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针对水气两相射流泵传能效率较低,吸气残压过大的问题,结合环形射流和自激振荡射流的优点,提出环形水气自激振荡脉冲射流的概念。以环形射流理论为基础,推导了混合相界面上的连续性方程和动量方程。采用Realizable k-ε紊流模型和欧拉多相流模型对环形水气自激振荡脉冲射流流场分别进行了定常和非定常数值模拟。计算了环形水气自激振荡射流泵的流量比q、压力比h和效率η等性能参数。对下喷嘴处的流体平均速度进行了非定常模拟计算。对下喷嘴处混合相瞬时速度脉冲进行了频率分析。与普通环形水气射流相比,环形自激振荡射流对气体的卷吸作用能力得到增强,且下喷嘴处的混合相瞬时速度值具有显著的脉冲主频。 相似文献
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研究收缩型喷嘴在初始压力为100 MPa,出口直径为1 mm的情况下喷嘴流场的速度、压力、湍动能等物理量的分布规律。选择不可压Reynolds方程作为动量方程,利用Fluent的SIMPLEC算法进行求解,对收缩型喷嘴射流进行数值模拟。结果表明:流体速度在喷嘴收缩段迅速增加,在离开喷嘴后出现等速流核区;流体动压在喷嘴收缩段增长快速,在等速流核区保持不变;仿真结果与理论推导相符合。 相似文献
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提出将中心体喷嘴与异形喷嘴组合以产生更好的空化射流效果的思路。采用Mixture多相流模型,在15MPa的射流压力下,对正方形出口、三角形出口和圆形出口3种中心体喷嘴产生的淹没射流流场进行数值计算,重点对轴向速度、径向速度、湍动能和空泡相体积份额进行了对比分析。研究表明:圆形出口的中心体喷嘴比另两种异形出口的中心体喷嘴产生更高的射流速度和湍动能;正方形出口比三角形出口的中心体喷嘴的射流稳定性能更强,圆形出口的中心体喷嘴产生的集束性能较强;异形出口的中心体喷嘴产生的流场中,空泡相延伸距离更长,异形出口的中心体喷嘴产生的空化射流效果更好。 相似文献
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The Selective Catalytic Reduction (SCR) technology allows the transformation of the Nitrous Oxide emissions present in exhaust gases into gaseous nitrogen and water. For a proper operation of the SCR, a urea-water solution (UWS) injector must dose an adequate amount of liquid into the exhaust pipe in order to avoid deposit formation and to guarantee the SCR system efficiency. This task requires the knowledge of the performance of the injector. Then, the goal of this work is to study the hydraulic performance of a UWS injector, by means of measuring the spray momentum flux in order to understand the influence of different variables as injected fluid, injection pressure, counter pressure and cooling temperature of the injector on the flow characteristics. The tested injector was cooled at three different temperatures, 60, 90 and 120 °C, the injection pressure of the UWS was set at 5, 7 and 9 bar, with counter pressures of 750, 900, 1000 and 2000 mbar for the two tested fluids, water and UWS. The measurements were carried out using an experimental facility developed at CMT-Motores Térmicos for the determination of spray momentum flux, where a piezoelectric pressure sensor was located near the nozzle exit of the injector, which measures the impact force of the spray. Additionally, the proposed methodology allowed to determine the injected mass flow and to capture the transient injection events, such as the opening and closing stages. Moreover, mass flow rate measurements of the injector were performed under the same operating conditions, determining the influence of the injection pressure, cooling temperature, counter pressure and fluid properties. Regarding the pressure, the tendency was as expected, the higher the injection pressure the higher the Momentum flux and flow rate. Results showed that an increment of the cooling temperature of the injector induces the appearance of flash boiling conditions, having an impact on the total injected mass and momentum flux, changing the behaviour of the spray. For the same conditions, water has a higher momentum flux than the UWS due to differences in fluid properties and velocity at the nozzle exit. 相似文献
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Weiming Wang Dayong Li Jie Hu Yinghong Peng Yishun Zhang Deyuan Li 《The International Journal of Advanced Manufacturing Technology》2005,26(5-6):537-543
A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained . 相似文献
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Weiming Wang Dayong Li Jie Hu Yinghong Peng Yishun Zhang Deyuan Li 《The International Journal of Advanced Manufacturing Technology》2005,26(5):537-543
A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained . 相似文献
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Hong Sung Kook Park Sang-il Jeon Soo-Yeon Lee Kwan-Soo 《Journal of Mechanical Science and Technology》2015,29(5):2243-2247
An experimental study was conducted on a water-spray-bed heat exchanger to investigate the heat transfer characteristics. A laboratory-scale test rig was built and its heat transfer characteristics were investigated with respect to various design and operation parameters such as the water spray flow rate, exhaust gas flow rate and number of tube rows. It was found that the implementation of the water spray increased the heat transfer rate to about 1.3 - 2.2 times that of a heat exchanger without water spray, although with a slight increase in the pressure loss. It was thus confirmed that the water spray was effective for enhancing condensing heat recovery from an exhaust gas.
相似文献15.
Seung-hwan Choi Chunghwan Jeon Young June Chang 《Journal of Mechanical Science and Technology》2002,16(7):986-998
Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection
diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and
emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on
spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the
spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection)
Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using
a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble
in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow
coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ
and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer)
system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization
characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio.
As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly. 相似文献
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Jeekuen Lee Shinjae Kang Byoungjoon Rho 《Journal of Mechanical Science and Technology》2002,16(8):1135-1143
The intermittent spray characteristics of the single-hole diesel nozzle (dn=0.32 mm) used in the fuel injection system of heavy-duty diesel engines were experimentally investigated. The mean velocity
and turbulent characteristics of the diesel spray injected intermittently into the still ambient were measured by using a
2-D PDPA (phase Doppler particle analyzer). The gradient of spray half-width linearly increased with time from the start of
injection, and it approximated to 0.04 at the end of the injection. The axial mean velocity of the fuel spray measured along
the radial direction was similar to that of the free air jet within R/b=1.0-1.5 regardless of elapsing time, and its non-dimensional
distribution corresponds to the theoretical velocity distributions suggested by Hinze in the downstream of the spray flow
fields. The turbulent intensity of the axial velocity components measured along the radial direction represented the 20-30% of the Ūcl and tended to decrease in the outer region. The turbulent intensity in the trailing edge was higher than that in the leading
edge. 相似文献
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Effects of injector nozzle geometry and operating pressure conditions such as opening pressure, ambient pressure, and injection
pressure on the transient fuel spray behavior have been examined by experiments. In order to clarify the effect of internal
flow inside nozzle on the external spray, flow details inside model nozzle and real nozzle were also investigated both experimentally
and numerically. For the effect of injection pressures, droplet sizes and velocities were obtained at maximum line pressure
of 21 MPa and 105 MPa. Droplet sizes produced from the round inlet nozzle were larger than those from the sharp inlet nozzle
and the spray angle of the round inlet nozzle was narrower than that from the sharp inlet nozzle. With the increase of opening
pressure, spray tip penetration and spray angle were increased at both lower ambient pressure and higher ambient pressure.
The velocity and size profiles maintained similarity despite of the substantial change in injection pressure, however, the
increased injection pressure produced a higher percentage of droplet that are likely to breakup. 相似文献
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Jeongkuk Yeom 《Journal of Mechanical Science and Technology》2008,22(9):1785-1792
In this study, the effects of change in injection pressure on spray structure have been investigated on the high temperature
and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation
process. Also emissions of diesel engines can be controlled by the analyzed results. Therefore, this study examines the evaporating
spray structure in a constant volume chamber. The injection pressure is selected as the experimental parameter, is changed
from 72 MPa to 112 MPa with a high pressure injection system (ECD-U2). The PIV (Particle Image Velocimetry) technique was
used to capture behavior variation of the evaporative diesel spray. Analysis of the mixture formation process of diesel spray
was executed by the results of flow analysis in this study. Consequentially the large-scale vortex flow could be found in
downstream spray and the formed vortex governs the mixture formation process in diesel spray. 相似文献
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:对一种气旋耦合喷嘴喷雾特性进行了试验研究,分析总结了气液比及液相压力对其喷雾特性 的影响规律。试验中使用水为工质,利用工业相机对其液雾进行拍摄并利用 MATLAB进行图像处理,获得 喷雾锥角,利用相位多普勒粒子分析仪(PDPA)对雾化粒径进行测量。研究表明,在液相压力一定时,随着 气液比增加,平行于预膜片方向喷雾锥角几乎不受影响,垂直于预膜片方向喷雾锥角先增大后略有减小;增 加液相压力,平行于预膜片方向喷雾锥角增大,垂直于预膜片方向喷雾锥角最大值和其对应的气液比减小; 气旋耦合喷嘴雾化粒径沿径向分布规律为中间雾化粒径较小向两侧逐渐增大;雾化粒径在液相压力较低时 受气液比影响大,随着液相压力增加受气液比影响减小。 相似文献