高速水喷流实验装置方案及其性能仿真

为了研究水下武器高速水喷流噪声问题,设计了高速水喷流实验装置,并运用相关理论建立了整个装置实验过程的数学模型,并进行了数字仿真,求取了实验过程中气瓶和气水缸的压力以及水喷流速度的变化规律。仿真结果表明,该方案可在一定时间内保持喷口高速水流速度的稳定性,可以满足实验要求,为下一步的实验研究提供参考。

水射流等离子弧高速切割及其在我国船厂的适用性

本文介绍了水射流等离子弧切割的原理、特点和设备，并就其实际应用的可行性从工件材质、切割质量、经济性、使用条件等方面进行了分析、计算和比较。指出目前在我国只适用于加工数量大的非铁金属、不锈钢板材和厚3～8mm的钢板，切割钢材厚度超过8mm时，经济性不及火焰切割。

水射流切割技术

本文介绍了水射流切割技术的发展历史及国内外的应用现状，并阐述了这项技术的原理与特点、数控水射流切割机的组成和研制的技术关键。本文指出，这项新颖的切割技术在军工领域和民用市场上具有广泛的应用前景，并对开发应用这项技术的研究方向和途径作了探讨。

HT4001水射流等离子弧切割机

本文基于水下等离子孤切割机的研制，介绍了美国HYPERTHERM公司先进的HT4001水射流等离子孤切割系统．并阐述了我国船厂对板材切割的新要求。

CFD modeling of gas−liquid flow phenomenon in lead smelting oxygen-enriched side-blown furnace

A validated numerical model was established to simulate gas−liquid flow behaviors in the oxygen-enriched side-blown bath furnace.This model included the slip velocity between phases and the gas thermal expansion effect.Its modeling results were verified with theoretical correlations and experiments,and the nozzle-eroded states in practice were also involved in the analysis.Through comparison,it is confirmed that the thermal expansion effect influences the flow pattern significantly,which may lead to the backward motion of airflow and create a potential risk to production safety.Consequently,the influences of air injection velocity and furnace width on airflow behavior were investigated to provide operating and design guidance.It is found that the thin layer melt,which avoids high-rate oxygen airflow eroding nozzles,shrinks as the injection velocity increases,but safety can be guaranteed when the velocity ranges from 175 to 275 m/s.Moreover,the isoline patterns and heights of thin layers change slightly when the furnace width increases from 2.2 to 2.8 m,indicating that the furnace width shows a limited influence on production safety.

Numerical Simulation of Atomization due to Flood Discharges of Hydropower Stations

To mitigate the damages produced by flood discharges of hydropower stations, a three-dimensional numerical model of the aerated water jet restricted by gravity, air resistance and air buoyancy is proposed. Based on theoretical analysis and prototype data, a three-dimensional stochastic model is constructed using Monte Carlo method to evaluate the range of atomization and intensity of rainfall in gorges, which are strongly affected by complex terrain and various wind conditions. The prototype data observed from two hydropower stations are selected in the feedback and verification analysis to verify the proposed model. The result shows that the computational solutions fit the prototype data well. This model can be used to forecast the atomization of a hydropower station that is being designed or constructed.

Experiments on Deflecting & Oscillating Waterjet

A new type jet, the oscillating & deflecting jet, is put forward and its oscillating and deflecting characteristics are investigated. The nozzle of the self-oscillating & deflecting water jet consists of an upstream nozzle, a downstream nozzle, an oscillating chamber and two switches. It is experimentally shown that the deflective angle may reach 9.53 degree. The generated pressure fluctuation is very regular and the jet can efficiently increase the ability for breaking and cutting by eliminating the water cushion effect associated with a continuous jet.

Reaction thrust characteristics of high-pressure submerged water jet of cylinder nozzles

The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. The simulation of the flow field characteristics was conducted via the FLUENT computational fluid dynamics package. Effects of the inlet conditions and the nozzle dimensions on the reaction thrust of a water jet were addressed particularly. The reaction thrust experiments were performed on a custom-designed test apparatus. The experimental results reveal that a） the nozzle diameter and the inlet conditions exert great influence on the water jet reaction thrust; and b） for L≤4d0, where the nozzle is treated as a thin plate-orifice, the reaction thrust is independent of nozzle length; for L〉4d0, where the nozzle is treated as a long orifice, the reaction thrust can reach maximum under the condition of a certain flow rate. These findings lay a theoretical foundation for the design of nozzles and have significant value, especially for the future development of high-oressure water-let orooulsion technology.

Natural orifice transluminal endoscopic wedge hepatic resection with a water-jet hybrid knife in a non-survival porcine model

AIM: To explore the feasibility of a water-jet hybrid knife to facilitate wedge hepatic resection using a natural orifice transluminal endoscopic surgery (NOTES) approach in a non-survival porcine model. METHODS: The Erbe Jet2 water-jet system allows a needleless, tissue-selective hydro-dissection with a pre-selected pressure. Using this system, wedge hepatic resection was performed through three natural routes (trans-anal, trans-vaginal and trans-umbilical) in three female pigs weighing 35 kg under general anesthesia. Entry into the peritoneal cavity was via a 15-mm incision using a hook knife. The targeted liver segment was marked by an APC probe, followed by wedge hepatic resection performed using a water-jet hybrid knife with the aid of a 4-mm transparent distance soft cap mounted onto the tip of the endoscope for holding up the desired plane. The exposed vascular and ductal structures were clipped with Endoclips. Hemostasis was applied to the bleeding cut edges of the liver parenchyma by electrocautery. After the procedure, the incision site was left open, and the animal was euthanized followed by necropsy. RESULTS: Using the Erbe Jet2 water-jet system, trans-anal and trans-vaginal wedge hepatic resection was successfully performed in two pigs without laparoscopic assistance. Trans-umbilical attempt failed due to an unstable operating platform. The incision for peritoneal entry took 1 min, and about 2 h was spent on excision of the liver tissue. The intra-operative blood loss ranged from 100 to 250 mL. Microscopically, the hydro-dissections were relatively precise and gentle, preserving most vessels. CONCLUSION: The Erbe Jet2 water-jet system can safely accomplish non-anatomic wedge hepatic resection in NOTES, which deserves further studies to shorten the dissection time.

Numerical simulation of bubble chaotic motion in a cavitating water jet

A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.

Research of chemical induction unit on mixing effect and chlorine saving

Rapid mixing and chlorine saving are two important problems that most drinking water industries are focus on, and this paper adopts chemical induction unit to compare with water jet injector to study what merits chemical induction unit has. The experiment chose coefficient of variability of chlorine concentration to evaluate the mix effect and used chlorine consumption to compare the two equipments. Distribution reservoir experiments show that chemical induction unit can completely mix chlorine less than 6.2 seconds and water jet injector can not completely mix in 3 minutes. Mixing pool experiments show that chemical induction unit can save chlorine compared with water jet injector, and can save more if more chlorine is consumed.

Research on Critical Flow of Water under Supercritical Pressures in Nozzles

An experiment on critical flow of water was conducted in two nozzles of 1.41 mm in diameter and 4.35 mm in length with rounded-edge and sharp-edge respectively, covering the ranges of inlet pressure of 22.1-29.1 MPa and inlet temperature of 38-474 ℃. More than 200 data points were obtained and the characteristics and parametric trends were investigated. In the region of near and beyond pseudo-critical temperature the thermal-equilibrium is dominant, and the flow rate can be estimated by the modified homogeneous equilibrium model. In the below pseudo-critical region the results exhibit scattered feature as a result of hysteresis effect in the onset of vaporization, characterizing a bifurcation behavior. This effect is more significant in the nozzle with sharp-edge, especially at higher pressure. For temperature well below the pseudo-critical point, the flow is not at critical condition and the flow rate can be represented by the Bernoulli equation reasonably.

Thermal transfer experimental research of a horizontal tube evaporative condenser

The thermal resistances distribution in different wet-bulb temperatures, air velocities and spraying water densities were achieved by the experimental test. The fluctuation of the water film convection and the water-air interfacial thermal resistance were reviewed especially. In the distribution of thermal resistance, the rank of the thermal resistance proportion （from max to min） is air flow heat transfer resistance, heat transfer resistance between refrigerant and wall, water film convection resistance and wall heat transfer resistance. When the heat flux is constant, the total resistance lowers nearly along with the increasing of air flow and water spray density. But there are a best air flow value of 2.98 m/s and a best spray water density of 0.064 kg/（m ·s） respectively, if continue to increase them, condensation performance is not significantly improved any more. The test results are available to improve the evaporative condenser performance and the designing lever.

Dynamic effects of high-pressure pulsed water jet in low-permeability coal seams

Mine gas extraction in China is difficult due to the characteristics such as micro-porosity,low-permeability and high adsorption of coal seams.The pulsed mechanismof a high-pressure pulsed water jet was studied through theoretical analysis,experimentand field measurement.The results show that high-pressure pulsed water jet has threedynamic properties.What's more,the three dynamic effects can be found in low-permeabilitycoal seams.A new pulsed water jet with 200-1 000 Hz oscillation frequency andpeak pressure 2.5 times than average pressure was introduced.During bubble collapsing,sound vibration and instantaneous high pressures over 100 MPa enhanced the cuttingability of the high-pressure jet.Through high-pressure pulsed water jet drilling and slotting,the exposure area of coal bodies was greatly enlarged and pressure of the coal seamsrapidly decreased.Therefore,the permeability of coal seams was improved and gas absorptionrate also decreased.Application results show that gas adsorption rate decreasedby 30%-40%and the penetrability coefficient increased 100 times.This proves that high-pressurepulsed water is more efficient than other conventional methods.

Flame development characteristics at variable swirl level inductions in a stratified CNG direct injection combustion engine

The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine （CNG） in a single cylinder direct injection （DI） engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 （λ=2.35）. Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves （SCV） at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble （no swirl）, medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever）, 2 CA degrees after ignition timing （AIT） for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble.

Pressure drop of the film-enlarged tube bundles in air-water two-phase cross flow in evaporative air cooler

An experiment was carried out to investigate the relation of the maximum velocity of air passing through narrowest passage, mass flux of spray water in one square meter in one hour and the pressure drop of tube bundles. Twelve equations were obtained for the relation. The results show that the pressure drop of the tube bundles increases with increase of the maximum velocity of air and the mass flux of spray water. Comparing the pressure drop of the bare tube bundles with that of the film-enhanced tube bundles, it is found that the pressure drop of the film-enhanced tube bundles is lower about 11% and the surface roughness of the film-enhanced plates is a main factor that influences the pressure drop. The data and method obtained in the paper can be used to compute the pressure drop of the film-enhanced tube bundles and is helpful for selection of fan.

削铁如泥的“水刀”

大家平时所看到的静水显得非常“温柔”,毫无冲击力。然而,在一定的条件下,使水以较高的速度流动起来,它就会有足够的能量,从而会变得强劲有力。根据这个原理,早在上个世纪80年代以前,科学家已经研究、开发出了一项新的加工技术——高压水喷流切割技术,也常被称为“水刀”。