Abstract
Thermal harvesting devices based on transformation optics, which can manipulate the heat flux concentration significantly through rational arrangements of the conductivities, have attracted considerable interest owing to several great potential applications of the technique for high-efficiency thermal conversion and collection. However, quantitative studies on the geometrical effects, particularly wedge angles, on the harvesting behaviors are rare. In this paper, we adopt wedge structure-based thermal harvesting schemes, and focus on the effects of the geometrical parameters including the radii ratios and wedge angles on the harvesting performance. The temperature deformations at the boundaries of the compressional region and temperature gradients for the different schemes with varying design parameters are investigated. Moreover, a concept for temperature stabilization was derived to evaluate the fluctuation in the energy distributions. In addition, the effects of interface thermal resistances have been investigated. Considering the changes in the radii ratios and wedge angles, we proposed a modification of the harvesting efficiency to quantitatively assess the concentration performance, which was verified through random tests and previously fabricated devices. In general, this study indicates that a smaller radii ratio contributes to a better harvesting behavior, but causes larger perturbations in the thermal profiles owing to a larger heat loss. We also find that a smaller wedge angle is beneficial to ensuring a higher concentration efficiency with less energy perturbations. These findings can be used to guide the improvement of a thermal concentrator with a high efficiency in reference to its potential applications as novel heat storage, thermal sensors, solar cells, and thermoelectric devices.
Highlights
The use of transformation optics[1] (TO) for active management and regulation of physical fields, including optics,[2,3] electromagnetism,[4] acoustics,[5] and elasticity,[6] was a research focus because of its significant impact on both fundamental researches and engineering applications
To investigate the geometrical effects of the structural parameters including the ratio of the inner and outer radii and wedge angles in the fan structure, the filling material in Parts I and II was chosen as nickel steel (25% Ni) with a thermal conductivity κ0 = 13 W·m-1·K-1, and the filling fraction of both materials A and B was 0.5
The geometrical effects of the radii ratios and wedge angles on the concentrating behavior were investigated
Summary
The use of transformation optics[1] (TO) for active management and regulation of physical fields, including optics,[2,3] electromagnetism,[4] acoustics,[5] and elasticity,[6] was a research focus because of its significant impact on both fundamental researches and engineering applications. To realize local heat harvesting, alternative composite materials with a wedge-like structure (e.g., spoke, fan, and sensu) were widely adopted in previous studies.[14,15,16,17,18,19,21,22,23] The feasible method for fabricating a thermal concentrator is reversing the conductivity components[15] in the transformational domain, i.e., keeping the radial component considerably larger than the azimuthal component Based on this concept, theoretical 3D thermal harvesting cells[16] have been demonstrated by employing naturally available materials with tunable anisotropy. We proposed a modification of the harvesting efficiency by considering the geometrical effects and verified its accuracy and effectiveness through random tests and previous fabricated devices.[17,18,21,34]
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