Kouji Satou

Increase of the thermoelectric power factor in Cu∕Bi∕Cu,Ni∕Bi∕Ni, and Cu∕Bi∕Ni composite materials

The resultant thermoelectric power factors P of three types of Cu∕Bi∕Cu,Ni∕Bi∕Ni, and Cu∕Bi∕Ni composite materials welded with Bi were measured at 298 K as a function of relative thickness of Bi and compared with P values calculated by treating these devices as an electrical and thermal circuit. It was first demonstrated experimentally that the observed P values of composite devices have a local maximum at an optimum volume fraction (corresponding to the thickness) of Bi, as predicted theoretically. The maximum P values of composite materials were several times higher than those of pure Ni and Bi and were about 100 times larger than that of pure Cu. The dependence of P on the thickness of Bi was found to be explained roughly by introducing the modified thermal conductivity and an enhancement factor in the Seebeck coefficient to our simple model in which a device was treated as an electrical and thermal circuit.

Enhancement of the thermoelectric figure of merit in M∕T∕M (M=Cu or Ni and T=Bi0.88Sb0.12) composite materials

The resultant thermoelectric figure of merit ZT of M∕T∕M (M=Cu or Ni and T=Bi0.88Sb0.12) composite materials welded with Bi–Sb alloy was measured at 298K as a function of relative thickness of Bi–Sb alloy and compared with ZT values calculated by treating it as an electrical and thermal circuit. It was first clarified experimentally that the observed ZT values of composite materials have a local maximum at an optimum volume fraction (corresponding to the thickness) of Bi–Sb alloy in spite of macroscopic composite materials, owing to a significant enhancement in the Seebeck coefficient. It is sure that the enhancement in α is caused by the boundary Seebeck coefficient generated at the interface between Bi–Sb alloy and a metal. It was thus clarified that the interface effect appears clearly in macroscopic systems. The observed maximum ZT values at 298K reached a surprisingly great value of 0.44 at a relative thickness of approximately 0.7, which corresponds to approximately 1.7 times as large as 0.26 of Bi0...

Energy conversion efficiency of a thermoelectric generator under the periodically alternating temperature gradients

The thermo-emf ΔV and thermoelectric current ΔI generated by imposing the temperature gradient (TG) alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and T was varied from 8s to ∞. The alternating TG was produced by switching a voltage of 2.6V across two Peltier modules (20×20×4.0mm3) connected in series. Two different types of TE generators were employed as a generator and sandwiched between Peltier modules. The dimensions of the generators (1) and (2) were 15×15×4.0 and 20×20×3.8mm3, respectively. The input power Winput fed to two Peltier modules increases abruptly with an increase of 1∕T, but the effective temperature difference ΔTeff produced between two Peltier modules has a local maximum at 1∕T=1∕240s−1 for the generator (1) and at 1∕120s−1 for the generator (2), whose maximum values are 2.59 and 3.65 times as large as those obtained at 1∕T=0s−1. The local maxima of ΔVeff, ΔIeff, and ΔWeff, generated by a generator, appeared ...

Geometrical effect in magneto-Peltier cooling of single crystal Bi

The cooling temperatures of rectangular parallelepiped Bi single crystals with various widths W and thickness t were measured at 293 K as a function of electric current in the magnetic field B up to 2.17 T. The magnetic field was aligned along the thickness of a sample and the current flows along its length L through the copper leads soldered to both end surfaces of cross section (W×t), where W, t, and L are parallel to the binary, bisector, and trigonal axes of Bi single crystal, respectively. The thermoelement was not in contact with a heat sink. The cooling temperature at the cooled surface increased with increasing the magnetic field, and it depended strongly on the thickness rather than the width of the crystal in high magnetic fields. The largest maximum cooling temperature was achieved when a thermoelement has optimum dimensions so that no heat energy is generated at the cold side. The cooling temperature of Bi single crystal with optimum dimensions of L=15 mm, W=4 mm, and t=2 mm increased from 4.1...