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عنوان فارسی مقاله:
بهبود پیش بینی انتقال حرارت به مایعات فشار فوق بحرانی با مدل های شار حرارتی جبری
عنوان انگلیسی مقاله:
Improvements in the prediction of heat transfer to supercritical pressure fluids by the use of algebraic heat flux models
سال انتشار : 2017
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مقدمه انگلیسی مقاله:
1. Introduction
The development of a Supercritical Water-Cooled Reactor still represents the objective of researches carried out in different Countries. In particular, a new Coordinated Research Project (CRP) started in November 2013 under the aegis of IAEA with the aim of improving the present understanding of the complex phenomena occurring when working with supercritical fluids. Support to these studies is also provided by the Generation Four International Forum (GIF), which encourages cooperation and exchanges between the various research teams. One of the most challenging issues in the development of SCWRs is the problem of correctly predicting heat transfer deterioration and enhancement in the reactor core. In particular, heat transfer deterioration could represent a dangerous situation, since it may lead to high temperatures that could cause reactor fuel failures. Consequently, this heat transfer regime must be avoided or, at least, controlled by selecting suitable working conditions. According to Jackson and Hall (1979), heat transfer deterioration may be due to three different aspects. The most important ones are the exceeding of the so called pseudo-critical temperature, which impairs the heat transfer capabilities of the fluid, and the re-laminarization due to buoyancy effects, which reduces the turbulence in the vicinity of the wall thus impairing heat transfer. Unfortunately, up to the present time most of the commonly used simulation techniques cannot adequately deal with this problem, reporting insufficient matching with the available experimental data: in particular, j-e models usually over-predict the measured trends while the j-x ones tend not to detect the phenomenon (Sharabi, 2008; Sharabi and Ambrosini, 2009; De Rosa, 2010; Badiali, 2011). During the last years, researchers tried to improve the situation with new modelling proposals. Zhang et al. (2010) suggested the adoption of a four-equation turbulence model in association with the algebraic heat flux model (AHFM) for the calculation of the buoyancy production terms, reporting interesting results for a few addressed cases. The AHFM relation was firstly introduced by Launder (1987) and Launder (1988) as a steady–state algebraic simplification of the turbulent heat flux balance differential equation and allows calculating this variable without requiring the definition of a turbulent Prandtl number. However, together with the definition of four coefficients, the relation requires the calculation of the temperature variance distribution thus implying a larger computational cost by introducing two additional partial differential equation for this variable and its dissipation.
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کلمات کلیدی:
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