Channel half-height

Figure 2.68 Results from numerical calculations for combustion-assisted methane steam reforming, (a) Outlet conversion dependence on channel half-height (b) wall temperature as a function of dimensionless reactor length. Calculation results determined at constant inlet velocity [108]...

There exist several possibilities to generate such turbulent fluctuations at the inflow boundary [19]. Batten et al. [3] reformulated on the ideas of Kraichnan [14] and Smirnov et al. [21] for wall bounded flows. The velocity signal is generated by a sum of sines and cosines with random phases and amplitudes. The wave numbers are calculated from a three-dimensional spectrum and are scaled by the values of the Reynolds-stress tensor. A special wall treatment was applied to elongate near-wall structures. A transition length to physical turbulence of about ten channel half heights was obtained at low Reynolds number channel flow. 

We can assume that velocity profile is fully developed and developing diffusion boundary layer thickness is small in comparison to the channel half-height. Let us estimate by substituting the above linear profile to... 

Streamwise profiles of the local catalytic and gas-phase methane conversion rates are provided in Fig. 6.3 for four combinations of h and /jn (indicated by points A through D in Fig. 6.2). Cases A-C are atp = 5 bar and Tin = 700 K, and Case D is at= 1 bar and Tin = 700 K. For direct comparisons with the catalytic surface conversion rates, the volumetric gaseous conversion rates have been integrated across the channel half-height in Fig. 6.3 to provide a eonversion rate per unit reactor wall area. The corresponding catalyst surface temperatures are shown in Fig. 6.4. There is significant gas-phase methane conversion in Case A (Fig. 6.3A)... 

Corresponding streamwise profiles of the local catalytic and gas-phase (the latter integrated over the channel half-height b) fuel conversion rates for the conditions of Fig. 7.2 are provided in Fig. 7.3. Catalytic reactions are initiated after the first inert... 

An orthogonal staggered grid with 100 x 24 points in x- and y-direction, respectively, over the channel half-height produced a grid-independent solution for the flow domain. Finer spacing towards the channel wall and entry section was used. A 100 grid node resolution in the x-direction was also used to discretize the solid wall. At the inlet (x = 0), uniform profiles of species, temperature and axial velocity were applied, while zero-Neumann conditions were set at the outlet (x = L) and plane of symmetry (y = 0). No-slip was apphed for both velocity components at the gas-wall interface (y = b). 

Active-to-geometrical surface ratio Channel half-height... 

CO = rotation speed (rad s-1) Vf = volume flow rate (cm3 s 1 ) rT = radius of wall-tube U = linear velocity of solution (cm s 1 ) 0 = angle between cone surface and rotation axis x = length of tubular/channel electrode w = width of channel electrode d — width of channel h = half-height of channel co = rotation speed of solution (rad s 1) co" = rotation speed of rotating disc (rad s-1). 

To further characterize the mobility of the IRE loop, time-resolved isotropic fluorescence emission decay components of the IRE RNAs were determined as a function of temperature. Some details of the measurements and data assessment will be necessary here to appreciate both the utility of the information and caveats about its literal interpretation. Considering first the TCSPC instrument itself, some uncertainty in the measurements arise from its intrinsic parameters. With 300 nm incident light, the IRF of the photomultiplier tube ranged from 190 to 276 ps full-width at half-height (FWHH). The width of the IRF and the time resolution (32.5 ps/channel) limit the short components that can be reliably extracted from the fit, and certainly those <200 ps will have large errors on their amplitudes and lifetimes. Fluorescence emission decay components as short as 9—20 ps (Larsen et al., 2001) and 30—70 ps (Guest el al., 1991) (and much shorter by Wan et al., 2000) have been measured for 2AP in a stacked conformation, but in our instrument, a fit to such a short lifetime would be inaccurate. 

The reflector above the active core is composed of two layers, a layer of full-height elements over a layer of half-height elements. The top reflector elements channel coolant flow to the active core and provide for the insertion by gravity, of reseirve shutdown material into the active core. They have the same array of coolant holes as the fuel element and the same holes for the insertion of reactivity control devices. 

The bottom reflector under the active core is also composed of two layers, a layer of three-quarter height elements over a layer of half-height elements. The bottom reflector elements provide for the passage of coolant from the active core into the core support. In the standard columns, this is accomplished by collecting the coolant channel flows into six intermediate coolant holes 68 mm (2.68 in.) in diameter. The channel for the reserve shutdown material is blind and stops in the lower reflector. 

Here, P is the local pressure, x is the streamwise coordinate, and h is the half height of the channel. The pressure gradient can be measured by mounting pressure taps along the channel before and after the shear stress sensor location. 

In this equation, the mass transport limited current /lim is given by n, the number of electrons transferred per molecule diffusing to the electrode surface, F, the Faraday constant, c, the bulk concentration, D, the diffusion coefficient, w, the electrode width, x, the electrode length, h, the electrode half height, and Vf, the volume flow rate. By comparison with the total flux of redox-active material in the channel, VfXcxnxF, the degree of conversion can be expressed (Eq. 2). 

Channel Length x, width w, half height h /ita = 0.925nFcD ft f Vy ... 

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