A refrigerant 22 vapor compression system includes a liquid-to-suction heat exchanger in the system. The heat exchanger warms saturated vapor coming from the evaporator from -10 to 5 C with liquid which comes from the condenser at 30 C. The compressions are isentropic in both cases listed below. (a) Calculate the coefficient of performance of the system without the heat exchanger but with the condensing temperature at 30 C and an evaporating temperature of -10 C. (b) Calculate the coefficient of performance of the system with the heat exchanger?
A refrigerant 22 vapor compression system includes a liquid-to-suction heat exchanger in the system. The heat exchanger warms saturated vapor coming from the evaporator from -10 to 5 C with liquid which comes from the condenser at 30 C. The compressions are isentropic in both cases listed below. (a) Calculate the coefficient of performance of the system without the heat exchanger but with the condensing temperature at 30 C and an evaporating temperature of -10 C. (b) Calculate the coefficient of performance of the system with the heat exchanger?
Refrigeration and Air Conditioning Technology (MindTap Course List)
8th Edition
ISBN:9781305578296
Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson
Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson
Chapter47: High-pressure, Low-pressure, And Absorption Chilled-water Systems
Section: Chapter Questions
Problem 13RQ: The subcooling temperature in a condenser can be measured by taking the difference between the A....
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In this problem, I can't figure out where in the Table A-7 I can find the h_2 needed for both (a) and (b), please tell me how to find it, also how are they different with or without heat exchanger, when it comes to the same Table?
This is the Solution manual for the, Stoecker, W. F., Jones, J. W. (1982). Refrigeration and Air Conditioning, 2nd ed., McGraw-Hill, Inc.
Transcribed Image Text:10-7.
A refrigerant 22 vapor compression system includes a liquid-to-suction heat exchanger in the system. The
heat exchanger warms saturated vapor coming from the evaporator from -10 to 5 C with liquid which comes
from the condenser at 30 C. The compressions are isentropic in both cases listed below.
(a)
Calculate the coefficient of performance of the system without the heat exchanger but with the
condensing temperature at 30 C and an evaporating temperature of -10 C.
Calculate the coefficient of performance of the system with the heat exchanger?
(b)
Solution:
(a)
Without heat exchanger
At 1,6, -10 C, Table A-6.
h₁ = 401.555 kJ/kg
s₁ = 1.76713 kJ/kg.K
At 2, 30 C, constant entropy, Table A-7
h₂ = 431.787 kJ/kg
(b)
At 3,4, 30 C, Table A-6.
h₂ = 236.664 kJ/kg
At 5, h =h₂ = 236.664 kJ/kg
h₁-h5
h₂ h₁
coefficient of performance = 5.46 . . .Ans.
coefficient of performance =
With heat exchanger
At 6, -10 C, Table A-6
h = 401.555 kJ/kg
=
401.555-236.664
431.787-401.555
At 1,-10 C evaporator temperature, 5 C, Table A-7
h₁ = 411.845 kJ/kg
At 3, 30 C, table A-6
h₂ = 236.664 kJ/kg.
At 2, 30 C, constant entropy, Table A-7
h₂ = 444.407 kJ/kg
Since no mention of subcooling.
h=h₂=h₂ = 236.664 kJ/kg
=
411.845-236.664
444.407-411.845
coefficient of performance =
h₁-h5
h₂-h₁
coefficient of performance = 5.38... Ans.
Table A-7 Refrigerant 22: properties of superheated vapor
1,"C
v, L/kg
v, L/kg h, kJ/kg
s, kJ/kg - K
Saturation temperature, -20°C
1.7841
1.7969
92.8432 397.467
400.737
95.1474
404.017
97.4256
99.6808
101.915
104.130
407.307
1.8095
1.8219
1.8341
1.8461
1.8580
1.8697
1.8813
1.8928
-20
-15
-10
-5
0
5
10
15
20
25
5
10
15
20
25
30
35
40
45
50
20
25
30
35
40
45
50
55
60
65
106.328
108.510
110.678
112.832
35
40
45
50
55
60
65
70
75
80
410.610
413.926
417.258
420.606
423.970
426.353
Saturation temperature, 5°C
40.3556 407.143
41.4580
42.5379
410.851
414.542
43.5979
44.6401
45.6665 425.562
418.222
421.894
Table A-7 (continued)
46.6786 429.229
47.6779 432.897
436.569
48.6656
49.6427
440.247
1.7446
1.7578
1.7708
1.7834
1.7958
1.8080
1.8200
1.8319
1.8435
1.8550
Saturation temperature, 20°C
26.0032 411.918
26.7900 415.977
27.5542 419.991
28.2989 423.970
29.0264 427.922
29.7389 431.852
30.4379 435.766
31.1250 439.668
31.8012 443.561
32.4678 447.450
Saturation temperature, 32°C
19.0907 417,648
19.7093 422.014
20.3062 426.310
20.8847 430.549
21.4471 434.743
438.900
21.9956
443.028
22.5318
23.0571 447.133
451.219
23.5726
24.0794 455.292
1.7246
1.7383
1.7517
1.7646
1.7774
1.7899
1.8021
1.8141
1.8258
1.8374
1.7182
1.7322
1.7458
1.7591
1.7719
1.7845
1.7968
1.8089
1.8207
1.8323
h, kJ/kg
s, kJ/kg - K
Saturation temperature, -10°C
401.555
65.3399
67.0081 404.983
68.6524 408.412
70.2751 411.845
415.283
71.8785
418.730
73.4644
75.0346 422.186
425.653
76.5904
1.7671
1.7800
1.7927
1.8052
1.8174
1.8295
1.8414
1.8531
Saturation temperature, 10°C
34.7136 408.835
35.6907 412.651
416.442
36.6454
420.215
37.5804
38.4981
423.974
39.4002
427.724
431.469
40.2884
41.1642 435.211
42.0286
438.954
Saturation temperature, 25°C
22.6242 413.289
23.3389 417.487
24.0306 421.627
24.7027 425.721
25.3575 429.779
25.9974 433.807
26.6239 437.813
27.2386 441.801
27.8427 445.777
1.7377
1.7511
1.7642
1.7769
1.7894
1.8017
1.8137
1.8256
1.8373
1.7183
1.7322
1.7458
1.7590
1.7718
1.7844
1.7967
1.8087
1.8206
Saturation temperature, 34°C
1.7099
1.7243
1.7382
1.7517
1.7647
1.7775
1.7899
1.8021
1.8141
1.8258
17.8590 416.325
18.4675 420.792
19.0526 425.174
429.487
19.6178
20.1660 433.747
20.6994 437.963
21.2199 442.143
21.7289 446.294
22.2278 450.424
454.535
22.7176
v, L/kg
h, kJ/kg s, kJ/kg K
Saturation temperature, 0°C
1.7518
1.7649
1.7777
1.7903
1.8026
1.8148
Saturation temperature, 15°C
405.361
47.1354
48.3899 408.969
416.159
49.6215 412.567
50.8328
52.0259
53.2028
29.9874
30.8606
419.649
423.339
410.430
414.362
31.7114
418.260
32.5427 422.133
33.3568 425.985
34.1556 429.823
34.9409 433.650
35.7139 437.470
Saturation temperature, 30°C
19.7417 414.530
20.3962 418.881
21.0272 423.159
21.6381 427.378
22.2316 431.549
22.8101 435.683
23.3733 439.787
23.9288 443.867
1.7120
1.7262
1.7400
1.7534
1.7664
1.7791
1.7915
1.8036
Saturation temperature, 36°C
17.2953 419.483
17.8708 423.961
18.4247 428.358
18.9603 432.690
19.4802 436.970
19.9865 441.207
20.4807 445.410
20.9643
449.586
21.4385
453.739
1.7162
1.7304
1.7442
1.7575
1.7704
1.7830
1.7954
1.8074
1.8193
1.7311
1.7556
1.7578
1.7707
1.7833
1.7956
1.8078
1.8197
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