Wärmeübertragung durch Strahlung

Siegel, Robert J.; Howell, John R.; Lohrengel, Joachim

doi:10.1007/978-3-642-84711-0

Cited by 16 publications

(9 citation statements)

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“…For air at a temperature of 12 000 K and a pressure of 1 atm the dependence of on the frequency is given in [17]. The variation of is weak.…”

Section: Radiative Coolingmentioning

confidence: 99%

“…The power, which is emitted from a gas volume element in a wavelength interval is given by [17] (7) Equation (7) is valid for any gaseous material. It contains the spectral radiant emittance of a black body [18] for which Stefan's law is valid [18], [19]: (7) is the absorption coefficient (extinction coefficient) of the emitting medium.…”

Section: Radiative Coolingmentioning

confidence: 99%

“…On the other hand the spectrum is composed of a continuous and a line spectrum, where the spectral position of the lines are determined by the energy levels of the atoms and molecules, which are contained in the gas. Furthermore, the dependence on temperature and pressure must be considered [17].…”

Section: Radiative Coolingmentioning

confidence: 99%

“…It contains the spectral radiant emittance of a black body [18] for which Stefan's law is valid [18], [19]: (7) is the absorption coefficient (extinction coefficient) of the emitting medium. It is defined by Lambert's law, which is given (for constant by [17], [19] (9)…”

Section: Radiative Coolingmentioning

confidence: 99%

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Simulation of the gasdynamic and electromagnetic processes in low voltage switching arcs

Karetta

Lindmayer

1998

IEEE Trans. Comp., Packag., Manufact. Technol. A

103

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The switching arc in a low voltage circuit breaker is a very complex phenomenon, which is determined by the interaction between heat conduction, gas flow, current flow, and magnetic forces. A realistic simulation of the switching arc must consider all these effects.In this paper, a three-dimensional (3-D) simulation model is described, which is based on the differential equations for the mass, momentum, and heat balance. Furthermore, it contains a differential equation for the calculation of the current flow and the resulting magnetic field. This set of equations is solved by the finite volume method.First results are presented, which show the shape of the arc and the gas flow while the arc is moving between rail electrodes in a simple arc chamber.

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“…For air at a temperature of 12 000 K and a pressure of 1 atm the dependence of on the frequency is given in [17]. The variation of is weak.…”

Section: Radiative Coolingmentioning

confidence: 99%

Section: Radiative Coolingmentioning

confidence: 99%

Section: Radiative Coolingmentioning

confidence: 99%

Section: Radiative Coolingmentioning

confidence: 99%

See 2 more Smart Citations

Simulation of the gasdynamic and electromagnetic processes in low voltage switching arcs

Karetta

Lindmayer

1998

IEEE Trans. Comp., Packag., Manufact. Technol. A

103

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“…This simplification already has been applied to perlite in the temperature range between 10 and 250 K [2]. The result is an expression for the radiative heat flux that is similar to Fourier's law of heat conduction [28]. In other words, the heat diffusion model can be applied to infrared photons, and a temperature-dependent radiative thermal conductivity k r can be introduced [6,29] …”

Section: Heat Transfer By Thermal Radiationmentioning

confidence: 99%

Heat Transport in Evacuated Perlite Powders for Super-Insulated Long-Term Storages up to 300 °C

Beikircher¹,

Demharter

2013

Journal of Heat Transfer

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Vacuum super insulation (VSI) with expanded perlite powder is commonly used at cryogenic temperatures, but principally can also be adapted to applications at higher temperatures, such as the long-term storage of hot water in solar thermal systems. Due to the lack of experimental data in the respective temperature range, especially without external load, thermal conductivity measurements have been performed with commercial perlite powder up to 150 C mean sample temperature, corresponding to storage temperatures of around 300 C. Two different experimental geometries have been used: a guarded hot plate (GHP) setup and a cut-off concentric cylinder (CCC) apparatus. Furthermore, the radiative heat transport has been determined separately by extinction measurements using Fourier transform infrared (FTIR) spectroscopy. In addition to the laboratory experiments, a real-size prototype of a solar VSI-storage tank with 16.4 m 3 water storage volume has been constructed, and the effective thermal conductivity of the perlite insulation has been determined from a heat loss measurement. The heat transport in evacuated perlite has also been treated theoretically using common models and approaches for gas heat conduction, solid-body conduction and heat transfer by thermal radiation. For the coupling between solid-body and gas conduction which occurs in the intergranular spaces of a powder material, a simple model has been developed. The total effective thermal conductivity k eff of a vacuum super insulation with dry, evacuated perlite powder (p 0:01 mbar; q % 60 kg=m 3 ) amounts to 0.007-0.016 W/mK for mean sample temperatures between 50 C and 150 C, compared to 0.003-0.005 W/mK at cryogenic temperatures. For the real-size storage prototype, the value k eff ¼ 0:009 W=mK has been obtained at T ¼ 90 C (storage temperature), p ¼ 0.08 mbar and q ¼ 92:4 kg=m 3 , which compares to 0.03-0.06 W/mK for dry conventional storage insulations. With the applied theoretical models and approaches, the effective thermal conductivity of evacuated perlite and its individual contributions can successfully be described at different densities (55 À 95 kg=m 3 ), compression methods, vacuum pressures (10 À3 À 1000 mbar) and filling gases (air, Ar, Kr) up to mean sample temperatures of T ¼ 150 C. With regard to practical purposes, it has shown that vacuum super insulation with perlite is a suitable and economic method to achieve low thermal conductivities also at medium storage temperatures.

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