(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 : , : . . , : , /() = 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: : , ∆: , ∆ , ∆ = ∆ 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: = = − + − + + : electrical power, W =I 2 R L : supplied heat flow, W : figure of merit : temperature on the hot side, K : temperature on the cold side, K TEG : methods for heat transfer q p,wand Medium Heat transfer coefficient Heat transfer mode Temperature difference [kW/m 2 ] [W/m 2 K] [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) mm 2 T hot =300°C T cold =30°C 415 W 393 W 21,6 W el wall heat flux density in TEGpro modul: 132,3 kW/m 2 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) mm 2 T hot =600°C T cold =30°C 224 W 15,3 W el wall heat flux density in thermalforce modul: 140 kW/m 2 213 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