Evaluation of Mixing Uniformity for Inline Mixers by Image Processing

HighlightsFour inline mixers with different structures are designed and tested for DNIS applications.A new method for evaluating inline mixing uniformity by image processing is presented.While higher carrier flow rates cause better uniformity, changes due to higher mixing ratios are complicated.The multi-injection jet mixer has simplified structure and relatively satisfactory mixing efficacy.Abstract. Effective and specialized mixing devices that can achieve pesticide injection and inline mixing simultaneously are required to achieve better mixing efficacy in direct nozzle injection systems (DNISs), especially when high-viscosity pesticides are used. To evaluate the inline mixing efficacies of four inline mixers with different structures under various application conditions and to propose optimized structures for those inline mixers, a new method for evaluating uniformity based on image processing is presented. The results of experiments show that the proposed method is adequate for determining mixing uniformity. The mixing uniformity of each mixer increased with carrier flow rates (Q) ranging from 800 to 2,000 mL min-1, but the variations were less significant than those achieved by varying the mixing ratio (P) from 1:100 to 10:100. The mixing uniformity in the jet mixer (mixer A) clearly decreased with an increase in P at different values of Q because the pesticide gradually concentrated on one side of the detection tube. The layered mixer (mixer B) performed better than mixer A, especially at high P. The extension tube installed downstream of mixer B to improve uniformity was shorter than that of mixer A. Mixer C, whose structure was a combination of mixers A and B, had optimal mixing efficacy and the most complicated structure. The uniformity of the multi-injection jet mixer (mixer D) (Haverage = 12.46) obtained by simplifying mixer C was superior to that of mixers A (Haverage = 15.35) and B (Haverage = 14.65) but inferior to that of mixer C (Haverage = 4.08). With a relatively simple structure, mixer D may generally meet the uniformity requirements, thus resulting in advantages for practical use in DNISs, although further structural optimization of mixer D seems necessary. Keywords: Direct nozzle injection system, Image processing, Inline mixers, Mixing uniformity, Principal component analysis, Various application conditions.

Multiscale fluid–particle thermal interaction in isotropic turbulence

We use direct numerical simulations to investigate the interaction between the temperature field of a fluid and the temperature of small particles suspended in the flow, employing both one- and two-way thermal coupling, in a statistically stationary, isotropic turbulent flow. Using statistical analysis, we investigate this variegated interaction at the different scales of the flow. We find that the variance of the carrier flow temperature gradients decreases as the thermal response time of the suspended particles is increased. The probability density function (PDF) of the carrier flow temperature gradients scales with its variance, while the PDF of the rate of change of the particle temperature, whose variance is associated with the thermal dissipation due to the particles, does not scale in such a self-similar way. The modification of the fluid temperature field due to the particles is examined by computing the particle concentration and particle heat fluxes conditioned on the magnitude of the local fluid temperature gradient. These statistics highlight that the particles cluster on the fluid temperature fronts, and the important role played by the alignments of the particle velocity and the local fluid temperature gradient. The temperature structure functions, which characterize the temperature fluctuations across the scales of the flow, clearly show that the fluctuations of the carrier flow temperature increments are monotonically suppressed in the two-way coupled regime as the particle thermal response time is increased. Thermal caustics dominate the particle temperature increments at small scales, that is, particles that come into contact are likely to have very large differences in their temperatures. This is caused by the non-local thermal dynamics of the particles: the scaling exponents of the inertial particle temperature structure functions in the dissipation range reveal very strong multifractal behaviour. Further insight is provided by the flux of temperature increments across the scales. Altogether, these results reveal a number of non-trivial effects, with a number of important practical consequences.

Development and Preliminary Evaluation of an Integrated Individual Nozzle Direct Injection and Carrier Flow Rate Control System for Pesticide Applications

Direct injection systems for agricultural spray applications continue to present challenges in terms of commercialization and adoption by end users. Such systems have typically suffered from lag time and mixing uniformity issues, which have outweighed the potential benefits of keeping chemical and carrier separate or reducing improper tank-mixed concentration by eliminating operator measurements. The proposed system sought to combine high-pressure direct nozzle injection with an automated variable-flow nozzle to improve chemical mixing and response times. The specific objectives were to: (1) integrate a high-pressure direct nozzle injection system with variable-flow carrier control into a prototype for testing, (2) assess the chemical metering accuracy and proper mixing at different combinations of injection valve frequency and duty cycle along with chemical pressure, and (3) assess the ability of the control system to ensure proper chemical dilutions and concentrations in the nozzle effluent resulting from step changes in target application rates. Laboratory experiments were conducted using the combined system. Results of these experiments showed that the open-loop control of the injectors could provide a means of accurately metering the chemical concentrate into the carrier stream. Chemical injection rates could be achieved with an average error of 5.4% compared to the target rates. Injection at higher duty cycles resulted in less error in the chemical concentration predictions. Discrete Fourier transform analysis showed that the injection frequency was noticeable in the nozzle effluent when the injector was operated at 3.04 MPa and 5 Hz (particularly at lower duty cycles). Increasing the injection pressure and operating frequency to 5.87 MPa and 7 Hz, respectively, improved mixing, as the injection frequency component was no longer noticed in the effluent samples. The variable-flow nozzle was able to maintain appropriate carrier flow rates to achieve product label chemical concentrations. In one case, the maximum allowable concentrate was exceeded, although the nozzle was able to recover in 0.5 s. Steady-state errors ranged from 2.5% to 7.5% for chemical concentrations compared to the selected chemical to carrier ratio (0.03614). This test scenario represented an application rate of 4.68 L ha-1 with velocity increases from 4.0 to 7.1 m s-1 and decreases from 7.1 to 4.0 m s-1, which were typical of the example field application data. Keywords: Pesticides, Precision agriculture, Spraying equipment, Variable-rate application.

Facilitating the charge transfer of ZnMoS4/CuS p–n heterojunctions through ZnO intercalation for efficient photocatalytic hydrogen generation

A thin intercalation in a p–n heterojunction is utilized to induce interfacial band bending, thus generating a favorable carrier flow for photocatalytic reactions.