Modern Engineering Thermodynamics

13.23 Second Law Analysis of Vapor and Gas Power Cycles 519
CASE STUDIES IN APPLIED THERMODYNAMICS
The following are examples of typical case studies in the field of
applied thermodynamics. They are meant to demonstrate the practical
use of the material presented in this chapter. The examples are
chosen from a wide variety of well-known technologies, and the
thermodynamic analysis has been presented essentially as a diagnostic
tool. In this way, we can develop a quick understanding of
how some simple and some complex items behave from a thermodynamic
point of view.
Case study 13.1. The Stanley Steamer automobile
In 1897, a Rankine cycle steam-powered automobile was introduced
by the twin brothers Francis Edgar Stanley (1849–1918) and
Freelan Oscar Stanley (1849–1940). Their automobiles were affectionately
known as Stanley Steamers (Figure 13.57), and most had a
two-cylinder, 30.0 hp reciprocating steam engine with a 4.0 in
bore and a 5.0 in stroke. The boiler operated at 600. psia and
600.°F and was fueled with gasoline or kerosene. The engine was
mounted in the rear of the automobile and connected directly to
the drive wheels. Therefore, Stanley Steamers did not require a
drive shaft, transmission, or differential. The engine (and the automobile’s)
speed was controlled simply by altering the amount of
steam reaching the engine with a hand-operated throttle valve. The
Stanley Steamers did not have a condenser until 1917. Before then,
they exhausted their spent steam directly into the atmosphere.
When a condenser was finally added to the engine, its main function
was to conserve and recycle water and not to improve the efficiency
of the power plant. Consequently, the condenser looked and
operated very much like a standard automobile radiator, condensing
at atmospheric pressure instead of a vacuum. Under these conditions,
the engine produced 30.0 hp with an isentropic efficiency
of about 80.0%. Using basic engineering thermodynamics, we can
estimate the steam flow rate required for the engine and the
amount of water consumed in traveling 1 mile at 55.0 mph.
Station1—Engineinlet Station2s—Condenserinlet
p 1 = 600: psia
T 1 = 600°F
p 2s = p 2 = 14:7 psia
s 2s = s 1 = 1:5322Btu/lbm.R
h 1 = 1289:5Btu/lbm x 2s = ð1:5322−0:3122Þ/1:4447 = 0:8445
s 1 = 1:5322Btu/lbm.R h 2s = 180:1 + 0:8445ð970:4Þ = 999:6Btu/lbm
Station3—Pumpinlet
p 3 = p 2s = 14:7 psia
x 3 = 0:00
h 3 = 180:1Btu/lbm
Station4s—Boiler inlet
p 4s = p 1 = 600: psia
s 4s = s 3 = 0:3122Btu/lbm.R
h 4s = h 3 + v 3 ðp 4s – p 3 Þ
s 3 = 0:3122Btu/lbm.R = 180:1
v 3 = 0:01672ft 3 /lbm
+ 0:01672ð600: – 14:7Þð144/778:16Þ
= 181:9Btu/lbm
Then, since _W = (30.0 hp)(2545 Btu/hp · h)=76,400Btu/h,and
(η s ) engine = 0.800, the required steam mass flow rate is
_m =
_W
ðh 1 − h 2s Þðη s Þ engine
=
76,400 Btu/h
= 329: lbm/h
ð1289:5 − 999:6 Btu/lbmÞð0:800Þ
and, if the vehicle is traveling at 55.0 mph, it uses
329 lbm/h
55:0 mi/h
= 5:98 lbm/mi
or about 3 4
of a gallon of water per mile.
Wire winding
Boiler
Superheater
Stanley steamer boiler
FIGURE 13.57
1909 Stanley Steamer car and boiler.
(Continued )