Predicting performance of fiber thermoelectric generator arrays in wearable electronic applications
Graphical abstract
Introduction
Fiber-based thermoelectric generators (FTEGs) are flexible, conformable and light-weight devices, which can directly convert heat into electricity without any moving parts or working fluids [1]. At present, the output performance of such devices is generally lower, in the range of ~1 μW/cm2, close to body temperature with a small temperature difference, say ~15 K [2,3]. These devices are great candidates to provide energy to the wearable electronics. To this end, high output power and energy conversion efficient are essential for FTEGs in wearable applications. However, up to date, there is no quantitative analytical tool that can guide the engineering design of FTEGs, including selection of thermoelectric (TE), electric and structural materials, the device structure and fabrication processes with particular application conditions.
To achieve high energy conversion efficiency of rigid thermoelectric generators (TEGs), significant progress has been made to explore TE materials of high figure of merit, , where is the electrical conductivity; is the Seebeck coefficient; is the temperature; is the thermal conductivity [[4], [5], [6], [7], [8], [9]]. For the power generation application, these materials include Bi2Te3 and its alloy [10], silicides [11], PbTe [[12], [13], [14]], half-Heusler [15], poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) [16], and graphene and composites [17]. The theoretical studies of traditional TEGs have been conducted for solid cuboid structure, usually with a large temperature difference and under conditions of conductive heat transfer [[18], [19], [20]]. These models have provided important engineering design guidelines in traditional rigid TEGs by changing the cross-sectional area, length and segment of solid p- and n-type TE legs for the high output performance [[21], [22], [23], [24]]. However, these models cannot be applied in the wearable applications where the temperature at one end is fixed but at the other end is free. For example, the surface temperature of human torso can be regarded as a constant. Under this condition, the temperature at the other end is the result of the heat transfer.
Three-dimensional (3D) spacer fabric structure may offer high specific output power from the FTEGs because of the light weight and the large temperature difference between the face and back sides connected by numerous one-dimensional (1D) FTEG units1. The output performance of the 3D FTEGs is determined by those of 1D FTEGs. Compared with the thick TE columns in traditional rigid TEG arrays, the 1D FTEG units have much higher aspect ratio, which results in the large deformability and flexibility. A recent work reported 3D space fabric FTEGs comprising 1D FTEG units where the core was a carbon nanotube yarn (CNTY) acting as a continuous electrode3. The sheath was coated with p-type PEDOT: PSS and n-type polyethyleneimine (PEI). It is not desirable that in the FTEGs much thermal energy was conducted from the hot to cold end through the CNTY of high thermal conductivity. Therefore, higher performance of the FTEG can be achieved with a more appropriate consideration of materials and device structure, ideally guided by a quantitative analytical tool.
Hence, this paper presents a quantitative approach to predict the performance of 3D FTEG composed of 1D FTEG array in simulated wearable conditions, that is, under conductive and radiative heat transfer with low temperature differences. The single 1D FTEG unit, consisting of core/sheath fiber TEG leg and electrodes, is dealt with under conduction and radiation heat transfer. The influences of the radius and the length of filament, the thickness of TE coating layer, the distance between the adjacent surfaces of 1D FTEGs and the surface emissivity are quantified. Finally, the upper limits of output power and conversion efficiency of the FTEG array device with various TE materials are given if worn on a human torso back under a range of ambient temperature.
Section snippets
Mathematical model
FTEG devices convert thermal energy into electrical energy according to the Seebeck effect. Fig. 1(a) illustrates a 1D FTEG unit comprising a polymer core filament coated with TE material in the middle and conductive material at its both ends. Based on the Seebeck effect, the equivalent voltage source, U, induced by the temperature difference can be estimated by the following equationwhere α is the Seebeck coefficient of TE material, is the temperature difference between the hot and
Influencing factors on performance of 1D FTEG array
In this section, for quantifying the importance of factors, the single 1D FTEG is studied under conductive and radiative heat transfer at first. Then, the 1D FTEG array formed by the single ones is investigated with the consideration of the influence of the controlled parameter.
Upper limit of performance of array devices
Suppose the 3D FTEG composed of 1D FTEG arrays is worn on the back of a human with the surface temperature of around , as shown in Fig. 1(b). The ambient temperature is in the range of . The model in Section 3.2 is applied to investigate the upper limit of the performance of the 1D FTEG array composed of different TE materials (in Table 1) under different ambient temperature. The control parameter and the emissivity of the 1D FTEG array are 1 and 0.5, respectively. The
Conclusion
This paper reports new theoretical models for 1D FTEGs and 3D FTEG array device, working under conductive and radiative thermal transfer with a low temperature difference comparable to wearable applications, and their numerical simulation results. The influences on output power and energy conversion efficiency of the FTEGs have been given in terms of the fiber dimension, the thickness of TE coating layer, packing density of the array and the surface emissivity. The theoretical model for single
CRediT authorship contribution statement
Li-sha Zhang: Conceptualization, Formal analysis, Investigation, Validation, Visualization, Writing - original draft. Bao Yang: Conceptualization, Methodology. Shu-ping Lin: Investigation, Methodology. Tao Hua: Supervision. Xiaoming Tao: Conceptualization, Data curation, Funding acquisition, Methodology, Resources, Supervision, Writing review & editing.
Declaration of competing interest
The authors declare that there is no conflict of interests.
Acknowledgements
The work has been partially supported by Research Grants Council, Hong Kong, China (Grant No. 15201419E, 15200917E, 15204715E) and Hong Kong Polytechnic University (Grant No. AAB3 and 847A). L.Z. acknowledges a postgraduate scholarship from Hong Kong Polytechnic University.
References (42)
- et al.
Defect-engineered reduced graphene oxide sheets with high electric conductivity and controlled thermal conductivity for soft and flexible wearable thermoelectric generators
Nano Energy
(2018) - et al.
Hybrid composite of screen-printed inorganic thermoelectric film and organic conducting polymer for flexible thermoelectric power generator
Energy
(2014) - et al.
Enhanced thermoelectric performance from self-assembled alkyl chain-linked naphthalenediimide/single walled carbon nanotubes composites
Chem. Eng. J.
(2020) - et al.
Texture anisotropy of higher manganese silicide following arc-melting and hot-pressing
Intermetallics
(2016) - et al.
Numerical analysis on the segmented annular thermoelectric generator for waste heat recovery
Energy
(2019) - et al.
A comprehensive model of a lead telluride thermoelectric generator
Energy
(2018) - et al.
Optimized high performance thermoelectric generator with combined segmented and asymmetrical legs under pulsed heat input power
J. Power Sources
(2019) - et al.
Geometry optimization of two-stage thermoelectric generators using simplified conjugate-gradient method
Appl. Energy
(2017) - et al.
Multi-objective and multi-parameter optimization of a thermoelectric generator module
Energy
(2014) (Bi,Sb)2(Te,Se)3-based thin film thermoelectric generators
Mater. Lett.
(2000)
Fabrication and characterization of bismuth-telluride-based alloy thin film thermoelectric generators by flash evaporation method
Sens. Actuators, A
Hierarchical Bi-Te based flexible thin-film solar thermoelectric generator with light sensing feature
Energy Convers. Manag.
Optimization of Bi2Te3 and Sb2Te3 thin films deposited by co-evaporation on polyimide for thermoelectric applications
Vacuum
A comprehensive and time-efficient model for determination of thermoelectric generator length and cross-section area
Energy Convers. Manag.
A comprehensive design method for segmented thermoelectric generator
Energy Convers. Manag.
Elucidating modeling aspects of thermoelectric generator
Int. J. Heat Mass Tran.
Optimal design for micro-thermoelectric generators using finite element analysis
Microelectron. Eng.
Toward self-powered sensor networks
Nano Today
Fiber‐based thermoelectric generators: materials, device structures, fabrication, characterization, and applications
Adv. Energy Mater.
Carbon nanotube yarn based thermoelectric textiles for harvesting thermal energy and powering electronics
J. Mater. Chem.
Discovery of colossal Seebeck effect in metallic Cu2Se
Nat. Commun.
Cited by (22)
Large scale energy storage systems based on carbon dioxide thermal cycles: A critical review
2024, Renewable and Sustainable Energy ReviewsHigh performance single material-based triboelectric nanogenerators made of hetero-triboelectric half-cell plant skins
2022, Nano EnergyCitation Excerpt :Such a difference in the intensity was found to be directly relevant to the output of TENGs, which will be discussed below. The triboelectric effects of organic and inorganic materials are usually characterized using different methods [4,32,33], and their charge affinities during the triboelectrification process could be estimated based on their physical properties, such as the work function [34] and the energy gap of the molecular orbitals [35]. However, biological materials cannot be easily estimated in that way because of the complexity of their chemical and biological structures.
Efficiently synthesized n-type CoSb<inf>3</inf> thermoelectric alloys under TGZM effect
2021, Materials Science in Semiconductor ProcessingWKYMVm ameliorates acute lung injury via neutrophil antimicrobial peptide derived STAT1/IRF1 pathway
2020, Biochemical and Biophysical Research CommunicationsCitation Excerpt :In fact, various ligands-based FPR2 conformational changes differentially exhibit proinflammatory response, including chemotaxis and the release of inflammatory cytokines or anti-inflammatory/pre-resolving response. Ye and colleagues reported that Ac2-26 the N-terminal of annexin AI for anti-inflammation and amyloid beta 42 for pro-inflammation are major modulators that are involved in the induction of distinct conformational changes of FPR2 through biased allosteric modulation [16]. Despite the modification of FPR2 by ligands, Fpr2-deficient mice developed susceptibility and bacteria load in the liver with reduced antimicrobial activity of the neutrophils against to Listeria monocytogenes [17].
Weavable thermoelectrics: advances, controversies, and future developments
2024, Materials Futures