B.V.K. Reddy

Thermoelectric Performance of Novel Composite and Integrated Devices Applied to Waste Heat Recovery

Thermoelectric elements, made of semiconductor slices laminated onto highly conductive interconnector materials, are termed composite thermoelectric device (TED). An integrated TED is a composite TED with the interconnector designed as an internal heat exchanger with flow channels directing the working fluid between the source and element legs. In this work, novel composite and integrated TEDs are proposed as an alternative to conventional TEDs, and their performance in terms of power output P 0 , heat input Q h , conversion efficiency η, and the produced electrical current I is studied using analytical solutions. The top and bottom surfaces of the TED are subjected to a temperature differential while the side surfaces are exposed to either ambient or adiabatic conditions. An increment in temperature differential results in enhanced device performance. For a fixed temperature differential, the integrated TED shows nearly an eight-fold increase in both P o and Q h and a four-fold increase in I, whereas the composite TED shows approximately a two-fold increase in P 0 , Q h , and I when compared to the conventional TED values. Both novel TED designs have a minimal impact on efficiency predictions. However, an increase in semiconductor slice thickness resulted in an exponential decrease in P 0 , Q h , and I, and an exponential increase in η values and reaches a limit of conventional TED values. The effect of semiconductor slice thickness on η in the novel TEDs is remarkable when it is less than 1 mm. The change in ambient conditions via convective heat transfer coefficient has negligible effects on P 0 ; however, a substantial change in η occurs when it is less than 100 Wm ―2 K ―1 .

Three-Dimensional Multiphysics Coupled Field Analysis of an Integrated Thermoelectric Device

Thermoelectric elements made of semiconductor plates laminated onto a highly electrical and thermally conductive inter-connector with a flow channel configuration can be treated as an integrated thermoelectric device (iTED). An element constructed with bulk crystalline n- and p-type (Bismuth-Telluride) semiconducting materials and copper as a conducting material is considered. In this study, the thermoelectric performance of such an element using fluid-thermoelectric coupled field numerical methods has been investigated. The iTED is subjected to constant cold temperature at the bottom and top surfaces, while the inter-connector channel walls are exposed to hot fluid flow; the remaining surfaces are kept adiabatic. The performance of the iTED element is studied in terms of heat input Q h , power output P 0, conversion efficiency η, produced electric current and Ohmic and Seebeck voltages for different load resistances, inlet hot fluid temperatures T in , semiconductor material heights d, and flow rates Re. For fixed T in and Re, an optimum η is shown at a load resistance which is slightly lesser than total internal resistance value. An increase in T in results in an enhancement in P 0 and η; however, it has a minimal effect on the variation of optimum load resistance. At higher T in values, the increment in load resistance showed a significant change in the heat input values. Both semiconductor material height and fluid flow rate had a prominent effect on iTED performance. The P 0 and η are increased nearly three-fold and 1.6 times, respectively, at Re = 500 in comparison to Re = 100. Further, when d = 5 mm, approximately 1.7 times in P 0 and 3.3 times in η are achieved compared to d = 1 mm values. It is recommended that for an accurate modeling, design and optimization of state-of-the-art TED with flow channels be carried out using multiphysics coupling field simulations.

Comprehensive Numerical Modeling of Thermoelectric Devices Applied to Automotive Exhaust Gas Waste-Heat Recovery

This study investigates using numerical methods the performance of thermoelectric devices (TEDs) integrated with heat exchangers and applied to automotive exhaust gas waste-heat recovery. Air as an exhaust gas and water as a cooling fluid are used. The effects of temperature-dependent properties of materials (TE elements, ceramic plates, connectors, insulation materials and fluids) and interface electrical and thermal contact resistances on TED’s performance are included in the analysis. Additionally, the fluid heat exchangers and the insulation materials are modeled using a porous media approach. The response of hot and cold fluid inlet temperatures (Thi, Tci) and flow rates, number of modules N, permeability of heat exchangers and TE materials type on TED’s hydro-thermoelectric characteristics is studied. An increase in either Thi or a decrease in Tci is resulted in an enhancement in TED’s performance. The addition of modules is shown a significant effect on heat input Qh and power output P0 predictions; however, a minimal impact on efficiency η is displayed with N. For instance, at Thi = 873.15 K and Tci = 353.15 K with clathrate n-Ba8Ga16Ge30 and p-PbTe material’s combination, compared to single module case, TED with four modules showed 3.77- and 3.7-fold increase in P0 and Qh, respectively. In the studied 1–4 modules range, the cold fluid flow rate and the permeability of heat exchangers are exhibited a negligible effect on TED’s P0 and η, whereas the hot fluid flow rate is shown an appreciable change in η values. Further, when Thi is less than 500 K, TED with bismuth-tellurides showed a higher performance when compared to the clathrates and lead-tellurides materials combination.Copyright