A forward-feed double-effect evaporator with equal heating areas in each effect is fed with 6 kg/s of a liquor of constant specific heat 4.2 kJ/kg.K, and with no boiling point rise in each effect, so that half of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect is three-quarters of that in the first. Steam is fed in at 400 K and the boiling point in the second effect is 380 K. The feed is heated by an external heater to the boiling point in the first effect. Assume that heat transferred in both effects is equal. (a) Sketch the process and locate different variables listed above within the evaporator setup. (b) Calculate the steam consumption
A forward-feed double-effect evaporator with equal heating areas in each effect is fed with 6 kg/s of a liquor of constant specific heat 4.2 kJ/kg.K, and with no boiling point rise in each effect, so that half of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect is three-quarters of that in the first. Steam is fed in at 400 K and the boiling point in the second effect is 380 K. The feed is heated by an external heater to the boiling point in the first effect. Assume that heat transferred in both effects is equal. (a) Sketch the process and locate different variables listed above within the evaporator setup. (b) Calculate the steam consumption
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
Related questions
Question
A forward-feed double-effect evaporator with equal heating areas in each effect is fed with 6 kg/s
of a liquor of constant specific heat 4.2 kJ/kg.K, and with no boiling point rise in each effect, so
that half of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect
is three-quarters of that in the first. Steam is fed in at 400 K and the boiling point in the second
effect is 380 K. The feed is heated by an external heater to the boiling point in the first effect.
Assume that heat transferred in both effects is equal.
(a) Sketch the process and locate different variables listed above within the evaporator setup.
(b) Calculate the steam consumption

Transcribed Image Text:300
600
300 F
250
- (148.9°C)
500
250 E
(121.1°C):
200
400
200 F-
150
(93.3°C):
300
-I50 F
100
(65.6°C):
200
100°F-
(37.8°C)
100
50
(10°C).
-50°F
0.30
0.40
0.50
0.60
0.10
0.20
Concentration (wt fraction NaOH)
Enthalpy (btu/lbm solution)
Enthalphy (kJ/kg solution)

Transcribed Image Text:Thermophysical Properties of Saturated Water"
Heat of
Vapor-
ization,
Expansion
Coeffi-
Thermal
Specific
Volume
(m/kg)
Specifie
Heat
Conductivity
(W/m K)
Surface
Tension,
a 10
(Nm)
(k/kg • K)
Viscosity
(N sm)
Prandti
Number
Тempera
ture, T
(K)
cient,
Temper-
ature,
T(K)
Pressure,
P (bar) v- 10
(kke
H-10 H,'10 ky- 10 , 10
Pr, Pr,
273.15
0.00611 1.000 206.3
8.02
18.2
75.5
2502
2497
4.217 1.854
4.211
1.855
1750
569
12.99 0.815
-68.05
273.15
275
0.00697
1.000
181.7
1652
8.09
574
18.3
12.22 0.817
75.3
-32.74
275
0.00990
0.01387
582
590
280
1.000
130.4
1422
8.29
18.6
10.26 0.825
0.833
8.81
2485
4.198
1.858
74.8
46.04
280
285
1.000
99.4
2473
4.189
1.861
1225
8,49
18.9
74.3
114.1
285
290
0.01917 1.001
69.7
2461
4.184
1.864
1080
8.69
598
19.3
7.56
0.841
73.7
174.0
290
0.02617
1.002
4.181
227.5
276.1
295
51.94
2449
1.868
959
8.89
606
19.5
6.62
0.849
72.7
295
19.6
20.1
300
0.03531
1.003
39.13
2438
4.179
1.872
855
9.09
613
620
5.83 0.857
71.7
300
305
310
29.74
22.93
2426
4.178
4.178 1.882
0.04712 1.005
1.877
769
9.29
5.20 0.865
70.9
320.6
305
0.06221 1.007
0.873
361.9
2414
2402
695
9.49
628
20.4
4.62
70.0
310
315
315
0.08132 1.009
17.82
4.179
1.888
631
9.69
634
20.7
4.16
0.883
69.2
400.4
320
325
0.1053
1.011
13.98
2390
4.180
1.895
57
9.89
640
21.0
3.77 0.894
68.3
436.7
320
0.1351
1.013
11.06
2378
4.182
1.903
528
10.09
645
21.3
3.42 0.901
67.5
471.2
325
330
0.1719
1.016
8.82
2366
4.184
1.911
489
10.29
650
21.7
3.15
0.908
66.6
504.0
330
335
0.2167
1.018
7.09
2354
4.186
1.920
453
10.49
656
22.0
2.88
0.916
65.8
535.5
335
340
0.2713
1.021
5.74
2342
4.188
1.930
420
10.69
660
22.3
2.66
0.925
64.9
566.0
340
345
0.3372
1.024
4.683
2329
4.191
1.941
389
10.89
664
22.6
2.45
0.933
64.1
595.4
345
350
0.4163
0.5100
1.027
2317
4.195
1.954
365
343
3.846
11.09
668
23.0
2.29
0.942
63.2
624.2
350
355
1.030
3.180
2304
4.199
1.968
11.29
671
23.3
2.14
0.951
62.3
652.3
355
360
365
0.6209
1.034
2.645
2291
4.203
1.983
324
11.49
674
23.7
2.02
0.960
61.4
697.9
360
0.7514
1.038
2.212
2278
4.209
1.999
306
11.69
677
24.1
1.91
0.969
60.5
707.1
365
1.041
1.861
4.214
4.217
370
0.9040
2265
2.017
289
11.89
679
24.5
1.80
0.978
59.5
728.7
370
373.15
1.0133
1.044
1.679
2257
2.029
279
12.02
680
24.8
1.76
0.984
58.9
750.1
373.15
375
1.0815
1.045
1.574
2252
2239
4.220
2.036
4.226 2.057
274
12.09
12.29
681
24.9
1.70
0.987
58.6
761
375
1.2869
1.5233
1.337
S7.6
0.999
L004
380
1.049
260
683
25.4
1.61
788
380
385
1.053
1.142
2225
4.232 2.080
248
12.49
685
25.8
1.53
56.6
814
385
390
1.794
1.058
0.980
0,731
2212
4.239
2.104
237
12.69
686
26.3
1.47
1.013
55.6
841
390
400
2.455
1.067
2183
1.34
4.256 2.158
4.278 2.221
217
13.05
688
27.2
1.033
53.6
896
400
410
3.302
1.077
0.553
13.42
2153
2123
200
688
28.2
1.24
1.054
51.5
952
410
420
4.370
1.088
0.425
4.302 2.291
185
13.79
688
29.8
1.16
1.075
49.4
1010
420
430
5.699
1.099
0.331
2091
4.331
2.369
173
14.14
685
30.4
1.09
L.10
47.2
430
Table 1: Thermo-physical Properties of Saturated Water
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