scispace - formally typeset
SciSpace - Your AI assistant to discover and understand research papers | Product Hunt

Proceedings ArticleDOI

A comparison of four modelling techniques for thermoelectric generator

28 Mar 2017-

TL;DR: Four ways of TEG modelling are introduced and finding the answers to three TEG related questions using STAR-CCM+, Simscape and MATLAB function based Simulink model respectively are demonstrated.

AbstractThe application of state-of-art thermoelectric generator (TEG) in automotive engine has potential to reduce more than 2% fuel consumption and hence the CO2 emissions. This figure is expected to be increased to 5%~10% in the near future when new thermoelectric material with higher properties is fabricated. However, in order to maximize the TEG output power, there are a few issues need to be considered in the design stage such as the number of modules, the connection of modules, the geometry of the thermoelectric module, the DC-DC converter circuit, the geometry of the heat exchanger especially the hot side heat exchanger etc. These issues can only be investigated via a proper TEG model. The authors introduced four ways of TEG modelling which in the increasing complexity order are MATLB function based model, MATLAB Simscape based Simulink model, GT-power TEG model and CFD STAR-CCM+ model. Both Simscape model and GT-Power model have intrinsic dynamic model performance. MATLAB function based model and STAR-CCM+ model can be developed to have only steady state performance or to include dynamic performance. Steady state model can be used in quick assessment of TEG performance and for initial design optimization. However, only dynamic model can give the accurate prediction of TEG output during engine transient cycles. This paper also demonstrates finding the answers to three TEG related questions using STAR-CCM+, Simscape and MATLAB function based Simulink model respectively.

Topics: Thermoelectric generator (56%)

Summary (3 min read)

Introduction

  • Thermoelectric device is a bi-direction energy converter between thermal energy and electrical energy.
  • So far, in the domain of automotive application, the majority research efforts are focused on the optimization and prediction of the TEG performance and the reduction of the device cost related to the waste thermal energy harvest in both diesel and gasoline engines [2~9].
  • Hence, the modelling of a TEG device needs proper software environment.
  • Since the TEG device has both thermal and electrical mechanism and the thermal phenomenon can be modelled as equivalent electric circuit, the electric circuit and analysis software SPICE can be used for modelling the TEG device [10,11].
  • In section 3, Simscape exhaust system model was developed and validated against engine test data.

TEG Engine Test Result w/o Aluminum Plate

  • Since the maximum exhaust gas temperature is normal higher than 500°C, the hot side heat exchanger for TEG device is made from stainless steel which has as low as 16 W/m.K thermal conductivity.
  • Figure 1 shows a TEG device with four commercial TEMs was tested in a diesel engine Exhaust Gas Recirculation (EGR) path.
  • Two test data set were collected at the same gas in conditions and the same clamping force.
  • For the case with aluminium plates, one aluminium plate was placed between the two top TEMs and the top surface of hot side exchanger and the other was placed between the two bottom TEMs and the bottom surface of the hot side exchanger.
  • The maximum uncertainty of the voltage and current measurement is around ±0.2%.

What is the Optimal Thickness of the Aluminum Plate?

  • Now here comes a question, how much the thickness of the aluminum plate should be.
  • STAR-CCM+ is an entire engineering process for solving problems involving flow (of fluids or solids), heat transfer, and stress [16].
  • By using 1mm aluminum, these two curves have been not only straightened but also lifted to higher value.
  • When the thickness of the aluminum plate increases, the temperature of the upstream TEM tends to decrease, while the temperature of the downstream TEM tends to increase.
  • Figure 6 is the plot of average delta temperature of the hot side and the cold side of two TEMs verse the thickness of the aluminum plate.

GT-Power TEG Model

  • When the system level optimization and prediction work need to be carried out for the application of TEG in engine waste energy harvest, GT-Power is a good choice.
  • A TEG unit model with one TEM has been built in GT-Power version 2016, See Figure 7.
  • It is a dynamic TEG model which includes the dynamic of exhaust gas, thermal inertia of the TEM and heat exchanger.
  • Hence, it can simulate the transient response of the TEG device.

Modelling the TEM

  • A complete TEM is mainly made up by two ceramic wafers and the thermoelectric elements between them.
  • Air-Cond is the air gap between the ceramic wafer.
  • The required input parameters for the TEM block are shown in Figure 9.
  • Unavoidably, there is properties loss during the manufacture process of a TEM.
  • The main tuning parameter for the TEM model is the thermal contact conductance (Cond-Hot and Cond-Cold).

Modelling the heat exchanger

  • Because the TEM is closely integrated with the heat exchanger to form a TEG, the heat exchanger templates within the GT-Power do not fit the TEG scenario.
  • So that the heat exchanger has to be modelled using pipe and thermal mass blocks.
  • The heat transfer coefficient which is correlated to both gas flow rate and gas temperature needs to be input as known function.
  • The validation of a TEG GT-Power model which consists multiple TEM units against engine test results is undergoing.
  • This result together with its integration into engine model for system level optimization, prediction and control design will be discussed in another forth coming paper.

Modelling the Engine Exhaust System

  • Simscape provides a quick way to develop physical model within MATLAB/Simulink environment.
  • The element blocks in Simscaps are very basic.
  • A model of the exhaust system of a 2 liters GTDi gasoline engine was developed using Simscape, see Figure 11.
  • The average gas temperature within the pipe was estimated using a subsystem which is displayed in Figure 12.
  • This validation result using engine test data is displayed in Figure 14.

Prediction the Output of the TEG Mounted Directly to the External Surface of the Engine Exhaust System

  • It can be seen from Figure 14 that the gas out temperature after the fourth pipe segment is still as high as 500°C.
  • These two questions can be answered by using the validated exhaust system Simscape model in the previous section.
  • So that the harvested electrical energy is very low.
  • Subsystem for computing the average gas temperature includes the Peltier heat pumping effect.

Model Structure

  • The physical equations about the TEM multiple mechanism have been well studied [19, 20].
  • As it is indicated in Figure 19, this model includes modelling the influence from the geometry of TEM and heat exchanger and the temperature dependent TEM properties and heat exchanger properties.
  • The Impact of Thermal Inertia on TEG Performance.
  • The sum of maximum power output of the TEG device for these 6 conditions were plotted together in Figure 25.

Summary/Conclusions

  • Four modelling techniques which are 3D CFD, GT-Power, Simscape and MATLAB function have been used in modeling TEG device.
  • The existing heat exchanger template does not fit for TEG application.
  • Since the GTPower is popular in modelling automotive engine, GT-power TEG model can be seamlessly integrated with engine model and then be used for system level optimization.
  • Learning Simscape language needs a lot of effort.
  • The conclusion is the TEG performance is not very sensitive to thermal inertia.

Did you find this useful? Give us your feedback

...read more

Content maybe subject to copyright    Report

Page 1 of 12
10/19/2016
2017-01-0144
A Comparison of Four Modelling Techniques for Thermoelectric Generator
Author, co-author (Do NOT enter this information. It will be pulled from participant tab in
MyTechZone)
Affiliation (Do NOT enter this information. It will be pulled from participant tab in MyTechZone)
Abstract
The application of state-of-art thermoelectric generator (TEG) in
automotive engine has potential to reduce more than 2% fuel
consumption and hence the CO
2
emissions. This figure is expected to
be increased to 5%~10% in the near future when new thermoelectric
material with higher properties is fabricated. However, in order to
maximize the TEG output power, there are a few issues need to be
considered in the design stage such as the number of modules, the
connection of modules, the geometry of the thermoelectric module,
the DC-DC converter circuit, the geometry of the heat exchanger
especially the hot side heat exchanger etc. These issues can only be
investigated via a proper TEG model. The authors introduced four
ways of TEG modelling which in the increasing complexity order are
MATLB function based model, MATLAB Simscape based Simulink
model, GT-power TEG model and CFD STAR-CCM+ model. Both
Simscape model and GT-Power model have intrinsic dynamic model
performance. MATLAB function based model and STAR-CCM+
model can be developed to have only steady state performance or to
include dynamic performance. Steady state model can be used in
quick assessment of TEG performance and for initial design
optimization. However, only dynamic model can give the accurate
prediction of TEG output during engine transient cycles. This paper
also demonstrates finding the answers to three TEG related questions
using STAR-CCM+, Simscape and MATLAB function based
Simulink model respectively.
Introduction
Thermoelectric device is a bi-direction energy converter between
thermal energy and electrical energy. When there is thermal gradient
developed across a couple which is consisted of one n-type leg and
one p-type leg, this couple will work as a small voltage battery which
is Seebeck mode. On the other hand, if an external voltage applied to
the two terminals of the couple, there will be heat be pumped from
one end of the legs to the other end of the legs though the legs. This
is known as Peltier mode [1]. This reversible energy conversion
property makes the thermoelectric device have big potential for being
an actuator in future thermal management systems in vehicle other
than working only in uni-function, either Thermoelectric Generator
(TEG) for thermal energy harvest or Thermoelectric Cooler (TEC)
for heating, refrigerator and air-conditioner. For example, it can be
used in heating battery, catalyst, fuel, oil and engine coolant up
before engine cold start and then it can harvest the thermal energy
when the engine works in warm and heavy load condition. This will
provide another control freedom in the online optimization of the
whole vehicle system in fuel consumption and CO
2
emissions. The
very open prediction for the future could be that most thermal
sensitive components and the whole engine surface together with the
exhaust system in the vehicle will possibly be wrapped or integrated
with thermoelectric layers.
So far, in the domain of automotive application, the majority
research efforts are focused on the optimization and prediction of the
TEG performance and the reduction of the device cost related to the
waste thermal energy harvest in both diesel and gasoline engines
[2~9]. The optimization and prediction work unavoidably has to be
based on device and system level model. There are multiple choices
of modelling technique or environment for doing both the device and
system level modelling work. If the hot side and cold side
temperature is equally distributed, the basic equations for Seebeck,
Peltier, Thomas effect and energy conservative of one thermoelectric
module (TEM) can be clearly stated and be numerically calculated
using Excel, calculator, Fortran or C language or MATLAB scripts.
However, there will be numbers of TEMs in a TEG used in engine
exhaust waste energy harvest and the boundary conditions for each
TEM are not the same. Hence, the modelling of a TEG device needs
proper software environment.
Since the TEG device has both thermal and electrical mechanism and
the thermal phenomenon can be modelled as equivalent electric
circuit, the electric circuit and analysis software SPICE can be used
for modelling the TEG device [10,11]. The temperature depended
properties of the thermoelectric material can be modelled using
polynomial function within the circuit block. But this type of model
is purely steady state. If the TEG model needs to be coupled to
engine model, MATLAB/Simulink, Simscape or GT-Power can be
chosen as the modelling environment. They all can model the TEG
dynamic behaviour. Simscape has both fundamental thermal and
electrical elements. A physical TEG model together with DC/DC
converter circuit can be built up based on the physical connections of
thermal and electrical elements [12]. A Simscape TEG model can run
directly within Simullink model frame. If the engine model is also a
Simscape model or a Mean Value Engine Model (MVEM) developed
in Simulink environment, there will be seamless integration of TEG
model with engine model. In 2016b version of MATLAB, other than
electrical and thermal elements, there are elements for gas system
which make the modelling of engine exhaust system more
convenient. GT-power is a commonly used software for engine
modelling. There is also a TEM block in the GT-Power library in
later than 2013 version. The development of one TEM unit model is
quite straightforward using GT-power [13]. The analysis of heat
flux, stress, pressure drop, heat exchanger performance is best to be
carried out using 3D CAD and CFD modelling techniques
[3,4,14,15].

Page 2 of 12
10/19/2016
This paper presents the applications of four modelling techniques in
solving TEG related optimization problem or questions. It is
organized as this: In section 2, STAR-CCM+ was used in the analysis
of the TEG performance improved using Aluminium plate between
the hot side stainless heat exchanger and the TEMs. In section 3,
Simscape exhaust system model was developed and validated against
engine test data. This model then was used to demonstrate that only
stainless pipe without inner fins will not give acceptable TEG output
performance. The development of TEG GT-power model and its
validation was discussed in Section 4. Then it was followed by the
introduction of a Simulink dynamic TEG model which is based on
MATLAB function block. This model was also validated against
engine transient cycle and was used to explore the impact of thermal
inertia on the TEG performance.
STAR-CCM+ TEG Model
TEG Engine Test Result w/o Aluminum Plate
Since the maximum exhaust gas temperature is normal higher than
500°C, the hot side heat exchanger for TEG device is made from
stainless steel which has as low as 16 W/m.K thermal conductivity. It
can be expected that the temperature distribution within the TEM
contact surface with the hot side heat exchanger surface will be very
uneven. This prediction was proved by the experiment results. Figure
1 shows a TEG device with four commercial TEMs was tested in a
diesel engine Exhaust Gas Recirculation (EGR) path. The sandwich
assembly of this TEG device is displayed in Figure 2. Two test data
set were collected at the same gas in conditions and the same
clamping force. One is without aluminium plates, one is with adding
two 3mm aluminium plates. For the case with aluminium plates, one
aluminium plate was placed between the two top TEMs and the top
surface of hot side exchanger and the other was placed between the
two bottom TEMs and the bottom surface of the hot side exchanger.
The width and length of the aluminium plates are the same to those of
the hot side surface of the hot side heat exchanger. These four TEMs
were wired together electrically in series and with an external PWM
current sweep circuit. The comparison of power output of the top two
TEMs are shown in Figure 3. There is obvious power improvement
of both two TEMs by using the aluminium plate.
Figure 1. TEG testing in a diesel engine EGR path
The data acquisition system used in the experimental work in this
study consists of NI cRIO chassis and 16bit analog input module. The
maximum uncertainty of the voltage and current measurement is
around ±0.2%. Hence the maximum uncertainty of computed
electrical power is around ±0.3% according to the theory of the
propagation of uncertainty.
Figure 2. (a) Four TEMs and one hot side heat exchanger and two cold side
exchangers; (b) TEG consisted of four TEMs in work mode
(a) (b)
( c) (d)
Figure 3. Test results: (a) Electrical power of the first top TEM in the
upstream position; (b) increased power percentage by using aluminum plate;
(c) Electrical power of the second top TEM in the downstream position; (b)
increased power percentage by using aluminum plate;
What is the Optimal Thickness of the Aluminum Plate?
Now here comes a question, how much the thickness of the
aluminum plate should be. Instead of repeating the experimental test
with various thickness of the aluminum plate, this work was done
using a STAR-CCM+ TEG model. STAR-CCM+ is an entire
engineering process for solving problems involving flow (of fluids or
solids), heat transfer, and stress [16]. The version of the STAR-
CCM+ used in this study is 9.06. When developing the TEG model,
perfect contact between each pair surface was assumed.
Figure 4 shows the temperature distribution of three cases which are
1) without aluminum plate, 2) with 1mm aluminum plate and 3) with
7mm aluminum plate respectively. It can be seen that there is

Page 3 of 12
10/19/2016
changes of temperature distribution pattern among these three
situations. The sampled temperatures along the middle line of the top
two TEMs along the gas flow direction are depicted in Figure 5.
Figure 5 plays an important role in the interpretation of the benefit
from using aluminum plate and the TEG performance evolves with
the thickness of the aluminum plate. When there is no aluminum
plate, the temperature along the middle line of both TEMs is very
curved toward lower temperature value. By using 1mm aluminum,
these two curves have been not only straightened but also lifted to
higher value. This can be explained as the big jump thermal
conductivity from stainless steel to aluminum plate of which the
thermal conductivity is around 237 W/m.K. The lateral thermal
conduction heat transfer has contributed to this phenomenon. When
the thickness of the aluminum plate increases, the temperature of the
upstream TEM tends to decrease, while the temperature of the
downstream TEM tends to increase. These two lines both become
more level and straight. This is also because the thicker the aluminum
plate, the more lateral heat transfer from upstream to downstream.
Figure 4. Top: the surface temperature distribution of the hot side heat
exchanger without aluminum plate; Bottom left: the surface temperature
distribution of the hot side heat exchanger using 1mm aluminum plate;
Bottom right: the surface temperature distribution of the hot side heat
exchanger using 7mm aluminum plate.
Figure 5. Temperature samples along the middle line of the TEMs along the
gas flow direction
Figure 6. The average of delta temperature along the middle line of the top
two TEMs varies with the thickness of the aluminum plate.
Figure 6 is the plot of average delta temperature of the hot side and
the cold side of two TEMs verse the thickness of the aluminum plate.
It shows that the average delta temperature reaches the plateau at
4mm. Similar simulation results have been obtained for other gas in
conditions. This suggests that placing an aluminum plate with even
only 1mm thickness will help to improve the TEG output
performance and that plate thickness greater than 4mm provides no
additional benefit. Other metal plate which has high thermal
conductivity such as copper can be used in steady of aluminum plate
but will add more into the cost of the TEG [17].
1D models do not include the lateral heat conduction mechanism and
they are developed under the assumption that there is even
temperature distribution within the contact surface area of one TEM.
2D modelling techniques like the 3D modelling techniques can be
used in this simulation work.
GT-Power TEG Model
When the system level optimization and prediction work need to be
carried out for the application of TEG in engine waste energy harvest,
GT-Power is a good choice. No only it is convenient in modelling
engine system, but also there is ready to use TEM block in the library
and its strong capability in modelling the gas and coolant flow, heat
exchanger thermal behavior etc.
A TEG unit model with one TEM has been built in GT-Power
version 2016, See Figure 7. It is a basic unit brick for building future
complete TEG device. The aim of this modelling task is to investigate
the behaviour of TEG when it works under wide range of engine
operating conditions, to explore the influence of TEG on engine
performance and to design a model-based control system to maintain
the energy balance and prevent the possible damage of the TEG. It is
a dynamic TEG model which includes the dynamic of exhaust gas,
thermal inertia of the TEM and heat exchanger. Hence, it can
simulate the transient response of the TEG device.
Figure 7. (can be found at the end of this paper)
Modelling the TEM
A complete TEM is mainly made up by two ceramic wafers and the
thermoelectric elements between them. A basic TEM unit model
which consists a hot-wafer, a cold-wafer and a TEM block is shown

Page 4 of 12
10/19/2016
in Figure 8. There is one ceramic wafer on TEM hot side and cold
side respectively. Cond-Hot-1 and Cond-Cold-1 are used to simulate
the contact thermal resistance. Air-Cond is the air gap between the
ceramic wafer. TEM-1 is the block for emulating both thermal and
electrical behavior of a TEM. The required input parameters for the
TEM block are shown in Figure 9. These input parameters include
TEM geometrical parameters and thermoelectric properties.
Unavoidably, there is properties loss during the manufacture process
of a TEM. In order to have high accuracy of the TEM model,
validated module based thermoelectric properties should be used in
this setup.
Figure 8. A unit TEM GT-Power model
Figure 9. Setup window of input parameters for TEM Block
The main tuning parameter for the TEM model is the thermal contact
conductance (Cond-Hot and Cond-Cold). Figure 10 shows the best
tuned result of the TEM model to match a module performance given
in the datasheet for steady state conditions.
(a)
(a)
Figure 10. TEM model performance at steady state: (a) OCV; (b) Maximum
electrical power
Modelling the heat exchanger
Because the TEM is closely integrated with the heat exchanger to
form a TEG, the heat exchanger templates within the GT-Power do
not fit the TEG scenario. So that the heat exchanger has to be
modelled using pipe and thermal mass blocks. The structure of both
hot side and cold side heat exchanger can be seen in Figure 7. The
pipes are used to calculate the temperature and pressure along the
heat exchanger. The heat transfer coefficient which is correlated to
both gas flow rate and gas temperature needs to be input as known
function. The validation of a TEG GT-Power model which consists
multiple TEM units against engine test results is undergoing. This
result together with its integration into engine model for system level
optimization, prediction and control design will be discussed in
another forth coming paper.
Simscape TEG Model
Modelling the Engine Exhaust System
Simscape provides a quick way to develop physical model within
MATLAB/Simulink environment. The element blocks in Simscaps
are very basic. Users can create their own custom component models
using MATLAB based Simscape language which enables text-based
authoring of physical modelling components, domains and libraries

Page 5 of 12
10/19/2016
[18]. A model of the exhaust system of a 2 liters GTDi gasoline
engine was developed using Simscape, see Figure 11. The exhaust
system was divided into four segments. Each segment pipe was
modelling using one internal convection heat transfer and one
external convection heat transfer element. The average gas
temperature within the pipe was estimated using a subsystem which
is displayed in Figure 12. This subsystem also gives the estimated
value for gas out temperature. Figure 13 is the diagram of this engine
which was installed on a dyno engine test bed. This validation result
using engine test data is displayed in Figure 14.
Figure 11. (can be found at the end of this paper)
Figure 12. (can be found at the end of this paper)
Figure 13. A diagram of the 2 liters GTDi gasoline engine
Figure 14. Validation result of the Simscape exhaust system model
Prediction the Output of the TEG Mounted Directly to
the External Surface of the Engine Exhaust System
It can be seen from Figure 14 that the gas out temperature after the
fourth pipe segment is still as high as 500°C. Hence, here comes a
couple of questions. The first is how is the TEG performance if the
TEMs are mounted to the external surface of the exhaust pipe without
change the exhaust pipe. The second is will the hot side temperature
of the TEMs is over the commercial module limit which is 250°C?
These two questions can be answered by using the validated exhaust
system Simscape model in the previous section. But before doing
that, the model in Figure 11 and the subsystem in Figure 12 need to
be modified to include TEM component and Peltier effect. For
simplicity, Joule heat effect and Thomas effect were neglected. To
further simplify the problem, only one pipe segment model was used
for this simulation. Two conduction heat transfer elements ware
added and to replace the external convection heat transfer element,
see Figure 15. The cold side was simulated as a constant temperature
source. Figure 16 shows the Peltier pumping heat transfer was
extracted in computing the average gas temperature within one pipe
segment.
The simulation result shows that even though the gas in temperature
is very high, the hot side temperature of the TEM is very low with
maximum value is at 50°C. So that the harvested electrical energy is
very low. It is because the heat transfer from gas to the exhaust pipe
wall is not big enough to give high hot side temperature.
In R2016b MATLAB, there is gas system element block in Simscape
, which will help to build more accurate model. However, if a
dynamic TEG model which is used for predicting TEG output during
an engine transient cycle is to be developed, customized heat
exchanger block and customized temperature dependent TEM block
need to be created first.
Figure 15 (can be found at the end of this paper)
Figure 16. Subsystem for computing the average gas temperature includes the
Peltier heat pumping effect.
A Simulink TEG Model
Model Structure
The physical equations about the TEM multiple mechanism have
been well studied [19, 20]. Figure 17 shows the energy flow within a
TEM. The heat flow cause by Thomas effect was not included. When
there is current flow through the TEM, the Peltier pumping energy
developed from hot side to cold side. The Peltier pumping thermal
energy into the hot side of the TEM is higher than the Peltier
pumping thermal energy out the cold side of the TEM. Their
difference equals to the sum of joule heating

and electrical
output power

. The energy flow within a unit TEG which consist
of one TEM is depicted in Figure 18.



are respectively
the heat exchanger thermal resistance, the hot side contact thermal
resistance and the cold side thermal resistance.

is the mass
weight of the heat exchanger.

is the maximum electrical output
of the TEM. Letter represents the thermal energy and letter
represents the temperature. The detailed physical equations for TEM
and heat exchanger used in this modelling work can be found in
reference [21].

Citations
More filters

Journal ArticleDOI
Abstract: Waste heat recovery using a thermoelectric generator (TEG) is a promising approach for vehicle original equipment manufacturers to reduce fuel consumption and lower CO2 emissions. A TEG can convert otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems. This paper focuses on the development of a dynamic model of TEG system designed for vehicle waste heat recovery, which is made up of counter-flow heat exchangers (HXRs) and commercial thermoelectric modules (TEMs). The model is built from thermoelectric materials into a TEM and then into a TEG system. Compared to other TEG models, the tuning and validation process of the proposed model is more complete. Experiments are done on both a TEM test rig and a heavy-duty diesel engine, which is equipped with a prototype TEG on the exhaust gas recirculation (EGR) path. Simulations of steady-state operating points as well as the response to typical engine cycle test show good agreement with experimental data. A TEG installed upstream of the after-treatment system in a heavy-duty truck has been modelled to predict the temperatures and power output in a dynamic driving cycle. The simulation results of temperatures show the model can be used as a basis to develop a control system for dynamic operation to ensure safety operation of TEG and efficient operation of the after-treatment system. A comparison of power output of the systems under different scenarios underlines the importance of integration of TEM with HXRs. Based on the simulation results, around 20% average power output increase can be expected by optimizing the thermal contact conductance and the heat transfer coefficient of hot side HXR.

91 citations


Cites background from "A comparison of four modelling tech..."

  • ...Since the thermal masses of both sides of the HXRs are significantly larger than the TEMs and dominate the thermal dynamics of the TEG system, energy transfer at the hot and cold end of the TEG system are simulated by dynamic models....

    [...]

  • ...The heat transfer area, mass of the HXRs and aluminium plate for each control volume can be expressed as follow: =A A nhxr CV hxr CV ....

    [...]

  • ...Thermal inertia of the HXRs is taken into account in the model so that dynamic behaviour of the system is included....

    [...]

  • ...A comparison of power output of the systems under different scenarios underlines the importance of integration of TEM with HXRs. Based on the simulation results, around 20% average power output increase can be expected by optimizing the thermal contact conductance and the heat transfer coefficient of hot side HXR....

    [...]

  • ...The configuration of a TEG system with counter flow type HXRs is presented in Fig....

    [...]


Journal Article
Abstract: A numerical model has been developed to simulate coupled thermal and electrical energy transfer processes in a thermoelectric generator (TEG) designed for automotive waste heat recovery systems. This model is capable of computing the overall heat transferred, the electrical power output, and the associated pressure drop for given inlet conditions of the exhaust gas and the available TEG volume. Multiple-filled skutterudites and conventional bismuth telluride are considered for thermoelectric modules (TEMs) for conversion of waste heat from exhaust into usable electrical power. Heat transfer between the hot exhaust gas and the hot side of the TEMs is enhanced with the use of a plate-fin heat exchanger integrated within the TEG and using liquid coolant on the cold side. The TEG is discretized along the exhaust flow direction using a finite-volume method. Each control volume is modeled as a thermal resistance network which consists of integrated submodels including a heat exchanger and a thermoelectric device. The pressure drop along the TEG is calculated using standard pressure loss correlations and viscous drag models. The model is validated to preserve global energy balances and is applied to analyze a prototype TEG with data provided by General Motors. Detailed results are provided for local and global heat transfer and electric power generation. In the companion paper, the model is then applied to consider various TEG topologies using skutterudite and bismuth telluride TEMs.

24 citations


Proceedings ArticleDOI
28 Mar 2017
Abstract: Thermoelectric generator (TEG) has received more and more attention in its application in the harvesting of waste thermal energy in automotive engines. Even though the commercial Bismuth Telluride thermoelectric material only have 5% efficiency and 250°C hot side temperature limit, it is possible to generate peak 1kW electrical energy from a heavy-duty engine. If being equipped with 500W TEG, a passenger car has potential to save more than 2% fuel consumption and hence CO2 emission reduction. TEG has advantages of compact and motionless parts over other thermal harvest technologies such as Organic Rankine Cycle (ORC) and Turbo-Compound (TC). Intense research works are being carried on improving the thermal efficiency of the thermoelectric materials and increasing the hot side temperature limit. Future thermoelectric modules are expected to have 10% to 20% efficiency and over 500°C hot side temperature limit. This paper presents the experimental synthesis procedure of both p-type and n-type skutterudite thermoelectric materials and the fabrication procedure of the thermoelectric modules using this material. These skutterudite materials were manufactured in the chemical lab in the University of Reading and then was fabricated into modules in the lab in Cardiff University. These thermoelectric materials can work up to as high as 500°C temperature and the corresponding modules can work at maximum 400°C hot side temperature. The performance loss from materials to modules has been investigated and discussed in this paper. By using a validated TEG model, the performance improvement using these modules has been estimated compared to commercial Bisemous Telluride modules.

13 citations


Cites methods from "A comparison of four modelling tech..."

  • ...The model structure and validation results were discussed in another paper [25]....

    [...]


Journal ArticleDOI
Abstract: This paper reports results of the transient modeling of thermoelectric cooling/heating modules as power generators with the aim to select preferable ones for use in thermal energy harvesting wireless sensor network nodes. A study is conducted using the selected commercial thermoelectric generators within the node of a compact design with aluminum PCBs. Their equivalent electro-thermal models suitable for SPICE-like simulators are presented. Model components are extracted from the geometrical, physical and thermo-electrical parameters and/or experimentally. SPICE simulation results mismatch within 7% in comparison with the experimental measurements. The presented model is used for the characterization of different thermoelectric generators within the wireless sensor network node from the aspects of harvesting efficiency, cold boot time, node dimensions and compactness, and maximum applicable temperature. The choice of the preferred generator is determined by its electrical resistance, the number of thermoelectric pairs, external area and thermoelectric legs length, depending on the primary design goal and imposed thermal operating conditions. The node can provide load power of 1.3 m W and the cold boot time of 66 s for generator with 31 thermoelectric pairs at a temperature difference of 15 ° C with respect to the ambient, and 7.6 m W of load power and the cold boot time of 40 s for generator with 71 thermoelectric pairs at a temperature difference of 25 ° C .

3 citations


Dissertation
01 Jan 2018
Abstract: In the face of the internationally tightened requirements and regulations for CO2 emissions from the transportation sector, waste heat recovery using a thermoelectric generator (TEG) has become the most significant research interest. A vehicular TEG, converting otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems, is a promising approach for vehicle original equipment manufacturers (OEMs) to reduce fuel consumption and lower CO2 emissions. This thesis aims to explore the main challenges to be faced in the commercialization of TEGs. Based on a review of the literature, four research gaps have been identified, which are respectively: * Translating the material improvements into TEG Performance, * Transient behaviors of vehicular TEGs under driving cycles, * Fuel saving percentage and cost-benefit estimation of TEG, * Bidirectional characteristic of TEM and bifunctional vehicular TEG. To directly address these research gaps, a quasi-static TEM model, a dynamic TEG model, a semi-empirical vehicular TEG model, and a dual-model TEM model have been respectively developed and validated through experiments on both TEM test rigs and TEG engine test benches. These developed models are used as tools to investigate the performance of TEG, parameters sensitivity, and integration effects. Model-based TEG control, TEG cost benefit ratio and feasibility of a bifunctional TEG are also explored based on the developed models. The simulation results show that TEG power generation is highly sensitive to the heat transfer coefficient of hot side heat exchanger and thermal contact resistance. The TEG installation position is identified as the most important integration effect. It has been found by the simulation result that the fuel saving with TEG installed upstream of the three-way catalyst (TWC) is 50% higher than the fuel saving with TEG installed downstream of the TWC. The fuel saving percentage for a skutterudite vehicular TEG, which can generate around 400-600W in constant speed 120km/h, is 0.5-3.6% depending on the integration position in the exhaust line. A 3-minute faster warm-up effect of engine oil can be obtained when the bifunctional TEG works in engine warm-up mode with electrical current applied.

Cites background from "A comparison of four modelling tech..."

  • ...Although aluminium plates contribute to an increase of thermal resistance, an optimal thickness of aluminium plate can increase the average delta temperature of all TEMs on the HXRs [141]....

    [...]


References
More filters

Proceedings ArticleDOI
10 Aug 1994
Abstract: Hi‐Z Technology, Inc. (Hi‐Z) has been developing a 1 kW thermoelectric generator for class eight Diesel truck engines under U.S. Department of Energy and California Energy Commission funding since 1992. The purpose of this generator is to replace the currently used shaft‐driven alternator by converting part of the waste heat in the engine’s exhaust directly to electricity. The preliminary design of this generator was reported at the 1992 meeting of the XI‐ICT in Arlington, Texas. This paper will report on the final mechanical, thermal and thermoelectric design of this generator. The generator uses seventy‐two of Hi‐Z’s 13 Watt bismuth‐telluride thermoelectric modules for energy conversion. The number of modules and their arrangement has remained constant through the program. The 1 kW generator was tested on several engines during the development process. Many of the design features were changed during this development as more information was obtained. We have only recently reached our design goal of 1 kW output. The output parameters of the generator are reported.

160 citations


Journal ArticleDOI

123 citations


"A comparison of four modelling tech..." refers methods in this paper

  • ...The authors introduced four ways of TEG modelling which in the increasing complexity order are MATLB function based model, MATLAB Simscape based Simulink model, GT-power TEG model and CFD STAR-CCM+ model....

    [...]

  • ...The development of one TEM unit model is quite straightforward using GT-power [13]....

    [...]

  • ...The development of TEG GT-power model and its validation was discussed in Section 4....

    [...]

  • ...Since the GTPower is popular in modelling automotive engine, GT-power TEG model can be seamlessly integrated with engine model and then be used for system level optimization....

    [...]

  • ...GT-power is a commonly used software for engine modelling....

    [...]


Journal ArticleDOI
Abstract: A numerical model has been developed to simulate coupled thermal and electrical energy transfer processes in a thermoelectric generator (TEG) designed for automotive waste heat recovery systems. This model is capable of computing the overall heat transferred, the electrical power output, and the associated pressure drop for given inlet conditions of the exhaust gas and the available TEG volume. Multiple-filled skutterudites and conventional bismuth telluride are considered for thermoelectric modules (TEMs) for conversion of waste heat from exhaust into usable electrical power. Heat transfer between the hot exhaust gas and the hot side of the TEMs is enhanced with the use of a plate-fin heat exchanger integrated within the TEG and using liquid coolant on the cold side. The TEG is discretized along the exhaust flow direction using a finite-volume method. Each control volume is modeled as a thermal resistance network which consists of integrated submodels including a heat exchanger and a thermoelectric device. The pressure drop along the TEG is calculated using standard pressure loss correlations and viscous drag models. The model is validated to preserve global energy balances and is applied to analyze a prototype TEG with data provided by General Motors. Detailed results are provided for local and global heat transfer and electric power generation. In the companion paper, the model is then applied to consider various TEG topologies using skutterudite and bismuth telluride TEMs.

118 citations


Journal ArticleDOI
Abstract: A high-temperature thermoelectric generator (TEG) was recently integrated into two passenger vehicles: a BMW X6 and a Lincoln MKT. This effort was the culmination of a recently completed Department of Energy (DOE)-sponsored thermoelectric (TE) waste heat recovery program for vehicles (award #DE-FC26-04NT42279). During this 7-year program, several generations of thermoelectric generators were modeled, designed, built, and tested at the couple, engine, and full-device level, as well as being modeled and integrated at the vehicle level. In this paper, we summarize the history of the development efforts and results achieved during the project, which is a motivation for ongoing research in this field. Results are presented and discussed for bench, engine dynamometer, and on-vehicle tests conducted on the current-generation TEG. On the test bench, over 700 W of power was produced. Over 600 W was produced in on-vehicle tests. Both steady-state and transient models were validated against the measured performance of these TEGs. The success of this work has led to a follow-on DOE-sponsored TE waste heat recovery program for passenger vehicles focused on addressing key technical and business-related topics that are meant to enable TEGs to be considered as a viable automotive product in the future.

96 citations


Journal ArticleDOI
Abstract: As global consumption of energy continues to increase at an exponential rate, the need to find technologies that can help reduce this rate of consumption, particularly in passenger vehicles, is imperative. This paper provides a progress report on the BSST-led US Department of Energy-sponsored automotive thermoelectric waste heat recovery project, which has transitioned from phase 3 and is completing phase 4. Thermoelectric generator (TEG) development will be discussed, including modeling and thermal cycling of subassemblies. The design includes the division of the TEG into different temperature zones, where the subassembly materials and aspect ratios are optimized to match the temperature gradients for the particular zone. Test results for a phase 3 quarter-scale device of the phase 4 high-temperature TEG will be discussed, where power outputs of up to 125 W were achieved on a 600°C hot-air test bench. The design of the TEG, which uses high-power-density segmented thermoelectric elements, has evolved from a planar design in phase 3 to a cylindrical design in phase 4. The culmination of phase 4 includes testing of the generator on a dynamometer at the National Renewable Energy Laboratory with a high-performance production engine.

88 citations


Frequently Asked Questions (1)
Q1. What are the contributions in "A comparison of four modelling techniques for thermoelectric generator" ?

The authors introduced four ways of TEG modelling which in the increasing complexity order are MATLB function based model, MATLAB Simscape based Simulink model, GT-power TEG model and CFD STAR-CCM+ model. This paper also demonstrates finding the answers to three TEG related questions using STAR-CCM+, Simscape and MATLAB function based Simulink model respectively.