Page 419 - Handbook of Energy Engineering Calculations

To compute the linear feet L of finned tubing required, use the relation L =
2
A/(ft /ft), or L = 14,650/5.8 = 2530 lin ft (771.1 m) of tubing.

7. Compute the number of individual tubes required
Assume a length for the radiator tubes. Typical lengths range between 4 and
20 ft (1.2 and 6.1 m), depending on the size of the radiator. With a length of

16 ft (4.9 m) per tube, the total number of tubes required = 2530/16 = 158
tubes. This number is typical for finned-tube heat exchangers having large
6
heat-transfer rates [more than 10 Btu/h (100 kW)].

8. Determine the fan hp required
The fan hp required can be computed by determining the quantity of air that
must be moved through the heat exchanger, after assuming a resistance—say
1.0 in of water (0.025 Pa)—for the exchanger. However, the more common

way of determining the fan hp is by referring to the manufacturer’s
engineering data.
Thus, one manufacturer recommends three 5-hp (3.7-kW) fans for this
cooling load, and another recommends two 8-hp (5.9-kW) fans. Hence, about

16 hp (11.9 kW) is required for the radiator.

Related Calculations. The steps given here are suitable for the initial sizing
of finned-tube heat exchangers for a variety of applications. For exact sizing,
it may be necessary to apply a correction factor to the LMTD. These
correction factors are published in Kern—Process Heat Transfer, McGraw-

Hill, 1997, and McAdams—Heat Transfer, McGraw-Hill, 1997.
The method presented here can be used for finned-tube heat exchangers
used for air heating or cooling, gas heating or cooling, and similar industrial

and commercial applications.

SELECTION OF SPIRAL-TYPE HEATING COILS

How many feet of heating coil are required to heat 1000 gal/h (1.1 L/s) of

0.85-specific-gravity oil if the specific heat of the oil is 0.50 Btu/(lb · °F) [2.1
2
kJ/(kg · °C)], the heating medium is 65-lb/in (gage) (448.2-kPa) steam, and
the oil enters at 60°F (15.6°C) and leaves at 125°F (51.7°C)? There is no