Development of drift–flux correlation for predicting void fraction in downcomer regions

Figures & data

Figure 1. Illustration of Downcomer boiling two-phase flow characteristics [4].

Table 1. Test conditions of KAERI’s downcomer boiling experiment [4]

Parameter	TECC (°C)	Psys (kPa)	WECC (kg/s)	q″ (kW/m^2)
R1	110.1	162.8	1.22	50.2
R2	110.2	161.4	1.16	69.7
R3	109.6	166.5	1.20	82.1
R4	109.5	170.8	1.20	91.1
R2-1a	110.7	158.5	1.33	70.5

Figure 2. Downcomer boiling experimental facility [4].

Figure 3. Axial void fraction data on downcomer boiling [4].

Table 2. Drift–flux correlations utilized in RELAP5/MOD3.2 code for bubbly and slug flow regimes (RELAP5 Manual)

Flow rates	Rod bundles	Small pipes D < 0.018 m	Intermediate pipes 0.018 m< D < 0.08 m	Large pipes 0.08 m < D
High upflow rates G > 100 Kg/m^2•s	EPR I(2) (eprij)	EPRI (3) (eprij)	EPRI (9) (eprij)	Clum turbulent bubbly flow (14) transition (15) Koltaoka–Ishii(16) (katokj)
		Transition (5)	Transition (13)
Low up, down, and countercurrent flow rates G < 50 Kg/m^2•s G > −50 Kg/m^2•s		Zuber–Findaly slug flow (4) (zfslgi)	Clum turbulent bubbly flow (10) transition (11) Koltaoka–Ishii (12) (katokj)
		Transition (5)	Transition (13)
High downflow rates G<-100 kg/m^2•s		EPRI (3) (eprij)	EPRI (9) (eprij)

Figure 4. Downcomer region analysis model.

Figure 5. Distribution parameter using BLT model.

Figure 6. Newly developed distribution parameter model.

Figure 7. RELAP5 nodalization.

Figure 8. Axial void fraction development for the test condition R1.

Figure 9. Axial void fraction development for the test condition R2.

Figure 10. Axial void fraction development for the test condition R3.

Figure 11. Axial void fraction development for the test condition R4.

Figure 12. Axial void fraction development for the test condition R2-1a.

Figure 13. Performance evaluation of RELAP5 void fraction calculation.

Table

Ci	Drag coefficient
C0	Distribution parameter
D	Channel diameter
$D^{\ast }$	Hydraulic diameter-dependent Bond number
G	Mass flux
g	Gravitational acceleration
j	Mixture volumetric flux
$j_g$	Superficial gas velocity
$j_f$	Superficial liquid velocity
$j_f^{\ast }$	Nondimensional superficial liquid velocity
L	Upflow channel width
m	Constant for volumetric flow profile
n	Constant for void fraction profile
$p$	Pressure
$q^{\prime \prime }$	Heat flux
TECC	ECC temperature
$\mathit{v}$	Velocity
$V_{gj}$	Drift velocity
${\mathit{v}}_r$	Relative velocity
${\mathit{v}}_{r\mathrm{\infty }}$	Relative velocity between single gas particle and liquid phase
WECC	ECC mass flow rate
x	Radial position of flow channel
x0	Peak total superficial velocity location
Greek symbol
$\alpha$	Void fraction
${\alpha }_w$	Near wall void fraction
σ	Surface tension
$\rho$	Density
$\mathrm{\Delta }\rho$	Density difference between two phases
$\mu$	Dynamic viscosity
Subscripts
f	Liquid phase
g	Gas phase
i	Value at interface
m	Mixture
max	Maximum value
Mathematical symbol
< >	Area averaged quantity
≪ ≫	Void-weighted area averaged quantity