Experiment on mixing performance of on-line mixing spray system

Abstract: The aim of this study was to research the influence of the jet-mixing apparatus (one core component) on working state of the on-line mixing spray system. Due to the need of making the mixing process visible, the pesticide was simulated by carmine solution. The working states of the on-line mixing spray system with 3 types of different flow characteristics produced by 3 kinds of nozzles respectively, i.e. TR80-005c, ST110-01 and F110-015 were examined, as well as the jet-mixing apparatus with 24 different structural parameters made up of 4 types of mixing tube's diameters and 6 types of jet nozzle's outlet diameters. Based on spectrophotometric method, the mixing solution from the on-line mixing spray system was collected and measured by the visible spectrophotometer of UV-2102 PCS type. The absorption wavelength of carmine solution was firstly scanned, and 508 nm was selected as the measuring wavelength. Then a series of carmine standard solutions with different concentrations of 0.01, 0.02, 0.04, 0.06, 0.08 and 0.1 g/L were prepared to establish a mathematical expression of carmine solution concentration and the absorbance under the selected wavelength; finally, the concentrations of the collected samples were calculated according to the mathematical expression. The mixture homogeneity of the on-line mixing spray system operated with the nozzle of F110-015 was analyzed by the above method when jet nozzle's outlet diameter of jet-mixing apparatus, d, was set to 2.00 mm, and the area ratio m was set to 4.00. The results of experiments indicated that the structural parameters of the jet-mixing apparatus had a significant effect on the working condition of the on-line mixing spray system. In the same kind of spray system, when the structural parameters of the jet-mixing apparatus changed, the working state of the on-line mixing spray system also changed. And there are two working states for spray system in different experiments: inhalation and backflow. The inhalation is a state that liquid water provided by hydraulic pump is imported into the jet nozzle through the water inlet A of the jet-mixing apparatus, and forms a pressure small enough to make the pesticide sucked into the sucking chamber through the pesticide inlet B. And when the water is imported into the jet-mixing apparatus and then flows out from the pesticide inlet and diffuses, the pesticide can't be sucked; and this state is called as the backflow. Based on the theoretical analysis and experiments, two methods to solve the problem of liquid backflow were given: change the structural parameters of jet nozzle by increasing inlet diameter or decreasing outlet diameter of jet nozzle, and reduce the drag coefficient of the spraying system. In the spray system operated with the nozzle of F110-015 type, CV ( the space coefficients of variation ) of mixture concentration under 4 types of spray pressures (0.26, 0.30, 0.34 and 0.36 MPa) were 2.983%, 3.599%, 4.287% and 4.647%, respectively, all less than 5%. In conclusion, the jet-mixing apparatus can be well applied to the on-line mixing spray system.