Some approaches to investigation of the influence of variable energy release on heat transfer and temperature fields of
- PDF / 456,666 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 177 Views
Approaches to Investigation of the Influence of Variable Energy Release on Heat Transfer and Temperature Fields of Fuel Elements of Nuclear Reactors A. V. Zhukov, Yu. A. Kuzina, and A. P. Sorokin* FSUE Institute of Physics and Power Engineering, pl. Bondarenko 1, Obninsk, 249033 Russia Received December 12, 2007
Abstract—Different methods for estimating the effect of energy release reduction in the second half of the active core on the temperature field of fuel elements are considered: analytical solution of the problem, recal culation of the temperature field obtained at constant energy release for variable energy release, and so on. An enhanced role of this effect for peripheral fuel elements of fuel assemblies of fast reactors is noted. DOI: 10.1134/S1063778810130089
1. ANALYSIS OF AVAILABLE STUDIES ON HEAT EXCHANGE AT VARIABLE ENERGY RELEASE At present, there exist a number of papers devoted to the study of convective heat exchange in channels with arbitrary thermal flux distribution along the wall (Fig. 1). (1) Analytical solution of the problem is performed for channels with simple shape (circular pipe, plane gaps) when temperature fields do not change along the channel perimeter. The problem is solved under the assumption that physical parameters are constant, the flux is hydrodynamically stabilized and symmetric with respect to the longitudinal axis, and the velocity profiles and the distribution of turbulent thermal con ductivity coefficients along the channel radius are determined.
For δshaped energy release (f(ξ) = δ(ξ)), the influ Tw – T ρC p U and ence function is written as G(ξ) = q(ξ) ∞
∫
normalized by the condition G ( ξ ) dξ = A, which is 0
connected with the relaxation length as L = ∞
1 ξG ( ξ ) dξ . The value of A is determined using the A
∫ 0
Fourier transform. The function f(ξ) is expanded in a Taylor series, and we obtain 1/St(ξ) ⬵ Af(ξ – L). The conclusion is made that the local heat release
Nu
In [1], the ideal case of a δshaped heat input in the channel is considered. The function G(z) is intro duced; this function of heat release influence describes the change in temperature difference in the channel whose local value is determined by the equality
q = var q = const
q
z
Π ( T w – T )ρC p US = q ( z' )G ( z – z' ) dz', 2
z
∫
–∞
Tw – T or 1 = ρC p U = St q(ξ)
ξ
∫ f ( ξ' )G ( ξ – ξ' ) dξ',
–∞
z
where f(ξ') = q(ξ')/q(ξ), ξ = z/r0.
Fig. 1. Nu number variation for variable energy release in comparison with that for constant energy release.
* Email: [email protected]
2222
SOME APPROACHES TO INVESTIGATION OF THE INFLUENCE
coefficient is determined by the heat input at the dis tance L in the flux direction. The energy equation for the heat carrier flux is solved with the variable q(ξ) in the form ∂t = U ( R ) Pe t 1 ∂ Rg ( R ) ∂, (1) R ∂R ∂R 2 ∂ξ where R = r/r0 is the dimensionless current radius, ξ = z/r0 is the dimensionless longitudinal coordinate, g(R) = (a + aτ)/a is the function of turbulent thermal c
Data Loading...
