Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

A thermodynamic model of a skin-wearable annular thermoelectric generator (WATEG) system for harvesting human body heat is developed. The human skin is recognized as a three-layer structure, consisting of the subcutis layer, the dermis, and the epidermis. The heat exchange caused by blood perfusion and metabolic heat generation within skin tissue are taken into account using dual-phase-lag (DPL) bioheat conduction theory. Based on the maximum power density, the matched external load resistance, optimal fill factor, and optimal configuration dimensions of thermoelectric semiconductors and fin heat sink are provided through the numerical results. Additionally, the dynamic thermal responses of the WATEGs under various convective heat dissipation conditions at heat sink which occur during physical activities of the human body such as walking, jogging, and sprinting are also studied. The influence of metabolic heat generation within skin tissue is found to be relatively small and can be disregarded. However, neglecting blood perfusion results in a significant underestimation by approximately 30% in the steady-state energy conversion performance of the WATEG. The optimal fin height for achieving the maximum power density per unit mass of the aluminum-based heat sink is identified, and it is established at 10 mm, aligning with a heat convection coefficient of 10 W/m² K. The analytical model developed in this paper proves to be highly beneficial in the design and fabrication of actual WATEGs used for self-powered wearable microelectronic devices.