LE VU ANH PHUONG (U1320848B)CHEMICAL AND BIOMEDICALENGINEERING(Division of Chemical & Biomolecular Engineering)Nanyang TechnologicalUniversity

Yr 2 / SEMESTER 2 N1.2-B4-16 CH2702 Experiment C8Vapour Compression CycleName: Le Vu Anh Phuong Student ID: U1320848B Group: 14 Date: 24/3/15

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LE VU ANH PHUONG (U1320848B)

unit 1 2 3 4 5

Condenser mater mass flow rate, mwKg/s (x0.001) 10 20 30 40 50

Compressor electrical input, Wc kW 0.58 0.53 0.51 0.51 0.51Absolute pressure of condenser, PH kPa 1551.3 1201.3 1071.3 1016.3 991.3Absolute Pressure of evaporator, PL kPa 376.3 361.3 351.3 346.3 346.3HFC134a teperature at compressor inlet, T1 oC 17.4 16.7 16.4 16 15.5HFC134a teperature at compressor outlet, T2 oC 94.6 86.5 83.6 82.2 81.4HFC134a teperature of condensed liquid, T3 oC 55 45.3 41.1 39.2 37.8HFC134a teperature at expansion valve outlet, T4 oC 10.1 9.1 8.6 8 7.5Compressor cooling water inlet temperature, T5 oC 28.2 28.9 29.2 29.6 29.8Compressor cooling water outlet temperature, T6 oC 28.7 29.1 29.3 29.7 29.9Condenser water outlet temperature, T7 oC 61.5 47.3 41.7 38.9 37.3Refrigerant mass flow rate, m g/s 8 8 8 7.9 7.9

Heat delivered to condenser, QH W1371.0

4 1521.521554.9

6 1538.24 1546.60Heat removal from evaporator, QL W 104.40 115.60 121.60 120.87 121.66Compressor waste heat, Qcmp W 20.90 16.72 12.54 16.72 20.90

Total heat delivered, QT W1391.9

4 1538.241567.5

0 1554.96 1567.50Performance of air refrigerator, COPR 0.180 0.218 0.238 0.237 0.239Performance of heat pump, COPH 0.884 1.267 1.451 1.514 1.560Performance of heat pump, COPH-T 2.400 2.902 3.074 3.049 3.074Source temperature (oC) 21.2

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LE VU ANH PHUONG (U1320848B)

2. Sample calculation with mw=50g/s

QH=m❑wC pw (T 7−T 6 )=0.05×4180× (37.3−29.9 )=1546.6W

QL=m (H 2−H 1 )=0.0079× (155−309 )×1000=121.66W (refer to P-H graph at Q4)

COPR=QL

WC

=121.66510

=0.2385

COPH=QHWC

=1546.6510

=1.560

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LE VU ANH PHUONG (U1320848B)

3.

(i) QH shows positive trend with cooling water flow rate mw. This is in agreement with the theory of heat exchange. Since the temperature difference of the refrigerant at the inlet and outlet of the condenser is almost constant, the enthalpy change of the refrigerant in the condenser is relatively constant, and so is the amount of heat available for removal. As more cooling water available for heat exchange at the condenser, more heat is able to be removed by the cooling water for a change in the enthalpy of the refrigerant. Thus QH increases as mw increases.

Wc shows a negative relationship with mw. This is reasonable according to the conservation of energy because a lower cooling water flow rate across the compressor results in less heat is removed from. Thus the temperature and enthalpy difference across the compressor increase. Hence more work Wc

needs to be delivered by the compressor to achieve a higher ΔH.

0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.0550.0000

0.2000

0.4000

0.6000

0.8000

1.0000

1.2000

1.4000

1.6000

1.8000

1.25

1.3

1.35

1.4

1.45

1.5

1.55

1.6

COPH

QH

mw (kg/s)

QH

(kW

)

COPH

(ii) The values of COPH show a reasonable positive relationship with mw. COPH is defined as the ratio of QH removed to the work provided by the compressor WC. Since WC shows a slight trend of decrease while QH generally increases as more cooling water is used as explained in (i), the result is that COPH will increase. Thus the heat pump performance will be better when more cooling water is available for better heat transfer.

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0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.0550

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

QH

Wc

mw (kg/s)

kW

LE VU ANH PHUONG (U1320848B)

4.

5H3*= 330 H3=

H2= H1=

50g/s

15.5

81.4

7.5

37.8

LE VU ANH PHUONG (U1320848B)

6 H3= H3*= 340

H2= H1= 182.5

10g/s

17.4

94

10.1

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LE VU ANH PHUONG (U1320848B)

For each P-H diagram, the solid light green line represents the actual process of the compressor while the dashed green line represents the ideal isentropic line. The corresponding enthalpy values are H3 and H3

* respectively.

At mw=50 g/s, the difference in ΔH between the actual and ideal case is about 35 kJ/kmol

At mw=10 g/s, the difference in ΔH between the actual and ideal case is about 32 kJ/kmol

Hence the deviation of the compressor from the ideal operation is almost constant. This is in good agreement with theory as each compressor maintains a constant efficiency value at a fixed rotating speed. Also, the actual ΔH of the fluid in the compressor is consistently higher than the ideal case (isentropic). This is in good agreement with the theory as the ideal condition represent the minimum work required in the compressor; there will always be lost work in reality.

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