Soot layer thickness

For a= 1, soot in the catalytic layer is oxidized fast leaving the soot in the thermal layer unreacted. This has been observed with some early catalytic filters. As a decreases the soot from the top layer replaces more rapidly the soot oxidized in the catalytic layer increasing the global oxidation rate. The corresponding soot layer thickness evolution is shown in Fig. 22. For values of a close to 1 (e.g. 0.9) the catalytic layer is totally depleted from soot at some instances, followed by sudden penetration events from the soot of the thermal layer. These events are clearly shown in the thickness evolution for oc = 0.9 in... 

Cell density Wall thickness (cpsi) (mm) Channel size (mm) Soot layer thickness (pm) Open area fraction... 

Sinee in the DPF the gas flows through a solid bed, with a non-Arrhenius reaction rate given by k = koTQxp —E/RT), we redefine, for the DPF, the following parameters the charaeteristic reaction time tr d (such that Td = tjty d) the eharacteristic time for thermal convection tc,d (such that the cooling parameter 3 = tr /tc ), the dimensionless adiabatic temperature rise Bd, and the Lewis number. Led, s the ratio of the total heat capaeity of the soot bed to that of the substrate wall. Z = w/w is the dimensionless soot layer thickness, and 6 is the dimensionless temperature, defined earlier. 

The evolution of the dimensionless density profile across the soot layer is shown in Fig. 23. The initial gradual replenishment of the soot in the catalytic layer (at t = 140 s) is followed by sudden penetration events (t — 262 and 326 s) before the establishment of a steady state profile (at =531 and 778 s). Regarding the non-catalytic (thermal) layer only a gradual reduction of its thickness, accompanied by a very small reduction of its uniform density is observed. This simple microstructural model exhibits a rich dynamic behavior, however we have also established an experimental program to study the soot cake microstructure under reactive conditions. 

The MCVD modified chemical vapor deposition) method also relies on the production of glass from halide vapors. The deposition process occurs inside a vitreous silica tube, which is heated from the outside and which serves as the cladding for the fiber. The reaction of the vapors now occurs without contamination by gases from the flames, which never contact the deposited material. Consolidation of the soot occurs simultaneously with deposition. The process continues until the desired layer thickness is reached, after which the entire tube is collapsed by increasing the external temperature to complete the preform. 

A low O2 condition is produced at a corrosion interface in the presence of protective scales, and complex corrosion reactions such as chlorination, sulfidation and oxidation occur below the corrosive deposit layer. Thick scales have pores and cracks due to temperature fluctuations and the vaporization of chlorides. As the thickness increases, the scales easily peel off from the surface. In particular, severe thermal cycles or increased gas velocities due to soot blowing accelerate the breakdown and spalling of the scale. Also, as a result of continuously repeated variations of gas conditions on the scales, the balance of chlorination, sulfidation and oxidation reactions at the corrosion interface and in the scales is forced to be changed by the penetration of O2. An increase of the partial pressure of O2 ( /qj ) temporarily halts the chlorination and sulfidation reactions. Therefore, a multi-layered scale stracture is produced. The presence of multi-layered oxides formed by corrosion resistant elements such as chromium, nickel, aluminum, silicon and molybdenum increases the protective effect of the scales against the... 

Wrapped nanocrystals. Metal crystallites covered with well-developed graphitic layers are found in soot-like material deposited on the outer surface of a cathode slag. Figure 6 shows a TEM picture of an a(bcc)-Fe particle grown in the cathode soot. Generally, iron crystallites in the tv-Fe phase are faceted. The outer shell is uniform in thickness, and it usually con-... 

According to Schack(55), a single particle of soot transmits approximately 95 per cent of the incident radiation and a cloud must contain a very large number of particles before an appreciable emission can occur. If the concentration of particles is K, then the product of K and the thickness of the layer L is equivalent to the product PgLe in the radiation of gases. For a known or measured emissivity of the flame ey, the heat transfer rate per unit time to a wall is given by. 

With the purpose of increase in a specific surface and electroconductivity of GPSi the technology of gas-phase pyrolitic sedimentation of a layer carbon fibrous nanomaterial on a surface of macropores is developed [8]. Process of sedimentation carbon fibrous nanomaterial at catalytic decomposition of the ethanol steam proceeds strictly selectively, and the received material practically does not contain some soot. The nano-fibrous layer of carbon is homogeneously enough located on all surface of macropores (Fig. 8), thickness of a layer makes about 0,1-0,4 microns and depends basically on modes of sedimentation. The layer represents a mix nano-... 

Coating substrates with other C-diffusion barrier layers has also been attempted. A 25 nm thick film of TiN coated on a Fe substrate was found to be sufficient to prevent soot from formation on the Fe substrate and to inhibit C diffusion into the Fe substrate,... 

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