Lecture 16, continued Radiation Heat Transfer
What Is Covered in This Class
In this class we will cover only the radiation exchange in an enclosure composed of various gray
or black surfaces. At each surface there will be two quantities of interest, namel
Lecture 3 Conduction Heat Transfer, continued
One-Dimensional Conduction Equation
In the last lecture we have obtained the generic heat conduction equation for one-dimensional
slabs, which is repeated here:
A x or r
x 2 or r 2
MAE 105D, Transport Phenomena
Transient Heat Transfer Experiment
DUE DATE: Thursday, March 3
You may work individually or in pairs.
This is intended to be an open-ended experimental investigation in which you can explore the
behavior on your own initiativ
The objective of this experiment is to measure the convective coefficient for each air flow
velocity. So you set the air flow velocity from the PWM controller, and you can get the velocity
of the free stream.
You then heat up the sphere a
Homework # 5
Due in class Thursday February 18, 2016
Note that u is given so you dont have to look for
Leading edge is at x 0 while trailing edge is at x L
Stagnation point is at r 0 on the surface
hx h d is
Homework # 2
Due in class Thu Jan 21
I know this is a lot of homework for one week, but bear with me this time since I got the book
rather late in the quarter. Better to sweat during homework time than to bleed during exams!
Problems in text book:
Solution to my own questions on homework # 2
1. 10 people on each side of the room, left side $5 each, right side $3 each
a. Exchange 5 people from one side to the other and split the money equally. Each
person on the left now has 5 $5 5* $3 10 $4 . Each
KNOWN: Sphere with embedded electrical heater is maintained at a uniform surface temperature
when suspended in various media.
FIND: Required electrical power for these media: (a) atmospheric air, (b) water, (c) ethylene glycol.
KNOWN: Flow rate and properties of oil flowing in pipe. Dimensions of pipe.
FIND: Pressure drop, flow work, temperature rise caused by flow work.
L = 100 km
m = 500 kg/s
= 900 kg/m3
cp = 2000 J/kgK
D = 1.2 m
KNOWN: Water freezing under conditions for which the air temperature exceeds 0 C.
FIND: (a) Lowest air temperature, T , before freezing occurs, neglecting evaporation, (b)
The mass transfer coefficient, hm, for the evaporation process, (c) Lo
KNOWN: Aluminum plate (alloy 2024) at an initial uniform temperature of 227 C is suspended in a
room where the ambient air and surroundings are at 27 C.
FIND: (a) Expression for time rate of change of the plate, (b) Initial rate of cooling (K
KNOWN: Geometry and surface conditions of a truncated solid cone.
FIND: (a) Temperature distribution, (b) Rate of heat transfer across the cone.
ASSUMPTIONS: (1) Steady-state conditions, (2) One-dimensional conduction in x, (3)
Lecture 4 Conduction Heat Transfer, continued
More on Thermal Resistances
In the last lecture we ended the discussion with the thermal resistances for all three geometries,
namely plane slab, cylindrical shells and spherical shells. We now continue with a
Lecture 5 Extended Surfaces, a.k.a. Fins
In convection cooling applications, we often are faced with the fact that the heat transfer
coefficients are too limited to remove heat efficiently from a surface. One solution is to increase
the flow velocity to i
Lecture 15 Heat Exchanger
Heat exchangers are used to transfer heat from a hot fluid stream to another cold fluid stream
without mixing them. As an example, the radiator in your car is a heat exchanger which
allows the hot water circulating in
Lecture 17 Boiling Heat Transfer
Boiling heat transfer is a form of convection where the bulk motion is augmented by the motion
and detachment of bubbles from the heated surface. Heat transfer is also enhanced further by
evaporation feeding the
Lecture 16 Radiation Heat Transfer
All materials emit radiation via electromagnetic waves, basically the same as light. This is
caused by the transitions in energy levels of the electrons that make up the materials. As such, it
is emitted throu
Lecture 14 Natural Convection, a.k.a. Free Convection
Natural convection occurs when there is a temperature difference between a surface and the
surrounding quiescent fluid. If the plate is heated, the fluid around the plate will become heated
Lectures 9 & 10 Convection Heat and Mass Transfer
So far we have considered diffusion in stationary media such as conduction through slabs,
cylinders, etc. In all these problems, there is no bulk motion of the materials.
We now learn about convection from
Lectures 12 & 13 Internal Flow Convection
So far we have considered external flow convection such as flow over a flat plate, a cylinder or a
sphere. Internal flow is characterized by the fact that the flow is confined inside walled passages
Lecture 7 Mass Diffusion
We have learned so far that heat is conducted (diffused) from high temperature to low
temperature. Likewise, a mass species in a mixture will also diffuse from regions of high
concentration (e.g. salt in a solution of
Lecture 11 Convection Correlation
Since this is only an introductory class, I will only hold you responsible for simple geometries,
namely flow over flat plates, cross-flow over long cylinders, and flow over spheres. Those are
Lecture 8 Mass Diffusion Boundary Conditions
Even though the mass diffusion equation are essentially identical to the conduction equation, and
conduction solutions can often be used to obtain mass transfer results, there is a fundamental
difference in the
Lecture 6 Transient Conduction
Most of what we have discussed in this class up to this point did not account for time variation.
In some cases, we are actually interested in how temperatures and heat fluxes evolve in both time
and space. In other words, t
So what exactly is Transport Phenomena? The answer is simple, it is the mechanism by which
we move certain things from one place to another. What are those certain things then? As
mechanical engineers, we are mostly concerned with the t
Lecture 2 Conduction Heat Transfer
More on Fouriers Law
In the last lecture we have touched on Fouriers law of conduction where the heat flux vector is
q kT k i
where i , j and k are unit vectors in the positive directi
KNOWN: Partial pressures and temperature for a mixture of CO2 and N2.
FIND: Molar concentration, mass density, mole fraction and mass fraction of each species.
CO2 , M A
N 2 , MB
44 kg / kmol
28 kg / kmol
ASSUMPTIONS: (1) Perfe
PROBLEM 3.45 (Cont.)
and from Eq. 3.31 the temperature distribution is
ln r1 r2
Or we can use thermal circuit to find T(r)
(please see the following page: part b)
As shown below, the outer surface temperature of the insulation