(TEG) Thermoelectric Generator Test Bench Verfasser: Prof. Dr.-Ing. Stefan Beer; M. Eng. Ludwig Kinzler

TEG – 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

𝛂: 𝐒𝐞𝐞𝐛𝐞𝐜𝐤𝐜𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭,𝛍𝐕

𝐊

𝛔: 𝐬𝐩𝐞𝐜𝐢𝐟𝐢𝐜. 𝐞𝐥. 𝐜𝐨𝐧𝐝𝐮𝐜𝐭𝐢𝐯𝐢𝐭𝐲,𝐒

𝐦

𝛌: 𝐭𝐡𝐞𝐫𝐦𝐚𝐥 𝐜𝐨𝐧𝐝𝐮𝐜𝐭𝐢𝐯𝐢𝐭𝐲,𝐖/(𝐦𝐊)

𝐳𝐓 =𝛂𝟐𝛔 𝐓

𝛌

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 – 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:

𝛂: 𝐒𝐞𝐞𝐛𝐞𝐜𝐤𝐜𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭,𝛍𝐕

𝐊 ∆𝐔:𝐩𝐨𝐭𝐞𝐧𝐭𝐢𝐚𝐥 𝐝𝐢𝐟𝐞𝐫𝐞𝐧𝐜𝐞, 𝛍𝐕 ∆𝐓 𝐭𝐞𝐦𝐩𝐞𝐫𝐚𝐭𝐮𝐫𝐞 𝐝𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐜𝐞, 𝐊 ∆𝐔 = 𝛂∆𝐓

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=600°C, t_cold=30°C, eta_carnot = 0.653

Efficiency of TEG:

𝛈 =𝐏𝐞𝐥

𝐐 𝐳𝐮=𝐓𝐡𝐨𝐭 − 𝐓𝐜𝐨𝐥𝐝

𝐓𝐡𝐨𝐭

𝟏 + 𝐙𝐓 − 𝟏

𝟏 + 𝐙𝐓 +𝐓𝐜𝐨𝐥𝐝𝐓𝐡𝐨𝐭

𝐏𝐞𝐥: electrical power,W = I2RL 𝐐 𝐳𝐮: supplied heat flow,W 𝐙𝐓: figure of merit

𝐓𝐡𝐨𝐭: temperature on the hot side, K 𝐓𝐜𝐨𝐥𝐝: 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 Thermoöl 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 =300°C

Tcold =30°C

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 ° C -- cold surface: 40 ° 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 Stück)

First reflections with the TEGpro modul

[2]

thermo couple of two semiconductors:

thermoelectric generator module:

TEG 070-600-6, „Selenium/Tin-Telluride“, 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 ΔT = 570K

Max. Temp

mm V A Ω α κ W °C

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 SIDÉ)

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 =600°C

Tcold =30°C

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