Showing papers on "Thermal radiation published in 2013"
TL;DR: In this article, the authors make extensive use of the growing number of surface observations to constrain the global energy balance not only from space, but also from the surface, and combine these observations with the latest modeling efforts performed for the 5th IPCC assessment report to infer best estimates for the global mean surface radiative components.
Abstract: In the framework of the global energy balance, the radiative energy exchanges between Sun, Earth and space are now accurately quantified from new satellite missions. Much less is known about the magnitude of the energy flows within the climate system and at the Earth surface, which cannot be directly measured by satellites. In addition to satellite observations, here we make extensive use of the growing number of surface observations to constrain the global energy balance not only from space, but also from the surface. We combine these observations with the latest modeling efforts performed for the 5th IPCC assessment report to infer best estimates for the global mean surface radiative components. Our analyses favor global mean downward surface solar and thermal radiation values near 185 and 342 Wm−2, respectively, which are most compatible with surface observations. Combined with an estimated surface absorbed solar radiation and thermal emission of 161 and 397 Wm−2, respectively, this leaves 106 Wm−2 of surface net radiation available globally for distribution amongst the non-radiative surface energy balance components. The climate models overestimate the downward solar and underestimate the downward thermal radiation, thereby simulating nevertheless an adequate global mean surface net radiation by error compensation. This also suggests that, globally, the simulated surface sensible and latent heat fluxes, around 20 and 85 Wm−2 on average, state realistic values. The findings of this study are compiled into a new global energy balance diagram, which may be able to reconcile currently disputed inconsistencies between energy and water cycle estimates.
412 citations
01 Jan 2013
TL;DR: In this paper, the inverse heat transfer analysis (INTA) problem is studied, where the necessary geometry, temperatures, and radiative properties are known, enabling us to calculate the radiative intensity and heat fluxes in such enclosures.
Abstract: Up to this point we have concerned ourselves with radiative heat transfer problems, where the necessary geometry, temperatures, and radiative properties are known, enabling us to calculate the radiative intensity and radiative heat fluxes in such enclosures. Such cases are sometimes called “direct” heat transfer problems. However, there are many important engineering applications where knowledge of one or more input parameters is desired that cause a certain radiative intensity field. For example, it may be desired to control the temperatures of heating elements in a furnace, in order to achieve a specified temperature distribution or radiative heat load on an object being heated. Or the aim may be to deduce difficult to measure parameters (such as radiative properties, temperature fields inside a furnace, etc.) based on measurements of radiative intensity or radiative flux. Such calculations are known as inverse heat transfer analyses.
354 citations
TL;DR: In this article, a radiative thermal diode which rectifies heat transport thanks to the phase transitions of materials is presented. But it is not suitable for use in contactless thermal circuits or in the conception of radiative coatings for thermal management.
Abstract: A thermal diode transports heat mainly in one preferential direction rather than in the opposite direction. This behavior is generally due to the non-linear dependence of certain physical properties with respect to the temperature. Here we introduce a radiative thermal diode which rectifies heat transport thanks to the phase transitions of materials. Rectification coefficients greater than 70% and up to 90% are shown, even for small temperature differences. This result could have important applications in the development of future contactless thermal circuits or in the conception of radiative coatings for thermal management.
205 citations
TL;DR: In this article, the boundary layer flow and heat transfer towards a porous exponential stretching sheet in presence of a magnetic field is presented in the analysis, where velocity slip and thermal slip are considered instead of no-slip conditions at the boundary.
204 citations
TL;DR: In this paper, the thermal performance of porous media receiver was investigated by combining the Monte Carlo Ray Tracing (MCRT) method and FLUENT software with user defined functions (UDFs).
181 citations
TL;DR: In this article, a fractal-intersecting sphere model was proposed for the nano-porous silica aerogel in which the scale effect on gas conduction and solid-matrix conduction were both considered.
180 citations
TL;DR: In this paper, the authors report strong thermal rectification effect based on the near-field thermal radiation between silicon dioxide (SiO2) and a phase transition material, vanadium dioxide (VO2), separated by nanometer vacuum gaps under the framework of fluctuational electrodynamics.
Abstract: The capability of manipulating heat flow has promising applications in thermal management and thermal circuits. In this Letter, we report strong thermal rectification effect based on the near-field thermal radiation between silicon dioxide (SiO2) and a phase transition material, vanadium dioxide (VO2), separated by nanometer vacuum gaps under the framework of fluctuational electrodynamics. Strong coupling of surface phonon polaritons between SiO2 and insulating VO2 leads to enhanced near-field radiative transfer, which on the other hand is suppressed when VO2 becomes metallic, resulting in thermal rectification. The rectification factor is close to 1 when vacuum gap is at 1 μm and it increases to almost 2 at sub-20-nm gaps when emitter and receiver temperatures are set to 400 and 300 K, respectively. Replacing bulk SiO2 with a thin film of several nanometers, rectification factor of 3 can be achieved when the vacuum gap is around 100 nm.
179 citations
TL;DR: In this paper, an experimental approach for direct measurement and extraction of wavelength and temperature-dependent thermal emittance was proposed, which can find applications in infrared camouflage, thermal regulation, and infrared tagging and labeling.
Abstract: thermal radiation and appears colder on an infrared camera. Our experimental approach allows for a direct measurement and extraction of wavelength- and temperature-dependent thermal emittance. We anticipate that emissivity engineering with thin-film geometries comprising VO2 and other thermochromic materials will find applications in infrared camouflage, thermal regulation, and infrared tagging and labeling.
174 citations
TL;DR: In this paper, the clear-sky radiation limits at line-by-line spectral resolution for a planet with the same amount of incident solar radiation as Earth has today were calculated.
Abstract: Terrestrial planet atmospheres must be in long-term radiation balance, with solar radiation absorbed matched by thermal radiation emitted. For hot moist atmospheres, however, there is an upper limit on the thermal emission which is decoupled from the surface temperature. If net absorbed solar radiation exceeds this limit the planet will heat uncontrollably, the so-called \runaway greenhouse". Here we show that a runaway greenhouse induced steam atmosphere may be a stable state for a planet with the same amount of incident solar radiation as Earth has today, contrary to previous results. We have calculated the clear-sky radiation limits at line-by-line spectral resolution for the first time. The thermal radiation limit is lower than previously reported (282 W/sq m rather than 310W/sq m) and much more solar radiation would be absorbed (294W/sq m rather than 222W/sq m). Avoiding a runaway greenhouse under the present solar constant requires that the atmosphere is subsaturated with water, and that cloud albedo forcing exceeds cloud greenhouse forcing. Greenhouse warming could in theory trigger a runaway greenhouse but palaeoclimate comparisons suggest that foreseeable increases in greenhouse gases will be insufficient to do this.
169 citations
TL;DR: In this article, the problem of steady, laminar, mixed convection boundary-layer flow over a vertical cone embedded in a porous medium saturated with a nanofluid is studied, in the presence of thermal radiation.
Abstract: The problem of steady, laminar, mixed convection boundary-layer flow over a vertical cone embedded in a porous medium saturated with a nanofluid is studied, in the presence of thermal radiation. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis with Rosseland diffusion approximation. The cone surface is maintained at a constant temperature and a constant nanoparticle volume fraction. The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results in the literature, and our results are in very good agreement with the known results. A parametric study of the physical parameters is made and a representative set of numerical results for the local Nusselt and Sherwood numbers are presented graphically. Also, the salient features of the results are analyzed and discussed.
137 citations
TL;DR: In this article, the thermal rectification effect enabled by near-field thermal radiation between intrinsic silicon and other materials was investigated at various temperatures and vacuum gap distances, and a thermal rectifier made of gold and intrinsic Si was shown to have a rectification factor arou...
Abstract: Thermal rectification has recently attracted great attention because it could allow heat to flow in a preferred direction and may have promising applications in thermal management and energy systems. In addition to phonon engineering, photon transport at the near-field regime has been recently proposed to realize thermal rectification between planar structures. In the present study, the thermal rectification effect enabled by near-field thermal radiation between intrinsic silicon and other materials was investigated at various temperatures and vacuum gap distances. Strong thermal rectification between intrinsic Si and doped Si (rectification R = 2.7) and between intrinsic Si and SiO2 (R = 9.9) can be achieved with a 5 nm vacuum gap at temperatures of 1000 and 300 K. Rectification larger than one can be obtained in sub-10 nm vacuum gaps for the former configuration and sub-20 nm gaps for the latter configuration. A thermal rectifier made of gold and intrinsic Si is shown to have a rectification factor arou...
TL;DR: In this paper, a broadband near-field thermal emitter/absorber based on hyperbolic metamaterials is presented, which can significantly enhance near field radiative heat transfer with infrared surface-polariton-resonance materials and maintain the monochromatic characteristic of heat transfer.
Abstract: In the near field, radiative heat transfer can exceed the prediction from Planck's law by several orders of magnitude, when the interacting materials support surface polaritons in the infrared range. However, if the emitter and absorber are made from two different materials, which support surface polariton resonances at different frequencies, the mismatch between surface polariton resonance frequencies will drastically reduce near-field radiative heat transfer. Here, we present a broadband near-field thermal emitter/absorber based on hyperbolic metamaterials, which can significantly enhance near-field radiative heat transfer with infrared surface-polariton-resonance materials and maintain the monochromatic characteristic of heat transfer. Instead of using an effective medium approximation, we perform a direct numerical simulation to accurately investigate the heat transfer mechanisms of metamaterials based on the Wiener chaos expansion method.
TL;DR: The ability of this spectroscopy to probe the frequency dependence of the electromagnetic local density of states is evaluated, using a tungsten tip as a local scatterer coupling the near-field thermal emission to the far field.
Abstract: We report local spectra of the near-field thermal emission recorded by a Fourier transform infrared spectrometer, using a tungsten tip as a local scatterer coupling the near-field thermal emission to the far field. Spectra recorded on silicon carbide and silicon dioxide exhibit temporal coherence due to thermally excited surface waves. Finally, we evaluate the ability of this spectroscopy to probe the frequency dependence of the electromagnetic local density of states.
TL;DR: In this article, the effect of radiation on the Sakiadis flow along a moving plate in a calm fluid was considered and the results in that paper have been produced using a linearized Rosseland approximation, which is valid only for small temperature differences between the plate and the ambient fluid.
Abstract: In a recent paper by Cortell (2008 Chin. Phys. Lett. 25 1340–2) the effect of radiation on the classical Sakiadis flow along a moving plate in a calm fluid was considered. The results in that paper have been produced using a linearized Rosseland approximation, which is valid only for small temperature differences between the plate and the ambient fluid. In the present work, we extend the above work to a nonlinear Rosseland approximation, which is valid for both small and large temperature differences.
TL;DR: In this paper, a general fluctuation-electrodynamic theory is developed to investigate radiative heat exchanges between objects that are assumed to be small compared with their thermal wavelength (dipolar approximation) in N-body immersed in a thermal bath.
Abstract: A general fluctuation-electrodynamic theory is developed to investigate radiative heat exchanges between
objects that are assumed to be small compared with their thermal wavelength (dipolar approximation) in N-body
systems immersed in a thermal bath. This theoretical framework is applied to study the dynamic of heating or
cooling of three-body systems. We show that many-body interactions allow us to tailor the temperature field
distribution and to drastically change the time scale of thermal relaxation processes.
TL;DR: In this paper, a local similarity solution of unsteady MHD natural convection heat and mass transfer boundary layer flow past a flat porous plate within the presence of thermal radiation is investigated.
Abstract: A local similarity solution of unsteady MHD natural convection heat and mass transfer boundary layer flow past a flat porous plate within the presence of thermal radiation is investigated. The effects of exothermic and endothermic chemical reactions with Arrhenius activation energy on the velocity, temperature, and concentration are also studied in this paper. The governing partial differential equations are reduced to ordinary differential equations by introducing locally similarity transformation (Maleque (2010)). Numerical solutions to the reduced nonlinear similarity equations are then obtained by adopting Runge-Kutta and shooting methods using the Nachtsheim-Swigert iteration technique. The results of the numerical solution are obtained for both steady and unsteady cases then presented graphically in the form of velocity, temperature, and concentration profiles. Comparison has been made for steady flow () and shows excellent agreement with Bestman (1990), hence encouragement for the use of the present computations.
TL;DR: In this article, the authors considered the two-dimensional magnetohydrodynamic (MHD) stagnation-point flow of electrically conducting non-Newtonian Casson fluid and heat transfer towards a stretching sheet.
Abstract: The two-dimensional magnetohydrodynamic (MHD) stagnation-point flow of electrically conducting non-Newtonian Casson fluid and heat transfer towards a stretching sheet have been considered. The effect of thermal radiation is also investigated. Implementing similarity transformations, the governing momentum, and energy equations are transformed to self-similar nonlinear ODEs and numerical computations are performed to solve those. The investigation reveals many important aspects of flow and heat transfer. If velocity ratio parameter (B) and magnetic parameter (M) increase, then the velocity boundary layer thickness becomes thinner. On the other hand, for Casson fluid it is found that the velocity boundary layer thickness is larger compared to that of Newtonian fluid. The magnitude of wall skin-friction coefficient reduces with Casson parameter (β). The velocity ratio parameter, Casson parameter, and magnetic parameter also have major effects on temperature distribution. The heat transfer rate is enhanced with increasing values of velocity ratio parameter. The rate of heat transfer is enhanced with increasing magnetic parameter M for B > 1 and it decreases with M for B < 1. Moreover, the presence of thermal radiation reduces temperature and thermal boundary layer thickness.
TL;DR: In this paper, the near-field radiative heat transfer for two hyperbolic metamaterials, namely, graphite and vertically aligned carbon nanotubes (CNTs), is investigated.
Abstract: The near-field radiative heat transfer for two hyperbolic metamaterials, namely, graphite and vertically aligned carbon nanotubes (CNTs), is investigated. Graphite is a naturally existing uniaxial medium, while CNT arrays can be modeled as an effective anisotropic medium. Different hyperbolic modes can be separately supported by these materials in certain infrared regions, resulting in a strong enhancement in near-field heat transfer. It is predicted that the heat flux between two CNT arrays can exceed that between SiC plates at any vacuum gap distance and is about 10 times higher with a 10 nm gap.
TL;DR: It is shown that the thermal emission of a finite-size blackbody emitter can be enhanced and a four-fold enhancement of the far-field thermal emitted of a carbonblack emitter having an emissivity of 0.85 is observed.
Abstract: The control of thermal radiation is of great current importance for applications such as energy conversions and radiative cooling. Here we show theoretically that the thermal emission of a finite-size blackbody emitter can be enhanced in a thermal extraction scheme, where one places the emitter in optical contact with an extraction device consisting of a transparent object, as long as both the emitter and the extraction device have an internal density of state higher than vacuum, and the extraction device has an area larger than the emitter and moreover has a geometry that enables light extraction. As an experimental demonstration of the thermal extraction scheme, we observe a four-fold enhancement of the far-field thermal emission of a carbon-black emitter having an emissivity of 0.85.
TL;DR: In this paper, both gas and particle radiation are modelled in an axi-symmetric cross section of a cylindrical furnace and differences in the radiative transfer between air-and oxy-firing are investigated.
TL;DR: In this paper, the authors review the recent advances in near-field radiative energy transfer, particularly in its fundamentals and applications, covering from the essential physics to the most recent theoretical as well as experimental findings that will further promote the fundamental understanding.
Abstract: This article reviews the recent advances in near-field radiative energy transfer, particularly in its fundamentals and applications. When the geometrical features of radiating objects or their separating distances fall into the sub-wavelength range, near-field phenomena such as photon tunneling and surface polaritons begin to play a key role in energy transfer. The resulting heat transfer rate can greatly exceed the blackbody radiation limit by several orders magnitude. This astonishing feature cannot be conveyed by the conventional theory of thermal radiation, generating strong demands in fundamental research that can address thermal radiation in the near field. Important breakthroughs of near-field thermal radiation are presented here, covering from the essential physics that will help better understand the basics of near-field thermal radiation to the most recent theoretical as well as experimental findings that will further promote the fundamental understanding. Applications of near-field thermal radiation in various fields are also discussed, including the radiative property manipulation, near-field thermophotovoltaics, nanoinstrumentation and nanomanufacturing, and thermal rectification.
TL;DR: In this article, the spectral, spatial, resonant, and coherence properties of the evanescent thermal near-field have been characterized for systems with thermally excited molecular, surface plasmon polariton, and surface phonon polariton (SPhP) resonances.
TL;DR: In this article, the authors exploit the unique properties of optical waves in nanophotonic structures to enhance the capabilities for active control of electromagnetic thermal transfer at nanoscale, and show that the near-field thermal transfer between two nanospheres can exhibit a thermal rectification effect with very high contrast and large operating bandwidth.
Abstract: We exploit the unique properties of optical waves in nanophotonic structures to enhance the capabilities for active control of electromagnetic thermal transfer at nanoscale. We show that the near-field thermal transfer between two nanospheres can exhibit a thermal rectification effect with very high contrast and large operating bandwidth. In this system, the scale invariance properties of the resonance modes result in a large difference in the coupling constants between relevant modes in the forward and reverse scenarios. Such a difference provides a mechanism for thermal rectification. The two-sphere system can also exhibit negative differential thermal conductance.
TL;DR: In this article, the three-dimensional stretched flow of the Jeffrey fluid with thermal radiation was analyzed and the local Nusselt number was compared with the existing limiting solutions, showing good agreement with each other.
Abstract: This article addresses the three-dimensional stretched flow of the Jeffrey fluid with thermal radiation. The thermal conductivity of the fluid varies linearly with respect to temperature. Computations are performed for the velocity and temperature fields. Graphs for the velocity and temperature are plotted to examine the behaviors with different parameters. Numerical values of the local Nusselt number are presented and discussed. The present results are compared with the existing limiting solutions, showing good agreement with each other.
TL;DR: In this article, a fundamental theoretical study made to understand the interaction of surface radiation and natural convection in an air-filled cavity with a centrally placed thin heated plate was presented, which indicated a better homogenization of temperature field within the cavity by radiation.
TL;DR: In this article, a fully coupled transient model of the volumetric solar air receiver is developed to predict the transient behaviors of the receiver under various working conditions, including pressure drop of the absorber, interfacial heat transfer between the flowing fluid and solid, and radiative heat transfer due to concentrated solar radiation absorption by ceramic foam and the radiation transport inside the media.
TL;DR: In this article, the state-of-the-art knowledge and research results of thermal transport in open celled cellular metal foams, which covers the effective thermal conductivity, forced convection, natural convection and thermal radiation, pool boiling and flow boiling heat transfer, solid/liquid phase change heat transfer and catalytic reactor were provided.
Abstract: Thermal transport in metal foams has received growing attention in both academic research and industrial applications. In this paper the recent research progress of thermal transport in metal foams has been reviewed. This paper aims to provide the comprehensive state-of-the-art knowledge and research results of thermal transport in open celled cellular metal foams, which covers the effective thermal conductivity, forced convection, natural convection, thermal radiation, pool boiling and flow boiling heat transfer, solid/liquid phase change heat transfer and catalytic reactor. The forced convection and thermal conductivity have been extensively investigated, while less research were performed on two-phase (boiling and solid/liquid phase change heat transfer) and thermal radiation in metal foams. Also most research still treats the metal foam as one type of effective continuous porous media, very few researchers investigated the detailed thermal behaviours at the pore level either by numerical or experimental approaches.
Abstract: In this paper, a theoretical analysis is presented for magnetohydrodynamic flow of blood in a capillary, its lumen being porous and wall permeable The unsteadiness in the flow and temperature fields is caused by the time-dependence of the stretching velocity and the surface temperature Thermal radiation, velocity slip and thermal slip conditions are taken into account In order to study the flow field as well as the temperature field, the problem is formulated as a boundary value problem consisting of a system of nonlinear coupled partial differential equations The problem is analysed by using similarity transformation and boundary layer approximation Solution of the problem is achieved by developing a suitable numerical method and using high speed computers Computational results for the variation in velocity, temperature, skin-friction co-efficient and Nusselt number are presented in graphical/tabular form Effects of different parameters are adequately discussed Since the study takes care of thermal radiation in blood flow, the results reported here are likely to have an important bearing on the therapeutic procedure of hyperthermia, particularly in understanding/regulating blood flow and heat transfer in capillaries
TL;DR: In this paper, the authors investigated the unsteady flow of a Casson fluid and heat transfer over a stretching surface in presence of suction/blowing and solved numerically by using the shooting method.
Abstract: The unsteady flow of a Casson fluid and heat transfer over a stretching surface in presence of suction/blowing are investigated. The transformed equations are solved numerically by using the shooting method. The exact solution corresponding to the momentum equation for the steady case is obtained. Fluid velocity initially decreases with the increase of unsteadiness parameter. Due to an increasing Casson parameter the velocity field is suppressed. Thermal radiation enhances the effective thermal diffusivity and the temperature rises.
TL;DR: Numerical simulations show that the light absorbance can be controlled from near zero to 100% by tuning the Fermi energy and a set of periodically located absorption peaks is observed at near grazing incidence.
Abstract: Graphene is a two-dimensional material with exotic electronic, optical and thermal properties. The optical absorption in monolayer graphene is limited by the fine structure constant α. Here we demonstrated the strong enhancement of light absorption and thermal radiation in homogeneous graphene. Numerical simulations show that the light absorbance can be controlled from near zero to 100% by tuning the Fermi energy. Moreover, a set of periodically located absorption peaks is observed at near grazing incidence. Based on this unique property, highly directive comb-like thermal radiation at near-infrared frequencies is demonstrated.