Longitudinal pitch

Two other terms need definition transverse pitch a and longitudinal pitch b. For a drawing of these dimensions see the source article. For our purposes appropriate lengths are shown in Table 3. 

Flow-through Tube Banks Ahgned and staggered tube banks are sketched in Fig. 5-6. The tube diameter is D, and the transverse and longitudinal pitches are ST and SL, respectively. The fluid velocity upstream... 

Example 3.11 Atmospheric air (p = 0.1 MPa) is to be heated in a tube bundle heat exchanger from 10 °C to 30 °C. The exchanger consists of 4 neighbouring rows and zr rows of tubes aligned one behind the other. The outer diameter of the tubes is 25 mm, their length 1.5m, the longitudinal pitch is the same as the transverse pitch s /d = sq/d = 2. The wall temperature of the tubes is 80 °C with an initial velocity of the air of 4m/s. Calculate the required number zr of tube rows. 

Let us note that for the checkerboard pattern L is understood to be the transverse and longitudinal pitch of the tubes. For a straight-row tube pattern,... 

The best results were obtained when the transversal pitch was twice the outside diameter and the longitudinal pitch divided by the outside diameter was between 1.1 and 3.0—with this optimal geometry for Re (Reynolds Number) and Sc (Schmidt Number) each between 1 and 1000, with Re based on the external fiber diameter. In another study, Yang [71] used hydrophobic hollow fibers for the removal of oxygen or CO2 from water into nitrogen. The authors obtained the following correlations for closely and loosely packed fibers, respectively ... 

Remarks Re == DmaJfi, where D is the outside diameter of tubes, G ax Mmin with is the minimum open free-flow area between tubes Xj- is the transverse pitch/tube outside diameter N is the total number of tubes in line of flow is the longitudinal pitch/tube outside diameter = 0.43 + (1.13/ ). Fluid properties for all relations are evaluated at the mean film temperature, T = 0.5 (T. + Tf,), where T. is the tube wall temperature and is the bulk temperature of fluid. See Fig. 5.5 for tube arrangement. 

A rotating propeller traces out a helix in the fluid, from which a full revolution moves the liquid longitudinally to a fixed distance, depending on its pitch, i.e., the ratio of this distance to the propeller diameter. Pitch may be computed from the following formula ... 

Corrosion allowance Tube diameters Square pitch cleaning lane Mm. shell thickness Transverse baffle and support plate thickness Min. thickness longitudinal battles... 

The minimum number of the tube rows recommended to establish a proper air flow pattern is 4, although 3 rows can be used. The typical unit has 4-6 rows of tubes, but more can be used. Although more heat can be transferred by increasing the number of tubes, the required fan horsepower will be increased however, this balance must be optimized for an effective economical design. Tubes are laid out on transverse or longitudinal patterns however, the transverse is usually used due to the improved performance related to pressure drop and heat transfer. The tube pitch is quite important for best air-side performance. A typical representative tube arrangement for design optimization is for hare-tube O.D., tinned-tube O.D., and tube pitch ... 

This 1s a frequent occurrence since the natural longitudinal wave frequency of liquid Inside a process vessel Is typically 1n the range of 6 to 12 seconds, corresponding very closely to typical pitch and surge excitation frequencies of tankers, barges and sem1-submer 1b1es (10 - 16 seconds). 

While the minimum residence time is significant for dispersive mixing, the residence time distribution in the extruder influences distributive mixing as a measure for longitudinal mixing performance [20]. The average residence time depends only on screw pitch and screw speed in partially-filled screw sections, and only on throughput in fully-filled screw sections. 

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. 

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