带阶梯型谐振腔的Hartmann低频超声雾化喷嘴的设计及试验

发布时间：2019-07-10 14:53

【摘要】：流体动力式超声雾化喷嘴比一般的二相流喷嘴雾滴质量更好,比压电式超声雾化喷嘴雾化量大,且可以定向喷雾。而在农业大规模雾化栽培领域对雾滴质量及喷嘴喷雾量均有较高的要求,因此研制一种适用于大规模雾化栽培的流体动力式超声雾化喷头是很有必要的。鉴于此,本文根据哈特曼谐振腔的基本原理,设计出了结构参数可调节的带阶梯型谐振腔的Hartmann低频超声雾化喷嘴,包括拉瓦尔管、可旋涡流叶轮、阶梯腔深度比可调的阶梯型谐振管、锥型整流罩。并通过CFD瞬态数值模拟的方法,对锥型整流罩和阶梯型谐振管的结构参数的变化对谐振腔谐振状态的影响做了参数化研究,并据此确定阶梯型谐振腔的关键尺寸。在相同参数条件下,当谐振腔的总深度相等时,阶梯型谐振腔的谐振频率比传统圆柱型谐振腔的谐振频率高,当阶梯型谐振腔深度比超过2时其谐振频率即维持在传统圆柱型谐振腔谐振频率的1.6至1.7倍;锥型整流罩的加入对腔内气体的入流和出流造成周期性的扰动,从而对谐振腔的谐振状态造成影响;阶梯孔孔径比的变化会引起谐振模式的改变。根据以上结果,选用较优设计参数即孔径比D1/D2=2进行谐振腔的试制,并选用较优的拉瓦尔管与谐振腔距离X=5.5mm作为喷雾特性对比测试试验的初始结构参数值。首先,对不同工况和不同结构型式的喷嘴进行了雾滴粒径测定试验,并对喷嘴喷雾系统的流量特性进行了测定。试验结果表明:(1)锥型整流罩使得低压时的雾滴粒径随供气压力变化更加敏感,而在高压时其雾滴粒径与没有加装锥型整流罩的带有阶梯腔的喷嘴相比基本一致;对于带阶梯腔的喷嘴,喷嘴与腔体距离为6.5mm附近SMD达到最小值;雾滴SMD与腔内流体压力、声压级以及谐振腔谐振状态等因素密切相关。阶梯腔式超声雾化喷嘴的最小雾滴粒径为42μm,雾化量约为2L/h。(2)供气压力的变化会使液路流体的流量和流体压力呈现出相反的变化趋势,而供气压力的变大使气路流量随着变大。其次,由于声压级是影响阶梯型谐振腔式超声雾化喷嘴雾化效果的重要参数。为了对阶梯腔式哈特曼谐振腔的声场特性做进一步了解,对阶梯腔式喷嘴的声场特性进行试验,对影响阶梯型谐振腔声场特性的因素进行了研究。采用均匀设计的试验方法,对各因素影响主次顺序进行分析。试验结果表明:锥型整流罩能够有效使喷嘴的声场能量聚拢在锥型罩的范围内,与无圆锥罩相比,其声压级最大提升了13dB;供气压力是影响声压级变化的最主要因素。且试验表明,供气压力一定时,声压级最大点在阶梯腔深度比为0.6至0.8时出现。将声场特性试验结果与雾滴粒径测试结果和数值模拟结果进行对比分析,再次印证声压级是影响雾滴粒径重要参数的结论。最后,在不同的结构参数和工作参数下对喷雾角及喷雾距离的影响进行了试验测定;并设计了两段式雾化栽培器,对带锥型整流罩和可旋涡流叶轮的阶梯腔式超声雾化喷嘴在雾化栽培中应用的可行性进行了分析。结果表明:(1)供气压力在0.3MPa以下时,可旋涡流叶轮的旋转使雾滴群在锥型整流罩的辐射范围内分布的更加均匀扩散的范围更大,喷雾距离更长;(2)雾化角最大值出现在供气压力处于0.15MPa至0.25MPa范围时。这对雾化栽培器内喷嘴的布局有一定的指导意义。
[Abstract]:The fluid dynamic type ultrasonic atomizing nozzle has better fog drop quality than the general two-phase flow nozzle, is larger than the atomization amount of the piezoelectric ultrasonic atomizing nozzle, and can be directionally sprayed. However, in the field of large-scale agricultural atomization, it is necessary to develop a hydrodynamic ultrasonic atomizing nozzle suitable for large-scale atomization cultivation. In view of this, the Hartmann low-frequency ultrasonic atomizing nozzle with step-type resonant cavity with adjustable structure parameters is designed according to the basic principle of the Hartmann resonant cavity, which comprises a Laval tube, a vortex flow impeller, a stepped cavity depth ratio adjustable stepped resonance tube and a conical fairing. Through the method of CFD transient numerical simulation, the influence of the structural parameters of the cone-shaped fairing and the stepped-type resonant tube on the resonant state of the resonant cavity is studied, and the critical dimension of the step-shaped resonant cavity is determined accordingly. under the condition of the same parameter, when the total depth of the resonant cavity is equal, the resonance frequency of the step type resonant cavity is higher than that of the conventional cylindrical resonant cavity, and when the depth ratio of the step type resonant cavity is more than 2, the resonance frequency is 1.6 to 1.7 times of the resonance frequency of the conventional cylindrical resonant cavity; The addition of the cone-shaped cowling causes periodic disturbance to the inflow and outflow of the gas in the cavity, so as to influence the resonance state of the resonant cavity, and the change of the aperture ratio of the step hole can cause the change of the resonance mode. According to the above results, the optimal design parameters, i.e., the aperture ratio D1/ D2 = 2, are selected for the production of the resonant cavity, and the optimal Laval tube and the cavity distance X = 5.5mm are selected as the initial structural parameter values of the test for the contrast test of the spray characteristics. First, the droplet size determination test was carried out on the nozzle of different working conditions and different structure types, and the flow characteristics of the nozzle spray system were measured. The experimental results show that: (1) the size of the fog drops at low pressure is more sensitive with the change of the air supply pressure, and the particle size of the fog drops at high pressure is basically the same as that of the nozzle with the step cavity without the conical fairing; for the nozzle with the step cavity, The distance between the nozzle and the cavity is 6.5 mm, and the SMD reaches the minimum value; the droplet SMD is closely related to the pressure of the fluid in the cavity, the sound pressure level and the resonance state of the resonant cavity. The minimum droplet size of the step-cavity ultrasonic atomizing nozzle is 42. m u.m, and the atomization amount is about 2 L/ h. (2) The change of air supply pressure will make the flow and fluid pressure of the fluid flow in the reverse direction, and the gas path flow of the change of the air supply pressure will increase with the increase. Secondly, the sound pressure level is an important parameter that affects the atomization effect of the step-type resonant cavity type ultrasonic atomizing nozzle. In order to further understand the sound field characteristics of the stepped cavity type Hartmann resonator, the sound field characteristics of the stepped cavity type nozzle are tested, and the factors that influence the sound field characteristics of the stepped cavity are studied. By means of the method of uniform design, the primary and secondary order of each factor is analyzed. The experimental results show that the cone-shaped fairing can effectively gather the sound field energy of the nozzle in the range of the cone-shaped cover, and the sound pressure level of the cone-shaped cowling is up to 13 dB as compared with the non-conical cover, and the air supply pressure is the most important factor affecting the change of the sound pressure level. And the test results show that when the air supply pressure is constant, the maximum point of the sound pressure level appears when the depth ratio of the step cavity is 0.6 to 0.8. The result of sound field characteristic test is compared with the result of the particle size test and the numerical simulation result, and the conclusion that the sound pressure level is the important parameter to influence the particle size of the fog drop is confirmed again. finally, the influence of the spray angle and the spraying distance is tested under different structural parameters and working parameters, and a two-section type atomization culture device is designed, The feasibility of the application of the step-cavity ultrasonic atomizing nozzle with a cone-shaped fairing and a vortex-flow impeller in the atomization cultivation is analyzed. The results show that (1) when the air supply pressure is less than 0.3 MPa, the rotation of the vortex flow impeller causes the droplets to be distributed more uniformly in the radiation range of the cone-shaped fairing, and the spraying distance is longer; and (2) the maximum of the atomization angle occurs when the gas supply pressure is in the range of 0.15 MPa to 0.25 MPa. It is of great significance to the layout of the nozzle in the atomizer.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S237

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