Effect of Heat Flux Oscillation Amplitude

oscillation.

The effect of the amplitude of the heat flux oscillation on the time periodic flow boiling of R-410A is examined further, too. The results in Fig. 5.25 for three different amplitudes of the imposed heat flux oscillation with ∆q/q� = 10, 30 and 50% at t^p = 60 seconds show that the T_w oscillation is significantly stronger for a larger amplitude of the imposed heat flux oscillation. Note that the time lag in Tw

5.6 Time Periodic Bubble Characteristics in Saturated Flow Boiling

oscillation increases substantially when the amplitude of the imposed heat flux oscillation is raised from 10% to 30%. But a further increase in the amplitude of the heat flux oscillation does not increase the time lag noticeably.

To elucidate the time periodic saturated flow boiling heat transfer characteristics resulting from the imposed heat flux oscillation, 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 imposed heat fluxes are shown in Figs. 5.26-5.43 for selected cases for the time periodic saturated flow boiling. In these figures the symbol

〝 t=to 〞signifies the time instant at which the instantaneous heat flux is at the highest level and starts to decrease with time. The bubble behavior in the intermittent flow boiling for the cases with given intermediate imposed heat fluxes is manifested in Figs. 5.26-5.34.

The results clearly indicates that initially in the beginning of the cycle the instantaneous heat flux decreases with time but is still well above q�_ONB, bubbles nucleation from the heated surface is clearly seen. Note that the number and size of the bubbles decrease noticeably with time in the first quarter of the periodic cycle for the continuing decrease of the heat flux. Then the bubble nucleation gradually disappears and finally boiling stops at certain time instant slightly after t0+3tp/8 when the heat flux is slightly below q�ONB and bubble nucleation stops completely. The flow is in single-phase state. But after a certain

time instant slightly after t₀+6t_p/8 at which the imposed heat flux is raised to a certain high level, T_w

Then, we illustrate here how the time periodic bubble characteristics are affected by the amplitude and period of the heat flux oscillation for the persistent boiling in Figs.

5.35-5.43. The results indicate that for given G, q� , ∆q/q� and t

rises to exceed the wall superheat required for the onset of nucleate boiling so that bubble nucleation on the heated surface is seen and more bubbles nucleate on the heated surface as time increases. Two-phase boiling flow again dominates in the duct. We have to wait until about the end of the first quarter of the next cycle to see the bubble nucleation gradually disappears 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.

p

To be more quantitative on the bubble characteristics in the time periodic flow boiling due to the heat flux oscillation, we estimate the bubble departure diameter and frequency and the number density of the active nucleation sites on the heating surface in a typical periodic cycle at the middle axial location for the persistent flow boiling. The results in Figs. 5.44 – 5.49 show the effects of the experimental parameters on d

the departure bubbles get smaller in the duct in the first half of the cycle in which the heat flux decreases. The opposite processes take place in the second half of the cycle in which the heat flux increases with time. These changes of the bubble characteristics with the instantaneous heat flux become more significant for an increase in the amplitude of the heat flux oscillation, as shown from the results in the Figs. 5.35~5.37. Besides, the bubble coalescence occurs more frequently and more large bubbles appear in the duct for the cases with a longer period of the heat flux oscillation (Figs. 5.38&5.39). The results given in Figs. 5.42&5.43 indicate that for a higher refrigerant saturated temperature, more large bubbles appear in the duct. This is due to lower surface tension of R-410A at higher refrigerant saturated temperature.

p, f and n_ac. In these plots time〝t = 0〞denotes the instant of time the imposed heat flux is at the highest level and starts to decrease in a typical periodic cycle. The results in Figs. 5.44 and 5.45 indicate that as the imposed heat flux oscillates time periodically, the bubble departure diameter also varies time periodically and to some degree like a triangular wave as the imposed heat flux oscillation. Note that the effect of the time lag on the T_w oscillation is clearly seen.

More specifically, the size of the departing bubbles does not decrease immediately with

time in the first half of the periodic cycle in which the heat flux decreases with time. In fact, the bubble size increases in the initial transient for t < t_l and then for t > t_l the bubble departure diameter decreases. While in the second half of the cycle an opposite process is noted when heat flux increases with time. The results in Fig. 5.44(a) show that at the larger amplitude of the heat flux oscillation and mean imposed head flux the time variation of bubble departure diameter is somewhat stronger. Moreover, the results in Fig. 5.44(b) indicate that to some degree the bubble departure diameter varies stronger with time for a longer period of the heat flux oscillation. Furthermore, the results in Figs. 5.45(a) and (b) show that increases in the refrigerant mass flux and saturated temperature cause the departing bubbles to become smaller but do not change the wave form of the dp

How the temporal variation of the bubble departure frequency is affected by the heat flux oscillation is shown in Figs. 5.46 and 5.47. Note that the bubble frequency also varies like a triangular wave. At first, for t < t

variation with time.

1 the bubble departure frequency increases with time. Then, for an oscillation heat flux after the time lag for t > t₁ the bubbles depart from the heated surface at a decreasing rate in the first half of the periodic cycle in which the heat flux decreases with time (Fig. 5.46(a)). Apparently, in the second half of the cycle in which the heat flux increases the opposite process takes place. Moreover, the results in Fig.

5.46(a) indicate that at the larger amplitude of the heat flux oscillation and mean imposed heat flux the bubble departure frequency exhibits a stronger variation with time. Then, the results in Fig. 5.46(b) indicate that the bubble departure frequency oscillates in a larger amplitude at a longer period of the heat flux oscillation. Finally, at higher G and T_sat

The data given in Figs 5.48 and 5.49 show the time variations of the associated number density of the active nucleation sites on the heating surface affected by the heat flux oscillation. The results clearly indicate that in the time periodic flow boiling the active nucleation site density also varies like a triangular wave. Besides, n

the bubble departure frequency is higher (Figs. 5.47(a) and (b)).

ac decreases substantially with time after the time lag for t > t1 in the first half of the periodic cycle in which the heat flux decreases with time. The reverse process appears in the second half of the cycle in which the heat flux rises. At higher amplitude of the heat flux oscillation and mean imposed heat flux the temporal variation of nac is also stronger (Fig. 5.48(a)).

Moreover, for a longer period of the heat flux oscillation the time variation of nac is also

stronger (Fig. 5.48(b)). Finally, n_ac is significantly higher at a lower G and higher T_sat

It’s worth mentioning that the time instants at which d

(Figs.

5.49(a) and (b)).

p, f and nac attain their maximums and minimums are not exactly at the instants the imposed heat flux is at its highest and lowest levels respectively at t = 0 and t = tp

Based on the data in Figs. 5.44 – 5.49, in the persistent boiling at a high q the dependence of the quantitative bubble characteristics on the R-410A heat flux oscillation can be approximately expressed as d

/2. This is a direct consequence of the significant time lag in the time response of the heated surface temperature in the present time periodic flow boiling subject to the imposed heat flux oscillation.

p α q^a, f α q^b, and nac α q^c when the time lag in the Tw

oscillation is neglected. Here the exponents a, b and c range respectively from 0.02 to 0.13, 0.36 to 0.64 and 0.77 to 1.18, as shown in Fig. 5.50. Note that the latent heat transfer resulting from bubble nucleation in the persistent boiling qb is proportional to dp3

, f and nac, as discussed in the previous study [8]. Thus, q_b α q^d, here d varies from 1.19 to 2.21. This result clearly indicates that flow boiling heat transfer gets better at increasing heat flux since q_b prevails in the boiling heat transfer. Besides, the dominant effect of the heat flux oscillation on the boiling heat transfer comes from the very strong influence of the heat flux on the active nucleation site density.

Table 5.1 Time scales for transient R-410A saturated flow boiling (

δ

=2mm)

Time scales (sec)

Conduction time scale

t₁=L_c²/α_w 1.247 × 10^-11

Convection time scale t₂=L/(G/ρ₁)

T_sat =10 C° ,G = 300kw/m²s 0.6016 T_sat =10 C° ,G = 400kw/m²s 0.4512 Tsat =10 C° ,G = 500kw/m²s 0.3610 Tsat =15 C° ,G = 400kw/m²s 0.4436

t₃ = dp

2000�μ₁/(ρ₁D_h)�

Time scale of saturated flow boiling

0.00109

Time constant t4 = tc

Tsat =10 C° ,G = 300kw/m²s

30 (Single-phase) 24.4 (Saturated flow boiling)

Tsat =10 C° ,G = 400kw/m²s

29.4 (Single-phase) 23.5 (Saturated flow boiling)

T_sat =10 C° ,G = 500kw/m²s

28.5(Single-phase) 22.7(Saturated flow boiling)

Tsat =15 C° ,G = 400kw/m²s

27.9 (Single-phase) 23.4(Saturated flow boiling)

Fig. 5.1 Time-average flow boiling curves for R-410A for (a) various amplitudes of

(a) Time-Average R-410A Saturated Flow Boiling Curves at T_sat =10°C, G = 400 kg/m²s, t_p = 60s

(b) Time-Average R-410A Saturated Flow Boiling Curves at T_sat =10°C, G = 400 kg/m²s, q/ q = 30%

Fig. 5.2 Time-average flow boiling heat transfer coefficients for R-410A for (a)

(a) Time-Average R-410A Saturated Flow Boiling Curves at T_sat =10°C, G = 400 kg/m²s, t_p = 60s

(b) Time-Average R-410A Saturated Flow Boiling Curves at T_sat =10°C, G = 400 kg/m²s, q/ q = 30%

Δq/q=30%

Fig. 5.3 Time variations of imposed heat flux and measured wall temperature in

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G= 400kg/m²s, q/ q=10%, tp=60sec

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=10%, tp=60sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.4 Time variations of imposed heat flux and measured wall temperature in

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=30%, tp=60sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.5 Time variations of imposed heat flux and measured wall temperature in time periodic saturated flow boiling of R-410A at T_sat = 10℃, δ = 2.0mm,

0 10 20 30 40 50 60 70 80 90

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q/ q =50%, tp=60sec

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =50%, tp=60sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.6 Time variations of imposed heat flux and measured wall temperature in time periodic saturated flow boiling of R-410A at Tsat = 10℃, δ = 2.0mm, tp = 20 sec and G = 400kg/m²s with ∆q/q� = 30%.

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=30%, tp=20sec

 boiling starts  boiling stops

2(single phase)

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q/ q =30%, tp=20sec

Fig. 5.7 Time variations of imposed heat flux and measured wall temperature in time periodic saturated flow boiling of R-410A at T_sat = 10℃, δ = 2.0mm,

0 20 40 60 80 100 120 140 160 180

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =30%, tp=120sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.8 Time variations of imposed heat flux and measured wall temperature in time periodic saturated flow boiling of R-410A at Tsat = 10℃, δ = 2.0mm, tp = 60 sec and G =300kg/m²s with ∆q/q� = 30%.

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 300kg/m²s, q/ q =30%, tp= 60sec

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 300kg/m²s, q/ q =30%, tp= 60sec

 boiling starts  boiling stops

1(single phase)

Fig. 5.9 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 500kg/m²s, q/ q=30%, tp=60sec

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 500kg/m²s, q/ q =30%, tp= 60sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.10 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 15°C, δ= 2.0 mm, G = 400kg/m²s, q/ q=30%, tp=60sec

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 15°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =30%, tp= 60sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.11 Time variations of imposed heat flux and heat transfer coefficient in time

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 5°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =30%, tp= 60 sec

 boiling starts  boiling stops

2(single phase)

Fig. 5.12 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =10%, tp=60 sec

Fig. 5.13 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G= 400kg/m²s, q/ q=30%, tp=60sec

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q = 30%, tp=60 sec

15

Fig. 5.14 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q = 50%, tp=60sec

Oscillation of Heat Flux for R-410A at T_sat = 10°C, δ= 2.0 mm, G= 400kg/m²s, q/ q=50%, tp=60sec

Fig. 5.15 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q = 30%, tp=60sec

15

Fig. 5.16 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G= 400kg/m²s, q/ q=30%, tp=120sec

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =30%, tp= 120sec

15

Fig. 5.17 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G= 300kg/m²s, q/ q = 30%, tp= 60 sec

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 300kg/m²s, q/ q =30%, tp= 60 sec

Fig. 5.18 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G= 500kg/m²s, q/ q = 30%, tp=60sec

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 10°C, δ = 2.0 mm, G = 500kg/m²s, q/ q =30%, tp= 60 sec

15

Fig. 5.19 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of Heat Flux for R-410A at T_sat= 15°C, δ= 2.0 mm, G= 400kg/m²s, q/ q = 30%, tp= 60 sec

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 15°C, δ = 2.0 mm, G = 400kg/m²s, q/ q =30%, tp= 60 sec

15

Fig. 5.20 Time variations of imposed heat flux and heat transfer coefficient in time

Oscillation of flow boiling heat transfer coefficients for R-410A at T_sat= 5°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=30%, tp= 60 sec

Fig. 5.21 Flow regime map for time periodic R-410A flow boiling regimes atδ

=2mm and t_p = 60 sec for various saturated temperatures and mass fluxes.

0 10 20 30 40

G/ G(%) 0

0.0001 0.0002 0.0003 0.0004

Bo

Tsat=10^oC, G = 300kg/m²s T_sat=15^oC, G = 400kg/m²s T_sat=10^oC, G = 400kg/m²s

Time periodic R-410A saturated flow boiling at d= 2.0 mm, t_p=60sec

Persistent Flow Boiling

Intermittent Boiling

Single Phase Flow

Fig. 5.22 Time variations of imposed heat flux and wall temperature at z = 80 mm for tp = 2 sec.

0 20 40 60 80 100 120

t(sec)

0 10 20 30 40 50

q(kw/m2)

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q/ q=50%, tp=2sec

q =20.0(kW/m²)

q =15.0(kW/m²)

0 20 40 60 80 100 120

t(sec) 10

12 14 16 18 20

Tw(°C)

The wall temperature for oscillating flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=50%, tp = 2sec

q = 20.0 (kW/m²) q = 15.0 (kW/m²)

Fig. 5.23 Time variations of imposed heat flux and wall temperature at z = 80 mm for t_p = 120 sec.

0 150 300 450 600 750 900

t(sec)

0 10 20 30 40 50

q(kw/m2)

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q/ q=50%, tp= 120 sec

q =20.0(kW/m²)

q =15.0(kW/m²)

0 150 300 450 600 750 900

t(sec) 10

12 14 16 18 20

Tw(°C)

The wall temperature for oscillating flow boiling of R-410A

at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=50%, tp = 120 sec

q = 20.0 (kW/m²)

q = 15.0 (kW/m²)

Fig. 5.24 Time variations of imposed heat flux and wall temperature at z = 80 mm for t_p = 600 sec.

0 150 300 450 600 750 900

t(sec)

0 10 20 30 40 50

q(kw/m2)

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q/ q=50%, tp= 600 sec

q =20.0(kW/m²)

q =15.0(kW/m²)

0 150 300 450 600 750 900

t(sec) 10

12 14 16 18 20

Tw(°C)

The wall temperature for oscillating flow boiling of R-410A

at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q/ q=50%, tp = 600 sec

q = 20.0 (kW/m²)

q = 15.0 (kW/m²)

Fig. 5.25 Time variations of imposed heat flux and wall temperature at z = 80 mm for various .

0 10 20 30 40 50 60 70 80 90

t(sec)

0 10 20 30 40 50

q(kw/m2 )

Oscillation of Heat Flux for R-410A at T_sat= 10°C, δ= 2.0 mm, G = 400kg/m²s, q = 21kW/m², t_p=60sec

q/q =10%

q/q =30%

q/q =50%

0 10 20 30 40 50 60 70 80 90

t(sec) 10

12 14 16 18

Tw(°C)

The wall temperature for oscillating saturated flow boiling of R-410A at T_sat= 10°C, δ = 2.0 mm, G = 400kg/m²s, q = 21 kW/m², tp=60sec

q/ q = 10%

q/ q = 30%

q/ q = 50%

Δq/q

Tsat =10℃, δ=2mm,G =400 kg/m²s, q� ^{= 4kW/ m2,} ∆q/q� ^{=10%, tP}=60 sec.

6mm

(1)t=t₀, q=4.39kW/m² (5) t=t₀+ 4t_P/8, q=3.60kW/m²

(2)t=t₀+ t_P/8, q=4.2kW/m² (6) t=t₀+ 5t_P/8, q=3.82kW/m²

(3) t=t0+2 tP/8, q=4.00kW/m² (7) t=t0+ 6tP/8, q=3.99kW/m²

(4) t=t₀+ 3t_P/8 , q=3.80kW/m² (8) t=t₀+ 7t_P/8, q=4.20kW/m²

Fig. 5.26 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 4kW/m², ∆q/q� = 10%.

← →

flow

→

Tsat =10℃, δ=2mm,G =400 kg/m²s, q� ^{= 4kW/ m2,} ∆q/q� ^{=30%, tP=60 sec.}

6mm

(1)t=t₀, q=5.19kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=2.81kW/m²

(2)t=t₀+ t_P/8, q=4.61kW/m² (6) t=t₀+ 5t_P/8, q=3.41kW/m²

(3) t=t0+2 tP/8, q=3.97kW/m² (7) t=t0+ 6tP/8, q=4.07kW/m²

(4) t=t₀+ 3t_P/8 , q=3.36kW/m² (8) t=t₀+ 7t_P/8, q=4.58kW/m²

Fig. 5.27 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 4kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{= 4kW/ m2,} ∆q/q� ^{=50%, tP=60 sec.}

6mm

(1)t=t₀, q=5.95kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=2.18kW/m²

(2)t=t₀+ t_P/8, q=4.96kW/m² (6) t=t₀+ 5t_P/8, q=3.16kW/m²

(3) t=t0+2 tP/8, q=3.90kW/m² (7) t=t0+ 6tP/8, q=4.14kW/m²

(4) t=t₀+ 3t_P/8 , q=2.89kW/m² (8) t=t₀+ 7t_P/8, q=5.10kW/m²

Fig. 5.28 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 4kW/m², ∆q/q� = 50%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{= 4kW/ m2,} ∆q/q� ^{=30%, tP=20 sec.}

6mm

(1)t=t₀, q=5.18kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=2.81kW/m²

(2)t=t₀+ t_P/8, q=4.60kW/m² (6) t=t₀+ 5t_P/8, q=3.4kW/m²

(3) t=t0+2 tP/8, q=4.02kW/m² (7) t=t0+ 6tP/8, q=3.98kW/m²

(4) t=t₀+ 3t_P/8 , q=3.36kW/m² (8) t=t₀+ 7t_P/8, q=4.56kW/m²

Fig. 5.29 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 20 sec for q� = 4kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{= 4kW/ m2,} ∆q/q� ^{=30%, tP}= 120 sec.

6mm

(1)t=t₀, q=5.39kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=3.05kW/m²

(2)t=t₀+ t_P/8, q=4.77kW/m² (6) t=t₀+ 5t_P/8, q=3.65kW/m²

(3) t=t0+2 tP/8, q=4.16kW/m² (7) t=t0+ 6tP/8, q=4.23kW/m²

(4) t=t₀+ 3t_P/8 , q=3.58kW/m² (8) t=t₀+ 7t_P/8, q=4.85kW/m²

Fig. 5.30 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 120 sec for q� = 4kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =300 kg/m²s, q�^{= 3 kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=3.85kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=2.18kW/m²

(2)t=t₀+ t_P/8, q=3.41kW/m² (6) t=t₀+ 5t_P/8, q=2.60kW/m²

(3) t=t0+2 tP/8, q=2.98kW/m² (7) t=t0+ 6tP/8, q=3.07kW/m²

(4) t=t₀+ 3t_P/8 , q=2.50kW/m² (8) t=t₀+ 7t_P/8, q=3.55kW/m²

Fig. 5.31 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 3kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =500 kg/m²s, q� ^{= 5kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=6.37kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=3.65kW/m²

(2)t=t₀+ t_P/8, q=5.64kW/m² (6) t=t₀+ 5t_P/8, q=4.47kW/m²

(3) t=t0+2 tP/8, q=4.90kW/m² (7) t=t0+ 6tP/8, q=5.19kW/m²

(4) t=t₀+ 3t_P/8 , q=4.20kW/m² (8) t=t₀+ 7t_P/8, q=6.00W/m²

Fig. 5.32 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 5kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =5℃, δ=2mm,G =400 kg/m²s, q� ^{= 5kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=6.42kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=3.61kW/m²

(2)t=t₀+ t_P/8, q=5.70kW/m² (6) t=t₀+ 5t_P/8, q=4.35kW/m²

(3) t=t0+2 tP/8, q=4.98kW/m² (7) t=t0+ 6tP/8, q=5.07kW/m²

(4) t=t₀+ 3t_P/8 , q=4.15kW/m² (8) t=t₀+ 7t_P/8, q=5.90kW/m²

Fig. 5.33 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat = 5℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 5kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =15℃, δ=2mm, G =400 kg/m²s, q� ^{=4kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=5.16kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=2.91kW/m²

(2)t=t₀+ t_P/8, q=4.56kW/m² (6) t=t₀+ 5t_P/8, q=3.48kW/m²

(3) t=t0+2 tP/8, q=3.93kW/m² (7) t=t0+ 6tP/8, q=4.14kW/m²

(4) t=t₀+ 3t_P/8 , q=3.32kW/m² (8) t=t₀+ 7t_P/8, q=4.72kW/m²

Fig. 5.34 Photos of time periodic intermittent flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat = 15℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 4kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=10%, tP}= 60 sec.

6mm

(1)t=t₀, q=10.98kW/m² (5) t=t₀+ 4t_P/8, q=9.05kW/m²

(2)t=t₀+ t_P/8, q=10.52kW/m² (6) t=t₀+ 5t_P/8, q=9.54kW/m²

(3) t=t0+2 tP/8, q=10.03kW/m² (7) t=t0+ 6tP/8, q=10.05kW/m²

(4) t=t₀+ 3t_P/8 , q=9.52kW/m² (8) t=t₀+ 7t_P/8, q=10.53kW/m²

Fig. 5.35 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 10kW/m², ∆q/q� = 10%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=12.89kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=7.27kW/m²

(2)t=t₀+ t_P/8, q=11.44kW/m² (6) t=t₀+ 5t_P/8, q=8.74kW/m²

(3) t=t0+2 tP/8, q=9.79kW/m² (7) t=t0+ 6tP/8, q=10.34kW/m²

(4) t=t₀+ 3t_P/8 , q=8.31kW/m² (8) t=t₀+ 7t_P/8, G= q=11.83kW/m²

Fig. 5.36 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=50%, tP= 60 sec.}

6mm

(1)t=t₀, q=14.99kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=5.02kW/m²

(2)t=t₀+ t_P/8, q=12.56kW/m² (6) t=t₀+ 5t_P/8, q=7.48kW/m²

(3) t=t0+2 tP/8, q=9.82kW/m² (7) t=t0+ 6tP/8, q=9.30kW/m²

(4) t=t₀+ 3t_P/8 , q=7.37kW/m² (8) t=t₀+ 7t_P/8, G= q=12.67kW/m²

Fig. 5.37 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 60 sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 20 sec.}

6mm

(1)t=t₀, q=12.91kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=7.06kW/m²

(2)t=t₀+ t_P/8, q=11.38kW/m² (6) t=t₀+ 5t_P/8, q=8.52kW/m²

(3) t=t0+2 tP/8, q=9.90kW/m² (7) t=t0+ 6tP/8, q=9.96kW/m²

(4) t=t₀+ 3t_P/8 , q=8.44kW/m² (8) t=t₀+ 7t_P/8, G= q=11.44kW/m²

Fig. 5.38 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 400 kg/m²s, δ =2.0mm and tp= 20 sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP}= 120 sec.

6mm

(1)t=t₀, q=13.02kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=7.14kW/m²

(2)t=t₀+ t_P/8, q=11.46kW/m² (6) t=t₀+ 5t_P/8, q=8.61kW/m²

(3) t=t0+2 tP/8, q=9.99kW/m² (7) t=t0+ 6tP/8, q=10.16kW/m²

(4) t=t₀+ 3t_P/8 , q=8.43kW/m² (8) t=t₀+ 7t_P/8, G= q=11.60kW/m²

Fig. 5.39 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at Tsat =10 ℃ , G = 400 kg/m²s, δ =2.0mm and tp= 120 sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =300 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=12.86kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=7.22kW/m²

(2)t=t₀+ t_P/8, q=11.41kW/m² (6) t=t₀+ 5t_P/8, q=8.69kW/m²

(3) t=t0+2 tP/8, q=9.93kW/m² (7) t=t0+ 6tP/8, q=10.16kW/m²

(4) t=t₀+ 3t_P/8 , q=8.28kW/m² (8) t=t₀+ 7t_P/8, G= q=11.80kW/m²

Fig. 5.40 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at T_sat =10℃, G = 300 kg/m²s, δ =2.0mm and tp= 60sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =10℃, δ=2mm,G =500 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

6mm

(1)t=t₀, q=12.93kW/m²

6mm

(5) t=t₀+ 4t_P/8, q=7.26kW/m²

(2)t=t₀+ t_P/8, q=11.32kW/m² (6) t=t₀+ 5t_P/8, q=8.89kW/m²

(3) t=t0+2 tP/8, q=9.78kW/m² (7) t=t0+ 6tP/8, q=10.35kW/m²

(4) t=t₀+ 3t_P/8 , q=8.32kW/m² (8) t=t₀+ 7t_P/8, G= q=11.84kW/m²

Fig. 5.41 Photos of time periodic saturated flow boiling of R-410A at selected time instants in a typical periodic cycle at Tsat =10℃, G = 500 kg/m²s, δ =2.0mm and tp= 60sec for q� = 10kW/m², ∆q/q� = 30%.

flow

→

← →

Tsat =5℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

Tsat =5℃, δ=2mm,G =400 kg/m²s, q�^{=10kW/ m2,} ∆q/q� ^{=30%, tP= 60 sec.}

在文檔中 狹窄水平雙套管中R-410A冷媒流量震盪與可變功率之週期性流動沸騰研究 (頁 130-186)