A Bi-15 at.%Sb alloy, homogenized by equal channel angular extrusion (ECAE) at T = 523 K, has been treated just above its solidus temperature, causing segregation of a secondary Bi-rich phase at the grain boundaries. This process results in an in situ composite. The thermoelectric properties of the composite have been measured in the range of 5 K < T < 300 K. The results are compared with those of the homogeneous alloy. The presence of a Bi-rich phase improves the Seebeck coefficient at T < 50 K, and enhances the electrical conductivity by a factor of 1.4 at T = 300 K up to a factor of 3.4 at T = 50 K; unfortunately, the thermal conductivity also increases by about 50% in the same temperature range. As a result, the figure of merit, Z, is slightly suppressed above T = 110 K, but increases at lower temperatures, reaching a peak value of 4.2 9 10 À3 K À1 at T = 90 K. The power factor considerably increases over the whole temperature range, rendering this material suitable as the n-type leg of a cryogenic thermoelectric generator for cold energy recovery in a liquefied natural gas plant.
An autonomous heat-radiating gas heater for commercial outdoor environments has been selected as a test case for implementing cogeneration in autonomous gas heaters and stoves, permitting its installation and operation without the need of a connection to the electrical network. A thermoelectric generator (TEG) was selected for this purpose[1], designed for converting an amount of the produced heat into electrical power for auxiliary (ventilation, battery recharge) or ancillary functions (high efficiency LED illumination). The design approach, the layout and structure of the TEG are discussed, as well as the constraints for its integration in the existing gas heater. Design features and main components are examined: hot side heat collector for capturing heat from the flame; thermoelectric module (TEGM) technology and model selection; natural convection heat radiator at cold side; analysis and optimization of the thermal chain; TEG's assembly and its design as a whole. A prototype has been built and tested, its functional behavior has been modeled through multi-physics numerical simulation[2] to allow for further optimization and extrapolation of the results towards larger and/or more complex designs. A patent application has been issued jointly by the authors, covering the design hereinafter described.
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