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A 1kWₑ thermoelectric stack for geothermal power generation – Modeling and geometrical optimization

Suter, C., Jovanovic, Z.R., Steinfeld, A.
Applied energy 2012 v.99 pp. 379-385
aluminum oxide, cold, copper, electric power, geothermal energy, heat exchangers, heat transfer, models, power generation, temperature
A thermoelectric stack comprising an array of Bi–Te based thermoelectric converter (TEC) modules is considered for geothermal heat conversion. Each TEC module consists of 127 (Bi₀.₂Sb₀.₈)₂Te₃/Bi₂(Te₀.₉₆Se₀.₀₄)₃p/n-type thermoelement pairs, fastened by 30×30mm² Al₂O₃ plates. The thermoelement pairs have leg cross-section of 1.05×1.05mm², a figure-of-merit equal to 1, and a theoretical heat-to-electricity conversion efficiency of ∼5% when the module is operated at a temperature difference of 200K. A temperature gradient across the thermoelement legs within an array is imposed via a Cu parallel-plate heat exchanger adhering to the Al₂O₃ plates and operating hot and cold water in counter-flow channel configuration. A heat transfer model coupling conduction through the thermoelement legs with convection to and from the Al₂O₃ plates is formulated to investigate the performance of the stack as function of the following parameters: hot water inlet and outlet temperatures (313–413K and 303–393K, respectively), stack length (300–1500mm), thermoelement leg length (0.5–4mm) and hot/cold channel heights (0.2–2mm). The open-circuit voltages resulting from the temperature differences are within 3% mean relative error of those resulting from temperature differences computed via CFD. The heat transfer model is then applied to optimize a 1kWₑ stack with hot water inlet and outlet temperatures of 413K and 393K, respectively, for either a maximum heat-to-electricity efficiency of 4.2% or for a minimum volume of 0.0021m³.