Low emissivity surfaces

The effects of surface emissivity are exaggerated in high-temperature applications, and particular attention should be paid to the selection of the type of surface of the insulation system. Low-emissivity surfaces such as bright polished aluminum reduce heat loss by inhibiting the radiation of heat from the surface to the surrounding ambient... 

Many familiar heal transfer application. involve natural convection as the primary mechanism of heat transfer. Some examples are cooling of electronic equipment such as power transistors, TVs, and DVDs heat transfer from electric baseboard heaters or steam radiators heat transfer from the refrigeration coils and power transmission lines and heat transfer from the bodies of animals and human beings. Natural convection in gases is usually accompanied by radiation of comparable magnitude except for low-emissivity surfaces. 

Infrared Mirrors and Low-Emissivity Surfaces Data for materials of high reflectivity do not present as severe a problem. Sources of information about IR mirrors are provided in Section 9.10.2. The most common reflectors are aluminum, silver, and gold their reflectance from 0.2-5.0 pm is shown in Figure 9.3. 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

The insertion of low-emissivity floating shields within the evacuated space can effectively reduce the heat transport by radiation. The effect of the shields is to greatly reduce the emissivity factor. For example, for N shields or N + 2) surfaces, an emissivity of the outer and inner surface of and an emissivity of the shields of the emissivity factor reduces to... 

The Mossbauer effect can only be detected in the solid state because the absorption and emission events must occur without energy losses due to recoil effects. The fraction of the absorption and emission events without exchange of recoil energy is called the recoilless fraction, f. It depends on temperature and on the energy of the lattice vibrations /is high for a rigid lattice, but low for surface atoms. 

Figure 4. Comparison of GHG emissions from shale gas and conventional natural gas with low and high estimates of fugitive methane emissions, surface-mined coal, deep-mined coal, and diesel oil time horizon equal to 100 years [27]...

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

The performance of TWC and its durability should be further improved to meet the new requirements for low-emission vehicles. It is described in this chapter that the sintering of Pt depends on the characteristic of supports and the re-dispersion of Pt is occurred on Ce02 through the interaction between Pt and the surface oxygen of Ce02. 

PHOTOEMISSION AND PHOTOMULTIPLIERS. Photoemission is the ejection of electrons from a substance as a result of radiation filling on it Photomultipliers make use of the phenomena of photoemission and secondary-electron emission in order to detect very low light levels The electrons released from the photocathode by incident light are accelerated and focused onto a secondary-emission surface (called a dynode). Several electrons are emitted from the dynode for each incident primary electron. These secondary electrons are then directed onto a second dynode where more electrons are released. The whole process is repealed a number of times depending upon the number of dynodes used, In this manner, it is possible to amplify the initial photocurrent by a factor of 10s or more in practical photomultipliers. Thus, the photomultiplier is a very sensitive detector of light. 

Low temperature/surface-only thermal extraction/microchamber methods have recently been evaluated to see if the results obtained provide better correlation with standard emissions tests (GUT, 2008 VDI, 2008 Schripp et al., 2007 HEMICPD, 2009) and whether or not they can be used to accurately and rapidly predict product performance with respect to chemical emissions after 3 or 28 days. Some of these studies are still on going but results have been very positive and have already led to the consideration/development of several low temperature, surface extraction methods for emissions screening (ASTM, 2008 GUT, 2008 VDI, 2008). 

The low emission rates measured in this study indicate that salt marshes are a minor source of sulfur to the global atmosphere. Furthermore, our measurement of deposition rates show the potential for losses to the same soil surfaces at times of elevated atmospheric concentration. 

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