Page 325 - Mechanical Engineers' Handbook (Volume 4)

314 Heat Exchangers, Vaporizers, Condensers

Table 5 Reboiler MTD Estimation
Reboiler Type a T A T B MTD
HS/K T 1 t 2 T 2 t 2 Eq. (4), F 1
HS/X,G,H T 1 t 1 T 2 t 2 Eq. (4), F 0.9
VT/E T 1 t 2 T 2 t 1 Eq. (4), F 1
(F)HT/E or (F)HS/E T 1 t 2 T 2 t 1 Eq. (4), F 0.9
All types Isothermal T A T B T A
a V, vertical; H, horizontal; S, shellside boiling; T, tubeside boiling; (F), forced flow, else natural convection; /E, G, H,
K, TEMA shell styles.

the MTD values in Table 5 are intended to be on the safe side and that excessive fouling
factors are not necessary as additional safety factors if these values are used. See Section
4.1 for suggested fouling factor ranges.

Heat-Transfer Coefficients
The two basic types of boiling mechanisms that must be taken into account in determining
boiling heat-transfer coefficients are nucleate boiling and convective boiling. A detailed de-
scription of both types is given by Collier. 27 For all reboilers, the nucleate and convective
boiling contributions are additive, as follows:
h h nb h cb (46a)
b
or

Figure 16 Reboiler temperature profiles illustrated: (a)
use for kettle and horizontal thermosiphon; (b) use for
tubeside boiling vertical thermosiphon.