. 5.5
q¢ = a¢(t¢ - t¢), q¢ = -l¢(dt¢/dx¢). t¢ - t¢ = Dt¢ , :
a¢ Dt¢ = -l¢ (dt¢ / dx¢). (5.29)
:
a² Dt² = -l² (dt² / dx²). (5.30)
, :
(5.31)
(5.30), :
aa¢ tDt¢ = -Cll¢ (Ctdt¢ / Cldx¢). (5.32)
(5.32) (5.29) at = ClCt/Cl, t :
. (5.33)
(5.33) (5.31), :
. (5.34)
, αl / l . ( ):
. (5.35)
Re = wl / n , . Gr = bgl3Dt / n2 , , . Pr = n / . n - ; b - ; .
, , , , .
(5.35) . - Nu, a, Nu , Re, Gr, Pr . :
Nu = f(Re, Gr, Pr). (5.36)
. , , .
, . , (5.36) :
Nu = f(Re, Pr). (5.37)
, , Re Gr:
Nu = f(Gr, Pr). (5.38)
, . (Re ³ 104) :
|
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Nu = 0,021 Re0,8 Pr0,43. (5.39)
. , , , : d = 4f / .
- (Re < 2000) :
Nu = 0,15Re0,33 Pr0,43 Gr0,1. (5.40)
:
Re £ 1000
Nu = 0,5 Re0,5 Pr0,38; (5.41)
Re = 1000 ¸ 200000
Nu = 0,25 Re0,6 Pr0,38. (5.42)
, :
Nu = C (Gr × Pr)n. (5.43)
n Gr×Pr . 5.1.
5.1
C n
Gr × Pr | C | n |
10-3 - 5×102 | 1,180 | 0,125 |
5×102 - 2×107 | 0,540 | 0,250 |
2×107 - 1013 | 0,135 | 0,333 |
(5.43) , .
, , ( ) a . . . (Pr/Pr)0,25, (5.39) (5.42). - Nu a, , .
. (. 5.6) t1 t2, d, l.
. t1 , Dt1 = q(1/a1). , Dt2 = q(d/l). Dt3 = q(1/a2). , Dt = t1 - t2 = Dt1 + Dt2 + Dt3. :
. (5.44)
. (5.45)
(5.45)
R = 1/a1 + d/l + 1/a2 , , , , . . . , :
|
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, (5.46)
di, li .
, , , /(2×K):
, (5.47)
, 1 2 1 K.
(5.45) :
q = k Dt. (5.48)
F
Q = k F Dt. (5.49)
, , , d1 d2:
. (5.50)
, /(2×K): 25; -
50; 300; 1000; 2500.
t¢ t² (. . 5.6) :
(5.51)
, . . . c l n:
c = ln = 0,3×109 /. 0,4 0,8 , . l = 0,8 - 40 , .
Q, Q , QR , QD . = QA / Q , R = QR / Q , D = QD / Q , A + R + D = 1.
D = 0, , A + R=1.
( = 1; R = 0; D = 0), . , R = 1; A = 0; D = 0, . , D = 1; R = 0; A = 0 .
. Iλ l :
, (5.52)
1 2 , 3,74×10-16 ∙2 1,44×10-2 ∙.
! .
. 5.7 . 5.8
( lmax ), . , , , .
lmax : lmax = 2,9 ∙K.
(5.53)
Iλ (5.52).
, -:
0 = s0 4, (5.54)
s0 = 5,67∙10-8 /(2∙K4) .
:
, (5.55)
0 = 5,67 /(2∙K4) .
, . , , (. 5.8).
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. , , , , . . , , . . 5.8 . , , , :
= ( / 100)4, (5.56)
.
, , : , , . .
. (5.57)
, : ,
0 = 1.
/ 0 = = e .
, = 0×e, :
= 0×e ( / 100)4. (5.58)
, 1 2, 1 > 2 (. 5.9).
1, e21 , (1 - e2)1 . 2. , , q1, , q2.
,
q1 = E1 + (1 - e1) q2; (5.59)
q2 = E2 + (1 - e2) q1. (5.60)
, q2 (5.60),
, (5.61)
-
. (5.62)
q q1 q2:
. (5.63)
1 2 (5.56), :
. (5.64)
, (5.65)
, :
. (5.66)
, F1 F2, :
. (5.67)
, . , F1 1 F2 2, :
, (5.68)
= φ12F1 = φ21F2 ; φ12, φ21 1 2 2 1; e ,
. (5.69)
φ12 = φ21 = 1, (5.69) (5.65). F1 F2,
. (5.70)
φ12 φ21, .
. n
e1 = e2 = e, (n + 1) .
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. - , . , () . , , . . . :
. (5.71)
e , . , e, :
, (5.72)
e¢ .
, , . .
q = q + q. :
q = (a + a) (t - t), (5.73)
a ,
. (5.74)
, a > a, . . . 400 , .
, . , , . . . , , . ( 150 ), , .
. , , , , .
, . , , . , .
. , . . , , , .
. , . (), . , ; , . . . . , .
: , , , . , , , , , . .
|
|
, , , , , , , .
: . , , , . , .
, .
: .
:
(5.75)
:
, (5.76)
Q , ; h = 0,96 - 0,98 , ; , /; c , /(×); 1 2 ; - , /, , K, ; - .
, , :
Q = k F Dt, (5.77)
k , /(2×K); F , 2; Dt , K.
, 2,5 , , :
, (5.78)
a1, a2 , /(2×K); d1, l1 d2, l2 , , , /(2×K), ; d, l .
( ), .
. . 5.10.