(3) are T
3
= 300°C, and v
3
= 0.2 m
3
/ kg. On scanning the
superheat
tables
we find that the closest values lie somewhere between 1.2 MPa
and 1.4 MPa, thus we use linear interpolation techniqes to determine
the actual pressure P
3
as shown below:
Two kilograms of water at 25°C are placed in a piston cylinder device under
3.2 MPa pressure as shown in the diagram (State (1)). Heat is added to the
water at constant pressure until the temperature of the fluid reaches 350°C
(State (2)). Determine the final volume of the fluid at state (2).
In this example since the pressure is known (3.2 MPa) and remains constant
throughout the process, we find it convenient to draw a
P-v
diagram

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indicating the process (1) - (2) as follows.
As in the previous example, on scanning the
superheat tables
we find that
we need to interpolate between pressure P = 3.0 MPa and P = 3.5 MPa in
order to determine the specific volume at the required pressure of 3.2 MPa
as follows:

PROBLEM 3
A piston-cylinder device contains a saturated mixture of steam and water
having a total mass of 0.5 kg at a pressure of 160 kPa and an initial volume
of 100 liters. Heat is then added and the fluid expands at constant pressure
until it reaches a saturated vapor state.
a) Draw a diagram representing the process showing the initial and final
states of the system.
b) Sketch this process on a
P-v
diagram with respect to the saturation lines,
critical point, and relevant constant temperature lines, clearly indicating the
initial and final states.
c) Determine the initial quality and temperature of the fluid mixture prior to
heating.
[quality x
1
= 0.182, T
1
= 113.3°C]
d) Determine the final volume of the steam after heating.
[0.546 m
3
(546
liters)]

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PROBLEM 4
A pressure cooker allows much faster (and more tender) cooking by
maintaining a higher boiling temperature of the water inside. It is well
sealed, and steam can only escape through an opening on the lid, on which
sits a metal petcock. When the pressure overcomes the weight of the
petcock, the steam escapes, maintaining a constant high pressure while the
water boils.
Assuming that the opening under the petcock has an area of 8 mm
2
,
determine :
a) the mass of the petcock required in order to maintain an operating
pressure of 99 kPa gage.
[80.7gm]
b) the corresponding temperature of the boiling water.
[120.2°C]
Note: Assume that the atmospheric pressure is 101 kPa. Draw a free body
diagram of the petcock.

- Fall '19