Chapter 3 Flashcards
Diffusion
net transfer of energy by random molecular motion
Thermal Resistance for Conduction
L/KA
Thermal Resistance for Convection
1/hA
T infinity
Temperature of Bulk Fluid
q
Heat flow rate
h
Heat transfer coefficient convection
1/hA
Thermal Resistance convection
L/KA
Thermal Resistance conduction
Units for Rt
K/W
Units for Rt’’
m^2*K/W
hr meaning
Radiation heat Transfer Coefficient
hr formula
hr= εσ(Ts+Tsur)(Ts^2+Tsur^2)
saturated media
solid phase and a single fluid phase
Unsaturated media
consist of solid liquid and gas phases
ε
porosity-fraction of the volume of the voids over the total volume
what is heat transfer of convection mostly due to
velocity
heat rate composite wall
T inf1- Tinf/Sum RT
RTotal
sum of all resistances
As Roughness Increases, Contact Resistance _______________.
Increases.
Rt cond in a cylindrical wall
=ln(r2/1r1)/ 2 πLk
Rt
delta T/q
qradiation
epsilon*sigma(Ts^4-Tsur^4)
hr
epsilonsigma(Ts+Tsur)(Ts^2-Tsur^2)
q”
Heat flux (W/m^2)
Is the Temperature Distribution in a Cylindrical Wall with Steady State and no Heat generation linear or nonlinear? Why?
T1-T2 T(r)= -------------- * ln(r / r2) + T2
ln(r1 / r2)
Nonlinear because of the ln(r) term
Is the Heat Flux in a Cylindrical Wall with Steady State & No Heat Generated variable or constant? Why?
(Ts1-Ts2) q"= -k -----------
r*ln(r2/r1)
Variable because of 1/r.
Is the Heat Rate in a Cylindrical Wall with Steady State & No Heat Generated variable or constant? Why?
2pi*L*k q = ------------* (Ts1-Ts2)
ln(r2/r1)
Constant because there is no r term.
Epsilon(f)
Fin Effectiveness
>1
Eta(f): ηf
Fin efficiency <1
