Modern Engineering Thermodynamics

94 CHAPTER 3: Thermodynamic Properties
40. Determine the temperature of carbon dioxide (CO 2 ) gas when it
is at a pressure of 2500. psia and has a density of 32.0 lbm/ft 3 .
Assume constant specific heat ideal gas behavior.
41. Calculate the specific volume of propane at 1000. psia and
300.°F using
a. The ideal gas equation of state.
b. The Clausius equation of state (use the van der Waals value
for b).
42. Determine the pressure exerted by 10.00 lbm of steam at a
temperature of 1300.°F in a volume of 3.285 ft 3 using
a. The steam tables.
b. The ideal gas equation of state.
c. The van der Waals equation of state.
43. a. Write down the van der Waals equation.
b. Indicate which term corrects for the fact that the molecules
occupy a finite volume.
c. Indicate which term corrects for the fact that there are
attractive forces between the molecules.
d. How are the constants a and b in van der Waals equation
determined, and are they the same for all gases?
44. For superheated Refrigerant-134a at 100. psia and 100.°F,
determine the value of the specific volume
a. From the superheated vapor table.
b. Assuming it to be an ideal gas.
c. From the van der Waals equation of state.
45. Estimate the temperature to which water at the bottom of a 500. ft
deep lake would have to be heated before it would begin to
boil (Figure 3.30). (Note: Hydrostatic pressure = γz, where
γ = 62.4 lbf/ft 3 isthespecificweightofwater,andz is the
depth below the free surface.)
FIGURE 3.30
Problem 45.
T sat = ?
z = 500. ft
46. One of the reasons for wearing a pressure suit in high
altitude or space work is that, without it, the pressure in the
body might become low enough to cause the blood to boil.
Assume blood behaves essentially as pure water (which is its
primary component) and that the body core temperature is
100.°F. Find the pressure at which this blood begins to
“boil.”
47. Refrigerant-134a contained in a tank at a pressure of 101.37 psia
has a specific volume of 0.4682 ft 3 /lbm. Using the proper
thermodynamic table, determine the value of the enthalpy of
the Refrigerant-134a under these conditions.
48.* The vapor produced when the pressure on saturated liquid
water is suddenly reduced during a constant enthalpy process
is called flash steam, because it occurs so quickly that part of
the liquid appears to “flash” into vapor. Determine the final
temperature and the percentage of flash steam (i.e., the
quality) produced as the pressure on saturated liquid water at
2.00 MPa is suddenly reduced to 1.00 MPa in a constant
enthalpy process (Figure 3.31)
FIGURE 3.31
Problem 48.
p 1 = 2.00 MPa
x 1 = 0.00
h 1 = h f
Process:
h 2 = h 1
p 2 = 1.00 MPa
x 2 = ?
h 2 = h 1
State 1 State 2
49. What total mass of water must be put into a 1.00 ft 3 sealed,
rigid container so that, when the container is heated, the
contents pass through the saturated vapor curve exactly at the
point where p = 2000. psia (Figure 3.32)
FIGURE 3.32
Problem 49.
2000. psia
p
2
1
1.00 ft 3
"
50.* A rigid container contains 1.00 kg of water at the critical state.
Determine the volume of the vapor present in the container
after it has been cooled to 100.°C.
51. Suppose 0.667 lbm of water is put into a 1.00 ft 3 rigid container
at 14.7 psia and 212°F and sealed. The container is then heated.
a. At what temperature do the contents become a saturated
vapor or saturated liquid?
b. Which will it be—a saturated vapor or a saturated liquid?
c. Sketch this process on a p-v diagram.
52. A closed rigid container contains water in an equilibrium mixture
of liquid and vapor at 70.0°F. The mass of the liquid initially
present is 10.236 times the mass of the vapor. The container is
then heated until all the liquid becomes vapor. Determine
a. The initial quality.
b. The pressure in the container when the last bit of water
becomes vapor.
c. Sketch this process on a p-v diagram.
53.* It is desired to carry out an experiment that allows a visual
observation of a material passing through the critical state. An
empty, transparent, rigid, sealed container with a 2.00 × 10 −6 m 3
internal volume is to be used.
a. How many kilograms of solid CO 2 (dry ice) should be put
into the container so that, when it is sealed and heated, its
contents pass directly through the critical state?
b. To what temperature (in °C) must the contents be heated to
be at the critical state?
c. What will be the pressure (in MPa) inside the container at
the critical state?
54.* Using the tables for compressed liquid water (Tables C.4),
determine the pressure increase required to raise the