Search results for "thermal radiation"
showing 10 items of 27 documents
The optical constants of atmospheric aerosol particles in the 7.5–12 ?m spectral region
2011
Thin films of atmospheric aerosol particles which have been collected by an automatic jet impactor are used to obtain the real and imaginary part of the mean complex refractive index of aerosol particles of various types in the 7.5–12 ?m spectral region. A dispersion analysis of the measured ir-spectra of absorption of the particle films is performed. By applying the Lorentz theory of continuous dielectrics to the particle films a mathematical relation between the optical constants of the particle films and those of the aerosol particles themselves is obtained. The resulting complex refractive indices are applied to Mie computations to indicate the importance of scattering and absorbing aer…
Non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
2017
Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters due to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large one. This information is used to compute the synchrotron and inverse Compton emission fr…
Heat transfer simulation in a vertical Bridgman CdTe growth configuration
1999
Modelling and numerical simulation of crystal growth processes have been shown to be powerful tools in order to understand the physical effects of different parameters on the growth conditions. In this study a finite difference/control volume technique for the study of heat transfer has been employed. This model takes into account the whole system: furnace temperature profile, air gap between furnace walls and ampoule, ampoule geometry, crucible coating if any, solid and liquid CdTe thermal properties, conduction, convection and radiation of heat and phase change. We have used the commercial code FLUENT for the numerical resolution that can be running on a personal computer. Results show th…
Magnetic field controlled FZ single crystal growth of intermetallic compounds
2005
Abstract Intermetallic rare-earth-transition-metal compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of bulk single crystals is very often unsuccessful due to an unfavorable solid–liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by th…
Modelling of phase boundaries for large industrial FZ silicon crystal growth with the needle-eye technique
2003
In order to facilitate the numerical calculations of the phase boundaries in large industrial floating zone silicon crystal growth with the needle-eye technique, the chain of improved mathematical models is developed. The phase boundaries are solved in a partly transient way and the modelling improvements cover the open melting front, the inner triple point and the free melt surface. The view factors model is applied for the radiative heat transfer. The electromagnetic field is calculated with account of a multiple-slit inductor.
Transient Modelling of Thermal Conditions in Test Buildings Including Radiation
2015
Abstract To increase the energy efficiency of buildings in Latvia's climate a comparative study with five experimental test buildings have been set up in Riga, Latvia. Different thermo physical quantities such as temperature, humidity, air velocity, etc. were monitored to better understand different behaviour of the building envelope. This gives an excellent validation possibility for the CFD model that in future could predict conditions in buildings with different envelopes. Previously a stationary model and transient model were considered without taking into consideration the thermal radiation. This study continues the previous work that was done and proposes a transient model which takes…
Convergence of the finite volume method for a conductive-radiative heat transfer problem
2013
We show that the finite volume method rigorously converges to the solution of a conductive-radiative heat transfer problem with nonlocal and nonlinear boundary conditions. To get this result, we start by proving existence of solutions for a finite volume discretization of the original problem. Then, by obtaining uniform boundedness of discrete solutions and their discrete gradients with respect to mesh size, we finally get L 2type convergence of discrete solutions.
Automatic shape detection of ice crystals
2021
Abstract Clouds have a crucial impact on the energy balance of the Earth-Atmosphere system. They can cool the system by partly reflecting or scattering of the incoming solar radiation (albedo effect); moreover, thermal radiation as emitted from the Earth's surface can be absorbed and partly re-emitted by clouds leading to a warming of the atmosphere (greenhouse effect). The effectiveness of both effects crucially depends on the size and the shape of a cloud's particulate constituents, i.e. liquid water droplets or solid ice crystals. For studying cloud microphysics, in situ measurements on board of aircraft are commonly used. An important class of measurement techniques comprises optical ar…
Numerical models of blackbody-dominated gamma-ray bursts – I. Hydrodynamics and the origin of the thermal emission
2014
GRB 101225A is a prototype of the class of blackbody-dominated (BBD) gamma-ray bursts (GRBs). It has been suggested that BBD-GRBs result from the merger of a binary system formed by a neutron star and the helium core of an evolved star. We have modelled the propagation of ultrarelativistic jets through the environment left behind the merger by means of relativistic hydrodynamic simulations. In this paper, the output of our numerical models is post-processed to obtain the (thermal) radiative signature of the resulting outflow. We outline the most relevant dynamical details of the jet propagation and connect them to the generation of thermal radiation in GRB events akin to that of GRB 101225A…
EINSTEIN–PLANCK FORMULA, EQUIVALENCE PRINCIPLE, AND BLACK HOLE RADIANCE
2005
The presence of gravity implies corrections to the Einstein-Planck formula $E=h \nu$. This gives hope that the divergent blueshift in frequency, associated to the presence of a black hole horizon, could be smoothed out for the energy. Using simple arguments based on Einstein's equivalence principle we show that this is only possible if a black hole emits, in first approximation, not just a single particle, but thermal radiation.