KNOWN: Net power output, average compressor and turbine temperatures, shaft dimensions and
FIND: (a) Comparison of the conduction rate through the shaft to the predicted net power output of
the device, (b) Plot of the rat
KNOWN: Temperature and velocity of engine oil. Temperature and length of flat plate.
FIND: (a) Velocity and thermal boundary layer thickness at trailing edge, (b) Heat flux and surface shear
stress at trailing edge, (c) Total drag force and he
KNOWN: Form of the velocity and temperature profiles for flow over a surface.
FIND: Expressions for the friction and convection coefficients.
ANALYSIS: The shear stress at the wall is
A + 2By 3Cy 2
y=0 = A .
KNOWN: Velocity and temperature profiles for laminar flow in a parallel plate channel.
FIND: Mean velocity, um, and mean (or bulk) temperature, Tm, at this axial position. Plot the velocity
and temperature distributions. Comment on whether val
A rate equation that allows determination of the conduction heat flux
from knowledge of the temperature distribution in a medium
Its most general (vector) form for multidimensional
Sections 1.1 and 1.2
Heat Transfer and Thermal Energy
What is heat transfer?
Heat transfer is thermal energy in transit due to a temperature
What is thermal energy?
Thermal Energy Generation
Sections 3.1 through 3.4
Methodology of a Conduction Analysis
Specify appropriate form of the heat equation.
Solve for the temperature distribution.
Heat Transfer Coefficient
Flows across cylinders and
spheres, in general, involve flow
separation, which is difficult to
Flow across cylinders and
spheres has been studied
experimentally by numerous
investigators, and several
FLOW ACROSS TUBE BANKS
Cross-flow over tube banks is commonly encountered in
practice in heat transfer equipment, e.g., heat
In such equipment, one fluid moves through the tubes
while the other moves over the tubes in a perpendicular
KNOWN: Diameter and initial temperature of steel balls cooling in air.
FIND: Time required to cool to a prescribed temperature.
ASSUMPTIONS: (1) Negligible radiation effects, (2) Constant properties.
ANALYSIS: Applying Eq. 5.10 to a
KNOWN: A layer of fatty tissue With ﬁxed inside temperature can experience different
outside convection conditions.
FIND: (a) Ratio of heat loss for different convection conditions, (b) Outer surface
temperature for different convection condi
Exam No.1 Heat Transfer (EML 4142, Section 1)
Problem 1 (50 Points)
A cylindrical wall is composed of two materials ofthermal conductivity kA and k8 , which are separated by
a very thin, electric resistance heater for which interfacial contact resistances
EXKIT) #5 golpli‘ftw)
i“ ': ‘1 K Tab - T38;
k l 3L
1;, ~ am
Mu : LLL : 'FLXI‘FJAQL ) P')
2 TS“) )
b; t 95% (H80 “100)
02 122.143 kw] ML
_ 122142.86 \Al ( M
N) K taut)
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.
ASSUMPTIONS: (1) Both walls subjecte
KNOWN: Rod consisting of two materials with same lengths. Ratio of thermal conductivities.
FIND: Sketch temperature and heat flux distributions.
T1 < T2
ASSUMPTIONS: (1) Steady-state conditions, (2) One-dimension
KNOWN: Nodal point on boundary between two materials.
FIND: Finite-difference equation for steady-state conditions.
ASSUMPTIONS: (1) Steady-state conditions, (2) Two-dimensional conduction, (3) Constant
properties, (4) No internal
Eml 4142 Heat Transfer
Heat Transfer from finned surfaces
Instructor: Tian Tian
Suggested Problems: 3-118~3-122, 3-125~3-126, 3.128, 3.130, 3.132
For plane wall
For Cylindrical Walls
3-6 Heat transfer from extended surf
82 CHAPTER 2 UNIDIKECTIONAL sreaov CONDUCTION
n the Biot number based on tin transveisal
r is small whe
dimension (e.g., thickness, if plate fin) is small when compared with 1.
(L) all around a n is only an
2.22 The idea of a constant fluid temperature
rop, eneg/ Wane ,
- hpCT-Te) -JDCAC
4 Ac =
Sion kov noco
k f (T-T = O
eura 12 11k
L + t/2 p/ak
2c-L + V2 pin f, n
( 1-0 = o
06 know n