8878Р2.771659Р= 0.692321Р则：Р&o ® — t fР1Рch(m/)РРР血"卷沽20”Р换热量为：Р0 = 22m/i90th(m/) = 2 x 45 x 0.8524 x 0.0007069 x (250 - 20) x 0.692321 = 8.64 W 3.Р已知：ri =40mm=0.04m, ti=827°C,g] = 0.8Р厂3=150mm=0.15m, t3=227°C,g] =0.6Р厂2=60mm=0.06m, sx — 0.28Р则：好=4打=0.02 n?,打=4巧$ =0.2827 m2, F2 = 4^2 = 0.0452 m2, =5.65x10 8 xT；4 =5.67 xlO^xllOO4 =83014РEh} = 5.65 xl0_8x 可=5.67 xl0_8 x 5004 = 3543Р热阻分别为:Р1-刍Р1Р013耳Р1_0$?_]25,—勺 _?1_0.6?=2 35£, 1_*2Р0.8x0.02?e3F3 0.6 x 0.2827?e2F2Р1Р012好Р— = 50,Р0.02Р1Р023场Р0.0452 _ 22-12Р1 — 0.28Р0.28x0.0452Р= 56.89РРР没有辐射屏时换热量：Р- 83014 - 3543 =曲 13?1 —勺 |?1?| 1_&3?12.5 + 50 + 2.358Р5耳 013珂 &3卩3Р有辐射屏是换热：Р??Em-已…???83014-3543?Р■3 _ 1 —刍 | 1 | 1_&2」_&2 |?1 」丐_ 12.5 + 50 + 56.89 + 56.89 + 22.12 + 2.358Р&1耳?%耳 &2爲 &2场?023巧 即3Р4.Р解：由传热公式:Рx15 = 776WР20 + 25Р丄 (X36 丄Р10 + O.F+20Р
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