Post on 30-Apr-2022
(TEG) Thermoelectric Generator Test Bench Verfasser: Prof. Dr.-Ing. Stefan Beer; M. Eng. Ludwig Kinzler
TEG โ Thermoelectric Generator Test Bench
This project is co-funded by the Science and Technology Network Upper Palatinate and the CHP Technology Campus of the OTH Amberg-Weiden
Physical basics:
Test bench: Hot Air
First results:
[1]
Problem with TEG:
[3]
figure of merit (zT) dimensionless
Important characteristic of the thermoelectric material
๐: ๐๐๐๐๐๐๐ค๐๐จ๐๐๐๐ข๐๐ข๐๐ง๐ญ,๐๐
๐
๐: ๐ฌ๐ฉ๐๐๐ข๐๐ข๐. ๐๐ฅ. ๐๐จ๐ง๐๐ฎ๐๐ญ๐ข๐ฏ๐ข๐ญ๐ฒ,๐
๐ฆ
๐: ๐ญ๐ก๐๐ซ๐ฆ๐๐ฅ ๐๐จ๐ง๐๐ฎ๐๐ญ๐ข๐ฏ๐ข๐ญ๐ฒ,๐/(๐ฆ๐)
๐ณ๐ =๐๐๐ ๐
๐
The generation of electrical power from the heat flux passing through an el. conductor is known as the Seebeck effect. (Thomas Seebeck, 1821) The greater the temperature difference of the hot side compared to the cold side, the greater is the power output (Watts). Two critical factors dictate power output : 1. The amount of heat flux that can successfully move through the module (HEAT FLOW) 2. Delta โ the temperature of the hot side minus the temperature of the cold side Thermoelectric generator: Materials for TEG In general, thermoelectric materials can be categorized into conventional and new materials: Conventional materials: Low temperature materials : Alloys based on Bismuth in combinations with Antimony, Tellurium or Selenium. Intermediate temperature : materials based on alloys of Lead Highest temperatures material : materials fabricated from silicon germanium alloys. Potential difference by thermal diffusion of charge carriers as a result of temperature difference:
๐: ๐๐๐๐๐๐๐ค๐๐จ๐๐๐๐ข๐๐ข๐๐ง๐ญ,๐๐
๐ โ๐:๐ฉ๐จ๐ญ๐๐ง๐ญ๐ข๐๐ฅ ๐๐ข๐๐๐ซ๐๐ง๐๐, ๐๐ โ๐ ๐ญ๐๐ฆ๐ฉ๐๐ซ๐๐ญ๐ฎ๐ซ๐ ๐๐ข๐๐๐๐ซ๐๐ง๐๐, ๐ โ๐ = ๐โ๐
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0,18
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
eta
ZT
Efficiency eta TEG t_hot=600ยฐC, t_cold=30ยฐC, eta_carnot = 0.653
Efficiency of TEG:
๐ =๐๐๐ฅ
๐ ๐ณ๐ฎ=๐๐ก๐จ๐ญ โ ๐๐๐จ๐ฅ๐
๐๐ก๐จ๐ญ
๐ + ๐๐ โ ๐
๐ + ๐๐ +๐๐๐จ๐ฅ๐๐๐ก๐จ๐ญ
๐๐๐ฅ: electrical power,W = I2RL ๐ ๐ณ๐ฎ: supplied heat flow,W ๐๐: figure of merit
๐๐ก๐จ๐ญ: temperature on the hot side, K ๐๐๐จ๐ฅ๐: temperature on the cold side, K
TEG : methods for heat transfer
qp,wand Medium Heat transfer
coefficient Heat transfer
mode Temperature
difference
[kW/m2] [W/m2K] [K]
132,3 Gas 200 convection 661,5
132,3 water 2000 convection 66,15
132,3 Thermoรถl 1000 convection 132,3
132,3 Cu/Al >= 5000 contact 26,46
132,3 water 10000 nucleate boiling 13,23
132,3 steam 10000 film condensation 13,23
TEG (56 x 56) mm2
Thot =300ยฐC
Tcold =30ยฐC
415 W
393 W
21,6 W el
wall heat flux density in TEGpro modul: 132,3 kW/m2
Outlook:
Design solutions to minimize the thermal contact
resistance , especially on the hot gas side
- Analytical studies on the coupling of TEG to fluid flows ,
profitability
- CFD studies for optimizing the geometry of the contact
body
- Measurement of TEG modules by means of heated and
cooled fluid flows (cold side water , hot side thermal oil
or hot gas )
- Development of modules for stirling engine , biomass
boilers , combustion engine , industrial waste heat
Analysis of results:
Performance remains significantly below expectations
high temperature gradient between gas and hot side of the
TEG as a result of the thermal contact resistance
thermal expansion of the mounting screws (32-64 kg /
module)
Reasons:
Solution:
spring-loaded
fastening elements
[4]
Electrical power output of one module : 5,4 W
Heat input to one module: 107,5 W -- Dissipated heat output: 102,1 W
Temperature of the hot contact surface: about 410 ยฐ C -- cold surface: 40 ยฐ C
Efficiency: 5 %
[4]
Solving approaches:
Forced convection with liquids through a contact body with surface enlargement
Flow with hot gas is only possible with ribbed contact body with high surface
enlargement (fins)
Direct flow with liquids
Conclusion:
Quelle: TEGpro, Modulpreis ca. 60 US$ pro Stรผck)
First reflections with the TEGpro modul
[2]
thermo couple of two semiconductors:
thermoelectric generator module:
TEG 070-600-6, โSelenium/Tin-Tellurideโ, 40mm x 40 mm
dimensions l*b*h
open circuit voltage
short circuit current
electric resistance Ri,at 300k
thermal-force (V/K)
thermal- conductivity
(W/K)
electric power at ฮT = 570K
Max. Temp
mm V A ฮฉ ฮฑ ฮบ W ยฐC
40x40x4 8,29 7,36 0,42 0,012 0,360 15,28 650
ribbed contact body with very large surface (HOT SIDE)
TEG modules on contact body (HOT SIDE)
TEG modules between contact body (HOT SIDร)
and cooling plate (COLD SIDE)
entire test bench
Selected TEG for first test bench:
For the test bench are used 4 TEGs
TEG (40 x 40) mm2
Thot =600ยฐC
Tcold =30ยฐC
224 W
15,3 W el
wall heat flux density in thermalforce modul: 140 kW/m2
213 W
sources:
[1] http://www.mpoweruk.com/semiconductors.htm [2] http://www.sciencedirect.com/science/article/pii/S1359431115012685
[3] Leipner, H.S., 2008 [4] www.thermalforce.de