Heat Transfer, 6502481
Name: Prof. F. J. Diez
9/21/2016
Quiz No. 1
An electric heater with the total surface area of 0.25 m2 and emissivity 0.75 is in a room where the air has a
temperature of 20 C and the walls are at 10 C. When the heater consumes 500 W
I Problem
The therrnophysical properties of the bar are p =
2600 kg/m3, c = 1030 J/kg-K, and k = 3.50 W/m-K.
(a) How long should the bar remain in the bath in
order that, when it is removed and allowed to equi-
librate while isolated from any surroundings
4-32
Chapter 7 l External Flow
The rate of heat transfer from the fth heater is then
gm, = (74 WIm2 - K x 0.25 m 67 W/m2 - K x 0.20 m)
X 1 m(230 25)C
qcouv,5 : 1050 W
Similarly, the power requirement for the sixth heater may be obtained by subtracting the
I Problems
(d) What advantage, if any, is there in not making
Ax = Ay for this situation?
With Ax = Ay = 2 mm, calculate the temperature
eld within the plate and the rate of heat transfer
from the plate. Under no circumstances may the
temperature at any l
4-36
Chapter 7 l External Flow
7.4.2 Convection Heat Transfer
Experimental results for the variation of the local Nusselt number with 0 are shown in
Figure 7.10 for the cylinder in a cross ow of air. Not unexpectedly, the results are strongly
inuenced by
378 Chapter 6 I Introduction to Convection
i hus far we have focused on heat transfer by conduction and have considered convection
only to the extent that it provides a possible boundary condition for conduction problems. In
Section 1.2.2 we used the term
I Problem
of 60C be recorded if the convection coefcient is
300 W/m2 - K?
Assess the effect of thermal diffusivity on the ther-
mal response of the material by computing center
and surface temperature histories for a = 106,
105, and 104 m2/s. Plot your re
362
Chapter 5 l Transient Conduction
5.75 A sphere 30 mm in diameter initially at 800 K is
quenched in a large bath having a constant temperature
of 320 K with a convection heat transfer coefcient of
75 W/mZ-K. The therrnophysical properties of the
sphere
530 Chapter 8 l Internal F low
Friction factor correlations for turbulent ow are based on limited data. Furthermore,
heat transfer augmentation due to the secondary ow is minor when the ow is turbulent
and is less than 10% for C/D Z 20. As such, augmentat
872
(e) Determine F12 using the results of Figure 13.4 if
the dimensions are increased to w = L = 2 m.
13.13 Consider the parallel planes of innite extent normal
to the page having opposite edges aligned as shown in
the sketch.
rZmw
:I
1m|
J'i:l
idZmbi
(a
392 Chapter 6 I Introduction to Convection
always be treated as incompressible, density variations in owing gases should be considered
when the velocity approaches or exceeds the speed of sound. Specically, a gradual transition
from incompressible to comp
RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY
Department of Mechanical and Aerospace Engineering
650:481 HEAT TRANSFER
Quiz # 2
October 27, 2015
OPEN BOOK
40 Minutes
NOTE: Draw a sketch of the problem and clearly indicate any assumptions made.
Name: _ Stude
RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY
Department of Mechanical and Aerospace Engineering
650:481 HEAT TRANSFER
Quiz # 2
October 27, 2015
OPEN BOOK
40 Minutes
NOTE: Draw a sketch of the problem and clearly indicate any assumptions made.
Name: _ Stude
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 1.30
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 1.26
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 1.18
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
650:460 Aerodynamics
Chapter 5
Prof. Doyle Knight
Tel: 848 445 4464, Email: doyleknight@gmx.com
Oce hours: Tues 4:30 pm - 6:00 pm and Thurs 3:30 pm 5:00 pm and by appointment
Fall 2015
1
Aerodynamic Forces and Moments
There are two types of forces acting
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 1.2
KNOWN: Thickness and thermal conductivity of a wall. Heat flux applied to one face and
temperatures of both surfaces.
FIND: Whether steady-state conditions exist.
SCHEMATIC:
L = 10 mm
T2 = 30C
q = 20 W/m2
T1 = 50C
qcond
k = 12 W/mK
ASSUMPTIONS
PROBLEM 1.7
KNOWN: Inner and outer surface temperatures of a glass window of prescribed dimensions.
FIND: Heat loss through window.
SCHEMATIC:
ASSUMPTIONS: (1) One-dimensional conduction in the x-direction, (2) Steady-state
conditions, (3) Constant proper
PROBLEM 1.73
KNOWN: Hot plate suspended in a room, plate temperature, room temperature and surroundings
temperature, convection coefficient and plate emissivity, mass and specific heat of the plate.
FIND: (a) The time rate of change of the plate temperatu
PROBLEM 1.62
KNOWN: Elapsed times corresponding to a temperature change from 15 to 14C for a reference
sphere and test sphere of unknown composition suddenly immersed in a stirred water-ice mixture.
Mass and specific heat of reference sphere.
FIND: Specif
PROBLEM 1.81
KNOWN: Conditions associated with surface cooling of plate glass which is initially at 600C.
Maximum allowable temperature gradient in the glass.
FIND: Lowest allowable air temperature, T.
SCHEMATIC:
ASSUMPTIONS: (1) Surface of glass exchange
PROBLEM 1.44
KNOWN: Radial distribution of heat dissipation in a cylindrical container of radioactive
wastes. Surface convection conditions.
FIND: Total energy generation rate and surface temperature.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (