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.

Non-contact medical thermometer with stray radiation shielding

Abstract: A non-contact infrared (IR) thermometer for measuring temperature from the surface of an object includes an IR radiation sensor attached to a heating element and a thermal shield having an interior surface positioned within the sensor's field of view that has a high emissivity. An electronic circuit controlling the heating element maintains the temperatures of the sensor and shield substantially close to an anticipated surface temperature of the object. The IR radiation sensor is further thermally coupled to a reference temperature sensor. An optical system positioned in front of the shield focuses thermal radiation from the object on the surface of the sensor, while the shield prevents stray radiation from reaching the sensor. Signals from the IR and reference sensors are used to calculate the object's surface temperature.

Nonlinear thermal radiation in flow induced by a slendering surface accounting thermophoresis and Brownian diffusion

Abstract: Our attention here in this research is on scrutinizing the nonlinear convection characteristics in a flow induced by a slendering surface. Flow expression is developed through electrically conducting Williamson nanomaterial. Nonlinear forms of stretching and free stream velocities are imposed. Consideration of nonlinear thermal radiation, non-uniform heat generation/absorption, Joule and convective heating aspects describe the phenomenon of heat transfer. The zero-mass condition for concentration is also considered. The compatible transformations produce strong nonlinear differential systems. The problems are computed analytically utilizing the bvp4c procedure. Heat transfer rate and drag force are also explained for various physical variables. Our analysis reveals that the heat transfer rate augments via larger radiation parameter and Biot number. Moreover, larger Brownian motion and thermophoresis parameters have opposite characteristics on concentration field. For the verification of the present findings, the results of the presented analysis have been compared with the available works in particular situations and reasonable agreement is noted.

Three-body radiative heat transfer and Casimir-Lifshitz force out of thermal equilibrium for arbitrary bodies

Abstract: We study the Casimir-Lifshitz force and the radiative heat transfer in a system consisting of three bodies held at three independent temperatures and immersed in a thermal environment, the whole system being in a stationary configuration out of thermal equilibrium. The theory we develop is valid for arbitrary bodies, i.e., for any set of temperatures, dielectric, and geometrical properties, and describes each body by means of its scattering operators. For the three-body system we provide a closed-form unified expression of the radiative heat transfer and of the Casimir-Lifshitz force (both in and out of thermal equilibrium). This expression is thus first applied to the case of three planar parallel slabs. In this context we discuss the nonadditivity of the force at thermal equilibrium, as well as the equilibrium temperature of the intermediate slab as a function of its position between two external slabs having different temperatures. Finally, we consider the force acting on an atom inside a planar cavity. We show that, differently from the equilibrium configuration, the absence of thermal equilibrium admits one or more positions of minima for the atomic potential. While the corresponding atomic potential depths are very small for typical ground-state atoms, they may become particularly relevant for Rydberg atoms, becoming a promising tool to produce an atomic trap.

X-ray generation in a cavity heated by 1.3- or 0.44-μm laser light. III. Comparison of the experimental results with theoretical predictions for x-ray confinement

Abstract: Radiation confinement in laser-heated gold cavities is analyzed on the basis of self-similar solutions of the hydrodynamic equations. The analysis is extended to include radiation losses through holes in the cavity. The possibility that a conversion layer on the inner wall of the cavity contributes to the measured radiation is also taken into account. The comparison with experiments performed at laser wavelengths of 0.44 and 1.3 /mu/m with the Asterix iodine laser shows reasonable agreement with the theoretical predictions. The major difficulty in the comparison is the lack of detailed information about the conversion of laser light into x rays, especially in the 1.3-/mu/m experiments.

Thermal radiation control from hot graphene electrons coupled to a photonic crystal nanocavity

Abstract: Controlling thermal radiation is central in a range of applications including sensing, energy harvesting, and lighting. The thermal emission spectrum can be strongly modified through the electromagnetic local density of states (EM LDOS) in nanoscale-patterned metals and semiconductors. However, these materials become unstable at high temperature, preventing improvements in radiative efficiency and applications such as thermophotovoltaics. Here, we report stable high-temperature thermal emission based on hot electrons (>2000 K) in graphene coupled to a photonic crystal nanocavity, which strongly modifies the EM LDOS. The electron bath in graphene is highly decoupled from lattice phonons, allowing a comparatively cool temperature (700 K) of the photonic crystal nanocavity. This thermal decoupling of hot electrons from the LDOS-engineered substrate opens a broad design space for thermal emission control that would be challenging or impossible with heated nanoscale-patterned metals or semiconductor materials. Efficient control of thermal radiation is at the core of device design for a variety of applications. Here, the authors demonstrate a high-temperature thermal emitter with selective emission from a graphene-silicon photonic crystal nanocavity.