Optimized thermal coupling of micro thermoelectric generators for improved output performance

• Published in: Renewable energy Vol. 60; pp. 746 - 753
• Main Authors: Wojtas, N., Rüthemann, L., Glatz, W., Hierold, C.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2013; Elsevier
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Flow rate; Harvesters; heat tolerance; Heat transfer; Micro heat transfer system (μHTS); Micro thermoelectric generator (μTEG); Natural energy; Performance enhancement; Power factor; renewable energy sources; temperature; Temperature gradient; Theoretical studies. Data and constants. Metering; Thermal contact resistance; Thermal coupling; Thermal resistance; Thermoelectric generators; Waste heat recovery; Micro thermoelectric generator (μTEG); Power factor; Waste heat recovery; Thermal contact resistance; Micro heat transfer system (μHTS); Waste recovery; Renewable energy; Heat recovery; Heat transfer
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2013.06.031

There is a significant push to increase the output power of thermoelectric generators (TEGs) in order to make them more competitive energy harvesters. The thermal coupling of TEGs has a major impact on the effective temperature gradient across the generator and therefore the power output achieved. The application of micro fluidic heat transfer systems (μHTS) can significantly reduce the thermal contact resistance and thus enhance the TEG's performance. This paper reports on the characterization and optimization of a μTEG integrated with a two layer μHTS. The main advantage of the presented system is the combination of very low heat transfer resistances with small pumping powers in a compact volume. The influence of the most relevant system parameters, i.e. microchannel width, applied flow rate and the μTEG thickness on the system's net output performance are investigated. The dimensions of the μHTS/μTEG system can be optimized for specific temperature application ranges, and the maximum net power can be tracked by adjusting the heat transfer resistance during operation. A system net output power of 126 mW/cm2 was achieved with a module ZT of 0.1 at a fluid flow rate of 0.07 l/min and an applied temperature difference of 95K. It was concluded that for systems with good thermal coupling, the thermoelectric material optimization should focus more on the power factor than on the figure of merit ZT itself, since the influence of the thermal resistance of the TE material is negligible. •Two-layer μHTS were integrated with μTEGs for an output power enhancement.•The influence of the system parameters on the net output performance was investigated.•Optimal parameter combinations for specific operation temperatures were found.•A net output power of 126.3 mW/cm2 was achieved with a ZT of 0.1 at ΔT of 95K.•The importance of the power factor for high heat flux applications was emphasized.