Evaluation of Spray Characteristics in Pharmaceutical Tablet Coating Processes: The Influences of Drum Rotational Speed and Drying Air Flow Rate

2009 ◽  
Author(s):  
Ariel R. Muliadi ◽  
Paul E. Sojka
Keyword(s):  
Drop Size ◽  
Air Flow ◽  
Air Pressure ◽  
Volume Flux ◽  
Supply Rate ◽  
Drop Velocity ◽  
Pan Coater ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

In this study, drop size, velocity, and volume flux for sprays produced by a pharmaceutical nozzle (Spraying Systems 1/4-JAU-SUE15A-PA67288–45°-SS) were characterized using a Fiber-PDA system (Dantec). Spraying was performed in a 120 cm (24 in) diameter tablet pan-coater (Accela-Cota Model 10, Thomas Engineering, UK). The separate influences of drum rotational speed and drying air flow rate were studied by making measurements at four different pan-coater operating conditions: stationary drum with drying air turned on/off, and 8 rpm rotating drum with drying air turned on/off. For each case, four different spraying conditions (liquid supply rate and atomizing air pressure) were used. PDA scans were performed along the spray semi-major and semi-minor axes at two different axial distances (7.5 and 10 cm) from the atomizer tip. Results were as follows. When both the drying air and drum rotation were absent, increasing liquid supply rate while operating the atomizer at the lower of two atomizing air pressures decreased drop size. The opposite occurred when operating at the higher of the two atomizing air pressures. This suggests that the nozzle operated as a simplex pressure-swirl atomizer at lower levels of atomizing air pressure, but as an air-assist atomizer at higher levels of atomizing air pressure. Regardless, liquid supply rate had no significant effect on drop velocity. In contrast, a decrease in atomizing air pressure or an increase in axial distance always led to an increase in drop size and a decrease in drop velocity. Supplying drying air to the pan-coater resulted in up to a 6 m/s increase in drop velocity, but had mixed effects on drop size. When the spray gun was operated as an air assist atomizer, supplying drying air to the drum led to an increase in D32. The reverse was observed when the gun operated as a simplex pressure-swirl atomizer. These two observations are most evident when operating at the lower liquid supply rate (70 g/min), suggesting that they may have arisen from drop evaporation. Increasing the drying air supply rate also reduced spray extent and volume flux magnitude. Adding drum rotation to the process generally led to (i) increased drop size and (ii) increased drop velocity. (i) likely arose from the transport of small drops away from the spray zone, while (ii) likely resulted from changes in droplet trajectories. Both are the result of the gas-phase swirling motion that is due to the drum rotation. (i) was most noticeable when the nozzle was operated as an air-assist atomizer. In addition, drum rotation decreased spray volume flux magnitude at the spray center, but increased it at other locations, essentially making the spray more dumbbell-shaped. Finally, the influence of drum rotation on drop velocity diminished when drying air flow was included. This was because the drying air momentum helped the drops oppose the effects of the swirling flow induced by the drum rotations.

Hybrid Pressure-Swirl/Twin-Fluid Atomizer for Emission Controls

2006 ◽  
Author(s):  
Andrew C. S. Lee ◽  
Paul E. Sojka
Keyword(s):  
Flow Field ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Drop Size ◽  
Air Flow ◽  
Exit Plane ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

An experimental study was conducted to characterize the performance of a hybrid atomizer used in emission control devices. Characterization included drop size distribution, measured using a forward light-scattering instrument, the air flow field (axial and radial velocities), measured using 2-D PIV, and turbulence characteristics of the air flow field, measured using LDA. The air flow field showed characteristics common to turbulent free round jets beyond approximately 8 exit orifice diameters from the atomizer exit plane. The centerline velocity increased with an increase in mass flow rate, while radial velocities were two orders of magnitude smaller than centerline values. The jet spreading factor initially increased with an increase in axial distance from the exit; however, it stabilized at a value of 0.09 at z/Do=11.8. Turbulence intensity along the jet centerline stabilized at 25% at z/Do=7.9. Drop size data showed complex dependencies on liquid and air mass flow rates, and on internal geometry. The influence of liquid mass flow rate on drop size was significantly smaller for the hybrid atomizer than for the pressure swirl atomizer component housed inside the hybrid unit, thus indicating a higher turndown ratio for the hybrid device. Drop size distributions produced by the hybrid atomizer showed multiple peaks, indicating there is more than one important atomizing mechanism. Finally, reducing the gap between the pressure-swirl atomizer and the exit plane of the outer casing resulted in a reduction in drop size.

Influence of Ambient Air Pressure on Pressure-Swirl Atomizer Spray Characteristics

2001 ◽  
Author(s):  
Arvind K. Jasuja ◽  
Arthur H. Lefebvre
Keyword(s):  
Gas Turbines ◽  
Drop Size ◽  
Cone Angle ◽  
Ambient Air ◽  
Air Pressure ◽  
Spray Characteristics ◽  
Spray Cone ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

A single-component PDPA is used to evaluate the spray characteristics of a simplex pressure-swirl atomizer when operating at high liquid flow rates and elevated ambient air pressures. Attention is focused on the effects of air pressure on mean drop size, drop-size distribution, mean velocity, volume flux, and number density. Using a constant flow rate of 75 g/s, measurements are carried out along the spray radii at a fixed distance downstream from the atomizer face of 50 mm. The air pressures of 1, 8, and 12 bars chosen for these tests correspond to air densities of 1.2, 9.6, and 14.4 kg/m3. The purpose of the investigation is to supplement the existing body of information on pressure-swirl spray characteristics, most of which were obtained at normal atmospheric ambient pressures, with new data that correspond more closely to the conditions prevailing in the primary combustion zones of modern gas turbines. The results obtained are explained mainly in terms of the influence of air pressure on spray structure, in particular spray cone angle and Weber number.

Prediction of drop size distribution in a spray from a pressure swirl atomizer using maximum entropy formalism

2003 ◽  
Vol 217 (7) ◽  
pp. 831-838 ◽  
Author(s):  
D Mondal ◽  
A Datta ◽  
A Sarkar
Keyword(s):  
Maximum Entropy ◽  
Size Distribution ◽  
Drop Size ◽  
Drop Size Distribution ◽  
Pressure Differential ◽  
Liquid Mass ◽  
Atomization Efficiency ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

Drop size distribution is an important characterizing parameter of a spray. In the present work a theoretical model has been described, based on the maximum entropy formalism principle, for the determination of the drop size distribution in a spray issued from a pressure swirl atomizer. The atomization efficiency is also derived from the model, assuming the velocities of all the drop sizes to be uniform. The results show that the drop size distribution, described from the present model, resembles the Rosin-Rammler type distribution very well, with a dispersion parameter of 3.47. The atomization efficiency is found to decrease with the increase in liquid mass flowrates, when the pressure differential across the atomizer remains the same. On the other hand, an increase in the orifice diameter increases the atomization efficiency, when the liquid mass flow rate and pressure differential are the same. The ratio of the surface energy to the kinetic energy at the atomizer exit is seen to influence the atomization efficiency.

Experimental Investigations of Performance Parameters of Pressure Swirl Atomizer for Kerosene Type Fuel

2009 ◽  
Author(s):  
Saurabh Dikshit ◽  
Salim Channiwala ◽  
Digvijay Kulshreshtha ◽  
Kamlesh Chaudhari
Keyword(s):  
Drop Size ◽  
Mechanical Energy ◽  
Cone Angle ◽  
Experimental Investigations ◽  
Performance Parameters ◽  
Spray Cone ◽  
Spray Penetration ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

The process of atomization is one in which a liquid jet or sheet is disintegrated by the kinetic energy of the liquid itself, or by exposure to high velocity air or gas, or as a result of mechanical energy applied externally. Combustion of liquid fuels in engines and industrial furnaces is dependent on effective atomization to increase the specific surface area of the fuel and thereby achieve high rate of mixing and evaporation. The pressure swirl atomizer is most common type atomizer used for combustion in gas turbine engines and industrial furnaces. The spray penetration is of prime importance for combustion designs. Over penetration of the spray leads to impingement of the fuel on walls of furnaces and combustors. On the other hand, if spray penetration is inadequate, fuel–air mixing is unsatisfactory. Optimum engine performance is obtained when the spray penetration is matched to the size and geometry of combustors. Methods for calculating penetration are therefore essential to sound engine design. Equally important are the spray cone angles and the drop size distribution in the sprays. An attempt is being made to experimentally investigate pressure swirl atomizer performance parameters such as spray cone angle, penetration length and drop size at different injection pressures ranging from 6 bar to 18 bar.

Investigation of Spray Formation and Turbulent Droplet Transport in High Momentum Jet Stabilized Combustor Injection Systems

2020 ◽  
Author(s):  
Dominik Schäfer ◽  
Fabian Hampp ◽  
Oliver Lammel ◽  
Manfred Aigner
Keyword(s):  
Mass Flow ◽  
Gas Turbines ◽  
Liquid Fuel ◽  
Fuel Injection ◽  
Air Flow ◽  
High Momentum ◽  
Droplet Distribution ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

Abstract This work investigates the influence of coaxial air flow on droplet distribution, velocity, and size generated by a pressure-swirl atomizer. The experiments were performed inside a generic test section with large optical access at atmospheric conditions. The flow conditions replicate the mixing duct sections of high momentum jet stabilized combustors for gas turbines, e.g. high axial air velocities without swirl generation and high preheat temperatures. High momentum jet stabilized combustors based on the FLOX® burner concept are used successfully in gas turbines due to its fuel and load flexibility and very low pollutant emissions. In previous and ongoing studies, different model combustors have been under investigation mainly with the focus of broadening fuel flexibility and operational limits. Operation with different liquid fuel injection systems in high pressure experiments showed a significant impact from the injector shape and injection strategy on the fuel air mixing behavior, the flame position and stability, and thus NOx emissions. This experiment will give a more detailed understanding of the turbulent mixing and interaction of primary and secondary atomization with the surrounding air in such burners. The setup will also allow for the testing of different injection systems for various burner configurations by the variation of injection type, location, fuel, and air flow properties. In the present experiments a pressure-swirl atomizer was set to a constant pressure drop and mass flow. Liquid fuel was replaced by deionized water due to safety concerns. The coaxial air mass flow was preheated up to 473 K and set to bulk velocities of 20 m/s, 50 m/s, and 80 m/s. Particle Image Velocimetry (PIV) was used to characterize the flow field downstream of the point of injection. The droplet size and velocity distributions were quantified by double frame shadow imaging combined with a long-distance microscope with a resolution below 1 μm per pixel. Moreover, the formation of ligaments as well as primary spray break-up was visualized. The results show a significant change of the spatial droplet distribution with increasing co-flow velocity for a given atomizer geometry. The spray cone angle widens at high co-flow velocities due to the formation of a pronounced recirculation zone behind the backward facing step of the injector near the nozzle orifice. This also leads to a change in the initial droplet momentum and the spatial distribution of large droplets. Smaller droplets are concentrated to the center of the spray due to turbulent transport. These findings assist the ongoing developments of liquid fuel injection systems for high momentum jet based combustors and provide validation data for numerical simulations of primary and secondary atomization.

scholarly journals Experimental and Analytical Investigation on the Variation of Spray Characteristics Along Radial Distance Downstream of a Pressure Swirl Atomizer

1986 ◽  
Vol 108 (3) ◽  
pp. 473-478 ◽  
Author(s):  
Y. H. Zhao ◽  
W. M. Li ◽  
J. S. Chin
Keyword(s):  
Drop Size ◽  
Laser Light ◽  
Radial Distance ◽  
Analytical Investigation ◽  
Laser Light Scattering ◽  
Sauter Mean Diameter ◽  
Spray Characteristics ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

The variation of spray characteristics (Sauter Mean Diameter and Rosin-Rammler drop-size distribution parameter) downstream of a pressure swirl atomizer along radial distance has been measured by laser light scattering technology. An analytical model has been developed that is capable of predicting the variation of spray characteristics along radial distance. A comparison between the prediction and experimental data shows excellent agreement. It shows that the spray model proposed, although relatively simple, is correct and can be used with some expansion and modification to predict more complicated spray systems.

INTERNAL AND NEAR-NOZZLE FLOW OF A PRESSURE-SWIRL ATOMIZER UNDER VARIED FUEL TEMPERATURE

2007 ◽  
Vol 17 (6) ◽  
pp. 529-550 ◽  
Author(s):  
Seoksu Moon ◽  
Choongsik Bae ◽  
Essam F. Abo-Serie ◽  
Jaejoon Choi
Keyword(s):  
Nozzle Flow ◽  
Fuel Temperature ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

Study of pressure swirl atomizer with tangential input at design point and outside of design point

2020 ◽  
Vol 32 (12) ◽  
pp. 127113
Author(s):  
Kiumars Khani Aminjan ◽  
Balaram Kundu ◽  
D. D. Ganji
Keyword(s):  
Design Point ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

Studies on air core size in a simplex pressure-swirl atomizer

2017 ◽  
Vol 42 (29) ◽  
pp. 18649-18657 ◽  
Author(s):  
Zhilin Liu ◽  
Yong Huang ◽  
Lei Sun
Keyword(s):  
Core Size ◽  
Air Core ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

A Numerical Approach for the Simulation of Internal Nozzle Flow in a Pressure Swirl Atomizer Using Different Turbulent Models and Towards an Effective Inlet Weber Number

2013 ◽  
Author(s):  
Ahmadreza Abbasi Baharanchi ◽  
Seckin Gokaltun ◽  
Shahla Eshraghi
Keyword(s):  
Weber Number ◽  
Computational Cost ◽  
Internal Flow ◽  
Numerical Approach ◽  
Reynolds Stress Model ◽  
Multiphase Model ◽  
Vof Model ◽  
Swirl Atomizer ◽  
Pressure Swirl ◽  
Pressure Swirl Atomizer

VOF Multiphase model is used to simulate the flow inside a pressure-swirl-atomizer. The capability of the Reynolds Stress Model and variants of the K-ε and K-ω models in modeling of turbulence has been investigated in the commercial computational fluid dynamics (CFD) software FLUENT 6.3. The Implicit scheme available in the volume-of-fluid (VOF) model is used to calculate the interface representation between phases. The atomization characteristics have been investigated as well as the influence of the inlet swirl strength of the internal flow. The numerical results have been successfully validated against experimental data available for the computed parameters. The performance of the RNG K-ε model was found to be satisfactory in reducing the computational cost and introducing an effective Weber number for the flow simulated in this study.

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