Page 421 - Handbook of Energy Engineering Calculations

made of steel.

5. Compute the heating steam flow required
To determine the steam flow rate required, use the relation S = Q/h , where S
fg
= steam flow, lb/h; h = latent heat of vaporization of the heating steam,
fg
Btu/lb, from the steam tables; other symbols as before. Hence, S =
230,000/901.1 = 256 lb/h (0.03 kg/s), closely.

6. Compute the heating coil pipe diameter
Steam-heating coils submerged in the liquid being heated are usually chosen
for a steam velocity of 4000 to 5000 ft/min (20.3 to 25.4 m/s). Compute the
2
heating pipe cross-sectional area a in from a = 2.4 Su /V, whereu = specific
g
g
3
volume of the steam at the coil operating pressure, ft /lb, from the steam
tables; V = steam velocity in the heating coil, ft/min; other symbols as before.
With a steam velocity of 4000 ft/min (20.3 m/s), a = 2.4(256) (5.47)/4000 =
2
2
0.838 in (5.4 cm ).
Refer to a tabulation of pipe properties. Such a tabulation shows that the
internal transverse area of a schedule 40 1-in (2.5-cm) diameter nominal steel
2
2
pipe is 0.863 in (5.6 cm ). Hence, a 1-in (2.5-cm) pipe will be suitable for
this heating coil.

7. Determine the length of coil required
A pipe property tabulation shows that 2.9 lin ft (0.9 m) of 1-in (2.5-cm)
2
2
schedule 40 pipe has 1.0 ft (0.09 m ) of external area. Hence, the total length
2
2
of pipe required in this heating coil = (33.1 ft ) (2.9 ft/ft ) = 96 ft (29.3 m).
Related Calculations. Use this general procedure to find the area and length
of spiral heating coil required to heat water, industrial solutions, oils, etc.
This procedure also can be used to find the area and length of cooling coils

used to cool brine, oils, alcohol, wine, etc. In every case, be certain to
substitute the correct specific heat for the liquid being heated or cooled. For
typical values of U, consult Perry—Chemical Engineers’ Handbook,
McGraw-Hill, 2007; McAdams—Heat Transmission, McGraw-Hill, 1985; or
Kern—Process Heat Transfer, McGraw-Hill, 1997.