Limited distribution permitted only to teachers and educators for course preparation.. If you are a student using this Manual, you are using it without permission.. The thermal efficienc
Trang 1PROPRIETARY MATERIAL © 2011 The McGraw-Hill Companies, Inc Limited distribution permitted only to teachers and educators for course preparation If you are a student using this Manual, you are using it without permission
9-35
9-54 An ideal dual cycle has a compression ratio of 14 and cutoff ratio of 1.2 The thermal efficiency, amount of heat added, and the maximum gas pressure and temperature are to be determined
Assumptions 1 The air-standard assumptions are applicable 2 Kinetic and potential energy changes are negligible 3 Air is
an ideal gas with constant specific heats
Properties The properties of air at room temperature are c p = 1.005 kJ/kg·K, cv = 0.718 kJ/kg·K, R = 0.287 kJ/kg·K, and
k = 1.4 (Table A-2)
Analysis The specific volume of the air at the start of the compression is
/kg m 9076 0 kPa
80
K) 253 )(
K /kg m kPa 287 0
1
1
P
RT
v
and the specific volume at the end of the compression is
/kg m 06483 0 14
/kg m 9076
1
r
v
v
The pressure at the end of the compression is
14 3219kPa kPa)
80
1 2
1 1
k
r P P
P
v v
and the maximum pressure is
kPa 4829
The temperature at the end of the compression is
14 727.1K K)
253
1 1 1
2
1 1
k k
r T T
T
v v
kPa 3219
kPa 4829 K) 1 727 (
2
3
P
P T
T x
From the definition of cutoff ratio
/kg m 07780 0 ) /kg m 06483 0 )(
2 1
2
v
c x
r
The remaining state temperatures are then
K 1309
0.06483
0.07780 K)
1091 (
3 3
x x
T
T
v v
K 0 490 0.9076
0.07780 K)
1309 (
1 4 1 1
4
3 3
k
T
T
v v
Applying the first law and work expression to the heat addition processes gives
kJ/kg 480.4
K ) 1091 1309 )(
K kJ/kg 005 1 ( K ) 1 727 1091 )(
K kJ/kg 718 0
(
) ( )
in c T x T c p T T x
The heat rejected is
kJ/kg 2 170 K ) 253 0 490 )(
K kJ/kg 718 0 ( )
kJ/kg 480.4
kJ/kg 170.2 1 1
in
out th
q
q
v
P
4
1
2
3
qout
x
qin
Downloaded by Pham Quang Huy (ebook4you.online@gmail.com)
lOMoARcPSD|3280145