Thermal radiation incident

Thermal radiation incident upon a body may be absorbed and its energy converted into heat, reflected from the surface or transmitted through the material following the balance ... 

Blackbody Radiation Engineering calculations of thermal radiation from surfaces are best keyed to the radiation characteristics of the blackbody, or ideal radiator. The characteristic properties of a blackbody are that it absorbs all the radiation incident on its surface and that the quality and intensity of the radiation it emits are completely determined by its temperature. The total radiative fliix throughout a hemisphere from a black surface of area A and absolute temperature T is given by the Stefan-Boltzmann law ... 

Absorptivity The fraction of the energy incident on a body that is absorbed by that body (absorbance). Relating to thermal radiation and acoustics. 

A massive amount of propane is instantaneously released in an open field. The cloud assumes a flat, circular shape as it spreads. When the internal fuel concentration in the cloud is about 10% by volume, the cloud s dimensions are approximately 1 m deep and 100 m in diameter. Then the cloud reaches an ignition source at its edge. Because turbulence-inducing effects are absent in this situation, blast effects are not anticipated. Therefore, thermal radiation and direct flame contact are the only hazardous effects encountered. Wind speed is 2 m/s. Relative humidity is 50%. Compute the incident heat flux as a function of time through a vertical surface at 100 m distance from the center of the cloud. 

Ozone forms a layer around the Earth that insulates against thermal radiation. This layer is being destroyed by pollutants (principally fluorocarbons). The effect of the depletion of the ozone layer is to warm the Earth (and hence exacerbate the greenhouse effect) and may also lead to an increase in the incidence of skin cancers. 

Irradiation G Total thermal radiation energy incident on a surface per unit time per unit area Irradiation (G), and Radiosity J) are all energy fluxes (i.e., rate... 

Damage Caused at Various Incident Levels of Thermal Radiation (Theodore et al., 1989)... 

For the more general case of a body which reflects and transmits part of the incident radiation, so that it has absorptivity a(fouS) < 1, Kirchoff found (even before Planck) that the intensity of thermal radiation is proportional to the absorptivity of the body, i.e.,... 

Solar radiation is a form of thermal radiation having a particular wavelength distribution. Its intensity is strongly dependent on atmospheric conditions, time of year, and the angle of incidence for the sun s rays on the surface of the earth. At the outer limit of the atmosphere the total solar irradiation when the earth is at its mean distance from the sun is 1395 W/m2. This number is called the solar constant and is subject to modification upon collection of more precise experimental data. 

Fused quartz transmits 90 percent of the incident thermal radiation between 0.2 and 4 fim. Suppose a certain heat source is viewed through a quartz window. Vhat heat flux in watts will be transmitted through the material from blackbody radiation sources at (a) 800°C, (b) 550°C, (c) 250°C, and (d) 70°C ... 

Blackbody Radiation Engineering calculations involving thermal radiation normally employ the hemispherical blackbody emissive power as the thermal driving force analogous to temperature in the cases of conduction and convection. A blackbody is a theoretical idealization for a perfect theoretical radiator i.e., it absorbs all incident radiation without reflection and emits isotropically. In practice, soot-covered surfaces sometimes approximate blackbody behavior. Let /.V, = /. A... 

The absorption of thermal radiation will be treated in more depth in chapter 5. The connection between emission and absorption will also be looked at this is known as Kirchhoff s law, see section 5.1.6. It basically says that a good emitter of radiation is also a good absorber. For the ideal radiator, the black body, both absorptivity a and emissivity e are equal to the maximum value of one. The black body, which absorbs all incident radiation (a = 1), also emits more than any other radiator, agreeing with (1.58), the law from Stefan and Boltzmann. 

Photo/thermal Degradation. Samples of etched ( <2.5 pm) and unetched ( X/7.5 pm) POP film were placed in quartz tubes which were continuously evacuated while being heated at temperatures >450 C in a constant temperature block, controlled to 2 C. Other film samples contained in quartz tubes evacuated to <10 Torr were exposed to a Hanovia 450-watt mercury lamp with the etched side facing the lamp. At 14 cm from the lamp, the intensity of the uv radiation incident on the films was equivalent to <5.9 times that of the Sun in the 2000-3500-A range at 1 astronomical unit, i.e., just outside the atmosphere. At that distance from the lamp, the temperature of... 

The concept of hlackhody is determining the basis for describing the radiation properties of real surfaces. The black body denotes an ideal radiative surface which absorb all incident radiation, being a diffuse emitter and emit a maximum amount of energy as thermal radiation for a given wavelength and temperature. The black body can be considered as a perfect absorber and emitter. 

The Golay cell uses the distortion of a reflecting Sb-coated collodion membrane, closing one of the ends of a so-called pneumatic chamber. This distortion is caused by the thermal expansion of a gas heated by the radiation incident in the cell, and produces the deflection of a beam of visible light, which is detected by a photocell. The Golay cell was used, fitted with a diamond window, with the first far IR FTS and its responsivity and response time were comparable to those of the radiation thermocouple. For more details on these detectors, see [15]. 

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