Page 318 - Mechanical Engineers' Handbook (Volume 4)

3 Rating Methods 307

Equation (17) is approximate in that it neglects pass partition gaps in the tube field, it
approximates the bundle average chord, and it assumes an equilateral triangular layout. For
more accurate equations see Ref. 11.
The tubeside velocity V and the shellside velocity V are calculated as follows:
s
t
V W t (18)
t
S t
t
W
V s (19)
s
s
S s
Heat-Transfer Coefficients
The individual heat-transfer coefficients, h and h , in Eq. (1) can be calculated with reason-
o
i
ably good accuracy ( 20–30%) by semiempirical equations found in several design-oriented
textbooks. 11,12 Simplified approximate equations are the following:
(a) Tubeside Flow
DV
Re ot t (20)
t
where tubeside fluid viscosity.
t
If Re 2000, laminar flow,
h 1.86 Re Pr 0.14
0.33
k

ƒ
f
D i
i
D i L w (21)
If Re 10,000, turbulent flow,
h 0.024 Pr 0.14
k

ƒ
ƒ
i Re 0.8 0.4 (22)
D i w
If 2000 Re 10,000, prorate linearly.
(b) Shellside Flow
DV
Re os s (23)
s
where shellside fluid viscosity.
s
If Re 500, see Refs. 11 and 12.
If Re 500,
h 0.38 C 0.6 Pr 0.14

k
ƒ
ƒ
0.33
0.6
b
o
D Re (24)
o w
The term Pr is the Prandtl number and is calculated as C /k.
p
The constant (C ) in Eq. (24) depends on the amount of bypassing or leakage around
b
the tube bundle. 13 As a first approximation, the values in Table 2 may be used.
Pressure Drop
Pressure drop is much more sensitive to exchanger geometry, and, therefore, more difficult
to accurately estimate than heat transfer, especially for the shellside. The so-called Bell–
11
Delaware method is considered the most accurate method in open literature, which can be