FIG. 11-6 Estimation of fraction of tubes in cross-flow Fc [Eq. (11-8)]. To convert inches to meters, multiply by 0.0254. Note that l and Ds have units of inches.

6. Cross-flow area at or near centerline for one cross-flow section Sm a. For rotated and in-line square layouts:

Jotl

Pn b. For triangular layouts:

Fraction of cross-flow area available for bypass flow Fbp r (Ds - Dotl) ls

8. Tube-to-baffle leakage area for one baffle Stb Estimate from

where b = (6.223)(10~4) (SI) or (1.701)(10-4) (U.S. customary). These values are based on Tubular Exchanger Manufacturers Association (TEMA) Class R construction which specifies h-in diametral clearance between tube and baffle. Values should be modified if extra tight or loose construction is specified or if clogging by dirt is anticipated.

9. Shell-to-baffle leakage area for one baffle Ssb. If diametral shell-baffle clearance 8,b is known, Ssb can be calculated from

where the value of the term cos-1 (1 — 2 lc/Ds) is in radians and is between 0 and jc/2. Ssb is plotted in Fig. 11-7, based on TEMA Class R standards. Since pipe shells are generally limited to diameters below 24 in, the larger sizes are shown by using the rolled-shell specification. Allowance should be made for especially tight or loose construction.

10. Area for flow through window Sw. This area is obtained as the difference between the gross window area Swg and the window area occupied by tubes Swt:

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