15、用一套管换热器将2000kg/h的甲苯饱和蒸气（110oC）冷凝为饱和液体，甲苯的气化热为363KJ/kg。冷却水于16 oC及5000kg/h的流量进入套管内管（内径50mm）作强制湍流流动，其传热膜系数为1740w/(m 2 K)。水的比热可取为4.19KJ/(kg oC)，假设甲苯侧热阻和管壁热阻远小于水侧热阻。 （20分） (1) Q?Whr?WcCp(t2?t1)? t2?2000?363?1000?2.01?105w

3600Whr2000?363?1000?t1??16?50.65 oC (2分)

WcCp5000?4.19?1000K??i?1740 w/(m2?oC) ?t1?110?16?94 oC ?t2?110?50.65?59.35

?t1?t2?2

?tm?(?t1??t2)2?(94?59.35)2?76.8 oC

Q?KA?tm??i?dL?tm (3分)

KA?tm2.01?105L???9.6m (1分)

?i?d?tm1740???0.05?76.8(2) A??dL?3.14?0.05?9.6?1.5m

2??t1?)?KA?tm??KA Q??WCp(t2?)?(T?t2?)(T?t1

2 5000?4.19??)(110?25)?(110?t21000??25)?1740?1.5(t2

36002??56.1 (3分) t2??T?t1??110?25?85 oC 升温后 ?t1??T?t2??110?56.1?53.9 oC ?t2??t1?2 ??t2??t1?)?5000?4.19?Q??WCp(t21000(56.1?25)?1.81?105w 3600 31

Q?Q?2.01?105?1.81?105??9.9% (3分) Q2.01?105(3)

?i??iW???(W)0.8?20.8?1.74

?i??1.74?1740?3027.6w/(m2?K)

???2WCp(t2??25) (2分) Q???K?A?tm ?t???2?110?t?2?25195?t2?m2?2

根据给出数据算得： t??52.8o2C ?t???195?t?22?195?52.8m2?71.1oC Q???K?A?t?m??3027.6?1.5?71.1?3.23?105w W?Cp(t?2?t1?)?WCp(t2?t1) 2WCp(t2??25)?WCp(50.65?16) t?2?42.3 oC ?t1?110?25?85 oC ?to2?110?42.3?67.7 C

?t1?t＜2 ?t????t1??t2?76.4 o22C Q???K?A?t???3027.6?1.5?76.4?3.47?105w Q?Q??2.01?105Q??3.47?1052.01?105?72.6% 32

(2分)