PROBLEM 1.8
KNOWN: Net power output, average compressor and turbine temperatures, shaft dimensions and
thermal conductivity.
FIND: (a) Comparison of the conduction rate through the shaft to the predicted net power output of
the device, (b) Plot of the rat
PROBLEM 1.40
KNOWN: Width, surface emissivity and maximum allowable temperature of an electronic chip.
Temperature of air and surroundings. Convection coefficient.
2
1/4
FIND: (a) Maximum power dissipation for free convection with h(W/m K) = 4.2(T - T) ,
PROBLEM 1.39
KNOWN: Hot and cold reservoir temperatures of an internally reversible refrigerator. Thermal
resistances between refrigerator and hot and cold reservoirs under clean and dusty conditions. Desired
cooling rate.
FIND: Modified Coefficient of Pe
PROBLEM 1.38
KNOWN: Hot and cold reservoir temperatures of an internally reversible refrigerator. Thermal
resistances between refrigerator and hot and cold reservoirs.
FIND: Expressions for modified Coefficient of Performance and power input of refrigerat
PROBLEM 1.37
KNOWN: Flow of water in a vertical tube. Tube dimensions. Mass flow rate. Inlet pressure and
temperature. Heat rate. Outlet pressure.
FIND: (a) Outlet temperature, (b) change in combined thermal and flow work, (c) change in
mechanical energy,
PROBLEM 1.36
KNOWN: Inlet and outlet conditions for flow of water in a vertical tube.
FIND: (a) Change in combined thermal and flow work, (b) change in mechanical energy, and (c)
change in total energy of the water from the inlet to the outlet of the tube
PROBLEM 1.35
KNOWN: Resistor connected to a battery operating at a prescribed temperature in air.
&
FIND: (a) Considering the resistor as the system, determine corresponding values for Ein ( W ) ,
&
&
&
E g ( W ) , E out ( W ) and Est ( W ) . If a control
PROBLEM 1.34
KNOWN: Vacuum enclosure maintained at 77 K by liquid nitrogen shroud while baseplate is
maintained at 300 K by an electrical heater.
FIND: (a) Electrical power required to maintain baseplate, (b) Liquid nitrogen consumption rate, (c)
Effect o
PROBLEM 1.33
KNOWN: Exact and approximate expressions for the linearized radiation coefficient, hr and hra,
respectively.
FIND: (a) Comparison of the coefficients with = 0.05 and 0.9 and surface temperatures which may
exceed that of the surroundings (Tsur
PROBLEM 1.32
KNOWN: Hot plate suspended in vacuum and surroundings temperature. Mass, specific heat, area
and time rate of change of plate temperature.
FIND: (a) The emissivity of the plate, and (b) The rate at which radiation is emitted from the plate.
S
PROBLEM 1.31
KNOWN: Spherical shaped instrumentation package with prescribed surface emissivity within a
large space-simulation chamber having walls at 77 K.
FIND: Acceptable power dissipation for operating the package surface temperature in the range Ts
PROBLEM 1.30
KNOWN: Diameter and emissivity of spherical interplanetary probe. Power dissipation
within probe.
FIND: Probe surface temperature.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) Negligible radiation incident on the probe.
ANALYSIS:
PROBLEM 1.29
KNOWN: Air and wall temperatures of a room. Surface temperature, convection coefficient
and emissivity of a person in the room.
FIND: Basis for difference in comfort level between summer and winter.
SCHEMATIC:
ASSUMPTIONS: (1) Person may be a
PROBLEM 1.28
KNOWN: Length, diameter, surface temperature and emissivity of steam line. Temperature
and convection coefficient associated with ambient air. Efficiency and fuel cost for gas fired
furnace.
FIND: (a) Rate of heat loss, (b) Annual cost of hea
PROBLEM 1.27
KNOWN: Upper temperature set point, Tset, of a bimetallic switch and convection heat
transfer coefficient between clothes dryer air and exposed surface of switch.
FIND: Electrical power for heater to maintain Tset when air temperature is T =
PROBLEM 1.26
KNOWN: Chip width and maximum allowable temperature. Coolant conditions.
FIND: Maximum allowable chip power for air and liquid coolants.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) Negligible heat transfer from sides and
bottom,
PROBLEM 1.25
KNOWN: Length, diameter and calibration of a hot wire anemometer. Temperature of air
stream. Current, voltage drop and surface temperature of wire for a particular application.
FIND: Air velocity
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state condi
PROBLEM 1.24
KNOWN: Dimensions of a cartridge heater. Heater power. Convection coefficients in air
and water at a prescribed temperature.
FIND: Heater surface temperatures in water and air.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) All of t
PROBLEM 1.23
KNOWN: Width, input power and efficiency of a transmission. Temperature and convection
coefficient associated with air flow over the casing.
FIND: Surface temperature of casing.
SCHEMATIC:
ASSUMPTIONS: (1) Steady state, (2) Uniform convection
PROBLEM 1.22
KNOWN: Hot vertical plate suspended in cool, still air. Change in plate temperature with time at the
instant when the plate temperature is 225C.
FIND: Convection heat transfer coefficient for this condition.
SCHEMATIC:
-0.022
-0.022 K/s
ASSUM
PROBLEM 1.21
KNOWN: Long, 30mm-diameter cylinder with embedded electrical heater; power required
to maintain a specified surface temperature for water and air flows.
FIND: Convection coefficients for the water and air flow convection processes, hw and ha,
PROBLEM 1.20
KNOWN: Inner and outer surface temperatures of a wall. Inner and outer air temperatures and
convection heat transfer coefficients.
FIND: Heat flux from inner air to wall. Heat flux from wall to outer air. Heat flux from wall to
inner air. Whe
PROBLEM 1.19
KNOWN: Power required to maintain the surface temperature of a long, 25-mm diameter cylinder
with an imbedded electrical heater for different air velocities.
FIND: (a) Determine the convection coefficient for each of the air velocity conditio
PROBLEM 1.18
KNOWN: Hand experiencing convection heat transfer with moving air and water.
FIND: Determine which condition feels colder. Contrast these results with a heat loss of 30 W/m2 under
normal room conditions.
SCHEMATIC:
ASSUMPTIONS: (1) Temperatur
PROBLEM 1.17
KNOWN: Heat flux and convection heat transfer coefficient for boiling water. Saturation
temperature and convection heat transfer coefficient for boiling dielectric fluid.
FIND: Upper surface temperature of plate when water is boiling. Whether
PROBLEM 1.16
KNOWN: Dimensions and thermal conductivity of a chip. Power dissipated on one surface.
FIND: Temperature drop across the chip.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) Constant properties, (3) Uniform heat
dissipation, (4) Neg
PROBLEM 1.15
KNOWN: Thickness, diameter and inner surface temperature of bottom of pan used to boil
water. Rate of heat transfer to the pan.
FIND: Outer surface temperature of pan for an aluminum and a copper bottom.
SCHEMATIC:
ASSUMPTIONS: (1) One-dimens
PROBLEM 1.14
KNOWN: Expression for variable thermal conductivity of a wall. Constant heat flux.
Temperature at x = 0.
FIND: Expression for temperature gradient and temperature distribution.
SCHEMATIC:
k = ax + b
q
T1
x
ASSUMPTIONS: (1) One-dimensional con
PROBLEM 1.13
KNOWN: Masonry wall of known thermal conductivity has a heat rate which is 80% of that
through a composite wall of prescribed thermal conductivity and thickness.
FIND: Thickness of masonry wall.
SCHEMATIC:
ASSUMPTIONS: (1) Both walls subjecte
PROBLEM 1.12
KNOWN: Dimensions and thermal conductivity of food/beverage container. Inner and outer
surface temperatures.
FIND: Heat flux through container wall and total heat load.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) Negligible heat