Screen Reynolds number

The discharge coefficient for the screen C with aperture D, is given as a function of screen Reynolds number Re = Ds(Wa)p/p in Fig. 6-16 for plain square-mesh screens, a = 0.14 to 0.79. This curve fits most of the data within 20 percent. In the laminar flow region, Re < 20, the discharge coefficient can be computed from... 

FIGURE 3.11 Friction Factor versus Screen Reynolds Number for Dutch Twill Weaves. 

FIGURE 7.22 Screen Reynolds Number at Bubble Breakthrough as a Function of Liquid Subcooling. 

Naturally, there are two more Peclet numbers defined for the transverse direction dispersions. In these ranges of Reynolds number, the Peclet number for transverse mass transfer is 11, but the Peclet number for transverse heat transfer is not well agreed upon (121, 122). None of these dispersions numbers is known in the metal screen bed. A special problem is created in the monolith where transverse dispersion of mass must be zero, and the parallel dispersion of mass can be estimated by the Taylor axial dispersion theory (123). The dispersion of heat would depend principally on the properties of the monolith substrate. Often, these Peclet numbers for individual pellets are replaced by the Bodenstein numbers for the entire bed... 

Yabannavar et al. [81] proposed a proportionality relationship valid for spin-filters based on an analogy to Eq. (15). They defined the Reynolds number based on the tangential velocity at the screen surface. Since in spin-filters the permeation velocity, or perfusion flux, is given by Eq. (16), and it can be assumed that the screen porosity e will be maintained constant throughout the scale-up process, it is possible to write a proportionaHty relationship for the ratio from drag to lift force in spin-filters as given by Eq. (17). 

The authors in association with Oxford University, undertook research, to determine how the arrangement of heat exchanger bundles at the base of a tower affects the tower s internal flow and its sensitivity to cross winds. To learn more about these effects, experiments were conducted with model towers in which heat exchanger bundles were represented by gauze screens. Two types of tests were conducted The first study involved a tower flow in the absence of cross winds which was made at high Reynolds numbers. The second was a study of cross-wind effects made at much reduced Reynolds numbers in a 4m by 2m wind tunnel. 8 refs, cited. 

To consolidate the experimental screening data quantitatively it is desirable to obtain information on the fluid mechanics of the reactant flow in the reactor. Experimental data are difficult to evaluate if the experimental conditions and, especially, the fluid dynamic behavior of the reactants flow are not known. This is, for example, the case in a typical tubular reactor filled with a packed bed of porous beads. The porosity of the beads in combination with the unknown flow of the reactants around the beads makes it difficult to describe the flow close to the catalyst surface. A way to achieve a well-described flow in the reactor is to reduce its dimensions. This reduces the Reynolds number to a region of laminar flow conditions, which can be described analytically. 

Yen and Yao [16] used a fin-type titanium cathodic current feeder (Fig. 2) in a fluidized-bed electrode to achieve enhanced copper recovery from dilute solutions. Copper particles served as the fluidized-bed cathode and platinized titanium screens were used as the anode, where oxygen evolution occurred. The feeder with the longer fin yielded higher current densities at increasing Reynolds numbers and larger bed expansions as compared with the short fin or the planar current feeder. The increased currents were due to the increased rate of copper deposition on the fluidized particles. 

P11-7b The oxidation of ammonia is to be carried out over platinum gauze. The molar flow rate of ammonia is 10 mol/min at a temperature of 500 K and a pressure of 202.6 kPa. Is one 250-mesh screen 10 cm in diameter sufficient to achieve 60% conversion The wire diameter is 0.044 mm. Assume 25% excess air, and ignore the effects of volume changes on the Reynolds number. 

Cartellier, A. (2003) Screening mechanisms and induced agitation in bubble flows at finite particle Reynolds numbers experiments and preliminary modelling attempts using a hybrid model, ERCOFTAC Bulletin. 56, 27-33. 

As their solutions approach the 6 state, Haas and co-workers (25, 26, 49) observe a more sharply critical transition with a shorter apparent relaxation time, which they ascribe to the Zimm relaxation time in the limit of hydrodynamic screening. Figure 19 shows the flow resistance as a function of Reynolds number for a range of concentrations. They identify the condition... 

There have been several studies of mass and heat transfer to wire screens, and the work by Shah and Roberts [19] covers the range of Reynolds numbers typical of commercial ammonia oxidation. They studied the decomposition of H2O2 on Ag or Pt screens of different mesh size and presented an empirical correlation for the jjj factor For 5 < Re, y < 245,... 

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