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.

Melting heat transfer on hydromagnetic flow of a nanofluid over a stretching sheet with radiation and second-order slip

Abstract: The present paper is devoted to the analysis of MHD flow and melting heat transfer of a nanofluid over a stretching surface taking into account a second-order slip model and thermal radiation. Similarity solutions for the transformed governing equations are obtained. The reduced equations are solved numerically by applying a shooting technique using the Runge-Kutta Fehlberg method. The influences of the various involved parameters on velocity profiles, temperature profiles, concentration profiles as well as reduced skin friction coefficient, Nusselt number and Sherwood number are discussed through graphs and tables. These results show that the second-order slip flow model is necessary to predict the flow characteristics accurately in the presence of thermal radiation and melting effect.

Measurement Techniques for Thermal Conductivity and Interfacial Thermal Conductance of Bulk and Thin Film Materials

Abstract: Thermal conductivity and interfacial thermal conductance play crucial roles in the design of engineering systems where temperature and thermal stress are of concerns. To date, a variety of measurement techniques are available for both bulk and thin film solid-state materials with a broad temperature range. For thermal characterization of bulk material, the steady-state absolute method, laser flash diffusivity method, and transient plane source method are most used. For thin film measurement, the 3{\omega} method and transient thermoreflectance technique including both frequency-domain and time-domain analysis are employed widely. This work reviews several most commonly used measurement techniques. In general, it is a very challenging task to determine thermal conductivity and interface contact resistance with less than 5% error. Selecting a specific measurement technique to characterize thermal properties need to be based on: 1) knowledge on the sample whose thermophysical properties is to be determined, including the sample geometry and size, and preparation method; 2) understanding of fundamentals and procedures of the testing technique and equipment, for example, some techniques are limited to samples with specific geometrics and some are limited to specific range of thermophysical properties; 3) understanding of the potential error sources which might affect the final results, for example, the convection and radiation heat losses.

Observation of thermal Hawking radiation and its temperature in an analogue black hole.

Abstract: The entropy of a black hole1 and Hawking radiation2 should have the same temperature given by the surface gravity, within a numerical factor of the order of unity In addition, Hawking radiation should have a thermal spectrum, which creates an information paradox3,4 However, the thermality should be limited by greybody factors5, at the very least6 It has been proposed that the physics of Hawking radiation could be verified in an analogue system7, an idea that has been carefully studied and developed theoretically8–18 Classical white-hole analogues have been investigated experimentally19–21, and other analogue systems have been presented22,23 The theoretical works and our long-term study of this subject15,24–27 enabled us to observe spontaneous Hawking radiation in an analogue black hole28 The observed correlation spectrum showed thermality at the lowest and highest energies, but the overall spectrum was not of the thermal form, and no temperature could be ascribed to it Theoretical studies of our observation made predictions about the thermality and Hawking temperature29–33 Here we construct an analogue black hole with improvements compared with our previous setup, such as reduced magnetic field noise, enhanced mechanical and thermal stability and redesigned optics We find that the correlation spectrum of Hawking radiation agrees well with a thermal spectrum, and its temperature is given by the surface gravity, confirming the predictions of Hawking’s theory The Hawking radiation observed is in the regime of linear dispersion, in analogy with a real black hole, and the radiation inside the black hole is composed of negative-energy partner modes only, as predicted The spectrum of Hawking radiation is measured in an analogue black hole composed of rubidium atoms, confirming Hawking’s prediction that Hawking radiation is thermal with a temperature given by the surface gravity

Radiative heating and cooling with spectrally selective surfaces.

Abstract: Matter continuously exchanges energy with its surroundings. This exchange can be dominated by radiation, conduction, or convection. In this brief review we discuss how proper design of radiative surface properties can be used for heating and cooling purposes. The desired properties can be understood once it is realized that solar and terrestrial radiation take place in different wavelength ranges and that only part of the solar spectrum is useful for vision and for photosynthesis in plants. These facts allow the possibility of tailoring the spectral absorptance, emittance, reflectance, and transmittance of a surface to meet different demands in different wavelength intervals, i.e., to take advantage of spectral selectivity. One example is the selective surface for efficient photothermal conversion of solar energy, which has high absorptance over the solar spectrum but low emittance for the longer wavelengths relevant to thermal reradiation. Below we discuss the pertinent spectral radiative properties of our ambience. These data are then used as background to the subsequent sections treating four examples of spectrally selective surfaces. The first example is the previously mentioned selective surface for converting solar radiation to useful heat. The second example considers surfaces capable of reaching low temperatures by benefiting from the spectral emittance of the clear night sky. The third example concerns two related types of transparent heat mirror. The fourth example, finally, treats radiative cooling of green leaves; this part is included since it gives a nice example of how nature solves a difficult problem in an elegant and efficient way. This example hence provides an interesting background to the other cruder types of artificial selective surfaces. Throughout our discussion we treat the ideal spectral properties, give an illustrative experimental example of how well this goal can be realized, and—where this is possible—show a corresponding theoretical curve indicating to what extent the measured results can be theoretically understood.