Numerical simulation and validation of gas-particle rectangular jets in crossflow

This paper presents a numerical study of a gas-particle flow in three inclined rectangular jets in crossflow. The predicted gas phase velocities and particle phase velocities are validated against previously reported experimental data. Two turbulence models, the standard k-? model and Shear Stress Transfer (SST) model, are used to model the gas phase turbulence. This work shows that both models provide acceptable predictions of the gas flow and mixing generated by the three jets. Neither model could accurately reproduce the jet core and the flow near bottom wall. The particle phase in this flow comprises a large number of small particles. Thus particles follow the gas phase flow closely and any errors in the turbulence model and gas flow predictions are passed on to the particle phase simulation. This paper also includes a literature review on rectangular jets in crossflow and gas-particle laden jets in crossflow.     

A jet mixing study in two phase gas-liquid systems

All studies concerned with jet mixing have been focused on liquid phase systems and no studies have been found on jet mixing for gas-liquid two phase systems. In the present study the use of jet fluid as a mixer in gas-liquid systems was proposed. Further by installing an experimental setup, the mixing behavior of liquid phase was studied. Gas flow and jet flow are injected to the mixing vessel countercurrently. In this study, the effect of jet injection, location of the conductivity probe, aeration rate and jet Reynolds number on the mixing time are investigated. The created flow pattern was extracted for each condition and the results often analyzed on the basis of them. It is observed that, for low aeration rates, the injection of jet decreases the mixing time considerably. By increasing the aeration rate, the difference in mixing times between the two cases of jet injection and without jet is reduced. Results also show that the closer the probe is to encounter location of the jet and airflow, the lower the mixing time obtained. Dependence of mixing time on the probe location decreases by increasing the mixing intensity and eliminating dead zones. It is obtained, on the basis of Re_j and the amount of jet travelling in the vessel, increasing the aeration rate has different effects on the performance of mixing. Generally, four different trends for the variation of mixing time with increasing the aeration rate are observed.     

Effect of jet angle and orifice shape in gas-gas mixer using CFD

Mixing of gases using jets in cross-flow is investigated with the help of Computational Fluid Dynamics (CFD) modeling. This is particularly encountered in hydrocarbon oxidation reactions. A mixture of such gaseous reactants results in the flammable zones inside the mixer. In the present work, CFD simulations have been carried out for various jet angles (30°, 45° downstream, 90° and 45° upstream) and for different orifice shapes (defined in terms of aspect ratio, AR). The model has been validated with experimental data reported in the past literature. Results have been analyzed in terms of volume of mixing region and turbulent viscosity. Also, the characteristics mixing time is calculated for different conditions.     

喷砂射孔降破技术在川西地区的应用研究

喷砂射孔作为降低地层破裂压力的预处理技术,在川西地区已被广泛地使用。本文对喷砂射孔降低地层破裂压力技术的机理进行了研究,对近几年来川西地区喷砂射孔现场试验的9个主要施工参数（喷嘴直径、喷嘴个数、磨料体积浓度、磨料性质、砂量、施工排量、施工泵压、喷射速度、喷砂时间）进行了研究分析。分析得出：喷射速度和喷砂时间为两个最关键的参数,为了达到降低破裂压力的效果,喷射速度应大于260m/s,喷砂时间应达到20~30m in。研究分析结果经过应用后,施工参数得到了优化,进行现场试验取得了良好的施工效果。     

新型不等距抛光机磨头创新设计及动力学分析

为了研究大规格瓷砖加工设备,提出一种新型不等距抛光机磨头。从结构原理上进行了创新设计,并继承了摆动式抛光磨头的优势,弥补了存在的缺陷。以新型不等距抛光磨头为研究对象,建立磨块距方程和磨头动力学模型。得出不等距磨块的分布规律改变了各个磨块切出磨削状态的隔间时间,同时分析得出不等距磨头垂直方向的磨削力平稳,振动减小。     

Experimental study on the hazards of the jet diffusion flame of liquefied dimethyl ether

Dimethyl ether (DME) has been considered as a substitute for diesel fuel because it has a low auto-ignition temperature and produces less NO_x, SO_x, and particulate matter. However, the introduction of DME vehicles needs widely available DME supply stations. Moreover, the preparation of safety regulations for DME supply stations is very important, and so safety data is needed. Therefore, the present paper reports the hazards of the DME jet diffusion flame, which is one of several hazardous properties of DME, by studying the results of leaking gas and liquid DME. DME jets were released horizontally from circular nozzles whose diameters were 0.2, 0.4, 0.8 and 2 mm, and the release pressure was varied from the saturated vapor pressure to 2 MPa. When gaseous DME was released at the saturated vapor pressure, the flame was blown out. However, when liquefied DME was released, the flame formed. We obtained the experimental equations for estimating the scale and thermal hazards of DME diffusion flames.     

Supercooling of water droplets in jet aviation fuel

Ice formation in aircraft fuel systems is an ongoing problem with potentially disastrous consequences. Unfortunately, the icing of fuel systems is poorly understood. It is well known that at temperatures below 0 °C particles of H₂O suspended in fuel can exist as crystalline ice or metastable supercooled water. In this paper we show that micron sized water droplets immersed in Jet A-1 aviation fuel can exist in a metastable supercooled state to around −36 °C. In fact, the majority of droplets in our experiments froze homogeneously showing that the fuel itself did not catalyse ice formation. We suggest that H₂O particles will remain in a supercooled liquid state until they come into contact with a suitable solid surface in an aircraft’s fuel system or the temperature falls below the homogeneous freezing limit.     

Permeability of soft porous media under one-dimensional compaction

A novel experimental approach to measure permeability of porous material samples under variable longitudinal compaction has been developed. The material has a non-linear structural behavior and exhibits a small hysteresis during mechanical loading and unloading experiments. The new permeameter includes a piston moving inside a Plexiglas cylinder with controllable speed and a test section where the porous material sample is placed under compaction by two grids with adjustable positions. Time-dependent pressure was recorded at four different locations along the sample together with the velocity of the piston. Experiments with two different sample lengths have been performed at three different Reynolds numbers based on the apparatus diameter. The results show that pressure gradient and permeability data do not depend on initial uncompacted sample length. All experiments included measurements at various compaction ratios of the material followed by measurements during relaxation/expansion of the material. No hysteresis was observed in the pressure gradient and permeability data during compaction and expansion of the material for a wide range of compaction ratio. The effects of small velocity fluctuations due to variable friction of the moving piston with cylinder’s wall were also considered. These velocity fluctuations cause pressure fluctuations within the sample which are high close to the inlet part of the material sample and are reduced almost completely towards its outlet. However these pressure fluctuations when scaled with the corresponding mean pressure retained their time-dependent amplitude and phase unchanged along the material. These relative pressure fluctuations cancelled out the flow velocity fluctuations resulting insignificant fluctuations in permeability. It was found that permeability, which is a material property, is drastically reduced with increased compaction ratio of the material while its solid fraction changes substantially but its porosity remains practically unchanged. A comparison with the Cármán–Kozeny expression for random porous media was also examined. Cármán–Kozeny expression predicts qualitatively the reduction of permeability with compaction. However, the predicted values of permeability are very sensitive to the initial value of porosity.     

Dynamic characteristics of binary mixtures in a two-jet fluidized bed

Aiming to understand biomass-related pyrolysis and gasification processes, which have received particular interests recently due to increasing concerns over fossil fuels and carbon emissions, this work conducts a detailed experimental study of the fluidization characteristics and jet dynamics of biomass mixtures in a fluidized bed. Both single jet and two jets dynamics are investigated, and a parametric study of the influence of particle properties and operational conditions on the dynamic performance of the bed, especially on the jet penetration depth and jet frequency of the binary mixtures, is conducted. Detailed frame-by-frame image analysis coupled with physical parameters reveals many interesting phenomena, which includes multistage flow pattern development and a stochastic nature of jet dynamics, as well as a strong dependence of the jet penetration depth and jet frequency on the bed materials.     

An experimental investigation on the breakup of surfactant-laden non-Newtonian jets

The combined effect of polymers and soluble surfactants on the dynamics of jet breakup, and especially on satellite drop formation, was experimentally investigated. Xanthan gum and Carbopol^® 934 NF were dissolved in water with Sodium Dodecyl Sulfate as the surfactant. Controlled disturbances were imposed at the laminar jet interface using a piezoelectric vibrating nozzle with breakup dynamics recorded using a high-speed camera. Drop and ligament diameters were measured from the digital images. The focus of the work was investigating how bulk and interfacial properties of the prepared fluids influenced ligament and drop evolution. It was found that if the proper concentration of surfactant (close to the critical micelle concentration, CMC) was selected, and if the flow time scales were large enough, Marangoni interfacial stresses may lead to an increase in satellite drop size as previously reported for breakup simulations of shear-thinning jets covered with insoluble surfactant. It was also experimentally confirmed that the introduction of surfactant contributes to a delay in jet breakup.