Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual page 40

Velocity of Steam
General Heating Applications—
4,000 to 6,000 fpm.
Process Pipe—
6,000 to 12,000 fpm.
Sample Problem Using Steam Velocity
Charts (Fig. 10).
General Heating Application—2,000 Ibs./hr.
Required at 30 psi supply pressure.
Size Pipe and Determine Velocity and
Pressure Drop
Step 1
Correct 30 psi flow rate to O psi on basic
chart. This is done by entering bottom at
2,000 Ibs./hr. Follow this point vertically to
the 30 Ib. Iine, then follow slope to the 0 psi
line.
Step 2
Draw vertical line from 0 point into upper
curve. Stop at some point above 6,000 fpm.
Velocity shown is O psi steam and requires
correction.
Velocity Multiplier Chart
Figure 10 (continued)
Reprinted by permission from ASHRAE 1972
Handbook of Fundamentals
Step 3
Try 3 inch pipe showing 10,000 fpm velocity
and pressure drop of approximately .9 psi
per 100 feet.
Step 4
Use velocity multiplier chart. Enter left column
at 10,000 fpm, follow sloping line to 30 psi.
Read corrected velocity of 6,000 fpm in right
column.
NOTE:
1. Use velocity chart to correct 6,000 fpm,
required velocity, to 10,000 fpm before using
basic chart.
2. Heat exchanger steam entrance nozzles
are normally sized at reduced velocities to
avoid impingement damage to the tube bun-
dle. Check with heat exchange manufacturer
for nozzle size.
Example of Use of Basic and Velocity Multiplier Charts.
Given:
a. Weight-Flow Rate = 6700 Ib. per hr.
b. Initial Steam Pressure = 100 psig.
c. Pressure Drop = 11 psi per 100 ft.
Find:
a. Size of Schedule 40 pipe required.
b. Velocity of steam in pipe.
Solution: The following steps are illustrated by the broken line on Fig. 10:
Step 1. Enter Fig. 10 at a weight-flow rate of 6700 Ib. per hr. and move
vertically to the horizontal line at 100 psig.
Step 2. Follow along inclined multiplier line (upward and to the left) to
horizontal 0 psig line. The equivalent weight flow at 0 psig is about
2500 Ib. per hr.
Step 3. Follow the 2500 Ib. per hr. Iine vertically until it intersects the hori-
zontal line at 11 psi per 100 ft. pressure drop. The nominal pipe size is
2 1 ⁄ in. The equivalent steam velocity at 0 psig is about 32,700 fpm.
2
Step 4. To find the steam velocity at 100 psig, locate the value of
32,700 fpm on the ordinate of the velocity multiplier chart at 0 psig.
Step 5. Move along the inclined multiplier line (downward and to the right)
until it intersects the vertical 100 psig pressure line. The velocity as read
from the right (or left) scale is about 13,000 fpm.
NOTE: The preceding Steps 1 to 5 would be rearranged or reversed if
different data were given.
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