Heat transfer plays an important role in thermoelectric (TE) power generation because the higher the heat-transfer rate from the hot to the cold side of the TE material, the higher is the generation of electric power. However, high heat-transfer rate is difficult to achieve compactly when the hot and/or the cold sources are maintained by a flow of gas such as waste heat from the gas exhaust of an engine or a power plant. Also, when the temperature of the hot and the cold sources differs considerably, thermal stress can create damage and thereby affect reliability and service life.

In this study, computational fluid dynamics (CFD) analyses were performed to evaluate two compact gas-phase heat exchangers (HXs) on their ability to enable high heat-transfer rates from the hot to the cold sides of the TE material with minimal thermal stress. One HX utilizes the leading portion of developing momentum and thermal boundary layers, and the other HX involves jet impingement. The CFD analyses take into account the convection heat transfer of the hot gas in the HX flow passages and the conduction heat transfer in the HX walls, the TE materials, the electrical conducting plates, and the insulation material that fills the space between the TE material, the conducting plates, and the HX walls. Both laminar and turbulent flows in the HX flow passages were investigated. When the flow is turbulent, the analysis of the gas phase is based on the ensemble-averaged continuity, Navier-Stokes, and energy equations, closed by the realizable k-e turbulence model that are integrated to the wall (i.e., wall functions were not used). The analysis of the solid phase is based on the Fourier law.

Results obtained show the two HX designs studied to be useful in increasing heat-transfer rate through the TE material with minimal thermal stresses. For the HX that utilizes the leading part of the boundary-layer flow, a heat-transfer rate of 1 W/cm2 could be achieved with reasonable pressure loss. For the HX with jet impingement, a heat-transfer rate of about 3 W/cm2 could be achieved but the pressure loss is considerably higher.