有：Redf?u???3?0.014f0.517?10?6?8.12?104 查表得：c?0.26,n?0.6，即：Nu0.60.37?Pr0.25f?f?0.26RefPrf??Pr?w?
??0.26?0.25fdRe0.60.37?Prf?fPrf??Pr??19.4kW/(m2?K)
w?Q????dl?(tw?tf)?51.2kW
33.已知：d?12mm,u??14m/s,tf?30.1?C,tw?12?C
求：?
解：按tf?55?C查表得：
?f?16.04?10?6m2/s,?f?0.0264W/(m?K)
有：Re?df?u??14?0.0124f16.04?10?6?1.05?10 按Rec?0.26,n?0.6，即：Nunf查表得：f?0.88cRef
??0.88?0.26?(1.05?104)0.6?130.2W/(m2??C)
34.已知：P?6,u??S1max?15.5m/s,tf?19.4C,tw?67.8C,d?S2d?1.2,d?19mm求：?
解：按tf?19.4?C查表得：
?f?15.06?10?6m2/s,?f?0.02567W/(m?K),Prf?0.713
Prw?0.709,?z?0.95
有：Reumaxdf???15.5?0.01915.06?10?1.96?104?6 f查表有：Nu?0.027Re0.630.36?Pr?0.25fffPrf??Pr??z
w????0.027?0.25fdRe0.630.36??Prf?fPrf?Pr??z?155.5W/(m2?K)
w? 36
35.已知：P?5,umax?4.87m/s,tf?20.2C,tw?25.2C,??S1S2??1.25,d?19mm dd求：?
解：按tf?20.2?C查表得：
?6f?1.002?10?m2/s,?f?59.94?10?2W/(m?K),Prf?6.99,Prw?6.14
有：Red0.019f?umax??4.87?1.002?10?6?9.23?104 f查表有：?z?0.92
0.250.2Nu0.60.36?Prf??f?0.35RefPrf??Pr??S1?w??S???z 2???0.35?0.25f0.36?Pr?0.2f?dRe0.6fPrf??Pr??S1?w??S???21.1W/(m2z??K) 236.已知：P?12,d?25mm,S45mm,u?1?50mm,S2?max?5m/s,tf?60C
求：?叉，?顺
解：按tf?60?C查表得：
?6f?18.9?10?m2/s,?f?0.0285W/(m?K)
有：Remaxd?0.025f?u??5f18.9?10?6?6.61?103 对于叉排查表得：??0.98，另:S1zS?0.9 20.2Nu0.31Re0.6?S1?f?f??S??z 2????0.31?0.2fdRe0.6?f?S1??S??z?66.4W/(m2?K) 2?对于顺排有：?'z?0.98
???0.24?fRe0.6?'2dfz?68.4W/(m?K)
37-39.略
37
40.已知：d?30mm,tf?37.1?C,tw?64.5?C
求：? 解：按tm?1(tf?tw)?50.8?C查表得： 2?m?0.55?10?6m2/s,Prm?3.495,?m?64.89?10?2W/(m?K),?m?4.63?10?41K 故有：?GrPr?m?g?m?td3?m2Prm
9.81?(64.5?37.1)?(0.03)3?3.4956 ? ?1.81?104?624.63?10?(0.55?10) 查表得：c?0.48,n?1
4 ?Num?0.48(GrPr)m4 ??0.481?md(GrPr)m4?0.48?110.6489?(1.81?106)4?380.1W/(m2?K) 0.03 作为常壁温处理的原因：在水中的自然对换热。 41.已知：d?50mm,h?0.5m,tw?90C,tf?20C
求：? 解：按tm???1(tf?tw)?55?C查表得： 2?m?18.42?10?6m2/s,?m?0.02814W/(m?K),Prm?0.71
故有：?GrPr?m?g??th3?2Prm ??1 Tm9.81?(90?20)?(0.5)3?0.718 ? ?5.48?10?62(273?55)?(18.42?10) 查表得：c?0.59,n?1
4 ??0.59?mh(GrPr)m4?0.59???110.02814?(5.48?108)4?5.08W/(m2?K) 0.542.已知：d?0.3m,tw?450C,tf?30C
求：ql 解：按tm?1(tf?tw)?240?C查表得： 2?m?39.86?10?6m2/s,?m?0.0414W/(m?K),Prm?0.681
38
g??td3 故有：?GrPr?m??2Prm?9.3?107
m 查表得：c?0.125,n?13
??0.125?md(GrPr)1m3
q0.125?(GrPr)1l???d(tw?tf)?m3?m(tw?tf)?3094W/m 43.同42题的解法。 解：t1m?2(tf?tw)?59?C
?9?3?12m?2.8W0m/?(K?m?),?18.?867m210sm?/,P ??1T?3.01?1?301mK
故有：?GrPr?m?g?m?td3?2Prm?2?107
m查表得：c?0.125,n?13
?Nu1m?0.125(GrPr)m3
q1l???d(tw?tf)?0.125?(GrPr)m3?m(tw?tf)?252.9W/m 44.已知：t??2w?13C,tf?25C,F?4?5m
求：?,Q 解：按t1m?2(tf?tw)?19?C查表得： ?m?15.02?10?6m2/s,?m?0.02563W/(m?K),Prm?0.7111?m?1T?3.425??1301
mK3故有：?GrPr??m?tlm?g?Pr l?12mm2(4?5)?4.5m
即：?GrPr?m?9.81?3.425?10?3?(25?13)?4.53?0.711(15.02?10?6)2?1.64?1011 639
0.96r
查表得：c?0.15,n?1
3 ??0.15?ml(GrPr)m3?0.15?110.02563?(1.64?1011)3?4.7W/(m2?K) 4.5Q??F(tf?tw)?4.7?4?5?(25?13)?1128W
45.略
46.已知：d?5.5m,tw?355?C,tf?35?C
(1)tw1?80?C,tf1?20?C;(2)tw2?80?C,tf2?80?C 求：d1,d2 解： 按tm?1(tf?tw)?195?C查表得： 2?m?34.26?10?6m2/s,?m?3.893?10?2W/(m?K),Prm?0.68
有：?GrPr?m?按tm1?g?m?tl3?m29.81?(355?35)?5.53Prm??0.68?6.46?1011 ?62(273?195)?(34.26?10)1(tf1?tw1)?50?C查表（空气）得： 2?m1?17.95?10?6m2/s,?m?2.83?10?2W/(m?K),Prm1?0.698
故有：?GrPr?m1?g?m1?tl3?m12Prm1
根据自模化有：?GrPr?m??GrPr?m1
??3?m1 得：d1??(GrPr)m?
g??tPr???m11m1??(273?50)?(17.95?10?6)2??6.46?1011? ???9.81?(80?20)?0.698?1?再按tm2?(tf2?tw2)?50C查表（水）得：
21321?5.47m
?m2?0.556?10?6m2/s,Prm2?3.54,?m2?4.57?10?41K ??3?m2同理得：d2??(GrPr)m?
???g?m2?t2Prm2?21 40