0.6 a.=0.023×如×137608×66704=3021w/m2K 0.02 K =1517 1250.002525 K —+ X+0.0001 3021204522.5 1.2×10 35×1000 nIdaL ×4x103×(t2-20)=1517×(x×025×2×90)×△m 3600 133133 20 t2-20 △t t=67.9C 13133-t1 n 可以选用 133-t可以选用 0.6 0.8 0.4 2 0.023 13760 6.67 3021 / 0.02 i = = w m K ( ) ( ) 0 2 4 3 2 1 1517 1 25 0.0025 25 1 0.0001 3021 20 45 22.5 1.2 10 35 1000 4 10 20 1517 0.025 2 90 3600 n d L m K w m K Q t t = = + + + = − = 2 2 2 2 133 133 20 20 113 133 113 ln 133 m t t t t t − = − − 0 2 t C = 67.9