第十章 對流換熱.

1、10-1 xAq dAwfxxAhttdAwfwfxtttt常數(shù)wfxAtth dA1xAhh dAAwfxxxqhtt 11ppvvtt wf,hfuttcll310Knl luy0,xyxtqy 流體導熱系數(shù)流體導熱系數(shù)wxxxqhtt0,yxty w0,xyxxthtty w0ythtty qxdxxdyy02xDupFudx 2yDvpFvdy 2222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxy0uvxydxxdyy0 xh xdh x+ xdx+ xyh ydy+ ydh y+ yddhUptttcuvxy2222ttxy2Dtatd 2tat 0uvxy2

2、222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxyptttcuvxy2222ttxyw, , ,qf x y zwwqtnw, , ,tf x y z0.99uul0yuy56c2 10 3 10cuxRe5c5 10Re ww0.99tttttPrattttl、0uvxy2222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxyptttcuvxy2222ttxytl、yxuv0uvxy221uudpuuvxydxy ttuvxy22tayddddpuuxx 0uvxy22uuduuuvuxydxyttuvxy22tay212pu常常數(shù)數(shù)dpduudx

3、dx w0ythtty 0YlY w0YwtthttlY 0YhlY0YNuYww,ttxyuvXYUVlluutthlNu0uvxy22uuuuvxyyttuvxy22tay0UVXY221UUUUVXYReY221UVXYRe PrYu lRe(, ,)Uf X Y Re(, ,)Vf X Y Re(, ,)f X Y Re,Pr0YNuY,Nuf Re Pr,Nuf Re Prwf,hfuttcl1/25.0 xRexxu xRew,0,xyxuy2f,2xucf,xcff,01dlxccxl1/2f,22lClc1/201dlCxxlu lRe1/2f,0.664xxcRe1/2f1.

4、328cRe1/3tPrxu xRe1/21/30.332xxxh xNuRePr01dlxhhxl1/201 dlC xxl1/22 2x lC lh22lx lhlhlNuNu1/21/30.664NuRePrmw12tttxu xRe1/21/30.453xxNuRePr1/21/30.332xxNuRePrwxxfxqhttq常數(shù)wfxtt常數(shù)ww01dlffxttttxl01dlxqxlh0dlxqxxlNuhlNu1/21/30.680NuRePr1/21/30.664NuRePrwfqltt20dlxlxxNu221UUUUVXYReY221UVXYRe PrYpNuhStReP

5、rC u1/21/30.664NuRePr2/31/20.664St PrRe1/2f1.328cRe2/3f2cSt Prf2cSt ,ABC ,AAAC ,BBBC ,CCCC,ABCCCC312123 TCTC/,/TT312123lrrrRdlCrrrRdllC/,/rR rR 30121230uuuuuCuuuuuC0/u u331122000000,uuuuuuuuuuuuw0 ythtty 0wythtty ,lxylCxyl hhCh0hlwyC CthCtty ww ,ttttCCttt1hlC CC h lh l NuNuRe = Re ,Pr = PrnmNuf Re ,

6、 PrCRe PrnNuf RecRelglglgNucnRehlulNuRe、wfhA ttnmNuCRe Pr m2300u dRe4230010Re410Re 64fRe2m2lupfd wwf0ttx ttwftt、wwfwfr Rr Rtttrrttttwfwfwfxxxhttqhttttxh 0.05tlRePrd0.05lRedxxxqht,xxht lnttttt 0.5/2tt12ttt ce4AdP當量直徑管道流通截面積濕周0.141/3ffffw1.86dNuRe Prlf0.4816700Pr0.141/3fffw2dRe Prlfw0.00449.75靠近壁面處流體的

7、動力粘性系數(shù)按壁面溫度tw查取主流流體的動力粘度按tf查取0.8fff0.023nNuRePrwfwf0.40.3ttntt4f10 , /60Rel df0.7160 ,Pr0.140.81/3ffffw0.027NuRePr4ff0.716700 ,10,/60PrRel d2/3ff1/22/38100011 12.781tfRePrdNuclfPr6ff0.52000 , 23005 10PrRe 2f0.79ln1.64fRe0.45ffww, 0.51.5tTTcTT0.11ffww, 0.0520tPrPrcPrPr0.452/30.80.4ffffw0.02141001dTNu

8、RePrlT6fffw0.61.5, 0.51.5, 230010TPrReT0.112/30.870.4ffffw0.0122801dPrNuRePrlPr6fffw1.5500 , 0.0520 ,230010PrPrRePr2/3ff8fStPrffffpNuhStRe PrC u1/21/30.332xxNuRePr1/21/30.664NuRePr1/21/30.453xxNuRePr1/21/30.680NuRePr55 10 xRe 0.51000Pr4/51/30.0296xxNuRePr4/51/30.0308xxNuRePr0.660Pr575 1010 xRe,l,t01

9、ccxlxxxhh dxh dxl4/51/30.037871NuRePr0.660Pr575 1010 xRemw12tttu dRe551.2 10Re80 8551.2 10Re 140h dNuwnmNuCRe PrPr Pr60.7500, 110PrRewnmNuCRe PrPr Pr9030 9021 0.54cos 為流體流動方向與圓柱體軸向夾角（沖擊角）0.250.36ffffwmnPrNuCRe PrPr6ff12 100.6500RePr、90w0ythtty 0uvxy22xuudpuuvFxydxyttuvxy22tayxFg dpgdx 22uuuuvgxyyg11

10、ppvvtt 1tt tt22uuuuvgxyy w00w,ttxyuvXYUVlluutt22uuuuvgxyy 2212UUGrUUVXYReReY32gtlGr0UVXY221UVXYRe PrY2212UUGrUUVXYReReY0YNuY2/Gr Re2/Gr Re(,)Nuf Re Gr Pr2/1Gr Re (,)Nuf Re Pr2/1Gr Re (,)Nuf Gr Prf f TT1/44xGryx1/22xuxfGr ttttT*wtRaGr Pr()nnNuC GrPrcRamw12ttt壁面形狀與位置 流動情況 特征長度 Cn適用范圍GrPr 垂直平壁或圓柱 壁面高度 0.59 0.101/4 1/3 水平圓柱 圓柱外徑d0.850.480.1250.1881/41/3 4910 1091310 102410 104710 1071210 104710 1071110 1051110 10水平熱壁上面或水平冷壁下面平壁面積與周長之比A/U圓盤取0.9d0.54 0.15 1/4 1/3 水平熱壁下面或水平冷壁上面平壁面積與周長之比A/U圓盤取0.9d 0.27 1/4 1/435dHGr43w22xxxxh xg q x