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:fire: HEAT TRANSFER :fire: - Coggle Diagram
:fire:
HEAT TRANSFER
:fire:
Heat radiator
Heat flux (q) [W/m²]
: The heat flow rate per unit of area
Stefan-Boltzmann law
T (K):
Temperature
σ
, is 5.670374×10−8 W/m2·K4
The intensity of this radiant energy flux depends upon the temperature of the body and the nature of its surface.
Black bodies.
The model for the perfect thermal radiator is a so-called black body. This is
a body which absorbs all energy that reaches it and reflects nothing
.
Forms of the electromagnetic wave spectrum Characterization (Pg 28)
The heat transfer rate (Q) [W]:
How much heat was transfered
In special case of a small object, in a much larger isothermal environment
F1–2:
Transfer factor
Heat conduction
Heat flux (q) [W/m²]
: The heat flow rate per unit of area
Fourier's Law:
Only for unidirectional flow and steady condition
k [W/mK]:
Thermal conductivity
dT/dx [K/m]:
Temperature variation in relation of the x
P.S.:
In this conditions, q is a constant.
If i have a
unidirectional
and
unsteady heat flow
, I need to use a general way to write it
p
: [kg/m³]
Density
c: [J/K]
Specific heat capacity
∂t:
partial derivative on the time
α: [m²/s]
Thermal diffusivity
The heat diffusion equation
Joseph Fourier
The heat transfer rate (Q) [W]:
How much heat was transfered
A [m²]:
Area
q [W/m²]
: Heat flux
Energy equation [W]:
We are going to divide in 4 parts
Generated energy
or
S [W/m³]:
Heat generation rate per unit volume
S>0:
Source
Stored energy
Energy getting in/out
But we can make cut some parts in specifics situations:
Steady:
d
T/
d
t = 0
No heat generation
S=0
1 more item...
Heat generation
1 more item...
Unsteady
No heat generation
S=0
Heat generation
Always decide which coordinate systems must be used.
Temperature Profile
Heat convection
:
Heat flux (q) [W/m²]
: The heat flow rate per unit of area
Newton's Law of cooling
h (W/m²K):
film coefficient or heat transfer coefficie
T (K):
Temperature
Isaac Newton
Natural convection x Forced convection:
Forced convection:
h really is independent of ∆T in situations forced past a body and ∆T is not too large
Natural convection:
When fluid buoys up from a hot body or down from a cold one, h varies as some weak power of ∆T—typically as ∆Te1/4 or ∆Te1/3
