Channeling radiation axial

Bech Nielsen et a/. s experimental channeling data for the (100) axial channels is shown in Fig. 14. Together with 111 planar data, which showed a pronounced flux peak, these data clearly indicate a near bond-center site for the 2H. According to Bech Nielsen s analysis, the best fit to the data was obtained with 87% of the 2H atoms in the sample assigned to near BC sites and the rest to T sites. However, the attribution of the minority component could be influenced by radiation effects during the analysis, as will be discussed later. 

In catalytic channels, the flat plate surface temperature in Eq. (3.32) is attained at the channel entry (x O). As the catalytic channel is not amenable to analytical solutions, simulations are provided next for the channel geometry shown in Fig. 3.3. A planar channel is considered in Fig. 3.3, with a length L = 75 mm, height 21) = 1.2 mm, and a wall thickness 5s = 50 pm. A 2D steady model for the gas and solid (described in Section 3.3) is used. The sohd thermal conductivity is k = 6W/m/K referring to FeCr alloy, a common material for catalytic honeycomb reactors in power generation (Carroni et al., 2003). Surface radiation heat transfer was accounted for, with an emissivity = 0.6 for each discretized catalytic surface element, while the inlet and outlet sections were treated as black bodies ( = 1.0). To illustrate differences between the surface temperatures of fuel-lean and fuel-rich hydrogen/air catalytic combustion, computed axial temperature profiles at the gas—wall interface y=h in Fig. 3.3) are shown in Fig. 3.4 for a lean (cp = 0.3) and a rich cp = 6.9) equivalence ratio, p = 1 bar, inlet temperature, and velocity Tj = 300 K and Uin = 10 m/s, respectively. The two selected equivalence ratios have the same adiabatic equilibrium temperature, T d=1189 K. 

In addition to the high-temperature region of the annular plasma, there are also other operationally defined zones (1) the initial radiation zone (IRZ), in the axial channel aligned with the RF load coil (2) the normal analytical zone (NAZ), which is located immediately above the IRZ (usually 10-20 mm) and (3) the preheating zone (PHZ), which is located in the axial channel before reaching the plasma. These zones are shown in Figure 3.9. Solvent vaporization and dry aerosol decomposition to individual molecules or species usually occurs in the PHZ prior to the sample entering the plasma. Atomization or decomposition of crystalline materials and dissociation of molecules occurs in the IRZ. Finally, ionization of atomic species, produced in the IRZ, occurs in the NAZ. 

Here the asterisks denote excited electronic stales of the ions or neutral atoms. These reactions lie farther to the right as temperature increases. Some of these steps can actually be seen to occur in the axial channel when a concentrated solution of yttrium is introduced (fig. 2). The initial radiation zone low in the plasma corresponds to emission from both excited Y atoms and YO molecules. As these species travel further up the axial channel, atomization becomes more extensive and ionization also occurs, so the red emission is supplanted by strong blue emisssion from singly charged, positive Y ions. These events can also be seen from vertical profiles of emission from various species (fig. 3). Many rare earths show a similar spatial pattern of emission, i.e., oxide or hydroxide bands and neutral atom lines are emited low in the initial radiation zone, ion lines are seen higher in the normal analytical zone of the plasma. The latter region is observed almost exclusively in emission spectrometric measurements. 

Fig. 5.1. ICP and ion sampling interface. A = torch and load coil (HV = high voltage), B = induction region of ICP C = a solution aerosol being injected into axial channel, D = initial radiation zone, E = normal analytical zone, F — nickel cone with sampling orifice in tip, G = skimmer cone, H = boundary layer of ICP gas deflected outside sampling orifice, I — expanding jet of C gas sampled from ICP and J = ion lens elements. Reproduced from Afial. Chem. [5] with permission of American Chemical Society.

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