Download Full-Text PDF

inventions
Article
Design, Manufacture and Performance Test of the
Thermoelectric Generator System for Waste Heat
Recovery of Engine Exhaust
Tzer-Ming Jeng † , Sheng-Chung Tzeng *,† , Bo-Jun Yang and Yi-Chun Li
Received: 26 November 2015; Accepted: 5 January 2016; Published: 11 January 2016
Academic Editor: Chien-Hung Liu
Department of Mechanical Engineering, Chienkuo Technology University, Changhua City 500, Taiwan;
[email protected] (T.-M.J.); [email protected] (B.-J.Y.); [email protected] (Y.-C.L.)
* Correspondence: [email protected]; Tel.: +886-4-711-1111 (ext. 3190); Fax: +886-4-713-5677
† These authors contributed equally to this work.
Abstract: This study integrated the techniques of the high-performance heat transfer and
thermoelectric conversion to build a thermoelectric generator system installed at the exhaust pipe of a
real single-cylinder and four-stroke engine of 35.8 c.c. displacement. This system was made of the heat
absorber, thermoelectric generator modules and the external heat sink. The pin-fin array was inserted
into the circuitous duct to form the heat absorber, which could increase the heat-exchange surface
area and the heat-exchange time to reach the object of absorbing heat and increasing thermoelectric
conversion effectively.
Keywords: heat recovery; thermoelectric generator system; heat absorber of pin-fin array
1. Introduction
Thermoelectric conversion was discovered towards the end of the 19th century. Electrons are
capable of carrying heat, as well as electricity. When a temperature difference exists between the two
end faces of a thermoelectric material, many electrons will travel from the hot end face to the cold
one. This phenomenon is known as the Seebeck effect and forms the basis on which the thermoelectric
generation module was developed. As we are all aware, the global energy crisis is becoming worse
and much emphasis is being placed on environment protection and the recovery of energy resources.
These include waste heat from cooling water, exhaust gas, and steam power plants, amongst others.
TEG modules are light and silent, have no moving parts and can convert recycled heat directly
into electricity.
Champier et al. [1] pointed out that developing countries are currently using massive bio-fuel
furnaces to mitigate global warming. The efficiency of these bio-fuel furnaces has been significantly
improved in laboratory prototypes which give better combustion efficiency and produce less pollution.
TEGs have been installed in them and the electricity generated can be used for lighting or to power
circulation fans to improve the fuel-air ratio which, in turn, results in more complete combustion.
Experiments were first carried out to verify the thermoelectric conversion ratio of a Bi2 Te3 TEG module
and then the feasibility of combining the TEG module with a bio-fuel furnace and determination of the
optimal position for installation was studied. Finally it was demonstrated that 6 W could be generated
by thermoelectric conversion. Karri et al. [2] studied the efficiency of waste heat electricity generation
using thermoelectric conversion in two practical cases: a sport utility vehicle (SUV) and a compressed
natural gas (CNG)-fueled generator engine. Two different thermoelectric modules (available on the
market) were used: (1) bismuth telluride (Bi2 Te3 ), and (2) quantum-well (QW) device. Tests of the
CNG engine and the SUV under the same conditions and the same generated AC output, showed the
Inventions 2016, 1, 2; doi:10.3390/inventions1010002
www.mdpi.com/journal/inventions
Inventions 2016, 1, 2
2 of 16
QW device to be more efficient than the Bi2 Te3 TEG. In other words, more electricity was generated
from the same amount of heat and more fuel was saved. Zhou et al. [3] pointed out that because
water is a good heat conductor, combining commercial water heaters with thermoelectric modules
in a thermoelectric conversion generator system was a good idea. They employed Carnot efficiency
and the Coupled Physical Energy Balance Method that combines Joule heating, with the Seebeck,
Peltier, and Thomson effects to predict the efficiency of a thermoelectric conversion generator system.
Thirty different configurations involving a number of parameters were investigated, these included:
the water flow model, hot water inlet temperature, pressure drop, cross-sectional area of the duct, duct
length, the number of ducts, and so on. Systematic analysis showed that the upper modules would
rival the upstream module in heat absorption, resulting in a lower temperature difference between the
two faces of the thermoelectric module. They also pointed out that reducing coverage by modules
in the downstream of an exhaust duct might result in its wall temperature being higher than the
temperature of the hot-face of the upstream modules, which offers an opportunity to maximize overall
power generation. Wang and Huang [4] investigated the conversion of vehicle engine exhaust heat to
electrical power using thermoelectric generator modules. They employed numerical simulation to
analyze multiple thermoelectric modules attached to heat exchanger surfaces in a series arrangement.
They found that using more modules did not necessarily generate more power, and that the average
generation ratio of each module actually decreased as the number of modules rose. The reason
for this was that the temperature of the exhaust duct wall decreased rapidly along the direction of
flow and this resulted in poor performance by the downstream TEGs. Jang and Tsai [5] considered
attaching multiple TEG modules on stacked wall faces and found the amount of unit area generation
was strongly affected by the spacing of the modules. Their thermoelectric generator configuration
consisted of thermal plates (a stack wall), heat distribution plates, TEG modules, and water-cooled
cooling plates. They used limited element analysis to simulate the overall thermoelectric conversion
of the modules with different spacing and also with different thickness of heat distribution plates.
The variable operation parameters included the temperature difference between the hot exhaust gas
and the cooling water (∆T = 200–800 K) and heat conductance coefficient of the heat distribution plate
(h = 20–80 W/m2 /K). The aim of the simulation was determination of the optimal spacing between
modules and the ideal thickness of heat distribution plates that gave the maximum generation per
unit area. It has become clear that as the conversion efficiency of TEG material has increased so has
the attention being paid to studies and applications involving combinations of TEG modules and
waste heat sources from both domestic and industrial activity. These include heat from vehicle engine
exhausts, cooling water circulation systems in vehicle engines, generators using internal combustion
engines, waste heat gas stacks, bio-fuel furnaces, ground heat from hot springs, etc. These many heat
sources can provide suitable environments for thermoelectric modules that generate power using
differential temperatures. With proper cooling, the temperature difference between the cold and hot
sides of TEG modules can be raised to achieve ideal power generation.
Many current studies have addressed waste heat recovery from engines using TEG devices and
many have claimed patents. Most studies on thermoelectric generation by the recovery of engine
waste heat emphasize integrated thermo-electric conversion devices and performance simulations
involving vehicle systems. A patent filed by Cumming [6] claimed that power can be generated and
saved in batteries using a thermoelectric semi-conductor installed on the outside of an engine exhaust
pipe used for driving a hybrid vehicle. A patent filed by Handa and Nagoya [7] involved the adding of
an insulator on both the heated and cooled faces of a TEG module to widen the temperature difference
between the faces and give better generation efficiency. Shinohara et al. [8] invented an electronic
power supply control system that utilizes a thermoelectric device to generate electric power from
exhaust gas as a secondary system generator. After a summary of applications, Rowe [9] pointed out
that thermoelectric conversion systems using temperatures above 140 ˝ C are commercially competitive.
Hendricks and Lustbader [10] analyzed systems using waste heat thermoelectric conversion systems
on medium and high power vehicles and found that they were capable of generating 5–6 kW power.
Inventions 2016, 1, 2
3 of 16
However, there are three technical impediments to the achievement of a high-performance system:
the thermoelectric conversion system itself, optimal integration with the vehicle, and design of the
thermoelectric interface. A study team at the Ohio State University accomplished waste heat recovery
using a thallium-doped lead telluride thermoelectric module [11], which characterizes a thermoelectric
effect. Heating up one end of the material will cause the electrons to move to the colder end, therefore
generating electrical current. If used on vehicles, waste heat from the vehicle can be converted into
electricity and fed back to the vehicle for re-use. Jeng et al. [12] investigated the performance of a
heat absorber made of packed brass beads in a thermoelectric conversion system. This packed bead
heat absorber was installed in a square channel and various flow orientations, both straight and jet,
were investigated as well as the ratio of channel width to bead diameter. Their studies showed the
local and average heat transfer characteristics for several parameters and can be used as a basis for the
design of a novel porous heat absorber for thermoelectric conversion systems.
This study establishes an initial performance test platform for thermoelectric modules, examines
the relationships between the external load resistance and the output voltage/current of the TEG
and investigates the influence of temperature difference between the hot and cold faces and their
average against maximum power generation. Using high-temperature exhaust gas from an actual
35.8 c.c. engine as the heat source and a patent applied for by the authors [13] as the blueprint,
a complete thermoelectric conversion system (including heat absorber, thermoelectric generation
module and heat sink) was constructed. The experiments were conducted under controlled laboratory
conditions and careful measurements of the displacement of the engine, operation speed, temperature,
and composition of the high temperature exhaust gas were made. The effects of the installation position
of the thermoelectric conversion system and the corresponding external cooling airflow were studied
and the results may be used as important references for the future design of vehicle thermoelectric
conversion systems.
2. Experimental Method
2.1. Design of Waste Heat Recovery Thermoelectric Conversion System
A thermoelectric conversion system normally consists of heat absorbers, TEG modules, and heat
sinks, where heat absorbers function as heat collectors to heat up the TEG, and the heat sink functions
to dissipate heat from the cold end of the TEG module as rapidly and efficiently as possible to widen
the temperature difference between the hot and cold faces, to enhance performance of the TEG module.
The thermoelectric conversion heat recovery device constructed for this study is illustrated in Figure 1.
The pin-fin heat absorber is situated inside the duct and the exhaust gases are guided along a circuitous
path from the inlet across them as can be seen in Figure 1. The absorbed heat is conducted to the hot
face of the TEG modules which are bolted to the surface of the heat absorbers. The exhaust gases
are forced past the pin-finned heat absorbers and the resulting turbulence enhances heat exchange
between the hot exhaust gases and the extensive surface of the heat exchangers. The device also
acts as a silencer and reduces the noise of the engine. The parts are anodized to protect them from
corrosion and this also improves their aesthetic appearance. The fin pins are all the same length and
make contact with the baffle box in the center of the chamber. This arrangement guides the flow so
that it is impossible for the exhaust gasses to get to the outlet without the development of turbulence
and close contact with the large heat exchange surfaces on all four sides of the chamber, see Figure 1.
The bases of the finned heat exchange units are fastened to the body of the device with machine screws.
The TEG modules are clamped between the top of the heat exchangers and the cooling heat sinks,
also with machine screws. This arrangement effectively stays the hot waste gas and achieves massive
heat exchange. Figure 1 also shows an assembled heat exchange device with one heat exchanger block,
TEG and cooling fin assembly removed for clarity. In use, the outer housing has four heat exchange
blocks bolted to it and the ends of the heater exchange pins make contact with the central baffle box
which acts to guide the hot gasses on the proper path across all the heat exchange surfaces to the outlet.
Inventions 2016, 1, 2
4 of 16
All the components, the heat absorbers, heat sinks, aluminum housing, and central baffle, are made of
aluminum
alloy
Inventions 2016,
1, 2and have been anodized.
4 of 16
Inventions 2016, 1, 2
4 of 16
(a)
(b)
Figure 1. The thermoelectric conversion
device used herein. (a) Cross-sectional
view; (b) Photo of
(a)
(b)
Figure
1. The thermoelectric conversion
device used herein. (a) Cross-sectional
view; (b) Photo
prototype.
of prototype.
Figure 1. The thermoelectric conversion device used herein. (a) Cross-sectional view; (b) Photo of
prototype.
2.2. Generation Performance Test of a Single-Chip TEG Module
2.2. Generation Performance Test of a Single-Chip TEG Module
2.2.
Performance
a Single-Chipperformance
TEG Module test of a single chip TEG module was
TheGeneration
experimental
setupTest
forof generation
The experimental setup for generation performance test of a single chip TEG module was shown
shown inThe
Figure
2. The setup
(1) an air
supply system,
a TEGchip
module,
a testwas
section
experimental
setupincludes
for generation
performance
test of(2)
a single
TEG (3)
module
in Figure 2. The setup includes (1) an air supply system; (2) a TEG module; (3) a test section (heating
(heating
and
cooling2. devices,
(4) the(1)data
acquisition
equipment.
The
air supply
shown
in Figure
The setupand
includes
an air
supply system,
(2) a TEG
module,
(3) a for
test cooling
section the
and cooling
devices);
anddevices,
(4) theand
data(4)acquisition
equipment.
The air The
supply
for cooling
the cold
side
cooling
the data
equipment.
air supply for
the in
cold(heating
side of and
the TEG
module was
provided
byacquisition
an air compressor.
The compressed
aircooling
was stored
of thecold
TEG
module
was
provided
by
an
air
compressor.
The
compressed
air
was
stored
in
an
800
TEG module
by an
air compressor.
Thewas
compressed
air was stored
in andL
an 800 Lside
tankoftothe
ensure
a steadywas
andprovided
pulse-free
supply.
The air flow
passed through
a dryer
tank
to
ensure
a
steady
and
pulse-free
supply.
The
air
flow
was
passed
through
a
dryer
and
filter
to
L tankwater
to ensure
steady and pulse-free
supply. The
air flow (SIN-DP)
was passed
through
and the
filteranto800
remove
anda impurities
and an electronic
controller
was
used atodryer
regulate
remove
water
and
impurities
and
electronic
controller
(SIN-DP)
was
used
to regulate
the the
air
flow
filter
to remove
water
andto
impurities
and device
an electronic
(SIN-DP)
was rates
used
to
air flow
which
was
guided
thean
cooling
of thecontroller
test
section.
Air flow
ofregulate
350–450
L/min
airwas
flow
which to
was
guided
to the
cooling
device
of
the testAir
section.
Air
flow
rates of 350–450
L/min
which
guided
the
cooling
device
of
the
test
section.
flow
rates
of
350–450
L/min
were
used
were used for cooling the heat sink of cooling device, and then the temperature differences between
were used
for
cooling
thecooling
heat sink
of cooling
and
then the temperature
differences
for
the
heat
sinkofof
device,
and device,
then
the
temperature
differences
betweenbetween
the hot and
thecooling
hot and
cold
faces
the TEG module
were
controlled
to be 80, 100
and 120 °C.
˝
the
hot
and
cold
faces
of
the
TEG
module
were
controlled
to
be
80,
100
and
120
°C.
cold faces of the TEG module were controlled to be 80, 100 and 120 C.
Figure 2. Experimental setup for the single-chip thermoelectric module experiment.
Figure 2. Experimental setup for the single-chip thermoelectric module experiment.
Figure 2. Experimental setup for the single-chip thermoelectric module experiment.
As shown in Figure 3, the TEG used in this experiment was manufactured by Russian Kryotherm
As
ininFigure
TEG
in
was
manufactured
by Russian
Russian
Kryotherm
(Model:
TGM-287-1.0-1.5;
dimensions:
mm
×experiment
40 mm × 3.8
mm).
Figure 4 shows
the present
test
Asshown
shown
Figure3,3,the
the
TEGused
used40
inthis
thisexperiment
was
manufactured
by
Kryotherm
section.
In
this
experiment,
the
hot
side
of
the
TEG
module
was
fastened
to
the
heater
using
thermal
(Model:
TGM-287-1.0-1.5;
dimensions:
40
mm
ˆ
40
mm
ˆ
3.8
mm).
Figure
4
shows
the
present
(Model: TGM-287-1.0-1.5; dimensions: 40 mm × 40 mm × 3.8 mm). Figure 4 shows the present
test
grease.
The
heater
was
made
of
Bakelite
(85
mm
×
85
mm
×
65
mm)
with
a
stainless
steel
heating
test
section.
In this
experiment,
theside
hotofside
themodule
TEG module
was fastened
to theusing
heater
using
section.
In this
experiment,
the hot
the of
TEG
was fastened
to the heater
thermal
element (40 The
mm heater
× 40 mm)
was of
powered
by a DC
power
supply.
The
coldwith
side aofstainless
the TEG steel
thermal
wasand
Bakelite
ˆ ×8565mm
ˆ with
65
mm)
grease. grease.
The heater was
made
ofmade
Bakelite
(85 mm(85
× 85mm
mm
mm)
a stainless
steel heating
module was fastened by thermal grease to an aluminum alloy heat sink with an array of round pin
heating
element
(40×mm
ˆ 40 mm)
and powered
was powered
a DC
power
supply.
The
coldside
sideofofthe
theTEG
TEG
element
(40 mm
40 mm)
and was
by aby
DC
power
supply.
The
cold
fins (see Figure 5). The heat sink, with an acrylic duct and cool air source, formed the cooling device
module
was fastened
by
thermal
grease to
with an
an array
array of
of round
roundpin
pin
module
fastened
byof
thermal
toan
an aluminum
aluminum alloy heat sink with
used was
for the
cold side
the TEGgrease
module.
fins (see Figure 5). The heat sink, with an acrylic duct and cool air source, formed the cooling device
used for the cold side of the TEG module.
Inventions 2016, 1, 2
5 of 16
fins (see Figure 5). The heat sink, with an acrylic duct and cool air source, formed the cooling device
1, 2
5 of 16
usedInventions
for the 2016,
cold
of the TEG module.
Inventions
2016, 1,side
2
5 of 16
Inventions 2016, 1, 2
5 of 16
Figure
3. Photo
TEGmodule.
module. (Russian Kryotherm:
TGM-287-1.0-1.5).
Figure
3. Photo
ofof
TEG
Kryotherm:
TGM-287-1.0-1.5).
Figure
3. Photo
of
TEG module.(Russian
(Russian Kryotherm:
TGM-287-1.0-1.5).
Figure 3. Photo of TEG module. (Russian Kryotherm: TGM-287-1.0-1.5).
Figure4.4.Exploded
Exploded view ofoftest
Figure
testsection.
section.
Figure 4. Exploded view
view of test
section.
Figure 4. Exploded view of test section.
Figure 5. Configuration and dimensions of heat sink for cooling device. (Unit: mm).
Figure
5. Configuration
and dimensionsof
of heat
heat sink
for
cooling
device.
(Unit:
mm).
Figure
5. Configuration
and
sinkfor
forcooling
cooling
device.
(Unit:
Figure
5. Configuration
anddimensions
dimensions heat
sink
device.
(Unit:
mm).mm).
Inventions 2016, 1, 2
6 of 16
TT-T-30SLE T-Type thermocouples were embedded in the center of both the cold and hot faces of
TEG module. Differential potential signals were retrieved by a YOKOGAWA MX-100 data recorder
and converted into temperature readings. The TEG was connected to an external resistor load and the
output voltage was measured by a multi-meter in parallel with the circuit. Power generated by the
TEG module can be calculated using the voltage and resistor values. All data readings for computer
processing were made at thermal equilibrium condition, when temperature fluctuation was less than
0.2 ˝ C over 15 min.
The main target parameter of the experiment was generated power (P) which was measured using
voltage values with resistors of different values connected in series to the external circuit. The formula
for the calculation of TEG power generation is:
P “ V 2 {R
(1)
where V stands for voltage, R for load resistance.
2.3. Generation Performance Test of the Thermoelectric Conversion System for a Real Engine
This experiment investigated power generation by a TEG system installed on the exhaust pipe
of a 38.5 c.c. four-stroke engine. Figure 6 shows the layout used in this experiment, the equipment
used includes (1) the engine; (2) the TEG conversion system; (3) an external air source (fan); and (4) the
data acquisition system. The high-temperature exhaust gases from engine operation were guided
through the thermoelectric conversion device in a way that ensures that maximum heat exchange took
place. The thermoelectric conversion system, as shown in Figure 7, includes (1) the heat absorber;
(2) the TEG modules; (3) the heat sinks; (4) the aluminum-alloy duct and other fittings. As the engine
exhaust gases flowed through the duct, the internal heat absorber of pin-fin arrays conveyed heat
rapidly to their external surface to which the TEG modules were fixed by machine screws and thermal
grease. The other side (cold side) of each TEG was fastened in the same way to an outer heat sink.
The substantial temperature difference between heat absorber and heat sink resulted in the efficient
conversion of thermal energy into electricity. Figure 8 shows the assembled thermoelectric conversion
system, an exploded diagram of the components, and the dimensions of the aluminum alloy duct.
The heat absorber was made of 6061 aluminum alloy, and the configuration is shown in Figure 9.
The heat sinks were made by extrusion from 6061 aluminum alloy and had evenly spaced rows
of pin fins on the surface as shown in Figure 10. The four TEG modules used on the device were
connected in series. The thermal grease was applied to the contact surfaces to ensure good heat
conduction between the TEG surfaces and the heat absorber as well as heat sink. A fan drove air
across the front of the engine, to simulate the oncoming air flow of a moving vehicle, and cooled the
thermoelectric conversion system. The data acquisition system monitored and recorded the relevant
temperatures, rotation speed, air flow rate, and the voltage and power outputs in real time. A K-type
thermocouple was located at the inlet and outlet of the aluminum-alloy duct with built-in heat absorber.
Thermocouples were also embedded between the TEG modules and heat-absorber plates as well as the
TEG modules and the heat sinks. A one-point T-type thermocouple was embedded at the fan outlet.
Measurements of the voltage generated by the TEGs were monitored by a micro-voltmeter in real time.
The output of the thermocouples was measured through a data recorder and sent to the PC for real
time analysis and recording. The speed of cooling air delivered by the fan was measured at the fan
outlet and downstream of the test section using the airflow meter. The mean velocity (U) of air passing
through the heat sink was estimated based on the average value of the air speeds measured at these
two positions. Engine rotation speed, controlled by the throttle valve, was measured by a tachometer.
The accuracy of measurements made during engineering tests of this kind is always affected by
unpredictable factors. These may be physical and connected with the equipment, or may be caused
by the environment. Inaccuracy of some degree is inevitable in all engineering measurements and
control. Once encountered, steps can be taken to reduce the sources of error and predictions can be
Inventions 2016, 1, 2
7 of 16
made of the likelihood of future occurrence. Measures can be taken to reduce and control inaccuracy
of measurements
test procedures to eliminate the source, or at least reduce the degree
of1616error.
Inventions
7 7ofof
Inventions2016,
2016,1,during
1,2 2
The effects of inaccuracy in measurement should be estimated in advance, before the collection of data,
error.
ininexperimental
measurement
before
the
error. The
The effects
effects
of inaccuracy
inaccuracy
measurement should
should be
be estimated
estimated
advance,
before
the
and modifications
can of
be
made
to the
conditions
to
reduceinin
oradvance,
eliminate
the problem.
collection
of
data,
and
modifications
can
be
made
to
the
experimental
conditions
to
reduce
oror
collection
ofto
data,
and modifications
caninclude
be made
to the
experimentaland
conditions
to reduce
The likely
errors
be found
in test results
both
measurement
calculation
parameters.
eliminate
problem. The
errors
be
inintest
include both
and
eliminatethe
the
Thelikely
likely
errorstotocan
befound
found
testresults
results
bothmeasurement
measurement
The uncertainty
of problem.
measurement
parameter
be
attributed
to theinclude
instrument
system itself and
and/or
calculation
parameters.
The
uncertainty
of
measurement
parameter
can
be
attributed
to
calculation parameters. The uncertainty of measurement parameter can be attributed to the
the
human
error,
and
the
uncertainty
of
calculation
parameters
results
from
both
parameters.
We
used
instrument
instrumentsystem
systemitself
itselfand/or
and/orhuman
humanerror,
error,and
andthe
theuncertainty
uncertaintyofofcalculation
calculationparameters
parametersresults
results
Moffat’s
[14] uncertainty
analysis
to assess[14]
our experiment
and the uncertainty
of power generation
from
fromboth
bothparameters.
parameters.We
Weused
usedMoffat’s
Moffat’s [14]uncertainty
uncertaintyanalysis
analysistotoassess
assessour
ourexperiment
experimentand
andthe
the
(P) was
determined
to
be
˘2.1%.
uncertainty
uncertaintyofofpower
powergeneration
generation(P)
(P)was
wasdetermined
determinedtotobe
be±2.1%.
±2.1%.
(a)
(a)
(b)
(b)
Figure
6.6.The
experimental
setup
system
installed
atataareal
Figure
The
experimentalsetup
setupof
ofthermoelectric
thermoelectricconversion
conversion
system
installed
real
engine.
(a)
Figure
6. The
experimental
of
thermoelectric
conversion
system
installed
atengine.
a real (a)
engine.
(b)
The
4-stroke
engine
and
the
waste
heat
recovery
Layout
ofofthe
experimental
equipment;
and
(b)
The
4-stroke
engine
and
the
waste
heat
recovery
Layout
the
experimental
equipment;
and
(a) Layout of the experimental equipment; and (b) The 4-stroke engine and the waste heat
device.
device.
recovery
device.
Figure
the
thermoelectric
Figure
7.Diagram
Diagram
thethermoelectric
thermoelectricconversion
conversionsystem.
system.
Figure
7. 7.
Diagram
ofofof
the
conversion
system.
Inventions 2016, 1, 2
8 of 16
Inventions 2016, 1, 2
8 of 16
Inventions 2016, 1, 2
8 of 16
(a)
(b)
(a)
(b)
(c)
(c)
Figure 8. Configuration and dimensions of thermoelectric
conversion system. (Unit: mm). (a) The
Figure 8. Configuration and dimensions of thermoelectric conversion system. (Unit: mm). (a) The
assembled
thermoelectric
conversion
device;
(b)
Exploded conversion
view of thesystem.
thermoelectric
conversion
Figure 8. Configuration and dimensions of thermoelectric
(Unit: mm).
(a) The
assembled thermoelectric conversion device; (b) Exploded view of the
thermoelectric
conversion
device;
(c)
Configuration
and
dimensions
of
aluminum-alloy
duct.
assembled thermoelectric conversion device; (b) Exploded view of the thermoelectric conversion
device; (c) Configuration and dimensions of aluminum-alloy duct.
device; (c) Configuration and dimensions of aluminum-alloy duct.
Figure 9. Pin-fin array used in heat absorber. (Unit: mm).
Figure
9. Pin-fin
arrayused
usedin
in heat
heat absorber.
Figure
9. Pin-fin
array
absorber.(Unit:
(Unit:mm).
mm).
Inventions 2016, 1, 2
Inventions 2016, 1, 2
9 of 16
9 of 16
Figure 10.
10. Pin-fin
Pin-fin array
array used
used in
in heat
heat sink.
sink. (Unit:
(Unit: mm).
Figure
mm).
3. Results
3.
Resultsand
andDiscussions
Discussions
3.1. Generation
TEG
3.1.
Generation Results
Results of
of Single-Chip
Single-Chip TEG
Figure 11
11 shows
shows relationship
relationship between
between external
Figure
external load
load resistor
resistor (R)
(R) and
and TEG
TEG output
output voltage
voltage (V).
(V).
The results
temperature
difference
between
hot and
the TEG
is TEG
ΔT = Tish
The
results show
showthat
thatwhen
when
temperature
difference
between
hot cold
and faces
cold of
faces
of the
− Tc,=a T
larger
load resistor (R) corresponds to a greater TEG output voltage (V). TEG voltage resulting
∆T
h ´ Tc , a larger load resistor (R) corresponds to a greater TEG output voltage (V). TEG
from Seebeck
effect
is Seebeck
the product
ofisSeebeck
coefficient
multiplied
by ΔT.
Therefore,
of
voltage
resulting
from
effect
the product
of Seebeck
coefficient
multiplied
by an
∆T.increase
Therefore,
the
external
load
resistor
(R)
may
also
increase
the
Seebeck
coefficient
of
the
TEG.
Figure
12
shows
an increase of the external load resistor (R) may also increase the Seebeck coefficient of the TEG.
the relationship
between
TEG output
voltage
(V) andvoltage
output(V)
current
(I). When
ΔT is
Figure
12 shows the
relationship
between
TEG output
and output
current
(I).constant,
When ∆Tthe
is
output current
(I) has
an almost
linear
tendency
to decrease
with TEG
voltage
(V). The
constant,
the output
current
(I) has an
almost
linear tendency
to decrease
withoutput
TEG output
voltage
(V).
relationship
between
the the
TEGTEG
generation
power
(P)(P)
and
external
load
The
relationship
between
generation
power
and
external
loadresistor
resistor(R)
(R)(see
(seeFigure
Figure 13)
13)
shows that,
that, at
at the
the load
load range
rangeof
of2–20
2–20Ω,
Ω,the
themaximum
maximumTEG
TEGgeneration
generation power
power output
output (P)
(P) is
is achieved
achieved
shows
when RR==6.8
6.8Ω.
Ω.Based
Basedonon
maximum
power
transfer
theory,
the maximum
conversion
when
thethe
maximum
power
transfer
theory,
the maximum
powerpower
conversion
occurs
occurs
when
the
external
load
resistor
(R)
equals
the
internal
resistance
(r).
The
internal
resistance
of
when the external load resistor (R) equals the internal resistance (r). The internal resistance of the TEG
the TEG(TGM-287-1.0-1.5
module (TGM-287-1.0-1.5
KRYOTHERM)
about
7 Ω,with
which
present
module
KRYOTHERM)
is about 7 Ω, is
which
agrees
the agrees
present with
result.the
Figures
14
result.
Figures
14
and
15
show
the
relationships
between
TEG
output
voltage
(V)
and
TEG
and 15 show the relationships between TEG output voltage (V) and TEG generation Power (P), as well
generation
Power
(P), (V)
as well
as TEG output
voltage
and
generation
efficiency
(η). The
results
as
TEG output
voltage
and generation
efficiency
(η).(V)
The
results
show that
there exists
an optimal
show that
there that
exists
an yield
optimal
voltage
that will power
yield the
generation
power
(P)
output
voltage
will
theoutput
maximum
generation
(P)maximum
and efficiency
(η); this
voltage
and
efficiency
(η);
this
voltage
corresponds
to
an
external
load
resistance
of
6.8
Ω,
which
is
closest
to
corresponds to an external load resistance of 6.8 Ω, which is closest to the internal resistance of the
the internal
of the
selected
TEG.WAwas
maximum
W was achieved
the
selected
TEG.resistance
A maximum
output
of 2.716
achievedoutput
when of
the2.716
temperature
differencewhen
between
temperature
difference
between
the ∆T
hot=and
cold
TEG
ΔT = generation
Th − Tc = 120
°C, where
the
hot and cold
faces of the
TEG was
Th ´
Tc =faces
120 ˝of
C,the
where
thewas
optimal
efficiency
(η)
the
optimal
generation
efficiency
(η)
is
3.61%.
Figure
16
shows
the
relationship
between
temperature
is 3.61%. Figure 16 shows the relationship between temperature difference (∆T = Th ´ Tc ) and optimal
difference (ΔT
= Th(P
−max
Tc))and
optimal
generation
power (P
) when
the average
ofalso
the
generation
power
when
the average
temperature
ofmax
the
TEG was
89–117 ˝temperature
C. This figure
TEG
was
89–117
°C.
This
figure
also
shows
that
maximum
power
(P
max
)
increases
as
the
temperature
shows that maximum power (Pmax ) increases as the temperature difference between the hot and cold
difference
thethe
hot
and cold
of the
TEG rises;difference
the reason
is that the
a larger
temperature
faces
of thebetween
TEG rises;
reason
is thatfaces
a larger
temperature
between
hot and
cold faces
difference
between
hot and
results
in voltage.
higher heat
rate and
results
in higher
heatthe
transfer
ratecold
andfaces
output
electric
Aftertransfer
summarizing
all output
the test electric
results,
voltage.
After
summarizing
all
the
test
results,
we
could
write
a
correlation
regarding
maximum
we could write a correlation regarding maximum generation power (Pmax ) and temperature difference
generation
power
(Pmax) and temperature difference (ΔT = Th − Tc) between the hot2 and cold faces of
(∆T
= Th ´ T
c ) between the hot and cold faces of the TEG: Pmax “ 0.0002 ˆ pTh ´ Tc q . Figure 17 shows
the relationship
TEG: Pmax between
. Figure 17 difference
shows the(∆T
relationship
between
the
= Th ´ Tc ) and
V/(Ththe
´ Tcaverage
) when
(Thaverage
= 0.0002 ×
− Tc ) 2 temperature
˝
∆T
=
T
´
T
=
80–120
C.
This
figure
shows
that
the
difference
of
the
Seebeck
coefficient
(S
´ SA)
c
B
h
temperature difference (ΔT = Th − Tc) and V/(Th − Tc) when ΔT = Th − Tc = 80–120 °C. This figure shows
of
the
TEG
decreases
with
its
average
temperature
((T
´
T
)/2).
This
must
be
caused
by
the
smaller
that the difference of the Seebeck coefficient (SB −h SA) cof the TEG decreases with its average
difference
of ((T
theh TEG
Seebeck
) when
its average
temperature
also
B ´ SA
temperature
− Tc)/2).
Thiscoefficient
must be (S
caused
by
the smaller
difference
of the rises.
TEG We
Seebeck
arrived
at
a
correlation
regarding
the
(S
´
S
)
of
the
single-chip
TEG
used
in
the
experiment
and
B
A
coefficient (SB − SA) when its average temperature
rises. We also arrived at a correlation regarding
´0.142
q
{2s
the
average
temperature
of
the
hot
and
cold
faces:
S
´
S
“
0.0708
ˆ
rpT
`
T
,
within
the
c
B
A and the average
h
the (SB − SA) of the single-chip TEG used in the experiment
temperature
of the hot
current
range
of test
(SB ´ the
S A ) current
is seen, at
an approximately
constanta
and cold
faces:
S B −temperature,
S A = 0.0708 × a(minor
Th + Tc )variation
/ 2  −0.142 ,ofwithin
range
of test temperature,
value of 0.0368.
minor variation of (SB − SA) is seen, at an approximately constant value of 0.0368.
Inventions 2016, 1, 2
10 of 16
Inventions 2016, 1, 2
Inventions 2016, 1, 2
Inventions 2016, 1, 2
10 of 16
10 of 16
10 of 16
Figure 11. External resistance (R) vs. TEG output voltage (V).
Figure
11.11.External
vs. TEG
TEGoutput
outputvoltage
voltage
(V).
Figure
Externalresistance
resistance (R)
(R) vs.
(V).
Figure 11. External resistance (R) vs. TEG output voltage (V).
Figure 12. TEG output voltage (V) vs output current (I).
Figure 12. TEG output voltage (V) vs output current (I).
Figure
12.12.TEG
vs.output
output
current
Figure
TEGoutput
outputvoltage
voltage (V)
(V) vs
current
(I).(I).
Figure 13. External load resistance (R) vs. TEG power generation (P).
Figure 13. External load resistance (R) vs. TEG power generation (P).
Figure 13. External load resistance (R) vs. TEG power generation (P).
Figure 13. External load resistance (R) vs. TEG power generation (P).
Inventions 2016, 1, 2
11 of 16
Inventions 2016, 1, 2
Inventions 2016, 1, 2
Inventions 2016, 1, 2
11 of 16
11 of 16
11 of 16
Figure 14. TEG output voltage (V) vs. generation power (P).
Figure
14.14.TEG
vs.generation
generationpower
power
Figure
TEGoutput
outputvoltage
voltage (V)
(V) vs.
(P).(P).
Figure 14. TEG output voltage (V) vs. generation power (P).
Figure 15. TEG output voltage (V) vs. generation efficiency (η).
Figure 15. TEG output voltage (V) vs. generation efficiency (η).
Figure
15.15.
TEG
vs.generation
generationefficiency
efficiency
Figure
TEGoutput
outputvoltage
voltage (V)
(V) vs.
(η).(η).
Figure 16. Temperature difference between TEG hot/cold faces (Th − Tc) vs. maximum generation power (Pmax).
Figure 16. Temperature difference between TEG hot/cold faces (Th − Tc) vs. maximum generation power (Pmax).
Figure 16. Temperature difference between TEG hot/cold faces (Th − Tc) vs. maximum generation power (Pmax).
Figure 16. Temperature difference between TEG hot/cold faces (Th ´ Tc ) vs. maximum generation
power (Pmax ).
Inventions 2016, 1, 2
Inventions 2016, 1, 2
12 of 16
12 of 16
Figure 17. Average TEG temperature (Th − Tc)/2 vs. Seebeck-coefficient difference V/(Th − Tc).
Figure 17. Average TEG temperature (Th ´ Tc )/2 vs. Seebeck-coefficient difference V/(Th ´ Tc ).
3.2. Generation Results of Thermoelectric Conversion System on a Real Engine
3.2. Generation Results of Thermoelectric Conversion System on a Real Engine
Based on the power transfer theory, the resistance of the load must equal the internal resistance
on thesource
powerfor
transfer
theory,
thetransference
resistance of
equalathe
internal
resistance
ofBased
the voltage
maximum
power
tothe
the load
load.must
Therefore,
variable
resistance
of the
voltage
for maximum
poweroftransference
to thethe
load.
Therefore,
variable
resistance
load
systemsource
was connected
to the output
the TEG to adjust
resistance
of theaload.
The output
voltage
different
loads
was
recorded.
loadcurrent
systemand
wasoutput
connected
to under
the output
of the
TEG
to measured
adjust theand
resistance
of We
the calculated
load. The the
output
maximum
power voltage
under different
andloads
foundwas
that measured
the load resistance
that gaveWe
thecalculated
maximum the
current
and output
under loads,
different
and recorded.
power complied
with the
internalloads,
resistance
the TEG
was
taken as the
maximum
power under
different
and of
found
thatand
thethis
load
resistance
thatmaximum
gave thepower.
maximum
The
main
target
parameter
of
the
experiment
was
generation
power
(P).
The variable
power complied with the internal resistance of the TEG and this was taken as the maximum
power.
parameters included engine rotation speed (Ω [rpm]) and mean velocity (U) of air passing through
The main target parameter of the experiment was generation power (P). The variable parameters
the heat sink, where (U) is achieved by adjusting the switch to control the speed of the fan’s motor.
included engine rotation speed (Ω [rpm]) and mean velocity (U) of air passing through the heat sink,
The engine speed was controlled by the throttle valve and change in engine speed (Ω) caused the
where (U) is achieved by adjusting the switch to control the speed of the fan’s motor. The engine
change in the quantity (Qflow) of exhaust gas and the temperature (Ti) of the exhaust gasses entering
speed
controlled by
the throttle
valveIncreasing
and change
engine
caused
change in
thewas
thermoelectric
conversion
system.
Qflowin and
Ti speed
would (Ω)
increase
thethehot-side
the temperature
quantity (Q fof
)
of
exhaust
gas
and
the
temperature
(T
)
of
the
exhaust
gasses
entering
i
low TEG, promoting the generating performance
of TEG. Figure 18 shows the the
thermoelectric
conversion
system.
Increasing
Q
and
T
would
increase
hot-side
temperature
f low
relationship between engine rotation (Ω) and quantity
of iexhaust gas (Qflow).the
From
the near
idle (Ω = of
TEG,2700
promoting
Figure
18the
shows
the relationship
between
engine
rpm) to the
thegenerating
maximum performance
torque outputof(ΩTEG.
= 5400
rpm),
exhaust
gas discharge
(Qflow) was
rotation
(Ω) and
quantity
of exhaust
gasincreases
(Q f low ).asFrom
the nearasidle
(Ω =
rpm)(2):
to the maximum
estimated
from
500 to 1350
c.c./s. Qflow
Ω increases,
shown
in2700
Equation
torque output (Ω = 5400 rpm), the exhaust gas
1 1discharge (Q f low ) was estimated from 500 to 1350 c.c./s.
× × (Total(2):
displacement) × ϕ
(2)
flow = Ω ×in Equation
Q f low increases as Ω increases, asQshown
60 2
The total displacement is 35.8 c.c. and
1 the
1 volume efficiency φ is between 0 and 1 and increases
Q
“
Ω
ˆ
ˆ
ˆ pTotal displacementq ˆ ϕ
(2)
f
low
with Ω. Altering engine rotation speed
60(Ω) 2also affects the temperature (Ti) of the exhaust gasses
entering the thermoelectric conversion system. Since combustion is more efficient at higher engine
The total
displacement
is 35.8
c.c. and the
volume
efficiencyof
ϕ the
is between
and
1 and
increases
speed,
more
combustion heat
is generated
and
the temperature
exhaust 0
gas
goes
up when
withengine
Ω. Altering
engine
rotation
speed
(Ω)
also
affects
the
temperature
(T
)
of
the
exhaust
gasses
speed (Ω) is raised. From Figure 19 it can be seen that an increase in engine
speed (Ω) from
i
entering
thermoelectric
conversion
system.
Since combustion
is more
at to
higher
engine
2700 the
to 5400
rpm, results
in a change
of exhaust
gas temperature
(Ti) efficient
from 230
325 °C.
Additionally,
no significant
was seen
thetemperature
exhaust gas temperature
(Ti) gas
withgoes
the up
mean
speed,
more combustion
heat change
is generated
andinthe
of the exhaust
when
cooling
air
velocity
(U)
used
in
the
experiments.
The
range
of
U
may
be
too
small
to
reveal
the
engine speed (Ω) is raised. From Figure 19 it can be seen that an increase in engine speed (Ω) from
˝ C.the
in Ti.results
Furthermore,
the 10ofcm
distance
between
the engine
exhaust
and
inlet of
2700influence
to 5400 rpm,
in a change
exhaust
gas
temperature
(Ti ) from
230outlet
to 325
Additionally,
the
thermoelectric
conversion
system
accounts
for
a
drop
of
25–50
°C
at
the
inlet
of velocity
the
no significant change was seen in the exhaust gas temperature (Ti ) with the mean cooling air
thermoelectric conversion system due to heat loss.
(U) used in the experiments. The range of U may be too small to reveal the influence in Ti . Furthermore,
During the generation power (P) test a voltmeter and a variable resistor are connected in series
the 10 cm distance between the engine exhaust outlet and the inlet of the thermoelectric conversion
in the TEG circuit as an external load.
The value of the external load resistor (R) must be equal to the
system accounts for a drop of 25–50 ˝ C at the inlet of the thermoelectric conversion system due to
internal resistance of the TEG to give the maximum output power. The equation for calculating
heatgeneration
loss.
power (P) is the same as Equation (1) in Section 2.2.
During the generation power (P) test a voltmeter and a variable resistor are connected in series
in the TEG circuit as an external load. The value of the external load resistor (R) must be equal to
Inventions 2016, 1, 2
13 of 16
the internal resistance of the TEG to give the maximum output power. The equation for calculating
generation
Inventionspower
2016, 1, 2(P) is the same as Equation (1) in Section 2.2.
13 of 16
Inventions 2016, 1, 2
13 of 16
3000
3000
Qflow
[c.c./s]
Qflow
[c.c./s]
2500
2500
2000
2000
1500
1500
1000
1000
500
500
0
0
0
0
2000
2000
4000
6000
4000Ω [rpm]
6000
Ω [rpm]
8000
8000
10000
10000
Figure
Engine
rotationspeed
speed (Ω)vs.
vs. exhaust gas
flow).
Figure
18. 18.
Engine
rotation
gasdischarge
discharge(Q
low ).
Figure
18.
Engine
rotation speed(Ω)
(Ω) vs. exhaust
exhaust gas
discharge
(Q(Q
flowf).
Figure 19. Mean air velocity vs. exhaust temperature.
Figure 19. Mean air velocity vs. exhaust temperature.
Figure 19. Mean air velocity vs. exhaust temperature.
In this study we used an actual engine to investigate waste heat recovery and the test results are
In this study we used an actual engine to investigate waste heat recovery and the test results are
from a specially designed thermoelectric conversion system installed on the exhaust. The variables
In this
study we
used anthermoelectric
actual engineconversion
to investigate
waste
heat recovery
and the
test
results are
from
a specially
designed
system
installed
on the exhaust.
The
variables
discussed include the mean velocity (U) of air driven by an external fan, the temperature difference
discussed
include
the mean
velocity (U) of
air driven system
by an external
fan,on
thethe
temperature
difference
from(ΔT)
a specially
designed
thermoelectric
conversion
installed
exhaust.
The
variables
between hot/cold faces of the TEGs, the engine rotation speed (Ω) and the quantity (Qflow
) of
(ΔT) between
hot/cold
faces
of the
TEGs,
the
engine
rotation
speed
(Ω)
and
the quantity
(Qflow) of(∆T)
discussed
include
the
mean
velocity
(U)
of
air
driven
by
an
external
fan,
the
temperature
difference
exhaust Gas. Figure 20 shows the relationship between the mean air velocity (U) and the mean
exhaust
Gas. Figure
20 the
shows
the relationship
between
the mean
airthe
velocity
(U) (Q
and the
between
hot/cold
of
TEGs,
rotation
speed
(Ω) and
quantity
ofmean
exhaust
temperature
of faces
the TEGs
and
it canthe
be engine
seen that
the mean
temperature
of the
TEGs goes
up )with
an
f low
temperature
of
the
TEGs
and
it
can
be
seen
that
the
mean
temperature
of
the
TEGs
goes
up
with
an
Gas.increase
Figure 20
relationship
between
the mean
air velocity
(U) and
mean
temperature
in shows
engine the
rotation
speed (Ω).
However,
no significant
change
wasthe
seen
in the
mean
increase in engine rotation speed (Ω). However, no significant change was seen in the mean
temperature
TEGs
with that
the mean
air velocity
(U) usedof
in the
the experiments.
This
means
the in
of the
TEGs andofitthe
can
be seen
the mean
temperature
TEGs goes up
with
an that
increase
temperature of the TEGs with the mean air velocity (U) used in the experiments. This means that the
mean
air velocity
(U)
mayHowever,
have beenno
setsignificant
too low andchange
coolingwas
was seen
insufficient.
Furthermore,
since the
engine
rotation
speed
(Ω).
in the mean
temperature
of the
mean air velocity (U) may have been set too low and cooling was insufficient. Furthermore, since the
operation
of the TEG
cannot
200 °C, the engine
rotation
speed
(Ω) in air
thevelocity
current (U)
TEGs
with thetemperature
mean air velocity
(U) used
inexceed
the experiments.
This means
that
the mean
operation temperature of the TEG cannot exceed 200 °C, the engine rotation speed (Ω) in the current
nottoo
cause
the TEGs.
Further studies with since
higher engine
rotation
speed
maystudy
have could
been set
lowoverheating
and coolingof
operation
temperature
study
could
not cause
overheating
ofwas
the insufficient.
TEGs. FurtherFurthermore,
studies with higherthe
engine
rotation
speed
(Ω)
can
be
conducted
in
the
future.
Figure
21
shows
the
relationship
between
the
mean
air
velocity
˝
of the
exceedin200
C, the Figure
engine21rotation
speed
(Ω) in the
currentthe
study
not cause
(Ω)TEG
can cannot
be conducted
the future.
shows the
relationship
between
meancould
air velocity
(U) and the temperature difference (ΔT) of TEGs. Within the current range of the mean velocity (U)
overheating
of the
TEGs. Further
studies
higher
engine
rotationrange
speed
can bevelocity
conducted
(U) and the
temperature
difference
(ΔT) with
of TEGs.
Within
the current
of (Ω)
the mean
(U) in
of air driven by an external fan, the trend was towards a significant connection between ΔT of TEGs
the future.
Figure
the
relationship
between
mean air connection
velocity (U)
and the
of air driven
by21
anshows
external
fan,
the trend was
towardsthe
a significant
between
ΔTtemperature
of TEGs
and engine rotation speed (Ω). When engine rotation speed (Ω) was increased from 2700 to 5400
and engine
rotation
speed
(Ω).
When
engine
rotation
speed velocity
(Ω) was (U)
increased
from 2700
to 5400
difference
(∆T)
of
TEGs.
Within
the
current
range
of
the
mean
of
air
driven
by
an
external
rpm, ΔT of TEGs increased from 20 to 58 °C.
rpm, ΔT of TEGs increased from 20 to 58 °C.
Inventions 2016, 1, 2
14 of 16
fan, the trend was towards a significant connection between ∆T of TEGs and engine rotation speed
(Ω). When engine rotation speed (Ω) was increased from 2700 to 5400 rpm, ∆T of TEGs increased from
20 toInventions
58 ˝ C. 2016, 1, 2
14 of 16
Inventions 2016, 1, 2
14 of 16
Figure 20. Mean air velocity vs. mean TEG temperature.
Figure
20. Mean air velocity vs. mean TEG temperature.
Figure 20. Mean air velocity vs. mean TEG temperature.
Figure 21. Mean air velocity (U) vs. ΔT of the TEGs.
Figure 21. Mean air velocity (U) vs. ΔT of the TEGs.
Figure 21. Mean air velocity (U) vs. ∆T of the TEGs.
From Figure 22 it can be seen that engine rotation speed (Ω) has a significant effect on power
From Figure
22 itgoes
can up
be with
seen an
that
engineofrotation
(Ω)
has a(Ω).
significant
effect
on power
generation
(P) which
increase
engine speed
rotation
speed
Within the
current
range
generation
(P)
which
goes
up
with
an
increase
of
engine
rotation
speed
(Ω).
Within
the
current
range
From
Figure
22
it
can
be
seen
that
engine
rotation
speed
(Ω)
has
a
significant
effect
on
power
of mean air velocity (U) used in our experiments, an increase of mean air velocity (U) did
not
of
mean
air
velocity
(U)
used
in
our
experiments,
an
increase
of
mean
air
velocity
(U)
did
not
generation
which goes
up(P).
with
increase
of engine
rotation
speed
(Ω).
current
range
increase(P)
generated
power
At an engine
rotation
speed
(Ω) of 5400
rpm,
theWithin
output the
power
(P) was
increase
generated
power
At an
engine generation
rotation
(Ω)of
of
5400
rpm,
the output
(P) increase
was
2.5 W.
on(U)
Seebeck
thermoelectric
theory,
the
TEG
voltage
(V)not
satisfies
of mean
air Based
velocity
used(P).
in
our
experiments,
an speed
increase
mean
airoutput
velocity
(U)power
did
2.5
W. power
Based
thermoelectric
TEG
Equation
(3): on
generated
(P).Seebeck
At an engine
rotationgeneration
speed (Ω)theory,
of 5400the
rpm,
theoutput
outputvoltage
power(V)
(P)satisfies
was 2.5 W.
Equation
(3):
Based on Seebeck thermoelectric generation theory,
V = ΔSthe
⋅ ΔTTEG output voltage (V) satisfies Equation
(3) (3):
V = ΔS ⋅ ΔT
(3)
where ΔS is the difference value of the Seebeck
V “ coefficient
∆S ¨ ∆T of the semiconductor material used in the (3)
where
ΔS isvalue
the difference
value
of the Seebeck
of the semiconductor
material
used in the
TEGs. The
of ΔS is not
a constant,
it varies coefficient
with temperature
of TEGs. However
this temperature
TEGs.
The
value of
ΔS
is not a constant,
it mean
varies value
with temperature
ofand
TEGs.
However
this
temperature
range
is
limited
as
is
variation
of
ΔS.
A
may
be
used
the
generated
power
(P) will
where ∆S is the difference value of the Seebeck coefficient of the semiconductor material used
in the
range
limited
as isofvariation
of ΔS. Avoltage
mean value
may be used
and external
the generated
power(R).
(P) will
equal isthe
square
the produced
(V) divided
by the
resistance
Our
TEGs. The value of ∆S is not a constant, it varies with temperature of TEGs. However this temperature
equal
the square
the produced
voltage (V) Furthermore,
divided by itthe
external that
resistance
(R). Our
experimental
resultsofcomply
with this assumption.
is predicted
by extending
the
range
is limited asresults
is variation
ofwith
∆S. this
A mean
value may
be used and
the
generated
power
(P) willthe
equal
experimental
comply
assumption.
Furthermore,
it
is
predicted
that
by
extending
experimental data to set the engine rotation speed at 6000 rpm, the output power (P) will be 3.8 W.
the square
of
the
produced
voltage
(V)
divided
by
the
external
resistance
(R).
Our
experimental
results
experimental
to set
engine
rotation
speed atby6000
thethermoelectric
output powerconversion
(P) will be system
3.8 W.
The generateddata
power
(P)the
is far
below
that achieved
the rpm,
similar
comply
with
this
assumption.
Furthermore,
it
is
predicted
that
by
extending
the
experimental
data to
The
generated
power
(P)
is
far
below
that
achieved
by
the
similar
thermoelectric
conversion
system
previously designed by the authors where the heat absorber had arrays of straight fins with copper
previously
designed
by
the
authors
where
the
heat
absorber
had
arrays
of
straight
fins
with
copper
foams in the gaps between fins, and were capable of generating 4.2 W at an engine rotation speed of
foams in the gaps between fins, and were capable of generating 4.2 W at an engine rotation speed of
Inventions 2016, 1, 2
15 of 16
set the engine rotation speed at 6000 rpm, the output power (P) will be 3.8 W. The generated power (P)
is far below that achieved by the similar thermoelectric conversion system previously designed by the
Inventions
2016,the
1, 2heat absorber had arrays of straight fins with copper foams in the gaps between
15 of 16 fins,
authors
where
and were capable of generating 4.2 W at an engine rotation speed of 6000 rpm. However, the pin-fin
6000 rpm. However, the pin-fin array heat absorber used here has lower flow resistance, and the
array heat absorber used here has lower flow resistance, and the back pressure is not so severe that it
back pressure is not so severe that it would impede normal operation of the engine. Finally,
would
impede normal operation of the engine. Finally, according to the Figure 22, the present system
according to the Figure 22, the present system may generate over 5 W when the present small
mayengine
generate
W when theispresent
small
engine
(35.8 c.c.
displacement)
is operating
at the
(35.8over
c.c. 5displacement)
operating
at the
maximum
power
output condition
(Ω = 7000
maximum
rpm). power output condition (Ω = 7000 rpm).
Figure 22. Engine rotation speed (Ω) vs. output power (P).
Figure 22. Engine rotation speed (Ω) vs. output power (P).
4. Conclusions
4. Conclusions
An actual four-stroke engine (35.8 c.c.) was used for these experiments on a test platform
An actualfor
four-stroke
engine (35.8
c.c.) was used
for these using
experiments
on a recovered
test platform
designed
designed
the investigation
of thermoelectric
generation
waste heat
from
the
engine
exhaust gases.
The study successfully
investigated
theheat
effects
of the engine
rotation
speed
for the
investigation
of thermoelectric
generation
using waste
recovered
from the
engine
exhaust
and
thestudy
meansuccessfully
velocity of external
coolingthe
aireffects
on theof
temperature
discharged
quantity
of engine
gases.
The
investigated
the engine and
rotation
speed and
the mean
velocity
exhaustcooling
gas. Experiments
were also performed
to measure
the relationship
betweengas.
theExperiments
external
of external
air on the temperature
and discharged
quantity
of engine exhaust
andtothe
TEG output
voltage/current,
as well
betweenload
TEGresistance
output voltage
andTEG
wereload
alsoresistance
performed
measure
the relationship
between
theasexternal
and the
generated power/efficiency. A correlation was derived for calculating the maximum generation
output voltage/current, as well as between TEG output voltage and generated power/efficiency.
power of a single-chip TEG and the temperature difference between the hot and cold faces of TEG.
A correlation was derived for calculating the maximum generation power of a single-chip TEG and the
The study also examined the influence of engine rotation speed and the velocity of external cooling
temperature difference between the hot and cold faces of TEG. The study also examined the influence
air against power generation of the thermoelectric conversion system, and found that power
of engine
rotation
speed
andengine
the velocity
external
cooling
air against
power
of the
generation
increased
with
rotation of
speed.
Within
the current
range of
mean generation
velocity of the
thermoelectric
conversion
system,ofand
found that
power
withpower.
engineIt rotation
external cooling
air, an increase
cooling-air
speed
wouldgeneration
not increaseincreased
the generated
was
speed.
Within
the
current
range
of
mean
velocity
of
the
external
cooling
air,
an
increase
cooling-air
found that four TEG modules in series could generate 2.5 W power at an engine rotationofspeed
of
speed
would
thetorque
generated
power.
It was
found
that
four TEG
modules
series could
5400
rpm not
(theincrease
maximum
output).
If the
present
small
engine
operates
at theinmaximum
generate
W power
at an(Ωengine
ofsystem
5400 rpm
maximum
torque output). If the
power2.5
output
condition
= 7000 rotation
rpm), thespeed
present
will (the
generate
over 5 W.
present
small engineThe
operates
the maximum
output
condition
(Ω = 7000ofrpm),
the present
Acknowledgment:
authors at
would
like to thank power
the Ministry
of Science
and Technology
the Republic
of
system
will
over
5 W. this research under Contract Nos. MOST 104-2221-E-270-005 and MOST
China
forgenerate
financially
supporting
104-2622-E-270-005-CC3.
Acknowledgments: The authors would like to thank the Ministry of Science and Technology of the Republic
AuthorforContributions:
Tzer-Ming Jeng
conductedunder
the experimental
measurements
and data analysis and
of China
financially supporting
this research
Contract Nos.
MOST 104-2221-E-270-005
Sheng-Chung
Tzeng led this work and participated discussions; and Bo-Jun Yang and Yi-Chun Li assisted in the
MOST
104-2622-E-270-005-CC3.
implementation of the experimental measurements.
Author Contributions: Tzer-Ming Jeng conducted the experimental measurements and data analysis
Conflicts ofTzeng
Interest:
authors
no conflict ofdiscussions;
interest.
Sheng-Chung
ledThe
this
work declare
and participated
and Bo-Jun Yang and Yi-Chun Li assisted
in the implementation of the experimental measurements.
References
Conflicts
of Interest: The authors declare no conflict of interest.
1.
Champier, D.; Bedecarrats, J.P.; Rivaletto, M.; Strub, F. Thermoelectric power generation from biomass
cook stoves. Energy 2010, 35, 935–942.
Inventions 2016, 1, 2
16 of 16
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Champier, D.; Bedecarrats, J.P.; Rivaletto, M.; Strub, F. Thermoelectric power generation from biomass cook
stoves. Energy 2010, 35, 935–942. [CrossRef]
Karri, M.A.; Thacher, E.F.; Helenbrook, B.T. Clarkson Exhaust energy conversion by thermoelectric generator:
Two case studies. Energy Convers. Manag. 2011, 52, 1596–1611. [CrossRef]
Zhou, S.; Sammakia, B.; White, B.; Borgesen, P. Multiscale modeling of thermoelectric generators for the
optimized conversion performance. Int. J. Heat Mass Transf. 2013, 62, 435–444. [CrossRef]
Weng, C.C.; Huang, M.J. A simulation study of automotive waste heat recovery using a thermoelectric
power generator. Int. J. Therm. Sci. 2013, 71, 302–309. [CrossRef]
Jang, J.Y.; Tsai, Y.C. Optimization of thermoelectric generator module spacing and spreader thickness used
in a waste heat recovery system. Appl. Therm. Eng. 2013, 51, 677–689. [CrossRef]
Cummings, T.A. Internal Combustion Electric Power Hybrid Power Plant. U.S. Patent 4,148,192,
23 November 1977.
Yoshida, S.; Aoki, K. Thermoelectric Converter for Heat-Exchanger. U.S. Patent 5,959,240, 2 December 1997.
Shinohara, K.; Kobayashi, M.; Furuya, K.; Kushibiki, K. Electric Energy Supply System for Vehicle. U.S. Patent
6,172,427, 12 February 1998.
Rowe, D.M. Thermoelectrics, an enviromentally-friendly source of electrical power. Renew. Energy 1999, 16,
1251–1256. [CrossRef]
Hendricks, T.J.; Lustbader, J.A. Advanced thermoelectric power system investigations for light-duty and
heavy-duty applications. In Proceedings of the 21st International Conference on Thermoelectrics, Long Beach,
CA, USA, 25–29 August 2002.
Lombardi, C. Researchers Squeeze More Electricity from Heat. Available online: http://news.cnet.com/
8301-17912_3-9999450-72.html (accessed on 25 July 2008).
Jeng, T.M.; Tzeng, S.C.; Chou, H.C. Experimental study of heat energy absorber with porous medium for
thermoelectric conversion system. Smart Sci. 2013, 1, 1–5.
Tzeng, S.C.; Jeng, T.M.; Ma, W.P.; Wang, J.R.; Chou, B.; Lin, J.B.; Xiao, Y.D.; Wu, M.Z.; Tang, F.Z. Exhaust Pipe
with Noise-reducing and Heat Recovery Functions. Taiwan, R.O.C. Patent I,350,878, 21 October 2011.
Moffat, R.J. Contributions to the theory of single-sample uncertainty analysis. ASME J. Fluids Eng. 1982, 104,
250–258. [CrossRef]
© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons by Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).