Page 219 - Handbook of Energy Engineering Calculations

Next, assume a size for the cooling-water piping. Experience shows that a
water velocity of 300 to 600 ft/min (91.4 to 182.9 m/min) is satisfactory for
internal-combustion engine cooling systems. Using the Hydraulic Institute’s
Pipe Friction Manual or Cameron’s Hydraulic Data, enter at 280 gal/min
(17.6 L/s), the approximate flow, and choose a pipe size to give a velocity of

400 to 500 ft/min (121.9 to 152.4 m/min), i.e., midway in the recommended
range.
Alternatively, compute the approximate pipe diameter from d = 4.95
0.5
[gpm/velocity, ft/min] . With a velocity of 450 ft/min (137.2 m/min), d =
0.5
4.95(281/450) = 3.92, say 4 in (101.6 mm). The Pipe Friction Manual
shows that the water velocity will be 7.06 ft/s (2.2 m/s), or 423.6 ft/min

(129.1 m/min), in a 4-in (101.6-mm) schedule 40 pipe. This is acceptable.
Using a 3½-in (88.9-mm) pipe would increase the cost because the size is not
readily available from pipe suppliers. A 3-in (76.2-mm) pipe would give a
velocity of 720 ft/min (219.5 m/min), which is too high.

3. Compute the piping-system head loss
Examine Fig. 7, which shows the cooling-system piping layout. Three flow
conditions are possible: (a) all the jacket water passes through the heat
exchanger, (b) a portion of the jacket water passes through the heat
exchanger, and (c) none of the jacket water passes through the heat exchanger

—instead, all the water passes through the bypass circuit. The greatest head
loss usually occurs when the largest amount of water passes through the
longest circuit (or flow condition a). Compute the head loss for this situation

first.
Using the method given in the piping section of this handbook, compute
the equivalent length of the cooling-system fitting and piping, as shown in
Table 8. Once the equivalent length of the pipe and fittings is known,
compute the head loss in the piping system, using the method given in the

piping section of this handbook with a Hazen-Williams constant of C = 130
and a rounded-off flow rate of 300 gal/min (18.9 L/s). Summarize the results
as shown in Table 8.

The total head loss is produced by the water flow through the piping,
fittings, engine, three-way valve, and heat exchanger. Find the head loss for
the last components in Fig. 8 for a flow of 300 gal/min (18.9 L/s). List the
losses in Table 8, and find the sum of all the losses. Thus, the total circuit