Analysis of the variability of pesticide concentration downstream of inline mixers for direct nozzle injection systems

Abstract

The injection of pesticide directly into spray nozzles results in concentration variations, both periodic discontinuities and pulses, caused by the use of injection pumps and solenoid valves. Such variations can lead to inaccurate application of pesticide. To avoid using long pipelines, long lag times and inaccurate application, efficient mixers are required to shorten the distance between the injection point and the spray nozzle. To analyse concentration variations and periodic pulses, a set of methods based on image processing were proposed and were tested using three inline mixers, a jet mixer (A), a layered mixer (B) which was specially designed, and simplified layered-jet mixer (C) which was developed as combination of mixer A and some simplified structures of mixer B. Results showed the characteristics of concentration variability for three mixers were generally different. The application conditions, carrier flow rate, mixing ratio, and injection frequency, need to be comprehensively considered to achieve improved concentration consistency and improve spraying accuracy. Concentration variability was the most obvious for mixer A with the average Coefficient of Variation (CV) as high as 4.12%. Using auto-correlation and complexity analysis, the concentration series exhibited strong periodicity and relatively lower complexity. Concentration variability for mixer B was less prominent with an average CV value 1.25% and concentration periodicity sometimes being indeterminable. Mixer C showed moderate concentration variability (CV 2.26%) although pulsation was still detectable. Mixers with similar structures to mixer C could be applied for direct nozzle injection systems to improve the spraying accuracy.