Comparison of simulated and measured data of a ...

4th Conference on Thermoelectrics at IAV

Comparison of simulated and measured data of a thermoelectric generator (TEG) developed in research project TEG 2020 and its hardware in the loop (HIL) results Roland Kühn1*, Olaf Koeppen1, Philipp Schulze1, Daniel Jänsch2, Markus Pohle2, Jens Kitte2, Jens Jäger3 1

TU Berlin, Institute of Energy Engineering, Marchstraße 18, DE-10587 Berlin IAV GmbH, Energy Management, Carnotstraße 1, DE-10587 Berlin, Germany 3 BTU Cottbus, Fahrzeugtechnik und -antriebe, Siemens-Halske-Ring 14, DE-03046 Cottbus * e-mail of corresponding author: [email protected] 2

Numerous research projects in automotive engineering focus on the industrialization of the thermoelectric generator (TEG). The development and the implementation of thermoelectric systems into the vehicle environment are commonly supported by virtual designing activities. In this presentation the data gained by a dynamic quasi-two-dimensional simulation model [1] are compared to measured data obtained from tests on a modular planar TEG. Both are developed in the German research project TEG 2020. In the undertaken simulation the main parameters as geometry and material properties are given. The only not yet quantified constraints, the thermal resistivity between the TE modules and the heat exchanger walls and the parasitic heat flow from exhaust gas to the cooling media by-passing the TE modules, are varied. At the end a good compliance of simulated and measured data over a wide range is given. The hereby justified simulation tool is used in a Hardware in the Loop (HiL) system. In this system the developed TEG is integrated into a vehicle, which is examined on a vehicle test bench. The TEG is assembled with two different commercial available TE modules using high temperature and low temperature materials. The hot and cold side contact temperatures on the heat exchanger walls are measured. Afterwards the electrical power output is gained by simulation with the material properties of own TE modules at the measured temperatures. [1] Jens Kitte, Roland Kühn, Hans-Friedtjof Pernau, Kristof Littmann, Daniel Jänsch, Dimensioning and Evaluating a Multi-Channel Thermoelectric Generator Using a Costumized Simulation Architecture, Themoelectric Goes Automotive II, expert verlag, Renningen, 2013, pp. 207-224.

Comparison of simulated and measured data of a thermoelectric generator (TEG) developed in research project TEG 2020 and its Hardware in the Loop (HiL) results Roland Kühn, Olaf Koeppen, Philipp Schulze, Daniel Jänsch, Markus Pohle, Jens Kitte, Jens Jäger

1. Steady-state measurements 2. Physical fitting of the simulation tool 3. Comparison of experiment and simulation

4. Hardware in the Loop (HiL) results 5. Conclusion Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

Division of work • IAV – assembly of the TEG – steady-state measurements on the TEG – integration of the TEG and the HiL into the vehicle

• BTU Cottbus Fahrzeugtechnik und -antriebe FTA – integration of the HiL into the vehicle test bench – measurements on the vehicle test bench

• TU Berlin Institute of Energy Engineering ETA – development of simulation software and its integration into the HiL

Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

3

Motivation • simulation of a complete TEG system is possible – a simulation model for planar TEGs has been developed – validation with CFD and FEM simulations has been done

• validation of simulation with measurements is necessary • behavior of the developed real TEG system is unknown – own developed modules should not be destroyed – commercial modules has been used


4

Steady-state measurements ~60 cm

• Hi-Z HZ-20 modules made of Bi2Te3 are used – long-term use at 250°C, short-time use up to 400°C

• modules are actuated by springs Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

5

Internal installation of TE module (TEM) top-view TEM

Ins HX area

Ins

fins hotswall Ins

TEM

TEM

coolant

TEM

coolant

TEM

coolant

front-view Ins

colds wall

gas

• TEM uses 75% of free area • free space is filled with insulating ceramics (Ins) • heat exchange (HX) area is increased in gas flow direction Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

6

Steady-state measurement results 300

MG = 110 kg/h, TG = 300°C, measured MG = 200 kg/h, TG = 300°C, measured

electrical power output in W

250

MG = 200 kg/h, TG = 400°C, measured MG = 220 kg/h, TG = 400°C, measured MG = 220 kg/h, TG = 415°C, measured

200

150

100

50

0 -20

-10

0

10

20

30 40 50 60 coolant inlet temperature in °C

70

80

90

• small power output at 90°C coolant inlet (typical for vehicles) • 250 W power output at 400K temperature difference Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

7

100

Physical fitting of the simulation • thermal resistivity of the frictional connection between the heat exchanger walls and the commercial TE modules is unknown – fitted to match contact temperature of first module

• parasitic heat flow from exhaust gas directly to the coolant bypassing the TE material is not yet quantified by measurements – fitted to match the electrical power output

• both are strongly influencing the TEG’s electrical power output hot wall Ins

TEM

Ins

front-view

cold wall


8

Estimating the parasitic heat flow 120

M = 110 kg/h, T = 300°C, measured G

simulated, parasitic heat flow = 8% simulated, parasitic heat flow = 12% simulated, parasitic heat flow = 15% simulated, parasitic heat flow = 18% simulated, parasitic heat flow = 21% simulated, parasitic heat flow = 24%

110 100


G

90 80 70 60 50 40 30 -20

-10

0

10

20

30 40 50 cooling temperature in °C

60

70

80

• parasitic heat flow is fitted to come up with the measured power outputs  one fix number as fitting parameter Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

9

90

100

Comparison of simulation and measurement 300

MG = 110 kg/h, TG = 300°C, measured MG = 110 kg/h, TG = 300°C, simulated MG = 200 kg/h, TG = 300°C, measured


250

MG = 200 kg/h, TG = 300°C, simulated MG = 200 kg/h, TG = 400°C, measured MG = 200 kg/h, TG = 400°C, simulated

200

MG = 220 kg/h, TG = 400°C, measured MG = 220 kg/h, TG = 400°C, simulated MG = 220 kg/h, TG = 415°C, measured

150

MG = 220 kg/h, TG = 415°C, simulated

100

50

0 -20

-10

0

10

20


70

80

90

• discrepancy is highest at low coolant temperatures – might be due to extrapolation of TE material properties < 50°C Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

10

100

Simulation of TEG2020 PbTe modules electrical power output in W

450 400 350 300 MG = 200 kg/h, TG = 300°C, measured

250

MG = 200 kg/h, TG = 300°C, simulated MG = 200 kg/h, TG = 400°C, measured MG = 200 kg/h, TG = 400°C, simulated

200

MG = 200 kg/h, TG = 607°C, simulated, PbTe TEG2020

150 100 50 -20

-10

0

10

20 30 40 50 60 coolant inlet temperature in °C

70

80

90

100

• heat exchanger stays the same, module design changes • PbTe modules have lower sensitivity on coolant temperature – design exhaust gas temperature for the TEG2020 PbTe module Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

11

Simulation of TEG2020 PbTe TEM (cohesive bond) 700 650


600 550 500 450 400 350 300 MG = 200 kg/h, TG = 300°C, measured

250

MG = 200 kg/h, TG = 400°C, measured

200

MG = 200 kg/h, TG = 607°C, simulated, TEG2020 PbTe

150

MG = 200 kg/h, TG = 607°C, simulated, TEG2020 PbTe, cohesive connection

100 50 0 -20

-10

0

10

20


70

80

90

• TEG2020 PbTe modules are connected cohesive to the heat exchanger compounds – strong increase in electrical power output Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

12

100

Dynamic Simulation 400 exhaust gas at entrance avg contact temperature 1st module, simulated avg contact temperature 1st module, measured

350

temperature in °C

300 250

['M_G = 110 kg/h, T_G = 300°C, simulated, \alpha = ' num2str(alpha(5))]

200 150 100 50

0 0

200

400

600

800 time in s

1000

1200

1400

• dynamic behavior of first module fits well Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

13

1600

Dynamic Simulation 400

exhaust gas at entrance avg contact temperature 2nd module, simulated avg contact temperature 3rd module, simulated avg contact temperature 2nd module, measured avg contact temperature 3rd module, measured

350

temperature in °C

300

250

200

['M_G = 110 kg/h, T_G = 300°C, simulated, \alpha = ' num2str(alpha(5))]

150

100

50

0 0

200

400

600

800 time in s

1000

1200

1400

• small discrapancy of heating up and cooling down at module 2 and 3 • not all peripheral devices are implemented into simulation Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

14

1600

Hardware in the Loop (HiL) • idea: temperature measurements in the exhaust gas feeding an overall TEG system simulation feeding back to the car – adaptions to measurements are necessary to obtain good stand-alone simulation results – integration of all system components of the TEG into a real time simulation is difficult – integration of a whole real time capable TEG system simulation into a HiL system is even more difficult

 implementation of a real TEG into a real car and simulation of each TE module on basis of measured data


15

HiL - schematic

feed back of simulated results into the vehicle

measured cold side temperature profile TEM TEM TEM TEM simulation simulation simulation simulation measured hot side temperature profile

TEM simulation

measured hot side temperature profile TEM TEM TEM TEM simulation simulation simulation simulation measured cold side temperature profile

TEM simulation


16

HiL system

• TEG integrated into the VW Golf’s exhaust gas system • driving cycles are driven on the shown vehicle test bench • measured data are used for single TE module simulation Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

17

HiL system

• butterfly valve for controlling • contact temperatures on TE modules are measured • exhaust gas and cooling media data are measured Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

18

HiL system

oxide module

oxide module

oxide module

Bi2Te3 module

Bi2Te3 module

250°C

• contact temperature of third row of TE modules (Bi2Te3) is controlled to 250°C by butterfly valve through internal bypass

• TEG2020 PbTe material data are used for simulation – proof of concept with well known TE material Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

19

HiL results – Motorway 150

• at driving cycle “Motorway 150” the bypass is open for long time  maximum power output below 450 W Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

20

HiL results – Motorway 150

• > 400 W at TEG design temperature of 607°C – < 350W at stand-alone simulation fitted to measurements Dipl.-Ing. Roland Kühn | Institute of Energy Engineering | 4th Thermoelectrics Conference – 12.12.2014

21

Conclusion • heat transfer resistivity between heat exchanger wall and TE material and parasitic heat loss need further theoretical investigation  cohesive connections are expedient • simulation fits to the measurement results • experimental results are promising • HiL system shows good accordance to expectations • simulation feed back into the HiL-system is planned


22

WLTP

Daniel Jänsch, Markus Pohle, Jana Topalova, IAV

NEDC

BAB 130

Motorway 150

Results: • A functional TEG system was successfully designed, built and proved at the Hot Air Test bench and in the test vehicle • Test data from relevant driving cycles (NEDC, WLTP, BAB130, MW150) is available for further investigation, simulation and validation

Actions: • Build-up TEG with different commercially available TE modules • Test and measure the TEG at the laboratory Hot Air Test bench • Install measurement equipment in the test vehicle and integrate the TEG • Start-up and test the TEG at chassis dynamometer • Measure thermal characteristics and determine exhaustback pressure in different driving cycles

Goals: • Design, develop, construct and prove a functional TEG prototype system • Determine the exhaust back pressure and temperatures at the TE modules for the relevant vehicle operating conditions • Provide adequate and sufficient experimantal data for simulation and validation purposes

TEG 2020 TEG Vehicle Demonstrator

copper 33%

steel sheet

copper sheet


copper wings

Results: • Optimally designed heat exchangers for different systems and operating conditions • Simulated and validated heat exchangers

Actions: • Design, simulation, and build of prototype heat exchangers out of different materials and with various geometry • Construction of a thermally closed measurement system with minimum heat flow exchange with the environment • Balancing the incoming and outgoing heat flows

Goals: Different heat exchangers should be characterised to evaluate their thermal and hydraulic properties

TEG 2020 Heat Exchanger Development

diffusion barrier

-XX

5 Exhaust channel (1.a: channel wall) Hot heat exchanger- WINGS Thermoelectric material (p- and n-legs) Thermal Isolation / casing (TE material / stabilizing structure)

4

IAV MM/JJJJ XXX XX

1.a

heat exchanger electronics

(Al, Cu, ceramics)

electrical contacts Cu, firmly-bonded to isolation plate heat exchanger

WINGS

7 6

3

1

6.a

5. Electrical contacs and isolation 6. Cold heat exchanger (6.a: water connector) 7. DC/DC converter with thermal coupling on coolant and case

2

electronics with housing

coolant

electrical isolation Al2O3 firmly-bonded to heat exchanger

stabilizing structure, isolation (mica, glass, ceramics) braze

diffusion barrier

single heat exchanger (Al, Cu, steel, ceramics)

module case, seal, isolation

electronics with housing

coolant

electrical isolation

braze

isolation

diffusion barrier

electrical contacts

heat exchanger (hot)

module case, seal, isolation


1. 2. 3. 4.

exhaust gas

-XX

p- and n-legs

braze

IAV MM/JJJJ XXX XX

Firmly-bonded Design

heat exchanger (cold) heat exchanger electronics

electrical contacts

diffusion barrier

p- and n - legs

braze

electrical isolation (substrate/foil)

exhaust gas

Friction-locked Design

Actions and results:

• Minimal number of parts • Minimal number of thermal interfaces

1

• Easy to adapt to different applications • Ready to operate • Fewer costs

Goals: • All components, which are needed for the module operation, are combined in one unit • Heat exchanger is firmly-bonded to the TE material • Each uni-couple has its own single heat exchanger (WING) • WINGs function also as electrical contacts at the hot side of the uni-couple

Motivation: The TE modules, which are currently available on the market, have to be friction-locked integrated in TEG systems. The challenge is, to establish an optimal contact between the module surface and the heat exchanger. To achieve this, both components should have extremely smooth surface and have to be uniformly injected. This results in high production complexity and costs. A firmly-bonded design of the TE modules eliminates the disadvantages of the conventional build-up pattern. Therefore the heat transfer and the TEG efficiency increase considerably.

TEG 2020 �All-in-one� TE Modules

TEG_in control_temperature

5

4

bypass

3

time [s]

2

1

flaps


100

200

300

400

500

600

700

row:

exhaust gas inlet

TEG 2020 Energy Management

Temperature in °C

Results: • Limitation of module temperature • Limited control of exhaust temperature and back pressure behind TEG • Limited control of coolant temperature/cooling system load • Optional adjustment of cooling water distribution • Limitation of working voltage • Adjustable transfer voltage of the DC/DC converter • Record, save and display of measurement and control data • Simulation of virtual TE modules and TEG

Actions: The test vehicle was equipped and operated with the following components, subsystems and functions: • Internal bypass with exhaust valve • Self-sustaining cooling system with water pump and radiator • DC/DC converter • Energy management control system with – controller, sensors, actuators, signal conditioning, measurement data processing – Simulation models of TE modules and TEG – Control functions for · exhaust bypass valve · TEG cooling system · DC/DC converter · monitoring and safety

Goals: Control and adjust the following system parameters: module temperature > components safety exhaust temperature > exhaust cooling exhaust back pressure > gas exchange cycle cooling system load > safety coolant temperature > safety coolant distribution > heating max. working voltage > safety overvoltage > electric system operation

5

4

bypass

3

CAN

WLTP

2

TEGControler

CAN

Measurement technology

After Treatment

1

CAN

flaps

ICE


NEDC

row:

PWM

Controler

PWM

TEG- Periphery and Control System

PWM

Fan

TEG

exhaust gas inlet

BAB 130

Motorway 150

Results: Calculated characteristics of virtual TE modules (e. g. open circuit voltage, single and total module output voltage) out of different TE materials with variable geometrical dimensions (module base area, legs hight and width) in a real TEG prototype system under real operating conditions

Actions: • Build test vehicle with the necessary measurement instrumentation and control system, which enables to simulate TEG and TE modules under real driving conditions • Develop simulation models of TEG, TE modules and other TE components • Start-up the simulation system (HiL) and conduct a variety of tests at chassis dynamometer test bench

Goals: • Simulate virtual thermoelectric generators (TEG) and thermoelectric modules (TE modules) in their real working environment and under real operating conditions (e.g. exhaust temperature and mass flow, cooling power) • Anticipate changes in the characteristic/properties of TEG, TE modules and other components (e. g. heat exchangers)

TEG 2020 Realtime-Simulation – Hardware in the loop (HiL)

Flaps