Page 435 - Handbook of Energy Engineering Calculations

7. Perform the second-trial computation for heat-transfer surface and

pressure drop
As a first step in adjusting the heat-transfer surface and pressure drop,
2
calculate the number of tubes to give a pressure drop of 10 lb/in (68.9 kPa)
on the tubeside. The pressure drop varies inversely as n 1.8. . Therefore,

1.8
14.3/10 = (n/89) , and n = 109.
Each individual product of the factors is then adjusted in accordance with

the applicable exponential function of the number of tubes. Since the tubeside
product is inversely proportional to the 0.2 power of the number of tubes, the
0.2
product from the preceding trial is multiplied by (n /n ) , where n is the
1
2
1
number of tubes used in the preceding trial, and n is the number to be used
2
in the new one. The shellside product of the preceding trial is multiplied
by(n /n ), 0.718 , and the tube-wall and fouling products by n /n . New adjusted
2
1
2
1
products are then calculated as follows:

8. Make the last trial calculation
For the third trial, baffle spacing is decreased to 3.5 in (88.9 mm) from 5 in