Thermal radiation

About: Thermal radiation is a research topic. Over the lifetime, 12290 publications have been published within this topic receiving 197186 citations. The topic is also known as: heat radiation.

Nonequilibrium Fluctuational Quantum Electrodynamics: Heat Radiation, Heat Transfer, and Force

Abstract: Quantum and thermal fluctuations of electromagnetic waves are the cornerstone of quantum and statistical physics, and inherent to such phenomena as thermal radiation and van der Waals forces. While the basic principles are the material of elementary texts, recent experimental and technological advances have made it necessary to come to terms with counterintuitive consequences of electromagnetic fluctuations at short scales -- in the so called {\it near-field} regime. We focus on three manifestations of such behavior: {\bf (i)} The Stefan--Boltzmann law describes thermal radiation from macroscopic bodies, but fails to account for magnitude, polarization and coherence of radiation from small objects (say compared to the skin depth). {\bf (ii)} The heat transfer between two bodies at similar close proximity is dominated by evanescent waves, and can be several orders of magnitude larger than the classical contribution due to propagating waves. {\bf (iii)} Casimir/van der Waals interactions are a dominant force between objects at sub-micron separation; the non-equilibrium analogs of this force (for objects at different temperatures) have not been sufficiently explored (at least experimentally). To explore these phenomena we introduce the tool of fluctuational quantum electrodynamics (QED) originally introduced by Rytov in the 1950s. Combined with a scattering formalism, this enables studies of heat radiation and transfer, equilibrium and non-equilibrium forces for objects of different material properties, shapes, separations and arrangements.

Circulating fluidized bed heat transfer

Abstract: Heat transfer to the walls of a circulating bed is due to conduction from clusters of particles falling along the walls, thermal radiation, and convection to uncovered surface areas. Important hydrodynamic factors are the fraction of the wall covered by particles and the average contact time of particles at the wall. Small active heat transfer probes will give an upper limit to the heat transfer in a circulating bed. Experimental results show lower heat transfer coefficients for larger walls; heat transfer is limited by the temperature change of particle clusters moving down the walls. The contact time for clusters is related to their average displacement before breakup. For displacements of 15 cm or less, the cluster displacement approximates constant gravitational acceleration. The most pressing needs for commercial bed designers are heat transfer and hydrodynamic results valid for large diameter beds.

Hierarchically Hollow Microfibers as a Scalable and Effective Thermal Insulating Cooler for Buildings.

Abstract: Daytime passive radiative cooling is a promising electricity-free pathway for cooling terrestrial buildings. Current research interest in this cooling strategy mainly lies in tailoring the optical spectra of materials for strong thermal emission and high solar reflection. However, environmental heat gain poses a crucial challenge to building cooling at subambient temperatures. Herein, we devise a scalable thermal insulating cooler (TIC) consisting of hierarchically hollow microfibers as the building envelope that simultaneously achieves passive daytime radiative cooling and thermal insulation to reduce environmental heat gain. The TIC demonstrates efficient solar reflection (94%) and long-wave infrared emission (94%), yielding a temperature drop of about 9 °C under sunlight of 900 W/m2. Notably, the thermal conductivity of the TIC is lower than that of air, thus preventing heat flow from external environments to indoor space in the summer, an additional benefit that does not sacrifice the radiative cooling performance. A building energy simulation shows that 48.5% of cooling energy could be saved if the TIC is widely deployed in China.

Numerical analysis of 3-D MHD hybrid nanofluid over a rotational disk in presence of thermal radiation with Joule heating and viscous dissipation effects using Lobatto IIIA technique

Abstract: In this research, the phenomenon of heat and mass transfer in 3D radiative flow of hybrid nanofluid over a rotational disk is investigated. Nanoparticles of Al2O3 and Cu are being used with water (H2O) as base fluid. The mathematical flow model in terms of PDEs is constructed by considering the heat transport mechanism due to Joule heating and viscous dissipation. This set of PDEs is converted into a system of ODEs by introducing the proper similarity transformations, which is then solved with the computational strength of Lobatto IIIA method. Demonstrations of graphical and numerical data are offered to examine the variation of velocity and thermal field against various physical constraints. The variable trend of heat transfer rate and skin friction coefficient through numerical data are also investigated. It is found that rate of heat transfer is proportional to Brinkman number, magnetic effect and concentration of nanoparticles. Achieved accuracy in term of relative error upto the level of 1e-14 shows the reliability and worth of solution methodology.