摘要
为了解不同压力比下的汽蚀特性,该文采用试验与数值分析相结合的方法,测量不同出口压力下(0.25、0.4、0.5、0.6、0.7、0.8、0.9、1.0、1.1、1.2、1.3、1.35 M'Pa)的工作流体、吸入流体与混合流体的质量流量,得到压力比与混药比的特性曲线;采用Mixture模型中的Zwart-Gerber-Belamri汽蚀模型,分析了不同出口压力下的内部静压分布和气相分布;对试验值与仿真值进行拟合分析,拟合优度R^2=0.9618,验证了模型的准确性;研究结果表明,当压力比大于0.6时,混药性能较差,甚至会出现逆流。当压力比在0.4~0.6之间时,混药比与压力比负相关。当压力比小于0.4时,混药比与压力比无关,即达到汽蚀混药比:在工作压力为2.0 MPa,吸入口压力为0下,当出口压力为0.8:MPa(压力比为0.4)时,内部流体发生汽蚀,且出口压力越低,汽蚀现象越严重。该研究为提高装置混药比稳定性能,保障流式混药装置高效运行提供理论依据。
The jet mixing apparatus （JMA） is a vitally important part for mixing water with a pesticide, including a working nozzle, suction inlet, diffuser, thumb lock, case, end cap, one-way ball, inserts, etc. The Jet Mixing Apparatus is a simple device with no moving parts, where a high velocity flow （water） is used to pump a second fluid （pesticide）. It was broadly used in large plant protection machinery. Its main property is efficiency and stability of the mixing ratio. Cavitation is a physical phenomenon in a Jet Mixing Apparatus happening at low pressure, seriously affecting the performance and wasting energy. In order to acquire the characteristic curve of the relation on the mixing ratio and pressure ratio, experimental and numerical analyses were used to measure the mass flow rate of working, intake, and mixed fluid. The test was conducted in the Key Laboratory of Modern Agricultural Equipment in accordance with the JB/T9782-1999 general test method for plant protection machinery. The outlet pressure was regulated to different levels （0.25, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.35 MPa） by a throttle valve, an electronic scale for mass flow rate, a U mercury manometer for vacuum, which was at 2.0 MPa working pressure and normal atmosphere intake. The computational fluid dynamics （CFD）software ANSYS fluent 15.0 was used for numerical simulation of the cavitation. The Zwart-Gerber-Belamri cavitation model in mixture model was adopted to capture cavitation, and obtained the internal static pressure distribution and gas distribution contour under different outlet pressures. Water was set as the main phase, with density of 1000 kg/m^3, and dynamic viscosity of 0.001 kg/（m.s）. Water vapor was set as the second phase, with density of 0.02558 kg/m^3, dynamic viscosity of 1.26×10^6, and the bubble radius of 0.01ram. Cavitation pressure was set 3 540 Pa. The two inlet boundary condition was set at pressure-inlet, turbulence intensity of 2%, and hydraulic diameter of 14 mm. The outlet
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2015年第7期60-65,共6页
Transactions of the Chinese Society of Agricultural Engineering
基金
公益性行业(农业科研专项经费)(201220025)
关键词
农业机械
农药
计算流体力学
数值分析
在线混药
射流
汽蚀
植保机械
agricultural machinery
pesticides
computational fluid dynamics
numerical analysis
online mixing
jet
cavitation
plant protection machine
