6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
4/51/3(3)湍流努塞尔数为:Nux?0.0296?(Rex)?Pr
24.74412 22.75457 21.17943 19.89216 18.81447 17.89501 17.09846 16.39967 15.78014 15.22593 14.72631 14.27287 13.8589 13.47898 13.1287 12.80438 12.50298 12.2219 11.95897 11.71232
因此对流换热系数为: hx?0.0296?x/5Re4Pr1/3?0.332?(u/?)4/5Pr1/3x?1/5 x 因此,金属片上的平均表面传热系数为:
2114/51/3?1/54/51/34/5x2h?0.0296?(u/?)Prxdx?0.037?(u/?)Prx|x1?(x2?x1)x1(x2?x1)x 设所求金属片的序号为t:
1.01t4/51/34/54/5ht?0.037?(u/?)4/5Pr1/3x4/5|0?0.37?(u/?)Pr(t?(t?1))0.01(t?1)0.01 1. u=2时t号金属片的散热速率为:
?t?htA(tw?t?)?76.7?(t4/5?(t?1)4/5)?0.002?475??1(t4/5?(t?1)4/5)?72.865?(t4/5?(t?1)4/5)
1 2 3 4
72.865 54.00033 48.60996 45.41008
41
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
2. u=5时t号金属片的散热速率为:
43.16998 41.46488 40.09861 38.96494 38.00015 37.16314 36.42592 35.76863 35.17667 34.63906 34.14727 33.69463 33.27577 32.88634 32.52275 32.18203 31.86167 31.55954 31.27383 31.00297 30.7456
?t?htA(tw?t?)?159.64?(t4/5?(t?1)4/5)?0.002?475??1(t4/5?(t?1)4/5)?151.658?(t4/5?(t?1)4/5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
151.658 112.3939 101.1746 94.51455 89.85209 86.30317 83.45947 81.09991 79.09184 77.34972 75.8153 74.44724 73.21518 72.0962 71.07263 70.13052 69.25872 68.44818 67.69143
42
20 21 22 23 24 25
3. u=5时t号金属片的散热速率为:
66.98226 66.31547 65.68664 65.09197 64.52821 63.99254
?t?htA(tw?t?)?277.95?(t4/5?(t?1)4/5)?0.002?475??1(t4/5?(t?1)4/5)?264?(t4/5?(t?1)4/5)
1 264 2 195.6507 3 176.1206 4 164.527 5 156.4108 6 150.233 7 145.2828 8 141.1754 9 137.6798 10 134.6472 11 131.9762 12 129.5947 13 127.45 14 125.5021 15 123.7203 16 122.0803 17 120.5627 1