Based on thermodynamic calculations and dilatometry experiments performed over a wide range of cooling rates with on two continuously cast steels, an empirical model was developed to describe the relationship between the critical temperatures of austenite transformation, the cooling rates, and the equilibrium temperatures of phase transformation, written as Ar(uC)5Ae2exp(BzC/C r ). The model was verified to be applicable to the calculation of Ar 3 and Ar 1 temperatures at various cooling rates for different steel blanks during continuous casting process. Results indicated that, the Ar 3 and Ar 1 temperatures decreased with increasing cooling rate; and the temperature window for ferrite formation enlarged while the cooling rate was increasing. The influence of cooling rate on the linear and bulk thermal expansion coefficients was discussed. Results showed that the peaks of thermal expansion coefficients during new phase formation apparently moved toward low temperatures as the cooling rate increased; The linear and bulk thermal expansion coefficients of single austenite phase were steady at 2.1610 25 and 6.8610 25 uC 21 respectively. The relative contraction of steels would be larger at lower cooling rate during continuous casting.
To provide a flexible calibration method and make an accurate machine vision (MV) based flatness measurement strategy a reality in routine production line, an area scan charge coupled device (CCD) laser stripe scanning approach is presented. The applicability of the proposed method is not tied to the strip exclusively. First, we devise an automatic laser stripe imaging quality evaluation method through analysing the characteristics of the image grey gradient of laser stripe, which is a prerequisite for precisely extracting the laser stripe modulated information in hot or reflective object surface; second, a fast system calibration method is designed based on the area scan CCD imaging principle and spatial measurement technologies; here, the practical calibration is an indispensable technique for MV based measurement with large field of view in modern steelmaking lines. The proposed method performs competitively with the state-of-the-art as seen from the comparison of the experimental results. Through online testing, this method also showed considerable promise for hot rolled strip flatness measurement. However, the scheme for eliminating the influence of vibrations related to different applications is not taken into account in the current work.
In pressurized water reactors (PWRs), the spacer grids of the fuel assembly has significant impact on the thermal-hydraulic performance of the fuel assembly. Particularly, the spacer grids with the mixing vanes can dramatically enhance the secondary flow and have significant effect on the void distribution in the fuel assembly. In this paper, the CFD study has been carried out to analyze the effects of the spacer grid with the steel contacts, dimples and mixing vanes on the boiling two-phase flow characteristics, such as the two-phase flow field, the void distribution, and so on. Considered the influence of the boiling phase change on two-phase flow, a boiling model was proposed and applied in the CFD simulation by using the UDF (User Defined Function) method. Furthermore, in order to analyze the effects of the spacer grid with mixing vanes, the adiabatic (without boiling) two-phase flow has also been investigated as comparison with the boiling two-phase flow in the fuel assembly with spacer grids. The CFD simulation on two-phase flow in the fuel assembly with the proposed boiling model can predict the characteristics of two-phase flow better.
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