CH 7. External Flow
7 E ternal Flo
(
Nu x = f x* , Re L , Pr
Nu =
)
hL
= f ( Re L , Pr )
kf
Empirical Method
by experiments: Nu L = C Re m Pr n
L
empirical correlation
Ts + T
properties: evaluated at film T T f =
2
Heat Transfer
Chapter 7-1, #1
The Flat P
CH 3 1 D Stead State Cond ction
3. 1-D, Steady-State Conduction
One-dimensional
Only one coordinate is needed to describe the spatial variation of
the dependent variables
Temperature gradients exist along only a single coordinate
direction
Heat transfer o
CH 9. Free Convection
Free
no external device no forced velocity : free or natural
body force + density gradients buoyancy force induces free
convection.
body force: gravitational force, centrifugal force, Coriolis force
density gradients: due to T gradie
CH 2. Introduction to Cond ction
2 Introd ction Conduction
Fourier s
Fouriers Law : the conduction rate equation
Phenomenological; developed from observed phenomena
Generalization based on experimental evidence
p
Steady state conduction experiment
q A, T,
CH 8. Internal Flow
Internal flow
The fluid is confined by a surface
ex) flow in a pipe
Laminar, hydrodynamic consideration
ReD,c = 2,300
Heat Transfer
x fd ,h
x fd ,h
= 0.05 Re D , 10
60
D lam
D turb
Chapter 8-1, #1
Velocity Profile in the Fully
CH 5 Transient Cond ction
5.
Conduction
Lumped Capacitance Method
assumption
T of the solid is spatially uniform at any instance
T gradients within the solid are negligible.
di t ithi th
lid
li ibl
Closely approximated if the R to conduction within the s
Conduction with Thermal Energy Generation
Consider situations for which thermal energy is being
generated due to conversion from some other energy
form.
Conversion from electrical to thermal energy
2
&
(Ohmic or resistance heating) E g = I Re
Result of th
CH 6. Introduction to Convection
The convection problem
local heat flux: q" = h (Ts - T)
local heat flux, q", and local convection coefficient, h, vary
along the surface, because flow conditions vary from point
to point
total heat transfer rate:
q = qdAs
What is Mechanical Engineering?
Technique / Technology / Engineering
T h i
T h l
E i
i
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with the materials, energy and forces of nature for the
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