EXPERIMENTAL STUDY OF MEAN DROPLET SIZE FROM PRESSURE SWIRL ATOMIZER

This experimental study undertakes the measurements of droplet Sauter Mean Diameter (SMD) at different axial distances for the hollow-cone nozzle and different radial distances from the spray centreline using a laser-diffraction-based drop size analyser in order to validate atomization model. The study also investigates the influence of injection pressure and the evaluation of two exit orifice diameters on the Sauter Mean Diameter (SMD). The drop size distributions along the nozzle centreline as well as the radial drop distributions from spray centreline are also evaluated. To enhance the physics of liquid sheet instability and liquid film breakup mechanisms, visualization of liquid film breakup as a function of injection pressure was carried out. The results show that mean droplet size (SMD) increases in the axial distance on the spray centreline but decreases with an increasing injection pressure on the spray centreline. It was observed that larger sized drops occupy the spray periphery compared to those occupying the spray core. For the nozzle exit orifice diameters of 3.5 mm and 1.5 mm, the results show that the small nozzle exhibits smaller SMDs than the bigger nozzle and the break-up lengths are different for the two nozzles. The drop size distributions at radial positions showed an increase in droplet formation through the spray downstream distances and become more uniform. The visualisation of the spray was carried out using high-speed camera and it was noted that a well-defined hollow-cone spray was captured and that the spray angle increases with the injection pressure but reduces with the liquid film length.

Design and Validation of a Portable Handheld Device to Produce Fine Fibers Using Centrifugal Forces

In the present research project, a novel portable battery-powered handheld device able to produce micron and submicron fibers using centrifugal forces is proposed. The design includes spinnerets with a clamshell configuration with multiple chambers or reservoirs (2, 4, and 8) and different exit orifice diameters (400, 500, 600, and 800 µm). The rotational speed is controlled via an Arduino microcontroller. To validate the design, a series of experiments were conducted and the effect of the orifice diameter, number of chambers, and velocity on the resulting fibers’ diameter and yield was studied. For the experiments, a polymeric solution of Polyvinyl Alcohol (PVA) was prepared. The fiber yield was gravimetrically quantified, and the fiber morphology and diameter were analyzed by means of scanning electron microscopy (SEM). The experimental results showed that spinnerets with an orifice diameter of 500 microns yielded the greatest amount of fibers (0.0777 g). In addition, the number of chambers also affected the amount of fibers produced, and it was determined that the fiber diameter size is dependent on the spinneret speed. Fibers 80 nm in diameter were observed at 6500 rpm.

Air-Core–Liquid-Ring (ACLR) Atomization Part II: Influence of Process Parameters on the Stability of Internal Liquid Film Thickness and Resulting Spray Droplet Sizes

Air-core–liquid-ring (ACLR) atomization presents a specific type of internal mixing pneumatic atomization. It can be used for disintegration of high viscous feed liquids into small droplets at relatively low gas consumptions. However, the specific principle of ACLR atomization is still under research and no guidelines for process and atomizer design are available. Regarding literature on pre-filming atomizers, it can be hypothesized for ACLR atomization that the liquid film thickness inside the exit orifice of the atomizer, as well as the resulting spray droplet sizes decrease with increasing air-to-liquid ratio (ALR) and decreasing feed viscosity. In this study, the time dependent liquid film thickness inside the exit orifice of the atomizer was predicted by means of computational fluid dynamics (CFD) analysis. Results were compared to high speed video images and correlated to measured spray droplet sizes. In conclusion, the hypothesis could be validated by simulation and experimental data, however, at high viscosity and low ALR, periodic gas core breakups were detected in optical measurements. These breakups could not be predicted in CFD simulations, as the simplification of an incompressible gas phase was applied in order to reduce computational costs and time. Nevertheless, the presented methods show good potential for improvement of atomizer geometry and process design as well as for further investigation of the ACLR atomization principle.

A Numerical Study of the Internal Flow in a Pressure Swirl Atomizer

The internal flow and discharge parameters of a pressure swirl atomizer (PSA) are numerically investigated using a coupled Level-Set (LS)/Volume-of-Fluid (VOF) solver that combines the advantages of LS and algebraic VOF methods by maintaining the mass conservation and the interface sharpness simultaneously. Internal flow velocity profile and discharge parameters including discharge coefficient, film thickness, and spray cone angle are compared between simulation results and the experimental data that are available in the literature. A parametrical study is also performed to investigate the effects of the key geometric parameters of the PSA configuration on the discharge parameters. The geometric parameters studied are the length to diameter ratio of the swirl chamber, the length to diameter ratio of the exit orifice, the swirl chamber diameter to exit orifice diameter ratio, and the swirl chamber convergence angle.

New insights into Plectospira genus (Oomycetes, Straminipila): morphological and molecular analyses

We analyzed the morphology and phylogenetic placement of three isolates of Plectospira belonging to Plectospira gemmifera and P. myriandra that were isolated from soil, water bodies and reservoir sediment. The molecular data are from the partial large subunit and the complete internal transcribed regions of the ribosomal DNA. The genus is characterized by the presence of lobulated zoosporangia and mode of zoospore discharge forming an evanescent cluster in the exit orifice. Our isolates clustered together with the single isolate of the genus available in GenBank, however, our phylogenetic analysis and morphological characterization showed that the isolate identified as Plectospira myriandra CBS 523.87 is possibly another taxon. In addition, P. gemmifera is recorded for the first time in Brazil and its sequences were inserted for the first time in a phylogenetic reconstruction.