热工基础练习题

23 A t tw tD
24
A
dS f = T
C
B D
D
B
C
D
A
B
C
D
A
B D
C
t
tw
B t tD tw p2 = pb
C t= tD = tw
C
tD D tw = tD t
B
C
D
25 A C
26 A
27 A B C D
C
,
B
C
B D
C
D
C
28
A C 29 A C 30 A C 31
A C 32 A C 33 A C D 34 A B C D 35
h
60 ln 34 20 277.3355 W/(m2
5 60
80 20
hR 277.3355 0.04
Bi Bi
0.0287 0.1
386
17
1
1200 K
3
600 K
1
=0.2 2=0.5 3 =0.8
2
2
15
123 3
A1 A2 A X1 2=X2 1
Eb1 Eb2
Eb1 Eb2
d2 d1
7
800K
400K
Eb T 4
E T4
4
4
T1
T2
T14
4
T2
4
400 0.54 0.0625 800
8
12
3 F 1 = 2 m2 F 2 = 4 m2 F 3 = 6 m2,
X3,2 = 0.16 X3 1+2 = 0.18 X1 3
X3 1+2 = X3 1 + X3,2 X3,1= X3 1+ X3,2=0.1
p1 0.17M P a h1 1570 k J / k g
p2 6.47 p1
h1 h4 1570 450 4.39 h2 h1 1825 1570
Q2 m(h1 h4) 0.0137 (1570 450) / 3.86 3.98
P
3.5
qm h2 h1 1825 1570 0.0137 kg/s
T2 T1 V1 V2
1
300 140.4 862.1 K
V2 V
V1 14V
2 3 4.
=14
15 14
500 T3 500 / cv T2 0.718 862.1 1558.5 K
500 T4 500 / c p T3 1.005 1558.5 2056.0 K
4 5.
V3 V2 V
V4
T4 T3
(15 )
3
cp cV
300 (10 )
U mcV (T2 T1)
U
334.96
cV m(T2 T1) 2(333 573) 0.6978 kJ/(kg K)
H Q Wt 83.736 1.2 418.68 418.68 kJ
H mc p (T2 T1)
H
418.68
c p m(T2 T1) 2(333 573) 0.8723 kJ/(kg K)
U/kJ
1-2
1390
2-3
0
3-4
-1000
4-1
0
0
1390
395
-395
0
-1000
-5
5
2
bc
uab= uac
uab uac sab sac
sab sac
T1=1000K
T2=400K
1360
kJ
833 kJ
t
w0 q1
833 1360
61.25 %
tc 1 T2 1 400 60 %
T1
7 3 kg
80
kJ/(kg K)
5 kg
20
15
4.187
cp = cV = c
H
C
Q UW Q 0, W 0
U0 UH UC 0
mH cV T2 TH1 mC cV T2 TC1 0
T2
mH TH1 mCTC1 mH mC
3 353 5 293 315.5 K
35
cp = cV = c
mcdT dS
84 kJ/kg kJ/kg
10
100 kg/min 200 kPa
200 kPa
20
200 kPa
300
3072
100
419 kJ/kg
Q
H
1 c2 2
mg z Ws
Q 0, 1 c2 0, mg z 0, Ws 0 2
H0
(m1 m2 )h (m1h1 m2h2 ) 0 m2 m1(h h1) 12.63 k g / m i n
1000
t tc
4
p1=0.3MPa
t1=24
0.1 MPa
1.4 cf1
pb 0.1 MPa
=0.528
p1 p0 0.3 M Pa
0.1
pb / p1
0.528
0.3
5 lg p h
q2
w0
6
B
H
d1
d2
de=4A/U = 4BH/ 2H+B
1 d22 d12 de 4A/U 4 4
d2 d1
w0 q1 q2 1152.446 320.946 831.5 k J / k g
t
w0 q1
1 q2 q1
0.7215 72.15 %
10
1000 kJ/kg
100 kPa 27
1
2
p1 100 kPa T1 273 27 300 K
1 2.
q1 q2 3 q3 4 1000 k J / k g
1 .4
h2 h
12.63 kg
5g kJ/(kg K)
V2=3V1 1
10
p1=6.0 105 Pa T1=600K
Rg=0.208 kJ/(kg K) cp=0.523
T2
p2 2
U=0
T2 = T1 = 600 K
p1V1 p2V2 3 p2V1
T1
T2
T1
U= H=0
p2
1 p1
2.0 105 Pa
V
D
B D
B D
B D
B D
Bi 0.1
B D
B D BiV 0.1M B
D
C
B B
C
A 36
B
C
D
X1,2
B
A 1 B 1/2 C 1/3 D /2
37
B
A
B
C
D
38 A T1=T2
T1 T2
D
B T1 = T2
C T1 T2 39
D T2 T1
D
A
B
C
D
40 A C D
C
B
5
50
1
Q/kJ
W/kJ
m1 g A
195 9.8 10 3 102
100 10 4
V1 AH 100 10 4 10 10 2 10 3 m3
T1 (273 27) 300 K
293.1 kPa
2
p2
pb
pg2
pb
m2 g A
(195 100) 9.8 10 3 102
100 10 4
195.1 kPa
T2 T1 300 K
练习题
1
80
1.
2.
3.
4.
5.
p-v
6.
7.
8.
9.
w = u wt = h
10. 11. 12. 13. 14. 15. 16. 17. 18.
19.
20.
21.
22.
n
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
h = cp T
37.
38.
39.
40.
Rg T2 pb
287 267.2 0.7669 m3/kg 105
qm
A2 c2 v2
0.02 256.67 6.6937 (kg/s ) 401.622 (kg/min )
0.7669
9 t4=2000 2
p4 =75bar 1kg
p1 =0.85 bar t1 = 40
=15
t5=760 K
1 p-v T-s
15
(1)
p-v T-s
2
T1 T4
T5
T2
T3
1 p1 =0.85 bar T1 =273+40=313 K
k
2
p2 p1 V1
p1 k 0.85 151.4 37.6658 bar
V2
k1
T2
T1
V1 V2
T1 k 1 300 151.4 1 886.253 K
3 p3 p4 75 bar
T3 T2 p3 866.253 75 1724.8797 K
450
h =24W/ m2 ·K
kJ/ m3·K
=35W/ m·K
10 min
15
Bi
hR
24 50 10 3 2
0.017 0.1
35
hA
e cV
0
h6
e cd
24 6
10 60
e 3721 103 50 10 3
0.6285
t t f 0.6285 0 t0 t f
= 3721
15 300
mm 36
V3
1.319 V
T5 T4 V4 V5
1
V5 V1 14 V
0.4
1.319
T5 2056.0 14
799.2 K
t
1 q2 q1
64.16 %
11
20 C
30 C
3.5 kW
1
3.86 k
W
T4 30 273 303 K T1 P H2 H1 3.5 kW
20 273 253 K
h4 h5 450 k J / k g p2 1.1 M P a h2 1825 k J / k g
90
d 50 mm
=85W/ (m· ) 15
a=2.95 10-5m2/s, 30 W/(m2· )
t0 300
90
hR 30 0.025
Bi
0.0088
85
t tf
hA
exp (
)
t0 t f
cV
cV t ln
tf
hA t0 t f
Vt ln
tf
ahA t0 t f
85 4 R3
3
90 36 ln
3
S m s mRg ln V2 V1
mRg ln p2 0.005 0.208 ln 3 p1
1.1426 10 3 kJ / K 1.1426 (J/K)
5 (10 )
q =cp T u= cV T
cp = cV+Rg
w =Rg T
6 2kg 60
n=1.2 418.68 kJ
83.736 kJ
p2
37.6658
T4=2000+273=2273 K
1kg
T5=760 K
q1 q1 q1 cV (T3 T2 ) c p (T4 T3 ) 0.718(1724.880 886.253) 1.004(2273 1724.880) 602.134 550.312 1152.446 k J / k g
F 1 X1 3=F 3 X3,1 X1 3=F 3 X3,1/F 1=6×0.02/2=0.06
9
q
q
k (tf1 tf 2 )
(tf1 tf 2 ) rk
(tf1 tf 2 )
1
1
h1
h2
10
1 0.45 m
0.4 m
150 kPa
D1 = 0.4 m k =375 kPa/m
p1 =150 kPa
15
1
c1
pb
1 0.667 0.528
p1 1.5
pb= 1bar 2
2
1
c 2 ccr
cp=1.004 kJ/
1
1.4 1
T2
T1
p2 p1
1 1.4
300
267.2 K
1.5
c2 2(h1 h2 ) 2 1.004 103 (300 267.2) 256.67 m/s
3)
v2
Rg T2 p2
dW pdV kD d ( D3) kD3dD
6
2
W
D2 kD3dD 2 D1
k (D24 8
D14 )
2.27 kJ
2.27 kJ
W 10 p = kD
m1 195 kg
Q
g 9.8 m/s2
15
A 100 cm2 pb 102 kPa 100 kg
H 10 cm t0 27 C
1
p1
pb
pg1
pb
T
S 2 mcdT cm ln T2
1T
T1
Siso SH SC c mH ln T2 c mC ln T2
TH1
TC1
315.5
315.3
4.187 3 ln
5 ln
0.1249 kJ / K
353Fra Baidu bibliotek
293
Siso 0
8
t1 =27
kg K Rg
kJ/ kg K
3 A2 = 0.02 m2
p1 =1.5 bar 1
V2 V1 p1 10 3 293.1 1.5023 10-3 m3
p2
195.1
H (V2 V1) (1.5023 1) 10 3 0.05023 m 5.023 cm
A
100 10 4
Q =W=97.999 J 1
Q= U+W T2 = T1
U=0
2
W pdV
1
2
97.999 J
pg2 V
pb V
C
B D
D
B D
A
B D
5
A pg
6 pv
B pb B
D C pv
D pb + pg pb pv
A 7
A
B
q = cV T + w
C
C
D
C
B
D
8
D
A
B
C
D
9
B
A
B
C
D
10
A
AQ
BQW
C W Q=0
D Q W=0
11
B
AW0 12
B W=0
CW0
D
A
AW0
B W=0
CW0
D
13
C
A
B
C
D
14
ab cb
12
104 W m2
3mm
1 W/ m·K) 110
t1
t2
t1 q
q t t1 t2 r/
t2 4.24 104 0.003 127.2 1
13
20 mm
1 300 C 30 C
q
t
1
2
1
2
2
t q
1 2
1
1300 30 0.02 0.35 0.2375 m
1830 1.3
237.5 mm
14
50mm
A
A U ab U cb Sab Scb
B U ab U cb S ab Scb
C U ab U cb S ab Scb
D U ab U cb Sab Scb
15
C
A
B
C
D
16
D
A C 17 A C 18 A C D
B D
100 kJ
100 kJ
B
B DA B
C
B
19 A C
20 A
21 A
22 A C
2.95 10 5 30 4 R2 300 36
1270 s
21.17 m i n
16
80
34
=386W/ (m )
8954 k g / m3 h
0.08 m 0.2m 8954 kg/m3
t0 80
t f 20
20
5
383.1 J/(kg )
15
t 34
h
cV t ln
tf
A t0 tf
m
1
8954 383.1
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
0K
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
h
78.
79.
80.
k
2
80
D
A
B
C
D
2
A C 3 A C 4 A C