Takeyuki Fujisaka

Effects of Fluid Directions on Heat Exchange in Thermoelectric Generators

Thermal fluids can transport heat to the large surface of a thermoelectric (TE) panel from hot and/or cold sources. The TE power thus obtainable was precisely evaluated using numerical calculations based on fluid dynamics and heat transfer. The commercial software FLUENT was coupled with a TE model for this purpose. The fluid velocity distribution and the temperature profiles in the fluids and TE modules were calculated in two-dimensional space. The electromotive force was then evaluated for counter-flow and split-flow models to show the effect of a stagnation point. Friction along the fluid surface along a long, flat path was larger than that along a short path split into two parts. The power required to circulate the fluids along the flow path is not negligible and should be considered in TE generation system design.

Thermoelectric Analysis for Helical Power Generation Systems

The performance of a three-dimensional helical thermoelectric generation (TEG) system is examined by exposing it to a temperature difference with hot and cold sources. The helical paths for the two thermal fluids give the TEG device the potential to efficiently convert thermal energy. The characteristic performance of the helical system is numerically analyzed by using the finite-volume method in a compact system. The helical system is compared with a straight system in which all the thermoelectric (TE) elements present equivalent geometry. The difference in the TE performance between the two systems is not significant when the TE surfaces are maintained at constant temperatures. Both the electromotive force and the current in the TEG system increase linearly with the temperature difference ΔT applied at the two module surfaces. The current preferentially flows through a main path determined by the geometry of the TE element. The merits of the helical design are its compactness, space saving, and smooth fluid flow due to gravity, compared with the straight system.

Dimensional Analysis of Thermoelectric Modules Under Constant Heat Flux

Thermoelectric power generation is examined in the case of radiative heating. A constant heat flux is assumed in addition to consideration of the Seebeck effect, Peltier effect, and Joule heating with temperature-dependent material properties. Numerical evaluations are conducted using a combination of the finite-volume method and an original simultaneous solver for the heat transfer, thermoelectric, and electric transportation phenomena. Comparison with experimental results shows that the new solver could work well in the numerical calculations. The calculations predict that the Seebeck effect becomes larger for longer thermoelectric elements because of the larger temperature difference. The heat transfer to the cold surface is critical to determine the junction temperatures under a constant heat flux from the hot surface. The negative contribution from Peltier cooling and heating can be minimized when the current is smaller for longer elements. Therefore, a thicker TE module can generate more electric power even under a constant heat flux.

Power generation using the fluids blown perpendicular to the TE panel

Temperature difference is given to thermoelectric (TE) flat panel using two thermal fluids. The TE power is mathematically evaluated when a fluid is perpendicularly blown onto the center of the TE panel and when it divided to two opposite directions at the equivalent mass flow rate. The non-dimensional analysis shows that the output power becomes completely identical with that for the non-split flow along the single flat TE panel. The fluid velocity distribution and the temperature profiles were numerically calculated using the finite volume method to show the effect of stagnation and friction in the long flat path.

Dimensional optimization of thermoelectric modules for solar power generation

A thermoelectric generation system is examined based on heat transfer analysis when solar heat is taken as the heat source. Under a constant heat flux condition from a solar collector, external load and leg length were numerically optimized to obtain maximum power. The optimal external load is different from the traditional condition that the external and internal loads are equal. The optimal leg length was derived analytically by using a reasonable set of assumptions.

Thermoelectric Analysis for Π-type Thermoelectric Module with Tilted Elements

Abstract Thermoelectric (TE) legs in the Π-type module for TE generation are tilted as a shape of parallelogram, and three-dimensional flows of heat and electric charge are examined by using a numerical analysis of finite-volume method. The distributions of temperature and current density are significantly dependent on the module configuration and leg shape. The shortest path is chosen preferentially as mainstream of current. The Π-type module is the most favorable because the maximum performance is obtained in case that the tilting angle is 90°. Under the constant temperature difference, the charge-transporting ability of the stream is governed by the path length.

Thermoelectric Analysis for a Three-Dimensional Power Generator in Helical

Thermoelectric (TE) phenomenon of a helical generator is numerically analyzed by using the finite-volume method in combination with a three-dimensional finite-element (FE) model. The distributions of temperature and current density are significantly influenced by the generator dimension. The output power of helical generator is also affected by the geometric parameter, such as the helical pitch. The output power and conversion efficiency of helical generator are better than those of straight generator where all the TE elements aligned in a straight line. The helical geometry has a satisfactory potential to be a good TE generator.

Optimization of Module Shape in Thermoelectric Power Generation

Heat and electric charge transfer through the thermoelectric (TE) module were analyzed numerically. The thermal heat can expand or shrink in the trapezoid shape in comparison with the conventional Π type module, and the output and efficiency from the module with trapezoid TE elements was examined from the view of shape optimization. The temperature profile and some thermoelectric properties were calculated using the infinite volume method and the original code. The temperature profile in the module showed a complex distribution in the TE elements, however, the efficiency in power generation did not change from that of the rectangular TE module.