Effect area ratio

Effective Area. - The catalyst consists of active metal dispersed on a substrate material. Therefore, there is a difference between the effective area used in mass transfer calculations of chemical reaction and the effective area used in heat transfer culculations which corresponds to the monolith surface area including surface roughness. The ratio of both effective areas must be defined based on experimental results, as they depend on catalyst type and manufacturing processes. The Thiele number is sometimes used for this same purpose. The relationship between effective area ratio and conversion efficiency is shown in Figure 3. This effective area ratio may be one of the characteristic values of the catalyst, which affects catalyst performance and catalyst temperature. The effective area ratio in the present study is estimated to be 0.3 for mass transfer and 1 for heat transfer based on the experimental data. 

Figure 3 Effective area ratio of mass transfer to heat transfer versus effective overall reaction rate.

The coupling of dissimilar alloys in conductive, corrosive solutions such ts seawater is called galvanic corrosion and can lead to accelerated corrosion of the more anodic, electronegative alloy and protection of the more cathodic, electropositive alloy. The extent of galvanic corrosion depends on factors such as (1) the effective area ratio between the anodic and cathodic members of the couple (2) solution conductivity (3) flow characteristics of the solution (4) temperature (5) system geometry (6) the potential difference of the dissimilar alloys (7) solution composition and... 

The dimensionless packing parameter, p, can be considered as the ratio of the effective areas of the hydrophobic to hydrophilic segments. On the basis of the effective-area ratio of the hydrophobic to hydrophilic blocks, or p, it can be estimated that copolymers with large hydrophilic blocks (i.e., high curvature p < ), will form spherical micelles those with similar sizes olF the two blocks (i.e., very low curvature size ratios in between will possibly form rod-like or worm-like micelles. 

The integral cross section is therefore the effective area presented by each field particle B for scattering of the test particles A into all directions. The probability that the test particles are scattered into a given direction v ( /, ([)) is the ratio... 

It has become quite popular to optimize the manifold design using computational fluid dynamic codes, ie, FID AP, Phoenix, Fluent, etc, which solve the full Navier-Stokes equations for Newtonian fluids. The effect of the area ratio, on the flow distribution has been studied numerically and the flow distribution was reported to improve with decreasing yiR. 

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

FIG. 14-43 Overall (Murphree) efficiencies of sieve plates with hole/active area ratios of 0.08 and 0.14. Efficiency values greater than 1.0 (100%) result from crossflow effects (Figs. 14-38, 14-39). [Yanagi and Sakata, Ind. Eng. Chem., Proc. Des. Devel., 2i, 712 (J.9S2).] Reproduced with permission, copyright 1982 American Chemical Society. 

Area effects in galvanic corrosion are very important. An unfavorable area ratio is a large cathode and a small anode. Corrosion of the anode may be 100 to 1,000 times greater than if the two areas were the same. This is the reason why stainless steels are susceptible to rapid pitting in some environments. Steel rivets in a copper plate will corrode much more severely than a steel plate with copper rivets. 

A corresponding pressure effect on the flow stress was observed on hydrostatic extrusion of conical specimens of the same alloy through a die of 5 mm dia at 220°C. The basic alloy was extruded at P = 12 kbar up to the area ratio equal to 4.1 while the alloy hydrogenated to a = 0.20 extruded to the area ratio of 7.6 even at a lower pressure, P = 11 kbax . Similar pressure/hydrogen effects on the flow stress were also observed on hydrostatic extrusion of ZrH,c, VH,c and Nb,c alloys with x = 0 and 0.1-0.2 wt.%. 

Coefficient entry or discharge) The ratio of aerodynamic (effective) area to the measured area of an opening. The value for a square-edged hole of 0.61 is used for most building openings. 

A similar effect can be produced if a crevice is present in the steel, since the geometry of the system is such that whereas oxygen can diffuse readily to the metal surface outside the crevice it can only gain access to the metal within the crevice through its very narrow mouth (Fig. 1 A6d), and the large cathode anode area ratio leads to localised attack of the metal within the crevice. 

For further discussion of cathode to anode area ratio effects see References " and also refer to the section entitled Distribution of Bimetallic Corrosion in Real Systems, p. 1.238. 

In the flow of a gas through a nozzle, the pressure falls from its initial value Pi to a value P2 at some point along the nozzle at first the velocity rises more rapidly than the specific volume and therefore the area required for flow decreases. For low values of the pressure ratio P2/P1, however, the velocity changes much less rapidly than the specific volume so that the area for flow must increase again. The effective area for flow presented by the nozzle must therefore pass through a minimum. It is shown that this occurs if the pressure ratio P2/P1 is less than the critical pressure ratio (usually approximately 0.5) and that the velocity at the throat is then equal to the velocity of sound. For expansion... 

Because most applications for micro-channel heat sinks deal with liquids, most of the former studies were focused on micro-channel laminar flows. Several investigators obtained friction factors that were greater than those predicted by the standard theory for conventional size channels, and, as the diameter of the channels decreased, the deviation of the friction factor measurements from theory increased. The early transition to turbulence was also reported. These observations may have been due to the fact that the entrance effects were not appropriately accounted for. Losses from change in tube diameter, bends and tees must be determined and must be considered for any piping between the channel plenums and the pressure transducers. It is necessary to account for the loss coefficients associated with singlephase flow in micro-channels, which are comparable to those for large channels with the same area ratio. 

Effect of Draft Tube and Downcomer Area Ratio. When a draft tube of 9.55 cm I.D. (downcomer/draft tube area ratio = 7.8) was changed to a draft tube of 5 cm I.D. (downcomer/draft tube area ratio = 30) with other design parameters being the same, the gas bypassing reversed direction, as shown in Fig. 4. With the smaller draft tube (D/dD = 1), the gas bypasses from the draft tube side into the downcomer side for most experimental conditions, except for jet velocities in excess of 76 m/s at the concentric solids feeder with the larger draft tube (D/dD = 1.9), the gas bypasses from the downcomer side into the draft tube side in most experiments. 

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