Microsoft Word - Cengel and Boles TOC _2-03-05_.doc

188 | Thermodynamics

(b) The work done could be determined by integration, but for this case

it is much easier to find it from the area under the process curve on a P-V

diagram, shown in Fig. 4–32:

Therefore,

The work is done by the system (to raise the piston and to push the atmo-

spheric air out of the way), and thus it is work output.

(c) Under the stated assumptions and observations, the energy balance on

the system between the initial and final states (process 1–3) can be

expressed as

Net energy transfer Change in internal, kinetic,

by heat, work, and mass potential, etc., energies

The mass of the system can be determined from the ideal-gas relation:

The internal energies are determined from the air table (Table A–17) to be

Thus,

Discussion The positive sign verifies that heat is transferred to the system.

Qin
767 kJ

Qin140 kJ
 1 0.697 kg 231 1113.52214.07 2 kJ>kg 4

u 3 
u @ 1400 K
1113.52 kJ>kg

u 1 
u @ 300 K
214.07 kJ>kg

m

P 1 V 1

RT 1

1 150 kPa 21 0.4 m^32

1 0.287 kPa#m^3 >kg#K 21 300 K 2

0.697 kg

QinWb,out
¢U
m 1 u 3 u 12

EinEout¬


¬

¢Esystem

W 13 
140 kJ

A
1 V 2 V 12 P 2
1 0.4 m^321 350 kPa 2
140 m^3 #kPa

3

P, kPa

V, m^3

2

350

Q

AIR

P 1 = 150 kPa

V 1 = 400 L

0.4

T 1 = 27°C

150

1

A

0.8

FIGURE 4 –32

Schematic and P-Vdiagram for
Example 4 –10.

Use actual data from the experiment
shown here to obtain the specific heat
of aluminum. See end-of-chapter
problem 4 –180.

© Ronald Mullisen

Use actual data from the experiment
shown here to obtain the specific heat
of aluminum. See end-of-chapter
problem 4 –179.

© Ronald Mullisen

⎭⎪⎬⎪⎫ ⎭⎪⎬⎪⎫

EXPERIMENT

EXPERIMENT