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4643
www.ijifr.com Copyright © IJIFR 2015
Reviewed Paper
International Journal of Informative & Futuristic Research ISSN (Online): 2347-1697
Volume 2 Issue 12 August 2015
Abstract
Thermoelectric technology has revealed the potential for automotive exhaust-based thermoelectric generator (TEG), which contributes to the improvement of the fuel economy of the vehicles. Thermal capacity and heat transfer are major factors which effect on the thermal performance of TEG. As the thermal energy of exhaust gas extracted by thermoelectric modules, a temperature gradient appears on the heat exchanger surface. In order to achieve uniform temperature distribution and higher interface temperature, the thermal characteristics of fishbone heat exchangers with various heat transfer enhancement features are studied, such as internal structure and surface area. Combining the computational fluid dynamics simulations and test on an engine setup, the thermal performance of the fishbone heat exchanger is evaluated. Simulation and experiment results show that a plate-shaped heat exchanger made of brass with fishbone-shaped internal structure achieves best performance than heat exchanger without internal structure, which can practically improve overall thermal performance of the TEG.
Experimental Analysis Of Fishbone Heat
Exchangers In Thermoelectric Generator
For Automotive Application
Paper ID IJIFR/ V2/ E12/ 043 Page No. 4643-4648 Subject Area Mechanical
Engineering
Key Words Automotive Thermoelectric Generator, Fishbone, Heat Exchanger, Internal
Structure
Received On 18-08-2015 Accepted On 30-08-2015 Published On 31-08-2015
Kiran R. Sonawane 1
M E student, Department of Mechanical Engineering Matoshri College of Engineering, Eklahare, Nashik-Maharashtra
Nilesh C. Ghuge 2
Assistant Professor, Department of Mechanical Engineering Matoshri College of Engineering, Eklahare, Nashik-Maharashtra
4644
ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)
Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4643-4648
Kiran R. Sonawane , Nilesh C. Ghuge :: Experimental Analysis Of Fishbone Heat Exchangers In Thermoelectric Generator For Automotive Application
1. Introduction
About 40% of the fuel energy is lost to the surrounding in terms of exhaust gas which produces
energy crisis and environment pollution. The expression "Energy Crisis" has become a symbol of
the human concern about the increasing demands and consumption of energy on earth. For almost
two hundred years, the main energy resource has been fossil fuel. The world consumption of all
energy resources is forecasted to increase from 421 quadrillion Btu in 2003 to 563 quadrillion Btu
in 2015 then to 722 quadrillion Btu in 2030, as shown in, as shown in fig 1. Fossil fuels continue to
supply much of the increment in marketed energy use worldwide throughout the next two and half
decades. Oil remains the dominant energy source, but its share of total world energy consumption
declines from 38 % in 2003 to 33 % in 2030 as illustrated in Figure 2, largely in response to higher
world oil prices, which will dampen oil demand in the mid-term. Worldwide oil consumption is
expected to rise from 80 million barrels per day in 2003 to 98 million barrels per day in 2015 and
then to 118 million barrels per day in 2030. In parallel with the improvement of the efficiency of
the internal combustion engines, many researchers actively investigate the use of thermoelectric
(TE) technology to recover the waste heat energy for gasoline vehicles, and hybrid vehicles. If
some amount of the large waste heat could be recovered and converted into electricity, large
amount of heat would be saved and the efficiency of vehicle system would increase drastically.
Various thermodynamic cycles have been proposed and studied for waste heat recovery system. In
absorption cooling cycles which is used in hybrid and electric vehicles transfer waste heat from the
exhaust gases into the boiler of ejector for cabin cooling. The present work reviews the existing
exhaust heat exchangers and optimized shape, internal structures of exhaust heat exchanger to find
out best heat exchanger to get uniform temperature distribution.
Figure 1: World Market Energy Consumption 1980 – 2030, (IEO, 2006)
2. Selection Criteria Of Heat Exchanger
The geometry of thermoelectric module is of square plate with dimension, l*b*t
Where, l: Length of TEM,
b: Breadth of TEM,
t: Thickness of TEM.
l=b
Hence, for mounting of TEMs on heat exchanger flat surface is require. Concerning this
requirement we have selected two type of heat exchanger as given below:
Plate shape heat exchanger and
4645
ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)
Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4643-4648
Kiran R. Sonawane , Nilesh C. Ghuge :: Experimental Analysis Of Fishbone Heat Exchangers In Thermoelectric Generator For Automotive Application
Hexagonal prism shape heat exchanger.
Another advantages of these types of HE is that they i) Approach low temperature due to low
thickness and ii) Compact in structure.
2.1 Factors to Select One Out Of These Two Type of Heat Exchanger
I. Space availability: For installation of ATEG system after exhaust system less space is
available. As we know that Hexagonal prism shape heat exchanger required comparatively
large space than Plate shape heat exchanger.
II. Height: Distance between chassis and ground is short and height of plate shaped heat
exchanger is also short compare to Hexagonal prism shaped heat exchanger. The overall space
requirement and height of ATEG system with plate shaped heat exchanger is less than that of
ATEG with hexagonal prism shaped heat exchanger. Hence, we have selected Plate shaped
heat exchanger for ATEG system.
2.2. Heat Exchanger’s Internal Structure Optimization
As a major factor, thermal capacity and heat transfer of the heat exchanger affect the performance
of TEG effectively. With the thermal energy of exhaust gas harvested by thermoelectric modules, a
temperature gradient appears on the heat exchanger surface, so as the inferior flow distribution of
the heat exchanger. In order to achieve uniform temperature distribution and higher interface
temperature, the thermal characteristics of the heat exchanger with heat transfer enhancement,
internal structures are studied. In order to attempt the above concerned objective, fishbone and
Scattered heat exchanger gives uniform temperature difference and high interface temperature with
low back pressure. Hence, we have selected this two internal structure for our plate shape heat
exchanger.
3. Design of Baffles for Fishbone Heat Exchanger
By applying fundamental formula of heat transfer Ф=hAΔT, heat convection can be greatly
strengthened by the increase of the heat transfer area A. This target can be approached by changing
the structure of the conduction surface by fitting baffles i.e. fins. Another approach is to increase
the heat transfer coefficient h. According to the fluid dynamics theories, under the condition of
Reynolds number Re > 4000, turbulent fluid flow is a significant impact factor on improving the
heat transfer. Moreover, the greater the heat transfer coefficient h, the better the heat transfer
quantity. The thermal resistance of turbulent flow convective mostly exist in the boundary layer.
The field synergy principle was proposed as another indication of the synergy degree between
velocity and temperature field for the entire flow and heat transfer domain, the better the synergy
was between the temperature and velocity field, the better the heat transfer. According to both
theories above, the strengthening of the heat transfer can be approached by adding turbulence
device to enhance the fluid disturbance and damage the boundary. Hence, dimensions of fins for
fishbone and scattered is set on trial and error bases keeping in mind to have low back pressure and
simplicity in manufacturing with low material cost and having better optimum turbulence, with
arrangement of fins in symmetry.
3.1 Arrangement of Baffeles for Fishbone Type Plate Heat Exchanger
Number of fins = 14mm,
4646
ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)
Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4643-4648
Kiran R. Sonawane , Nilesh C. Ghuge :: Experimental Analysis Of Fishbone Heat Exchangers In Thermoelectric Generator For Automotive Application
Length of fins = 25mm,
Thickness of fins = 2mm,
Height of fins = 11mm.
Orientation of fins are kept concerning increase in time period of exhaust gases in heat exchanger to
utilize more heat and add additional heat by turbulence, to increase the interface temperature as
shown in figure.
Figure 2: Design And Orientation of Fins In Fishbone Type Plate Heat Exchanger.
4. Experimentation and Result Analysis
4.1 Experimental Setup
We assembled the heat exchangers with the sandwich arrangement of TEG modules between them
as shown in fig. Before assembly we applied the thermal grease on both the surfaces of TEG
modules to enhance the heat transfer. Insulation of glass wool with POP for binding is provided on
hot side except on mounting surface of modules as shown in figure. We made use of four scales of
iron with holes drill at ends for fitting of nut bolts for clamping of heat exchangers. Thermocouples
(K-Type) are connected along with the display for measurement.
.
Figure 3: Experimental Setup
4647
ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)
Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4643-4648
Kiran R. Sonawane , Nilesh C. Ghuge :: Experimental Analysis Of Fishbone Heat Exchangers In Thermoelectric Generator For Automotive Application
Table 1: Engine Specification
Items Engine (Gasoline)
Engine type Four stroke, Three cylinder
Bore (mm) 68.5
Stroke (mm) 72
Compression ratio 8.8/1
Fuel system Petrol (MPFI)
Cooling Water cooled
Engine working temperature (°C) 120
4.2 Result of Fishbone Type HE
Table 2: Experimental Result Table of Fishbone Type HE.
Sr.No Engine
Speed
(RPM)
Temp. Drop Voltage Current Pin Pout AETEG Overall
Efficiency
( Tex - Tin ) = ΔT V I mex *Cp*ΔT η= Pout /Pin
( oC) (V) (A) (W) (W) (%)
1 1500 8 3.6 0.35 108.108 1.26 1.165
2 2000 12 5.44 0.44 187.46 2.39 1.27
3 2500 15 6.7 0.89 263.075 5.96 2.265
4 3000 18 10.02 1.23 346.58 12.32 3.555
5 3500 19 13.78 1.54 397.08 21.22 5.344
5. Simulation of the Thermal Field of the Heat Exchanger
5.1 Simulation model
The plate-shaped heat exchanger of TEG is connected to the exhaust pipe of diameter 36 mm on
both sides. The section of the plate-shaped exchanger of 5 mm thickness is a 120-mm-long by 60-
mm-wide rectangle. There are 3 TMs placing on front and back surface of heat exchanger. The no-
slip boundary conditions are used at all the solid walls. As illustrated in Table 11 the inlet boundary
condition is a uniform flow of velocity 15.2 m/s and temperature is 300°C. The exit of the
exchanger is connected to the end of the rear muffler and this exit of heat exchanger is connected to
atmosphere. Additionally, brass has good thermal conductivity and heat convection. The heat
exchangers are made of brass, so the coefficient of convective heat transfer between the outer
surface of the exchanger and the air is set to 15 W/ (m2 • K). For our convenience, we used a fixed
value of convection heat transfer coefficient h = 15 W/ (m2• K) in all the simulations.
Figure 4 Simulation of the heat exchanger with Fishbone shape.
4648
ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)
Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4643-4648
Kiran R. Sonawane , Nilesh C. Ghuge :: Experimental Analysis Of Fishbone Heat Exchangers In Thermoelectric Generator For Automotive Application
Table 3: Boundary Parameter
Parameter Value
Engine Revolution 3500 r/min
Exhaust inlet temperature 300 °C
Exhaust flow speed 15.2 m/s
Each modules area 0.030*0.030 (m2)
Ambient temperature 25 °C
Ambient heat transfer coefficient 15 (W/(m2 • K))
Material of heat exchanger Brass
Dimension of heat exchanger 0.12*0.06(m2)
6. Conclusion
An Automobile Exhaust Thermoelectric System was designed and developed for the waste heat
recovery of an automobile engine. It is found that Automotive Thermo Electric Generator is an best
option for waste heat recovery from I.C.Engine. At high vehicle speeds, the total power that could
be extracted was increased. More power could also be extracted by improving the exhaust gas heat
exchanger. However with the current design the hot junction temperatures at or above 250oC were
allowed for the given material of TEG (Bi-Te) and results were obtained. Fishbone type plate heat
exchanger is more desirable. It gives high interface temperature and uniform temperature
distribution. Fishbone type heat exchanger has low back pressure. It is most effective to use
Fishbone type plate heat exchanger for ATEG system which give high power output of module than
heat exchanger without internal structure.
References
[1] Khalid Mohammad Mohiee El Dein Mansour Saqr “Design and Simulation of An Exhaust Based
Thermoelectric Generator (Teg) for Waste Heat Recovery in Passenger Vehicles” pp 2-6, 14-23
(2008)
[2] Andrew P. Freedman, “A Thermoelectric Generation Subsystem Model for Heat Recovery
Simulations”, pp 13-16, 24 ,31, 93-101,M.S. Thesis, Rochester Institute of Technology (2011)
[3] Chaung Yu, K.T. Chau, “Thermoelectric Automotive Waste Heat Energy Recovery Using
Maximum Power Point Tracking,” Journal of Energy Conversion And Management (2009)
[4] Jorge Vazquez, Miguel A. Sanz-bobi, Rafael Palacios, Anteneo Arenas, “State of the Art of
Thermoelectric Generators Based on Heat Recovered From The Exhaust Gases of Automobiles,”
Universidad Pontificia Comillas, Spain (2008)
[5] Francis Stabler “Automotive Thermoelectric Generator Design Issues,” DOE Thermoelectric
Applications Workshop.
[6] C. Ramesh Kumar, Ankit Sonthalia, Rahul Goel, “‘Experimental Study on Waste Heat Recovery
from An Internal Combustion Engine Using Thermoelectric Technology” Center of Excellence for
Automotive Research, VIT University, Vellore, India (2011)
[7] K. M. Saqr1, M. K. Mansour and M. N.Musa, “Thermal Design of Automobile Exhaust Based
Thermoelectric Generators: Objectives And Challenges,” International Journal Of Automotive
Technology (2007)
[8] V Ganesan, “Internal Combustion Engines,” pp 576, Third Edition, pub.-Tata McGraw-hill (2009)
[9] R K Rajput, “Heat and Mass Transfer,” Third Edition, pub.-Tata McGraw-hill (2009)
Sonawane K.R & Prof. Ghuge N.C ,” Hydrogen (H2) Fuelled I.C. Engine-An Overview”
International Journal Of Informative & Futuristic Research , Vol.2(3) ,Paper ID:IJIFR/ V2/ E3/ 023
Page No. 580- 586 .