Name:
EML 4140 Exam 2
Spring 2015
EML 4140 Heat Transfer
Exam 2 Spring 2015
Problem 1 (25 points)
A fluid flows through a pipe with inside diameter D = 0.12 m and length L = 75 m. The flow rate of the
fluid is 0.26 kg/s. The pipe is maintained at a consta
EML 4140 Radiation Heat Transfer
Fall 2011
Time: M W F, Period 2 (8:30 am 9:20 am)
Location: WM 0100
Instructor
Dr. Jrg Petrasch,
Department of Mechanical and Aerospace Engineering
330 MAEB
petrasch@ufl.e
PROBLEM 2.11
KNOWN: One-dimensional system with prescribed thermal conductivity and thickness.
FIND: Unknowns for various temperature conditions and sketch distribution.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) One-dimensional conduction,
PROBLEM 4.62
KNOWN: Nodal temperatures from a steady-state finite-difference analysis for a cylindrical fin of
prescribed diameter, thermal conductivity and convection conditions ( T , h).
FIND: (a) The fin heat rate, qf, and (b) Temperature at node 3, T3
PROBLEM 6.8
KNOWN: Variation of local convection coefficient with x for free convection from a
vertical heated plate.
FIND: Ratio of average to local convection coefficient.
SCHEMATIC:
ANALYSIS: The average coefficient from 0 to x is
1 x
C x -1/4
=
h
dx
x
PROBLEM 5.52
KNOWN: Thickness, initial temperature and properties of steel plate. Convection conditions at both
surfaces.
FIND: Time required to achieve a minimum temperature.
SCHEMATIC:
=7800 kg/m3
cp = 500 J/kg-K
k = 45 W/m-K
Steel plate:
Ti = 300oC
T(0
PROBLEM 7.17
KNOWN: Temperature, pressure and Reynolds number for air flow over a flat plate of uniform
surface temperature.
FIND: (a) Rate of heat transfer from the plate, (b) Rate of heat transfer if air velocity is doubled and
pressure is increased to
PROBLEM 7.6
KNOWN: Velocity and temperature profiles and shear stress-boundary layer thickness
relation for turbulent flow over a flat plate.
FIND: (a) Expressions for hydrodynamic boundary layer thickness and average friction
coefficient, (b) Expressions
PROBLEM 7.29
KNOWN: Dimensions of aluminum heat sink. Temperature and velocity of coolant (water) flow
through the heat sink. Power dissipation of electronic package attached to the heat sink.
FIND: Base temperature of heat sink.
SCHEMATIC:
w1 = 100 mm
S
PROBLEM 6.23
KNOWN: Velocity of water flowing over a flat plate. Length of plate. Variation of local convection
coefficient with x. Water temperature.
FIND: Average convection coefficient for roughness applied over the range 0 xr L.
SCHEMATIC:
u
T
xr
Ts
x
PROBLEM 8.1
KNOWN: Flowrate and temperature of water in fully developed flow through a tube of
prescribed diameter.
FIND: Maximum velocity and pressure gradient.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state conditions, (2) Isothermal flow, (3) Horizontal tube
PROBLEM 1.47
KNOWN: Dimensions of a milk carton. Temperatures of milk carton and surrounding air.
Convection heat transfer coefficient and surface emissivity.
FIND: Heat transferred to milk carton for durations of 10, 60, and 300 s.
SCHEMATIC:
Tsur
qconv
PROBLEl-I 8.10
KNOWN: Thermal energy equation describing laminar. fully developed ﬂow in a circular pipe with
viscous dissipation.
FIND: (a) Left hand side of equation integrated over the pipe volume. viscous dissipation term
integrated over the same volu
Heat Transfer Practice Problem 2
Consider a flat plate subject to parallel flow of air on the top with u 6
m
and T 25o C. The
s
surface temperature of the plate is 55o C .Find the average convective heat transfer coefficient and the
rate of heat transfer
Heat Transfer Practice Problem
A 25.4mm x 25.4mm square 2024-T6 aluminum bar of length 20 cm is heated to 400 K in an electric
furnace. The bar is then to be cooled by free convection in either a liquid h 300
W
or in air
m2 K
W
h 10 2
, both at 300
Heat Transfer Exam 2 Spring 2016
NAME:_
Closed book, 2 pages of notes allowed. 50 minute time limit.
1) A 2m x 5m flat plate with a constant surface temperature of 350 K has water at 1 bar and 300 K
flowing over it at 0.1 m/s across the short dimension. F
Heat Transfer Exam 1 Spring 2016
NAME:_
Closed book, 2 pages of notes allowed. 50 minute time limit.
1) A stone ( k = 2 W/m-K) wall of a castle is found to be 1 m thick. If the inside temperature is 20oC and
the outside temperature is -10oC find the heat
PROBLEJI 7.1
KNOW}? Temperature and velocity of ﬂuids in parallel ﬂow over a ﬂat plate.
FIND: [a] Velocity and thermal boundary layer thicknesses at a prescribed distance from the leading
edge. and For each ﬂuid plot the boundaly layer thicknesses as a fu
PROBLER-l 3.90
KNOW’X: Geometrj.r and boundary conditions of a nuclear fuel element.
FIND: (a) Expression for the temperature distribution in the fuel. {13) Form of temperature
distribution for the entire system.
S CHER-IATIC:
Sfeel—AE
ASSUMPTIONS: (I)
PROBLENI 5.5
IC‘JO‘WX: Geometries of various objects. Material and-"or properties. Cases {a} through {d}:
Convection heat transfer coefficient between object and surrounding ﬂuid. Case (e): Emissivity of
sphere. initial temperature. and temperature of sur
PROBLEIVI 5.49
KNOWN: Thickness. properties and initial temperature of steel slab. Convection conditions.
FIND: Heating time required to achieve a minimum temperatLu‘e of 550°C in the slab.
SCI-IEMATIC:
Combustion —D T = 800°C _
_._., I100: 250 100le '- ‘
PROBLEII 113
KNOWN: Dimensions and surface temperatures of a flat plate. Velocity and teniperatm'e of air
and water flow parallel to the plate.
FIND: {a} Average convective heat transfer coefficient. convective heat transfer rate. and drag
force when L =
PROBLEM 7.63
KNOWN: Dimensions of a rectangular fin in parallel flow. Circular pin fin of same cross-sectional
area.
FIND: (a) Fin heat transfer rate for both fins. (b) Diameter of cylindrical fin needed to produce the
same fin heat transfer rate as for t
PROBLEM 8.17
KNOWN: Surface heat flux for air flow through a rectangular channel.
FIND: (a) Differential equation describing variation in air mean temperature, (b) Air outlet
temperature for prescribed conditions.
SCHEMATIC:
ASSUMPTIONS: (1) Ideal gas wit
PROBLEM 12.52
KNOWN: Area, temperature, irradiation and spectral absorptivity of a surface.
FIND: Absorbed irradiation, emissive power, radiosity and net radiation transfer from the surface.
SCHEMATIC:
ASSUMPTIONS: (1) Opaque, diffuse surface behavior, (2
PROBLEM 12.37
KNOWN: Metallic surface with prescribed spectral, directional emissivity at 2000 K and 1 m (see
Example 12.7) and additional measurements of the spectral, hemispherical emissivity.
FIND: (a) Total hemispherical emissivity, , and the emissive
PROBLEM 12.56
KNOWN: Spectral, hemispherical absorptivity of an opaque surface.
FIND: (a) Solar absorptivity, (b) Total, hemispherical emissivity for Ts = 340K.
SCHEMATIC:
ASSUMPTIONS: (1) Surface is opaque, (2) = , (3) Solar spectrum has G = G,S proporti
PROBLEM 12.75
KNOWN: Window with prescribed and mounted on cooled vacuum chamber passing radiation
from a solar simulator.
FIND: (a) Solar transmissivity of the window material, (b) State-state temperature reached by
window with simulator operating, (c) N
PROBLEPUI 3.18
KNOW: Thicknesses of three materials which form a composite wall and thermal
conductivities of two of the materials. Inner and outer surface temperatures of the composite;
also, temperature and convection coefcient associated with adjoining
PROBLEDI 2.28
KNOWN: Steady-state temperature distribution in a cylindrical rod having uniform heat generation
of q] = 5x107 Win13.
FIND: (a) Steady-state centerline and surface heat transfer rates per unit length, (1. (b) Initial time
rate of change of t
Fall 2010
Tables are provided at the end of this document.
Duration: 50 minutes
Problem 1) Steam at 200 C ows in a cast iron (k=80 W/m.K) pipe Whose inner and outer
diameters are D1=5 cm and D2=6 cm, respectively. The pipe is covered with 5cmthick glass
I NAME Sgggglg Z; 2?. glad mm 5"
EML 4140 Exam 1: Conduction Heat Transfer Spring 2011
Tables are provided at the end of this document.
Duration: 2 hours
Surface area of a sphere: 4an Volume of a sphere: (4/3)1tr3
StephanBoltzmann: 0' = 5.670X10'8 W/m2K4
PROBLEM 1
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 tra