Abstract
Precise control of oil drop size optimizes oil retention on plants and oil discharge uniformity along thepipeline for foliar chemigation. However, control of oil drop size with existing chemigation injection systems is difficult. Anew system was developed that injects oil drops of known size distribution into a center pivot irrigation pipeline. Thesystem removes water from the irrigation pipeline, increases water pressure with a pump, injects oil into the water stream,increases dispersion velocity in small diameter tubes in order to break up oil drops, and finally injects the water-oildispersion back into the irrigation pipeline. In order to calculate the maximum drop size (dmax) of viscous oil drops in thedrop generator, a correction term with effective viscosity, effective density, and dispersed phase volume fraction wasadded to the Hinze (1955) equation for dmax in turbulent two-phase pipe flow. The new equation calculates dmax as afunction of water flow rate, oil and water viscosity, oil volume fraction, and other measurable parameters. The averagerelative error and root mean square deviation between dmax and literature data was 3 and 17%, respectively. The tubingin the drop generator is coiled in order to reduce the length of the system; thus, the coiled tubing friction factor must beused in the dmax equation. Two equations (the Ito and Srinivasen equations) for friction factor in helical coiled tubingwere evaluated in laboratory experiments with the drop generator. The Ito equation performed best; average root meansquare deviation between calculated friction factor and experimental data was 2%. Three equations for the effectiveviscosity of oil-water dispersions (the Einstein, Taylor, and Richardson equations) were evaluated with literature andexperimental data. The Richardson equation performed best; average root mean square deviation between calculatedviscosity and experimental and literature data was 7%.
Published Version
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