Abstract
Active control of heat flux can be realized with transformation optics (TO) thermal metamaterials. Recently, a new class of metamaterial tunable cells has been proposed, aiming to significantly reduce the difficulty of fabrication and to flexibly switch functions by employing several cells assembled on related positions following the TO design. However, owing to the integration and rotation of materials in tunable cells, they might lead to extra thermal losses as compared with the previous continuum design. This paper focuses on investigating the thermodynamic properties of tunable cells under related design parameters. The universal expression for the local entropy generation rate in such metamaterial systems is obtained considering the influence of rotation. A series of contrast schemes are established to describe the thermodynamic process and thermal energy distributions from the viewpoint of entropy analysis. Moreover, effects of design parameters on thermal dissipations and system irreversibility are investigated. In conclusion, more thermal dissipations and stronger thermodynamic processes occur in a system with larger conductivity ratios and rotation angles. This paper presents a detailed description of the thermodynamic properties of metamaterial tunable cells and provides reference for selecting appropriate design parameters on related positions to fabricate more efficient and energy-economical switchable TO devices.
Highlights
Innovations in the application of transformation optics (TO) [1] have been widely used to manipulate wave transformation in the fields of optics [2,3], electromagnetic [4,5], elastodynamics [6,7], and acoustics [8,9] through artificial structures by mapping the coordinate transformations onto the spatial distributions of material properties
In order to investigate the thermodynamic performances of the metamaterial tunable cell, entropy generation analysis [18,19,24,44,45] is introduced to define the thermal dissipations of different schemes with varying rotations and selected materials
To regulate heat flux vectors in pre-determined paths, the creation of the schematic of the metamaterial tunable cell with conductivity gradients in the function regions should be based on the rotation process described above
Summary
Innovations in the application of transformation optics (TO) [1] have been widely used to manipulate wave transformation in the fields of optics [2,3], electromagnetic [4,5], elastodynamics [6,7], and acoustics [8,9] through artificial structures by mapping the coordinate transformations onto the spatial distributions of material properties. Among all the early studies related to the above, the goals are mainly related to the design and verification of novel TO devices with single or multiple functions They are still far from practical application owing to the limitations of flexibly switching to different functions and fabricating large quantities of thermal metamaterials. Multiple functions can be performed and switched to flexibly by arranging several tunable cells on related positions based on pre-designed heat flux bending. Entropy generation analysis [18,19,24,44,45] considering the rotation of material layers in tunable cells was introduced to investigate thermodynamic properties under multiple variables. The thermal dissipations and system irreversibility were investigated by calculating the total entropy generation rate at varying thermal conductivity ratios and rotation angles
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