Lecture 14 Natural Convection, a.k.a. Free Convection
Background
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
Background
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
suc
Lecture 7 Mass Diffusion
Introduction
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
Using Correlations
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
given in
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
Lecture 1
Overview
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
given by:
T
T T
q kT k i
j
y
z
x
k
(2.1)
where i , j and k are unit vectors in the positive directi
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 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 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:
1
A x or r
x 2 or r 2
Cartesian Coordinates
Cy
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
105D Experiments
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
Textbook problems:
6.3
Note that u is given so you dont have to look for
6.7
Leading edge is at x 0 while trailing edge is at x L
6.14
Stagnation point is at r 0 on the surface
6.19
x
6.32
1
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:
1.5,
1.
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
Lecture 16 Radiation Heat Transfer
Background
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 17 Boiling Heat Transfer
Background
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 15 Heat Exchanger
Background
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
for an opaque surface
Then the radiation heat flux can be expressed as the difference between outgoing and
incoming energy,
q"_rad = J - G = E + rho*G - G = E - alpha*G (for tau = 0)
PROBLEM 7.38
KNOWN: Convection correlation for irregular surface due to electronic elements mounted on a
circuit board experiencing forced air cooling with prescribed temperature and velocity
FIND: Surface temperature when heat dissipation rate is 30 mW f
PROBLEM 3.119
KNOWN: Rod (D, k, 2L) that is perfectly insulated over the portion of its length L x 0 and
experiences convection (T , h) over the portion 0 x + L. One end is maintained at T 1 and the other
is separated from a heat sink at T3 with an interf
PROBLEM 1.69
KNOWN: Average heat sink temperature when total dissipation is 20 W with prescribed air and
surroundings temperature, sink surface area and emissivity.
FIND: Sink temperature when dissipation is 30 W.
SCHEMATIC:
ASSUMPTIONS: (1) Steady-state
PROBLEM 6.19
KNOWN: Air speed and temperature in a wind tunnel.
8
FIND: (a) Minimum plate length to achieve a Reynolds number of 10 , (b) Distance from
leading edge at which transition would occur.
SCHEMATIC:
ASSUMPTIONS: (1) Isothermal conditions, Ts = T
PROBLEM 3.5
KNOWN: Thermal conductivities and thicknesses of original wall, insulation layer, and glass layer.
Interior and exterior air temperatures and convection heat transfer coefficients.
FIND: Heat flux through original and retrofitted walls.
SCHEMA