Comparisons of Supercritical Loop Flow and Heat Transfer Behavior Under Uniform and Nonuniform High-Flux Heat Inputs

Abstract

The heat transfer characteristic of supercritical water is one of the crucial issues in SuperCritical Water-Cooled Reactors (SCWRs). The efficiency and safety of the SCWR system are largely dependent on the local heat transfer performance. This paper establishes the numerical model for supercritical water in a long vertical circular loop (inside diameter = 10 mm) and analyzes the flow and heat transfer mechanism during the transition process from subcritical to supercritical states under various heat fluxes (uniform and nonuniform). The results reveal that the difference in thermophysical properties between the boundary layer and the core region is the main reason for the heat transfer behavior, especially during the transition from subcritical to supercritical and liquidlike to gaslike. The flow structure on the buffer layer is a dominating factor for heat transfer deterioration. The cases under variable nonuniform heat fluxes have a higher heat transfer coefficient compared with uniform heat fluxes. But, this will cause large changes of the parameter locally. The dominating factors of heat transfer deterioration under these conditions are also identified.

Keywords:

• Supercritical water
• heat transfer
• variable heat fluxes
• boundary layer
• flow stability

Acronyms

HTD:	=	heat transfer deterioration
REFPROP:	=	REference Fluid PROPerties [database]
RKE:	=	realizable k-ε model
RNG:	=	Re-Normalization Group
RP-3:	=	Chinese No. 3 (RP-3) kerosene
SCWRs:	=	SuperCritical Water-cooled Reactors
SST:	=	Shear Stress Transport
UOIT:	=	University of Ontario Institute of Technology

Nomenclature

A	=	= cross-sectional area of the tube (m2)
cp	=	= specific heat at constant pressure (J/kg·K)
G	=	= mass flux (kg/m2·s)
g	=	= gravitational acceleration, 9.81 (m/s2)
H	=	= enthalpy (kJ/kg)
h	=	= uniform grid spacing
HTC	=	= heat transfer coefficient (W/m2·K)
i	=	= iteration number
ID	=	= inside diameter (m)
k	=	= turbulence kinetic energy (m2/s2)
L	=	= heated length (m)
p	=	= pressure (Pa)
q	=	= heat flux (W/m2)
Pr	=	= Prandtl number, $\left(\frac{\mu c_p}{\lambda }\right)$
R, r	=	= radial coordinate (m)
Sh	=	= source term
T	=	= temperature (°C)
Tu	=	= truncation error of the dicretization scheme
u	=	= radial velocity (m/s)
V	=	= volume (m3)
v	=	= vertical velocity (m/s)
x	=	= coordinate (m)
y+	=	= nondimensional distance from wall, $\frac{{\left({\rho }_w{\tau }_w\right)}^{0.5}}{{\mu }_w}y$
z	=	= axial coordinate (m)

Greek

ε	=	= turbulent dissipation rate (m2/s3)
μ	=	= dynamic viscosity (Pa·s)
σT	=	= turbulent Prandtl number
ϕ	=	= dependent variables
ω	=	= specific dissipation rate (1/s)

Subscripts

ave	=	= average
b	=	= bulk
e	=	= effective
exp.	=	= experimental
in	=	= inlet
pc	=	= pseudo-critical
t	=	= turbulent
w	=	= wall

Acknowledgments

The authors gratefully acknowledge support from the International Atomic Energy Agency Coordinated Research Project (CRP-I31034) (contract number 24858), the National Science Fund for Distinguished Young Scholars (contract number 51925604), National Natural Science Foundation of China (contract number 52006221), Key Research Program of the Chinese Academy of Sciences (CAS) Innovation Academy for Light-Duty Gas Turbine (contract number CXYJJ21-ZD-01), and the CAS Start-Up Fund. Peiyuan Xu and Huisi Zhou from Lin Chen’s laboratory also helped in the data processing. The authors are also grateful for the experimental discussions with Igor Pioro (UOIT) for this research.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the International Atomic Energy Agency (IAEA) [CRP-I31034 Contract 24858]; National Outstanding Youth Science Fund Project of National Natural Science Foundation of China [51925604]; National Natural Science Foundation of China [52006221]; Key Research Program of the CAS Innovation Academy for Light-duty Gas Turbine [CXYJJ21-ZD-01].