Liu Yinshui

Research on the Flow and Cavitation Characteristics of Multi-Stage Throttle in Water-Hydraulics

Abstract In water-hydraulic power systems cavitation is more likely to happen than in oil-hydraulic power systems because of the high vaporous pressure of water. A multi-stage throttle, which consists of two or more orifices in a throttle, is an effective way to avoid or reduce cavitation damage. In this research, the cavitation characteristics of two-stage throttles are analysed theoretically and compared with a single-stage. Then, experiments are conducted to investigate the flow and cavitation characteristics of multi-stage throttles including two kinds of two-stage throttles and one of a three-stage kind. All the experiments are carried out under the two cases with and without backpressure, respectively. The working medium is tap water. Experimental results show that the shape of the multi-stage throttle and operating conditions have remarkable effects on the flow and cavitation characteristics.

Materials screening of matching pairs in a water hydraulic piston pump

Purpose – The purpose of this paper is to present some design guidelines for the selection of the materials of the main frictional pairs in a water hydraulic piston pump.Design/methodology/approach – In the research, a specified test bench that can simulate the typical frictional pairs in a water hydraulic piston pump was built. The friction and wear behaviors of the three pairs in the pump with different materials combinations were tested on the test bench. The tested materials included metal, engineering ceramics and plastics. Some surface engineering technologies including plasma surface spray, laser clad and heat treatment were applied and tested. The matching schemes included hard‐to‐hard (such as ceramics‐to‐ceramics) and hard‐to‐soft (such as metal‐to‐plastics, ceramics‐to‐plastics).Findings – Some principles for the materials selection in a water hydraulic piston pump were obtained. According to the test results, the combination schemes for the main frictional pairs in a water hydraulic piston pum...

Flow and cavitation characteristics of a damping orifice in water hydraulics

Abstract The flow in damping orifices when using water as the working media is of high Reynolds number and cavitation is inevitable. In this article, experimental studies are made on the flow and cavitation characteristics of water hydraulic orifices and the coefficient formulae in previous documents are testified with the Reynolds number ranging from 104 to 105. All the orifices are made of transparent materials, so the flow and the occurrence process of the cavitation can be observed with the naked eye. The experiments for each orifice are carried out under the two cases with and without backpressure, respectively. Experimental results show that the flow coefficient with backpressure is larger than the case without it. The larger the aspect ratio, the less the flow characteristics are influenced by backpressure. The cavitation first occurs at the inlet of orifices and then shifts to the outlet gradually. When there is cavitation happening at the outlet, flow saturation emerges simultaneously.

A portable piston-type water mist fire extinguisher for spacecraft

A new type of water mist fire extinguisher was proposed to be used in the manned spacecraft. The goal of prototype is that it can extinguish class 8B fires on the ground and its mass is less than 2.5 kg. The prototype employed only water as suppression agents. In the extinguisher, a piston separated the water from nitrogen artificially, which dispels the influence of the gravity on discharging. It possesses some advantages, such as high reliability, easy refilling of water and nitrogen, long life span, and convenient maintenance. A pressure-swirl nozzle was employed to produce water mist. There was no part to keep the pressure constant at the nozzle’s entrance; the service pressure of nozzle was determined in the range from 6 to 15 MPa. In that scope, the variation of droplet size with pressure did not have a significant impact on suppression performance, and the suppression time increment due to velocity reduction was in the acceptable level. A series of tests were conducted to verify its performance. The vibration test presented that there was no nitrogen leakage and no obvious resonance happened, which meant it possessed high reliability. The fire suppression tests indicated that it can suppress different fire types of a certain scale. The simulation results showed that the spray performance is improved in the microgravity. Conclusion can be drawn that the prototype is feasible in the microgravity and it reached the requirements of the design.

Research on the pump of seawater hydraulic variable ballast system in submersible

Submersible is a very important apparatus for deep-sea exploration, scientific survey, martial detect and combat. Variable ballast system is a critical part in the deep submersible and seawater pump is a key component in the system. In this paper, development of seawater pump used in variable ballast system is introduced, the problems and solutions of seawater pump used in the special condition of variable ballast system are primarily studied and finally a new structure of seawater pump is proposed.

The experimental research of using water mist to extinguish smolding fire in enclosed space

The fire which occurs in enclosed space such as warehouse, underground cellar, aviation cockpit, ship control room plays an important role of daily common fire. In the event of fire, The poor emission of toxic gases such as carbon monoxide, carbon dioxide generated through combustion process are harmful to personnel on account of the confined space. Smoldering fire plays an important weight in the fire in the enclosed space. It is difficult to detect the smoldering. If it is not extinguished in time, it will spread and convert into naked flame, which causes serious losses of the surrounding environment. This paper focused on the experimental study on the application of water mist in extinguishing the common smoldering fire in enclosed space. Comparison and analysis of the air composition before and after the effect of water mist in enclosed space were made. Industrial dehumidifier was utilized to conduct post-processing. The results show that water mist can extinguish the smoldering fire effectively with high efficiency, with short time and little water consumption. The efficiency of fire extinguishing is directly related with the working time. The longer the water mist works on, the smaller possibility of after-combustion for smoldering. According to results of the after treatment for the toxic gases in enclosed space, dehumidifier can control the humidity effectively, as well as reduce the toxic gases through dehumidification.