper tube can be increased or decreased by choosing number of turns in helical geometry of the copper tube. This will help to increase the coefficient of thermal conductivity.



In this project water act as a medium of heat transfer throughout the system and the circulation of water is carried out with the help of small centrifugal pump. This pump inject water to the inlet of copper tube as shown in the figure and passes through the number of turns of the copper tube and absorb heat from the flue gas and exits through outlet of the copper tube. Finally this heated water reaches to the heating block through connecting pipe and transfer of heat takes place from water to the aluminum heating block. After heating of the block water accumulates in the water reservoir and again pumped to the inlet of the copper tube and the cycle continues.

Thermo-electric Generator Section
As discussed earlier heating block is heated up by the hot water received from the copper tube and thus it will help to maintain high temperature on one side of the TEG module and other side of the module is maintained at low temperature with the help of heat sink. Therefore we are trying to maintain the temperature difference on both side of the thermoelectric generator module.



A thermoelectric generator consists of two semiconductors i.e. n type and p type subjected to temperature difference (Thot - Tcold ). In n type semiconductor majority charge carrier are negatively charged electrons and in p type semiconductor majority charge carrier are positively charged holes. In a temperature gradient, electron and holes tends to accumulate on the cold side .An electric field E develops between the cold and hot side of each material, which gives us voltage when integrated over the length of each. Voltage of the p and n type semiconductor add up ad drive electrical current through an electrical load. Typical value of temperature difference and output voltage and current is indicated in the table given below:

Table of open circuit voltage of TEG

Above data indicates that as temperature difference increases developed voltage and current also increases accordingly.



Future Work
As we know that the amount of fossil fuel present in the reserve is limited and the process of formation of this fossil fuel takes millions of year to form i.e. it is a very slow process. Therefore we have to use our reserves efficiently and also sustainable development should be kept in the mind so that future generation should not be affected by our activity. We cannot form fossil fuel but can reduce the wastage of this fuel energy and in this project we are trying to do so. More efficient method can be developed in future to convert heat directly in into electricity and also method of recovering heat from the exhaust gas or flue gas. R&D team of Panasonic is still working on the development of thermo-electric tube at low cost. If they succeeded in developing cheap thermoelectric tube method will become very cheap and efficient. And this can be installed in each and every diesel generator set economically.

In this project development and research should be done in order to obtain following goal:
 * 1) Maximizing the temperature difference between two sides of thermo-electric devices by increasing heat flow through the device
 * 2) Enhancing thermo-electric characteristics seeking more thermo-electric material, such as Nano material
 * 3) Implementing effective heat dissipation on the cold side
 * 4) Design optimization and computer simulation to optimize the structure and thermo-electric conversion efficiency at present

Pros and Cons related to the project
Advantage:
 * This is a noninvasive method
 * Scalability: can be used for any size of the heat source
 * There is no moving part is present in the system
 * Frictional loss and dynamic loss are reduced due to absence of moving parts
 * Due to absence of moving part wear and tear in the system will be less
 * It does not pollute environment
 * Prevent excessive heat from exhaust to the atmosphere
 * Increases efficiency of the system
 * It increases fuel energy utilization
 * Reliable source of energy
 * Lower Cost of production

Disadvantage
 * Low conversion efficiency
 * Costly thermoelectric modules
 * Cleaning of copper tube is required at regular interval of time
 * Water must be replaced after regular interval of time for proper heat conduction

Conclusion
Exhaust gas of a DG engine contain around 30% of the fuel energy and this energy is directly wasted or given out to the environment. The overall efficiency of the diesel engine can be improved by reutilizing those 30% waste energy. In this project an environment friendly prototype for 40 KW diesel generator has been developed to estimate the power generated from the waste heat and to check the feasibility of the prototype. The effectiveness or efficiency of heat exchanger can be increased by replacing water as working fluid by ammonia, HFC-134a or other fluid. And also research work is required to develop more efficient thermoelectric generating device so that green energy will be available efficiently and economically.