Rotated square pitch

Boiling on shell side usually negligible unless tubes are very small and close together. For preferred 45° rotated square pitch with 1.25 d , Ap will be low. 

The third example shown in Fig. 19.7 is my favorite for sensible-heat transfer in fouling service. This consists of 1-in tubes set on lV2-in rotated square pitch. The pitch layout is the same as that of the square pitch. It is just the tube bundle that is rotated by 45°. The shell-side fluid cannot flow without interference between the tubes. Hence, the tubes promote turbulence, and improve heat transfer. The large tubes,... 

Tubes can be arranged in triangular, square, or rotated square pitch. Triangular tube layouts give better shell side heat transfer coefficients and provide more surface area for a given shell diameter. Alternatively, square pitch or rotated square pitch layouts are used when mechanical... 

The cost of the twisted tube bundle as compared to a new larger traditional shell-and-tube exchanger of comparable surface area with wide rotated square pitch for ease of cleaning. In some cases the traditional shell-and-tube exchanger (shell + bundle + installation) was the least expensive option. 

Figure 5 Four tube pitch layouts (1) triangular pitch. (2) rotated triangular pitch, (3) square pitch, (4) rotated square pitch.

In Figure 3-5e the square-pitch layout has been rotated 45, yet it is es,sentially the same as Figure 3-5a. In Figure 3-5d a mechanically clean-able modification of triangular pitch is shown. If the tubes are spread wide enough, it is possible to allow the cleaning lanes indicated. 

For plain tubing, the nominal O.D. replaces de. The volumetric equivalent diameter does not distinguish between square pitch and square pitch rotated by 45°. 

Figure 7.30 Experimental temperature increases for a Newtonian fluid (polypropylene glycol) as a function of the shearing time [47]. The data are for a square-pitched screw with a channel depth of 3.78 mm, a barrel diameter of 49.7 mm, and rotations at 55 rpm...

Figure 7.33 Screw and barrel temperature increase observed and predicted for an 11.1 mm deep channel screw with a square pitch (1 7.9°) for rotation rates of 55 rpm [5]...

For square pitched screws, Ls = Ds, and the flights are all perpendicular to the screw axis. Extruder screws range from 25 to 150 mm in diameter, with screw lengths typically of 25 to 30 screw diameters. They rotate at speeds from 50 to 150 rpm, and deliver melt at rates from 10 to 1000 kg/h with pressures up to 40 MN/m. ... 

Devolatilizing Screw Extruder A 150-mm-diameter, square-pitched, single-flighted screw extruder, with screw channel depth of 25 mm and 20-mm flight width is used to devolatilize a 1000-kg/h stream with 0.78-g/cm3 density at 200° C and 125 torr. (a) At what frequency of screw rotation will the channel be 30% or less full (b) With water injection, if density is halved by formation of 1-mm bubbles, how much surface area (per meter length) is created (c) How does... 

Fig. 10.8 Fully intermeshing, co-rotating elements in configurations matching square-pitch screws, (a) Forward screw conveying elements with different numbers of lobes (b) forward staggered kneading paddles (a.k.a., disk elements) representing leaky screw elements, and (c) neutral configuration. [Reprinted by permission from D. B. Todd, APV (Baker Perkins) Systems, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

The triangular and rotated square patterns give higher heat transfer rates, but at the expense of a higher pressure drop than the square pattern. A square or rotated square arrangement is used for heavily fouling fluids, where it is necessary to mechanically clean the outside of the tubes. The recommended tube pitch (distance between tube centers) is 1.25 times the tube outside diameter, and this will normally be used unless process requirements dictate otherwise. Where a square pattern is used for ease of cleaning, the recommended minimum clearance between the tubes is 0.25 in. (6.4 mm). 

Figure 13.9 Tube layout patterns (a) square pitch (b) trianguk pitch (c) square pitch rotated (d triangular pitch with cleaning lanes...

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