Page 178 - Fundamentals of Enhanced Oil and Gas Recovery

166 Forough Ameli et al.

5.2.9.3 Forced Convection /L (Normal to Tube)
The value of heat transfer by convection is calculated as follows:
Q lc 5 2πr 3 h c ðT 3 2 T a Þ (5.94)
where h c is the convective heat transfer coefficient based on outer tube diameter.

1000 # N Re # 50; 000
To calculate the convective heat transfer coefficient, there are correlations that are
applicable for covering a wide-spreading range of wind velocities. The following cor-
relation represented by McAdams [71] may be used for forced convection as a domi-
nated mechanism of heat transfer.

0:12k ha 0:6
h fc 5 N Re (5.95)
r 3

where k ha is the thermal cond. air (Btu/h ft F), h fc is the forced conv. htc (Btu/h ft F).

To calculate Reynolds number for air flowing into the pipe, use the following
correlation:
r 3 v a ρ a
N Re 5 4365 (5.96)
μ a
3
where ρ a is the air density at Ta (lbm/ft ), μ a is the air viscosity (cP), v a is the air
velocity normal to pipe (mi/h), k ha and μ a are calculated at film T 5 (T 3 1 T a )/2. As
T 3 is unknown, the solution technique would be trial and error.

5.2.9.4 Radiation Heat Loss/L
To calculate the value of surface heat transfer by the mechanism of radiation
(Fig. 5.9), use the following equation:

4 4 4
4
Q 5 πr 3 Eσ½ T 3 2 T sky 1 ðT 3 2 T g Þ (5.97)
lr

Figure 5.9 Radiation heat loss.