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Flow pattern, void fraction and pressure drop of refrigerant two-phase flow in a horizontal pipe—I. Experimental data
lal. J. Mu/tWkast Flow Vol. 9. No. 4, pp. }99.dl0. 1~3
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FLOW PATTERN, VOID FRACTION AND PRESSURE DROP OF REFRIGERANT TWO-PHASE FLOW IN A H O R I Z O N T A L P I P E - - I EXPERIMENTAL DATA KENICHI HASHIZUME Energy Science & Technology Laboratory. R&D Center. Toshiba Corporation. Ukishimacho 4-1, Kawasaki, Japan
(Received 2 March 1982; in revisedform 5 December 1982) Abstract--Experiments with refrigerant two-phase IIow in a horizontal pipe have been performed and data on flow pattern, void fraction and pressure drop have been obtained. Refrigerants used were RI2 and R22. and the range of saturation pressure was from 5.7 to 19.6bar. In this paper, the experimental equipment and procedure are described in detail, and the data are both tabulated and presented graphically. I, INTRODUCTION
Because of the complexity of the problem, theoretical treatment of gas/liquid two-phase flow is not easy. Therefore most investigations on two-phase flow have been carried out experimentally, and many empirical correlations to predict flow pattern, void fraction and pressure drop have been proposed. To clarify the range of applicability and the accuracy of these correlations, good experimental data are necessary. The purpose of this investigation was to produce good data on flow pattern, void fraction and pressure drop of refrigerants in such a pressure range as is encountered in practical situations. 2. RANGEOF EXPERIMENTALCONDITIONS A large amount of data has been obtained on gas/liquid two,phase flow. Much data are compiled in data banks, such as those of Dukler (1962) or HTFS. Most data, however, relate to air/water two-component systems, and only limited data are available for one-component systems of refrigerants in the higher pressure ranges. Chawla (1967) performed experiments with refrigerant RI i, and Bandel (1973) experimented with RII, RI2 and R22, where only one of three parameters, i.e. saturation temperature (pressure), flowrate and quality, was changed systematically. In these experiments, however, due to limitations of the apparatus, the pressure range was relatively low (from 0.6 to 3.6 bar), and void fraction was not measured. Taking this background into consideration, the pressure range in the presently expected experimental work was chosen to be from 5.7 to 19.6 bar; and the refrigerants chosen were RI2 and R22, which are used in practical applications, such as refrigerators or Rankine-cycle engines. The data have not been published before. The inner diameter of the horizontal measurement section was 10mm. The range of experimental conditions are summarized in table I, and the fluid property values after Hirschberg (1966) are shown in table 2. 3. EXPERIMENTAL EQUIPMENT
To produce controlled two-phase flow in the measurement section, a natural circulation loop. figure I, was used. From the condenser, which was located on the laboratory roof at a point about 10 metres above the horizontal measurement section, the refrigerant in liquid phase flows via the downcomer, strainer, flowmeter and control valve into the pre-cooler. After the MF Vol. q, No. 't E
399
K.HASHIZL'~IE
Table I. Experimentalrangeand conditions R12
Refrigeran~ Ts
[ "C
20
]
39
5.7
P s [ bar] [
50
9.4
R22 20
12.2
9.2
39
50
15.1
19.6
25, 35, 50, 70, 100
w [kg/h] x
1
]
0.1, 0.3, 0.5, (0.7), 0.8, (0.9)
Table 2. Property values Ts ['C]
20 39 50 20 39 50
R12 R22
Ps °L [bar] [kg/m3]
5.67 9.37 12.15 9.17 15.13 19.64
1329 1260 1213 1215. 1136 1084
UL OG (cPJ [kg/m3]
0.264 0.241 0.230 0.238 0.222
0.213
31.5 52.0 68.6 38.B 66.0 88.5
UG [uP]
124 129 132 127 134 138
quality was settled in the pre-heater, refrigerant two-phase flow reaches the measurement section, which consists of the entrance region, the pressure drop measurement section, the void fraction measurement section, the flow pattern observation section and the exit region. When refrigerant two-phase flow leaves the measurement section, it is heated to superheated gas in the after-heater, and returns, via the riser, to the condenser. Bypass opens only during void fraction measurement, when the shut-off valves close. Loop piping consists of 3/8-in. Cu-pipe (9.53 mm OD x 0.8 mm thick) for the liquid phase and 5/8-in Cu-pip¢ (15.88 mm O D x 1.0 mm thick) for the gas phase. The inner diameter of the measurement section including the two shut-off valves was 10--. 0.05 ram. All piping and components of the loop were thermally insulated with 50 mm glass wool, except for some parts of the void fraction measurement section and the flow pattern observation section. Further, the loop, except for the condenser, was located in a room with an air
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Figure I. Experimentalequipment(natural circulation loop).
--
VOID FRACTION/OlDPRESSUREDROIPOF REF~GERANTTWO-PHASEFLOW
401
conditioner, and the room temperature was held at a constant value, which was below 5-10 K than the saturation temperature in the measurement section. For cooling the condenser and the pre-cooler, cold brine pumped from cold brine tanks were used. The three heaters, i.e. the pre-heater, the after-heater and the startup-heater, were heated electrically. The flowmeter was a Rotameter with electrical output.
4. CALIBRATION RUNS The quality in the measurement section was calculated from the enthalpy rise based on the enthalpy at the inlet of the pre-heater, where the refrigerant flows in subcooled liquid phase. To calculate the quality accurately, calibration of the flowmeter was done and the heat loss from the pre-heater was measured. In the calibration runs, natural circulation was kept by heating of the after-heater and the startup-heater. The refrigerant in liquid phase through the flowmeter was cooled in the pre-cooler and then again so heated in the pre-heater, that the refrigerant temperature at the outlet of the pre-heater recovered to the value in the inlet of the pre-cooler. From the heat removal in the pre-cooler, the heat input in the pre-heater, the temperatures at the inlet and the outlet of the pre-cooler and the pre-heater, calibration curves were obtained as shown in figures 2 and 3. The heat loss in figure 2 is shown against the temperature differences between the inner surface of the insulation layer and the ambient. In the following measurement, these figures were used to determine the flowrate and the quality.
5. FLOW PATTERN OBSERVATION AND RESULTS The two-phase flow pattern was determined by visual observation after the sketches by Aires (1954). Flow pattern observed in this experiment were 5 types, i.e. stratified (St), wavy (W), slug ($1), semi-annular (SA) and annular (A) flow. Semi-annular flow is a transient flow pattern to annular flow, where although a continuous liquid film flow can be observed, but the liquid film at the top of the pipe is too thinner than at the bottom to be determined as annular flow. The flow patterns for various flowrates, quality and saturation temperature are shown in figure 4 and listed in tables 3 and 4.
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TEMPERA TURE DIFFERENCE IN K Figurc 2. Heat loss in the pro-heater.
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35
50
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Figure 4. Results of flow pattern observation.
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25
35
51 I
tOO
VOID FRACTIONAND PRESSUREDROPOF REFRIGERANTTWO-PHASEFLOW
Table 3. Experimental results with RI2 Tm
W
x
~
['Cl
[kg/h]
{-I
[-I
20
25
0.586 0.633 0.774 0.820 0.890 0.899 0.963 0.962
0.09 0.10 0.31 0.31 0.50 0.51 0.80 0.81
0.576 0.662 0.803 0.807 0.863 0.940 0.965 0.970
184 184 358 343 564 576
0.10 0.I0 0.30 0.30 0.50 0.50 0.79 0.81
0.801 0.694 0.850 0.847 0.906 0.903 0.954 0.961
405 405 736 736 1350 1350
51 S1 W W W W A A
70
0.I0 0.I0 0.30 0.30
0.474 0.743 0.803 0.021
009 809
S1 S1 SA SA
100
0.i0 0.11
0.609 0.662
515 540
S1 Sl
25
0.10 0.I0 0.30 0.30 0.50 0.50 0.79 0.80
0.567 0.514 0.720 0.747 0.842 0.046 0.951 0.947
46.6 46.6 78.5 83.9 113 123 109 194
St St St St St St St-W St-W
35
0.i0 0.11 0.30 0.3L 0.50 0.50 0.79 0.79
0.552 0.521 0.740 0.708 0.864 0.872 0.945 0.940
66.2 68.7 132 132 196 196 343 343
St St St St St-W St-W W W
50
0.I0 0.10 0.10 0.30 0.30 0.50 0.50 0.79 0.79
0.433 0.533 0.605 0.742 0.788 0.864 0.881 0.945 0.943
123 245 245 441 858 736
$I $1 SL W W W W W W
70
0.10 0.10 0.11 0.30 0.31 0.50 0.50 0.80 0.80
0.691 0.622 0.729 0.760 0.786 0.876 0.861 0.950 0.938
206 491 515 858 850 1590 1620
$1 S1 $1 W W SA SA k A
100
0.10 0.10 0.10 0.30
0.441 0.561 0.518 0.793
392 417 1030
$1 SL $1 SA
25
0.09 0.10 0.30 0.30 0.50 0.50 0.77 0.81
0.501 0.527 0.692 0.663 0.821 0.816 0.925 0.938
50
50
FP
{N/m~l
0.10 0.11 0.29 0.31 0.50 0.50 0.79 0.79
35
39
dP/dL
162 172 299 294
st St St St St St St St $1 Sl
45.1 46.6 73.6 90.7 94.2 145 150
St-W
St-W W W W W
St St St St St St St St
403
404
K. HASHIZU~E Table 3
(Contd) FP
[kg/h]
( ]
[-]
IN/m3|
0.10 0.I0 0.30 0.30 0.49 0.50 0.79 0.80
0.479 0.470 0.723 0.699 0.822 0.822 0.927 0.929
120 181 181 304 304
St st St St St-W St-W W W
50
0,10 0.11 0.30 0,30 0,50 0,50 0,80 0,80
0,520 0.571 0.710 0,726 0,827 0,830 0,922 0,925
98,1 108 221 216 353 353 579 559
$1 $1 W W W W W W
70
0,10 0.10 0.30 0.30 0,50 0.50 0.79 0.81
0,536 0.346 0.714 0.764 0,836 0.842 0.936 0,937
201 208 412 417 697 711 1100 1120
0,10 0,10 0,30 0,31
0,610 0,509 0,766 0,753
358 358 760 814
35
100
63.8
$1 S1 W W
W W
W-SA W-SA SI Sl SA SA
Table 4. Experiment~ results with R22 T|
W
x
~
I'C]
(kq/h]
[-I
[-]
[N/mal
20
25
0.10 0.10 0.10 0,29 0,30 0.30
-
0.51 0,80 0.80
0.620 0.615 0.588 0,727 0,762 0.772 0.880 0.883 0,972 0.963
0.10 0.11 0.30 0,30 0.51 0,51 0,79 0.81
0,520 0.555 0.788 0.787 0.900 0,900 0,960 0.976
135 135 282 270 466 454
0.10 0.11 0,30 0,31 0.49 0.50 0.79 0.80
0,530 0,723 0,788 0,805 0.884 0.900 0.957 0.959
123 123 319 294 515 491 981 981
0.I0 0.I0 0.II 0.11 0,30 0.30 0.48 0.49
0.686 0,788 0.687 0.744 0,832 0.800 0.879 0.889
221 638 638 1180 1202
$1 S1 S1 Sl SA SA A A
I00
0.I0 0.I0
0.752 0.624
491 491
Sl S1
25
0.09 0.10 0.10 0.29 0.30 0,30 0,49 0.50 0.50 0.79 0.80
0.507 0.547 0.517 0,707 0.720 0,703 0,819 0.828 0.846 0.939 0.944
0.49
35
50
70
39
dP/dL
-
123 123 213 221 -
221
44.1 73,6 68,7 95,6 98.1 98.1 147 147
FP
St St St St St St St St St St St-Sl St-Sl St St W W W W St S1 W
W W W
SA SA
St St St St St St St St St St St
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35
50
0.09 0.I0 0.12 0.30 0.30 0.31 0.48 0.52 0.78 0.80
0.381 0.440 0.425 0.679 0.681 0.672 0.798 0.820 0.920 0.923
0.i0
0.451
0.I0 0.ii 0.29
0.481
0.30
0.718
0.31
0.709
0 50
~ 50 5O
0.820 0.802
0 69 0.70 0.79
0.909 0.899 0.929 .927 969 0.976
~. 8 9 .81
0.91 70
0 0 0 0 0 0
I0 i0 11 ii 30 30
~ 30 50 0 50 0.73
~ i00
.80
.80
0.09 0 10 0.I0 0.12
0.30 0.30 .31
~ 1
0.50
52.7
94.4 122 122 196
80.9 167
270
.465 .488
412 417
157 162
0.540 0.723 0.717
~ .818 .829
0. 907 0.9]6 0.926 0.500 0 514 0 404
0.70] 0.691 .812
.853
314 466 540 7LI 760 760 319 319 319 343 613
971 961
St St St St St St St St St St St St St St St St w w w w W W W W W Sl Sl Sl Sl W W W W W W-SA WrSA W-SA Sl Sl Sl Sl W-SA W-SA W-SA SA SA
6. V O I D FRACTION MEASUREMENT AND RESULTS Void fraction measurement was performed by the shut-off method, the apparatus being shown in figure 5. A signal from the electrical circuit causes 3-way air solenoid-valves to move, and so allows air at about 5 bar from the compressed air tank to actuate the shut-off valves. The shut-off time, i.e. the time from the beginning to the end of shut-off, could be controlled from 0.05 to 2 sec by speed controllers. The time was measured with photocouplers and discs on the rotating axis of the shut-off valves. The signals from the photocouplers were recorded on photocorder via an electrical circuit. After the two shut-off valves have closed, the magnetic valve opens, allowing refrigerant to flow through the bypass. The gas/liquid mixture of refrigerant, which was isolated between the two shut-off valves, was expanded to the ambient pressure through a needle valve. Then, in a heat exchanger, it was heated to the room temperature, and its volume measured by a gas meter. Void fraction a was calculated from the measured total volume of refrigerant under ambient conditions (i.e. superheated gas phase). The mass of refrigerant M before measurement is M= M,+M,
[i]
M , = [ape; + (I - a)p,.] V, + Pl. t/.
[2]
M: = Ps. V~.
[3]
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Figure 5. Measurement of void fraction.
Here, PsH is the density of refrigerant in superheated gas phase under ambient conditions. VI, V2 and V3 are the volume of the measurement section between two shut-off valves, the volume between the measurement section and the needle valve, and the volume between the needle valve and the exit of the gas meter, respectively. Because the room temperature was held below the saturation temperature in the measurement section, the refrigerant in V., must be in liquid phase, whose density is nearly equal to PL in Vi. The refrigerant density in V~ is psH, because the exit of the gas meter was so sealed, that the air could not enter into the gas meter. The refrigerant mass after measurement must be also M, which can be described as: M = M,' + M:'+ Mo
[41
M,' = ps.( V, + V:)
[5]
M2'= ps.V3
[61
Mo= p s , Vo.
[7]
Here, Vo is the volume displacement of the gas meter. M,' and M:' are the mass remained in Vt, V2 and V3. Mo is the mass calculated by the gas meter displacement. From [I]-[7] we obtain the following equations for void fraction. PL -- pS,.! V, + V; + VO) -- et. V; o =
V,
[8]
gt. - Pn
The gas meter used was a wet type gas meter with a 0.5 I. rotating drutn, and its accuracy was -+0.5 ml after the specification of manufacturer. The influence of shut-off time on void fraction measurement was investigated in this experiment, because this has not been discussed in publications. Figure 6 shows the results, it is evident, that the influence of shut-off time is negligible. During the experiments, which
408
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Figure 6, Influence of shut-off, time on void fraction measurement.
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Figure 7. Results of void fraction measurement.
produced the data, shut-off time was kept at about 0.I sec, and the shut-off simultaneity of the two shut-off valves was always within _+0.5% of the shut-off time. Experimental results are shown in figure 7 and listed in tables 3 and 4. 7. PRESSURE DROP MEASUREMENT AND RESULTS Pressure drop was measured as shown in figure 8. For the pressure drop measurement, a
differential transducer with lineariser and amplifier was used. A pressure balancing valve between capillary tubes was closed only during the pressure drop measurement, to protect the transducer. To fill the capillary tubes with refrigerant in subcooled liquid phase, the room temperature
VOID FRACTION.~iD PRESSL'REDROPOF REFRIGERANTTWO-PHASEFLOW
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PRESSURGAUGE
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Figure 8. Measurement of pressure drop.
was held below the saturation temperature of refrigerant in the measurement section. The temperature of capillary tubes was watched during the measurement. Experimental results are shown in figures 9 and 10, and listed in tables 3 and 4.
8. CONCLUD[NG REMARKS Experiments with refrigerant two-phase flow in a horizontal pipe were performed to determine flow pattern, void fraction and pressure drop. Systematically produced experimental data, especially on void fraction, in this range have not been published previously, although they would be useful in practical applications. The experimental data will also help to clarify
FLOWRATE W IN kg/h 25 35 50 70 I00 25 35 50 70 I00 2
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R12 5o "c I
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Figure 9. Results of pressure drop measurement with RI2.
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K. HASHIZUME
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l
200
500
Figure 10. Results of pressure drop measurement with R22.
the applicability of the available correlations and their accuracy, and to develop theoretical models of two-phase flow. REFERENCES
ALVES, G. E. 1954 Concurrent liquid/gas flow in a pipe-line contactor. Chem. Engng Prog. S9, 449--456. BANDEL, J. 1973 Druckverlust and W~irmciibergang bei der Verdampfung siedener K~Jtemittel im durchstr6mten waagerechten Rohr. Dissertation der UniversitiitKarlsruhe. CH^WL^, J. M. 1967 W~irmeiJbergang und Druckabfall in waagerechten Rohren bci der St6mung yon verdampfenden Kiiltemitteln.VDI-Forsch.-H. 523. DUKLER,A. E. 1962 Two-Phase Flow Data Analysis and Correlation Studies. University of Houston. HIRSCHaERG,H. G. 1966 Kiiltermittd. Verlag C. F. M~iller, Karlssruhe.
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FLOW PATTERN, VOID FRACTION AND PRESSURE DROP OF REFRIGERANT TWO-PHASE FLOW IN A H O R I Z O N T A L P I P E - - I EXPERIMENTAL DATA KENICHI HASHIZUME Energy Science & Technology Laboratory. R&D Center. Toshiba Corporation. Ukishimacho 4-1, Kawasaki, Japan
(Received 2 March 1982; in revisedform 5 December 1982) Abstract--Experiments with refrigerant two-phase IIow in a horizontal pipe have been performed and data on flow pattern, void fraction and pressure drop have been obtained. Refrigerants used were RI2 and R22. and the range of saturation pressure was from 5.7 to 19.6bar. In this paper, the experimental equipment and procedure are described in detail, and the data are both tabulated and presented graphically. I, INTRODUCTION
Because of the complexity of the problem, theoretical treatment of gas/liquid two-phase flow is not easy. Therefore most investigations on two-phase flow have been carried out experimentally, and many empirical correlations to predict flow pattern, void fraction and pressure drop have been proposed. To clarify the range of applicability and the accuracy of these correlations, good experimental data are necessary. The purpose of this investigation was to produce good data on flow pattern, void fraction and pressure drop of refrigerants in such a pressure range as is encountered in practical situations. 2. RANGEOF EXPERIMENTALCONDITIONS A large amount of data has been obtained on gas/liquid two,phase flow. Much data are compiled in data banks, such as those of Dukler (1962) or HTFS. Most data, however, relate to air/water two-component systems, and only limited data are available for one-component systems of refrigerants in the higher pressure ranges. Chawla (1967) performed experiments with refrigerant RI i, and Bandel (1973) experimented with RII, RI2 and R22, where only one of three parameters, i.e. saturation temperature (pressure), flowrate and quality, was changed systematically. In these experiments, however, due to limitations of the apparatus, the pressure range was relatively low (from 0.6 to 3.6 bar), and void fraction was not measured. Taking this background into consideration, the pressure range in the presently expected experimental work was chosen to be from 5.7 to 19.6 bar; and the refrigerants chosen were RI2 and R22, which are used in practical applications, such as refrigerators or Rankine-cycle engines. The data have not been published before. The inner diameter of the horizontal measurement section was 10mm. The range of experimental conditions are summarized in table I, and the fluid property values after Hirschberg (1966) are shown in table 2. 3. EXPERIMENTAL EQUIPMENT
To produce controlled two-phase flow in the measurement section, a natural circulation loop. figure I, was used. From the condenser, which was located on the laboratory roof at a point about 10 metres above the horizontal measurement section, the refrigerant in liquid phase flows via the downcomer, strainer, flowmeter and control valve into the pre-cooler. After the MF Vol. q, No. 't E
399
K.HASHIZL'~IE
Table I. Experimentalrangeand conditions R12
Refrigeran~ Ts
[ "C
20
]
39
5.7
P s [ bar] [
50
9.4
R22 20
12.2
9.2
39
50
15.1
19.6
25, 35, 50, 70, 100
w [kg/h] x
1
]
0.1, 0.3, 0.5, (0.7), 0.8, (0.9)
Table 2. Property values Ts ['C]
20 39 50 20 39 50
R12 R22
Ps °L [bar] [kg/m3]
5.67 9.37 12.15 9.17 15.13 19.64
1329 1260 1213 1215. 1136 1084
UL OG (cPJ [kg/m3]
0.264 0.241 0.230 0.238 0.222
0.213
31.5 52.0 68.6 38.B 66.0 88.5
UG [uP]
124 129 132 127 134 138
quality was settled in the pre-heater, refrigerant two-phase flow reaches the measurement section, which consists of the entrance region, the pressure drop measurement section, the void fraction measurement section, the flow pattern observation section and the exit region. When refrigerant two-phase flow leaves the measurement section, it is heated to superheated gas in the after-heater, and returns, via the riser, to the condenser. Bypass opens only during void fraction measurement, when the shut-off valves close. Loop piping consists of 3/8-in. Cu-pipe (9.53 mm OD x 0.8 mm thick) for the liquid phase and 5/8-in Cu-pip¢ (15.88 mm O D x 1.0 mm thick) for the gas phase. The inner diameter of the measurement section including the two shut-off valves was 10--. 0.05 ram. All piping and components of the loop were thermally insulated with 50 mm glass wool, except for some parts of the void fraction measurement section and the flow pattern observation section. Further, the loop, except for the condenser, was located in a room with an air
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Figure I. Experimentalequipment(natural circulation loop).
--
VOID FRACTION/OlDPRESSUREDROIPOF REF~GERANTTWO-PHASEFLOW
401
conditioner, and the room temperature was held at a constant value, which was below 5-10 K than the saturation temperature in the measurement section. For cooling the condenser and the pre-cooler, cold brine pumped from cold brine tanks were used. The three heaters, i.e. the pre-heater, the after-heater and the startup-heater, were heated electrically. The flowmeter was a Rotameter with electrical output.
4. CALIBRATION RUNS The quality in the measurement section was calculated from the enthalpy rise based on the enthalpy at the inlet of the pre-heater, where the refrigerant flows in subcooled liquid phase. To calculate the quality accurately, calibration of the flowmeter was done and the heat loss from the pre-heater was measured. In the calibration runs, natural circulation was kept by heating of the after-heater and the startup-heater. The refrigerant in liquid phase through the flowmeter was cooled in the pre-cooler and then again so heated in the pre-heater, that the refrigerant temperature at the outlet of the pre-heater recovered to the value in the inlet of the pre-cooler. From the heat removal in the pre-cooler, the heat input in the pre-heater, the temperatures at the inlet and the outlet of the pre-cooler and the pre-heater, calibration curves were obtained as shown in figures 2 and 3. The heat loss in figure 2 is shown against the temperature differences between the inner surface of the insulation layer and the ambient. In the following measurement, these figures were used to determine the flowrate and the quality.
5. FLOW PATTERN OBSERVATION AND RESULTS The two-phase flow pattern was determined by visual observation after the sketches by Aires (1954). Flow pattern observed in this experiment were 5 types, i.e. stratified (St), wavy (W), slug ($1), semi-annular (SA) and annular (A) flow. Semi-annular flow is a transient flow pattern to annular flow, where although a continuous liquid film flow can be observed, but the liquid film at the top of the pipe is too thinner than at the bottom to be determined as annular flow. The flow patterns for various flowrates, quality and saturation temperature are shown in figure 4 and listed in tables 3 and 4.
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TEMPERA TURE DIFFERENCE IN K Figurc 2. Heat loss in the pro-heater.
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Figure 3. Calibration curve for the flowmelcr.
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Figure 4. Results of flow pattern observation.
J
25
35
51 I
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VOID FRACTIONAND PRESSUREDROPOF REFRIGERANTTWO-PHASEFLOW
Table 3. Experimental results with RI2 Tm
W
x
~
['Cl
[kg/h]
{-I
[-I
20
25
0.586 0.633 0.774 0.820 0.890 0.899 0.963 0.962
0.09 0.10 0.31 0.31 0.50 0.51 0.80 0.81
0.576 0.662 0.803 0.807 0.863 0.940 0.965 0.970
184 184 358 343 564 576
0.10 0.I0 0.30 0.30 0.50 0.50 0.79 0.81
0.801 0.694 0.850 0.847 0.906 0.903 0.954 0.961
405 405 736 736 1350 1350
51 S1 W W W W A A
70
0.I0 0.I0 0.30 0.30
0.474 0.743 0.803 0.021
009 809
S1 S1 SA SA
100
0.i0 0.11
0.609 0.662
515 540
S1 Sl
25
0.10 0.I0 0.30 0.30 0.50 0.50 0.79 0.80
0.567 0.514 0.720 0.747 0.842 0.046 0.951 0.947
46.6 46.6 78.5 83.9 113 123 109 194
St St St St St St St-W St-W
35
0.i0 0.11 0.30 0.3L 0.50 0.50 0.79 0.79
0.552 0.521 0.740 0.708 0.864 0.872 0.945 0.940
66.2 68.7 132 132 196 196 343 343
St St St St St-W St-W W W
50
0.I0 0.10 0.10 0.30 0.30 0.50 0.50 0.79 0.79
0.433 0.533 0.605 0.742 0.788 0.864 0.881 0.945 0.943
123 245 245 441 858 736
$I $1 SL W W W W W W
70
0.10 0.10 0.11 0.30 0.31 0.50 0.50 0.80 0.80
0.691 0.622 0.729 0.760 0.786 0.876 0.861 0.950 0.938
206 491 515 858 850 1590 1620
$1 S1 $1 W W SA SA k A
100
0.10 0.10 0.10 0.30
0.441 0.561 0.518 0.793
392 417 1030
$1 SL $1 SA
25
0.09 0.10 0.30 0.30 0.50 0.50 0.77 0.81
0.501 0.527 0.692 0.663 0.821 0.816 0.925 0.938
50
50
FP
{N/m~l
0.10 0.11 0.29 0.31 0.50 0.50 0.79 0.79
35
39
dP/dL
162 172 299 294
st St St St St St St St $1 Sl
45.1 46.6 73.6 90.7 94.2 145 150
St-W
St-W W W W W
St St St St St St St St
403
404
K. HASHIZU~E Table 3
(Contd) FP
[kg/h]
( ]
[-]
IN/m3|
0.10 0.I0 0.30 0.30 0.49 0.50 0.79 0.80
0.479 0.470 0.723 0.699 0.822 0.822 0.927 0.929
120 181 181 304 304
St st St St St-W St-W W W
50
0,10 0.11 0.30 0,30 0,50 0,50 0,80 0,80
0,520 0.571 0.710 0,726 0,827 0,830 0,922 0,925
98,1 108 221 216 353 353 579 559
$1 $1 W W W W W W
70
0,10 0.10 0.30 0.30 0,50 0.50 0.79 0.81
0,536 0.346 0.714 0.764 0,836 0.842 0.936 0,937
201 208 412 417 697 711 1100 1120
0,10 0,10 0,30 0,31
0,610 0,509 0,766 0,753
358 358 760 814
35
100
63.8
$1 S1 W W
W W
W-SA W-SA SI Sl SA SA
Table 4. Experiment~ results with R22 T|
W
x
~
I'C]
(kq/h]
[-I
[-]
[N/mal
20
25
0.10 0.10 0.10 0,29 0,30 0.30
-
0.51 0,80 0.80
0.620 0.615 0.588 0,727 0,762 0.772 0.880 0.883 0,972 0.963
0.10 0.11 0.30 0,30 0.51 0,51 0,79 0.81
0,520 0.555 0.788 0.787 0.900 0,900 0,960 0.976
135 135 282 270 466 454
0.10 0.11 0,30 0,31 0.49 0.50 0.79 0.80
0,530 0,723 0,788 0,805 0.884 0.900 0.957 0.959
123 123 319 294 515 491 981 981
0.I0 0.I0 0.II 0.11 0,30 0.30 0.48 0.49
0.686 0,788 0.687 0.744 0,832 0.800 0.879 0.889
221 638 638 1180 1202
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491 491
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0.507 0.547 0.517 0,707 0.720 0,703 0,819 0.828 0.846 0.939 0.944
0.49
35
50
70
39
dP/dL
-
123 123 213 221 -
221
44.1 73,6 68,7 95,6 98.1 98.1 147 147
FP
St St St St St St St St St St St-Sl St-Sl St St W W W W St S1 W
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0.381 0.440 0.425 0.679 0.681 0.672 0.798 0.820 0.920 0.923
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80.9 167
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412 417
157 162
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~ .818 .829
0. 907 0.9]6 0.926 0.500 0 514 0 404
0.70] 0.691 .812
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314 466 540 7LI 760 760 319 319 319 343 613
971 961
St St St St St St St St St St St St St St St St w w w w W W W W W Sl Sl Sl Sl W W W W W W-SA WrSA W-SA Sl Sl Sl Sl W-SA W-SA W-SA SA SA
6. V O I D FRACTION MEASUREMENT AND RESULTS Void fraction measurement was performed by the shut-off method, the apparatus being shown in figure 5. A signal from the electrical circuit causes 3-way air solenoid-valves to move, and so allows air at about 5 bar from the compressed air tank to actuate the shut-off valves. The shut-off time, i.e. the time from the beginning to the end of shut-off, could be controlled from 0.05 to 2 sec by speed controllers. The time was measured with photocouplers and discs on the rotating axis of the shut-off valves. The signals from the photocouplers were recorded on photocorder via an electrical circuit. After the two shut-off valves have closed, the magnetic valve opens, allowing refrigerant to flow through the bypass. The gas/liquid mixture of refrigerant, which was isolated between the two shut-off valves, was expanded to the ambient pressure through a needle valve. Then, in a heat exchanger, it was heated to the room temperature, and its volume measured by a gas meter. Void fraction a was calculated from the measured total volume of refrigerant under ambient conditions (i.e. superheated gas phase). The mass of refrigerant M before measurement is M= M,+M,
[i]
M , = [ape; + (I - a)p,.] V, + Pl. t/.
[2]
M: = Ps. V~.
[3]
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Figure 5. Measurement of void fraction.
Here, PsH is the density of refrigerant in superheated gas phase under ambient conditions. VI, V2 and V3 are the volume of the measurement section between two shut-off valves, the volume between the measurement section and the needle valve, and the volume between the needle valve and the exit of the gas meter, respectively. Because the room temperature was held below the saturation temperature in the measurement section, the refrigerant in V., must be in liquid phase, whose density is nearly equal to PL in Vi. The refrigerant density in V~ is psH, because the exit of the gas meter was so sealed, that the air could not enter into the gas meter. The refrigerant mass after measurement must be also M, which can be described as: M = M,' + M:'+ Mo
[41
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[5]
M2'= ps.V3
[61
Mo= p s , Vo.
[7]
Here, Vo is the volume displacement of the gas meter. M,' and M:' are the mass remained in Vt, V2 and V3. Mo is the mass calculated by the gas meter displacement. From [I]-[7] we obtain the following equations for void fraction. PL -- pS,.! V, + V; + VO) -- et. V; o =
V,
[8]
gt. - Pn
The gas meter used was a wet type gas meter with a 0.5 I. rotating drutn, and its accuracy was -+0.5 ml after the specification of manufacturer. The influence of shut-off time on void fraction measurement was investigated in this experiment, because this has not been discussed in publications. Figure 6 shows the results, it is evident, that the influence of shut-off time is negligible. During the experiments, which
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produced the data, shut-off time was kept at about 0.I sec, and the shut-off simultaneity of the two shut-off valves was always within _+0.5% of the shut-off time. Experimental results are shown in figure 7 and listed in tables 3 and 4. 7. PRESSURE DROP MEASUREMENT AND RESULTS Pressure drop was measured as shown in figure 8. For the pressure drop measurement, a
differential transducer with lineariser and amplifier was used. A pressure balancing valve between capillary tubes was closed only during the pressure drop measurement, to protect the transducer. To fill the capillary tubes with refrigerant in subcooled liquid phase, the room temperature
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was held below the saturation temperature of refrigerant in the measurement section. The temperature of capillary tubes was watched during the measurement. Experimental results are shown in figures 9 and 10, and listed in tables 3 and 4.
8. CONCLUD[NG REMARKS Experiments with refrigerant two-phase flow in a horizontal pipe were performed to determine flow pattern, void fraction and pressure drop. Systematically produced experimental data, especially on void fraction, in this range have not been published previously, although they would be useful in practical applications. The experimental data will also help to clarify
FLOWRATE W IN kg/h 25 35 50 70 I00 25 35 50 70 I00 2
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Figure 9. Results of pressure drop measurement with RI2.
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Figure 10. Results of pressure drop measurement with R22.
the applicability of the available correlations and their accuracy, and to develop theoretical models of two-phase flow. REFERENCES
ALVES, G. E. 1954 Concurrent liquid/gas flow in a pipe-line contactor. Chem. Engng Prog. S9, 449--456. BANDEL, J. 1973 Druckverlust and W~irmciibergang bei der Verdampfung siedener K~Jtemittel im durchstr6mten waagerechten Rohr. Dissertation der UniversitiitKarlsruhe. CH^WL^, J. M. 1967 W~irmeiJbergang und Druckabfall in waagerechten Rohren bci der St6mung yon verdampfenden Kiiltemitteln.VDI-Forsch.-H. 523. DUKLER,A. E. 1962 Two-Phase Flow Data Analysis and Correlation Studies. University of Houston. HIRSCHaERG,H. G. 1966 Kiiltermittd. Verlag C. F. M~iller, Karlssruhe.