CHAPTER 2 (HEAT CONDUCTION EQUATION) Flashcards
is defined as the transfer of thermal energy
from the more energetic particles of a medium to the
adjacent less energetic ones.
heat conduction
Conduction can take place in _____
provided that there is no bulk motion involved.
liquids, gases, and solids
Heat transfer has direction as well as magnitud making it a
vector quantity
The driving force for any form of heat transfer is the
temperature difference
T OR F
The larger ΔT, the larger the Heat transfer by conduction
T
Specification of the location of point: requires
coordinate system
coordinate
system such as the rectangular
x,y,z
coordinate system for cylindrical
(r, ϕ, z)
coordinate system for sphere
(r, ϕ, θ)
Transient heat transfer temperature
varies with
time and position
NOTE
Most heat transfer problems encountered in practice are transient in
nature, but they are usually analyzed under some presumed steady
conditions since steady processes are easier to analyze, and they
provide the answers to our questions.
not from ppt
the heat energy transferred through the medium is not constant. The heat flow rate keeps changing
transient
a line on a map or
chart of the earth’s surface
connecting points having the
same temperature at a given
time or the same mean
temperature for a given period.
isotherm
A heat transfer problem is said to be ______ if the temperature in the
medium varies in one direction only and thus heat is transferred in one
direction, and the variation of temperature and thus heat transfer in
other directions are negligible or zero.
1-D
1D 2D OR 3D
Heat transfer through the glass of a window
This is 1-D since heat transfer through the glass will occur
predominantly in one direction (the direction normal to the surface
of the glass) and heat transfer in other directions (from one side
edge to the other and from the top edge to the bottom) is
negligible.
1D 2D OR 3D
Heat transfer through a hot water pipe
This is 1-D since heat transfer through the pipe occurs predominantly
in the radial direction from the hot water to the ambient, and heat
transfer along the pipe and along the circumference of a cross section
z- and Ø directions) is typically negligible.
1D 2D OR 3D
Heat transfer to an egg dropped into boiling water.
Nearly 1-D because of symmetry. Heat will
be transferred to the egg in this case in
the radial direction, that is, along straight lines
passing through the midpoint of the egg
The conversion of electrical, nuclear, or chemical
energy into heat (or thermal) energy.
HEAT GENERATION
A volumetric phenomenon. That is, it occurs
throughout the body of a medium.
HEAT GENERATION
Examples heat generation
1. Heat is generated in the heating coils of an electric
range as a result of the conversion of electrical
energy to heat.
2. Nuclear power plant / Nuclear Reactors
The absorption of solar
radiation by water can be
treated as
heat generation
The rate of heat generation
may vary with ______ within the medium.
time and
position
Most heat transfer problems encountered in practice can be
approximated as being ______
one-dimensional
three-dimensional heat conduction through a
rectangular volume element.
steady state called the
Poisson equation
three-dimensional heat conduction through a
rectangular volume element.
transient, no heat generation called the
diffusion equation
three-dimensional heat conduction through a
rectangular volume element.
steady-state, no heat generation called the
Laplace equation
At ______conditions, the entire heat generated in a solid must leave the
solid through its outer surface.
steady
The maximum temperature in a
symmetrical solid with uniform
heat generation occurs at its
center
