🔥 HEAT TRANSFER 🔥
Heat radiator
Heat conduction
Heat flux (q) [W/m²]: The heat flow rate per unit of area
Heat convection :
Heat flux (q) [W/m²]: The heat flow rate per unit of area
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
Joseph Fourier
The heat transfer rate (Q) [W]: How much heat was transfered
A [m²]: Area
q [W/m²]: Heat flux
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
Energy equation [W]: We are going to divide in 4 parts
Generated energy
Stored energy
Energy getting in/out
or S [W/m³]: Heat generation rate per unit volume
But we can make cut some parts in specifics situations:
Steady: dT/dt = 0
Unsteady
No heat generation S=0
Heat generation
No heat generation S=0
Heat generation
Unidirectional:
Unidirectional:
Always decide which coordinate systems must be used.
S>0: Source
Newton's Law of cooling
Temperature Profile
Stefan-Boltzmann law
Isaac Newton
Natural convection x Forced convection:
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)
h (W/m²K): film coefficient or heat transfer coefficie
T (K): Temperature
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
The intensity of this radiant energy flux depends upon the temperature of the body and the nature of its surface.
T (K): Temperature
σ, is 5.670374×10−8 W/m2·K4
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