傳熱學(xué)v4-第二章穩(wěn)態(tài)熱傳導(dǎo)

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Heat導(dǎo)熱的基本定律tf(x,y,

ttf(x,y,z, t等溫線（面ShanghaiJiaoTong

Heat導(dǎo)熱的基本定律（基本概念ngradtttnt

t tgra

x

j

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HeatnAgradtAtAtnnqgradtttn

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qxx

qyy qzz

xyShanghaiJiaoTong

Heat定律幾點(diǎn)說明 ShanghaiJiaoTong

Heatqt qt金屬非金屬 固相液相氣

純銅λ純銅λ＝399碳鋼λ＝35～40λ＝0.599空氣λ＝0.0259HeatShanghaiJiaoTongttf(x,y,z, 定律+能量守恒定

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Heat（非穩(wěn)態(tài)項(xiàng)

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Heat

a

穩(wěn)態(tài)導(dǎo)熱的溫度分布取決于導(dǎo)熱系數(shù)ShanghaiJiaoTong

Heatxr

yr z xr zx x y y yr ztgxr x2yShanghaiJiaoTong

Heat

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Heat t(x,y,z,0)f(x,y,導(dǎo)熱問題的數(shù)學(xué)描述導(dǎo)熱問題的數(shù)學(xué)描述ShanghaiJiaoTong

Heat

tw第二類邊界條件

qw t t

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Heat 求解導(dǎo)熱問題的思路 ShanghaiJiaoTong

Heat典型

qdtt1

t2

qt(t(t1t22ShanghaiJiaoTong

Heat

q

tn

tn

nn nn i

i t q1(tt tq 11 11 q 2 t q 第i層

qi(t

tq i熱阻分析法適用范圍： ShanghaiJiaoTongcircuitforahollow

HeatAssumption:Surfacesnormaltoxareisothermal, betweenlayersisnegligible,radiationheattransferisnegligible.Find:Equivalentthermal

xShanghaiJiaoTong

Heat典型

溫度分

tt1

t2

ln(r

qdt

t1 W

rln(r2

Φ2rlq

t1 t1 ln(r22l

Adt2rl r2

t2

r1

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Heat

nln(r/r

i

逐層求解t2t3…熱阻分析法適用范圍： ShanghaiJiaoTong

Heat典型 (r2t)

r2

Adt4r2 r2

4r

t2t ShanghaiJiaoTong

Heat典型 右側(cè)為第三類邊界條ShanghaiJiaoTong

HeatKNOWN:Planewall,initiallyatauniformtemperature,is internalheatgeneration.

T

T

T x x z z

p ShanghaiJiaoTong

HeatProblem2.46(page

Differential

2T1 t0,T(x,0)x0, xL,

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Heat典型

Φ(t)A(x)d

x

t2t

t2t

t2 (tt)d

t2

t2t2(t

t2)(t1t2 2A(x ShanghaiJiaoTong

Heat ShanghaiJiaoTong

Heat Φ tf1tf

h2強(qiáng)化傳熱的措施 ShanghaiJiaoTong

Heat

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Heat 球壁等的區(qū)別）ShanghaiJiaoTong

Heat 等截面直已知：lHδAc

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Heat 等截面直能量守恒能量守恒 定＝H的邊界條件?？梢詫⒑穸确较虻谋砻鎸?duì)流換ShanghaiJiaoTong

Heat 等截面直能量守恒能量守恒 定能量守恒

Φx

定律

cd

d2Φxd

Φx xdxΦxd

ddx

Φsh(Pdx)(ttddx d2thP(t)cShanghaiJiaoTong

Heat 等截面直

d2tdx

(tt)x tx dtt

(xH

mexe

ΦA(chǔ)d

H0hPth(mH0

ch(x)

2exedx

th(x)

exeShanghaiJiaoTong

Heat2-4通過肋片的穩(wěn)態(tài)導(dǎo) 等截面直 兩點(diǎn)說明考慮末端的散熱，則可近似為H‘＝H+δ/2代入。ShanghaiJiaoTong

Heat2-4通過肋片的穩(wěn)態(tài)導(dǎo) 肋片效 mShanghaiJiaoTongm

Heat2-4通過肋片的穩(wěn)態(tài)導(dǎo) HhP(t H

hPth(mH

f

hPH

t

0 0

th(mHmHmH增加，ηtShanghaiJiaoTong

Heat2-4通過肋片的穩(wěn)態(tài)導(dǎo)t

mH H H

H3

t

H3/ ShanghaiJiaoTong

Heat2-4ShanghaiJiaoTong

Heat畢渥數(shù)畢渥數(shù)等截面直肋：δ/λ≤0.25(1/h)，加肋片有益。

Bi/1/ 的重量ShanghaiJiaoTongq

Heat t1 t q(A B

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