Development of spraying device for precise and deep application of liquid fertilizer in sowing period

To satisfy the technical requirements of precise and deep application of liquid fertilizer in sowing period of maize, a toward-target spot application system of liquid fertilizer is proposed in this paper, and a liquid fertilizer spraying device is designed. The device consisted of valve body, pressure regulation spring, valve seat, valve core and nozzle. The initial deformation of pressure regulating spring can be changed by adjusting the length of the nozzle screwed into the valve body, so the contact pressure between valve core and valve seat is changed. The liquid fertilizer spraying device is mainly divided into two states when working, open and closed, which were determined by the liquid fertilizer pressure and the contact pressure (which was the pressure between valve core and valve seat). The liquid fertilizer spraying device closes when liquid fertilizer pressure is less than the contact pressure, and in contrast, the liquid fertilizer spraying device open, thus the operation process of intermittent discharge of the liquid fertilizer was achieved. Nozzle is a key component of the fertilizer application, and the shape and parameters of nozzle are important factors affecting the performance of the liquid fertilizer spraying device. In order to obtain the best nozzle shape and parameters, two-dimensional geometric models of different shaped nozzles, such as conical straight, conical and cylindrical, are established in ANSYS Fluent. The geometric model is meshed and boundary conditions such as entrance boundary, exit boundary and symmetrical boundary are set. In the calculation model, VOF (fluid volume) is used as the multiphase flow model, in which the initial phase is air and the second phase is liquid fertilizer. And RNG k-ε model is used for viscous model and standard wall function is used for near wall. The non-submerged jet process of the nozzle is simulated by the non-coupled solver SIMPLE (semi-implicit method for pressure linked equation) algorithm. The velocity and total pressure of different nozzles in the direction of the central axis and the radial are analyzed, and obtained the bundle performance of different nozzles. According to the simulation results, the cone shape is determined as the best nozzle shape. In order to evaluate the working performance of the liquid fertilizer spraying device, a conical nozzle is selected to establish a fluid simulation model. And taking the fertilization amount as the evaluation index, the pump pressure and nozzle diameter as the test factors, the two-factor and five-level full factors experiment is designed, and the nalysis of variance (ANOVA) is performed to find the influence of parameters. The simulation results show that the factors of pump pressure and nozzle diameter have significant effects on fertilization amount (P<0.01), and the diameter of the nozzle has a greater influence than the pump pressure. A regression equation between the fertilization amount, the pump pressure and the nozzle diameter is established, and the R2 of the equation is 0.998. The bench experiments of liquid fertilizer spraying device with the nozzle diameters of 2.5 and 3.0 mm are carried out separately. The results show that the value of the fertilization amount increases gradually as the pump pressure increasing when the pump pressure is within the range of 0.2 to 0.6 MPa. The growth trend of the fertilization amount is basically consistent with the predicted value of the regression equation. The experiment value of fertilization amount average decreases by 1.62% (0.12 mL) than predicted value after the regression equation was corrected. The accuracy of the simulation model and the regression equation is verified. This study can lay a foundation for the further study of the toward-target spot application system of liquid fertilizer.