Heat transfer modeling for bio-heat recovery

Harvesting heat from the skin surface of humans or homoeothermic animals will provide a great opportunity for implementing wireless communication sensors and/or monitoring devices without the use of batteries. One of the bio-energy harvesting approaches, the thermoelectric generator is a promising candidate for converting the temperature difference between the body skin and the ambient air into electricity. Due to the surface curvature of the human body, a mechanically flexible and thin generator module is desired. Thus, we propose and investigate a new concept which is a woven fabric thermoelectric module made from weaving together thermoelectric strings which have a repeating [p-type - metal - n-type - metal] (p=m=n=m) pattern with Bismuth-Telluride (Bi₂Te₃) and insulation yarn. This paper reports the performance and cost estimation of the module compared with a conventional (π-structure) module that consists of a polymer based thermoelectric material, e.g., PEDOT-PSS. Heat Transfer through the thermoelectric element is not only the key to optimizing the module design for maximum power output but is also the series that spreads thermal resistances in laminate films, the parallel thermal path through the gap fill media, and the external heat sink thermal resistances. According to a previously developed generic model, the performance and cost per power production of the woven thermoelectric module is calculated and compared with that of a conventional polymer based module. The woven generator has been found to be able to produce power output that is nearly double that of the conventional polymer one. As a power generator system, the cold side heat sink can be designed to enhance the power output by extending the surface area. As one of the surface extensions, a pin-fin heat transfer is the most promising for the flexible thermoelectric generator module, but it has been found to produce a rather less encouraging enhancement except for a relatively longer pinfin of more than 1 cm.