Variation Of Thermal Emission Research Articles

Simulated Phase-dependent Spectra of Terrestrial Aquaplanets in M Dwarf Systems

Orbital phase-dependent variations in thermal emission and reflected stellar energy spectra can provide meaningful constraints on the climate states of terrestrial extrasolar planets orbiting M dwarf stars. Spatial distributions of water vapor, clouds, and surface ice are controlled by climate. In turn, water, in each of its thermodynamic phases, imposes significant modulations to thermal and reflected planetary spectra. Here we explore these characteristic spectral signals, based on 3D climate simulations of Earth-sized aquaplanets orbiting M dwarf stars near the habitable zone. By using 3D models, we can self-consistently predict surface temperatures and the location of water vapor, clouds, and surface ice in the climate system. Habitable zone planets in M dwarf systems are expected to be in synchronous rotation with their host star and thus present distinct differences in emitted and reflected energy fluxes depending on the observed hemisphere. Here we illustrate that icy, temperate, and incipient runaway greenhouse climate states exhibit phase-dependent spectral signals that enable their characterization.

The evolution of soot particles in premixed and diffusion flames by thermophoretic particle densitometry

In this study, an improved version of the thermophoretic particle densitometry (TPD) method, introduced by McEnally et al. (1997) has been used for quantitative and qualitative characterization of soot particles generated in both premixed and diffusion flames. To this aim, the dependence of thermocouple temperature response on particle concentration and properties of collected material has been exploited. A variety of values for the thermal emissivity of flame-formed carbonaceous particles are measured, ranging from ε ≈ 0.4–0.5 for freshly nucleated particles up to the value of ε=0.95, typical of a mature soot. The data demonstrate that a correct determination of ε is necessary to accurately evaluate the particle volume fraction at the early stage of the soot formation, where particle concentration measurement is indeed particularly challenging.Raman spectroscopy analysis of the carbon particles has been conducted with the aim to better understand and to support the observed variation in the thermal emissivity of the carbon particles. In particular, the variation of thermal emissivity is showed to take up with a variation of hydrogen percentage and optical bandgap.Data also evidence that oxidation has a severe role in affecting both the determination by TPD of soot emissivity and soot concentration. In flame regions where soot oxidation occurs, the present formulation of TPD technique severely underestimate soot concentration.

Focused thermal emission from a nanostructured SiC surface

Incandescent sources that produce light from electrically heated filaments or films tend to feature low efficiencies and offer poor spectral and angular control. We demonstrate that a judicious nanostructuring of a SiC surface can focus thermal emission of a preselected spectral range to a well-defined height above the surface. SiC is known to support electromagnetic surface waves that afford the required thermal emission control. Here, we provide general design rules for this type of focusing element that can be extended to other material systems, such as metals supporting surface plasmon-polariton waves. These rules are verified using full-wave calculations of the spatial variation of thermal emission. The obtained results establish a foundation for developing more complex algorithms for the design of complex thermal lenses.

Thermal emission from large area chemical vapor deposited graphene devices

The spatial variation of thermal emission from large area graphene grown by chemical vapor deposition, transferred onto SiO2/Si substrates and fabricated into field effect transistor structures, has been investigated using infra-red microscopy. A peak in thermal emission occurs, the position of which can be altered by reversal of the current direction. The experimental results are compared with a one dimensional finite element model, which accounts for Joule heating and electrostatic effects, and it is found that the thermal emission is governed by the charge distribution in the graphene and maximum Joule heating occurs at the point of minimum charge density.

Directional dependence of thermal emission from nonspherical carbon particles

The directional intensity distribution of thermal emission from nonspherical particles can be predicted in the geometric optics limit using the Kirchhoff's law, or, in general case, using the Rytov's theory based on the fluctuation–dissipation theorem. This study demonstrates the first experimental evidence of the directional variation of thermal emission from nonspherical particles of a size smaller than the geometric optics limit. We used a method of laser-induced incandescence with multi-angle detectors to observe the directional dependences of thermal emission from individual carbon particles. For laboratory carbon particles with various shapes, the measured directional dependences of thermal emission were consistent with theoretical calculations for model nonspherical particles. This study provides a new physical principle for measuring the shape of aerosols according to the directional dependence of their thermal emission and is especially useful for online, in situ shape classification of carbon particles.

Experimental device for temperature investigation at high spatial and temporal resolution

Non-contact optical methods can be used for micrometric surface thermal characterization of active semiconductor devices. In this work, an experimental device based on near infra-red radiometric method is presented. This device is breadboard to analyze a thermal behaviour of electronic component in steadied and transient state. The absolute temperature distribution is measured at the micron scale. The obtained results highlight the excellent spatial and temporal resolution of the experimental measurement apparatus and its great sensitivity for detection of weak thermal emission variations.

Large hydrocarbon fuel pool fires: Physical characteristics and thermal emission variations with height

In a recent paper [P.K. Raj, Large LNG fire thermal radiation-modeling issues and hazard criteria revisited, Process Safety Progr., 24 (3) (2005)] it was shown that large, turbulent fires on hydrocarbon liquid pools display several characteristics including, pulsating burning, production of smoke, and reduced thermal radiation, with increasing size. In this paper, a semi-empirical mathematical model is proposed which considers several of these important fire characteristics. Also included in this paper are the experimental results for the variation of the fire radiance from bottom to top of the fire (and their statistical distribution) from the largest land spill LNG pool fire test conducted to date. The purpose of the model described in this paper is to predict the variation of thermal radiation output along the fire plume and to estimate the overall thermal emission from the fire as a function its size taking into consideration the smoke effects. The model utilizes experimentally measured data for different parameters and uses correlations developed from laboratory and field tests with different fuels. The fire dynamics and combustion of the fuel are modeled using known entrainment and combustion efficiency parameter values. The mean emissive power data from field tests are compared with model predictions. Model results for the average emissive powers of large, hypothetical LNG fires are indicated.

Comparison between thermographic techniques for frescoes NDT

The use of infrared thermography in the architectural restoration field is examined. Three samples, made of a support of marble, brick, or tuff, covered with a layer of plaster with inclusions to simulate detachments or cracks in frescoes, are considered. Different techniques: pulse thermography, lateral heating thermography, lock-in or modulated thermography and pulse phase thermography are employed to detect the flaws artificially created; advantages and disadvantages of each technique are discussed. It is found that pulse thermography is easy and fast to use for information about the state of the art treasures, but data may be affected by non-uniform heating and local variation of thermal emission; the lateral heating can help to overcome interference effects due to non-uniform heating but it is more troublesome to use. When the evaluation regards rare art treasures the lock-in technique seems to be the only response since it is able to operate within very low increase of surface temperature; this technique is also able to give information about the material composition. The pulse phase thermography may be used to detect more in depth flaws but it needs higher temperature increase with respect to the ambient temperature and so it is recommended to control, before testing, the temperature sensitivity of the artefact.

Directional variations in thermal emission from geologic surfaces

We investigated the directional emission properties of geologic surfaces using a ground‐based, hand‐held infrared radiometer and thermistor probe. Field sites involved surfaces ranging from smooth playa and sand surfaces to a very rough aa lava flow in the Lunar Crater Volcanic Field, NV, as part of the Geological Remote Sensing Field Experiment. Large directional variations in thermal emission were found; they result from the presence of surface roughness–at large scales producing spatial variations in kinetic temperature and at small scales producing emissivity variations. These variations are important in remotely determining surface structure and understanding surface energy balance and emission spectra.

Systematic biases in radiometric diameter determinations

Radiometric diameters and albedos of asteroids and other Solar System bodies have generally been determined with the aid of a standard thermal model, which assumes a smooth nonrotating surface and relies on an empirical beaming factor to adjust model fluxes to the values observed for objects of known radius. It has been assumed that the need for a correction factor is generally due largely to the effects of roughness on the thermal emission from real surfaces. We show that in many cases the effects of rotation are also important and must be considered in radiometric diameter determinations. The thermal effect of rotation depends not only on the object's thermal inertia, rotation rate, and pole orientation, but also on its temperature: colder objects with constant rotation rate and thermal inertia radiate proportionally less of their heat on the day hemisphere and more on the night hemisphere. If the asteroids Ceres and Pallas have lunarlike thermal inertias the effect of rotation on their thermal emission is very important: in particular, large variations in thermal emission correlated with variations in subsolar latitude around their orbits are expected. Such variations are not observed, and we therefore suggest that these and other main-belt asteroids have thermal inertias ≤1.5 × 10 4 erg cm −2 sec −1 2 K −1 , ≤30% that of the Moon. We determine a disk-integrated beaming parameter of 0.72 for the Moon and use this value to correct empirically for roughness effects in our thermophysical models. As a result of the influence of temperature on the thermal effects of rotation, the standard thermal model systematically underestimates the diameters (and overestimates the albedos) of cold objects. For example, assuming a thermal inertia 20% of the lunar value and the Sun in the equatorial plane, a Trojan asteroid would be 11% larger than the diameter determined radiometrically at 10 μm, and if it had a lunar thermal inertia, it would be 67% larger than determined radiometrically at 10 μm. Errors at 20 μm are smaller. The error in radiometric diameter varies with the body's albedo, thermal inertia, and subsolar latitude in ways that we describe.