Modern Engineering Thermodynamics

200 CHAPTER 6: First Law Open System Applications
p = 200. psia
FIGURE 6.23
Problem 18.
Steam flow
T = 300.°F
p = 20.0 psia
19. Wet steam is throttled adiabatically and aergonically from 800. psia
to 5.00 psia and 200.°F. If the inlet and exit velocities and heights
are equal, what is the ratio of exit area to inlet area for this device?
20.* When the pressure on saturated liquid water is suddenly reduced
in an adiabatic, aergonic, steady flow process, the exit state
temperature must also be reduced to reach the new equilibrium
state. Consequently, part of the initial liquid is very quickly
converted into a saturated vapor at the lower pressure, with the
vaporization energy (i.e., heat of vaporization) coming from the
remaining liquid. In this way, the remaining liquid is cooled to
the new (lower) equilibrium temperature. The resulting vapor is
called flash steam because the liquid appears to “flash” into a
vapor as it expands into the low-pressure region. Determine the
exit temperature and percent of flash steam produced as saturated
liquid water at 10.0 MPa is throttled through a partially open
valve and discharged into the atmosphere adiabatically,
aergonically, and with no change in kinetic or potential energy.
21. Refrigerant-22 is flowing steadily through a refrigerator throttling
valve at the rate of 10.0 lbm/min. At the valve inlet, the R-22 is
a saturated liquid at 80.0°F. At the valve outlet, the pressure is
31.162 psia. If the process can be considered aergonic, adiabatic,
and with no change in kinetic or potential energy, find the
quality at the valve outlet.
22.* The insulated vortex tube shown in Figure 6.24 contains no
moving mechanical parts, yet it has the ability to separate the
inlet air flow stream into hot and cold outlet air flow streams.
Recorded test data are
23. Aerosol sprays are commonly used today for such things as hair
sprays, shaving creams, deodorants, paints, and perfumes. At
times, various inert gases have been used as the propellant
medium for the active chemicals. Consider the design of a new
deodorant that uses ammonia as the propellant medium. The
spraying process is a simple throttling process (neglect kinetic
and potential energy terms). If the can is at 80.0°F and 70.0 psia
and it is spread into the atmosphere at 15.0 psia, then (a) at
what temperature does the ammonia spray enter the
atmosphere? (b) Draw this process on an h-T diagram and label
all the relevant enthalpies and temperatures.
24.* Determine the inlet quality and the Joule-Thomson coefficient of
wet steam that is throttled from 1.00 to 0.100 MPa and 150.°C.
25.* Estimate the Joule-Thomson temperature change that occurs
as air is throttled from a pressure of 100. atm and 50.0°C to
1.00 atm.
26.* Estimate the Joule-Thomson temperature change as carbon
dioxide is throttled from a pressure of 60.0 atm and exactly 0°C
to 1.00 atm.
27. Refrigerant-22 enters a condenser at 30.0°F with a quality of
85.0% at a mass flow rate of 5.00 lbm/min. What is the
smallest diameter tubing that can be used if the velocity of the
refrigerant must not exceed 20.0 ft/s?
28.* How much electrical power (in kilowatts) is required to
isothermally convert 10.0 kg/min of water from a saturated
liquid to a saturated vapor at 100.°C in an electrically heated
and completely insulated electric boiler?
29.* The hot and cold water faucets on a bathroom sink have water
available at 80.0 and 15.0°C, respectively. When the faucets are
opened, the sink drain is also open so that water leaves the sink
as fast as it enters. Determine the ratio of hot water to cold
water mass flow rates needed to produce a mixture temperature
of 30.0°C in the sink.
30. The steady state, steady flow, adiabatic, aergonic feedwater
heater shown in Figure 6.25 is used in an electric power plant. It
mixes superheated steam with saturated liquid water to produce
a low-quality outflow, in which 10.0 lbm/s of superheated
steam at 80.0 psia and 500.°F is mixed with saturated liquid
water at 80.0 psia. The outlet stream has a quality of 10.0% at
80.0 psia. What is the mass flow rate of the saturated liquid
water flow stream?
Inlet pressure, p 1 = 0:690 MPa gauge
Inlet temperature, T 1 = 20:0°C
Hot side outlet temperature, T H = 82:0°C
Hot side mass flow rate, _m H = 0:136 kg/min
Cold side mass flow rate, _m C = 0:318 kg/min
Calculate the cold side temperature, T c .
Superheated
steam
Saturated
liquid water
FIGURE 6.25
Problem 30.
Feedwater
heater
Mixture at
80.0 psia and
10.0% quality
m H
FIGURE 6.24
Problem 22.
m in
p in
m C
T C = ?
31.* An insulated aergonic condenser for a large power plant receives
3.00 × 10 6 kg/h of saturated water vapor at 6.00 kPa from a
turbine and condenses it to saturated liquid at 6.00 kPa. Lake
water is used to condense the steam and it is desired to
maintain the inlet water temperature at 4.50°C and the outlet
water temperature at 15.5°C. (a) What flow rate of lake water is
required for an adiabatic, aergonic condenser and (b) what is
the rate of heat transfer from the condensing steam to the lake
water?