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Counter-flowing thermal fluids are conducive to generate a homogeneous temperature difference on thermoelectric (TE) generator. This study allowed the hot and cold fluids of having constant inlet temperature to flow in the opposite, and examined TE performance of module at different flow rates. The results show that TE performance gradually increases with flow rate in the initial stage of fluid flow, and reaches a transient peak value after the module surfaces are completely covered by thermal fluids, and then tends to be stable. High flow rate leads to larger performance and reduces the time of achieving them. Effect of flow rate on stable performance is slightly more than that of inlet temperature of thermal fluids, which makes regulating the flow rate to be a feasible way to harvest more heat for TE conversion. Module features present a specific trend and provide the supports for the benefit of counter-flowing thermal fluids.

Thermoelectric (TE) performance of a three-dimensional (3D) TE module is examined by exposing it between a pair of counter-flows of ideal fluids. The ideal fluids as thermal sources of TE module flow in the opposite direction at same flow rate and generate temperature difference on the hot and cold surfaces due to their different temperature at channel inlet. TE performance caused by different inlet temperature of thermal fluids are numerically analyzed by using finite-volume method on 3D meshed physical models and then compared with those of using constant boundary temperature. The results show that voltage and current of TE module increase gradually from a beginning moment to a steady flow and reach a stable value. The stable values increase with inlet temperature of hot fluid when inlet temperature of cold fluid is fixed. However, the time to get the stable values is almost consistent for all the temperature differences. Moreover, the trend of TE performance using fluid flow boundary is similar to that of using constant boundary temperature. Further, 3D contours of fluid pressure, temperature, enthalpy, electromotive force, current density and heat flux are exhibited in order to clarify the influence of counter-flows of ideal fluids on TE generation. The current density and heat flux homogeneously distribute on entire TE module, thus indicating that the counter-flows of thermal fluids have high potential to bring fine performance for TE module.