10–1C What is boiling? What mechanisms are responsible for the very high heat transfer coefficients in nucleate boiling
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10–2C
Does the amount of heat absorbed as 1 kg of saturated liquid water
boils at 100°C have to be equal to the amount of heat released as 1 kg
of saturated water vapor condenses at 100°C?
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10–3C What is the difference between evaporation and boiling
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10–4C What is the difference between pool boiling and flow boiling
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10–5C What is the difference between subcooled and saturated boiling
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10–6C Draw the boiling curve and identify the different boiling regimes. Also, explain the characteristics of each regime
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10–7C
How does film boiling differ from nucleate boiling? Is the boiling heat
flux necessarily higher in the stable film boiling regime than it is in
the nucleate boiling regime
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10–8C
Draw the boiling curve and identify the burnout point on the curve.
Explain how burnout is caused. Why is the burnout point avoided in the
design of boilers
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10–9C Discuss some methods of enhancing pool boiling heat transfer permanently
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10–10C Name the different boiling regimes in the order they occur in a vertical tube during flow boiling
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10–11
Water is to be boiled at atmospheric pressure in a mechanically
polished steel pan placed on top of a heating unit. The inner surface of
the bottom of the pan is maintained at 110°C. If the diameter of the
bottom of the pan is 25 cm, determine (a) the rate of heat transfer to
the water and (b) the rate of evaporation.
Get solution
10–12
Water is to be boiled at atmospheric pressure on a 3-cm-diameter
mechanically polished steel heater. Determine the maximum heat flux that
can be attained in the nucleate boiling regime and the surface
temperature of the heater surface in that case
Get solution
10–13
Reconsider Problem 10–12. Using EES (or other) software, investigate
the effect of local atmospheric pressure on the maximum heat flux and
the temperature difference Ts - Tsat. Let the atmospheric pressure vary
from 70 kPa and 101.3 kPa. Plot the maximum heat flux and the
temperature difference as a function of the atmospheric pressure, and
discuss the results
Get solution
10–14E
Water is boiled at atmospheric pressure by a horizontal polished copper
heating element of diameter D 0.5 in. and emissivity E=0.08 immersed in
water. If the surface temperature of the heating element is 788°F,
determine the rate of heat transfer to the water per unit length of the
heating element.
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10–15E Repeat Problem 10–14E for a heating element temperature of 988°F
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10–16
Water is to be boiled at sea level in a 30-cm-diameter mechanically
polished AISI 304 stainless steel pan placed on top of a 3-kW electric
burner. If 60 percent of the heat generated by the burner is transferred
to the water during boiling, determine the temperature of the inner
surface of the bottom of the pan. Also, determine the temperature
difference between the inner and outer surfaces of the bottom of the pan
if it is 6 mm thick.
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10–17
Repeat Problem 10–16 for a location at an elevation of 1500 m where the
atmospheric pressure is 84.5 kPa and thus the boiling temperature of
water is 95°C.
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10–18
Water is boiled at sea level in a coffee maker equipped with a 20-cm
long 0.4-cm-diameter immersion-type electric heating element made of
mechanically polished stainless steel. The coffee maker initially
contains 1 Lof water at 18°C. Once boiling starts, it is observed that
half of the water in the coffee maker evaporates in 25 min. Determine
the power rating of the electric heating element immersed in water and
the surface temperature of the heating element. Also determine how long
it will take for this heater to raise the temperature of 1 L of cold
water from 18°C to the boiling temperature
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10–19 Repeat Problem 10–18 for a copper heating element
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10–20
A65-cm-long, 2-cm-diameter brass heating element is to be used to boil
water at 120°C. If the surface temperature of the heating element is not
to exceed 125°C, determine the highest rate of steam production in the
boiler, in kg/h.
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10–21
To understand the burnout phenomenon, boiling experiments are conducted
in water at atmospheric pressure using an electrically heated
30-cm-long, 3-mm-diameter nickelplated horizontal wire. Determine (a)
the critical heat flux and (b) the increase in the temperature of the
wire as the operating point jumps from the nucleate boiling to the film
boiling regime at the critical heat flux. Take the emissivity of the
wire to be 0.5
Get solution
10–22
Reconsider Problem 10–21. Using EES (or other) software, investigate
the effects of the local atmospheric pressure and the emissivity of the
wire on the critical heat flux and the temperature rise of wire. Let the
atmospheric pressure vary from 70 kPa and 101.3 kPa and theemissivity
from 0.1 to 1.0. Plot the critical heat flux and the temperature rise as
functions of the atmospheric pressure and the emissivity, and discuss
the results
Get solution
10–23
Water is boiled at 1 atm pressure in a 20-cm-internaldiameter
teflon-pitted stainless steel pan on an electric range. If it is
observed that the water level in the pan drops by 10 cm in 30 min,
determine the inner surface temperature of the pan.
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10–24 Repeat Problem 10–23 for a polished copper pan
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10–25
In a gas-fired boiler, water is boiled at 150°C by hot gases flowing
through 50-m-long, 5-cm-outer-diameter mechanically polished stainless
steel pipes submerged in water. If the outer surface temperature of the
pipes is 165°C, determine (a) the rate of heat transfer from the hot
gases to water, (b) the rate of evaporation, (c) the ratio of the
critical heat flux to the present heat flux, and (d) the surface
temperature of the pipe at which critical heat flux occurs.
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10–26 Repeat Problem 10–25 for a boiling temperature of 160°C
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10–27E
Water is boiled at 250°F by a 2-ft-long and 0.5-in.diameter
nickel-plated electric heating element maintained at 280°F. Determine
(a) the boiling heat transfer coefficient,(b) the electric power
consumed by the heating element, and (c) the rate of evaporation of
water
Get solution
10–28E Repeat Problem 10–27E for a platinum-plated heating element
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10–29E
Reconsider Problem 10–27E. Using EES (or other) software, investigate
the effect of surface temperature of the heating element on the boiling
heat transfer coefficient, the electric power, and the rate of
evaporation of water. Let the surface temperature vary from 260°F to
300°F. Plot the boiling heat transfer coefficient, the electric power
consumption, and the rate of evaporation of water as a function of the
surface temperature, and discuss the results
Get solution
10–30
Cold water enters a steam generator at 15°C and leaves as saturated
steam at 100°C. Determine the fraction of heat used to preheat the
liquid water from 15°C to the saturation temperature of 100°C in the
steam generator.
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10–31
Cold water enters a steam generator at 20°C and leaves as saturated
steam at the boiler pressure. At what pressure will the amount of heat
needed to preheat the water to saturation temperature be equal to the
heat needed to vaporize the liquid at the boiler pressure
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10–32
Reconsider Problem 10–31. Using EES (or other) software, plot the
boiler pressure as a function of the cold water temperature as the
temperature varies from 0°C to 30°C, and discuss the results
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10–33
A 50-cm-long, 2-mm-diameter electric resistance wire submerged in water
is used to determine the boiling heat transfer coefficient in water at 1
atm experimentally. The wire temperature is measured to be 130°C when a
wattmeter indicates the electric power consumed to be 3.8 kW. Using
Newton’s law of cooling, determine the boiling heat transfer
coefficient.
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10–34C What is condensation? How does it occur
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10–35C What is the difference between film and dropwise condensation? Which is a more effective mechanism of heat transfer
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10–36C In condensate flow, how is the wetted perimeter defined? How does wetted perimeter differ from ordinary perimeter
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10–37C
What is the modified latent heat of vaporization? For what is it used?
How does it differ from the ordinary latent heat of vaporization
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10–38C
Consider film condensation on a vertical plate. Will the heat flux be
higher at the top or at the bottom of the plate? Why
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10–39C
Consider film condensation on the outer surfaces of a tube whose length
is 10 times its diameter. For which orientation of the tube will the
heat transfer rate be the highest: horizontal or vertical? Explain.
Disregard the base and top surfaces of the tube
Get solution
10–40C
Consider film condensation on the outer surfaces of four long tubes.
For which orientation of the tubes will the condensation heat transfer
coefficient be the highest: (a) vertical, (b) horizontal side by side,
(c) horizontal but in a vertical tier (directly on top of each other),
or (d) a horizontal stack of two tubes high and two tubes wide
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10–41C How does the presence of a noncondensable gas in a vapor influence the condensation heat transfer
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10–42
The Reynolds number for condensate flow is defined as Re = 4m · /pul,
where p is the wetted perimeter. Obtain simplified relations for the
Reynolds number by expressing p and m · by their equivalence for the
following geometries: (a) a vertical plate of height Land width w, (b) a
tilted plate of height L and width w inclined at an angle O from the
vertical, (c) a vertical cylinder of length L and diameter D, (d) a
horizontal cylinder of length L and diameter D, and (e) a sphere of
diameter D
Get solution
10–43
Consider film condensation on the outer surfaces of N horizontal tubes
arranged in a vertical tier. For what value of N will the average heat
transfer coefficient for the entire stack of tubes be equal to half of
what it is for a single horizontal tube?
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10–44
Saturated steam at 1 atm condenses on a 3-m-high and 5-m-wide vertical
plate that is maintained at 90°C by circulating cooling water through
the other side. Determine (a) the rate of heat transfer by condensation
to the plate, and (b) the rate at which the condensate drips off the
plate at the bottom.
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10–45 Repeat Problem 10–44 for the case of the plate being tilted 60° from the vertical
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10–46
Saturated steam at 30°C condenses on the outside of a
4-cm-outer-diameter, 2-m-long vertical tube. The temperature of the tube
is maintained at 20°C by the cooling water. Determine (a) the rate of
heat transfer from the steam to the cooling water, (b) the rate of
condensation of steam, and (c) the approximate thickness of the liquid
film at the bottom of the tube.
Get solution
10–47E
Saturated steam at 95°F is condensed on the outer surfaces of an array
of horizontal pipes through which cooling water circulates. The outer
diameter of the pipes is 1 in. and the outer surfaces of the pipes are
maintained at 85°F. Determine (a) the rate of heat transfer to the
cooling water circulating in the pipes and (b) the rate of condensation
of steam per unit length of a single horizontal pipe.
Get solution
10–48E
Repeat Problem 10–47E for the case of 32 horizontal pipes arranged in a
rectangular array of 4 pipes high and 8 pipes wide
Get solution
10–49
Saturated steam at 55°C is to be condensed at a rate of 10 kg/h on the
outside of a 3-cm-outer-diameter vertical tube whose surface is
maintained at 45°C by the cooling water. Determine the tube length
required
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10–50 Repeat Problem 10–49 for a horizontal tube.
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10–51
Saturated steam at 100°C condenses on a 2-m 2-m plate that is tilted
40°from the vertical. The plate is maintained at 80°C by cooling it from
the other side. Determine (a) the average heat transfer coefficient
over the entire plate and (b) the rate at which the condensate drips off
the plate at the bottom
Get solution
10–52
Reconsider Problem 10–51. Using EES (or other) software, investigate
the effects of plate temperature and the angle of the plate from the
vertical on the average heat transfer coefficient and the rate at which
the condensate drips of
f. Let the plate temperature vary from 40°C to 90°C and the plate
angle from 0° to 60°. Plot the heat transfer coefficient and the rate at
which the condensate drips off as the functions of the plate
temperature and the tilt angle, and discuss the results
Get solution
10–53
Saturated ammonia vapor at 10°C condenses on the outside of a
2-cm-outer-diameter, 8-m-long horizontal tube whose outer surface is
maintained at -10°C. Determine (a) the rate of heat transfer from the
ammonia and (b) the rate of condensation of ammonia
Get solution
10–54
The condenser of a steam power plant operates at a pressure of 4.25
kPa. The condenser consists of 100 horizontal tubes arranged in a 10 x
10 square array. The tubes are 8 m long and have an outer diameter of 3
cm. If the tube surfaces are at 20°C, determine (a) the rate of heat
transfer from the steam to the cooling water and (b) the rate of
condensation of steam in the condenser.
Get solution
10–55
Reconsider Problem 10–54. Using EES (or other) software, investigate
the effect of the condenser pressure on the rate of heat transfer and
the rate of condensation of the steam. Let the condenser pressure vary
from 3 kPa to 15 kPa. Plot the rate of heat transfer and the rate of
condensation of the steam as a function of the condenser pressure, and
discuss the results
Get solution
10–56
Alarge heat exchanger has several columns of tubes, with 20 tubes in
each column. The outer diameter of the tubes is 1.5 cm. Saturated steam
at 50°C condenses on the outer surfaces of the tubes, which are
maintained at 20°C. Determine (a) the average heat transfer coefficient
and (b) the rate of condensation of steam per m length of a column
Get solution
10–57
Saturated refrigerant-134a vapor at 30°C is to be condensed in a
5-m-long, 1-cm-diameter horizontal tube that is maintained at a
temperature of 20°C. If the refrigerant enters the tube at a rate of 2.5
kg/min, determine the fraction of the refrigerant that will have
condensed at the end of the tube
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10–58 Repeat Problem 10–57 for a tube length of 8 m.
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10–59
Reconsider Problem 10–57. Using EES (or other) software, plot the
fraction of the refrigerant condensed at the end of the tube as a
function of the temperature of the saturated R-134a vapor as the
temperature varies from 25°C to 50°C, and discuss the results.
Get solution
10–60C What is a heat pipe? How does it operate? Does it have any moving parts
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10–61C
Aheat pipe with water as the working fluid is said to have an effective
thermal conductivity of 100,000 W/m · °C, which is more than 100,000
times the conductivity of water. How can this happen
Get solution
10–62C What is the effect of a small amount of noncondensable gas such as air on the performance of a heat pipe
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10–63C Why do water-based heat pipes used in the cooling of electronic equipment operate below atmospheric pressure
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10–64C What happens when the wick of a heat pipe is too coarse or too fine
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10–65C
Does the orientation of a heat pipe affect its performance? Does it
matter if the evaporator end of the heat pipe is up or down? Explain
Get solution
10–66C
How can the liquid in a heat pipe move up against gravity without a
pump? For heat pipes that work against gravity, is it better to have
coarse or fine wicks? Why?
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10–67C What are the important considerations in the design and manufacture of heat pipes
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10–68C What is the major cause for the premature degradation of the performance of some heat pipes
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10–69
A40-cm-long cylindrical heat pipe having a diameter of 0.5 cm is
dissipating heat at a rate of 150 W, with a temperature difference of
4°C across the heat pipe. If we were to use a 40-cm-long copper rod (k
386 W/m · °C and 8950 kg/m3) instead to remove heat at the same rate,
determine the diameter and the mass of the copper rod that needs to be
installed
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10–70 Repeat Problem 10–69 for an aluminum rod instead of copper
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10–71E
Aplate that supports 10 power transistors, each dissipating 35 W, is to
be cooled with 1-ft-long heat pipes having a diameter of in. Using
Table 10–6, determine how many pipes need to be attached to this plate.
Get solution
10–72
Steam at 40°C condenses on the outside of a 3-cm diameter thin
horizontal copper tube by cooling water that enters the tube at 25°C at
an average velocity of 2 m/s and leaves at 35°C. Determine the rate of
condensation of steam, the average overall heat transfer coefficient
between the steam and the cooling water, and the tube length.
Get solution
10–73
Saturated ammonia vapor at 25°C condenses on the outside of a 2-m-long,
3.2-cm-outer-diameter vertical tube maintained at 15°C. Determine (a)
the average heat transfer coefficient, (b) the rate of heat transfer,
and (c) the rate of condensation of ammonia
Get solution
10–74
Saturated isobutane vapor in a binary geothermal power plant is to be
condensed outside an array of eight horizontal tubes. Determine the
ratio of the condensation rate for the cases of the tubes being arranged
in a horizontal tier versus in a vertical tier of horizontal tubes.
Get solution
10–75E
The condenser of a steam power plant operates at a pressure of 0.95
psia. The condenser consists of 144 horizontal tubes arranged in a 12 12
square array. The tubes are 15 ft long and have an outer diameter of
1.2 in. If the outer surfaces of the tubes are maintained at 80°F,
determine (a) the rate of heat transfer from the steam to the cooling
water and (b) the rate of condensation of steam in the condenser
Get solution
10–76E Repeat Problem 10–75E for a tube diameter of 2 in
Get solution
10–77
Water is boiled at 100°C electrically by a 80-cm-long, 2-mm-diameter
horizontal resistance wire made of chemically etched stainless steel.
Determine (a) the rate of heat transfer to the water and the rate of
evaporation of water if the temperature of the wire is 115°C and (b) the
maximum rate of evaporation in the nucleate boiling regime.
Get solution
10–78E
Saturated steam at 100°F is condensed on a 6-ft-high vertical plate
that is maintained at 80°F. Determine the rate of heat transfer from the
steam to the plate and the rate of condensation per foot width of the
plate
Get solution
10–79
Saturated refrigerant-134a vapor at 35°C is to be condensed on the
outer surface of a 7-m-long, 1.5-cm-diameter horizontal tube that is
maintained at a temperature of 25°C. Determine the rate at which the
refrigerant will condense, in kg/min
Get solution
10–80 Repeat Problem 10–79 for a tube diameter of 3 cm
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10–81
Saturated steam at 270.1 kPa condenses inside a horizontal, 6-m-long,
3-cm-internal-diameter pipe whose surface is maintained at 110°C.
Assuming low vapor velocity, determine the average heat transfer
coefficient and the rate of condensation of the steam inside the pipe.
Get solution
10–82
A 1.5-cm-diameter silver sphere initially at 30°C is suspended in a
room filled with saturated steam at 100°C. Using the lumped system
analysis, determine how long it will take for the temperature of the
ball to rise to 50°C. Also, determine the amount of steam that condenses
during this process and verify that the lumped system analysis is
applicable
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10–83 Repeat Problem 10–82 for a 3-cm-diameter copper ball
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10–84
You have probably noticed that water vapor that condenses on a canned
drink slides down, clearing the surface for further condensation.
Therefore, condensation in this case can be considered to be dropwise.
Determine the condensation heat transfer coefficient on a cold canned
drink at 5°C that is placed in a large container filled with saturated
steam at 95°C.
Get solution
10–85
A resistance heater made of 2-mm-diameter nickel wire is used to heat
water at 1 atm pressure. Determine the highest temperature at which this
heater can operate safely without the danger of burning out.
Get solution
