A - A Cross-section View
TIME PERIODIC SATURATED FLOW BOILING OF FC-72 OVER A SMALL HEATED COPPER PLATE
4.2 Time Periodic Saturated Flow Boiling Heat Transfer Characteristics
(4.3)
Their correlation is based on the experimental data procured from the same liquid and same flow configuration as the present data and the comparison is shown in Fig. 4.1 for the dimensional and dimensionless heat transfer coefficients. The results indicate that our data are in good agreement with their correlation.
It should be mentioned that the working fluid properties used in reducing the data for Fig. 4.1 from Equations (4.1) – (4.3) are calculated at the coolant inlet temperature. The copper plate diameter is chosen as the characteristic length in defining the Reynolds number and average Nusselt number
ReL
NuL because of its significant effect on the heat transfer performance [5].
4.2 Time Periodic Saturated Flow Boiling Heat Transfer Characteristics
The temporal boiling heat transfer characteristics for the FC-72 flow over the heated copper plate resulting from the imposed temporal heat flux and mass flux oscillations are illustrated by
34
presenting the time variations of the space-average heated surface temperature Tw and heat transfer coefficient h2φ for various G , q, △q/q, G△ /G and tp. First, the measured time variations of Tw for the limiting cases of stable flow boiling at constant G and q are shown in Fig.
4.2 for G= 300 and 400kg/m2s at various q. These data indicate that the fluctuations of the space-average heated surface temperatures with time for various q are relatively small. The resulting boiling in the flow for △G=0 and △q=0 can be regarded essentially as at a statistically stable state. The corresponding boiling curves are shown in Fig. 4.3. The data in Fig. 4.3 show that the required heat flux and wall superheat for the onset of nucleate boiling (ONB) are higher for a higher coolant mass flux.
Next, we move further to examine the Tw data for the imposed heat flux and coolant mass flux oscillating periodically in time respectively in forms of nearly a sinusoidal wave and a triangular wave. The results are given first in Fig. 4.4 for G=200kg/m2s and tp=20 sec. for +G G/ =10%
and +q q/ =30% at variousq. For comparison purpose the data for constant G ( G=0△ ) but oscillation q are also shown in the figure. Besides, the data for both in-phase and out-of-phase G and q oscillations are presented. Note that for each case the temporal oscillation of the heated surface temperature is also periodic in time and is at the same frequency as the heat flux and/or mass flux. Moreover, the Tw oscillation gets slightly stronger for a higher mean level of the heat flux oscillation irrespective of the in-phase or out-of-phase oscillations. A close inspection of these data further reveals that the heated surface temperature oscillation lags significantly behind the imposed heated flux oscillation for constant G and for both in-phase and out-of-phase G and q oscillations. This time lag in Tw results mainly from the thermal inertia of the copper plate since the time lag in Tw due to the mass flux oscillation is small [52]. We also note that in the single-phase flow prevailed only at low imposed heat flux the time lag is even longer than that for the flow boiling. Table 4.1 summarizes the quantitative data for the amplitude of the heated surface temperature oscillation ΔTw and the relative magnitude of the time lag tl/tp. The results clearly
35
manifest that the time lag in Tw is somewhat longer when G and q are in out-of-phase oscillations than the other situations. It is of interest to note that in the single-phase flow the Tw oscillation is strongest for the out-of-phase G and q oscillations. But the opposite is true for the flow boiling which prevails at high imposed heat flux, showing the Tw oscillation is suppressed by the out-of-phase oscillations. This unusual outcome requires in-depth examination of the detailed heat transfer mechanisms in the flow subject to the simultaneous G and q oscillations. Here we provide preliminary interpretation. When only the heat flux oscillation exists, the heated surface temperature increases with the heat flux for both single-and two-phase flows after accounting for the time lag, as evident from Fig. 4.4(a). But when only the mass flux oscillation exists, our previous study[52]
showed that in the two-phase boiling flow Tw decreases at decreasing mass flux due to drastic increase in the active bubble nucleation site density. The trend is reversed for the single-phase flow.
This explains why an out-of-phase mass flux oscillation can reduce the Tw oscillation resulting from the heat flux oscillation in the boiling flow and can intensify the Tw oscillation in the single-phase flow.
Effects of the experimental parameters on the Tw oscillation are illustrated in Figs. 4.5-4.15.
The results indicate that the heated surface temperature oscillates in a larger amplitude for higher oscillation amplitudes in the heat flux and mass flux. It is worth noting that an increase in the period of the G and q oscillations causes a much stronger Tw oscillation, are evident by comparing the data in Figs. 4.5-4.7 with that in Figs. 4.13-4.15. To be more quantitative, we summarize the present data for the amplitude and time lag of the Tw oscillation in Tables 4.2-4.6 for various G,+G G/ , tp, q
and +q q/ . It is of interest to note that the imposed out-of-phase G & q oscillations do not always weaken the Tw oscillation in the boiling flow. Similarly, in-phase G & q oscillations may not reduce the Tw oscillation in the single-phase flow especially at high +q q/ . We also note that the relative time lag tl/ tp varies nonmonotonically with the experimental parameters.
At this point we move further to investigate whether it is possible to completely suppress the
36
heated surface temperature oscillation driven by a given time periodic heat flux oscillation by choosing an appropriate in-phase or out-of-phase mass flux oscillation. It is note in this investigation that the chosen mass flux oscillation should be at a suitable amplitude and at the same period as the heat flux oscillation. Most importantly, the time lags in the Tw oscillation due to the q and G oscillations have to be taken into consideration. The results from this investigation are illustrated in Figs. 4.16 and 4.17 for G=300kg/m2s , +G G/ =15% & 20% and tp=20sec & 30sec for several q. Here in the single-phase flow an in-phase G oscillation is imposed. But an out-of-phase G oscillation is imposed in the two-phase flow. Note that a small time lag in the Tw
oscillation also exists due to the mass flux oscillation (Figs. 4.16(b) and 4.17(b)), as already montioned above. The results in Fig. 4.16 indicate that as the G oscillation is imposed at a time instant behind the q oscillation by the difference in the time lags respectively due to the q and G oscillations, the Tw oscillations can indeed be suppressed to be relatively small in magnitude (Fig.
4.16(c)). In fact, the resulting Tw oscillation amplitude is below 0.1℃ which is smaller than the thermal disturbances in the background and the experimental uncertainty in measuring the temperature by the thermocouples. Hence the heated surface temperature can be regarded at steady state. At a high q the Tw oscillation can only be reduced by the G oscillation to a significant degree((Fig. 4.17(c)). It cannot be completely suppressed.
The associated heat transfer coefficients for the single-phase and boiling flows affected by the imposed heat and mass flux oscillations are presented in Figs. 4.18-4.29. The results indicate that the oscillations in the heat transfer coefficient exhibit a similar trend to the heated surface temperature oscillation. Specifically, the h1Φ and h2Φ oscillations are also periodic in time and are at the same frequency as the heat flux and/or mass flux. Besides, at a higher q the oscillations in h1Φ
and h2Φ are slightly stronger. But the oscillation amplitudes in h1Φ and h2Φ depend only slightly on the in-phase or out-of-phase G and q oscillations. Moreover, h1Φ and h2Φ are in stronger oscillations for a higher amplitude and a longer period of the imposed G and q oscillations.
37
4.3 Bubble Characteristics
To elucidate the above time periodic flow boiling heat transfer characteristics, the data for the bubble characteristics of FC-72 obtained from the present flow visualization are examined in the following. The photos taken from the top view of the boiling flow in a small region around the geometric center of the heated surface for various coolant mass fluxes and imposed heat fluxes are shown in Figs. 4.32 - 4.49. At first, the bubble characteristics for the limiting cases of constant imposed heat and mass fluxes are illustrated by the photos in Fig. 4.32. It is noted in the flow visualization and the results in Fig. 4.32 that in the stable flow boiling the vapor bubbles begin to appear as the heated surface temperature exceeds that required for 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 bubble departure diameters. 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 for a given heat flux.
Next, the bubble characteristics in the time periodic flow boiling are illustrated by presenting the photos of the boiling flow at eight selected time instants in a typical periodic cycle in Figs.
4.33-4.49. In these figures the symbol “ t=to ” signifies the time instant at which the instantaneous heat fluxes is at the lowest level and starts to increase with time and the mass flux is also at the lowest level and starts to increase with time for the in-phase G and q oscillations. But for the out-of-phase G and q oscillations at to the mass flux is at the highest level and starts to decrease with time.
The results in Fig. 4.33 for an imposed heat flux oscillation at a given constant G of 200 kg/m2s qualitative indicate that in the first half of the periodic cycle in which the surface heat flux increases with time the bubbles grow with time and merge together to form big bubbles. Besides,
38
more bubbles nucleate from the heated surface. The bubbles are in rigorous motion and the photos become somewhat blurred as the heat flux exceeds certain level. In the second half of the cycle the opposite processes take place. It is important to point out that the bubble behavior in the boiling flow affected by the mass flux oscillation exhibits an opposite trend [52]. Specifically, at increasing mass flux in the first half of the periodic cycle the bubbles get smaller and become more disperse.
Besides, less bubble nucleation occurs on the heated surface. Thus, when the G and q oscillations are in-phase, the bubble behavior is counter-balanced by two opposite effects and its change with time is rather mild (Figs. 4.34, 4.37, 4.39, 4.42, 4.45) except for some cases with large differences in the amplitudes of heat and mass flux oscillations (Figs. 4.38, 4.42). But when G and q are in out-of-phase oscillations the two effects augment each other and the bubble behavior can show drastic variation with time (Figs. 4.35, 4.38, 4.40, 4.46, and 4.49). Moreover, at higher ΔG G/ and
/
Δq q and at a longer tp the bubble characteristics experience stronger time variations.
39
40
w osc and re en turated flow
boiling for
Table 4.1 Amplitudes of T illation lative time lags in transi t oscillatory sa G=2
at Δq/q= 30%,ΔG G/ =10% and tp=20sec. for 00kg/m2s.
G various q
= 200kg/m2s /
+G G
Period
tp(sec) +q q/ 2
q(W/cm ) ΔTW(K ) t1/tp
Heat flux oscillation only 0.24 0.375 In-phase G & q oscillations 0.23 0.375 1.01
(single-phase)
ons
Out-of-phase G & q oscillati 0.30 0.475 Heat flux oscillation only 0.33 0.25 In-phase G & q oscillations 0.39 0.225 2.37
Out-of-phase G & q oscillations 0.31 0.35 Heat flux oscillation only 0.43 0.175 In-phase G & q oscillations 0.43 0.2 4.05
tions
Out-of-phase G & q oscilla 0.41 0.225 Heat flux oscillation only 0.53 0.225 In-phase G & q oscillations 0.58 0.225 10% 20 30%
6.02
Out-of-phase G & q oscillations 0.51 0.25
Table 4.2 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30,50%,ΔG G/ =5% and tp=20sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/ 2
q(W/cm ) ΔTW( )K t1/tp
Heat flux oscillation only 0.11 0.4 In-phase G & q oscillations 0.11 0.4 1.02
(single-phase)
Out-of-phase G & q oscillations 0.11 0.4 Heat flux oscillation only 0.18 0.375 In-phase G & q oscillations 0.23 0.2 1.90
Out-of-phase G & q oscillations 0.17 0.3 Heat flux oscillation only 0.20 0.2 In-phase G & q oscillations 0.31 0.05 4.10
Out-of-phase G & q oscillations 0.24 0.35 Heat flux oscillation only 0.20 0.15 In-phase G & q oscillations 0.25 0.075 10%
5.08
Out-of-phase G & q oscillations 0.21 0.25 Heat flux oscillation only 0.28 0.375 In-phase G & q oscillations 0.27 0.35 1.02
(single-phase)
Out-of-phase G & q oscillations 0.26 0.425 Heat flux oscillation only 0.35 0.2 In-phase G & q oscillations 0.42 0.175 1.94
Out-of-phase G & q oscillations 0.35 0.2 Heat flux oscillation only 0.47 0.15 In-phase G & q oscillations 0.49 0.1 4.10
Out-of-phase G & q oscillations 0.48 0.225 Heat flux oscillation only 0.54 0.2 In-phase G & q oscillations 0.56 0.175 30%
5.10
Out-of-phase G & q oscillations 0.57 0.225 Heat flux oscillation only 0.42 0.4 In-phase G & q oscillations 0.41 0.375 1.02
(single-phase)
Out-of-phase G & q oscillations 0.43 0.3 Heat flux oscillation only 0.59 0.2 In-phase G & q oscillations 0.71 0.2 1.94
Out-of-phase G & q oscillations 0.62 0.25 Heat flux oscillation only 0.81 0.175 In-phase G & q oscillations 0.85 0.125 4.10
Out-of-phase G & q oscillations 0.77 0.15 Heat flux oscillation only 0.91 0.2 In-phase G & q oscillations 0.89 0.15 5% 20
50%
5.10
Out-of-phase G & q oscillations 0.83 0.175
41
Table 4.3 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30, 50%,ΔG G/ =10% and tp=20sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/ 2
q(W/cm ) ΔTW( )K t1/tp
Heat flux oscillation only 0.10 0.275 In-phase G & q oscillations 0.14 0.425 1.03
(single-phase)
Out-of-phase G & q oscillations 0.16 0.225 Heat flux oscillation only 0.14 0.325 In-phase G & q oscillations 0.27 0.075 2.67
Out-of-phase G & q oscillations 0.26 0.475 Heat flux oscillation only 0.15 0.225 In-phase G & q oscillations 0.34 0.025 4.03
Out-of-phase G & q oscillations 0.34 0.4 Heat flux oscillation only 0.19 0.2 In-phase G & q oscillations 0.33 0.05 10%
6.12
Out-of-phase G & q oscillations 0.34 0.475 Heat flux oscillation only 0.23 0.45 In-phase G & q oscillations 0.22 0.575 1.02
(single-phase)
Out-of-phase G & q oscillations 0.30 0.35 Heat flux oscillation only 0.38 0.3 In-phase G & q oscillations 0.44 0.225 2.35
Out-of-phase G & q oscillations 0.38 0.3 Heat flux oscillation only 0.51 0.275 In-phase G & q oscillations 0.59 0.15 5.04
Out-of-phase G & q oscillations 0.49 0.3 Heat flux oscillation only 0.56 0.25 In-phase G & q oscillations 0.66 0.2 30%
6.11
Out-of-phase G & q oscillations 0.57 0.3 Heat flux oscillation only 0.42 0.375 In-phase G & q oscillations 0.38 0.425 1.02
(single-phase)
Out-of-phase G & q oscillations 0.47 0.4 Heat flux oscillation only 0.64 0.3 In-phase G & q oscillations 0.68 0.25 2.16
Out-of-phase G & q oscillations 0.63 0.3 Heat flux oscillation only 0.77 0.25 In-phase G & q oscillations 0.85 0.25 4.07
Out-of-phase G & q oscillations 0.70 0.25 Heat flux oscillation only 0.94 0.275 In-phase G & q oscillations 1.04 0.225 10% 20
50%
6.09
Out-of-phase G & q oscillations 0.85 0.3
42
Table 4.4 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 30%,ΔG G/ =15% and tp=20sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/
q(W/cm )2 ΔTW( )K t1/tp
Heat flux oscillation only 0.26 0.375 In-phase G & q oscillations 0.24 0.475 1.01
(single-phase)
Out-of-phase G & q oscillations 0.30 0.375 Heat flux oscillation only 0.41 0.25 In-phase G & q oscillations 0.48 0.225 2.53
Out-of-phase G & q oscillations 0.37 0.3 Heat flux oscillation only 0.43 0.2 In-phase G & q oscillations 0.59 0.175 4.13
Out-of-phase G & q oscillations 0.42 0.325 Heat flux oscillation only 0.54 0.225 In-phase G & q oscillations 0.68 0.175 15% 20 30%
6.19
Out-of-phase G & q oscillations 0.50 0.25
Table 4.5 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 30%,ΔG G/ =10% and tp=20sec. for G=400kg/m2s.
G = 400kg/m2s /
+G G Period
tp(sec) +q q/
q(W/cm )2 ΔTW( )K t1/tp
Heat flux oscillation only 0.27 0.275 In-phase G & q oscillations 0.24 0.275 1.02
(single-phase)
Out-of-phase G & q oscillations 0.28 0.35 Heat flux oscillation only 0.45 0.225 In-phase G & q oscillations 0.63 0.225 3.03
Out-of-phase G & q oscillations 0.40 0.325 Heat flux oscillation only 0.48 0.2 In-phase G & q oscillations 0.68 0.175 4.12
Out-of-phase G & q oscillations 0.42 0.375 Heat flux oscillation only 0.55 0.2 In-phase G & q oscillations 0.69 0.175 10% 20 30%
6.13
Out-of-phase G & q oscillations 0.55 0.375
43
Table 4.6 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,30,50%,ΔG G/ =5% and tp=30sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/ 2
q(W/cm ) ΔTW( )K t1/tp
Heat flux oscillation only 0.16 0.233 In-phase G & q oscillations 0.12 0.433 1.04
(single-phase)
Out-of-phase G & q oscillations 0.19 0.283 Heat flux oscillation only 0.19 0.217 In-phase G & q oscillations 0.21 0.2 2.35
Out-of-phase G & q oscillations 0.16 0.233 Heat flux oscillation only 0.21 0.217 In-phase G & q oscillations 0.27 0.183 4.07
Out-of-phase G & q oscillations 0.18 0.267 Heat flux oscillation only 0.25 0.2 In-phase G & q oscillations 0.32 0.167 10%
6.04
Out-of-phase G & q oscillations 0.22 0.233 Heat flux oscillation only 0.41 0.3 In-phase G & q oscillations 0.37 0.367 1.02
(single-phase)
Out-of-phase G & q oscillations 0.45 0.317 Heat flux oscillation only 0.53 0.233 In-phase G & q oscillations 0.52 0.25 2.34
Out-of-phase G & q oscillations 0.46 0.233 Heat flux oscillation only 0.64 0.217 In-phase G & q oscillations 0.67 0.217 4.98
Out-of-phase G & q oscillations 0.59 0.217 Heat flux oscillation only 0.69 0.2 In-phase G & q oscillations 0.73 0.183 30%
6.01
Out-of-phase G & q oscillations 0.67 0.233 Heat flux oscillation only 0.68 0.35 In-phase G & q oscillations 0.69 0.35 1.01
(single-phase)
Out-of-phase G & q oscillations 0.69 0.333 Heat flux oscillation only 0.93 0.25 In-phase G & q oscillations 0.91 0.3 1.6
Out-of-phase G & q oscillations 0.88 0.283 Heat flux oscillation only 0.99 0.233 In-phase G & q oscillations 1.02 0.2 4.06
Out-of-phase G & q oscillations 0.88 0.183 Heat flux oscillation only 1.25 0.2 In-phase G & q oscillations 1.29 0.183 5% 30
50%
6.01
Out-of-phase G & q oscillations 1.20 0.183
44
Table 4.7 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,20%,ΔG G/ =15% and tp=20sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/
q(W/cm )2 ΔTW( )K t1/tp
Heat flux oscillation only 0.11 0.375 Mass flux oscillation only 0.11 0.175 1.09
(single-phase)
In-phase G & q oscillations 0.04 x Heat flux oscillation only 0.15 0.3 Mass flux oscillation only 0.14 0.075 10%
2.39
Out-of-phase G & q oscillations 0.06 x Heat flux oscillation only 0.29 0.225 Mass flux oscillation only 0.30 0.025 15% 20
20% 4.13
Out-of-phase G & q oscillations 0.08 x
Table 4.8 Amplitudes of Tw oscillation and relative time lags in transient oscillatory saturated flow boiling for various q at Δq/q= 10,15%,ΔG G/ =20% and tp=30sec. for G=300kg/m2s.
G = 300kg/m2s /
+G G Period
tp(sec) +q q/
q(W/cm )2 ΔTW( )K t1/tp
Heat flux oscillation only 0.18 0.250 Mass flux oscillation only 0.18 0.130
10% 1.03
(single-phase)
In-phase G & q oscillations 0.05 x Heat flux oscillation only 0.43 0.183 Mass flux oscillation only 0.42 0.017 20% 30
15% 8.08
Out-of-phase G & q oscillations 0.14 x
45
200 300 400 500 600 G(kg/m2s)
0 500 1000 1500 2000
h1f(W/cm2)
(a)FC-72 Single-phase liquid convective heat transfer at T- : in=30oC Correlation from Gersey and Mudawar(1992)
-:Present data
3000 4000 5000 6000 7000 8000
ReL 0
100 200 300 400
NuL
(b)FC-72 Single-phase liquid convective heat transfer at T- : in=30oC Correlation from Gersey and Mudawar(1992)
-:Present data
Fig. 4.1 Comparison of the present steady single-phase liquid convection heat transfer data with the correlation of Gersey and Mudawar (1992) for (a)h1φ vs. G and (b)NuL vs. ReL.
46
0 20 40 60 80 sec
100 60
65 70 75 80
Tw(oC)
1.02(W/cm2) 2.22(W/cm2)ONB
4.05(W/cm2) 6.06(W/cm2)
(a)Instantaneous wall temperature for stable saturated flow boiling at Tsat=55oC,G =300(kg/m2s)
0 20 40 60 80
sec
100 60
65 70 75 80
Tw(oC)
(b) Instantaneous wall temperature for stable saturated flow boiling at Tsat=55oC,G =400(kg/m2s)
1.01(W/cm2) 4.05(W/cm2) _
q=6.01(W/cm2)
2.4(W/cm2)ONB
Fig. 4.2 Time variations of the copper plate temperature in stable saturated flow boiling for various imposed heat fluxes at (a)G=300kg/m2s and (b) G=400kg/m2s
47
0 5 10 15 20 25 -Tsat(K)
0 2 4 6 8 10 12
q(W/cm2)
ÏONB(G300) ÏONB(G400) (a)Stable saturated flow boiling curve for FC-72 at Tin=55oC,G=300kg/m2s
ONB-Onset of Nucleate Boiling +:G=300kg/m2s
,:G=400kg/m2s
0 4 8 12
q(W/cm2) 0
1500 3000 4500 6000 7500
h2φ (W/m2Κ)
(b)FC-72 Saturated Flow Boiling Heat Transfer Coefficients at Tsat= 55oC
+:G = 300 kg/m2s ,:G = 400 kg/m2s
Fig. 4.3 (a) Stable saturated flow boiling curve and (b) stable saturated flow boiling heat transfer coefficients.
48
0 20 40 60 80 100 100
200 300
G (kg/m2s)
Constant mass flux of FC-72,G=200 kg/m2s
0 20 40 60 80 100
Oscillation of FC-72 mass flux
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
G =200 kg/m2s,-G/G = 10%,-q/q = 30%,tp=20sec ---:Out of phase G & q oscillation
(a) (b) (c)
Fig.4.4 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations
and (c) out-of-phase G and q oscillations at G 200kg/m s and 2 +G G/ =10% +q q/ =30%
49
= for and 20 sectp = .
0 20 40 60 80 100 200
300 400
G (kg/m2s) Constant FC-72 mass flux G=300 kg/m2s
0 20 40 60 80 100
Oscillation of FC-72 mass flux
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
G =300 kg/m2s,-G/G = 5%,-q/q = 10%,tp=20sec ---:Out of phase G & q oscillation
(a) (b) (c)
Fig.4.5 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at G 300kg m/ 2
50
s and
= +G G/ =5%for+q q/ =10%and 20 sectp = .
0 20 40 60 80 100 200
300 400
G (kg/m2s) Constant FC-72 mass flux G=300 kg/m2s
0 20 40 60 80 100
Oscillation of FC-72 mass flux
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
G =300 kg/m2s,-G/G = 5%,-q/q = 30%,tp=20sec ---:Out of phase G & q oscillation
(a) (b) (c)
Fig.4.6 Time variations of the measured instantaneous heated surface temperature for (a) imposed heat flux oscillation only, (b) in-phase G and q oscillations and (c) out-of-phase G and q oscillations at G 300kg/m s2 and / 5 / 30
51
= +G G= %for q q+ = % and 20sectp = .
0 20 40 60 80 100 200
300 400
G (kg/m2s) Constant FC-72 mass flux G=300 kg/m2s
0 20 40 60 80 100
Oscillation of FC-72 mass flux
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling
Instantaneous wall temperature for saturated flow boiling