Thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics

Júnior, Álvaro Ferreira; Shanafield, Daniel J.

doi:10.1590/s0366-69132004000300012

Cited by 91 publications

(25 citation statements)

References 12 publications

(35 reference statements)

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“…G is the shear modulus (147 GPa), ν is Poisson's ratio (0.252), e in is the residual strain applied in the in‐plane direction, and h is the thickness of the film. The thermal variations of the film and substrate can be calculated as c te × Δ T × m ∙ a epi or n ∙ a sub , where c te is the thermal expansion coefficient (BeO = 5.99; GaN = 3.43; ZnO = 4.31 × 10 −6 °C −1 ) and Δ T is the thermal change between the process (250°C) and room temperature (25°C). Thermally induced strains were added to the BeO films.…”

Section: Resultsmentioning

confidence: 99%

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

et al. 2018

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We demonstrated the growth of wurtzite‐crystalline beryllium oxide (BeO) thin films on GaN and ZnO substrates using atomic layer deposition (ALD). Single‐crystalline BeO were epitaxially grown on GaN. Despite the inherently large lattice mismatch of BeO and GaN atoms, the 6/5 and 7/6 domain‐matched structures dramatically reduced the residual strain in BeO thin films. On the other hand, the lattice mismatch of BeO and ZnO was not effectively accommodated in the mixed domains. X‐ray diffraction (XRD) confirmed the in‐plane crystallization of BeO‐on‐substrates in the (002){102}BeO||(002){102}Sub orientation and relaxation degrees of 20.8% (GaN), 100% (ZnO). The theoretical critical thicknesses of BeO for strain relaxation were 2.2 μm (GaN) and 1.6 nm (ZnO), calculated using a total film energy model. Transmission electron microscopy (TEM) and Fourier‐filtered imaging supported the bonding configuration and crystallinity of wurtzite BeO thin films on GaN and ZnO substrates.

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Section: Resultsmentioning

confidence: 99%

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

et al. 2018

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“…Thus, the nozzle layer was modelled for the hot core stream only. For reduction of parasitic temperature drops a layer of AlN with a high thermal conductivity of 170 Wm −1 K −1 [35] is introduced to form an electrical insulation between the TE uni-couple and the metallic nozzle. When considering the dielectric strength of AlN of 20 kVmm −1 [36], a minimum thickness of 325 µ m is set for this layer on both sides with regard to weight optimization and concurrent electric insulation effect in the presence of high DC voltages generated by the entire TEG at the nozzle.…”

Section: Methodsmentioning

confidence: 99%

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

2018

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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.

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“…Thus, the nozzle layer was modelled only for the hot core stream. For reduction of parasitic temperature drops a layer of AlN with a high thermal conductivity of 170 Wm -1 K -1 [30] is introduced to form an electrical insulation between the TE double leg and the metallic nozzle. Considering the dielectric strength of AlN of 20 kVmm -1 [31], a minimum thickness of 325 µm is set for this layer on both sides with regard to weight optimization and concurrent electric insulation effect in presence of high DC voltages generated by the entire TEG at the nozzle.…”

Section: Methodsmentioning

confidence: 99%

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

Ziółkowski¹,

Zabrocki²,

Müller³

2018

Preprint

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The application of thermoelectric generators (TEG) on the nozzle of an aviation jet engine was studied by finite element TEG-simulations. Against the background of system-level requirements of the reference aircraft this work reports the resulting requirements on the TEG design with respect to applied thermoelectric (TE) element lengths and fill factors (F) within the TE modules in order to maintain a positive effect on the specific fuel consumption. Assuming a virtual optimized TE material and varying the convective heat transfer coefficients at the nozzle surfaces 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%. Extrapolating TEG coverage to the full nozzle surface, the power output reaches 1.65 kW per engine. Assessment of further potential is demonstrated by a parametric study on the fill factor, convective heat transfer coefficients, 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 installation of TEG in consideration of the cost-specific power output of modern thermoelectric materials.

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Thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics

Cited by 91 publications

References 12 publications

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

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

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

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