Modern Engineering Thermodynamics

Problems 161
Problems (* indicates problems in SI units)
1.* One kg of liquid water at 20.0°C is poured from a height of
10.0 m directly onto the floor. After a short time, the specific
internal energy of the water on the floor has returned to its
initial value before it was poured.
a. What total heat transport of energy occurred during this
process (ignore evaporation effects)?
b. In which direction was this heat transport of energy, into or
out of the water?
2. Determine the direction and amount of heat transfer required to
raise the temperature of the contents of a rigid, sealed,
subterranean silicon sphere containing 10.0 lbm of saturated
water vapor from 280. to 1000.°F, 100. psia. Fill in the
following table (with correct units) and show all calculations.
Unknown: 1 Q 2 =?
Process ¼ ?
ƒƒƒƒƒƒƒ!
State 1
State 2
x 1 = 1:00
p 2 = 100: psia
T 1 = 208°F
T 2 = 1000:°F
p 1 = ? x 2 = ?
u 1 = ? u 2 = ?
3.* Determine the direction and amount of heat transfer that
occurs as 3.00 kg of superheated blood (essentially steam)
expands isothermally from 800.°C, 80.0 MPa to 0.100 MPa
doing 500. kJ of work in the process (Figure 5.9). Fill in the
following table (with correct units) and show all calculations.
Unknown: 1 Q 2 =?
FIGURE 5.9
Problem 3.
State 1
Process ¼ ?
ƒƒƒƒƒƒƒ! State 2
1W2 =500 kJ
p 1 = 80:0 MPa
p 2 = 0:100 MPa
T 1 = 800:°C
T 2 = ?
v 1 = ? v 2 = ?
u 1 = ? u 2 = ?
Piston
3.00 kg of superheated
blood
1 Q 2 = ?
4. A rigid, sealed 1936 Ford coupe contains an equilibrium water
liquid-vapor mixture with a quality of 8.8333% at 3.00 psia.
After 500. Btu of heat energy are added to the coupe, the
contents becomes a saturated vapor. What is the total mass of
water in the coupe? Fill in the following table (with correct
units) and show all calculations. Unknown: m =?
State 1
Process = ?
ƒƒƒƒƒƒƒƒƒ! State 2
1Q2 =500 Btu
p 1 = 3:00 psia p 2 = ?
x 1 = 0:088333
x 2 = 1:00
v 1 = ? v 2 = ?
T 1 = ? T 2 = ?
u 1 = ? u 2 = ?
5.* The makers of a new breakfast cereal have a process in which a
rigid, sealed vessel contains 1.00 kg of saturated water vapor at
10.0 MPa. Energy is removed from the vessel as heat transfer
until the pressure drops to 0.100 MPa. Determine the heat
transfer, state its direction, fill in the following table (with
correct units), and show all calculations. Unknown 1 Q 2 =?
State 1
Process = ?
ƒƒƒƒƒƒƒƒƒ! State 2
x 1 = 1:0 T 2 = ?
P 1 = 10:0 MPa
P 2 = 0:100 MPa
v 1 = ? v 2 = ?
T 1 = ? x 2 = ?
u 1 = ? u 2 = ?
6. A rigid sealed fossilized goat’s bladder contains water in a
liquid-vapor equilibrium at 70.0°F. After 300. Btu of heat are
added to the bladder, its contents are converted into a saturated
vapor with a specific volume of 50.2 ft 3 /lbm. What is the total
mass of water in the bladder?
7.* A rigid, sealed 1939 Buick having an internal volume of 6.00 m 3
is filled with steam at 0.70 MPa and 300.°C. Heat is then
transferred from the steam until it has a quality of 100.% while
the contents of the Buick are stirred with a blade requiring
10.0 W·h of work input. Determine (a) the final pressure in the
vessel and (b) the total heat transfer.
8.* Exactly 1.73 kg of water vapor is contained in a piston-cylinder
assembly at a pressure of 1.00 MPa and temperature 600.°C.
The vapor is isothermally compressed to 80.0 MPa. Determine
the sum of the work and heat energy transports in this process.
9. One pound of Refrigerant-134a is put into a piston-cylinder
assembly at an initial pressure and temperature of 200. psia and
200.°F. The R-134a is then slowly heated at constant pressure until
the temperature reaches 300.°F. Determine the work done on or
by the system and the heat transferred to or from the system.
10. The pressure in an isochoric automobile tire increases from
28.0 psia at 70.0°F to 35.0 psia on a trip during hot weather.
Assume the air behaves as an ideal gas. (a) What is the air
temperature inside the tire at the end of the trip. (b) How much
heat is absorbed per unit mass of air in the tire during the trip?
11.* A small room 5.0 × 5.0 × 3.0 m high contains air at 20.0°C and
0.101 MPa. It is the camera stage of a television broadcasting
studio and contains many bright lights for illumination. The
room is closed, sealed, and insulated to isolate the performers
from outside distractions. Assuming air is an ideal gas, find the
temperature and pressure in the room 1.00 h after eight 1000. W
lights are turned on. Assume there is no ventilation or air
conditioning and ignore the effect of people in the room.
12. A room heating system uses steam radiators to heat the room air.
A radiator that has a volume of 3.00 ft 3 is filled with saturated
vapor at a pressure of 15.3 psig and the inlet and exit valves are
closed. How much energy is transferred to the room air as heat at
a time when the pressure in the radiator reaches 3.30 psig.