دانلود رایگان مقاله انگلیسی بررسی در مورد مطالعات اخیر انتقال حرارت به فشار آب فوق بحرانی در کانال ها - الزویر 2018

Abstract

Recent studies on heat transfer to super-critical water (SCW) in tubes, annuli and rod bundles have been reviewed in support of the development of supercritical water-cooled reactors. Experimental investigations are primarily focused on the heat transfer deterioration (HTD) to examine its general behavior, transition boundary and physical mechanisms. Large amount of experimental data were obtained from the experiments supplementing the extensive database previously compiled for fossil fuel-fired power plants. Prediction methods for heat-transfer coefficient were developed from various databases. These methods provide reasonable predictions at normal and enhanced heat-transfer regions, but fail to capture HTD. The upstream effects have not been considered in the prediction methods and may have an impact on local heat transfer, particularly in a channel with a non-uniform axial power profile or with flow/pressure transients. Most numerical studies evaluated the applicability of turbulence models to SCW using the computational fluid dynamics tools. Significant challenges remain in establishing the reliability of the turbulence models and the modeling of buoyancy and turbulent heat flux. Direct numerical simulation and large eddy simulation have been applied in understanding the HTD phenomena. These studies are limited to simple channels over a short axial distance at relatively low Reynolds numbers.

Conclusions

The state-of-the-art R&D on heat transfer to SCW in simple geometry and bundle subassemblies has been presented through an extensive review of recent publications. Based on the analyses, the following conclusions could be drawn. A large number of experimental studies [27, 29, 33, 34, 55, 61-63] have been performed with simple geometry such as tubes and annuli. Effects of flow conditions, diameter (or flow area), flow direction and spacers on heat transfer were investigated extensively and confirmed with observations in previous studies. Experimental data obtained from these studies are ideal for validating correlations and analytical tools, or for developing new prediction methods. Several experimental studies on heat transfer to SCW have been performed with bundle subassemblies [58-60, 66-68, 70, 71]. The observed heat transfer characteristics are similar to those in simple tubes. However, the heat transfer in bundles appears to be improved compared to that in tubes at similar cross-sectional-averaged flow conditions. One of the major concerns has been the mal-distribution of wall temperature around the heated rod of the bundle, which could lead to rod distortion affecting the thermal-hydraulic performance. Experimental results indicated a relatively small circumferential temperature gradient within the range of test conditions.