Heat is one of the most important aspects of living organisms. Metabolic heat production and evaporative heat dissipation protect warm-blooded animals from adverse weather conditions. Heat management devices provide thermal comfort to human by climate control or thermal camouflage effect by blocking heat emission from the human body. Further, metabolism in living organisms can be investigated by monitoring heat signature because the metabolic heat production represents the overall enthalpy change during metabolic reactions in organisms. This dissertation presents two state-of-the-art devices and demonstrates their applications: 1) a wearable thermoelectric device (TED) for personal thermoregulation and camouflage, and 2) high-resolution calorimeter for measurement of single-cell metabolic heat generation.

Personalized cooling/heating by TEDs can drastically reduce energy consumption with small cooling volume, meet individual cooling needs and camouflage heat emission from the human body. However, a TED with sufficient flexibility and temperature regulation performance has yet to be realized because of lack of optimization of the thermal and mechanical design. In the first part of the dissertation, we demonstrated a wearable TED that can deliver over 10 °C cooling effect with a high coefficient of performance (COP>1.5). Our TED is the first to achieve long-term active cooling with high flexibility, thanks to a novel design of double elastomer layers embedding an air gap insulation and high-ZT rigid TE pillars. The TED was also applied to thermal camouflage using the large temperature regulation window, which enables to match the heat signature of human body with background temperature.

The last part of the dissertation focuses on fundamental study of cellular metabolism using direct calorimetry techique. We developed high-resolution calorimeter sufficient to measure heat generation from a single cell for investigation of heterogeneous metabolic activities. This non-invasive and label-free calorimetry technic is optimized to study the cell metabolic heat production without alter the nature of cells. Our single-cell calorimeter achieved the power resolution as low as 0.6 nW using the innovative one-dimensional microfluidic tube design. Single-cell measurements using the calorimeter revealed that the relationship between metabolic rate and cell size of individual Tetrahymena follows the allometric scaling relationship.