scholarly journals Thermal Analysis of AlGaN/GaN HEMTs Considering Anisotropic And Inhomogeneous Thermal Conductivity

2021 ◽  
Author(s):  
Yao Li ◽  
Zixuan Zheng ◽  
Qun Li ◽  
Hongbin Pu
Keyword(s):  
Thermal Conductivity ◽  
Temperature Rise ◽  
Power Dissipation ◽  
Thermal Characteristics ◽  
Maximum Temperature ◽  
Base Temperature ◽  
Initial Growth ◽  
Boltzmann Transport ◽  
Growth Interface ◽  
Anisotropic Thermal Conductivity

Abstract To examine the differences of thermal characteristics introduced by material thermal conductivity, anisotropic polycrystalline diamond (PCD) and GaN are analyzed based on the accurate model of grain sizes in the directions of parallel and vertical to the interface and an approximate solution of the phonon Boltzmann transport equation. Due to the space-variant grain structures of PCD, the inhomogeneous-anisotropic local thermal conductivity, homogeneous-anisotropic thermal conductivity averaged over the whole layer and the typical values of inhomogeneous-isotropic thermal conductivity are compared with/without anisotropic GaN thermal conductivity. The results show that the considerations of inhomogeneous-anisotropic PCD thermal conductivity and anisotropic GaN thermal conductivity are necessary for the accurate prediction of temperature rise in the GaN HEMT devices, and when ignoring both, the maximum temperature rise is undervalued by over 16 K for thermal boundary resistance (TBR) of 6.5 to 60 m2K/GW at power dissipation of 10 W/mm. Then the dependences of channel temperature on several parameters are discussed and the relations of thermal resistance with power dissipation are extracted at different base temperature. Compared with GaN, SiC and Si substrates, PCD is the most effective heat spreading layer though limited by the grain size at initial growth interface.

scholarly journals Ultralow and anisotropic thermal conductivity in semiconductor As2Se3

2018 ◽  
Vol 20 (3) ◽  
pp. 1809-1816 ◽  
Author(s):  
Robert L. González-Romero ◽  
Alex Antonelli ◽  
Anderson S. Chaves ◽  
Juan J. Meléndez
Keyword(s):  
Thermal Conductivity ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Lattice Thermal Conductivity ◽  
Boltzmann Transport Equation ◽  
First Principles Calculations ◽  
Boltzmann Transport ◽  
Functional Theory ◽  
Anisotropic Thermal Conductivity

An ultralow lattice thermal conductivity of 0.14 W m−1 K−1 along the b⃑ axis of As2Se3 single crystals was obtained at 300 K by first-principles calculations involving density functional theory and the resolution of the Boltzmann transport equation.

Steady-state heat conduction analysis for two-terminal microwave oscillator devices with rectangular integral heat sinks

1995 ◽  
Vol 451 (1942) ◽  
pp. 375-381 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Temperature Rise ◽  
Heat Sink ◽  
Microwave Oscillator ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Maximum Temperature Rise ◽  
Steady State Heat

The outline of a theoretical analysis to calculate the steady-state temperature distribution within a rectangular prism mounted on a semi-infinite heat sink is presented. The incident heat flux is uniform over a given centralized circular region on one face of the prism. The thermal conductivity of the material is treated as being dependent on the temperature. The model is used to calculate the maximum temperature rise within a heat sink configuration that is used to package contemporary two-terminal microwave oscillator devices. Results are presented that show how the maximum temperature rise within such commercially available heat sink packages depends on the input heat flux and the dimensions and thermal conductivity of the materials. These results are presented in a generalized form for device design purposes.

Adiabatic Temperature Rise and Heat Release Rates for Concrete With Application to a Large-Scale Multi-Step Grouting Process

2004 ◽  
Author(s):  
J. E. O’Brien ◽  
R. W. Johnson ◽  
A. S. Siahpush ◽  
C. M. Stoots
Keyword(s):  
Finite Element ◽  
Temperature Rise ◽  
Large Scale ◽  
Thermal Characteristics ◽  
Adiabatic Temperature ◽  
Time Dependent ◽  
Maximum Temperature ◽  
Heating Rates ◽  
Adiabatic Temperature Rise ◽  
Concrete Layer

An experimental study has been performed in order to determine the thermal characteristics of a specific concrete formula to be used for a large-scale tank-grouting project. The experimental results were incorporated into finite-element numerical simulations aimed at predicting local concrete temperatures over the duration of multiple concrete pours. The pours will occur in a stepwise fashion whereby each additional concrete layer will be added while the previous layers are still undergoing the curing process. The experimental portion of the project included a series of laboratory-scale tests aimed at determining the time-dependent adiabatic temperature rise of several concrete samples and the corresponding time-dependent concrete internal heating rates. Results of the experiments were incorporated directly into the finite-element thermal model. The finite-element simulations indicated that the pour schedule did not have a strong influence on the maximum temperature in the concrete.

scholarly journals Anisotropic Thermal Conductivity in Few-Layer and Bulk Titanium Trisulphide from First Principles

Nanomaterials ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 704 ◽  
Author(s):  
Fernan Saiz ◽  
Jesus Carrete ◽  
Riccardo Rurali
Keyword(s):  
Thermal Conductivity ◽  
Ab Initio ◽  
Transport Equation ◽  
First Principles ◽  
Boltzmann Transport Equation ◽  
Iterative Solution ◽  
Boltzmann Transport ◽  
Fundamental Symmetries ◽  
Phonon Branch ◽  
Anisotropic Thermal Conductivity

We study the thermal conductivity of monolayer, bilayer, and bulk titanium trisulphide (TiS 3 ) by means of an iterative solution of the Boltzmann transport equation based on ab-initio force constants. Our results show that the thermal conductivity of these layers is anisotropic and highlight the importance of enforcing the fundamental symmetries in order to accurately describe the quadratic dispersion of the flexural phonon branch near the center of the Brillouin zone.

Steady-state heat sink analysis for two-terminal microwave oscillator devices with temperature dependent thermal conductivity

1993 ◽  
Vol 441 (1911) ◽  
pp. 181-189 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Temperature Distribution ◽  
Temperature Rise ◽  
Heat Sink ◽  
Maximum Temperature ◽  
Microwave Oscillators ◽  
Steady State Temperature ◽  
Steady State Heat

A theoretical analysis to calculate the steady-state temperature distribution within a cylindrical heat sink configuration, where the thermal conductivity is dependent on the temperature, is outlined. The analysis applies to any heat sink arrangement that can be treated as one or more homogeneous solid cylinders mounted on a semi-infinite heat sink, where the heat flux incident on both faces of each cylinder is uniform over a given centralized circular region. The model is used to analyse the temperature distribution within the heat sink configurations used commonly to package two-terminal semiconductor devices that are operated as sources of electromagnetic radiation in microwave oscillators. Results are presented that show how the maximum temperature rise within commercially available heat sink packages, depends on the input heat flux and the dimensions and thermal conductivity of the materials. Furthermore, results that show how the temperature rise varies across the interfaces of given heat sink configurations, similar to those used commercially, are given also.

scholarly journals Heat Dissipation and Ripple Current Rating in Electrolytic Capacitors

1975 ◽  
Vol 2 (2) ◽  
pp. 109-114 ◽  
Author(s):  
F. G. Hayatee
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Temperature Rise ◽  
Mathematical Analysis ◽  
Heat Dissipation ◽  
Thermal Characteristics ◽  
Electrolytic Capacitors ◽  
Allowable Temperature

The ripple current rating in electrolytic capacitors is limited by the maximum allowable temperature rise inside the capacitor. The temperature rise is determined by the I2R losses inside the capacitor and the efficiency of heat flow from the interior to the surrounding. The ripple current rating can be extended by either reducing the tanδof the capacitor or by increasing the efficiency of heat flow to ambient.The heat flow is determined by the thermal characteristics of the capacitor surface and thermal conductivity of the medium separating the capacitor winding from the surrounding.In this article a mathematical analysis for the heat flow in capacitors is given. The effects of various parameters are examined and methods of extending the ripple current rating are discussed.

Conjugate Heat Transfer With Buoyancy Effects From Micro-Chip Sized Repeated Heaters

1997 ◽  
Vol 119 (4) ◽  
pp. 275-280 ◽  
Author(s):  
D. Yu ◽  
T. A. Ameel ◽  
R. O. Warrington ◽  
R. F. Barron
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mixed Convection ◽  
Forced Convection ◽  
Temperature Rise ◽  
Internal Heat ◽  
Maximum Temperature ◽  
Transient Heating ◽  
Maximum Temperature Rise ◽  
Laminar Mixed Convection

Laminar mixed convection heat transfer across five in-line microchipsized heaters, surface mounted on printed circuit board (PCB), was investigated by the weighted residual finite element method. The effects of axial heat conduction within the PCB for both mixed convection and pure forced convection are reported. The flow regime considered was 200 ≤ Re ≤ 800 and 0 ≤ Gr ≤ 58,000. Internal heat generation was included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the outer PCB walls, convective heat transfer conditions were given. Thermophysical and transport properties based on materials used in the electronics industry, including orthotropic thermal conductivity in PCB, were used. The flow and solid domains were solved simultaneously. A sensitivity study of PCB heat transfer coefficients, isotropic thermal conductivity, thermal conductivity variations, and spacing effects was performed. The mixed convection transient heating process was compared with the steady-state formulation to estimate the influence of flow oscillation in heat transfer. It was found that the maximum temperature rise in the microchips predicted by pure forced convection was, at most, 10 percent higher than that predicted by mixed convection. The difference in maximum temperature between the trailing and leading chips in the array was 30 percent.

scholarly journals Apparatus for routine measurements of the thermal conductivity of ice cores

1999 ◽  
Vol 29 ◽  
pp. 151-154 ◽  
Author(s):  
Crescenzo Festa ◽  
Aristide Rossi
Keyword(s):  
Thermal Conductivity ◽  
Ice Cores ◽  
Maximum Temperature ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Standard Samples ◽  
Experimental Conditions ◽  
Heating Source ◽  
Central Segment ◽  
Wire Method

AbstractAn apparatus is described for measuring the thermal conductivity of ice by the transient hot-wire method. Thermal conductivity A, is determined by tracking the thermal pulse induced in the sample by a heating source consisting of a platinum resistor. A central segment of the same platinum heating resistor acts also as a thermal sensor. A heat pulse transferred to the ice for a period of 40s gives a maximum temperature increment of about 7-14°C. In good experimental conditions, the expected reproducibility of the measurements is within ±3%. The accuracy of the method depends on whether the instrument has been calibrated by reliable standard samples, certified by absolute methods.

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