# Bridging heat-flow and guarded-heater methods for thermoelectric module efficiency evaluation

## TL;DR

This paper introduces a new method to improve the accuracy of thermoelectric module efficiency evaluations by reducing heat losses.

## Contribution

A guard ring with a vacuum gap is introduced to suppress lateral heat losses and improve measurement accuracy.

## Key findings

- The guarded configuration achieved input-output agreement within 0.5 W, while unguarded setups had discrepancies over 5 W.
- The new method achieved an expanded uncertainty of 1.4% under high-temperature operation.
- Thermal simulations and comparisons with a reference instrument confirmed the effectiveness of the guard ring.

## Abstract

Reliable efficiency evaluations are recognized as one of the major challenges in thermoelectric technology. Existing heat-flow and guarded-heater methods suffer from uncertainties due to heat losses from the lateral surfaces of the thermoelectric module. Here, we introduce an apparatus that encloses the module with a thermally matched guard ring, separated by a vacuum gap, establishing near-isothermal sidewalls that suppress radiative losses from the lateral surfaces. Measurements with the hot side up to 703 K and an input heat flow up to 124 W showed input-output agreement within 0.5 W. Conversely, the unguarded configurations exhibited discrepancies exceeding 5 W. Thermal simulations qualitatively supported these trends, and a comparison with a reference instrument confirmed the electrical consistency while revealing the differences in thermal boundary conditions. This measurement configuration connects the two approaches, enabling reproducible efficiency evaluations with an expanded uncertainty of 1.4% and providing a technical basis that may inform future international standardization.

•Guard ring suppresses lateral heat leakage in TEMs•Thermal-resistance matching ensures energy consistency•Axial/radial flux ratio confirms quasi-1D heat flow•1.4% expanded uncertainty under high-temperature operation for oxide TEMs

Guard ring suppresses lateral heat leakage in TEMs

Thermal-resistance matching ensures energy consistency

Axial/radial flux ratio confirms quasi-1D heat flow

1.4% expanded uncertainty under high-temperature operation for oxide TEMs

Electrical engineering; Energy engineering; Physics