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.

Photon and dilepton emission from the quark-gluon plasma: Some general considerations.

Abstract: The emission rates for photons and di-leptons from a quark-gluon plasma is related to the thermal expectation value of an electromagnetic current-current correlation function. This correlation function possesses an invariant tensor decomposition with structure functions entirely analogous to W/sub 1/ and W/sub 2/ of deep inelastic scattering of leptons from hadronic targets. The thermal scaling properties of the appropriate structure functions for thermal emission are derived. The thermal structure functions may be computed in a weak coupling expansion at high plasma temperature. The rates for thermal emission are estimated, and for di-leptons, the thermal emissions rate is argued to dominate over the Drell-Yan process for di-lepton masses 600 MeV < M < 1 to 2 GeV using conservative estimates of the plasma temperature. We argue that higher temperatures are entirely possible within the context of the inside-outside cascade model of matter formation, perhaps temperatures as high as 500 to 800 MeV. If these high temperatures are achieved, the maximum di-lepton masses arising from thermal emission are argued to be 5 GeV. Signals for thermal emission are presented as the relative magnitude of invariant thermal structure functions, thermal scaling relations, and transverse momenta of thermal di-lepton pairs increasing with and proportionalmore » to the di-lepton pair mass. The transverse mass spectra is given for a high temperature plasma. The dependence of the spectra of thermal emission upon the existence of a first phase transition is studied. We argue that if there is a first order phase transition, as beam energy or nuclear baryon number is raised through the threshold for production of a plasma, the rate for photon or di-lepton emission might dramatically increase.« less

Scalable and hierarchically designed polymer film as a selective thermal emitter for high-performance all-day radiative cooling.

Abstract: Traditional cooling systems consume tremendous amounts of energy and thus aggravate the greenhouse effect1,2. Passive radiative cooling, dissipating an object’s heat through an atmospheric transparency window (8–13 μm) to outer space without any energy consumption, has attracted much attention3–9. The unique feature of radiative cooling lies in the high emissivity in the atmospheric transparency window through which heat can be dissipated to the universe. Therefore, for achieving high cooling performance, the design and fabrication of selective emitters, with emission strongly dominant in the transparency window, is of essential importance, as such spectral selection suppresses parasitic absorption from the surrounding thermal radiation. Recently, various materials and structures with tailored spectrum responses have been investigated to achieve the effect of daytime radiative cooling6–8,10–15. However, most of the radiative cooling materials reported possess broad-band absorption/emission covering the whole mid-infrared wavelength11–15. Here we demonstrate that a hierarchically designed polymer nanofibre-based film, produced by a scalable electrostatic spinning process, enables selective mid-infrared emission, effective sunlight reflection and therefore excellent all-day radiative cooling performance. Specifically, the C–O–C (1,260–1,110 cm−1) and C–OH (1,239–1,030 cm−1) bonding endows the selective emissivity of 78% in 8–13 μm wavelength range, and the design of nanofibres with a controlled diameter allows for a high reflectivity of 96.3% in 0.3–2.5 μm wavelength range. As a result, we observe ~3 °C cooling improvement of this selective thermal emitter as compared to that of a non-selective emitter at night, and 5 °C sub-ambient cooling under sunlight. The impact of this hierarchically designed selective thermal emitter on alleviating global warming and temperature regulating an Earth-like planet is also analysed, with a significant advantage demonstrated. With its excellent cooling performance and a scalable process, this hierarchically designed selective thermal emitter opens a new pathway towards large-scale applications of all-day radiative cooling materials. A hierarchically designed polymer nanofibre-based film produced by a scalable electrospinning process enables selective mid-infrared emission and effective sunlight reflection, and thus realizes an excellent all-day radiative cooling performance.

Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty

Abstract: Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by the Earth and the thermal radiation emitted back to space. A revised analysis of measured changes in the net radiation imbalance at the top of the atmosphere, and the ocean heat content to a depth of 1,800 m, suggests that these two sets of observations are consistent within error margins.

Near-field Thermal Radiation Between Two Closely Spaced Glass Plates Exceeding Planck’s Blackbody Radiation Law

Abstract: This work reports experimental studies on radiative heat flux between two parallel glass surfaces. Small polystyrene particles are used as spacers to maintain a micron-sized gap between two optical flats. By carefully choosing the number of particles and performing the measurement in a high-vacuum environment, the experiment is designed to ensure that the radiative heat flux is the dominant mode of heat transfer. The experimental results clearly demonstrate that the radiative heat flux across micron-sized gaps can exceed the far-field upper limit given by Planck’s law of blackbody radiation. The measured radiative heat flux shows reasonable agreement with theoretical predictions.

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

Abstract: Interest in new thermal diodes, regulators, and switches has been rapidly growing because these components have the potential for rich transport phenomena that cannot be achieved using traditional thermal resistors and capacitors. Each of these thermal components has a signature functionality: Thermal diodes can rectify heat currents, thermal regulators can maintain a desired temperature, and thermal switches can actively control the heat transfer. Here, we review the fundamental physical mechanisms of switchable and nonlinear heat transfer which have been harnessed to make thermal diodes, switches, and regulators. The review focuses on experimental demonstrations, mainly near room temperature, and spans the fields of heat conduction, convection, and radiation. We emphasize the changes in thermal properties across phase transitions and thermal switching using electric and magnetic fields. After surveying fundamental mechanisms, we present various nonlinear and active thermal circuits that are based on ana...