Time-resolved temperature-jump measurements and steady-state thermal imaging of nanoscale heat transfer of gold nanostructures on AlGaN:Er3+ thin films

2020 ◽  
Vol 152 (3) ◽  
pp. 034706 ◽  
Author(s):  
Kristina Shrestha ◽  
Juvinch R. Vicente ◽  
Ali Rafiei Miandashti ◽  
Jixin Chen ◽  
Hugh H. Richardson
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Steady State ◽  
Thermal Imaging ◽  
Temperature Jump ◽  
Gold Nanostructures ◽  
Time Resolved ◽  
Nanoscale Heat Transfer

Time-Resolved Temperature-Jump Measurements and Theoretical Simulations of Nanoscale Heat Transfer Using NaYF4:Yb3+:Er3+ Upconverting Nanoparticles

2019 ◽  
Vol 123 (6) ◽  
pp. 3770-3780 ◽  
Author(s):  
Ali Rafiei Miandashti ◽  
Larousse Khosravi Khorashad ◽  
Alexander O. Govorov ◽  
Martin E. Kordesch ◽  
Hugh H. Richardson
Keyword(s):  
Heat Transfer ◽  
Temperature Jump ◽  
Time Resolved ◽  
Nanoscale Heat Transfer ◽  
Theoretical Simulations

Comparison of Steady and Unsteady Coupled Heat-Transfer Simulations of a High-Pressure Turbine Blade

2015 ◽  
Author(s):  
Markus Schmidt ◽  
Christoph Starke
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Steady State ◽  
Flow Field ◽  
Film Cooling ◽  
Strong Increase ◽  
Pressure Side ◽  
Turbine Stage ◽  
High Pressure Turbine ◽  
Time Resolved

This article presents results for the coupled simulation of a high-pressure turbine stage in consideration of unsteady hot gas flows. A semi-unsteady coupling process was developed to solve the conjugate heat transfer problem for turbine components of gas turbines. Time-resolved CFD simulations are coupled to a finite element solver for the steady state heat conduction inside of the blade material. A simplified turbine stage geometry is investigated in this paper to describe the influence of the unsteady flow field onto the time-averaged heat transfer. Comparisons of the time-resolved results to steady state results indicate the importance of a coupled simulation and the consideration of the time-dependent flow-field. Different film-cooling configurations for the turbine NGV are considered, resulting in different temperature and pressure deficits in the vane wake. Their contribution to non-linear effects causing the time-averaged heat load to differ from a steady result is discussed to further highlight the necessity of unsteady design methods for future turbine developments. A strong increase in the pressure side heat transfer coefficients for unsteady simulations is observed in all results. For higher film-cooling mass flows in the upstream row, the preferential migration of hot fluid towards the pressure side of a turbine blade is amplified as well, which leads to a strong increase in material temperature at the pressure side and also in the blade tip region.

Monte Carlo Simulation of Steady-State Microscale Phonon Heat Transport

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Jaona Randrianalisoa ◽  
Dominique Baillis
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Monte Carlo ◽  
Heat Conduction ◽  
Steady State ◽  
Monte Carlo Method ◽  
Silicon Nanowires ◽  
Silicon Film ◽  
Relaxation Times ◽  
Phonon Transport

Heat conduction in submicron crystalline materials can be well modeled by the Boltzmann transport equation (BTE). The Monte Carlo method is effective in computing the solution of the BTE. These past years, transient Monte Carlo simulations have been developed, but they are generally memory demanding. This paper presents an alternative Monte Carlo method for analyzing heat conduction in such materials. The numerical scheme is derived from past Monte Carlo algorithms for steady-state radiative heat transfer and enables us to understand well the steady-state nature of phonon transport. Moreover, this algorithm is not memory demanding and uses very few iteration to achieve convergence. It could be computationally more advantageous than transient Monte Carlo approaches in certain cases. Similar to the famous Mazumder and Majumdar’s transient algorithm (2001, “Monte Carlo Study of Phonon Transport in Solid Thin Films Including Dispersion and Polarization,” ASME J. Heat Transfer, 123, pp. 749–759), the dual polarizations of phonon propagation, the nonlinear dispersion relationships, the transition between the two polarization branches, and the nongray treatment of phonon relaxation times are accounted for. Scatterings by different mechanisms are treated individually, and the creation and/or destruction of phonons due to scattering is implicitly taken into account. The proposed method successfully predicts exact solutions of phonon transport across a gallium arsenide film in the ballistic regime and that across a silicon film in the diffusion regime. Its capability to model the phonon scattering by boundaries and impurities on the phonon transport has been verified. The current simulations agree well with the previous predictions and the measurement of thermal conductivity along silicon thin films and along silicon nanowires of widths greater than 22nm. This study confirms that the dispersion curves and relaxation times of bulk silicon are not appropriate to model phonon propagation along silicon nanowires of 22nm width.

Mixed-Carbene Cyclometalated Iridium Complexes with Saturated Blue Luminescence

2019 ◽  
Author(s):  
Hanah Na ◽  
Louise Cañada ◽  
Thomas Teets
Keyword(s):  
Thin Films ◽  
Steady State ◽  
Methyl Methacrylate ◽  
Nucleophilic Addition ◽  
Blue Luminescence ◽  
Iridium Complexes ◽  
Photoluminescence Properties ◽  
Time Resolved ◽  
Main Text ◽  
Time Resolved Photoluminescence

This work describes the synthesis and photoluminescence of new heteroleptic mixed-carbene cyclometalated iridium complexes. Complexes are synthesized via a nucleophilic addition cascade reaction with isocyanide-bound precursors. The steady-state and time-resolved photoluminescence properties of the compounds are measured, both in solution and in poly(methyl methacrylate) (PMMA) thin films. Full experimental details are given in the main text and supporting information.<br>

Guest Aggregation within Poly(L-lactic Acid)/Pluronic P104 Thin Films

2008 ◽  
Vol 62 (3) ◽  
pp. 290-294 ◽  
Author(s):  
Jordan M. Steves ◽  
Loraine T. Tan ◽  
Joseph A. Gardella ◽  
Robert Hard ◽  
Wesley L. Hicks ◽  
...  
Keyword(s):  
Thin Films ◽  
Lactic Acid ◽  
Steady State ◽  
Fluorescence Spectroscopy ◽  
Biodegradable Polymer ◽  
Rhodamine 6G ◽  
Time Resolved Fluorescence ◽  
Time Resolved ◽  
Microscope Slides ◽  
Glass Microscope

Rhodamine 6G (R6G) doped thin films composed of poly(L-lactic acid) (PLLA) and Pluronic P104 were spin cast onto glass microscope slides and characterized by ultraviolet–visible, steady-state, and time-resolved fluorescence spectroscopy. The results show that R6G aggregation within the film increases as the R6G concentration and P104 loading increases. These results suggest an approach for studying drug distributions (monomers, aggregates) within biodegradable polymer formulations.

scholarly journals Simulated sample heating from a nanofocused X-ray beam

2017 ◽  
Vol 24 (5) ◽  
pp. 925-933 ◽  
Author(s):  
Harald Wallander ◽  
Jesper Wallentin
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Three Dimensional ◽  
Interfacial Area ◽  
Maximum Temperature ◽  
Time Resolved ◽  
Semiconductor Nanowire ◽  
X Ray ◽  
Sample Heating ◽  
Reference Parameters

Recent developments in synchrotron brilliance and X-ray optics are pushing the flux density in nanofocusing experiments to unprecedented levels, which increases the risk of different types of radiation damage. The effect of X-ray induced sample heating has been investigated using time-resolved and steady-state three-dimensional finite-element modelling of representative nanostructures. Simulations of a semiconductor nanowire indicate that the heat generated by X-ray absorption is efficiently transported within the nanowire, and that the temperature becomes homogeneous after about 5 ns. The most important channel for heat loss is conduction to the substrate, where the heat transfer coefficient and the interfacial area are limiting the heat transport. While convective heat transfer to air is significant, the thermal radiation is negligible. The steady-state average temperature in the nanowire is 8 K above room temperature at the reference parameters. In the absence of heat transfer to the substrate, the temperature increase at the same flux reaches 55 K in air and far beyond the melting temperature in vacuum. Reducing the size of the X-ray focus at constant flux only increases the maximum temperature marginally. These results suggest that the key strategy for reducing the X-ray induced heating is to improve the heat transfer to the surrounding.

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