Thermal radiation reflectivity

In the case of thermal insulation that primarily reduces thermal radiation across air spaces, the term k, is not used. This type of insnlation is called reflective insulation, and R is not always directly proportional to thickness. The R-value of a reflective system is the temperature difference across the system divided by the heat flux. 

Radiosity J Total thermal radiation energy leaving a surface (emitted and reflected) per unit time per unit area of energy transfer per unit area). The three terms, Absorptivity (a), Reflectivity (p), and Transmissivity (x), are all surface properties... 

The parametric effect of bed temperature is expected to be reflected through higher thermal conductivity of gas and higher thermal radiation fluxes at higher temperatures. Basu and Nag (1996) show the combined effect (Fig. 23) which plots heat transfer coefficients as a function of bed temperature for data from four different sources. It is seen that for particles of approximately the same diameter, at a constant suspension density (solid concentration), the heat transfer coefficient increases by almost 300% as the bed temperatures increase from 600°C to 900°C. 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

Figure 4 illustrates the results of this type of analysis for a deep-basin solar still in the San Diego area. Thermal radiation from basin to cover is the largest loss, followed by reflection of solar radiation from the cover and air convection inside the still. Solar utilization efficiency is the height of the lowest curve as a fraction of the height of the top curve, ranging from about 30% in January to 50% through the summer months. 

Radiation from salt water surface to the wetted cover is the largest loss, but there seems to be no assurance that it can be reduced. There is some evidence that microscopic roughening of the underside of the cover may render that surface reflective for the bulk of the long wave radiation (peaking at about 8 to 10 microns) from the water surface, without appreciably reducing its transparency for short wave solar radiation. However, even a thin film of condensate on the cover is an effective absorber for thermal radiation, so the benefit of a thermally reflective cover may not be realized in ordinary basin-type stills. 

Ocean surface temperature AYHRR, ATSR-2/ERS-2, AATSR/ENYISAT, MODIS/ EOS-Terra/Aqua, AMSR-E/EOS-Aqua, OCTS/ADEOS. Spaceborne system EOS/Terra is equipped with radiometer ASTER to measure thermal radiation and its reflection from the ocean surface, spectrometers MODIS and MISRC, as well as MOPITT and CERES instruments to record pollutant and energy fluxes, respectively. 

The remote sounding of land covers is based on recording the properties of reflected and scattered electromagnetic radiation. Such a possibility to obtain information about land cover properties is connected here with the facts that the character of proper (thermal) radiation, and the mechanisms of scattering and reflection are closely connected with the physical and geometrical properties of the surface, inadequate knowledge of which can also lead to erroneous conclusions and, hence, is a source of controversy in the information space. 

An element in a thermally radiative environment absorbs, reflects, refracts, diffracts, and transmits incoming radiative heat fluxes as well as emits its own radiative heat flux. Most solid materials in gas-solid flows, including particles and pipe walls, can be reasonably approximated as gray bodies so that absorption and emission can be readily calculated from Stefan-Boltzmann s law (Eq. (1.59)) for total thermal radiation or from Planck s formula (Eq. (1.62)) for monochromatic radiation. Other means of transport of radiative... 

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.,... 

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... 

Dunkle, R.V. Emissivity and inter-reflection relationships for infinite parallel specular surfaces. In Symp. on Thermal Radiation of solids (S. Katzoff, Ed.) NASA SP-55... 

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