Compliant thermoelectric generators (TEGs) hold great promise in the field of self‐powered wearable electronics. Yet, the low heat transfer efficiency arising from large thermal resistance between elastic encapsulating materials and the contacted objects severely lowers the thermopower. This issue is much more challenging for organic TEG (oTEG) due to the high parasitic heat loss in the whole polymer system. Herein, guided by finite element analyses, a polydimethylsiloxane based composite coated with Cu is developed as a thermal interface without compromising the compliance of the oTEG, which possesses the merits of high thermal conductivity and significantly reduced thermal resistance, thus maximizing the temperature difference utilization ratio to 86%, which is 75.5% higher than for a routine oTEG. As a proof‐of‐concept, 50 pairs of p/n porous polyurethane/single‐wall carbon nanotube TE legs are integrated onto the designed substrate without further encapsulation. Both simulations and experiments on output performance under various thermal conditions are carried out, and show excellent agreement. The in situ output performance tests under various deformation conditions reveal the mechanical robustness of the oTEG. Finally, an oTEG functioning as a body heat harvester and an environment temperature sensor are demonstrated. The outstanding performances unambiguously demonstrate the success of the thermal interface design strategy for promoting oTEGs applied as wearable electronics.

With the increasing attention to clean and economical energy resources, geothermal energy and enhanced geothermal systems (EGS) have gained much importance in recent years. For the efficient development of deep geothermal reservoirs, it is crucial to understand the mechanical behavior of reservoir rock and its interaction with injected fluid under high-temperature and high confining pressure environments for employing hydraulic stimulation technologies. In the present study, we develop a novel numerical scheme based on the distinct element method (DEM) to simulate the failure behavior of rock by considering the influence of thermal stress cracks and high confining pressure for EGS. The proposed methodology is validated by comparing uniaxial compression tests at various temperatures and biaxial compression tests at different confining pressures with laboratory experimental results. The numerical results indicate a good agreement in terms of failure models and stress-strain curves with those of laboratory experiments. We then apply the developed scheme to the hydraulic fracturing simulations under various temperatures, confining pressures, and injection fluid conditions. Based on our numerical results, the number of hydraulic cracks is proportional to the temperature. At a high-temperature and low confining pressure environment, a complex crack network with large crack width can be observed, whereas the generation of the micro-cracks is suppressed in high confining pressure conditions. In addition, high-viscosity injection fluid tends to induce more hydraulic cracks. Since the crack network in the geothermal reservoir is an essential factor for the efficient production of geothermal energy, the combination of the above factors should be considered in hydraulic fracturing treatment in EGS.

With the increasing attention to clean and economical energy resources, geothermal energy and enhanced geothermal systems (EGS) have gained much importance. For the efficient development of deep geothermal reservoirs, it is crucial to understand the mechanical behavior of reservoir rock and its interaction with injected fluid under high temperature and high confining pressure environments. In the present study, we develop a novel numerical scheme based on the distinct element method (DEM) to simulate the failure behavior of rock by considering the influence of thermal stress cracks and high confining pressure for EGS. We validated the proposing method by comparing our numerical results with experimental laboratory results of uniaxial compression tests under various temperatures and biaxial compression tests under different confining pressure regarding failure patterns and stress-strain curves. We then apply the developed scheme to the hydraulic fracturing simulations under various temperatures, confining pressure, and injection fluid conditions. Our numerical results indicate that the number of hydraulic cracks is proportional to the temperature. At a high temperature and low confining pressure environment, a complex crack network with large crack width can be observed, whereas the generation of the micro cracks is suppressed in high confining pressure conditions. In addition, high-viscosity injection fluid tends to induce more hydraulic fractures. Since the fracture network in the geothermal reservoir is an essential factor for the efficient production of geothermal energy, the combination of the above factors should be considered in hydraulic fracturing treatment in EGS.

No abstract