Upper air flow

FIGURE 4.2 Extreme upper air flow over Central Europe during the gale Kyrill on January 15, 2007, 1200 UTC (ECMWF, with permission). Color figure on CD, Chapter 20.4. 

If then even the high level wind field ( jet stream ) moves around this vertically extended high pressure cell, the upper air flow track over northern Europe takes a curvature looking like an uppercase Omega (Fig. 4.26). Therefore this well-known weather situation, coined by bright sunshine and extended in space, is regarded as the Omega-weather type. 

Trays of product to be frozen can be loaded onto trollies, which are taken through an air blast tunnel. The evaporator coils will usually be in the upper part of the tunnel, with air flow across the trays. 

Methane is supplied to a burner in a room for an experiment at 10 g/s. The measurements indicate that air flow into the room doorway is 800 g/s and the door is the only opening. The exhaust leaves the room through the upper part of the doorway at a uniform temperature of 400 °C. Assume that the methane bums completely to C02 and H20 and that steady conditions prevail in the room. 

Feser et al. [214] used a radial flow apparatus to determine the viscous in-plane permeability of differenf DLs af various levels of compression (see Figure 4.26). A stack of round-shaped samples, wifh each layer of material separated with a brass shim, was placed inside two plates. Thicker shim stock was also used in order to control the total thickness of the stack of samples. Compressed air entered fhe apparafus fhrough the upper plate and was forced through the samples in the in-plane direction. After this, the air left the system and flowed through a pressure gage and a rotameter in order to measure the pressure drop and the air flow rate. The whole apparatus was compressed using a hydraulic press for each compression pressure, 10 different flow rates were used. 

In order to determine the viscous and inert through-plane gas permeabilities of diffusion layers at varied compression pressures, Gostick et al. [212] designed a simple method in which a circular specimen was sandwiched between two plates that have orifices in the middle, aligned with the location of the material. Pressurized air entered the upper plate, flowed through the DL, and exited the lower plate. The pressure drop between the inlet and the outlet was recorded for at least ten different flow rates for each sample. The inert and viscous permeabilities were then determined by fitting the Forchheimer equation to the pressure drop versus flow rate data as explained earlier. 

Fig. 6.6 Comparison of two alternative stagnation-flow configurations. The upper illustration shows the streamlines that result from a semi-infinite potential flow and the lower illustration shows streamlines that result from a uniform inlet velocity issuing through a manifold that is parallel to the stagnation plane. Both cases are for isothermal air flow at atmospheric pressure and T = 300 K. In both cases the axial inlet velocity is u = —5 cm/s. The separation between the manifold and the substrate is 3 cm. For the outer-potential-flow case, the streamlines are plotted over the same domain, but the flow itself varies in the entire half plane above the stagnation surface. The stagnation plane is illustrated as a 10 cm radius, but the solutions are for an infinite radius.

Primary air flow, supplied at the bottom of the bed, is insufficient for complete combustion of the fuel. The zone below the elevation of secondary-air jets is endothermic, cracking oil to yield carbon and fuel gas species. These burned in the upper, exothermic zone. Alumina product is withdrawn from a standpipe receiving solid from the upper zone, and burn-off of carbon in this zone is sufficient to yield a product that is acceptably white. Fluidizing-gas velocity being lower in the primary combustion zone than in the secondary, density is higher. Provision of the two zones accomplishes two purposes (1) affording a sufficient solid residence time in the primary zone and (2) reducing horsepower needed for air compression. 

Upper part of Table 2 gives specific surface area (Sbet), surface areas of micropores (Smicro) and mesopores (Smeso), total pore volume (Vt) and micropore volume (Vmicro) of fresh, equilibrium, 2.17 %C and 4.2 %C catalyst samples. Lower part of table 2 gives the same characteristics of equilibrium, calcined equilibrium, calcined coked 2.17 %C catalysts (calcination is operated at 873 K, during 24 hours, in air flow) as determined from N2-77 K or Ar-87 K isotherms. All values depend on the probe molecule and sorption temperature, which confirm the observations deduced from the isotherm shape. 

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