Example 2-4

PROBLEM STATEMENT:

A sealed volume of 2.0 cm3 contains saturated water. The container is heated from an initial pressure of 0.10 MPa until the vessel contains a single phase. Determine the final state of the water if the vessel contains:

(a) 0.10 gram and

(b) 1.0 gram.

Solution: Part a

Problem

State

P (kPa)

T (oC)

v (m3/kg)

(a)

1

100

99.63

?
 

2

?

?

?

The states are determined by the following steps:

The saturated water tables at 100 kPa = 1 bar are:

P (bar)

T (°C)

vf (m3/kg)
 vg (m3/kg)

 hf (kJ/kg)

 hfg (kJ/kg)
 hg (kJ/kg) 

1.00

99.63

0.0010432

1.694

 417.46

2258.0

2675.5

The quality is then:

since v is constant,

For the final state a saturated vapor, the saturated water tables near this point are:

P (bar)

T (°C)

vf (m3/kg)
 vg (m3/kg)

 hf (kJ/kg)

 hfg (kJ/kg)

hg (kJ/kg) 

90.0

303.4

0.0014178

0.02048

 1363.3

1378.9

 2742.1

100.

311.1

0.0014524

0.01803

1407.6

1317.1

2724.7

By interpolation:

Solution: Part b

Problem

State

P (kPa)

T (oC)

V (m3/kg)

(b)

1

100

99.63

?
 

2

?

?

?

The states are determined by the following steps:

The saturated water tables at 100 kPa = 1 bar are:

P (bar)

T (°C)

vf (m3/kg)
 vg (m3/kg)

 hf (kJ/kg)

 hfg (kJ/kg)
 hg (kJ/kg) 

1.00

99.63

0.0010432

1.694

 417.46

2258.0

2675.5

The quality is then:

since v is constant,

For the final state a saturated liquid, the saturated water tables near this point are:

P (bar)

T (°C)

vf (m3/kg)
 vg (m3/kg)

 hf (kJ/kg)

 hfg (kJ/kg)

hg (kJ/kg) 

190.

361.5

0.0019243

0.006657

 1776.5

688.0

 2464.5

200.

365.8

0.002036

0.005834

1826.3

583.4

2409.7

By interpolation:

Comments:

The specific volume at the critical point for water is 0.00311 m3/kg. This value shows directly that (a) is a saturated vapor (va > vcr) and that (b) is a saturated liquid (vb <vcr).