?47?4555.5?4?47.11?C
?0.162?980?0.5?4.18?103 可按tf?tf1?47?C查取物性：
?f?0.644W/(m?K),?f?0.587?10?6m2/s,Prf?3.77
umd 有：Ref??f?0.5?0.16?1.36?105?1?104 ?60.587?10 且：l/d?10,tw?tf 取：Nuf?0.023RefPrf
0.80.4?? ?t??fdNuf?0.023?(1.36?105)0.8?(3.77)0.4?0.644?2013W/(m2?K) 0.16QQ4555.5???1.8?C ?F?dl?0.16?2.5?2013???22.已知：G?2.5kg/s,tf1?40C,d?50mm,tw?85C,??0.0002,l?10m
求：tf2,Q
解：设tf2?70C,tf???1(tf1?tf2)?55?C 2 按tf?55C查表得： Cpf?1.005kJ/k(?gK?),f??2?2.871W0?m/?(Kf?),??6 1s18.246m0/,Prf?0.697,?f?1.077kg/m3
???1?um?,f??2?lg???1.74?
???????f?d24 由：St?Pr23G?2?f?) 得(St?8?fCpfum
???fCpfum2??1??8Pr3?1.74?2lg????????21.077?1.005?103??2.521.077??4?0.0522??1??8??0.697?3??1.74?2lg????0.0002???
?2437W/(m?K)
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2 再由： Q?GCpf(t'f2?tf1)??F(tw?tf) 得： tf2?tf1? ?40?'?FGCpf (tw?tf) F??dl2437?10?0.05?(85?55)?85?C ?32.5?1.005?10 t'f2?tf2，与假设不符，重新假设tf2的值，重复上述的步骤，直至计算得满足要求
的值。结果略！(tf?75?C,Q?3.67?105W?367kW)
23.略
24.已知：um?1.3m/s,d?19mm,l?5.5m,?P?42mmHg,t??w?80C,tf?55C 求：?
解：按tf?55?C查表得：
?2f?985.6kg/m3,Cpf?4.177kJ/(kg?K),?f?65.3?10?W/(m?K) ?f?0.517?10?6m2/s,Prf?3.265
知：f??P?42?133.32?2.323?10?2l?1?5.5?1
fu2m?985.6?1.32d20.0192由：St2f?Prf3?f8 (St???)得： fCpfum???f?2fCpfum?8?Prf3
?985.6?4.177?103?1.3?2.323?10?2?7061W/(m2?K)
8?3.26523若为光滑量，则有：Ref?umd1.3?0.019??f0.517?10?6?4.78?104?104 知：Nu0.80.4f?0.023RefPrf ?'??f?0.023R0.84dP0?.fefr40.?0.0.02653031?9?(4.7?80.180) ?703W0/m2(?K )相比较有：???'
632
.4(03.25)25.已知：um?1.27m/s,tf?38.5?C,tw?57.9?C,d?22mm,l?2.5m 求：?
解：按tf?38.5?C查表得：
?f?0.0269W/(m?K),?f?16.74?10?6m2/s,Prf?0.7113
知：Ref?umd?f1.27?22?10?33，层流 ??1.67?10?616.74?10??d?23??Tf?0.450.4?)?10f0P?r?1???
lT???????w?0.8 而：l/d?60，则： Nuf?0.0214(fR?e??d?23??Tf?0.450.4 得：??0.0214(Re0.8?100)Prff?1??????
dlT???????w??f
??0.022?23??311.5?0.450.80.0269?0.4?0.0214????1.67?103??100???0.7113??1????????0.022?25330.9?????????6.24W/(m2?K)
26.已知：um?3.5m/s,tf?58.1C,tw?90C,其他同25题
求：?
解：按tf?58.1C查表得：
????f?0.02836W/(m?K),?f?18.72?10?6m2/s,Prf?0.7092
知：Ref?umd?f?3.5?0.022?4.11?103，过渡流 ?618.72?10??d?23??Tf?0.450.42??0.0214(Re0.8f?100)Prf?1???????15.78W/(m?K)
lT???????w?27.已知：d1?12mm,d2?16mm,l?400mm,um?2.4m/s,tf?73.1C,tw?96C
求：?
解：按tf?73.1C查表得：
????f?0.67W/(m?K),?f?0.3995?10?6m2/s,Prf?2.445
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? 而：de?24F?4??d2?d1?4mm U?(d2?d1)d?42?d12? Ref?umde?f?fde4?10?3?2.4??2.4?104?104 ?60.3995?100.4?0.023Re0.8Prff
故可有：?? ?0.023?0.67?(2.4?104)0.8?(2.445)0.4?8897.2W/(m2?K) 0.004??28.已知：d?50mm,G?0.0125kg/s,l?6m,tf1?73.1C,tf2?62C 求：tw,?,Q 解：按tf?1(tf1?tf2)?42.75?C查表得： 2?f?0.0275W/(m?K),?f?17.24?10?6m2/s,Prf?0.711,Cpf?1.009kJ/(kg?K)
?f?1.175kg/m3
有：Ref?umd?f,um?G?f?d24?
G得：Ref??f?d4?d2?f?1.65?104?104
故有：??0.023?fd0.42Re0.8Pr?26.11W/(m?K) ff再由：Q?GCpf(tf2?tf1)????dl?(tw?tf)得： tw?tf?GCpf(tf2?tf1)???dl?62.5?C
?t'??t''??53.66C查表得： 再按：tf?tw??tm?tw?'?tln''?t?f?0.02805W/(m?K),?f?18.29?10?6m2/s,Prf?0.7097
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?3f?1.0808kg/m,Cpf?1.009kJ/(kg?K)
计算得（步骤同上）：
um?5.89m/s,Ref?1.61?104?104
0.55 有：??0.027?fRe0.8Pr13?Tf?dff??T??30W/(m2?K)
w? Q?GCpf(tf2?tf1)?485.6W tQw?tf????dl?70.82?C
29.略 30.略
31.已知：u?m?25.5m/s,d?35mm,l?0.5m,Q?900W,tf?25.3C
求：tw
解：按tf?25.3?C查表得：
??6f?15.6?10m2/s,?f?0.0261W/(m?K),Prf?0.7125
Reumd25.5?0.035f????5.72?104f15.6?10?6 查表知：c?0.26,n?0.6,取Prw?Prf,即：
0.25 Nu0.6Pr0.37?Prf?f?0.26Reff??Pr?
w? ???0.26??0.7125?0.37??5.72?104?0.6?0.02610.035?122W/(m2?K) 再由：Q????dl?(tw?tf)得： t?w?tf?Q???dl?159.C5
32.已知：d?14mm,l?1.5m,u?95???3m/s,tf?55C,tw?C
求：Q
解：按t?f?55C查表得：
?6f?0.517?10?m2/s,?f?66.35?10?2W/(m?K),Prf?3.26
按tw?95?C查表得：Prw?1.85
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