Prismatic Spreading–Constriction Expression for the Improvement of Impedance Spectroscopy Models and a More Accurate Determination of the Internal Thermal Contact Resistances of Thermoelectric Modules

Abstract

Thermoelectric (TE) devices can convert heat to electrical power or use electrical power to generate a temperature difference. Their characterization is essential to develop devices with higher efficiency. Impedance spectroscopy models have been developed in the last few years, and it has become a highly advantageous method for TE system characterization. Recently, it has been shown that this technique can also be used to determine internal thermal contacts (between the TE legs and the metallic strips that connect them and between the metallic strips and the outer layers). Here, we developed for the first time a spreading−constriction expression which does not assume cylindrical geometry. The enhanced model is also used to characterize four TE devices from different manufacturers, highlighting overestimations up to 13% when the previous cylindrical approximation is used. A code is provided in the Supporting Information ready to fit the experimental data. This study positions impedance spectroscopy as a powerful tool to detect and monitor issues during manufacturing or operation of TE devices, which typically occur at the contacts.

Determination of thermal conductivity, thermal diffusivity, and specific heat of liquids using a thermoelectric module

“…From this first fitting, r TC1 , λ TE , and λ C were determined (see table 1). It should be noted that r TC2 = 0 was found for this TE module, which was expected, since it is usual to find a good [15] and of this manuscript, respectively.…”

“…It was directly measured by recording the voltage and temperature difference between the outer surfaces of the ceramics of the TE module in suspended and vacuum conditions when different constant current values were applied. Figure 3(a) shows the experimental impedance spectrum of the TE module suspended in vacuum (dots) and its fitting (line) using the MATLAB code provided in the supplementary information of [15]. From this first fitting, r TC1 , λ TE , and λ C were determined (see table 1).…”

“…and the parameter z sc , present in equations ( 5) and ( 7), is the spreading-constriction impedance, which takes the form [15],…”

“…define all the possible solutions for the values n and m. The geometrical parameters x 1 = (A/η) 1/2 /2 + A 1/2 /2, x 2 = (A/η) 1/2 , y 1 = A 1/2 /2, and y 2 = (A/η) 1/2 /2, are defined in the supplementary information of [15].…”