Experimental study on dynamic pipe fracture in consideration of hydropower plant model

In the case of sudden valve closure, water hammer creates the most powerful pressure and damage to pipeline systems. The best way to protect the pipeline system is to eliminate water hammer. The main reasons for water hammer occurrence are valve closure, high initial velocity, and static pressure. However, it is difficult to eliminate water hammer. Water hammer tends to occur when the valve is being closed. In this study, the pipe fracture caused by static water pressure, gradually increasing pressure, and suddenly increasing pressure were compared experimentally in a breaking PVC test pipe. The quasi-static zone, the dynamic zone, and the transition zone are defined through the results of those experiments, with consideration of the fracture patterns of test pipes and impulses. The maximum pressure results were used to design the pipeline even though it is in the dynamic zone.

Computational fluid dynamic simulations on liquid film behaviors at flooding in an inclined pipe

The complex liquid film behaviors at flooding in an inclined pipe were investigated with computational fluid dynamic(CFD) approaches. The liquid film behaviors included the dynamic wave characteristics before flooding and the transition of flow pattern when flooding happened. The influences of the surface tension and liquid viscosity were specially analyzed. Comparisons of the calculated velocity at the onset of flooding with the available experimental results showed a good agreement. The calculations verify that the fluctuation frequency and the liquid film thickness are almost unaffected by the superficial gas velocity until the flooding is triggered due to the Kelvin–Helmholtz instability. When flooding triggered at the superficial liquid velocity larger than0.15 m·s-1, the interfacial wave developed to slug flow, while it developed to entrainment flow when it was smaller than 0.08 m·s-1. The interfacial waves were more easily torn into tiny droplets with smaller surface tension, eventually evolving into the mist flow. When the liquid viscosity increases, the liquid film has a thicker holdup with more intensive fluctuations, and more likely developed to the slug flow.

AXIAL HEAT CONDUCTION MODEL TO PREDICT MAXIMUM HEAT REMOVE OF MINIATURE HEAT PIPE BASED ON GREY MODEL THEORY

Computer chip is always accompanied by the increase of heat dissipation and miniaturization. The miniature heat pipes are widely used in notebook computer to resolve the heat dissipation problems. Maximum heat removed model of miniature heat pipes building by grey model is presented. In order to know the foundation for modeling, the smooth grade of error examination is inquired and the accuracy of grey relational grade is verified. The model can be used to select a suitable heat pipes to solve electric heat problems in the future. Final results show that the grey model only needs four experiment data and its error value is less than 10%, further, it is better than computational fluid dynamics （CFD） model.

A Dual-driven Intelligent Combination Control of Heat Pipe Space Cooling System

Effective thermal control systems are essential for reliable operation of spacecraft.A dual-driven intelligent combination control strategy is proposed to improve the temperate control and heat flux tracking effects.Both temperature regulation and heat flux tracking errors are employed to generate the final control action;their contributions are adaptively adjusted by a fuzzy fusing policy of control actions.To evaluate the control effects,describe a four-nodal mathematical model for analyzing the dynamic characteristics of the controlled heat pipe space cooling system（HP-SCS） consisting of an aluminum-ammonia heat pipe and a variable-emittance micro-electromechanical-system（MEMS） radiator.This dynamical model calculates the mass flow-rate and condensing pressure of the heat pipe working fluid directly from the systemic nodal temperatures,therefore,it is more suitable for control engineering applications.The closed-loop transient performances of four different control schemes have been numerically investigated.The results conclude that the proposed intelligent combination control scheme not only improves the thermal control effects but also benefits the safe operation of HP-SCS.