Onnoet size does fit all Fluidic MBUs offer solutions for fine atomization For decades, mechanical break-up (MBU) inserts have been widely used in aerosols to generate spray patterns and improve distribution of products. Some descriptors for product distribution include droplet size, distribution uniformity, coverage area size and shape. Historically, the “Swirl” MBU, which is comprised of tangential feed channels into a swirl chamber, is used for many aerosol applications. The fluid swirls and exits through the exit orifice as a spinning sheet and generates a cone spray. The Swirl MBU is typified by small drops, round pattern and relatively non-uniform distributions. For applications desiring fine mist (e.g. air care), the Swirl MBU is a good candidate. However for personal care (e.g. sun care, skin care), insect sprays (repellents) and household products (surface cleaners), uniform spray distributions with slightly coarser drops are preferred. The introduction of the “Fluidic” MBU with its uniform distribution, slightly coarser drops, customizable pattern shapes (oval, rectangular, square) can be a preferred alternative for such applications. Fluidic nozzles have been used for over fifty years in various applications ranging Gopalan Hartranft from automotive washers to irrigation nozzles to spa nozzles to showerheads. Much like the Swirl MBU, the Fluidic MBU has a plurality of feed channels that then lead into an interaction region (not a swirl chamber). As a result of the vortices formed inside and their interaction with the jets, the output is an oscillating sheet (or jet) that generates the spray. There are many instances where Swirl MBUs compensate with higher delivery rates to reduce “misting.” The Fluidic MBU Hester 28 Spray January 2016 can generate larger drops at half the delivery rate of a Swirl MBU while maintaining pattern uniformity, large coverage area and consistent pattern even during full depletion of a can’s contents when bag-in-valve (BOV) and compressed gas packages have diminished operating pressures. For this reason, Fluidic MBUs can also deliver the targeted spray pattern size at lower pressures than Swirl MBUs. Spray pattern uniformity Figures 1-3 show actual product distribution as obtained with Mie scattering. Generally, 20–50 instantaneous cross-section images are recorded and a mean cross-section is obtained as shown in the figures. In these examples, the product is an ethanol mixture at 110psi (BOV) sprayed with Fluidic MBUs and Swirl MBUs and also a Swirl MBU with a liquid propellant-based product (Swirl LPG). In Figure 2, the Swirl MBU produces a pattern that is quite non-uniform with peak values of 40 mg/cm2 while the Fluidic MBU (Figure 1) has peak values of 20 mg/cm2. A Swirl MBU with LPG has the most non-uniform distribution with values above 120 mg/ cm2 (Figure 3). These basic examples demonstrate Fluidic MBU’s pattern uniformity. The improved uniformity from the Fluidic MBU can generate a spray with higher residence time and minimal dripping for household applications. This result also yields reduced perceived “wetness” for personal care products when compared to Swirl MBUs. Droplet size The concept of “one size does not fit all applications” is most apparent when discussing droplet size. We see examples with Swirl MBUs where delivery rate is increased to combat excessive misting. For personal care, household products, insect repellents, etc., slightly coarser drops (DV50=100μm) are preferable to reduce inhalation, irritating odor/fumes and wind drift (when outdoors). The observed results are that the Fluidic MBU can generate these larger droplet sizes at half the delivery rate of a Swirl MBU. An ethanol formulation (for personal care) was tested with Swirl Shridhar Gopalan Ph.D. Evan Hartranft Russell Hester dlhBOWLES Inc. Columbia, MD Figure 1. FluidicMBU spray cross section Figure 2. Swirl MBU spray cross section
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