Page 224 - Handbook of Energy Engineering Calculations

Find the exhaust-heat recovered from H = Wc Δt , where the symbols are the
e
e
same as in the previous calculation procedures. Since the final temperature of
the exhaust gas is not given, a value must be assumed. Temperatures below

275°F (135°C) are undesirable because condensation of corrosive vapors in
the silencer may occur. Assume that the exhaust-gas outlet temperature from
the heat-recovery silencer is 300°F (148.9°C). The H = (1000)(13)(0.252)
e
(700 − 300) = 1,310,000 Btu/h (383.9 kW).

2. Compute the heated-water outlet temperature from the cooler
Using the temperature notation in Fig. 10, we see that the heated-water outlet
temperature from the jacket-water cooler is t = (w /w )(t − t ) + t ), where
1
z
4
z
1
5
w = heated-water flow, lb/h; w = jacket-water flow, lb/h; the other symbols
1
z
are indicated in Fig. 10. To convert gal/min of water flow to lb/h, multiply by
500. Thus, w = (100 gal/min)(500) = 50,000 lb/h (22,500 kg/h), and w =
1
z
(500 gal/min)(500) = 250,000 lb/h (112,500 kg/h). Then t =
z
(250,000/50,000)(180 − 170) + 60 = 110°F(43.4°C).

FIGURE 10 Internal-combustion engine cooling system.

3. Compute the heated-water outlet temperature from the silencer
The silencer outlet temperature t = H /w + t , or t = 1,310,000/50,000 +
e
3
1
3
z
110 = 136.2°F (57.9°C).