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.

Transient Thermal Effects of Radiant Energy in Translucent Materials

Abstract: When a solid or stationary fluid is translucent, energy can be transferred internally by radiation in addition to heat conduction. Since radiant propagation is very rapid, it can provide energy within a material more quickly than diffusion by heat conduction. Radiation emitted in a hot material can also be distributed rapidly in the interior. The result is that transient temperature responses including radiation can be significantly different from those by conduction alone. This is important for evaluating the thermal performance of translucent materials that are at elevated temperatures, are in high temperature surroundings, or are subjected to large incident radiation. Detailed transient solutions are necessary to examine heat transfer for forming and tempering of glass windows, evaluating ceramic components and thermal protection coatings, studying highly backscattering heat shields for atmospheric reentry, porous ceramic insulation systems, ignition and flame spread for translucent plastics, removal of ice layers, and other scientific and engineering applications involving heating and forming of optical materials. Radiation effects have been studied less for transients than for steady state because of the additional mathematical and computational complexities, but an appreciable literature has gradually developed. This paper will review the applications, types of conditions, and geometries that have been studied. Results from the literature are used to illustrate typical radiation effects on transient temperatures, and comparisons are made of transient measurements with numerical solutions.

Method and apparatus for wavevector selective pyrometry in rapid thermal processing systems

Abstract: A method and apparatus for optical pyrometry in a Rapid Thermal Processing (RTP) System, whereby the radiation used to heat the object to be processed in the RTP system is in part specularly reflected from specularly reflecting surfaces and is incident on the object with a particular angular distribution, and the thermal radiation from the object is measured at an angles different from the angle where the incident radiation specularly reflected from the surface of the object is a maximum.

Two-dimensional heat and mass transfer and thermodynamic analyses of porous microreactors with Soret and thermal radiation effects—An analytical approach

Abstract: Transport of heat and mass and the thermodynamics of porous microreactors with thermal diffusion and radiation effects are investigated analytically. The examined configuration includes an axisymmetric, thick-wall microchannel with an iso-flux thermal boundary condition imposed on the external surfaces. The microchannel is filled with porous materials and accommodates a zeroth order homogenous chemical reaction. Internal radiative heat transfer is modelled in addition to heat convection and conduction, while the local thermal non-equilibrium approach is taken within the porous section of the system. The transport of species is coupled with that of heat via the inclusion of thermodiffusion or Soret effect. Two-dimensional heat and mass transfer differential equations are solved analytically. The results are subsequently used to predict the thermodynamic irreversibilities inside the reactor and a thorough analysis of local and total entropy generation rates is performed. Also, the changes in Nusselt number, calculated on the internal walls of the microreactor, versus various parameters are reported. It is shown that the radiation effects can impact the temperature of the solid phase of the porous medium and lead to alteration of Nusselt number. It is further observed that the transfer of mass is the main source of irreversibility in the system. The findings are of particular use for the design and analysis of the microreactors with homogenous chemical reactions and can be also used for the validation of computational models.

Near-surface thermal gradients and mid-IR emission spectra: A new model including scattering and application to real data

Abstract: We model the radiative and conductive heat transfer in the top few millimeters of a particulate medium in order to investigate near-surface thermal gradients and their effects on mid-IR emission spectra for different planetary environments. The model extends our previous work by including scattering in the radiative heat transfer. Our results show that significant thermal gradients will form in the top few hundred microns of particulate materials on the surfaces of the Moon and Mercury. Their presence alters spectral contrast and creates emission maxima in the transparent regions of the spectra. The results also show that thermal gradients cause the wavelength position of the Christiansen emission peak to shift by as much as 0.5 μm with variations in thermal conductivity and grain size, in agreement with previous laboratory investigations. These wavelength shifts are due to increased emission in the transparent regions of the spectrum which are superimposed upon the emissivity signature. The results are applied to telescopic spectra of the surfaces of the Moon and Mercury and can account for certain features seen in these data. Additional calculations show that thermal gradients will be minor on the surface of Mars and negligible for Earth.