Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2000
Publication Date: N/A
Citation: Interpretive Summary: Accurate application of pest control agents is fundamental to the efficient use of chemicals and minimizing off-target loss of spray. One cause of spray variability is poor mixing in the sprayer tank before and during treatments; especially when using dry-formulations. Mixing will be more important when applying bio-control agents which often contain solid materials. Most agricultural sprayers use hydraulic agitation to stir the spray mixture. In this method, some of the output of the sprayer pump is returned to the tank through mixing nozzles. Earlier studies have shown that, even with good hydraulic mixing, some clay used as pesticide carriers is deposited on the bottom during emptying. Maintaining a suitable water velocity in the tank is an effective way to keep the tank mixture uniform. In this study, we used a commercial program to simulate water velocity in a sprayer tank with several mixing nozzle and operating systems. An attempt to simulate the mixing action on dry particles, while possible with the software used, was impractical due to time considerations. Water velocities were measured with a hot-film anemometer at 9 locations in the tank for 12 mixing systems. Water velocities computed using computer simulation were reasonable approximations for velocities measured with hot-film sensors. This is the first known study that compared simulated and measured water velocities in an agricultural sprayer tank. These results are very useful to sprayer manufacturers in the design of agitation systems. Sprayer operators also should benefit by becoming aware of possible problems in sprayer tank mixing and how sprayer operating conditions affect mixing effectiveness.
Technical Abstract: FLUENT, a computational fluid dynamics program, was used to investigate flow movements in sprayer tanks with hydraulic jet agitators. Two and three-dimensional simulations were carried out utilizing single phase (liquid phase only) and multiphase (solids particles in liquid) models of the software. Experimental studies of agitation effectiveness by Ucar et al. (2000) initiated the design of these simulations to determine the most important factors affecting the agitation effectiveness. Interpretations of the flow field predictions suggested that the system pressure was the most influential factor on agitation effectiveness due to the direct relationship between pressure and the jet velocity. If the jet velocity was kept constant, then the volume of fluid delivered into the tank was the most important factor in enhancing mixture uniformity. Multiphase predictions of particle deposit amounts at the tank bottom were not feasible due to the computational demand of the model, which was an attempt to simulate three-dimensional, turbulent flows with solid-liquid mixtures. Quantitative verification of single-phase simulations was accomplished by velocity measurements using hot-film sensors in an actual sprayer tank. Velocities were measured at 9 locations within the sprayer tank and 12 jet agitation systems were used. Of the 108 values obtained, 33 velocities calculated using FLUENT were within the 95% confidence limit of measured velocities, based on Student's t-test. FLUENT generated values tended to be greater than measured velocities near the top of the tank. In general, values calculated using FLUENT were reasonable approximations of measured values.