Influence of solenoid valve response times on water hammer in variable rate spraying system

Abstract: In order to study influence of solenoid valve's response times on water hammer in PWM controlled variable rate spraying system, Solidworks software was used to build a 3D geography model of solenoid valve's flow area based on 6013A type solenoid valve. Gambit was used to mesh the model and to define the boundary types. Fluent was to simulate the process of solenoid valve's operating process. The solver was 3D pressure based unsteady one. Turbulent model was realizable k-ε turbulent model. Response times of solenoid valve were set as 10, 20, 30, 40 and 50 ms. During the simulation, the pressure of solenoid valve's entrance was simulated and the outputs pressure curves with flow time was plotted with the output interval set as 0.001 s. According to the pressure curves, water hammer pressure in the pipe decreased while the response time increased when solenoid valve opened or closed. When the response time increased from 10 to 50 ms, water hammer pressure was reduced 78% when solenoid valve opened, while the water hammer pressure was reduced 79% when solenoid valve closed. A simplified PWM controlled variable rate spraying system was created and it consisted of pressure source (the living water supply system), pressure sensor, solenoid valve (opening time was 20 ms and closing time was 30 ms) and a hollow cone atomization nozzle. Experiments on the basis of this spraying system were carries out with the same working condition as simulation and the pressure curves were created. The results showed that the relative errors of experimental and simulated valued of water hammer pressures were below 10% with the same response times, suggesting that this model was accurate and the simulation results were reliable. Then, the solenoid valve's closing process in theory was analyzed according to indirect water hammer pressure formula. The theoretical analysis results were consistent with the simulation results, indicating that the indirect water hammer pressure formula could predict water hammer pressure generated by solenoid valve's closing process in PWM controlled variable rate spraying system with high frequencies. However, the indirect water hammer pressure formula could not calculate water hammer pressure generated by solenoid valve's opening process directly. Nevertheless, when the response times were the same, the water hammer pressures generated by solenoid valve's opening process were linearly related with those generated by solenoid valve's closing process, and the proportionality factor was 1.91 and the coefficient of determination was 0.99. This study was helpful in understanding the influence of solenoid valve's structure parameters on water hammer and in building the simulation model for the whole PWM variable rate spraying system and for optimizing the spraying system.