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A technology of active thermal cloaks that use thermoelectric (TE) devices to manipulate heat flow is devised, and its powerful adaptive function is studied quantitatively. Determining the distribution of adaptive heat sources is a critical mission in the design of active thermal cloaks. This can be accomplished by directly solving the heat conduction equation for the device being studied. The input electric current of the TE components can then be determined individually according to the heat source distribution. On this basis, the performance of our designed cloak system is tested by finite element analysis. Simulation results show that even if the thermal conductivity ratio m (of object-to-background) and/or the temperature gradient g of the background temperature field change over a very wide range, TE components can pump the heat flow accurately from one side of the cloak to the other side by adjusting the input current, so that the background temperature field can be restored to its original state to good approximation. Design of an active thermal cloak is no longer limited by material properties and can be adjusted freely according to the thermal environment. The feasibility of active thermal cloaks is demonstrated theoretically by this work.

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Effective water management plays a significant role in improving the performance and lifetime of proton exchange membrane fuel cells (PEMFCs). The ejector can take full advantage of the huge pressure potential between the high-pressure fuel tank and the PEMFCs to realize fuel gas recovery, and it is usually adopted for the auxiliary drainage of hydrogen/oxygen stacks. In this study, the dynamic behavior of liquid water droplets in the cathode flow channel of a PEMFC operating in ejector-based recirculation mode was numerically investigated. The effects of the operating current density of the fuel cell as well as the pore size of the water inlet boundary on the droplet behavior were studied, and the number of contact surfaces between the droplet and the flow channel were investigated. The results show that the speed of water removal from the flow channel with ejector-based recirculation can be increased by 37.5% when the fuel cell operates at 1.0 A cm–2. Moreover, the hydrophobic side and top surfaces are more suitable for water slug removal when the PEMFC operates at a high current density, owing to the shorter drainage period. We herein provide recommendations for effectively enhancing the water management of a PEMFC with ejector-based gas recirculation.