An experimental study of a solar thermoelectric generator with vortex tube for hybrid vehicle pdf

Scientific article about utilization of thermoelectricity in hybrid vehicle

1. An experimental study of a solar thermoelectric generator with vortex
tube for hybrid vehicle
Roni-Claudin Talawo
a,b,c,
*, Blaise Eugfiene Mtopi Fotso
a,b,c
,Mfledard Fogue
a,b,c
a
Industrial Systems and Environmental Engineering Research Unit (UR-ISIE), University of Dschang, Dschang 96, Cameroon
b
Mechanics and Modeling of Physical System Research Unit (UR-2MSP), University of Dschang, Dschang 96, Cameroon
c
Department of Mechanical Engineering and Computer Integrated Manufacturing, Fotso Victor Institute of Technology of Bandjoun, University of Dschang,
Cameroon
ARTICLE INFO
Article History:
Received 1 February 2021
Revised 8 March 2021
Accepted 10 March 2021
Available online 17 March 2021
ABSTRACT
An experimental study on a vehicle was carried out to evaluate the electrical potential of a STEG (Solar Ther-
moelectric Generator) made up of 20 thermoelectric modules of 127 torques each and a vortex tube in order
to supply the accessories of a vehicle hybrid while moving. This is because the device is supplied with air by
a turbocharger mounted at the front of the vehicle which sucks this air and delivers it to the vortex tube,
which in turn produces hot air and gas at each of its ends cold air. As a result, the temperature of the hot air
adding to that of the solar radiation allows a higher temperature to be obtained on one of the faces of the
STEG. On the other hand, the cold air coming out of the vortex tube contributes to obtaining a very low tem-
perature on the other side of the STEG. Thus, thanks to this temperature difference, an electric current is gen-
erated while the vehicle is moving. The experimental results obtained could be compared with those of a
validated and published mathematical modeling of the same device. As the results obtained, we have
observed that at rest significant values of current, voltage and electric power are obtained and these drop
and stabilize quickly when the vehicle starts to move. This decrease is justified by the impact of the wind
which cools the system. But the presence of the vortex tube compensates for this. Thus for a speed of
33.33 m/s the hot temperature is around 76.1 °C, the cold temperature is around 2.1 °C, the generated current
is 0.7742A, the voltage is 46.85 V and the power is 36.27 W. The results with those of a validated mathemati-
cal modeling of the same system made it possible to establish a certain similarity in their evolutions accord-
ing to the speed of the vehicle.
© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/)
1. Introduction
The major concern to protect our planet from global warming
continues to require car manufacturers to migrate to cleaner and
more environmentally friendly hybrid vehicles. So to reduce their
fuel consumption, many solutions are increasingly offered in these
vehicles to produce electrical energy from renewable energies,
including that of thermoelectricity[1fi7]. Much experimental work
on the contribution of thermoelectric systems in vehicles has been
done to assess their energy potential. Among these numerous works,
we can cite those of Ying Fan et al. (2010) who worked on the devel-
opment of a thermoelectric-photovoltaic hybrid energy system com-
posed of two TEGs (thermoelectric generator) and a photovoltaic
generator for hybrid electric vehicles. A multiple input DC-DC
converter (MIC) of the
fl
Cuk-
fl
Cuk-
fl
Cuk type (converter having an output
voltage amplitude higher or lower than that of the input voltage) was
adopted to represent the power obtained from different sources of
energy independently. The topology of this MIC was analysed, includ-
ing the base units and the synthesis approach. The strategy of maxi-
mum power point tracking and asynchronous trip control was also
adopted[8]. Mori et al. (2011) worked on the simulation of the fuel
saving efficiency of an exhaust heat recovery system using a thermo-
electric generator in a hybrid production vehicle. The properties of
the thermoelectric elements were obtained by self-assessment and
defined as conditions for estimating fuel economy. They concluded
that applying insulation to the exhaust system and forming the right
combination of elements with different temperature properties
inside the TEG could result in an improvement of about 3% of the fuel
economy. A real vehicle was also used to verify the calculation ele-
ments in the fuel economy simulation, and their reliability was thus
confirmed[9]. S. Kim et al. (2011) proposed and manufactured a ther-
moelectric generator (TEG) using the coolant from passenger vehicle
* Corresponding author at: Industrial Systems and Environmental Engineering
Research Unit (UR-ISIE), University of Dschang, Dschang 96, Cameroon.
E-mail addresses:[email protected](R.-C. Talawo),mtopi@univ-
dschang.org(B.E.M. Fotso),[email protected](M. Fogue).
https://doi.org/10.1016/j.ijft.2021.100079
2666-2027/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
International Journal of Thermofluids 10 (2021) 100079
Contents lists available atScienceDirect
International Journal of Thermofluids
journal homepage:www.elsevier.com/locate/ijtf

2. engines. Their experimental results revealed that the maximum out-
put power of the proposed thermoelectric generator was about
75 W, the calculated efficiency of the TEG thermoelectric module
was 2.1%, and the overall efficiency of electric power generation.
From the waste heat of the engine coolant was about 0.3% in
driving mode at 80 km/h. The conventional radiator could thus
be replaced by the proposed TEG without additional devices or
redesign of the water cooling system of the existing radiator
engine[1]. S.-K. Kim et al. (2011) studied a novel exhaust gas
waste heat recovery system for hybrid vehicles, using a thermo-
electric module (TEM) and heat pipes to generate electrical
energy. Their TEG system was directly connected to the exhaust
pipe, and the amount of electricity generated by the TEG modules
was directly proportional to their heated area. However, to com-
pensate for the fact that some exhaust pipes did not offer a suffi-
cient hot surface for the high efficiency required waste heat
recovery; they designed a new TEG system having an enlarged
hot surface by the addition of ten heat pipes, which acted as very
efficient heat transfer devices and allowed the heating of several
TEG modules. As a result, this new waste heat recovery system
produced a maximum power of 350 W when the exhaust gases
heatedthesurfaceoftheheatpipeevaporatorby170°C [10].
Sharan and Giftson, (2014) worked on the analysis of an improved
method of recharging batteries in hybrid vehicles using a ceramic
coated cast iron bar with afiberglass interior liner inside which is
placed a bar of bismuth telluride (thermoelectric material), mounted
on the cylinder head of the gasoline engine. The generated electricity
is sent directly to the battery, which allows its rapid recharging[11].
Ahmed et al. (2019) developed a TEG network model for hybrid-elec-
tric vehicles (HEV). The proposed system was implemented experi-
mentally by increasing the temperature difference between the two
sides of the TEG network. The hot side was in contact with the car's
exhaust manifold, and the other side was cooled by the automotive
air conditioning system. The voltage generated by this TEG was used
to achieve maximum energy to recharge a car battery. Their simula-
tion results were performed using Matlab / Simulink software pack-
age to study the performance of the system. The presented
experimental results demonstrated the effectiveness of the proposed
range of TEG for this type of vehicle[12].
Abbasi and Tabar, (2019) worked on the measurement and
optimization of the energy produced by a thermoelectric genera-
tor on a vehicle. For this they took into account the main parame-
ters that influence the temperatures of the exhaust gases and the
brake discs of a vehicle, namely the volume of air displaced, the
speed of the vehicle, the structure of the heat sink, the number
braking system while driving and running the engine in order to
assesstheamountofheatdissipatedandconvertitintoelectric-
ity by a thermoelectric generator. Therefore, in their work they
proposed aflexible measurement system with a reliable sensor
that transfers data at high speed to a computer[13].T.Y.Kim
et al. (2019) developed a compact thermoelectric generator for
waste heat recovery in an electric-hybrid vehicle of the sedan
type. The shape and dimensions of the thermoelectric generator
were precisely determined by performing a series of theoretical
analyses to meet the spatial and maximum permissible pressure
drop restrictions. The waste heat recovery performance of the
thermoelectric generator was experimentally evaluated using a
hybrid electric vehicle engine under the nine most common driv-
ing conditions. One surface of the thermoelectric modules is
heated by theflow of exhaust gas, while the other surface is
cooled by the engine coolant circulating at 10 L/min and a tem-
perature of 353 K. A maximum output power is of approximately
118 W and an energy conversion efficiency of the order of 2.1%
are obtained using 12 thermoelectric modules under engine oper-
ating conditions producing the highest rate of exhaust gasflow
and in temperature[14].
Fotso et al. (2019) performed thermal modeling and analysis
of a vortex-tube thermoelectric solar generator for hybrid
vehicles. Their model of STEG (Solar Thermoelectric Generator)
was equipped with a vortex tube and a turbocharger which,
installed on a vehicle, produces electrical energy from the heat
flows generated by the vortex tubes and solar radiation via the
Seebeck effect to power vehicle accessories and to compensate
for some of the heat loss caused by the airflow over the vehicle.
Theyfirst determined the energy input of the vortex tube by a
thermodynamic approach and carried out a thermal study of the
entire device to determine the heatflows on the hot side and the
cold side of the thermoelectric parts. They were also able to
mathematically determine for a number of thermocouples of
3042 the electric current, the power and the efficiency produced
according to parameters such as the speed of the vehicle, the
fraction of mass of cold air leaving the vortex tube and the solar
fluxes[15](Fig. 1).
Jouhara et al. (2021) presented in-depth analysis of TEGs,
beginning with a comprehensive overview of their working prin-
ciples such as the Seebeck effect, the Peltier effect, the Thomson
effect and Joule heating with their applications, materials used,
Figure of Merit, improvement techniques including different ther-
moelectric material arrangements and technologies used and sub-
strate types. Moreover, performance simulation examples such as
Nomenclature
I
Max Maximum electrical current (A)
U
Max Maximum electrical voltage (V)
P
Max Maximum electrical Power (W)
K Thermal conductivity
_m Massflow rate (kg/s)
P Electrical power (W)
DT Temperature difference (°C)
R Total electrical resistance of thermoelectric parts
STEG Solar Thermoelectric generator
S Area (m
2
)
t Time (s)
T Temperature (°C)
U Speed (m/s)
V
OU Electric voltage in open circuit (V)
V
S totalTotal electric voltage in output circuit (V)
Greek symbols
aa =apfian: Seebeck coefficient of the couple of
thermoelectric parts;
zf Cold mass fraction
zc Hot mass fraction
hEf ficiency
λ Compression ratio
r Density (kg/m
3
)
Subscript
_m
c Hot massflow rate (kg/s)
_m
e Massflow of air introduced into the vortex tube
(kg/s)
_m
f Cold massflow rate (kg/s)
P
max Maximum electrical power (W)
T
0 Atmospheric temperature
U
0 Speed of the vehicle (m/s)
2 R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079

3. COMSOL Multiphysics and ANSYS-Computational Fluid Dynamics
are investigated[16].
Thus in this article, we will focus on the model proposed by[15]
because of its novelty and the energy input it could generate to
power vehicle accessories. However, we will go well beyond their
work which, as said above, was limited to simple mathematical
modeling. To do this, to deepen this theme we propose as objectives
of this workfirst to carry out this device experimentally by associat-
ing it with sensors for data collection in order to test it, then we will
carry out a comparison between our experimental results and those
of mathematical modeling validated and published.
2. Experimental setup
2.1. Presentation of the STEG model
The system allows dynamic recharging of the batteries in the
hybrid vehicle by converting the heat of solar radiation and the
hot air exiting the vortex tube into electricity. The STEG genera-
tor consists of several modules arranged over the entire surface
of the vehicle exposed to solar radiation. In fact, this system is
designed to be placed on the external surface of the vehicle. The
upper surface constituting the model is made of glass, it has the
shape and characteristics of a solar plate collector in order to
trap under the greenhouse effect, the maximum radiation of the
sun. It also has in its longitudinal direction two rectangular cav-
ities through which circulates very hot and cold air from the
vortex tube. In fact, when moving the vehicle; the ambient air
causes the blade of the turbocharger to rotate. The inclination of
these blades allows it to absorb a quantity of air which is still
compressed and directed towards the vortex tube. At the outlet
of the vortex tube; it has hot air at one end and cold air at the
other where the difference between the two is about 200°C.
Each quantity of cold and hot air is redirected towards the inte-
rior STEG respectively to the cold and hot surfaces to maintain
at a high level the temperature difference
DT which, associated
with the thermoelectric characteristics of each pair of P and N
doped part, allows a conversion of thermal energy into electrical
energy[15].
2.2. Experimental procedure
The experimental setup is made up as shown inFig. 2below of
four sub-parts namely:
- The set of 20 TEG generators including 12 type TEC1-12705 and
08 type TEC1-12706 (Fig. 3c).
- A vortex tube (Fig. 3d).
- A data collection system consisting of an Arduino mega board, 05
DTH 22 type temperature sensors, 01 ACS 712 electric current
sensor, a 500 PSI air pressure sensor, a microcomputer (Fig. 3d
and3e).
- A mini Turbocharger. (Fig. 4b).
In the center of the device, the 20 TEGs are regularly arranged
as shown in (Fig. 3c). They are then soaked in thermal paste to
reduce thermal resistance by contact. Below them we have a cold
planar absorber which is constantly cooled by the passage of cold
air exiting from one side of the vortex tube. On it are mounted
two sensors which measure its temperature and that of the cold
air as shown in (Fig. 3f). Above these TEGs, we have a hot planar
absorber whose temperature is derived from that of the hot air
Fig. 1.3D Models proposed by Fotso et al.[15]a) Presentation of 3D modules and their positions on a car. b) Presentation of the STEG model proposed and incorporated on the
external surface of the vehicle.
R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079 3

4. exiting from the other side of the vortex tube and solar radiation.
On this absorber are also mounted two temperature sensors as
showninthefigure (Fig. 3a) which measure its temperature and
that of the air. All of the device's sensors are connected to an
Arduino board that collects data (Fig. 3e). This is connected to a
computeratthetimeofdatatransfer( Fig. 3d). The electric cur-
rent generated by the device is measured by a current sensor and
stored in a battery.
The last part of the device consists of a mini turbocharger
located at the front of the vehicle. While the vehicle is moving.
The blade of this compressor is rotated and thus causes suction,
compression and sending of ambient air to the vortex tube
(Fig. 4). The tests were carried out in the city of Bafoussam in
Cameroon one day in October 2020 at a time when the ambient
temperature was 30 °C. The vehicle speed range considered was
0fi120 km/h and the sensor collection speed was 9600 baud.
With each increase in vehicle speed in regular intervals of 5 km /
h, a waiting time of 3 minutes was observed before any recording
in order to be sure of the reliability of the information provided
by the sensors.
The characteristics of the thermoelectric modules used are listed
in the table below (Table 1).
Fig. 3.a): STEG in its box; b): STEG; c): 20 TEGs mounted in the device; d): Inside the experimental device and data collection on the computer; e) Connection ofall the sensors on
the Arduino board; f) Cold absorber and cold air temperature sensors; g) Arduino board.
Fig. 2.3D model of our device: a) assembled device; b) exploded view.
4 R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079

5. The characteristics of all other parts of the device are listed in the
table below (Table 2).
2.2. Modeling of the STEG
According to[19], one of the widely used electrical models of TEGs
is that of Thevenin's equivalent model with neglected contact ther-
mal resistances. Thus the electric voltage in open circuit and that of
output are respectively
V
OU¼a:DT ð1Þ
V
S¼a:DTfiRI ð2Þ
The electrical power supplied is
P¼V
S:I¼a:DT:IfiRI
2
ð3Þ
Fig. 5below shows an electrical model of TEGs mounted in series.
As indicated previously inTable 1, the system consists of 20 TEG
generators comprising 12 of the TEC1-12705 type and 08 of the
TEC1-12706 type; each having its maximum power, current and elec-
trical voltage. So for
@P
@I
¼0, these maximum values are obtained from
the following relations:
I
MAX¼
a:DT
2:R
ð4Þ
U
MAX¼
a:DT
2
ð5Þ
P
MAX¼
ða:DTÞ
2
4R
ð6Þ
The electrical resistance of each of the modules is respectively
2.84
Vand 2.53Vobtained fromEq. (7)
R¼
U
MAX
I
MAX
ð7Þ
For the entire device, we have as total electrical voltage
V
STotal¼8ða:DTfiR
1I
1Þþ12ð a:DTfiR
2I
2Þð 8Þ
ConsideringI
1flI
2flI
Fig. 4.a) Experimental device mounted on a vehicle b) Mini turbocharger c) Data collection on the computer.
Table 2
Calculations data.
Parts Quantity Materials Dimensions (m)
STEG Module housing 01 Steel sheet 0.250 £0.250£0.07
Thermal insulator
Turbocharger inlet port surface,
S
0,(m
2
)
01
Steel
0.00212
Vortex Tube inlet section, Se,
(m
2
)01
0.00007
Cold air outlet section of the vor-
tex tube, Sf, (m
2
)
0.00045
Hot air outlet section of the vor-
tex tube, Sc, (m
2
)
0.000091
Arduino Mega Card 01 / /
Glass cover 01 Glass 0.250 £0.250£0.03
Table 1
Properties of thermoelectric parts.
Parts Quantity Materials Dimension (mm) Number of pairs
of thermoelectric
parts per module
maximum
electric
voltage (V)
maximum
electric
power (W)
maximum
electric
Current (A)
Seebeck
coefficient
a=a
pfia
n(V/K)
Ref.
Module Peltier tec1-
12705 thermo-
electric effect
08 Bismuth
telluride
40£40£3.5 127 14.2 71.2 05 455 £10
fi6
[17]
Module Peltier tec1-
12706 thermo-
electric effect
12 Bismuth
telluride
40£40£3.5 127 15.2 91.2 06 455 £10
fi6
[18]
R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079 5

6. The total electric voltage becomes
V
STotal¼20a:DTfiIð8R
1þ12R
2Þð 9Þ
The total electric power is thus:
P¼20
a:DT:IfiI
2
ð8R1þ12R 2Þð 10Þ
The current in the circuit is that generated by a single resistor
moduleR
1.ais the sum of the Seebeck coefficient of all the ther-
moelectric couples (127£20) of all 20 modules and
DTis the
temperature difference between the hot and cold faces of the
TEG modules.
According to[15], this temperature difference depends on the
assumed constant solarflux, on the setting of the vortex tube, the
maximum efficiency of which is obtained when the mass fraction of
cold air
zf= 0.8 and vehicle speedU 0.
z
f
¼
_m
f
_m
e
ð12Þ
The values of
DTare obtained by making the difference between
the data of the hot and cold side sensors of the thermoelectric mod-
ules while the vehicle is moving.
According to[14]; the Thermoelectric conversion efficiency for
maximum electrical power is defined by the ratio of the electrical
power producedP
Max, over the heatflux passing through the hot face
Q
hot. Its expression is given below by the relation
h
TE
¼
PMax
Q
hot
(13)
With
Q
hot¼a:THot:IþK 4:DT:
S
4
L
4
fi
I
2
:R
2
(14)
And
ðL
4¼1:5mmÞ:Thermoelectricpiecelength;
ðK
4¼1:2W=m:
B
CÞ:Electricalconductivityof thermoelectricparts
ðS
4¼1:291:29mm
2
Þ:Areaofathermoelectricpart
T
Hot:Temperatureof hotsideofthermoelectricpart
8
>
>
>
<
>
>
>
:
The energy consumed by the system is only in thermal form, It is
given by the relation
_
W¼Q
hott ð15Þ
With t: time.
To reduce the influence of the weight of the device on excess fuel
consumption, low density materials were chosen for the parts consti-
tuting it. Thus the total mass of a STEG is 0.5 kg.
At the level of the turbocharger, according to[20]the mechanical
power is




_
W
e




¼
n
nfi1
_m
eR
0
T0H
f

n
nfi1
fi1

ð16Þ
This power is a function of the speed of the vehicle because it is
the current of air moving during the movement of the vehicle which
causes the rotation of the blades of the turbocharger. Withnis Poly-
tropic exponent of the compression process in the turbocharger;Ris
Constant gases;Toambient temperature;H
fratio between the pres-
sure at the outlet of the turbocharger and that at one end of the vor-
tex tube.
4. Results and discussions
4.1. Temperature obtained during movement
Fig. 6a shows the experimental results of the temperatures
obtained on the hot and cold sides of the thermoelectric module as a
function of vehicle speed. From thisfigure, we see that at rest, signifi-
cant values are obtained and these drop and stabilize quickly when
Fig. 6.a) Experimental Temperatures of the hot and cold side of the thermoelectric parts according to the speed of the vehicle. b) Comparison between the experimental results of
the temperature on the hot side and those of a mathematical modeling.
Fig. 5.Electrical model of STEG.
6 R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079

7. the vehicle starts to move. This decrease is justified by the impact of
the wind which cools the system. But the presence of the vortex tube
compensates for this. Thus for a speed of 33.33 m/s the hot tempera-
ture is around 76.1 °C and the cold temperature 2.1 °C.
Fig. 6b on the other hand presents a comparison between the
experimental data of the temperature on the hot side and those of a
validated mathematical model published recently by Fotso et al.[15].
From the analysis of the two curves in thisfigure, we see a similarity
in their evolution which results in obtaining high values at rest, and
then a rapid decline and convergence thereafter. However, there is
also an average difference of around 15 °C in the data. This is
explained by the difference in the values used of certain parameters
during experimental tests such as solarflux, dimensions and perfor-
mance of the turbocharger which were lower compared to the data
used by Fotso et al.[15].The data inFig. 6are the average tempera-
tures calculated from the data provided by the temperature sensors.
4.2. Maximum Electrical current
Fig. 7a shows the maximum current intensity obtained experi-
mentally as a function of vehicle speed. It also presents an evolution
similar to that of the current with high values at rest of the vehicle
and then a drop and stabilization of the data. The TEG modules being
connected in series, the electric current generated is equal to that
produced by a single TEG module. Thus the current intensity
obtained experimentally at 33.33 m/s is 0.7742 A. By comparing it
with the results of the modeling inFig. 7b, we also note a slight shift
of about 0.17A which can be justified by the reasons mentioned pre-
viously.
4.3. Maximum electrical voltage
Fig. 8abelowshowstheevolutionofthetotalelectricalvoltage
in the system as a function of vehicle speed. The data for this
curve was calculated from the values recorded by the electric cur-
rent sensor. We see large values when the vehicle is at rest, then
a drop and rapid convergence of the data as with current. The
modules being connected in series, contribute to obtaining a volt-
age equal to the sum of the electrical voltages of all the others.
Thus for a speed of 33.33 m/s, the system produces a voltage of
46.85 V. By comparing these results with those of the modeling
inFig. 8b, we see a difference of around 15 V. This is due to the
reasons presented above.
4.4. Maximum electric power
The electrical power generated by the system as a function of
vehicle speed is shown inFig. 9a below. It changes in the same way
as current and voltage. Thus the power obtained for 33.33 m/s of
speed is 36.27 W. By comparing it to the results of the modeling in
Fig. 9b, we see a difference of about 23 W due to the reasons men-
tioned above. Similarly, we also note that these experimental results
follow the same evolution as those of the modeling.
Fig. 7.a) Maximum Experimental electrical current according to the speed of the vehicle forz
f= 0.8. b) Comparison between the experimental results of electric current and those of
a mathematical modeling.
Fig. 8.a) Total electrical Voltage in open circuit value according to the speed of the vehicle forz
f= 0.8. b) Comparison between the experimental results of electric Voltage in open
circuit value and those of a mathematical modeling.
R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079 7

8. 4.5. Thermoelectric conversion efficiency for maximum electrical power
Fig. 10below shows the thermoelectric conversion efficiency for
maximum power as a function of vehicle speed. This efficiency in fact
dependsonthetemperaturedifferencebetweenthefacesoftheSTEG
module obtained at each speed. This temperature difference
DTalso
depends on the ambient temperature and the solarflux of the place of
the experiment. Thus from thisFig. 10, we note that this efficiency
varies between 65.83% and 67.1% which is quite encouraging given the
weak thermoelectric properties of the modules present on the market.
Conclusion
In this article; wefirst carried out an experimental study of a solar
thermoelectric generator equipped with a vortex tube to power the
accessories of a vehicle. The model was equipped with 20 thermo-
electric modules, 07 sensors to measure the generated current, air
pressure and temperatures in the device and a turbocharger. We
then compared our results with those of a validated and published
mathematical modeling of a similar device. As the results obtained,
we have observed that at rest significant values of current, voltage
and electric power are obtained and these drop and stabilize rapidly
when the vehicle starts to move. This decrease is justified by the
impact of the wind which cools the system. But the presence of the
vortex tube compensates for this. Thus for a speed of 33.33 m/s the
hot temperature is around 76.1 °C, the cold temperature is around
2.1 °C, the generated current is 0.7742A, the voltage is 46.85 V and
the power is 36.27 W. The comparison of the results with those of a
validated mathematical modeling of a similar system has made it
possible to establish a certain similarity in their evolution according
Fig. 9.a) Maximum electrical power according to the speed of the vehicle forz
f= 0.8. b) Comparison between the experimental results of electric power and those of a mathematical
modeling.
Fig. 10.Thermoelectric conversion efficiency for maximum electrical power according to the speed of the vehicle for z
f= 0.85.
8 R.-C. Talawo et al. / International Journal of Thermofluids 10 (2021) 100079

9. to the speed of the vehicle. As perspectives, it would be important to
consider an electrical production from waste heat in conventional
engines. An experimental study to assess the device's contribution to
fuel economy would also be very useful. Future work on this device
should be done by introducing STEG modules in the bodywork of the
vehicle so that they do not increase the aerodynamic parameters of
the vehicle to avoid additional fuel consumption.
Declaration of Competing Interest
The authors are no known conflicts of interest associate with this
publication
Acknowledgments
We are grateful to the Department of Mechanical Engineering and
Computer Integrated Manufacturing, Fotso Victor Institute of Tech-
nology of Bandjoun, University of Dschang, Cameroon for providing
us its specialized laboratory for this work
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