Air velocity and pressure drop

FIGURE 28.8 Relationship between superficial air velocity and pressure drop at selected static bed depths. (From Soponronnarit, S. and Prachayawarakorn, S., Drying TechnoL, 12, 1667, 1994.)... 

Figure 1 Relation between the air velocity and pressure drop. (From Ref. 19.)...

Air containing 5 mol% NH3 at a total flow rate of 20 kmol/h enters a packed column operating at 293 K and 1 atm where 90% of the ammonia is scrubbed by a counter-current flow of 1500 kg/h of pure liquid water. Estimate the superficial gas velocity and pressure drop at flooding, and the column inside diameter and pressure drop for operation at 70% of flooding for two packing materials ... 

Maximum superficial condensate velocities are about 25 m s . In a given line, the velocity increases as the pressure drops and more liquid vaporizes. Vendors of steam traps and condensate systems can provide guidance and line-sizing charts. Water lines usually have velocities up to 3ms . The designer must consider water hammer as well as velocity and pressure drop. Selection of valves and their closure time becomes important. Compressed air usually is transported at 5-8 m s. ... 

Calculate the air velocity, the pressure drop through the bed if the cross-sectional area is 0.3 m, and the bed height at a voidage 20% above the minimum. 

Velocity and pressure drop values based on air at 70°F. Data from Parsons (1988), Hanson and Danos (1982), and McCarthy (1980) ... 

Otner Collectors Tarry particulates and other difficult-to-handle hquids have been collected on a dry, expendable phenol formaldehyde-bonded glass-fiber mat (Goldfield, J. Air Pollut. Control A.SSOC., 20, 466 (1970)] in roll form which is advanced intermittently into a filter frame. Superficial gas velocities are 2.5 to 3.5 m/s (8.2 to 11.5 ft/s), and pressure drop is typically 41 to 46 cm (16 to 18 in) of water. CoUection efficiencies of 99 percent have been obtained on submicrometer particles. Brady [Chem. Eng. Prog., 73(8), 45 (1977)] has discussed a cleanable modification of this approach in which the gas is passed through a reticulated foam filter that is slowly rotated and solvent-cleaned. 

Air is to be heated by passing it over a bank of 3-m-long tubes inside which steam is condensing at 100°C. Air approaches the tube bank in the normal direction at 20 C and I aim with a mean velocity of 5.2 m/s. The outer diameter of the tubes is 1.6 cm, and die lubes are arranged staggered with longitudinal and transverse pitches of = Sj = 4 cm. There are 20 row.s in the flow direction with 10 tubes in each row. Determine (a) the rate of heat transfer, (f ) and pressure drop across the tube bank, and (c) the rate of condensation of steam inside the tubes. 

Figure 12 shows some results of pressure drop measurements over a 1-m-long internally finned round tube (4-mm internal diameter, six fins, fm height 1 mm, fin thickness 0.5 mm) with a cutoff angle at the bottom end of 60 . With n-decane as the liquid and air at ambient temperature and pressure as the gas, the pressure drop increases steadily with increasing gas velocity until a certain critical gas velocity is reached. Below this critical velocity, the pressure drop is low, viz., orders of magnitude lower than in a fixed bed of catalyst under comparable conditions. It can also be seen that under these conditions the superficial velocity of the liquid in the internally finned tube has little effect on the pressure drop. 

Exhaust gas from a power plant passes through a 15-by-20-ft rectangular duct at an average velocity of 50 ft/s. The total length of duct is 250 ft and there are two 90 bends. The gas is at 180 F and about 1 atm, and the properties are similar to those of air. Calculate the pressure drop in the duct and the power required to overcome pressure losses. 

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