热工基础第十章对流换热

1第十章 对流换热210-1 3xAq dAwfxxAhttdAwfwfxtttt常数wfxAtth dA1xAhh dAAwfxxxqhtt4 56711ppvvtt 8wf,hfuttcl910l310Knl l11uy0,xyxtqy 流体导热系数流体导热系数12wxxxqhtt0,yxty w0,xyxxthtty w0ythtty qx13dxxdyy02xDupFudx 2yDvpFvdy 2222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxy0uvxy14dxxdyy0 xh xdh x+xdx+xyh ydy+ydh y+yddhUptttcuvxy2222ttxy2Dtatd 2tat 150uvxy2222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxyptttcuvxy2222ttxy1617w,qf x y zwwqtnw,tf x y z18190.99uul0yuy2056c2 10 3 10cuxRe5c5 10Re ww0.99ttttt21Prattt22tl、230uvxy2222xuuupuuuvFxyxxy2222yvvvpvvuvFxyyxyptttcuvxy2222ttxytl、yxuv240uvxy221uudpuuvxydxy ttuvxy22tayddddpuuxx 250uvxy22uuduuuvuxydxyttuvxy22tay212pu常常数数dpduudxdx 2627w0ythtty 0YlY w0YwtthttlY 0YhlY0YNuYww,ttxyuvXYUVlluutthlNu280uvxy22uuuuvxyyttuvxy22tay0UVXY221UUUUVXYReY221UVXYRe PrYu lRe(,)Uf X Y Re(,)Vf X Y Re(,)f X Y Re,Pr0YNuY,Nuf Re Pr29,Nuf Re Prwf,hfuttcl1/25.0 xRexxu xRe30w,0,xyxuy2f,2xucf,xcff,01dlxccxl1/2f,22lClc1/201dlCxxlu lRe1/2f,0.664xxcRe1/2f1.328cRe1/3tPrxu xRe311/21/30.332xxxh xNuRePr01dlxhhxl1/201 dlC xxl1/22 2x lC lh22lx lhlhlNuNu1/21/30.664NuRePrmw12tttxu xRe321/21/30.453xxNuRePr1/21/30.332xxNuRePrwxxfxqhttq常数wfxtt常数ww01dlffxttttxl01dlxqxlh0dlxqxxlNuhlNu1/21/30.680NuRePr1/21/30.664NuRePrwfqltt20dlxlxxNu33221UUUUVXYReY221UVXYRe PrY34pNuhStRePrC u1/21/30.664NuRePr2/31/20.664St PrRe1/2f1.328cRe2/3f2cSt Prf2cSt 3536,ABC,AAAC,BBBC,CCCC,ABCCCC37312123 TCTC/,/TT38312123lrrrRdlCrrrRdllC/,/rR rR 39 30121230uuuuuCuuuuuC0/u u331122000000,uuuuuuuuuuuu40w0 ythtty 0wythtty,lxylCxyl hhCh0hlwyC CthCtty ww ,ttttCCttt1hlC CC h lh l NuNu41Re=Re,Pr=Pr42434445nmNuf Re,PrCRe PrnNuf RecRelglglgNucnRehlulNuRe、wfhA tt46nmNuCRe Pr4748 m2300u dRe4230010Re410Re 4964fRe2m2lupfd 50wwf0ttx ttwftt、wwfwfr Rr Rtttrrttttwfwfwfxxxhttqhttttxh 510.05tlRePrd0.05lRed52xxxqht,xxht 53 lnttttt 0.5/2tt12ttt 545556ce4AdP570.141/3ffffw1.86dNuRe Prlf0.4816700Pr0.141/3fffw2dRe Prlfw0.00449.75580.8fff0.023nNuRePrwfwf0.40.3ttntt4f10,/60Rel df0.7160,Pr0.140.81/3ffffw0.027NuRePr4ff0.716700,10,/60PrRel d592/3ff1/22/38100011 12.781tfRePrdNuclfPr6ff0.52000,23005 10PrRe 2f0.79ln1.64fRe0.45ffww,0.51.5tTTcTT0.11ffww,0.0520tPrPrcPrPr600.452/30.80.4ffffw0.02141001dTNuRePrlT6fffw0.61.5,0.51.5,230010TPrReT0.112/30.870.4ffffw0.0122801dPrNuRePrlPr6fffw1.5500,0.0520,230010PrPrRePr612/3ff8fStPrffffpNuhStRe PrC u621/21/30.332xxNuRePr1/21/30.664NuRePr1/21/30.453xxNuRePr1/21/30.680NuRePr55 10 xRe 0.51000Pr4/51/30.0296xxNuRePr4/51/30.0308xxNuRePr0.660Pr575 1010 xRe63,l,t01ccxlxxxhh dxh dxl4/51/30.037871NuRePr0.660Pr575 1010 xRemw12ttt64u dRe65551.2 10Re80 8551.2 10Re 14066h dNuwnmNuCRe PrPr Pr60.7500,110PrRe67wnmNuCRe PrPr Pr9030 9021 0.54cos 680.250.36ffffwmnPrNuCRe PrPr6ff12 100.6500RePr、906970w0ythtty 0uvxy22xuudpuuvFxydxyttuvxy22tayxFg dpgdx 7122uuuuvgxyyg11ppvvtt 1tt tt22uuuuvgxyy 72w00w,ttxyuvXYUVlluutt22uuuuvgxyy 2212UUGrUUVXYReReY32gtlGr730UVXY221UVXYRe PrY2212UUGrUUVXYReReY0YNuY2/Gr Re2/Gr Re(,)Nuf Re Gr Pr2/1Gr Re(,)Nuf Re Pr2/1Gr Re(,)Nuf Gr Pr74f f TT1/44xGryx1/22xuxfGr ttttT*w75tRaGr Pr76()nnNuC GrPrcRamw12ttt壁面形状与位置 流动情况 特征长度 Cn适用范围GrPr 垂直平壁或圆柱 壁面高度 0.59 0.101/4 1/3 水平圆柱 圆柱外径d0.850.480.1250.1881/41/3 4910 1091310 102410 104710 1071210 10774710 1071110 1051110 10水平热壁上面或水平冷壁下面平壁面积与周长之比A/U圆盘取0.9d0.54 0.15 1/4 1/3 水平热壁下面或水平冷壁上面平壁面积与周长之比A/U圆盘取0.9d 0.27 1/4 1/435dHGr7843w22xxxxh xg q xgtxGrGrNu 1/50.60 xxNuGrPr5111010 xGrPr1/40.17xxNuGrPr13162 1010 xGrPrm,xw,x12ttt7921/68/279/160.3870.82510.492RaNuPr1121010Ra60cosg21/68/279/160.3870.6010.559/RaNuPr1210Ra 8081