Improved jet mixer injection nozzle enhancing pesticide mixing uniformity and dynamic concentration consistency

Abstract: The pesticide injections in nozzle direct injection system (NDIS) applied in plant protection machinery generally have flow-rate inconsistency characteristics, which cause fluctuations of mixing concentration and inaccuracy of spraying. The purposes in this study were to evaluate the inline mixing efficacy comprehensively based on index of dynamic inconsistency of the mixing concentration and the inline static mixing uniformity in NDIS. A new inline mixer known as the layered mixer (mixer B) with special structures (perforated tubes) to weaken concentration inconsistency and a traditional jet mixer (mixer A) were presented to carry out the direct injection and mixing experiments under variable working conditions. Moreover, image processing methods to quantify mixture concentration discontinuities based on calculating coefficient of variation (CV) values of mean pixels brightness in ROIs was proposed. Static mixing non-uniformity index to identify static mixing non-uniformity based on principal component analysis (PCA) was also proposed. These 2 indices were used to scientifically measure the inline mixing efficacy of the mixers. The relative differences between the calculation results of horizontal viewing and the vertical viewing images were only 2.86% for static mixing non-uniformity index values and 5.37% for CV values, indicating that the single horizontal viewing images could be used to obtain higher accuracy. The threshold of static mixing non-uniformity index for judging whether the mixture was uniform or non-uniform was set to be 13.00 as there weren't non-scatted viscous pesticides remaining in the detection tube when the static mixing non-uniformity index values dropped below it. In addition, the threshold for determining the concentration consistency was set to be only 2% because there weren't apparent brightness differences between ROIs at different moments when the CV values were less than it. The increase of carrier flow rate and the mixing ratios could generally improve the static uniformity and dynamic concentration consistency of inline mixing. However, when it was under the condition of a large mixing ratio , the static mixing uniformity of the jet mixer would decline due to the pesticide accumulation in the side wall of the jet mixer. The average static non-uniformity index of the proposed mixer here reduced from 16.70 to 14.76, and reduced to about 13.00 only when mixing ratios was higher than 9:100 and carrier flow rate was higher than 1400 m/min, which could achieve uniform mixing efficacy completely. Although it was difficult for the new mixer to guarantee high static mixing uniformity under all working conditions, it could still significantly improve the dynamic consistency of the mixing concentration under the pulsation injection conditions with the average CV value decreased from 0.039 to only 0.011. Moreover, when the working condition could meet the requirements of injection frequency higher than 5.10 Hz or the mixing ratios was higher than 5:100, the CV values would decline to 0.020, which could fully satisfy the dynamic consistency requirements. The linear correlations between the static uniformity and dynamic consistency of jet mixer and layered mixer were 0.848 and 0.684, respectively. Therefore, a more efficient inline pesticide mixer should be proposed especially when the pesticide injection pulse was strong. The independent sample test results showed that the optimization of the static uniformity of the proposed mixer was less than that of the concentration consistency, which indicates that the new mixer structure has significant concentration pulsation attenuation efficacy. To conclude, further optimization on static uniformity of the proposed mixer should be proposed.