High-temperature infrared (IR) camouflage is crucial to the effective concealment of high-temperature objects but remains a challenging issue, as the thermal radiation of an object is proportional to the fourth power of temperature (T4). Here, we experimentally demonstrate high-temperature IR camouflage with efficient thermal management. By combining a silica aerogel for thermal insulation and a Ge/ZnS multilayer wavelength-selective emitter for simultaneous radiative cooling (high emittance in the 5–8 μm non-atmospheric window) and IR camouflage (low emittance in the 8–14 μm atmospheric window), the surface temperature of an object is reduced from 873 to 410 K. The IR camouflage is demonstrated by indoor/outdoor (with/without earthshine) radiation temperatures of 310/248 K for an object at 873/623 K and a 78% reduction in with-earthshine lock-on range. This scheme may introduce opportunities for high-temperature thermal management and infrared signal processing. The infrared signal from high-temperature structures such as jet engines and ship funnels could be significantly concealed by a composite material that reduces the radiation temperature of internally hot objects. Such “infrared camouflaging” is especially significant for military and civil applications, to reduce the threat from heat-seeking missiles and evade thermal imaging systems. Researchers in China, led by Qiang Li at Zhejiang University, built their layered thermal camouflage from a silica aerogel and a germanium/zinc sulfide blend. The highly porous aerogel forms effective insulation. The germanium/zinc sulfide layers achieve radiative cooling by emitting energy at wavelengths outside the atmosphere’s window. In tests on objects with an internal temperature of 600 °C, the camouflage material reduced the surface temperature and the radiation temperature to 137 °C and 37 °C, respectively.

/pdf/high-temperature-infrared-camouflage-with-efficient-thermal-37i3te1qaa.pdf

High-temperature infrared camouflage with efficient thermal management.

Electrodeposition has been used for decades to deposit various semiconductors on targeted surfaces. It is a powerful method for growing thin films and/or nanostructures with potential thermoelectric properties. It has a competitive edge over physical processes due to its cost-effective operation and facilities. This paper furnishes an overview of the evolution of research in the area of electrodeposition of thermoelectric compounds as a function of time and shape category (bulk, wire, and film). Selected results on V2VI3 compounds are organized in a synthetic presentation according to shape. Up-to-date literature coverage is provided, based on over 200 papers and proceedings. In this context, our research group is involved in complementary aspects concerning tailoring electrodeposited film morphology in order to enhance thermoelectric properties. Examples are given dealing with pulse electroplating and nanowires.

Thermoelectric Material Electroplating: a Historical Review

This work presents a comprehensive study of the fabrication and optimization of electrodeposited p- and n-type thermoelectric fi lms. The fi lms are deposited on Au and stainless steel substrates over a wide range of deposition potentials. The infl uence of the preparative parameters such as the composition of the electrolyte bath and the deposition potential are investigated. Furthermore, the p-doped (Bi x Sb 1−x ) 2 Te 3 and the n-doped Bi 2 (Te x Se 1−x ) 3 fi lms are annealed for a period of about 1 h under helium and under tellurium atmosphere at 250 ° C for 60h. Annealing in He already leads to signifi cant improvements in the thermoelectric performance. Furthermore, due to the equilibrium conditions during the process, annealing in Te atmosphere leads to a strongly improved fi lm composition, charge carrier density and mobility. The Seebeck coeffi cients increase to values up to + 182 μ V K − 1 for p-doped and‐130 μ V K − 1 for n-doped materials at room temperature. The power factors also exhibit improvements with 1320 μ W m − 1 K − 2 and 820 μ W m − 1 K − 2 for p-doped and n-doped fi lms, respectively. Additionally, in-situ XRD measurements performed during annealing of the fi lms up to 600K under He atmosphere show stepwise improvements of the crystal structure leading to the improvements in thermoelectric parameters. The thermal conductivity is between 1.2 W m − 1 K − 1 and 1.0 W m − 1 K − 1 .

Optimizations of Pulsed Plated p and n-type Bi2Te3-Based Ternary Compounds by Annealing in Different Ambient Atmospheres

Annealing effects on the structural and electrical transport properties of n-type Bi2Te2.7Se0.3 thin films deposited by flash evaporation

Fabrication and characterization of nickel contacts for magnesium silicide based thermoelectric generators

Bismuth telluride is the state-of-the-art thermoelectric (TE) material for cooling applications with a figure of merit of ∼1 at 300 K. There is a need for the development of TE materials based on t ...

Effects of Annealing and Doping on Nanostructured Bismuth Telluride Thick Films

Finite element model (FEM)-based simulations are conducted for the application of a thermoelectric generator (TEG) between the hot core stream and the cool bypass flow at the nozzle of an aviation turbofan engine. This work reports the resulting requirements on the TEG design with respect to applied thermoelectric (TE) element lengths and filling factors (F) of the TE modules in order to achieve a positive effect on the specific fuel consumption. Assuming a virtual optimized TE material and varying the convective heat transfer coefficients (HTC) between the nozzle surfaces and the gas flows, this work reports the achievable power output. System-level requirement on the gravimetric power density (>100 Wkg−1) can only be met for F ≤ 21%. When extrapolating TEG coverage to the full nozzle surface, the power output reaches 1.65 kW per engine. The assessment of further potential for power generation is demonstrated by a parametric study on F, convective HTC, and materials performance. This study confirms a feasible design range for TEG installation on the aircraft nozzle with a positive impact on the fuel consumption. This application translates into a reduction of operational costs, allowing for an economically efficient TEG-installation with respect to the cost-specific power output of modern thermoelectric materials.

/pdf/teg-design-for-waste-heat-recovery-at-an-aviation-jet-engine-5ah6pi17w3.pdf

TEG Design for Waste Heat Recovery at an Aviation Jet Engine Nozzle

The thermoelectric figure of merit ZT, which is defined using electrical conductivity, Seebeck coefficient, thermal conductivity, and absolute temperature T, has been widely used as a simple estimator of the conversion efficiency of a thermoelectric heat engine. When material properties are constant or slowly varying with T, a higher ZT ensures a higher maximum conversion efficiency of thermoelectric materials. However, as material properties can vary strongly with T, efficiency predictions based on ZT can be inaccurate, especially for wide-temperature applications. Moreover, although ZT values continue to increase, there has been no investigation of the relationship between ZT and the efficiency in the higher ZT regime. In this paper, we report a counterintuitive situation by comparing two materials: although one material has a higher ZT value over the whole operating temperature range, its maximum conversion efficiency is smaller than that of the other. This indicates that, for material comparisons, the evaluation of exact efficiencies as opposed to a simple comparison of ZTs is necessary in certain cases.

Counterintuitive example on relation between ZT and thermoelectric efficiency

https://www.mdpi.com/2076-3417/8/12/2637/pdf

TEG design for waste heat recovery at an aviation jet engine nozzle

The thermoelectric figure of merit ZT, which is defined using electrical conductivity, Seebeck coefficient, thermal conductivity, and absolute temperature T, has been widely used as a simple estimator of the conversion efficiency of a thermoelectric heat engine. When material properties are constant or slowly varying with T, a higher ZT ensures a higher maximum conversion efficiency of thermoelectric materials. However, as material properties can vary strongly with T, efficiency predictions based on ZT can be inaccurate, especially for wide-temperature applications. Moreover, although ZT values continue to increase, there has been no investigation of the relationship between ZT and the efficiency in the higher ZT regime. In this paper, we report a counterintuitive situation by comparing two materials: although one material has a higher ZT value over the whole operational temperature range, its maximum conversion efficiency is smaller than that of the other. This indicates that, for material comparisons, the evaluation of exact efficiencies as opposed to a simple comparison of the ZTs is necessary in certain cases.

Pawel Ziolkowski

Papers

Effects of Annealing and Doping on Nanostructured Bismuth Telluride Thick Films

TEG Design for Waste Heat Recovery at an Aviation Jet Engine Nozzle

Counterintuitive example on relation between ZT and thermoelectric efficiency

TEG design for waste heat recovery at an aviation jet engine nozzle

Counterintuitive example on relation between ZT and thermoelectric efficiency