Showing papers on "Thermal radiation published in 2017"
TL;DR: In this article, the authors show that four-phonon scattering is generally important in solids and can remedy such discrepancies and point out ways to improve thermoelectrics, thermal barrier coatings, nuclear materials, and radiative heat transfer.
Abstract: For decades, the three-phonon scattering process has been considered to govern thermal transport in solids, while the role of higher-order four-phonon scattering has been persistently unclear and so ignored. However, recent quantitative calculations of three-phonon scattering have often shown a significant overestimation of thermal conductivity as compared to experimental values. In this Rapid Communication we show that four-phonon scattering is generally important in solids and can remedy such discrepancies. For silicon and diamond, the predicted thermal conductivity is reduced by 30% at 1000 K after including four-phonon scattering, bringing predictions in excellent agreement with measurements. For the projected ultrahigh-thermal conductivity material, zinc-blende BAs, a competitor of diamond as a heat sink material, four-phonon scattering is found to be strikingly strong as three-phonon processes have an extremely limited phase space for scattering. The four-phonon scattering reduces the predicted thermal conductivity from 2200 to 1400 W/m K at room temperature. The reduction at 1000 K is 60%. We also find that optical phonon scattering rates are largely affected, being important in applications such as phonon bottlenecks in equilibrating electronic excitations. Recognizing that four-phonon scattering is expensive to calculate, in the end we provide some guidelines on how to quickly assess the significance of four-phonon scattering, based on energy surface anharmonicity and the scattering phase space. Our work clears the decades-long fundamental question of the significance of higher-order scattering, and points out ways to improve thermoelectrics, thermal barrier coatings, nuclear materials, and radiative heat transfer.
344 citations
TL;DR: In this paper, a double-layer coating consisting of a top reflective layer with high solar albedo and a bottom emissive layer are achieved by properly designed TiO 2, SiO 2, and SiC nanoparticles.
330 citations
TL;DR: In this paper, the fundamental physical mechanisms of switchable and nonlinear heat transfer have been harnessed to make thermal diodes, switches, and regulators, and various nonlinear and active thermal circuits are presented.
Abstract: Interest in new thermal diodes, regulators, and switches has been rapidly growing because these components have the potential for rich transport phenomena that cannot be achieved using traditional thermal resistors and capacitors. Each of these thermal components has a signature functionality: Thermal diodes can rectify heat currents, thermal regulators can maintain a desired temperature, and thermal switches can actively control the heat transfer. Here, we review the fundamental physical mechanisms of switchable and nonlinear heat transfer which have been harnessed to make thermal diodes, switches, and regulators. The review focuses on experimental demonstrations, mainly near room temperature, and spans the fields of heat conduction, convection, and radiation. We emphasize the changes in thermal properties across phase transitions and thermal switching using electric and magnetic fields. After surveying fundamental mechanisms, we present various nonlinear and active thermal circuits that are based on ana...
299 citations
TL;DR: In this article, the influence of Lorentz forces on Fe 3 O 4 -water nanofluid is presented, where the radiation source term is taken in to account in energy equation and newly suggested model is imposed for viscosity of ferrofluid.
251 citations
TL;DR: In this paper, the influence of thermal radiation on nanofluid heat transfer in existence of Lorentz forces is investigated, and a correlation for average Nusselt number is extracted.
223 citations
TL;DR: In this article, the authors address the simultaneous characteristics of thermal radiation and melting heat transfer effects in stagnation point flow of carbon nanotubes due to a stretching cylinder and compute numerical solutions numerically by fifth order Range-Kutta Fehlberg scheme.
202 citations
TL;DR: In this paper, the impact of thermal radiation on convection heat transfer was investigated in Fe3O4-H2O nanofluid hydrothermal behavior and an innovative numerical method was chosen namely Control volume based finite element method.
187 citations
TL;DR: In this article, the velocity distribution for local Weissenberg number in case of shear thinning liquid reduces whereas it increments for shear thickening liquid and the results demonstrated that the results of presented analysis are compared with the available works in particular situations and reasonable agreement is noted.
182 citations
TL;DR: In this paper, the influence of carbon nanotubes in the Marangoni convection boundary layer flow of viscous fluid has been investigated and convergent series solutions are established for the resulting differential systems.
158 citations
TL;DR: In this article, three dimensional magnetohydrodynamic flow and heat transfer analysis associated with thermal radiation as well as viscous dissipation of nanofluid over a shrinking surface has been investigated.
141 citations
TL;DR: In this paper, the influence of transverse magnetic field as well as thermal radiation on the three-dimensional free convective flow of nanofluid over a linear stretching sheet was studied and it was found that the presence of magnetic field slows down the fluid motion while it enhances the fluid temperature leading to a reduction in heat transfer rate.
TL;DR: In this article, the authors review the development of thermal photonics, which utilizes structures where at least one of the structural features is at a wavelength or subwavelength scale, for the control of thermal radiation.
TL;DR: In this paper, a multilayer graphene-hBN heterostructures are proposed to further enhance the near-field thermal radiation in hexagonal boron nitride (hBN) cells.
Abstract: Graphene-covered hexagonal boron nitride (hBN) can exceed blackbody thermal radiation in near-field due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). As previous research found that the thickness of hBN in a graphene-hBN cell can be very thin while still presenting strong radiation enhancement, multilayer graphene-hBN heterostructures are proposed in this paper to further enhance the near-field thermal radiation. We found that a heterostructure consisting of five or more graphene-hBN cells performs better than all existing graphene-hBN configurations, and the infinite cell limit exhibits 1.87- and 2.94-fold larger heat flux at 10 nm separation than sandwich and monocell structures do, respectively, due to the continuously and perfectly coupled modes. The heat flux is found to be 4 orders of magnitude larger than that of the blackbody. The effective tunability of the thermal radiation of the multicell structure is also observed by adjusting the chemical poten...
TL;DR: The presented methodology to form a nanometric gap with functional heat flux paves the way to the smart thermal management in various scenes ranging from highly integrated systems to macroscopic apparatus.
Abstract: Dynamic control of electromagnetic heat transfer without changing mechanical configuration opens possibilities in intelligent thermal management in nanoscale systems. We confirmed by experiment that the radiative heat transfer is dynamically modulated beyond the blackbody limit. The near-field electromagnetic heat exchange mediated by phonon–polariton is controlled by the metal–insulator transition of tungsten-doped vanadium dioxide. The functionalized heat flux is transferred over an area of 1.6 cm2 across a 370 nm gap, which is maintained by the microfabricated spacers and applied pressure. The uniformity of the gap is validated by optical interferometry, and the measured heat transfer is well modeled as the sum of the radiative and the parasitic conductive components. The presented methodology to form a nanometric gap with functional heat flux paves the way to the smart thermal management in various scenes ranging from highly integrated systems to macroscopic apparatus.
TL;DR: In this article, a complete CFD-DEM method coupled with particle-scale radiation is discussed for packed pebble beds, considering particle motion, fluid flow, particle-fluid interactions and heat convection, conduction and particle radiation.
TL;DR: In this article, a similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with appropriate boundary conditions, which are solved by Duan-Rach Approach (DRA).
Abstract: In this work, the unsteady squeezing MHD nanofluid flow and heat transfer between two parallel plates in the attendance of thermal radiation impact and considering Cattaneo–Christov heat flux model instead of conventional Fourier's law of heat conduction are examined. A similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with the appropriate boundary conditions. The gained non-linear ordinary differential equations are solved by Duan–Rach Approach (DRA). This method allows us to find a solution without using numerical methods to evaluate the undetermined coefficients. This method modifies the standard Adomian Decomposition Method by evaluating the inverse operators at the boundary conditions directly. The impacts of diverse active parameters such as the magnetic parameter, the squeeze number, the volume fraction of nanofluid, the heat source parameter, the thermal relaxation parameter and the radiation parameter on the velocity and temperature profiles are examined. In addition, the value of the Nusselt number is calculated and presented through figures. The outcomes indicate that the temperature distribution is fewer in the case of Cattaneo–Christov heat flux model as compared to Fourier's law. Furthermore, Nusselt number is an incrementing function of heat source parameter, while it is a diminishing function of the thermal relaxation parameter.
TL;DR: In this article, an attempt is made to study nonlinear radiation and chemical reactive magnetohydrodynamic (MHD) flow of nanofluid, which comprises water and copper (Cu) and silver (Ag) as nanoparticles.
Abstract: An attempt is accomplished to study nonlinear radiation and chemical reactive magnetohydrodynamic (MHD) flow of nanofluid. Nanofluid comprises water and copper (Cu) and silver (Ag) as nanoparticles. Effect of porous medium is also taken into account. Characteristics of heat and mass transfers are discussed via homogeneous-heterogeneous reactions. Correlation behavior of surface drag force and heat transfer rate is discussed. Probable error and statistical declaration for drag force and heat transfer rate are computed. Ordinary differential systems have been considered. Solutions of the problem are presented via a numerical technique namely Euler’s Explicit Method (EEM). The key roles of different embedded parameters on different characteristics of fluid are discussed graphically. The outcomes of the given problem demonstrate that non-linear radiation has noteworthy effect on both temperature and heat transfer coefficient.
TL;DR: In this article, the authors exploit the coupling of adjacent phonon-polaritonic nanostructures, demonstrating experimentally that the nanometer-scale gaps can control the thermal emission frequency while retaining emission line widths as narrow as 10 cm-1.
Abstract: A conventional thermal emitter exhibits a broad emission spectrum with a peak wavelength depending upon the operation temperature. Recently, narrowband thermal emission was realized with periodic gratings or single microstructures of polar crystals supporting distinct optical modes. Here, we exploit the coupling of adjacent phonon-polaritonic nanostructures, demonstrating experimentally that the nanometer-scale gaps can control the thermal emission frequency while retaining emission line widths as narrow as 10 cm–1. This was achieved by using deeply subdiffractional bowtie-shaped silicon carbide nanoantennas. Infrared far-field reflectance spectroscopy, near-field optical nanoimaging, and full-wave electromagnetic simulations were employed to prove that the thermal emission originates from strongly localized surface phonon-polariton resonances of nanoantenna structures. The observed narrow emission line widths and exceptionally small modal volumes provide new opportunities for the user-design of near- and...
TL;DR: In this article, the collective influence of thermal radiation and convection flow of Cu-water nanofluid due to a stretching cylinder in a porous medium along with viscous dissipation and slip boundary conditions was examined.
Abstract: The purpose of the present work is to examine the collective influence of thermal radiation and convection flow of Cu-water nanofluid due to a stretching cylinder in a porous medium along with viscous dissipation and slip boundary conditions. The governing non-linear ODEs and auxiliary boundary conditions those obtained by applying assisting similarity transformations have been handled numerically with shooting scheme through Runge-Kutta-integration procedure of fourth-fifth order. The non-dimensional velocity and temperature distribution are designed and also skin friction coefficient as well as heat transfer rate are tabulated for various values of relatable parameters. The results explain that Nusselt number depreciates with boost in radiation parameter, thermal slip parameter and Eckert number. Moreover, it is accelerated with increase in velocity slip parameter and natural convection parameter. The results are distinguished via published ones and excellent accord has been detected.
TL;DR: In this article, a similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with the appropriate boundary conditions, which are solved by Duan-Rach Approach (DRA).
TL;DR: In this paper, the boundary layer flow and heat transfer of an incompressible TiO2-water nanoparticle on micropolar fluid with homogeneously suspended dust particles in the presence of thermal radiation are analyzed.
TL;DR: In this article, the authors investigated the heat and mass transfer in an unsteady two-dimensional squeezing flow of magnetohydromagnetic (MHD) radiative non-Newtonian Eyring-Powell fluid between two parallel infinite plates in the presence of heat generation/absorption, thermal radiation and Joule heating effect.
TL;DR: An asymmetric Fabry-Perot emitter with a lossless dielectric spacer inserted between a vanadium dioxide (VO 2 ) thin film and an opaque aluminum substrate is proposed in this article.
Abstract: An asymmetric Fabry-Perot emitter is proposed with a lossless dielectric spacer inserted between a vanadium dioxide (VO 2 ) thin film and an opaque aluminum substrate. Switchable mid-infrared emittance has been achieved due to the insulator-to-metal transition of VO 2 . When VO 2 is dielectric below 341 K, the structure is highly reflective, thereby minimizing thermal radiation loss. Above 345 K, the VO 2 becomes metallic and forms a Fabry-Perot resonance cavity with high broadband emissivity around 10 µm wavelength, providing a radiative cooling effect due to enhanced thermal emission. The radiative properties are calculated via a uniaxial transfer matrix method and Bruggeman effective medium theory. The physical mechanisms that provide the observed absorption enhancements are elucidated by examining the total phase shift in the multilayer structure and the phonon modes of VO 2. When experiencing the VO 2 phase transition, the radiative power of the proposed coating achieves a 6.5 fold enhancement for extraterrestrial spacecraft systems, and 7.3 fold enhancement for terrestrial systems such as buildings, making it a promising choice for dynamic radiative cooling applications in a variable environment. The findings here will facilitate research and development of novel coating materials for radiative cooling applications.
TL;DR: In this article, an analysis of the magnetohydrodynamics flow of nanofluid towards nonlinear stretched surface with variable thickness in the presence of electric field is presented with viscous dissipation, Joule heating and chemical reaction.
Abstract: The present paper addresses magnetohydrodynamics (MHD) flow of nanofluid towards nonlinear stretched surface with variable thickness in the presence of electric field. The analysis is presented with viscous dissipation, Joule heating, and chemical reaction. Characteristics of heat transfer are analyzed with the electric field and variable thickness phenomenon. The partial differential equations are converted into dimensionless ordinary differential equations by employing suitable transformations. Implicit finite difference scheme is implemented to solve the governing dimensionless problems. Behaviors of several sundry variables on the flow and heat transfer are scrutinized. Skin friction coefficient, the local Nusselt number local Sherwood number are presented and evaluated. It is observed that the skin friction, the rate of heat and mass transfer reduces with a rise in wall thickness. Electric field enhances the nanofluid velocity and temperature but reduced the concentration. Thermal radiation is sensitive to an increase in the nanofluid temperature and thicker thermal boundary layer thickness. Obtained results are also compared with the available data in the limiting case and good agreement is noted.
TL;DR: In this article, the influence of nonlinear thermal radiation (via the Rosseland diffusion flux model) has been studied on the laminar, incompressible, dissipative peristaltic propulsive flow of a non-Newtonian (Jefferys viscoelastic) dusty fluid containing solid particles through a porous planar channel.
TL;DR: In this paper, the study of electrically conducting micropolar nanofluids flow over a stretching sheet influencing by thermal radiation and non-uniform heat source/sink in presence of transverse magnetic field investigated numerically and simulated with RungeKutta-Fehlberg method with shooting techniques.
TL;DR: In this paper, a spectral element method (SEM) is developed to solve coupled conductive, convective and radiative heat transfer in moving porous fins of trapezoidal, convex parabolic and concave parabolic profiles.
TL;DR: In this article, the combined effects of Hall currents and thermal radiation on unsteady MHD hybrid nanofluid flow in a rotating vertical channel were examined and closed form solutions were obtained after simplification and suitable consideration.
Abstract: The present analysis examines the combined effects of Hall currents and thermal radiation on unsteady MHD hybrid nanofluid flow in a rotating vertical channel. Closed form solutions are obtained after simplification and suitable consideration. Cu and CuO nanoparticles are chosen for manufacturing of hybrid nanofluid. Analysis is carried out for three different stable shapes of nanoparticles. It is concluded that brick shaped nanoparticles contribute to relative low temperature distribution while platelets shaped nanoparticles are efficient in a sense of rising fluid flow. Moreover, primary velocity is a decreasing function of rotation parameter while secondary velocity is an increasing function of K 2 . Both velocities lessen with the rise in thermal radiation near the left wall while their magnitude rises near the right wall of the vertical channel.
TL;DR: In this paper, the optical properties of the solar module were redesigned to eliminate parasitic absorption and enhance thermal emission to reduce the operating temperature of one-sun terrestrial solar modules up to 10 °C.
Abstract: For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20–30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of the solar module to eliminate parasitic absorption ( selective-spectral cooling ) and enhance thermal emission ( radiative cooling ). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. This self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.
TL;DR: In this article, a similarity transformation is used to transform the constitutive equations into a system of nonlinear ordinary differential equations, and the resultant system of equations is then solved numerically using implicit finite difference method.