Heat Transfer Characteristics of 5x5 Heater Rod Bundle Cooled with ...
Heat Transfer Characteristics of 5x5 Heater Rod Bundle Cooled with Refrigerant HFC-134a near the Critical Pressures Se-Young Chun*, Sung-Deok Hong, Chang-Hwan Shin PaRTSEE-5 Auckland, New Zealand, 28 – 29 April, 2005
Korea Atomic Energy Research Institute -0-
Thermal Hydraulic Tests for Reactor Core Safety in KAERI Core Coolability Experiments
- Critical heat flux (CHF) experiments - Fundamental study on heat transfer Reactor Core Thermal-Hydraulic Experiments during
LOCA Conditions - Post-CHF and reflood heat transfer: effect of spacer grid Hydraulic Tests for Reactor Core
- Hydraulic tests for various nuclear fuel bundles -1-
Core Coolability Experiments Freon Thermal-Hydraulic Experimental Loop CHF Experiments under Low and High Flow Conditions
- Nuclear fuel development Optimization of CHF promoter designs (e.g. high performance
spacer grid) - Next generation reactor development CHF behavior near critical pressure Heat transfer in supercritical pressure region
- Fluid-to-fluid modeling of boiling phenomena Experiments Performed
- Tube and single rod annulus CHF, 5x5 and 6x6 rod bundle CHF -2-
Contents Background Objective Experiments Experimental loop CHF and Pressure Transient Experiments Results & discussion Summary -3-
Background During normal operating conditions of Supercritical-
Pressure light Water Reactor (SCWR) , a CHF phenomenon does not exist. Fluids near to the thermodynamic critical point have a
special characteristic. When a heat removal system of SCWR is operated with a
sliding pressure start-up scheme, that is, the nuclear heating starts at sub-critical pressure. The CHF occurrence should be avoided during the power-
increasing phase under sub-critical pressure conditions. -4-
Critical Heat Flux (CHF) Two mechanisms under normal
pressure conditions Dryout Departure from nucleate boiling (DNB)
Little CHF information near the critical
pressure region What will be the CHF mechanism and characteristics near the critical pressure?
-5-
Objective For development of SCWR,
To find out problems from the viewpoint of thermal-hydraulics Understanding of the CHF phenomena
near the critical pressure conditions
-6-
Experimental loop Critical P and T of R-134a 4059 kPa and 101 oC Cooling
CONDENSER
Cooling Tower
Tower
TEST SECTION
COOLER
T R 2
STRAINER
BYPASS
PRESSURIZER I
T R 2
N2 BOTTLE
COOLER
FLOW METER
PREHEATER
- Max. operation press.: 4.5 MPa - Max. operation temp.: 150 oC - Flow rate: 15 kg/s - Test section power: 720 kW DC - Working fluid: R134a
Water Equivalent Data - Pressure: 27.5 MPa - Flow rate: 21 kg/s - Power: 9360 kW DC
PUMP
-7-
250
Test section P
TC
2000 (Heated section)
511
TC
66.9
Sg. 14.45
92.12
7. 09
R 3.0
OD : 114.3 ID : 106.3
OD : 165.2 ID : 143.2
325
.
P
TC
-8-
5x5 Fuel rod simulator 1
3
5
7
9
0.931
0.931
0.931
0.931
0.931
0.931 32 29
0.931 30 27
0.931 28
36
1.121
37
1.121
44
41
1.121
34
39
38
43
42
64
61
68
65
48
45
1.121
1.121
1.121
63
62
67
66
47
46
60
57
56
53
52
49
1.121
25
26
40
10
35
59
0.931
33
8
58
1.121 55
24
51
21
23
0.931
54
1.121
0.931 22
50
11
0.931 12 13
0.931 14 15
0.931 16
19
0.931 20
T/C CARRIER ASS'Y.
17
D=9.5mm, Pitch=12.85mm Radial Power distribution : Non-uniform Axial Power distribution : Uniform
T/C INSULATION
COPPER EXTENSION
0.931 18
10 mm
31
6
2000 mm (HEATED SECTION)
4
2
COPPER EXTENSION
Spacer grid
Without mixing vane
T/C (THERMOCOUPLE)
-9-
Experiments To observe the bundle total power at steady state CHF
conditions (Critical Power) near the critical pressure And the wall temperature behavior during pressure
reducing transient, from the supercritical to subcritical pressure Experimental conditions Pressure (outlet) 3200 ~ 4030 kPa: Steady State CHF Mass flux Subcooling
4300 3600 kPa: Transient 150 ~ 1500 kg/m2 ·s 40 ~ 85 kJ/kg -10-
Wall Temperature in Each Subchannel at CHF Conditions
Wall Temperature (°C)
Mass flux = 1500 kg/m2 ·s Pressure = 3899 kPa 150
Inlet subcooling = 70.5 kJ/kg Critical power = 143 kW
TC01, Corner Subchannel TC09, Side Subchannel TC46, Middle Subchannel TC65, Center Subchannel
130
110
90 550
600
650 700 Time (sec) Most of the locations of CHF occurrence distribute in the high power region.
750
-11-
Thermodynamic properties & CHF 1.0 ∆Tsub = 14.5 [K]
Critical quality, xCHF
0.5
Cp
0.0 -0.5 2
G [kg/m s] 501 1002 1502
-1.0 -1.5 -2.0
0
1
2 3 Pressure [MPa]
hlg
ρl
ρg
Pc
4
- In the vicinity of the critical pressure, the thermodynamic Fig. 5. Critical quality and thermodynamic properties with pressure properties of fluids vary rapidly also. Specific heat is increased sharply and the latent heat of vaporization falls to zero. -12-
Effect of Inlet subcooling & mass flux on CHF 250
150
Critical power (kW)
120
200
90 60
100 50
0
0 50
70
Inlet subcooling (kJ/kg)
90
Inlet Subcooling = 70.5 kJ/kg
150
30
30
3399 kPa 3798 kPa 3901 kPa 3949 kPa 3998 kPa
G = 550 kg/m²s
Critical power (kW)
3401 kPa 3802 kPa 3901 kPa 3950 kPa 3999 kPa
0
250
500
750
1000
1250
1500
Mass flux (kg/m²s)
-The CHF values with inlet subcooling show linear trends for the present pressure conditions. - From 3900 kPa to the critical pressure, the CHF measurement uncertainty is relatively large because the small pressure change leads to large change of a CHF value.
-13-
Effect of Pressure on CHF Inlet subcooling = 40 kJ/kg
Inlet Subcooling = 70.5 kJ/kg 300
G = 150 (kg/m²s) G = 550 (kg/m²s) G = 997 (kg/m²s) G = 1499 (kg/m²s)
200
100
0 3.0
3.2
3.4
3.6
3.8
Pressure (MPa)
4.0
Pc
Critical Power (kW)
Critical Power (kW)
300
G = 150 (kg/m²s) G = 550 (kg/m²s) G = 999 (kg/m²s) G = 1498 (kg/m²s)
P=3998kPa Threshold P Line
200
100
0 4.2
3.0
3.2
3.4
3.6
3.8
4.0
Pc
4.2
Pressure (MPa)
- The CHFs decrease with the system pressure and reduces very sharply in front of the critical pressure of R-134a. This sharp decreasing trend of CHF appears more strongly when the mass flux or the inlet subcooling is increased.
-14-
Wall Temperature Variation at CHF Conditions Wall temperature (°C)
140 P = 3998 kPa ∆h = 70.5 kJ/kg
G=150 kg/m²s, QCHF=25 kW
130 120
G=550 kg/m²s, QCHF=43 kW
110 G=999 kg/m²s, Q=50 ~ 65 kW
100 0
200
400
600
800
1000
1200
Time (sec)
- As the mass flux increases, the rise in the wall temperature at CHF conditions becomes slow. For high mass fluxes, the wall temperature increases monotonously according to the power input level. - There exists a threshold pressure at which the CHF phenomenon disappear.
-15-
Wall Temperature during Pressure Reduction Transients
4000
Outlet pressure
Critical temperature
100
3750
Tc.65 Tc.66 Tc.67 Tc.68
Wall temperature
4250
130 Critical pressure
120
4000
Outlet pressure
110 3750
Critical temperature
100
Outlet pressure [kPa]
4250
Critical pressure
110
4500 R-134a G=250 [kg/(m2s)] Q=33kW-01
140
Temperature [℃]
Tc.65 Tc.66 Tc.67 Tc.68
Wall temperature
120
Temperature [℃]
150
4500 R-134a 2 G=250 [kg/(m s)] Q=18kW
Outlet pressure [kPa]
130
Outlet Temperature
Outlet Temperature
0
20
40
60
80
100
120
140
160
180
200
220
3500 240
90
0
20
40
60
80
Time [s]
120
4250 Critical pressure
110
4000
Outlet pressure
Critical temperature
100
140
160
180
3500 200
3750
4500
R-134a 2 G=250 [kg/(m s)] Q=33kW-01
Tc.66
Wall (outlet) temperature [℃]
Tc.36 Tc.41 Tc.50 Tc.59
Outlet pressure [kPa]
Wall (outlet) temperature [℃]
150
4500 Tc.01 Tc.09 Tc.18 Tc.26
120
Time [s]
130 R-134a 2 G=250 [kg/(m s)] Q=18kW
100
140
4250 130 Critical pressure
120
Tc.01 Tc.09 Tc.18 Tc.26
Outlet pressure
110
Tc.36 Tc.41 Tc.50 Tc.59
Tc.66
3750
Critical temperature
100
4000
Outlet pressure [kPa]
90
Outlet Temperature
Outlet Temperature
90
0
20
40
60
80
100
120
Time [s]
140
160
180
200
220
3500 240
90
0
20
40
60
80
100
120
140
160
180
3500 200
Time [s]
-16-
Summary The CHF decreases very sharply in front of the critical pressure and this is closely related to the sharp variations of thermodynamic properties. In the region near the critical pressure, There exists a threshold pressure at which the CHF phenomenon disappears. For fixed inlet subcooling, the threshold pressure decreases as the mass flux increases. Consequently the wall temperature increases monotonously according to the power input level. In the pressure reduction transients, as soon as the pressure passes through the critical pressure from the supercritical pressure, the wall temperature rise rapidly up to very high values due to the occurrence of the DNB.
-17-
Korea Atomic Energy Research Institute -0-
Thermal Hydraulic Tests for Reactor Core Safety in KAERI Core Coolability Experiments
- Critical heat flux (CHF) experiments - Fundamental study on heat transfer Reactor Core Thermal-Hydraulic Experiments during
LOCA Conditions - Post-CHF and reflood heat transfer: effect of spacer grid Hydraulic Tests for Reactor Core
- Hydraulic tests for various nuclear fuel bundles -1-
Core Coolability Experiments Freon Thermal-Hydraulic Experimental Loop CHF Experiments under Low and High Flow Conditions
- Nuclear fuel development Optimization of CHF promoter designs (e.g. high performance
spacer grid) - Next generation reactor development CHF behavior near critical pressure Heat transfer in supercritical pressure region
- Fluid-to-fluid modeling of boiling phenomena Experiments Performed
- Tube and single rod annulus CHF, 5x5 and 6x6 rod bundle CHF -2-
Contents Background Objective Experiments Experimental loop CHF and Pressure Transient Experiments Results & discussion Summary -3-
Background During normal operating conditions of Supercritical-
Pressure light Water Reactor (SCWR) , a CHF phenomenon does not exist. Fluids near to the thermodynamic critical point have a
special characteristic. When a heat removal system of SCWR is operated with a
sliding pressure start-up scheme, that is, the nuclear heating starts at sub-critical pressure. The CHF occurrence should be avoided during the power-
increasing phase under sub-critical pressure conditions. -4-
Critical Heat Flux (CHF) Two mechanisms under normal
pressure conditions Dryout Departure from nucleate boiling (DNB)
Little CHF information near the critical
pressure region What will be the CHF mechanism and characteristics near the critical pressure?
-5-
Objective For development of SCWR,
To find out problems from the viewpoint of thermal-hydraulics Understanding of the CHF phenomena
near the critical pressure conditions
-6-
Experimental loop Critical P and T of R-134a 4059 kPa and 101 oC Cooling
CONDENSER
Cooling Tower
Tower
TEST SECTION
COOLER
T R 2
STRAINER
BYPASS
PRESSURIZER I
T R 2
N2 BOTTLE
COOLER
FLOW METER
PREHEATER
- Max. operation press.: 4.5 MPa - Max. operation temp.: 150 oC - Flow rate: 15 kg/s - Test section power: 720 kW DC - Working fluid: R134a
Water Equivalent Data - Pressure: 27.5 MPa - Flow rate: 21 kg/s - Power: 9360 kW DC
PUMP
-7-
250
Test section P
TC
2000 (Heated section)
511
TC
66.9
Sg. 14.45
92.12
7. 09
R 3.0
OD : 114.3 ID : 106.3
OD : 165.2 ID : 143.2
325
.
P
TC
-8-
5x5 Fuel rod simulator 1
3
5
7
9
0.931
0.931
0.931
0.931
0.931
0.931 32 29
0.931 30 27
0.931 28
36
1.121
37
1.121
44
41
1.121
34
39
38
43
42
64
61
68
65
48
45
1.121
1.121
1.121
63
62
67
66
47
46
60
57
56
53
52
49
1.121
25
26
40
10
35
59
0.931
33
8
58
1.121 55
24
51
21
23
0.931
54
1.121
0.931 22
50
11
0.931 12 13
0.931 14 15
0.931 16
19
0.931 20
T/C CARRIER ASS'Y.
17
D=9.5mm, Pitch=12.85mm Radial Power distribution : Non-uniform Axial Power distribution : Uniform
T/C INSULATION
COPPER EXTENSION
0.931 18
10 mm
31
6
2000 mm (HEATED SECTION)
4
2
COPPER EXTENSION
Spacer grid
Without mixing vane
T/C (THERMOCOUPLE)
-9-
Experiments To observe the bundle total power at steady state CHF
conditions (Critical Power) near the critical pressure And the wall temperature behavior during pressure
reducing transient, from the supercritical to subcritical pressure Experimental conditions Pressure (outlet) 3200 ~ 4030 kPa: Steady State CHF Mass flux Subcooling
4300 3600 kPa: Transient 150 ~ 1500 kg/m2 ·s 40 ~ 85 kJ/kg -10-
Wall Temperature in Each Subchannel at CHF Conditions
Wall Temperature (°C)
Mass flux = 1500 kg/m2 ·s Pressure = 3899 kPa 150
Inlet subcooling = 70.5 kJ/kg Critical power = 143 kW
TC01, Corner Subchannel TC09, Side Subchannel TC46, Middle Subchannel TC65, Center Subchannel
130
110
90 550
600
650 700 Time (sec) Most of the locations of CHF occurrence distribute in the high power region.
750
-11-
Thermodynamic properties & CHF 1.0 ∆Tsub = 14.5 [K]
Critical quality, xCHF
0.5
Cp
0.0 -0.5 2
G [kg/m s] 501 1002 1502
-1.0 -1.5 -2.0
0
1
2 3 Pressure [MPa]
hlg
ρl
ρg
Pc
4
- In the vicinity of the critical pressure, the thermodynamic Fig. 5. Critical quality and thermodynamic properties with pressure properties of fluids vary rapidly also. Specific heat is increased sharply and the latent heat of vaporization falls to zero. -12-
Effect of Inlet subcooling & mass flux on CHF 250
150
Critical power (kW)
120
200
90 60
100 50
0
0 50
70
Inlet subcooling (kJ/kg)
90
Inlet Subcooling = 70.5 kJ/kg
150
30
30
3399 kPa 3798 kPa 3901 kPa 3949 kPa 3998 kPa
G = 550 kg/m²s
Critical power (kW)
3401 kPa 3802 kPa 3901 kPa 3950 kPa 3999 kPa
0
250
500
750
1000
1250
1500
Mass flux (kg/m²s)
-The CHF values with inlet subcooling show linear trends for the present pressure conditions. - From 3900 kPa to the critical pressure, the CHF measurement uncertainty is relatively large because the small pressure change leads to large change of a CHF value.
-13-
Effect of Pressure on CHF Inlet subcooling = 40 kJ/kg
Inlet Subcooling = 70.5 kJ/kg 300
G = 150 (kg/m²s) G = 550 (kg/m²s) G = 997 (kg/m²s) G = 1499 (kg/m²s)
200
100
0 3.0
3.2
3.4
3.6
3.8
Pressure (MPa)
4.0
Pc
Critical Power (kW)
Critical Power (kW)
300
G = 150 (kg/m²s) G = 550 (kg/m²s) G = 999 (kg/m²s) G = 1498 (kg/m²s)
P=3998kPa Threshold P Line
200
100
0 4.2
3.0
3.2
3.4
3.6
3.8
4.0
Pc
4.2
Pressure (MPa)
- The CHFs decrease with the system pressure and reduces very sharply in front of the critical pressure of R-134a. This sharp decreasing trend of CHF appears more strongly when the mass flux or the inlet subcooling is increased.
-14-
Wall Temperature Variation at CHF Conditions Wall temperature (°C)
140 P = 3998 kPa ∆h = 70.5 kJ/kg
G=150 kg/m²s, QCHF=25 kW
130 120
G=550 kg/m²s, QCHF=43 kW
110 G=999 kg/m²s, Q=50 ~ 65 kW
100 0
200
400
600
800
1000
1200
Time (sec)
- As the mass flux increases, the rise in the wall temperature at CHF conditions becomes slow. For high mass fluxes, the wall temperature increases monotonously according to the power input level. - There exists a threshold pressure at which the CHF phenomenon disappear.
-15-
Wall Temperature during Pressure Reduction Transients
4000
Outlet pressure
Critical temperature
100
3750
Tc.65 Tc.66 Tc.67 Tc.68
Wall temperature
4250
130 Critical pressure
120
4000
Outlet pressure
110 3750
Critical temperature
100
Outlet pressure [kPa]
4250
Critical pressure
110
4500 R-134a G=250 [kg/(m2s)] Q=33kW-01
140
Temperature [℃]
Tc.65 Tc.66 Tc.67 Tc.68
Wall temperature
120
Temperature [℃]
150
4500 R-134a 2 G=250 [kg/(m s)] Q=18kW
Outlet pressure [kPa]
130
Outlet Temperature
Outlet Temperature
0
20
40
60
80
100
120
140
160
180
200
220
3500 240
90
0
20
40
60
80
Time [s]
120
4250 Critical pressure
110
4000
Outlet pressure
Critical temperature
100
140
160
180
3500 200
3750
4500
R-134a 2 G=250 [kg/(m s)] Q=33kW-01
Tc.66
Wall (outlet) temperature [℃]
Tc.36 Tc.41 Tc.50 Tc.59
Outlet pressure [kPa]
Wall (outlet) temperature [℃]
150
4500 Tc.01 Tc.09 Tc.18 Tc.26
120
Time [s]
130 R-134a 2 G=250 [kg/(m s)] Q=18kW
100
140
4250 130 Critical pressure
120
Tc.01 Tc.09 Tc.18 Tc.26
Outlet pressure
110
Tc.36 Tc.41 Tc.50 Tc.59
Tc.66
3750
Critical temperature
100
4000
Outlet pressure [kPa]
90
Outlet Temperature
Outlet Temperature
90
0
20
40
60
80
100
120
Time [s]
140
160
180
200
220
3500 240
90
0
20
40
60
80
100
120
140
160
180
3500 200
Time [s]
-16-
Summary The CHF decreases very sharply in front of the critical pressure and this is closely related to the sharp variations of thermodynamic properties. In the region near the critical pressure, There exists a threshold pressure at which the CHF phenomenon disappears. For fixed inlet subcooling, the threshold pressure decreases as the mass flux increases. Consequently the wall temperature increases monotonously according to the power input level. In the pressure reduction transients, as soon as the pressure passes through the critical pressure from the supercritical pressure, the wall temperature rise rapidly up to very high values due to the occurrence of the DNB.
-17-
