Page 223 - Handbook of Energy Engineering Calculations

pressure shows that NPSH = (10 − 1.02) + 2.31(21.4 − 21.4)/0.0954 = 8.98 ft
(2.7 m). This is close to the required 8-ft (2.4-m) head. However, the engine
could be safely operated at a slightly lower temperature, say 225°F
(107.2°C).

8. Compute the pressure at the pump suction flange
2
The pressure at the pump suction flange P lb/in (gage) = 0.433s(H − H ) =
s
f
2
(0.433)(0.974) (10,00 − 1.02) = 3.79 lb/in (gage) (26.1 kPa).
A positive pressure at the pump suction is needed to prevent the entry of
air along the shaft. To further ensure against air entry, a mechanical seal can
be used on the pump shaft in place of packing.

Related Calculations. Use this general procedure in designing the cooling

system for any type of reciprocating internal-combustion engine—gasoline,
diesel, gas, etc. Where a coolant other than water is used, follow the same
procedure but change the value of the constant in the denominator of the

equation of step 1. Thus, for a mixture of 50 percent glycol and 50 percent
water, the constant = 436, instead of 500.
The method presented here is the work of Duane E. Marquis, reported in
Mechanical Engineering.

ENERGY RECOVERY VIA HOT WATER FROM I-C
ENGINES

An internal-combustion engine fitted with a heat-recovery silencer and a
jacket-water cooler is rated at 1000 bhp (746 kW). It exhausts 13.0 lb/(bhp ·
h) [5.9 kg/(bhp · h)] of exhaust gas at 700°F (371.1°C). To what temperature
can hot water be heated when 500 gal/min (31.5 L/s) of jacket water is

circulated through the hookup in Fig. 10 and 100 gal/min (6.3 L/s) of 60°F
(15.6°C) water is heated? The jacket water enters the engine at 170°F
(76.7°C) and leaves at 180°F (82.2°C).

Calculation Procedure:

1. Compute the exhaust heat recovered