To elucidate the time-periodic saturated flow boiling heat transfer characteristics, the data for the bubble characteristics of R-410A flow boiling obtained from the present flow visualization are examined in the following. The side views of the boiling flow in a small region around the middle axial location of the duct for various refrigerant mass fluxes and imposed heat fluxes are shown in Figs. 4.31-4.48 for the time periodic saturated flow boiling. At first, the bubble characteristics for the limiting cases of constant mass fluxes are illustrated by the photos in Fig. 4.29 & 4.30. It is noted from the flow visualization and the results in Fig. 4.29 & 4.30 that the vapor bubbles begin to appear as the heated surface temperature exceeds the boiling incipient superheat. In the beginning, tiny bubbles are observed in the active nucleation sites. The bubbles grow and then detach from the heated surface with certain mean bubble departure diameter. As the imposed heat flux increases, more bubbles are generated on more active nucleation sites and more bubbles detach from the heated surface. Besides, the detached bubbles tend to merge into larger bubbles. Note that the large bubbles become distorted and elongated as they slide on the heating surface.
Moreover, at a higher mass flux the bubbles are smaller and the bubble coalescence is less significant. Next, the bubble characteristics in the time periodic flow boiling are shown by presenting the photos of the boiling flow at eight selected time instants in a typical periodic cycle in Figs. 4.31–4.48. In these figures the symbol〝 t=to 〞signifies the time instant at which the instantaneous mass flux is at the highest level and starts to decrease with time.
The results for the persistent flow boiling (Figs. 4.40-4.48) indicate that for a given imposed heat flux and fixed mean level, amplitude and period of the mass flux oscillation the bubbles get smaller and become more dispersed in the period of the time in which the instantaneous mass flux increases. The opposite processes take place when the instantaneous mass flux decreases with time. These changes of the bubble characteristics with the instantaneous mass flux become more significant for an increase in the amplitude of the mass flux oscillation.
Then, the bubble behavior in the intermittent flow boiling for the intermediate imposed heat fluxes is shown in Figs. 4.31 – 4.39. The results clearly indicate that initially
in the beginning of the cycle the instantaneous mass flux decreases with time but is still well above G no bubble nucleates from the heated surface. The flow is in single-phase state. Note that for the case shown in Fig. 4.31 the bubbles start to nucleate from the heated surface at a certain instant after t0+tp/8 at which the instantaneous mass flux already decreases to a certain level. Note that the number and size of the bubbles increase noticeably with time in second quarter of the periodic cycle for the continuing decrease of the mass flux. Then in the third quarter of the periodic cycle the number and size of the bubbles diminish noticeably with time due to the increase of the mass flux with time. The bubbles cease to nucleate from the heated surface at a certain time instant after t0+6tp
G
/8 when the mass flux slightly exceeds and bubble nucleation stops completely.
Single-phase flow again dominates. We have to wait until about the end of the first quarter of the next cycle to see the bubble nucleation appearing on the heated surface. The above processes repeat in each cycle. The precise instants of time at which the onset and termination of nucleate boiling vary with the flow condition. Similar bubble behavior is noted for other cases shown in Figs. 4.32-4.39.
To be more quantitative the bubble characteristics, the measured data for the time variations of the space-average bubble departure diameter and frequency and active nucleation site density on the heating surface in a typical periodic cycle are given in Figs.
4.49– 4.54 to illustrate the effects of the experimental parameters on dp, f and nac. The results in Figs. 4.49 and 4.50 indicate that as the refrigerant mass flux oscillates time periodically, the bubble departure diameter also varies time periodically and to some degree like a triangular wave as the mass flux oscillation. The case shown in Fig. 4.49(a) for the mass flux oscillation at low amplitude of 10% the bubble departure diameter varies mildly with time. More specifically, the size of the departing bubbles increases almost linearly in the first half of the periodic cycle in which the mass flux decreases with time.
While in the second half of the cycle an opposite process is noted since the mass flux increases with time. Similar trend is noted in Fig. 4.49(a) for higher ∆G/G of 20% and 30%. The results in Fig. 4.49(a) further manifest that at the larger amplitude of the mass flux oscillation the time variation of the bubble departure diameter is noticeably stronger.
Moreover, an increase in the period of the mass flux oscillation exhibits a relatively slight effect on the variation of the bubble departure diameter with time (Fig. 4.49(b)).
Furthermore, an increase in the mean refrigerant mass flux and saturation temperature
cause the departing bubbles to become smaller but do not significantly change the form of the dp variation with time (Figs. 4.50(a) and (b)).
Next, the data for the time variations of the space-average bubble departure frequency for various cases are shown in Figs. 4.51 & 4.52. Note that the bubble departure frequency also varies like a triangular wave. The increase of f with G is ascribed to the higher drag on the bubbles attaching to the heated surface by the liquid refrigerant moving at a higher speed for a higher G. This in turn, causes an earlier departure of the bubbles from the surface, resulting in a higher departure frequency. For an oscillation mass flux the bubbles depart from the heated surface at a decreasing rate in the first half of the periodic cycle in which the mass flux decreases with time. Apparently, in the second half of the cycle in which the mass flux increases with time the bubble departing rate increases. It should be pointed out that the time variations of the bubble departure frequency are stronger for the higher amplitude of the mass flux oscillation (Fig. 4.51(a)). But the effects of the period of the mass flux oscillation on the time variation of the bubble departure frequency are relatively small (Fig. 4.51(b)). Figure 4.52 shows that increasing G and Tsat mainly results in a higher mean level of the bubble departure frequency.
Finally, the time variation of the space-average active nucleation site density on the heated surface affected by the mass flux oscillation is illustrated in Figs. 4.53 & 4.54. Note that in the time periodic flow boiling the active nucleation site density increases with time in the first half of the periodic cycle in which the mss flux decreases with time. The reverse process appears in the second half of the cycle in which the mass flux increases with time.
At the higher amplitude of the mass flux oscillation the time variation of nac is stronger (Fig. 4.53(a)). The effects of the period of the mass flux oscillation on the time variation of nac are also relatively small (Fig. 4.53(b)). Besides, the results in Fig. 4.54 show that a lower mean refrigerant mass flux and a higher mean refrigerant saturation temperature mainly cause higher mean levels of nac
Based on the present data, the dependence of the quantitative bubble characteristics on the mass flux oscillation can be approximately expressed as dp α G-a , f α Gb and nac α G-c in Fig. 4.55, when the short time lag in the Tw oscillation is neglected. Here the exponents a, b and c range respectively from 0.415 to 0.375, 1.11 to 1.2 and 1.25 to 1.15.
Note that the latent heat transfer resulting from bubble nucleation in the persistent boiling . It is due to the lower surface tension for R-410A at a higher saturated temperature which in turn facilitates the bubble nucleation.
qb is proportional to dp3
, f and nac, as discussed in the previous study [8]. Thus qb α G-d, here d various from 1.385 to 1.075. This result clearly indicates that the flow boiling heat transfer gets better at decreasing refrigerant mass flux since qb prevails in the boiling heat transfer. This in turn causes the heated wall temperature to decrease at decreasing refrigerant mass flux in the time periodic flow boiling.
Fig. 4.1 Comparison of the preset single-phase liquid convection heat transfer data with the correlations of Gnielinski and Dittus-Boelter.
0 200 400 600 800 1000
G (kg/m2s) 0
500 1000 1500 2000 2500 3000 3500
hl (w/m2 °C)
:δ = 2mm
R-410A Single-Phase Liquid Convection Heat Transfer Coefficient at Tsat=15oC , Tsub=3oC
Dittus-Boelter correlation Ginielinski correlation
Fig. 4.2 Stable saturated flow boiling curves for R-410A for various refrigerant mass fluxes at Tsat = 10℃ and δ = 2.0mm.
ONB(300)
0 2 4 6 8
Tsat 0
10 20 30 40 50 60
q(kW/m2)
: G = 300kg/m2s : G = 400kg/m2s : G = 500kg/m2s
ONB(500) ONB(400)
R-410A Saturated Flow Boiling Curves at Tsat=10oC, δ = 2.0mm
ONB : Onset of Nucleate Boiling
Fig. 4.3 Stable saturated flow boiling curves for R-410A for various refrigerant saturated temperatures at G = 400 kg/m2s and δ = 2.0 mm.
ONB(10)
0 2 4 6 8
Tsat
0 10 20 30 40 50 60
q(kW/m2)
: Tsat =5°C : Tsat =10°C : Tsat =15°C
ONB(15)
R-410A Saturated Flow Boiling Curves at G = 400kg/m2s, δ = 2.0mm
ONB : Onset of Nucleate Boiling
ONB(5)
0 2 4 6 8
R-410A Time-Average Saturated Flow Boiling Heat Transfer Coefficient at Tsat = 10°C, δ = 2.0 mm, G = 400 kg/m2s, period = 60sec
Fig. 4.4 Time-average flow boiling curves for R-410A for (a) various amplitudes of refrigerant mass flux oscillation at T =10 Csat o , δ = 2.0 mm,G=400kg/m2and tp
= 60 sec. and (b) various periods of refrigerant mass flux oscillation at
o
R-410A Time-Average Saturated Flow Boiling Heat Transfer Coefficient at Tsat = 10°C, δ = 2.0 mm, G = 400 kg/m2s, G/ G = 20%
Fig. 4.5 Stable saturated flow boiling heat transfer coefficient for R-410A for various refrigerant mass fluxes at T =10 Csat o .
0 10 20 30 40 50
q (kW/m2) 0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
hr(W/m2 °C)
G = 300 kg/m2s G = 400 kg/m2s G = 500 kg/m2s
R-410A Saturated Flow Boiling Heat Transfer Coefficient at Tsat = 10°C, δ = 2.0 mm
Fig. 4.6 Stable saturated flow boiling heat transfer coefficient for R-410A for various refrigerant saturated temperatures at G = 400 kg/m2s and δ = 2.0 mm.
0 10 20 30 40 50
q (kW/m2) 0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
hr(W/m2 oC)
Tsat = 5°C Tsat = 10°C, Tsat = 15°C,
R-410A Saturated Flow Boiling Heat Transfer Coefficient at G = 400 kg/m2s, δ = 2.0 mm
0 10 20 30 40 50
R-410A Time-Average Saturated Flow Boiling Heat Transfer Coefficient at Tsat = 10°C, δ = 2.0 mm, G = 400 kg/m2s, period = 60sec
Fig. 4.7 Time-average heat transfer coefficients for R-410A for (a) variousΔG/Gat
sat o
R-410A Time-Average Saturated Flow Boiling Heat Transfer Coefficient at Tsat = 10°C, δ = 2.0 mm, G = 400 kg/m2s, G/ G= 20%
Fig. 4.8 Time variations of measured heated surface temperature for the stable saturated flow boiling of R-410A for various imposed heat fluxes at (a) G= 300 kg/m2
G
(a) Instantaneous wall temperature for R-410A saturated flow boiling at Tsat = 10°C, G = 400 kg/m2s, δ =2.0 mm
(a) Instantaneous wall temperature for R-410A saturated flow boiling at Tsat = 10°C, G = 300 kg/m2s, δ =2.0 mm
Fig. 4.9 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at T�sat = 10℃, δ = 2.0mm, tp = 60 sec and G� = 400
kg/m2s with ∆G/G� = 10%.
0 10 20 30 40 50 60 70 80 90
t(sec)
300 400 500
G (kg/m2 s)
Oscillation of Mass Flux for R-410A at Tsat= 10°C, δ= 2.0 mm, G= 400kg/m2s, G/ G=10%, tp=60sec
0 10 20 30 40 50 60 70 80 90
t(sec) 10
12 14 16 18
Tw(°C)
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=10%, tp=60sec
boiling starts boiling stops
1(single phase) 3(intermittent boiling) 5(persistent flow boiling)
7 11 21 q = 31(kw/m2)
Fig. 4.10 Time variations of oscillating refrigerant mass flux and measured heated wall
temperature in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at T =10 Csat o , δ = 2.0mm, tp = 60 sec andG=400kg/m2s
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
boiling starts boiling stops
1(single phase)
Fig. 4.11 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various
imposed heat fluxes at T =10 Csat o , δ = 2.0mm, tp = 60 sec and G= 400
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=30%, tp=60sec
boiling starts boiling stops
1(single phase)
Fig. 4.12 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at T =10 Csat o , δ = 2.0mm, tp = 20 sec and G= 400 kg/m2s
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=20sec
boiling starts boiling stops
Fig. 4.13 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at , δ = 2.0mm, tp = 120 sec and G= 400
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=120sec
boiling starts boiling stops
1(single phase)
Fig. 4.14 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at , δ = 2.0mm, tp = 60 sec and G= 300 kg/m2s
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 300kg/m2s, G/ G=20%, tp=60sec
boiling starts boiling stops
1(single phase)
Fig. 4.15 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at , δ = 2.0mm, tp = 60 sec and G= 500
The transient wall temperature for oscillating saturated flow boiling at Tsat= 10°C, δ = 2.0 mm, G= 500kg/m2s, G/ G=20%, tp=60sec
boiling starts boiling stops
2(single phase)
Fig. 4.16 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at , δ = 2.0mm, tp = 60 sec and G= 400 kg/m2s
The transient wall temperature for oscillating saturated flow boiling at Tsat= 5°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
boiling starts boiling stops
1(single phase)
Fig. 4.17 Time variations of oscillating refrigerant mass flux and measured heated wall temperature in time periodic saturated flow boiling of R-410A for various imposed heat flux at , δ = 2.0mm, tp = 60 sec and G= 400 kg/m2s
The transient wall temperature for oscillating saturated flow boiling at Tsat= 15°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
boiling starts boiling stops
1(single phase)
Fig. 4.18 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=10%, tp=60sec
Fig. 4.19 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
Fig. 4.20 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=30%, tp=60sec
Fig. 4.21 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=20sec
ΔG/G=20%
Fig. 4.22 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
sat o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=120sec
ΔG/G=20%
Fig. 4.23 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
sat o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 300kg/m2s, G/ G=20%, tp=60sec
ΔG/G=20%
Fig. 4.24 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
sat o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 10°C, δ = 2.0 mm, G= 500kg/m2s, G/ G=20%, tp=60sec
ΔG/G=20%
Fig. 4.25 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
sat o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 5°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
ΔG/G=20%
Fig. 4.26 Time variations of flow boiling heat transfer coefficients in time periodic saturated flow boiling of R-410A for various imposed heat fluxes at
sat o
Oscillation of flow boiling heat transfer coefficients for R-410A at Tsat= 15°C, δ = 2.0 mm, G= 400kg/m2s, G/ G=20%, tp=60sec
ΔG/G=20%
Fig. 4.27 Effects of imposed heat flux on amplitudes of wall temperature oscillation in time periodic saturated flow boiling of R-410A for various amplitudes of mass flux oscillation (a), periods of mass flux oscillation (b), mean mass fluxes (c), and refrigerant saturated temperatures (d). (
).
Fig. 4.27 continues
0 10 20 30 40 50
q(kW/m2) 0
0.1 0.2 0.3 0.4
ATw(°C)
G
400
300 500 (c) T sat=10°, δ =2.0 mm, G/ G = 20%, tp = 60 sec
0 10 20 30 40 50
q(kW/m2) 0
0.1 0.2 0.3 0.4
ATw(°C)
Tsat
5°
10°
15°
(d) δ =2.0 mm, tp = 60 sec, G = 400kg/m2s, G/ G = 20%
Fig. 4.28 Flow regime map for time periodic R-410A flow boiling atδ= 2.0 mm and tp
= 60 sec for various mean saturated temperatures and mean mass fluxes.
0 10 20 30 40
G/ G(%)
0 4E-005 8E-005 0.00012 0.00016
Bo
Tsat=10oC, G= 300kg/m2s Tsat=15oC, G = 400kg/m2s Tsat=10oC, G = 400kg/m2s
Time periodic R-410A saturated flow boiling d= 2.0 mm, tp=60sec
Persistent Flow Boiling
Intermittent Boiling
Single Phase Flow
δ=2mm, G = 400 kg/m2s 6mm
(a)q=10 kW/m2s, Tsat=10℃ (e)q=10 kW/m2s, Tsat=15℃
(b)q=15 kW/m2s, Tsat=10℃ (f)q=15 kW/m2s, Tsat=15℃
(c)q=20 kW/m2s, Tsat=10℃ (g)q=20 kW/m2s, Tsat=15℃
(d) q=25 kW/m2s, Tsat=10℃ (h) q=25 kW/m2s, Tsat=15℃
Fig. 4.29 Photos of boiling flow in stable saturated flow boiling of R-410A for various imposed heat fluxes at δ =2.0mm, G = 400 kg/m2s and .
flow
→
← →
o o
T =10 C & 15 Csat
δ=2mm, Tsat=10℃
6mm
(a)q=10 kW/m2s, G = 300 kg/m2s
6mm
(e)q=10 kW/m2s, G = 500 kg/m2s
(b)q=15 kW/m2s, G = 300 kg/m2s (f)q=15 kW/m2s, G = 500 kg/m2s
(c)q=20 kW/m2s, G = 300 kg/m2s (g)q=20 kW/m2s, G = 500 kg/m2s
(d) q=25 kW/m2s, G = 300 kg/m2s (h) q=25 kW/m2s, G = 500 kg/m2s
Fig. 4.30 Photos of boiling flow in stable saturated flow boiling of R-410A for various imposed heat fluxes at δ =2.0mm, , G =300kg/m2s and 500 kg/m2s.
flow
→
← →
o
T =10 C sat
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=10%, tP=60 sec., q=4kW/ m2 6mm
(1)t=t0, G=439.6kg/m2s
6mm
(5) t=t0+ 4tP/8, G=360.4kg/m2s
(2)t=t0+ tP/8, G=422.4kg/m2s (6) t=t0+ 5tP/8,G=381.9kg/m2s
(3) t=t0+2 tP/8, G=400.9kg/m2s (7) t=t0+ 6tP/8, G=403.4kg/m2s
(4) t=t0+ 3tP/8 ,G=381.3kg/m2s (8) t=t0+ 7tP/8, G=426.7kg/m2s
Fig. 4.31 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G=400 kg/m2s, ΔG/G 10%= ,
sat o
T =10 C , δ =2.0mm and tp= 60sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=60 sec., q=4kW/ m2 6mm
(1)t=t0, G=476.4kg/m2s
6mm
(5) t=t0+ 4tP/8, G=325.4kg/m2s
(2)t=t0+ tP/8, G=438.4kg/m2s (6) t=t0+ 5tP/8,G=358.6kg/m2s
(3) t=t0+2 tP/8, G=397.7kg/m2s (7) t=t0+ 6tP/8, G=400.3kg/m2s
(4) t=t0+ 3tP/8 ,G=357.4kg/m2s (8) t=t0+ 7tP/8, G=440.3kg/m2s
Fig. 4.32 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 20%= ,T =10 C sat o , δ =2.0mm and tp= 60sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=30%, tP=60 sec., q=4kW/ m2 6mm
(1)t=t0, G=519.5kg/m2s
6mm
(5) t=t0+ 4tP/8, G=280.2kg/m2s
(2)t=t0+ tP/8, G=461.1kg/m2s (6) t=t0+ 5tP/8,G=340.8kg/m2s
(3) t=t0+2 tP/8, G=402.2kg/m2s (7) t=t0+ 6tP/8, G=405.9kg/m2s
(4) t=t0+ 3tP/8 ,G=336.5kg/m2s (8) t=t0+ 7tP/8, G=467.2kg/m2s
Fig. 4.33 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 30%= ,T =10 C sat o , δ =2.0mm and tp= 60sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=20 sec., q=4kW/ m2 6mm
(1)t=t0, G=482.4kg/m2s
6mm
(5) t=t0+ 4tP/8, G=325.9kg/m2s
(2)t=t0+ tP/8, G=443.5kg/m2s (6) t=t0+ 5tP/8,G=361.3kg/m2s
(3) t=t0+2 tP/8, G=401.7kg/m2s (7) t=t0+ 6tP/8, G=401.2kg/m2s
(4) t=t0+ 3tP/8 ,G=357.8kg/m2s (8) t=t0+ 7tP/8, G=446.2kg/m2s
Fig. 4.34 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 20%= ,T =10 C sat o , δ =2.0mm and tp= 20sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=120 sec., q=4kW/ m2 6mm
(1)t=t0, G=478.9kg/m2s
6mm
(5) t=t0+ 4tP/8, G=326.0kg/m2s
(2)t=t0+ tP/8, G=447.0kg/m2s (6) t=t0+ 5tP/8,G=363.5kg/m2s
(3) t=t0+2 tP/8, G=403.8kg/m2s (7) t=t0+ 6tP/8, G=404.0kg/m2s
(4) t=t0+ 3tP/8 ,G=365.6kg/m2s (8) t=t0+ 7tP/8, G=442.1kg/m2s
Fig. 4.35 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 20%= ,T =10 C sat o , δ =2.0mm and tp= 120sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=300 kg/m2s,ΔG/G=20%, tP=60 sec., q=3kW/ m2 6mm
(1)t=t0, G=359.2kg/m2s
6mm
(5) t=t0+ 4tP/8, G=241.9kg/m2s
(2)t=t0+ tP/8, G=330.9kg/m2s (6) t=t0+ 5tP/8,G=267.1kg/m2s
(3) t=t0+2 tP/8, G=298.4kg/m2s (7) t=t0+ 6tP/8, G=297.8kg/m2s
(4) t=t0+ 3tP/8 ,G=267.7kg/m2s (8) t=t0+ 7tP/8, G=330.3kg/m2s
Fig. 4.36 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 3kW/m2at G =300 kg/m2s,
ΔG/G 20%= ,T =10 C sat o , δ =2.0mm and tp= 60sec.
flow
→
← →
Tsat=10℃, δ=2mm,G=500 kg/m2s,ΔG/G=20%, tP=60 sec., q=5qkW/ m2 6mm
(1)t=t0, G=596.4kg/m2s
6mm
(5) t=t0+ 4tP/8, G=401.0kg/m2s
(2)t=t0+ tP/8, G=550.8kg/m2s (6) t=t0+ 5tP/8,G=453.9kg/m2s
(3) t=t0+2 tP/8, G=502.3kg/m2s (7) t=t0+ 6tP/8, G=496.0kg/m2s
(4) t=t0+ 3tP/8 ,G=452.5kg/m2s (8) t=t0+ 7tP/8, G=548.2kg/m2s
Fig. 4.37 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 5kW/m2at G =500 kg/m2s,
ΔG/G 20%= ,T =10 C sat o , δ =2.0mm and tp= 60sec.
flow
→
← →
Tsat=5℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=60 sec., q=4qkW/ m2 6mm
(1)t=t0, G=476.3kg/m2s
6mm
(5) t=t0+ 4tP/8, G=321.7kg/m2s
(2)t=t0+ tP/8, G=445.7kg/m2s (6) t=t0+ 5tP/8,G=358.6kg/m2s
(3) t=t0+2 tP/8, G=402.5kg/m2s (7) t=t0+ 6tP/8, G=402.2kg/m2s
(4) t=t0+ 3tP/8 ,G=360.9kg/m2s (8) t=t0+ 7tP/8, G=442.1kg/m2s
Fig. 4.38 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 20%= , , δ =2.0mm and tp= 60sec.
flow
→
← →
sat o
T =5 C
Tsat=15℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=60 sec., q=4qkW/ m2 6mm
(1)t=t0, G=477.5kg/m2s
6mm
(5) t=t0+ 4tP/8, G=324.8kg/m2s
(2)t=t0+ tP/8, G=440.9kg/m2s (6) t=t0+ 5tP/8,G=359.2kg/m2s
(3) t=t0+2 tP/8, G=399.7kg/m2s (7) t=t0+ 6tP/8, G=403.3kg/m2s
(4) t=t0+ 3tP/8 ,G=357.9kg/m2s (8) t=t0+ 7tP/8, G=440.9kg/m2s
Fig. 4.39 Photos of intermittent saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 4kW/m2at G =400 kg/m2s,
ΔG/G 20%= , , δ =2.0mm and tp= 60sec.
flow
→
← →
sat o
T =15 C
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=10%, tP=60 sec., q=10kW/ m2 6mm
(1)t=t0, G=439.8kg/m2s
6mm
(5) t=t0+ 4tP/8, G=358.6kg/m2s
(2)t=t0+ tP/8, G=423.9kg/m2s (6) t=t0+ 5tP/8,G=374.6kg/m2s
(3) t=t0+2 tP/8, G=397.3kg/m2s (7) t=t0+ 6tP/8, G=398.1kg/m2s
(4) t=t0+ 3tP/8 ,G=377.6kg/m2s (8) t=t0+ 7tP/8, G=416.5kg/m2s
Fig. 4.40 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 10kW/m2at G=400 kg/m2s,
ΔG/G 10%= , , δ =2.0mm and tp= 60sec.
← →
flow
→
sat o
T =10 C
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=20%, tP=60 sec., q=10kW/ m2 6mm
(1)t=t0, G=481.5kg/m2s
6mm
(5) t=t0+ 4tP/8, G=324.2kg/m2s
(2)t=t0+ tP/8, G=438.4kg/m2s (6) t=t0+ 5tP/8,G=356.7kg/m2s
(3) t=t0+2 tP/8, G=399.1kg/m2s (7) t=t0+ 6tP/8, G=397.3kg/m2s
(4) t=t0+ 3tP/8 ,G=359.2kg/m2s (8) t=t0+ 7tP/8, G=437.8kg/m2s
Fig. 4.41 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 10kW/m2at G=400 kg/m2s,
ΔG/G 20%= , , δ =2.0mm and tp= 60sec.
← →
flow
→
sat o
T =10 C
Tsat=10℃, δ=2mm,G=400 kg/m2s,ΔG/G=30%, tP=60 sec., q=10kW/ m2 6mm
(1)t=t0, G=517.8kg/m2s
6mm
(5) t=t0+ 4tP/8, G=284.0kg/m2s
(2)t=t0+ tP/8, G=462.9kg/m2s (6) t=t0+ 5tP/8,G=343.8kg/m2s
(3) t=t0+2 tP/8, G=401.6kg/m2s (7) t=t0+ 6tP/8, G=401.2kg/m2s
(4) t=t0+ 3tP/8 ,G=336.5kg/m2s (8) t=t0+ 7tP/8, G=458.9kg/m2s
Fig. 4.42 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 10kW/m2at G=400 kg/m2s,
Fig. 4.42 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle for q= 10kW/m2at G=400 kg/m2s,