Sichao Tan

Application of Planar Laser-Induced Fluorescence to Measurement of Concentration Field in the Downcomer

In recent years, inhomogeneous boron dilution has recently become one of the most important issues in PWR safety. In this paper, planar laser-induced fluorescence (PLIF) was applied to the visualization measurement of concentration distribution of boron in a downcomer channel. An aqueous solution of a fluorescent dye simulated the boron solution. The visual mixing phenomena were recorded by the high-speed camera with high-resolution information. The laser dye used here was rhodamine B(RhB), and the 532-nm laser has eliminated the Gaussian distribution. Intensity distribution was measured by one CCD, and then according to the distribution of intensity, the concentration fields in the downcomer channel can be obtained. The concentration fields under different volume flow rates were discussed. The results show the diffusion process of boron and the concentration distribution of boron, which are important for the study of inhomogeneous boron dilution in the design and research of reactor system. Besides this technique has been specially developed to improve whole-field concentration measurements, which will have the extensive application of nuclear industry.

Wall Temperature Fluctuation Under Flow Pulsation in a Vertical Tube

Flow boiling has been receiving lots of attention and researches because it is commonly encountered in nuclear reactors and stream generators. Experimental studies on heat transfer in a circular tube with constant wall heat flux were carried out in laminar flow regime. The experiments were under steady and pulsating conditions and performed over a range of <500 Re <2000 and under atmospheric pressure. The wall temperature near inlet (T w1 ) was investigated. The experiment results show that in a pulsation period, the wall temperature fluctuates periodically and has a sharp drop when the inlet pressure fluctuates intensely. The rise time of T w1 accounts for 80–85% of one pulsation period. The experiment results demonstrate that the pulsating period and amplitude have a strong influence on this phenomenon. The pulsating period and amplitude influence the shape of the wall temperature curve. Only when the fluid in the wave trough starts boiling, the phenomenon of sharp drop of wall temperature occurs, and a small wave trough appears in the rising of the wall temperature if the boiling time is long. Furthermore, the flow regime transition induced by buoyancy or the intense fluctuation of inlet pressure could be the reasons for a sharp drop of wall temperature.

Prediction of Laminar to Turbulent Transition in 90° Curved Duct Based on Energy Gradient Theory

Study on laminar to turbulent transition in a 90° curved duct is carried out. Professional mesh generation tool ICEM is used to create geometry model and generate mesh, then the mesh is imported to the fluid dynamics software CFX to simulate three-dimensional flow. The dimensionless parameter K is calculated in the duct with velocity and pressure distribution obtained by numerical simulation. According to energy gradient theory, K is the ratio of energy gradient in the transverse direction to that in the streamwise direction, which can be used to measure stability of the flow field. It is found that fluid is most likely to lose its stability where the maximum K is, and laminar to turbulent transition occurs when K reaches a certain value, corresponding to the critical Reynolds number. The instability and transition characteristics predicted by energy gradient method agree well with former researchers’ results.Copyright

Study of Surrogate Data Method for Chaos Identification of Natural Circulation Flow Oscillation Under Rolling Motion

The identification of chaos in the two-phase natural circulation system under rolling motion can provide theoretical guidance for forecasting and control of natural circulation flow instability. The surrogate-data technique is one of effective methods to identify the chaos in the time series exactly. It can avoid the limitation of the positively identifying chaos. In this paper, correlation dimension and principal component analysis (PCA) was used as the identification evidence; the surrogate-data technique was used for the identification of chaos in time series of the irregular complex flow oscillations. The results indicate that there is chaos in the natural circulation system under rolling motion and the surrogate-data technique can identify chaos exactly.Copyright

Non-Linear Time Series Analysis of the Infuence of Rolling Motion on Natural Circulation System

Two-phase natural circulation flow instability under rolling motion condition was studied experimentally and theoretically. Experimental data were analyzed with nonlinear time series analysis methods. The embedding dimension, correlation dimension and K2 entropy were determined based on phase space reconstruction theory and G-P method. The maximal Lyapunov exponent was calculated according to the methods of small data sets. The nonlinear features of the two phase flow instability under rolling motion were analyzed with the results of geometric invariants coupling with the experimental data. The results indicated that rolling motion strengthened the nonlinear characteristics of two phase flow instability. Some typical nonlinear phenomena such as period-doubling bifurcations and chaotic oscillations were found in different cases.Copyright