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.

Thermal effects of acceleration for a classical dipole oscillator in classical electromagnetic zero-point radiation

Abstract: In 1976 Unruh showed that a scalar quantum particle in a box accelerating through the vacuum of scalar quantum field theory responded as though it were in a thermal bath at temperature $T=\frac{\ensuremath{\hbar}a}{2\ensuremath{\pi}\mathrm{ck}}$. Here we show an analogous result within classical electromagnetic theory. A classical electric dipole oscillator accelerating through classical electromagnetic zero-point radiation responds just as would a dipole oscillator in an inertial frame in classical thermal radiation with Planck's spectrum at temperature $T=\frac{\ensuremath{\hbar}a}{2\ensuremath{\pi}\mathrm{ck}}$. In an earlier work it was shown that the electromagnetic field correlation functions for an observer accelerating through classical electromagnetic zero-point radiation correspond to a spectrum different from Planck's. The same spectrum is found in the quantum analysis of a vector field where the departure from Planckian form is assigned to the change in the number of normal modes associated with the event horizon of the accelerating observer. The present work shows that the relativistic radiation reaction for an accelerating classical charge contains a term which exactly compensates the departure of the electromagnetic spectrum from Planckian form so as to bring the oscillator's behavior into precise agreement with the usual Planckian thermal form.

Thermal Radiation and Buoyancy Effects on Heat and Mass Transfer over a Semi-Infinite Stretching Surface with Suction and Blowing

Abstract: This study sought to investigate thermal radiation and buoyancy effects on heat and mass transfer over a semi-infinite stretching surface with suction and blowing. Appropriate transformations were employed to transform the governing differential equations to nonsimilar form. The transformed equations were solved numerically by an efficient implicit, iterative finite-difference scheme. A parametric study illustrating the influence of wall suction or injection, radiation, Schmidt number and Grashof number on the fluid velocity, temperature and concentration is conducted. We conclude from the study that the flow is appreciably influenced by thermal radiation, Schmidt number, as well as fluid injection or suction.

Thermal radiation sensor

Abstract: An instrument sensor member has positioning means to establish a fixed relationship between the member and a small selected area of a living organism. Thermal radiation flux from the area impinges on a concave surface on the member and is reflected to a radiometer fixed at the focus of the surface. The thermal radiation provides a measure of the temperature of the blood in the vessel or vessels immediately under the surface of the area which may be the tympanic membrane as disclosed herein.

Calculation of thermal emissivity for thin films by a direct method

Abstract: The emissivity variation of a body, according to the modifications of its surface, has been described by two kinds of arguments. A direct argument consists in adding the energy, leaving each element of volume $dV,$ considered as independent and incoherent Planckian radiators, weighted by its transmissions and its possible reflections. An indirect argument consists in assuming the validity of Kirchhoff's law. The emissivity is then deduced from the absorption coefficient calculated by using a huge collection of theoretical means. However, in the case of very thin films deposited on a substrate, the emissivity calculated according to their thickness does not give the same results, depending on the argument used. As a matter of fact, up to now the direct argument did not allow a description of interferential phenomena. Such phenomena are still observed when the film thickness is lower than, or of the same order of magnitude as the wavelength of the radiation concerned. On the other hand, the use of Kirchhoff's law requires delicate handling in the case of mesoscopical structure materials. Besides, the indirect method leads to an argument by default, which occults a part of the physics implied. Here, a direct model is proposed, only based on emission phenomena. This direct theory allows a description of the interferential behavior in thermal radiation, by taking into account the self-coherence of the emitted waves, in contrast to the previous direct approach. It is shown that this approach accounts for the experimental behavior of growing thin films.