conduction heat transfer
DESCRIPTION
Electrical engineeringTRANSCRIPT
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
1
1 (Principle of steady state heat )
1.1. (Introduction)
(Temperature gradient) (Temperature different) (Driving force) (Temperature gradient)
(1.1)
1.1 (Temperature
Gradient) (Conduction) (Convection) (Radiation)
1.1
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
2
(Steady state and Unsteady state) (Steady state)
T/t = 0
X X (Control volume) X X (Unsteady state Transient state)
T/t 0 1.2. (Conduction heat transfer)
(Temperature gradient ) A
(1.2)
(1.3)
qcond = (Wall or J/s) A = (m2) T = (K) X =
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
3
(Thermal Conductivity) k W/m K
(1.4)
(1.4) (Fouriers law of conduction)
X (1.4) (k) k k k k k k (conductor) k (insulator) k 1-1 1-1
(k), W/mK 35-430 20-200 9-90 () 0.2-2.0 () 0.02-20 0.02-0.40 0.002-0.2
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
4
a) (Conduction in plane walls)
+
(1.5)
1) Steady-state:
0 2) Transient, no heat generation: 0 3) Steady-state, no heat generation:
Steady state Fouriers law (1.6)
1.2 k A (boundary condition) T = T1 X = 0 T = T2 X = L
(1.7)
(1.7)
(1.8)
R= x/kA K/W h F/btu
Rate of heat conduction in the wall -
Rate of heat conduction out the wall
+ Rate of heat
generation inside the wall =
Rate of change of the energy content of the
wall
(1.6)
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
5
b) (plane walls in series)
1.3 (1.9)
(1.9)
T2 T3 (1.105)
(1.10)
c) (Conduction in hollow cylinder) (r) 1.4
Rate of heat conduction in the wall -
Rate of heat conduction out the wall
+ Rate of heat
generation inside the wall =
Rate of change of the energy content of the
wall
1.3
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
6
1.4
Steady state k Ar Fouriers law 1.11
(1.11)
Ar = 2rL
(1.12)
Boundary condition; Ti T0
(1.13)
d) (Multilayer cylinder) 1.5 Resistance 1.14
(1.14)
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
7
(1.15)
(1.16)
(1.17)
1.5
e) (Conduction in hollow spheres) A =4r2
(1.18)
Boundary condition;
(1.19)
(1.20)
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
8
f) Combined convection and conduction and overall coefficients
A Tw Tf 1.9
(1.21)
(1.22)
(1.23)
(
) (1.24)
(1.25)
Ai = 2Lri () , AA lm=log mean area of the tube A0 overall heat transfer coefficient (U) Ai Ao
(1.26)
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
9
(1.27)
(1.28)
1.6 (a) (b)
g) (Critical Thickness of Insulation)
() r1 T1 thermal conductivity (k) r2 T2 1.7 (1.29) T0
(1.29)
Thermal resistance Thermal resistance
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
10
Critical radius
1.7
1.3. Steady state conduction and shape factor
1.3.1. Introduction and graphical method for Two-dimensional conduction
Graphical method ( isotherm) 2 2 (steady-state)
maintained T1 maintained T2 (isotherm) heat flow line sketches Heat flow curvilinear-square (b) Fourier 1
(1.31)
This heat flow heat flow section heat flow lane Total heat flow
lane x y, heat flow T element T element heat flow lane T element
(1.33)
Critical radius
(1.30)
Critical radius
(1.31)
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
11
N is the number of temperature increments between the inner and outer surfaces Heat flow lane x y lane x y total heat transfer
(1.34)
M heat flow lane l
heat transfer curvilinear-square plots x y temperature increments (N) heat flow lanes (M)
1.8 Graphical curvilinear square method for two-dimensional heat conduction in a
rectangular flue
1.3.2. (shape factor in conduction)
(1.34) S=M/N
(1.35)
S
-
721-283 Transport Phenomena (Part 2 Heat Transfer) Dr.Jutarut Tasara
12
S S 1-2
1-2 Conduction shape factor for
Cylinder of length L in a square
0
Horizontal buried cylinder of length L
Two parallel cylinders of length L
[
]
Sphere buried