MIL-HDBK-1003/7
Tube Water Velocity. The maximum cooling water velocity through the tubes is
7.2.4
limited by erosion of the inlet ends of the tubes and by the water side pressure drop
(friction loss). Velocities in excess of 8 feet per second are seldom used. The normal
tube water velocity ranges from 6 to 8 feet per second. Higher velocities provide
higher heat transfer but will cause increased friction loss. Where conditions require
the use of stainless steel tubes, the tube water velocity should be at least 7 feet per
second to ensure that the tubes are continually scrubbed with oxygen for passivation of
the stainless steel and maximum protection against corrosion. As a general rule, 7.5
feet per second water velocity is used with stainless steel tubes. When using admiralty
tubes, water velocities should be limited to about 7 feet per second to prevent
excessive erosion. Previous studies indicate that varying cooling water tube velocities
from 6.8 to 7.6 feet per second has very little effect on the economics or performance
of the entire cooling water system.
Tube Outside Diameter and Gauge. Condenser tubes are available in the
7.2.5
following six outside diameters: 5/8-inch, 3/4-inch, 7/8-inch, 1-inch, 1-1/8 inch, and
1-1/4 inch. For power plants, 3/4-inch, 7/8-inch, and 1-inch OD tubes are the most
prevalent sizes. As a general rule, 3/4-inch tubes are used in small condensers up to
15,000 square feet, 7/8-inch tubes are used in condensers between 15,000 and 50,000
square feet. Condensers larger than 50,000 square feet normally use at least 1-inch
tubes. Condenser tubes are readily available in 14, 16, 18, 20, 22, and 24 gauge. For
inhibited Admiralty or arsenical copper, 18 BWG tubes are normally used. For stainless
steel tubes, 22 BWG tubes are normally used.
Tube Length. The length of tubes is important because of its direct relation
7.2.6
to friction loss and steam distribution over the tube bundle. The selection of tube
length depends on condenser surface required, space available for the installation, and
cooling water pump power required. Normally, economical tube length for single pass
condensers will fall in the ranges as shown in Table 14. Two pass condensers will
normally have shorter tube lengths.
Table 14
Typical Condenser Tube Length vs. Surface
+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),
*
*
Tube
Condenser
*
*
Length
Surface
*
*
Feet
Sq.Ft.
*
*
*
16 - 24
Less than 20,000
22
- 30
20,000 to 50,000
30
- 36
50,000 to 100,000
32
- 44
100,000 to 500,000
.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-
100
Previous Page
