Experiments of the Self-excited Oscillation Pulsed Jet Nozzle

The self-excited oscillation pulsed jet nozzle which proposed makes the continuous jet transform into pulsed jet . Comparing with general continuous jet, the pulsed jet has a higher peak of pressure and larger volume of erosion , therefore it increases the effective distance off of the jet under the same conditions. The laboratory and industry experiments of the Self-excited oscillation pulsed jet nozzle are introduced in the report.     

THE EROSION STUDY OF THE SELF-EXCITED OSCILLATION CAVITATION JET

Based on references [1, 2, 3], we designed a set of device of the self-excited oscillation cavitating jet. Its cavitation mechanism and the result of jet impact block are analysed. With erosive volume as the object, the effect of the self-excited oscillation cavitating jet is compared with that of conventional continuous jet under the same condition. It is found cxperimeetally that the position of suction air and the air quantities and the geometrical parameters of the device have great effect on the erosive effects of the self-excited oscillation cavitating jet. In certain range of stand off distance, it's not obvious that the erosive effects of the self-excited oscillation cavitating jet changed with stand off distance for pulse cavitating jet and cavitation bubblies and droplet impinging on the target. Compared with continuous jet, the erosive vo-l ume and area of the self-excited oscillation cavitating jet is more than one time larger than the continuous jet.     

Effect of Main Parameters on Cutting of the Pulsed Abrasive Water Jet

The relationship between abrasive concentration, length of oscillating chamber, standoff distance and cutting depth, erosion rate as well as cutting specific energy was investigated by experiments in the submerge and surface conditions. The cutting and erosion capabilities of the pre-mixed abrasive water jet and the pulsed abrasive water jet were analyzed in contrast. It is shown that the maximum cutting depth and erosion rate of the pulsed abrasive water jet are respectively 1.67,1.72 and 1.39, 1.47 than the pre-mixed abrasive water jet in submerge and surface conditions. These results attained from the research are useful to increase the cutting efficiency, decrease the energy ratio and expand the application domains of the abrasive water jet.     

Analysis on stress wave effect during the process ofrock breaking by pulsed jet

A mathematical model of rock breaking under pulsed jet is established by introducing the Johnson-Holmquist-Concrete constitutive relation and the smoothed particle hydrodynamics method. Based on this model, the formation, propagation and attenuation of stress wave during rock breaking by pulsed jet are simulated. The relations between pressure and time at different points on rock surface and the curve of peak stress wave versus distance to action spot are obtained. Destruction behaviors of rock under pulsed jet and effects on stress wave effect from jet velocity and lithology are studied according to the above calculation results, analysis results show that stress wave effect of pulsed jet acts locally and the peak stress wave shrinks sharply as the acting distance increases. The rock breaking mechanism of stress wave is tensile failure during the high speed process of load-unload. Power and effect range of stress wave is in high direct proportion with jet velocity. There is a threshold velocity before the macroscopic failure. Rocks of different lithologies have different destruction types under pulsed stress wave of pulsed jet. Destruction type of low strength rock like sandstone is crack propagation under the tensile stress during the high speed process of load-unload, while the destruction type of high strength brittle rocks like granite and limestone is vertical failure of stress concentration.     

Airlift Used to Dredging in the ThreeGorges Reservoir-Region

The method using the airlift assisted with the self oscillation pulsed jet for dredging in the Three Gorges Reservoir Region has been presented. The physical and mathematical model of airlift has been given. The feasibility of the self oscillation pulsed jet as breaker of the airlift is researched. It is theoretically and experimentally shown that the self oscillation pulsed jet not only crushes and looses mud deposit under water, but also lifts particles of solid on the clay and sand or mud bed. The oscillation cross flow caused by the self excited oscillation jet makes particles of solid enter the end of the suction pipe easily.     

Studies on Dust-Laying with Swirl-Water Jet

The main optimum parameters of laying dust for mine is introduced in this pa-per.The related parameters of laying dust with swirl,pulsed and ordinary water jet are analysed re-spectively at different water pressures.     

Mechanism analysis of permeability based on promoting coal matrix shrinkage by water jet

High pressure pulsed water jet (HPWJ) is a new technology of effectively improving coal seam permeability. However, the mechanism of increased permeability is not yet clear, which restricts the application of HPWJ in different coal seams. From the perspective of improving permeability by coal matrix shrinkage, the impelled dynamic equations is established based on analysis of coal dynamic effects by water jet. According to theoretical analysis of the stress state of coal matrix, it is concluded that HPWJ can promote coal matrix shrinkage, and the relationship equation between jet impact-coal matrix is derived. Besides, the gas seepage function in the coal slotted by the HPWJ is gained by using PM model, which provides theoretical support for generalizing the technology in the coal mine.     

LABORATORY INVESTIGATION OF ESSENTIAL CHARACTERISTICS PARAMETERS FOR THE INDUCED-NOZZLE DEVICE

The standoff of a submerged jet is smaller than a non-submerged jet in general. In order to increase the standoff of a submerged jet, the induced-nozzle device is presented with its inducing mechanism analysed in this paper. Under the various inducing medium, the effect of the ratio d2/d1 upon the device's properties is measured. Some reasonable parameters are given. When d2/d1=2.0, approximate straight region of the curve of the jet center line stagnation pressure varying with the standoff is L/d1= l0~12 for inducing air. The induced-nozzle device is compared with the conventional nozzle for shotting some samples. Several applied possibilities of the device are discussed.     

The Study on the New Method for Exploiting Deep Beach Placer

The method using the airlift and the self excited oscillation jet for exploiting deep beach placer has been presented. The physical and mathematical model of airlift is given in this paper. The feasibility of the self excited oscillation pulsed jet as breaker of the airlift is researched. It has been shown theoretically and experimentally that the self excited oscillation pulsed jet not only crushes and looses ore deposit under water, but also lifts particles of solid on the clay and sand bed. The oscillation cross flow caused by the self excited oscillation jet makes particles of solid enter the end of the suction pipe.     

Mechanism and application of protection againstoutburst for abrasive water jet slotting technology

Aiming at the status quote of long time for methane extraction and slow speed for laneway excavating in coal seams of Liziya south 2JHJ well, abrasive water jet slotting technology is adopted to improve the methane desorption and increase excavating speed in semi-coal laneway. Through analyzing damage model and protection against outburst mechanism, the process of Coal-Rock Mass being cut and fractured is studied. Through lab test on abrasive water jet cutting coal-bed gangue, a new abrasive water jet cutting device is successfully designed and made and all parameters are determined. It is showed that abrasive water jet can cut through a coal-bed gangue with thickness 60~80 mm and uniaxial compressive strength 62 MPa. After cutting coal seams by abrasive water jet, the surface area for methane is enlarged and then coal seams pressure fell rapidly. Therefore the permeability and desorption of coal seams are greatly increased. The results are as follows: the average productivity of single-hole was enhanced by 2.83 times.     

Average Temperature Distribution of the Ceiling Jet in Train Fires in Tunnels

The flame ceiling jet is easily formed while the on fire train stops in the tunnel. The iterative formula is derived to calculate the average temperature of the flame ceiling jet when the fire source is set on the center of the train by establishing a one dimensional model of the unit control volume, and the heat exchange is considered among the flame smoke and the wall of the tunnel and the train. Undetermined coefficients in the iterative formula are determined by small scale model experiments with the scale factor of 1:8 and numerical simulation. The calculated values of temperature by the iterative formula are consistent well with the measured values, and the maximum error of calculation is no more than 7%, which indicates that the iterative formula is reliable. The results show that the distributions of the average temperature of flame ceiling jet are in the exponential form, but there are some differences between that above the train and that in the tunnel. Two prediction formulas for the flame ceiling jet average temperature changing along the longitudinal tunnel are obtained by the sub fitting method. The results can provide reference for the alarm parameter selection, device settings in tunnel, safety evacuation of the passenger, as well as the analysis of the destructive effects on the tunnel lining structure caused by tunnel fire.     

Theoretically Investigation of Dynamic Characteristics of Spherical Bubble Collapse in Pulsed Abrasive Water Jet

This paper theoretically investigates the characteristics of cavitating bubbles in the pulsed abrasive water jet(PAWJ) and establishes the dynamic equations of cavitating bubbles. The effects of abrasive diameter and density on the spherical bubble collapse are also analyzed. It is found that the change of abrasive diameter rarely affects the bubble collapse when the abrasive diameter and density are small whereas the smaller abrasive greatly blocks the bubble collapse when the abrasive diameter and density are comparably big. It is also shown that when the abrasive density is increased, the fluid viscosity rises, and the kinetic energy of the abrasives near the collapsed bubble is enhanced and meanwhile the intensity of cavitating erosion is weakened.     

Mechanism of Self-excited Oscillation Pulsed Jet Aerator

Based on the theory of boundary layer theory and vortex theory of fluid mechanics, a self-suction self-excited oscillation pulsed jet aerator is introduced . This new type of jet aerator adopts self-excited oscillation cavity to replace the traditional mixing tube, and forces air and oxygen-demand water to intermix, compound and oxygenize violently in the cavity under the effect of self-excited oscillation, eject through the special shaped tail tube in the pulsed mode. Theoretical analysis and preliminary industrial experiments show that the new type of jet aerator has an excellent effect of intermixing, compounding and aerating, and that the oxygen-demand water ejected through the special shaped tail tube has an intensive pulsation effect.     

高低空急流在一次暴雨过程中的动力作用

利用常规台站降水资料和NCEP/NCAR一日四次的1°×1°再分析资料,使用天气动力学诊断方法,分析了高低空急流及其次级环流在辽宁2010年8月4至5日区域性暴雨过程中的动力作用。结果表此次暴雨过程发生在“东高西低”的大尺度环流形势下,强降水发生在584~588 dagpm 等值线之间,主要影响系统是高空槽、副热带高压外围西南气流和切变线。在暴雨过程中,高空急流的加强东移对低空急流加强和发展起着重要的作用,也是辽宁东部低空急流加强和发展的重要动力原因。辽宁东部的低空急流的北侧上升支刚好位于暴雨区上空,为暴雨过程提供了有利的动力条件。暴雨区出现在200hPa 高空急流入口区右侧、850hPa 西南低空急流左侧。高空急流入口区北侧上升,南侧下沉的次级环流圈是本次暴雨的独特特征。在高空急流强盛期间,影响暴雨区的次级环流是反环流圈,即在辽宁上升,在辽宁以南地区下沉;而在降水后期,随着高空急流减弱,快速东移,由辽宁东部低空急流北侧的上升支,与辽宁以北的西北风低空急流的南侧的下沉支形成正环流。本次过程中低空形成两支急流,且低空急流的次级环流恰好镶嵌在高空急流的次级环流中,次级环流的方向转变均是本次暴雨过程中的重要特征。     

Experimental Investigation on Chip-break Influenced by Cryogenical Cold Air jet

In machine cutting, the replacement of traditionalKGcutting solution with cryogenical cold air jet not only possesses a good cooling and lubricating efficiency, but also can avoid the occurrenceof environmental pollution. In order to clarify the manner and performance of discharged cutting chip under cryogenical cold air jet condition, an experiment was carried out for steel grade 45 in the dry and cryogenical cold air jet cutting comparatively. The effects of cryogenical cold air jet on the breaking of cutting chip are discussed. Experimental results reveal that, in the valid ranges of pressure and temperature, the cryogenical cold air jet can widen the chip broken region effectively. Different insufflating angle of cold air behaves different influence on the chip-break. From the experiment, it has been gained that the optimized jet insufflatingangle, temperature effecting range and pressure working range of cold air, which provides the foundation of industrial manufacturing.     

A STUDY OF THE MECHANISM OF HEAT-TRANSFER DURING METAL HEATING WITH IMPINGING JET

The mechanism of heat transfer during sheet metals heating with impinging jet in a rapid heating furnace is studied with experiments and mathematical simulating methods. It is shown that the heat exchange between metals and impinging jet occurs mainly in the lower region of the hearth,most of which is carried out in the manner of convective heat transfer,and the convective portion of the total heat fluxing to metal is up to 80%. Furthermore,it is also found that the reverse heat flux from metals to the wall, which is a new heat transfer phenomenon, takes place in the late heating period, and the intenser the convective heat transfer in the furnace is, the earlier the reverse radiation occurs.     

苹果片气体射流冲击干燥工艺的优化

采用一种新型的气体射流冲击干燥技术,对切片厚度6～8mm的苹果片进行了干燥试验研究。在喷嘴直径为16mm,喷嘴气流速度为16.8m/s的条件下,得出苹果片气体射流冲击干燥处理的最佳工艺参数为:喷嘴出口气体温度70℃,喷嘴与苹果片最佳距离120mm,干燥盒宽度为200mm,物料堆积高度为35mm。     

气体射流冲击技术在果蔬干燥中的应用

干燥处理是果蔬加工的一项重要技术,气体射流冲击作为一种新型的干燥技术在果蔬干燥方面具有很强的优势。本文综述了目前果蔬干燥常用的技术方法及其优缺点,阐述了气体射流冲击干燥技术的原理、特点、影响因素和干燥工艺。与传统干燥方法相比较,气体射流冲击干燥技术具有对流换热系数大、干燥速度快、产品质量高、能耗低等优点,在果蔬干燥方面应用前景广阔。     

Effect of Deflection Characters on Self oscillating Water Jet

The deflective mechanism of the oscillating water jet is analyzed and the effects of jet deflection on the self oscillating water jet are investigated. It is experimentally shown that the deflective angle may reach 9.53 degree, the pressure fluctuation is more intensive and more regular and the jet can efficiently eliminate the water cushion effect and increase the ability in cutting.     

Investigation and application of jet aeration technology in the oxidation process of desulfurization slurry

The calcium sulfite oxidation rate is an important indicator to judge the efficiency of wet limestone/gypsum flue gas desulfurization process used by high-sulfur-coal power plant. Jet aeration technology which integrates aeration and stir into one apparatus is proposed to implement the forced oxidation of limestone/gypsum flue gas desulfurization in order to improve the oxidation rate. The working principle of jet aeration oxidation in desulfurization slurry is investigated. ANSYS CFX is used to simulate the flow field inside the desulfurization slurry tank and obtain the best installation method of jet aerator which makes the mixing and stirring effect of slurry ideal: 3 jet aerators are uniformly installed at the height of 0.8m up from the bottom of slurry tank with their axis perpendicular to the tank wall. The air suction flowrate of jet aerators is tested under the best installation method in the on-site application test of the X protection company of Chongqing. The oxidation rate of calcium sulfite in desulfurization slurry is also tested by using iodometric method. The results show that the total air suction flowrate of jet aerators is 59.52 m 3/h which meets the requirement of slurry oxidation air quantity and the oxidation rate of calcium sulfite in desulfurization slurry reaches 87.6% after two-hour oxidation by using jet aeration.