Influence of external thermal resistance on thermoelectric cooling in thermal management systems: Operating modes and material selection

• External thermal resistances influence the operating mode of a thermoelectric cooler. • The cooler can operate in refrigeration mode even under high-temperature heat sources. • A material selection criterion is proposed based on external thermal resistances. • Experiment using a commercial thermoelectric cooler further validate our findings. Embedding thermoelectric coolers (TECs) within thermal management systems is a promising approach for addressing localized heat. The required thermoelectric (TE) material properties for achieving a high cooling rate depend on the operating mode of TECs—refrigeration or active cooling—which is determined by the internal Fourier heat direction within the TE legs. Therefore, analyzing the operating mode should be prioritized before employing TECs to ensure the selection of TE materials that maximize cooling performance. However, the influence of external thermal resistances has often been neglected, leading to misclassification of TEC operating modes and the selection of inappropriate TE materials, ultimately resulting in lower cooling rates. To address this, we analyze operating modes of TECs while accounting for external thermal resistances. Our findings reveal that TECs operate in active cooling mode only if the thermal conductivity of the TE material exceeds a specific threshold; otherwise, they operate in refrigeration mode. This threshold is determined by both material properties and external thermal resistances. Building on this insight, we identify the operating mode that achieves the highest cooling rate for given external thermal resistances and establish a criterion for selecting optimal TE materials. Experimental validation closely aligns with our theoretical analysis, further confirming our results. This study provides fundamental insights into the influence of external thermal resistances on TEC operating modes, facilitating the effective integration of TECs into thermal management systems by optimizing TE material selection.