In view of the three-stage flash evaporation system of the coal gasification plant, a combination of theoretical analysis and numerical simulation was used to establish the erosion damage evaluation model in the black water angle valve. The influence of the inlet flash evaporation ratio on the inlet velocity, the outlet flash evaporation ratio and the outlet velocity of the low-pressure black water angle valve are systematically studied, the mechanism of erosion damage to the carbon steel valve body by the solid medium in black water was analyzed according to the micro-cutting theory. The results show that the inlet velocity w
1, the outlet flash evaporation ratio x
2, the outlet velocity w
2 of angle valve have linear correlation with the inlet flash evaporation ratio x
1.The upstream volume erosion ratio of the angle valve at the inlet flash ratio x
1 = 3 wt.% is 114 times as much as that at zero inlet flash ratio. Meanwhile, the downstream volume erosion ratio of the angle valve at x
1 = 3 wt.% is only 2.7 times as much as that at zero inlet flash ratio. The prevention strategies to reduce the erosion damage to black water angle valve are proposed by inhibiting the inlet flash evaporation ratio and reducing the inlet flow rate etc. This study is expected to provide guidance for the erosion resistance design and operation of the black water angle valve.
Successive impingement of supersonic droplets after refining in plasma jet usually forms a fine-lamellar structured coating with high mechanical properties. However, the comprehensive process (such as flattening, rapid solidification and crystallization) of high-velocity impact of refined droplets is difficult to understand. In this study, an experimental study showed that the content of refinement droplets reached to 90 % and displayed the multi-scale equiaxed grains morphology at extremely rapid solidification rate. Phase-field model revealed a hybrid coalescence growth of oriented attachment and migration of grains boundary under the dynamic temperature gradient. Furthermore, an optimized numerical model that consisted of the Navier-Stokes and energy balance equations coupled with the Cahn-Hilliard and phase-field model for growth orientation of grains was developed to accurately reproduce the comprehensive process of refined supersonic droplets. The size distribution and crystallographic orientation of columnar grains for single or two flattened droplets were in a good agreement with the experimental results. The interface between two-flattened droplets exhibited an epitaxial growth of columnar grains. This optimized model can be an effective method in predicting the flattening and solidification with crystallization behavior of droplets during plasma spraying.
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