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• A modified cavitation model combining local flow characteristics, supervised learning and genetic algorithms is proposed. • The effect of empirical values of bubble diameter and nucleation volume fraction on mass flow rate are eliminated by local velocity characteristic correction. • Evaporation and condensation coefficients are determined by combining supervised learning and genetic algorithms to reduce the error in mass flow rates to within 5%. • The mechanism of the diameter ratio and pressure influence on the mass flow rate is investigated and an empirical formula for calculating the mass flow rate is derived. The flow systems in nuclear power plants and aircraft engine fuel pipelines are often subjected to extreme high-pressure conditions, which can induce cavitation and severely affect essential system components. Orifice plates are the most typical infrastructures representing the flow principle of the aboved flow systems. In this paper, a modified cavitation model combining local flow characteristics, supervised learning, and genetic algorithms is proposed to investigate the cavitation flow characteristics of orifice plates under high-pressure conditions. The modified cavitation model eliminates the influence of the bubble diameter and nucleation site volume fraction on mass flow rate and achieves dimensionality reduction at the physical level. The relationship between evaporation/condensation coefficients and mass flow rate is constructed by supervised learning, and the two coefficients are determined using the genetic algorithm. The mass flow rates are calculated by the modified cavitation model within a 5% experiment error, proving the accuracy of the modified cavitation model. The effect of the diameter ratio (the diameter of the pipe to the orifice plate) and pressure drop on the mass flow rate are obtained based on the validated cavitation model. Finally, an empirical formula for calculating the mass flow rate based on the diameter ratio and pressure drop is derived. The modified cavitation model shows great potential for cavitation prediction applications for throttling devices such as nuclear power safety valves and aircraft engine nozzles. [ABSTRACT FROM AUTHOR]

• High-fidelity CFD model for predicting fluid forces and vortices of hydraulic valve is developed. • Results of the CFD models are verified by self-built visualization test rig. • The difference in fluid forces between two typical valve discs is revealed. • The coupled effect of groove depth and valve opening on fluid force is quantified. Nuclear safety valve is a critical piece of equipment in a nuclear power plant, which is used to prevent irreversible damage caused by a sudden increase in pressure. However, there are some instances wherein valves may fail to function properly, which can have significantly impact the safety of the entire pressure/energy system. The main causes behind this phenomenon is the effect of fluid-structure coupling between the fluid force and valve disc. To better understand the fluid force, a high-fidelity computational fluid dynamics (CFD) model is established to predict the behavior of fluid forces and the location of vortices in the valve. Moreover, a visual fluid force test rig is used to verify the accuracy of the CFD model. Based on the validated CFD model, the mechanism of fluid force differences for two typical valve discs are analyzed in detail, together with the univariate effects of groove depth and valve opening on the fluid force. Based on the univariate analysis results, the coupling effect of groove depth and valve opening on fluid force is quantified using the supervised learning algorithm and Sobol sensitivity analysis. The study provides a new perspective on the characteristics of valve fluid force, and highlights the significant potential of dynamic control and energy conservation of valves. [Display omitted] [ABSTRACT FROM AUTHOR]

Pressure vessel-pipe-safety valve (PVPSV) is a commonly used combination in the industrial pressure systems. For the design optimization purpose, an in-depth investigation on the working mechanism of such a combination is essential. To this end, experimental and numerical analysis were performed in this paper. For measuring, an experimental test rig is specially designed and built, thereby dynamic tests were performed. The results indicate that the set-pressure of the safety valve and the valve spring stiffness have significant influence on the dynamics of the PVPSV. Upon certain operating conditions, the safety valve responds in unstable manners, e.g., flutter or chatter. To compensate the tests, a high-fidelity 2-D axis-symmetric system-level Computational Fluid Dynamics (CFD) model is used. The simulation results show that both the damping coefficient and the connecting pipe length have great influence on the dynamics of the PVPSV system. A PVPSV system with a small damping coefficient and/or a long connecting pipe is more likely to exhibit dynamic instability. Finally, combining the results of experiments and numerical simulations, a large enough net disc force coupled with insufficient kinetic energy loss of valve moving parts are considered to be the root cause of unstable operations of the PVPSV system. • An test rig containing a vessel, pipe and a valve is developed, thereby FSI of the PVPSV system can be studied in depth. • The FSI has a non-negligible influence on the dynamic response of the pressure vessel-pipe-safety valve system. • A better combination of the disc force and damping could avoid undesirable vibrations of the safety valve/PVPSV system. [ABSTRACT FROM AUTHOR]

• High-fidelity CFD model for predicting fluid forces and vortices of globe valve is developed. • The complex flow variation law of the globe valve is revealed. • The influence law of the valve core structure on the convection force is investigated. • The coupled effect of orifice size and valve opening on fluid force is quantified. The globe valve fails to open completely sometimes due to insufficient lifting of the valve disc during the operation of the nuclear power plant. The main reason is the inadequate understanding of changes in fluid force. Therefore, conducting research on the fluid force of the globe valve is crucial. In this study, we establish a high-fidelity computational fluid dynamics (CFD) numerical model to investigate the flow characteristics of a novel balanced globe valve. Based on the analysis results, we concluded that the size of the throttle orifice is an essential factor affecting fluid force. Therefore, the impact of the throttle orifice sizes on the fluid force is studied. Meanwhile, the coupling influence of different valve disc displacements and inlet pressures on fluid force is quantitatively analyzed. This study provides a basis for the design of globe valves and has potential value for the dynamic control and energy utilization. [ABSTRACT FROM AUTHOR]

The stoichiometric ratio and flow channel geometry play a vital role in the performance of high temperature proton exchange membrane (HT-PEM) fuel cells. Because of the high cost of experiments or simulations, most analyses and optimization of the stoichiometric ratio and flow channel geometry are limited to several points in the entire design domain. In this study, an analysis and optimization method for HT-PEM fuel cells based on the surrogate model was proposed. Surrogate models were constructed using some of the available budgets of samples to analyze and optimize the entire design domain. With this method, it was indicated that the effect of the cathode stoichiometric ratio is more significant to the cell performance than the anode stoichiometric ratio and there are significant nonlinear interactions among the flow channel geometry parameters. At the fixed operating voltage, the flow channel geometry with the maximum current density and that with the maximum real power were obtained. Compared with the base design, the designs obtained by the surrogate model improve the current density and real power by 10.54% and 3.93%, respectively. Thus, this analysis and optimization method is demonstrated to be helpful and deserves attention in future research. Image 1 • It is proved that the effect of cathode stoichiometric ratio was more significant. • The design obtained by the surrogate model improve current density by 10.54%. • The design obtained by the surrogate model improve real power by 3.93%. [ABSTRACT FROM AUTHOR]