Gas entrainment characteristics of diesel spray injected by a group-hole nozzle

In this study, gas entrainment characteristics of a diesel spray injected by a group of closely spaced two-orifices (group-hole nozzle) were investigated. Both free and wall-impinging sprays were considered. The gas entrainment characteristics of the group-hole nozzle spray were compared to those of single-hole nozzle sprays: one has the same total hole area with the group-hole nozzle, and the other has the same hole diameter. The gas entrainment characteristics of diesel sprays were investigated using a particle image velocitmetry technique coupled with a laser induced fluorescence technique (LIF-PIV technique).The spray tip penetration of the group-hole nozzle was the shortest among the applied nozzles in a free spray condition, while it was the longest in a wall-impinging condition. In the free spray condition, the gas entrainment of the spray was enhanced by the group-hole nozzle due to extensive momentum exchange with surrounding gas and superposed gas entrainment motion of the two-jets injected by the group-hole nozzle. After wall-impingement, the group-hole nozzle spray showed a stronger wall-jet vortex and increased gas entrainment compared to the single-hole nozzle sprays due to enhanced spray/wall interaction caused by the momentum interaction of the two-jets from the group-hole nozzle. Asymmetric shape of the group-hole nozzle spray resulted in an asymmetric gas velocity distribution of the spray both in the free and wall-impinging conditions.     

Combustion and emission characteristics of converging group-hole nozzle under lean engine operating conditions

This paper describes the combustion and emission characteristics of converging group-hole nozzles and compares the results to those of a single hole nozzle with the same overall nozzle exit hole area. Engine experiments were performed using a single-cylinder diesel engine operating under overall lean conditions (i.e., equivalence ratio 0.45). The considered nozzle configurations in the experiments included a converging group-hole nozzle (cGHN) with 3° converging angle, 0.090 mm hole diameter, and a single hole nozzle (SHN) of 0.128 mm hole diameter. The CFD calculations used the KIVA engine simulation code integrated with a Gasjet superposition model. Using the validated calculation models, the test conditions were also expanded to consider wider converging angle cGHNs (up to 12°). The results show that the evaporation of sprays from the cGHN-3° nozzle is more delayed than that of the SHN case and the cGHNs entrain more ambient gas due to smaller droplet sizes in the outer spray periphery. In addition, an increase in the converging angle of the cGHNs promotes fuel evaporation and produces a more homogeneous fuel–air mixture.     

高效导流体喷头理论分析

在高压水射流清洗设备中 ,射流喷头是关键部件 .为了提高喷头的喷射效率 ,提出了一种带有导流体的射流喷头 .由于喷头中有了导流体 ,避免了涡流的产生与剪切层的分离 ,从而大幅度地减少了喷头的能量损失 .文中对这种新型导流体喷头进行了理论分析与实验研究 .由实验室研究与现场清洗作业得到的结果表明 ,与没有导流体的喷头相比 ,这种新型导流体喷头具有更高的能量效率 .     

Optimization of fuel/air mixture formation for stoichiometric diesel combustion using a 2-spray-angle group-hole nozzle

This paper describes a numerical study of fuel/air mixing processes for stoichiometric diesel combustion. In order to overcome the deterioration of combustion efficiency that accompanies stoichiometric diesel combustion due to poor mixing and lack of available oxygen, a new nozzle layout, namely a 2-spray-angle group-hole nozzle, which consists a grouped upper spray plume (squish spray) and a lower spray plume (bowl spray) was investigated. The KIVA code with updated physical and chemistry models, including the KH-RT breakup model, 2-step phenomenological soot model, reduced n-heptane and GRI NOx mechanisms was used for the calculations. An optimized 2-spray-angle group-hole nozzle with 170° squish spray angle and 80° bowl spray angle showed significantly improved fuel consumption (178 g/kW h⁻¹) compared to the baseline nozzle layout (213 g/kW h⁻¹) and the 2-spray-angle nozzle without hole-grouping (193 g/kW h⁻¹).     

Millisecond mixing of liquids using a novel jet nozzle

A millisecond mixing process for liquids was implemented using a new mixer design, i.e., a jet nozzle connected with a trumpet-shaped module. The jet nozzle can facilitate two or three liquid channels, performing an initial impingement mixing of liquid sheets in the thickness at millimeters. Then, the joint liquids sheet out of the jet nozzle was stretched thinner and thinner on the expanded solid surface of the trumpet-shaped module, which significantly intensified the liquid mixing process. Accordingly, dual controls on the liquid mixing can be accomplished flexibly by optimizing the operating conditions and the module configuration. Experiments were carried out to investigate the influencing factors on the mixing performance, where the planar laser induced fluorescence (PLIF) technique was used to measure the mass transport of fluorescent dye between the liquids. The intensity of segregation (IOS) and 95% mixing time (τ₉₅) were employed to characterize the mixing performance. The results showed that the module with a greater curvature surface possessed a better mixing performance owing to the rapid reduction of the liquid sheet thickness, which strengthened the mixing process in the lateral direction along the flow development. The mixing behaviors are greatly influenced by the flow rate ratio between the liquids. An optimum mixing state could be achieved when Q_S1/Q_S2 is 1:1. An increase of Q_T under the same flow rate ratio does not affect the mixing pattern in space, but the corresponding τ₉₅ is almost linearly shortened. By splitting one liquid stream into two surrounding streams, the so called Sandwich operation brought further improved mixing performance compared with the two liquids mixing process. Using the novel jet nozzle design, millisecond(s) mixing of liquids can be easily achieved with flexible control.     

Simulation of thermophysical flow in axisymmetric nozzle with expansion chamber

Axisymmetric nozzle flows with a free‐jet expansion are simulated considering several substances and several flow conditions, and the thermophysical properties in the nozzle and the free‐jet region are predicted. The present numerical method is based on the preconditioning method developed by Yamamoto and the mathematical models of thermophysical properties of the substances. As numerical examples show, gas flows of carbon dioxide, water, and nitrogen under a subcritical pressure condition are first calculated. Calculated distances to the Mach disk are compared with the experimental results, and also the density distributions are compared among these three substances. Second, carbon dioxide flows while changing the pressure from subcritical to supercritical values are calculated and the effect of pressure on the flow field is investigated. Third, flows of water vapor with and without nonequilibrium condensation are calculated and the effect of condensation on the flow field is investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Effect of liquid viscosity on gas holdups in a reversed flow jet loop reactor

The effect of draft tube diameter and liquid viscosity on overall and annulus gas holdups were studied in a reversed flow jet loop reactor. The draft tube diameter to reader diameter ratio (D_d / D) and liquid viscosity were varied in the ranges 0.34-0.67 and 1.5-43 mPa. s, respectively. The maximum gas holdup was obtained when the D_d / D value ranged btween 0.47 and 0.61. The gas holdup decreased with increasing viscosity. Empirical correlations are presented to predict the gas holdups.     

高速雾化射流除尘研究及应用

国内外现有除尘技术存在着缺陷,推广应用受到了限制.故开发了高速雾化射流除尘技术和雾化喷嘴.通过优化实验,确定了文丘里风筒的关键参数;得到了捕尘效果最好的雾化喷嘴.实践表明,高速雾化捕尘是可行的,捕尘效果良好.     

高压水射流旋转喷头的参数分析及其应用

论述了高压水射流清洗技术中与喷嘴相关的性能参数、并根据相关公式确定各个参数的内在联系.同时研究了旋转喷头打击作用力,使射流参数合理匹配,指导选择合适的喷嘴.     

Effects of different nozzle materials on atomization results via CFD simulation

Spray drying, as a crucial operation in industrial production, converts solution to fine particle. The spray moiety directly affects the final particle morphology, size and distribution. Compared with the experimental method, computational fluid dynamics (CFD) modeling is a powerful and convenient tool for simulating the spray process. Based on the verified CFD model, different materials of atomizer were simulated to investigate the effect on droplet size and distribution in this work. The modeling result proved that the droplet size and distribution were influenced by the resistance coefficient of materials, wherein the Reynolds number could change the effect of roughness along with the change of mass flow rate on spray process. The results in this work have implication for controlling droplet size through developing new spray nozzle with different materials or surface coating.     

Hydrodynamic properties of a turbulent confined solid-liquid jet evaluated using PIV and CFD

Particle image velocimetry is used to evaluate liquid and solid velocities and turbulence levels in the developing region of a confined solid-liquid jet. The measurements are conducted utilizing the method of matching refractive indices together with digital phase separation. The diameters of the solids are and the maximum mean volume fractions for which measurements can be performed is 1.9%, a number estimated from image analysis. The experimental results are compared with those from numerical simulations using the mixture, dispersed and per-phase realizable k-ε models together with two models for the drag force. The results show that the differences in axial velocity between the two phases are small and the axial RMS velocities generally increases with increasing volume fraction and are larger for the dispersed phase compared to the continuous phase. The numerical simulations capture the flow structure well, but generally, the continuous-phase centreline velocities are underestimated close to the inlet and overestimated further downstream. Regardless of solid loading, the per-phase turbulence model in combination with a drag force modified by a correction factor as to take into account the turbulence of the carrier phase provides the best numerical results.     

Simulation and experimental validation of a methanol burner

This paper presents a computational fluid dynamics model of a methanol burner. Special emphasis was placed on the study of the liquid atomization and combustion process. Linearized Instability Sheet Atomization (LISA model) was employed to simulate the fuel atomization process. Predictions of droplet diameters, droplet trajectories, temperatures and gas concentrations are presented and compared with an experimental database presented by Widmann and Presser in their work abenchmarkexperimentaldatabaseformultiphasecombustionmodelinputandvalidation. The predicted and simulated data were found to be in good agreement, however some discrepancies in the amount of unburned species were found probably related with the mechanism of combustion employed.     

Effect of nozzle diameter and its orientation on the flow pattern and plume dimensions in gas-liquid jet reactors

Gas-liquid jet reactors are widely used in chemical industries in various applications such as feed-water heaters, metal processing, and thermal energy sources, etc. In all these applications, the principal requirement for the design is a prior knowledge of jet shape and dimensions, which primarily depend upon the nozzle type, size, submergence and its orientation. In the present study, CFD simulations of non-reacting (steam-water) and reacting (SF₆-Li) jets have been carried out to understand the variation in plume dimensions of gas-liquid jet reactors. For condensation jet and reaction jet, the criteria have been developed to identify the plume boundary based on the hold-up profile of steam/SF₆ gas and the evaporated fuel. The effect of nozzle diameter and its orientation, nozzle gas velocity and bath temperature on the plume dimensions have been studied for both the types of jets. It was observed that the extent of increase in the plume length is always higher in the case of reaction jet as compared to the condensation jet for all the cases. The analyses also proved that, the availability of reactant is much better with the horizontal orientation which leads to stable plume length. The CFD model has been extended for the prediction of the flow pattern and its effect on the rate of condensation/reaction and plume dimensions for both the jet systems.     

Shaping technology of coal gas sorbents by using a spray dryer

The goal of this study was to develop HTHP sorbents for adaptation in fluidized bed desulfurizers or Transport Reactors. For this purpose, we shaped zinc-based sorbents (ZAC series) by using a spray dryer with a pressurized nozzle atomizer. To prepare the slurry for spraying, raw materials in submicron units and organic additives were used. We characterized the sorbents by SEM, XRD, Mean Particle Size Analysis, BET Surface Area and Attrition Ratio. The mean particle size was about 112 μm, the attrition resistance was very good and the TGA sulfur capacity of the fresh sample was calculated at about 23–24 wt%.     

Gas holdup and gas entrainment of a plunging water jet with a constant entrainment guide

The gas holdup and gas entrainment of a plunging liquid jet with a gas entrainment guide in an air-water system was investigated. The measurement of the gas holdup was performed using an over-flow method. The turbulent jet velocity calculated on an inside nozzle diameter in the range from 4.4-26.5 m/s for this system has been used in our correlations. The gas holdup has been well correlated in terms of 1/H(v₀² + 2gH₁), H₁ d₀ and the gas entrainment in terms of 1/H_w(v₀² + 2gH₁), H₁, d₀. The jet power requirement was also obtained from experimental data.     

Simulation of particles and gas flow behavior in a riser using a filtered two-fluid model

Flow behavior of gas and particles is predicted by a filtered two-fluid model by taking into the effect of particle clustering on the interphase momentum-transfer account. The filtered gas–solid two-fluid model is proposed on the basis of the kinetic theory of granular flow. The subgrid closures for the solid pressure and drag coefficient (Andrews et al., 2005) and the solid viscosity (Riber et al., 2009) are used in the filtered two-fluid model. The model predicts the heterogeneous particle flow structure, and the distributions of gas and particle velocities and turbulent intensities. Simulated solids concentration and mass fluxes are in agreement with experimental data. Predicted effective solid phase viscosity and pressure increase with the increase of model constant c_g and c_s. At the low concentration of particles, simulations indicate that the anisotropy is obvious in the riser. Simulations show the subgrid closures for viscosity of gas phase and solid phase led to a qualitative change in the simulation results.     

Process Design of a Multistage Drying Process via Flowsheet Simulation

Multistage drying processes including spray drying and fluidized bed unit operations are challenging to design due to the dependencies of the preceding process steps. Flowsheet simulation offers the possibility to simulate a complete process by the application of suitable short-cut models. In this contribution a novel model for a spray dryer based on a population balance approach is presented. Furthermore, a dynamic model for a fluidized bed dryer is introduced. Experimental data is used for validation and parameter optimization. The calibrated models are then used to design an industrial drying process of multiple drying stages.     

利用气体喷射引流技术强化浸入式水口的预热效果

为了提高现有抽风式预热烘烤方式下浸入式水口的预热效果 ,利用气体喷射引流原理 ,在靠近烘烤箱的抽风机吸气管道上增设一压缩空气管 ,构成简单喷射器 ,通过压缩空气的喷射引流来增加抽风流量 ,强化升温效果。研究表明 ,采用压缩空气引流后 ,可使抽风式烘烤装置的抽风流量由原来的 0 .2m3·s- 1提高到 0 .36m3·s- 1,水口的预热升温曲线更趋合理。采用压缩空气引流强化抽风预热烘烤 90min时 ,水口颈部外壁的温度提高 1 4 .8% ,比现有结构提高约 1 0 0℃ ,效果十分明显