An amendment to this paper has been published and can be accessed via a link at the top of the pa... more An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Liquid atomization processes are used in several industries. The simulation of these processes re... more Liquid atomization processes are used in several industries. The simulation of these processes requires understanding of complex physical phenomena and overcoming various modelling challenges, including resolution of multiple flow scales, cavitation, liquid/gas interface instabilities and liquid and gas compressibility. The modelling of these processes has been an active area of research among a number of groups and organizations. The approaches developed thus far are very computationally intensive, and thus require new techniques to handle the simulation in an optimized fashion. However, with continued advancements in mathematical models and high-performance computing, simulating primary atomization is becoming more mainstream, which is evident by the increasing number of researchers in academics and engineers in industry running these detailed simulations. This paper summarizes our experience with such detailed simulation of liquid atomization. ANSYS, Inc. has developed a hybrid m...
Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enha... more Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation...
Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enha... more Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation...
Despite significant improvement in computational and observational capabilities, predicting inten... more Despite significant improvement in computational and observational capabilities, predicting intensity and intensification of major tropical cyclones remains a challenge. In 2017 Hurricane Maria intensified to a Category 5 storm within 24Â h, devastating Puerto Rico. In 2019 Hurricane Dorian, predicted to remain tropical storm, unexpectedly intensified into a Category 5 storm and destroyed the Bahamas. The official forecast and computer models were unable to predict rapid intensification of these storms. One possible reason for this is that key physics, including microscale processes at the air-sea interface, are poorly understood and parameterized in existing forecast models. Here we show that surfactants significantly affect the generation of sea spray, which provides some of the fuel for tropical cyclones and their intensification, but also provides some of the drag that limits intensity and intensification. Using a numerical model verified with a laboratory experiment, which predi...
The effect of turbulence closure on the spray dynamics and droplets’ dispersion is studied for a ... more The effect of turbulence closure on the spray dynamics and droplets’ dispersion is studied for a dilute Acetone spray jet using an Eulerian-Lagrangian approach with two-way coupling. A stochastic random walk methodology is employed to model the liquid droplets’ turbulent dispersion by the gas phase turbulent eddies. Simulations using different turbulence closure models (i.e. the isotropic SST-k-ω, the k-e realizable, and the non-isotropic Reynolds Stress Model (RSM)) are compared with the SP2 Sydney spray jet measurements. The experimental spray droplets inflow mean and rms velocity and size distributions profiles are matched with the different experimental data size bins at every injection time step. The three models shows very good comparisons with better match for the mean and rms profiles using the RSM. The gas flow field turbulence non-isotropy is found to be maximum at the centerline and decreases radially. The results show that turbulence non-isotropy modeling has a strong impact on the droplet’s dynamics. At the centerline, the RSM predicts slower decay rate downstream of the potential core and higher turbulent intensity. The SST-k-ω and k-e models, however, predicted higher droplets’ slip velocity and Reynolds number and consequently higher drag force than the RSM. In the radial direction, away from the centerline, the drag relationship is reversed between the RSM and the k models. The droplets’ tendency for cross-stream dispersion is found to be correlated with the droplet response and drag force, with highest radial dispersion observed at the shear layer location. Memory effect is observed for spray droplets where they lag the gas phase turbulence especially at downstream locations. The study shows the importance of the gas phase turbulence fluctuations modeling on the droplets dispersion and spray dynamics predictions.
... Bekir S. Yilba , Ahmet Z. ahin , Ahmed Z. Al-Garni , Syed AM Said , Zaki Ahmed , BJ Abdulalee... more ... Bekir S. Yilba , Ahmet Z. ahin , Ahmed Z. Al-Garni , Syed AM Said , Zaki Ahmed , BJ Abdulaleem and Muhammad Sami. Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, 31261, Dhahran, Saudi Arabia. ...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1999
Lasers are widely used as a machine tool in the metal industry. One of the important areas of las... more Lasers are widely used as a machine tool in the metal industry. One of the important areas of laser application is surface treatment of engineering metals. To improve the process parameters in the laser heating process, an exploration of the heating mechanism is fruitful. The present study is carried out to develop a three-dimensional model for a laser pulsed heating process using the electron kinetic theory approach. The heating model introduced relies on successive electronphonon collisions; therefore, it is this process that describes the heat conduction mechanism. This study is limited to heat conduction only. Consequently, the phase change process is not taken into account. To validate the theoretical predictions, an experiment is conducted to measure the surface temperature using an optical method. Moreover, a one-dimensional heating model developed previously is also considered and the predictions of three- and one-dimensional heating models as well as experimental results ar...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
The laser processing of engineering materials requires an in-depth analysis of the applicable hea... more The laser processing of engineering materials requires an in-depth analysis of the applicable heating mechanism. The modelling of the laser heating process offers improved understanding of the machining mechanism. In the present study, a closed-form solution for a step input laser heating pulse is obtained and a numerical scheme solving a three-dimensional heat transfer equation is introduced. The numerical solution provides a comparison of temperature profiles with those obtained from the analytical approach. To validate the analytical and numerical solutions, an experiment is conducted to measure the surface temperature and evaporating front velocity during the Nd—YAG laser heating process. It is found that the temperature profiles resulting from both theory and experiment are in a good agreement. However, a small discrepancy in temperatures at the upper end of the profiles occurs. This may be due to the assumptions made in both the numerical and the analytical approaches. In addi...
ARCHIVE: Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 1989-1996 (vols 203-210), 1996
Laser drilling may improve by proper selection of the laser parameters. One of the important para... more Laser drilling may improve by proper selection of the laser parameters. One of the important parameters in laser hole drilling is the focus setting of the focusing lens. In the present study, the effect of the beam waist position on the resulting hole exit/entry diameter ratio is investigated experimentally. An Nd-YAG laser is used to drill the holes in stainless steel and mild steel sheets at different thicknesses. The study was conducted to include the physical processes involved at different beam waist positions during the drilling operations. It is shown that altering the beam waist positions tends to produce converging and diverging hole walls for negative and positive positions respectively. The drilling improves at a certain beam waist position for a given workpiece thickness.
... NOTATION A, B Constants Cp Specific heat capacity (J/kg K) I Power intensity (W/m2) k Thermal... more ... NOTATION A, B Constants Cp Specific heat capacity (J/kg K) I Power intensity (W/m2) k Thermal conductivity (W/mK) ky Boltzmann's constant L Enthalpy of evaporation (kJ/kg) 53 54 Bekir S. Yilbas et al. ... Int. Commun. Heat Mass Transfer, 20 (1993), 545-55. ...
Lasers find wide applications in industry due to their precision operation and low cost. Laser ma... more Lasers find wide applications in industry due to their precision operation and low cost. Laser machining processes exhibit common characteristics such as heating, melting and evaporation. Modelling of the heating process may enhance understanding of the laser machining process, which in turn minimizes the optimization cost. This study is conducted to explore the laser heating process including evaporation through the
The present study examines the entropy generation during cooling and heating cycles of repetitive... more The present study examines the entropy generation during cooling and heating cycles of repetitive pulsed-laser heating. Two repetitive pulses are introduced in the analysis. The possible thermal integration occurring at the workpiece surface due to repetitive pulse heating is then related to the second-law efficiency of the heating process. It is found that the cooling periods and low intensity decay
An amendment to this paper has been published and can be accessed via a link at the top of the pa... more An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Liquid atomization processes are used in several industries. The simulation of these processes re... more Liquid atomization processes are used in several industries. The simulation of these processes requires understanding of complex physical phenomena and overcoming various modelling challenges, including resolution of multiple flow scales, cavitation, liquid/gas interface instabilities and liquid and gas compressibility. The modelling of these processes has been an active area of research among a number of groups and organizations. The approaches developed thus far are very computationally intensive, and thus require new techniques to handle the simulation in an optimized fashion. However, with continued advancements in mathematical models and high-performance computing, simulating primary atomization is becoming more mainstream, which is evident by the increasing number of researchers in academics and engineers in industry running these detailed simulations. This paper summarizes our experience with such detailed simulation of liquid atomization. ANSYS, Inc. has developed a hybrid m...
Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enha... more Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation...
Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enha... more Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation...
Despite significant improvement in computational and observational capabilities, predicting inten... more Despite significant improvement in computational and observational capabilities, predicting intensity and intensification of major tropical cyclones remains a challenge. In 2017 Hurricane Maria intensified to a Category 5 storm within 24Â h, devastating Puerto Rico. In 2019 Hurricane Dorian, predicted to remain tropical storm, unexpectedly intensified into a Category 5 storm and destroyed the Bahamas. The official forecast and computer models were unable to predict rapid intensification of these storms. One possible reason for this is that key physics, including microscale processes at the air-sea interface, are poorly understood and parameterized in existing forecast models. Here we show that surfactants significantly affect the generation of sea spray, which provides some of the fuel for tropical cyclones and their intensification, but also provides some of the drag that limits intensity and intensification. Using a numerical model verified with a laboratory experiment, which predi...
The effect of turbulence closure on the spray dynamics and droplets’ dispersion is studied for a ... more The effect of turbulence closure on the spray dynamics and droplets’ dispersion is studied for a dilute Acetone spray jet using an Eulerian-Lagrangian approach with two-way coupling. A stochastic random walk methodology is employed to model the liquid droplets’ turbulent dispersion by the gas phase turbulent eddies. Simulations using different turbulence closure models (i.e. the isotropic SST-k-ω, the k-e realizable, and the non-isotropic Reynolds Stress Model (RSM)) are compared with the SP2 Sydney spray jet measurements. The experimental spray droplets inflow mean and rms velocity and size distributions profiles are matched with the different experimental data size bins at every injection time step. The three models shows very good comparisons with better match for the mean and rms profiles using the RSM. The gas flow field turbulence non-isotropy is found to be maximum at the centerline and decreases radially. The results show that turbulence non-isotropy modeling has a strong impact on the droplet’s dynamics. At the centerline, the RSM predicts slower decay rate downstream of the potential core and higher turbulent intensity. The SST-k-ω and k-e models, however, predicted higher droplets’ slip velocity and Reynolds number and consequently higher drag force than the RSM. In the radial direction, away from the centerline, the drag relationship is reversed between the RSM and the k models. The droplets’ tendency for cross-stream dispersion is found to be correlated with the droplet response and drag force, with highest radial dispersion observed at the shear layer location. Memory effect is observed for spray droplets where they lag the gas phase turbulence especially at downstream locations. The study shows the importance of the gas phase turbulence fluctuations modeling on the droplets dispersion and spray dynamics predictions.
... Bekir S. Yilba , Ahmet Z. ahin , Ahmed Z. Al-Garni , Syed AM Said , Zaki Ahmed , BJ Abdulalee... more ... Bekir S. Yilba , Ahmet Z. ahin , Ahmed Z. Al-Garni , Syed AM Said , Zaki Ahmed , BJ Abdulaleem and Muhammad Sami. Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, 31261, Dhahran, Saudi Arabia. ...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1999
Lasers are widely used as a machine tool in the metal industry. One of the important areas of las... more Lasers are widely used as a machine tool in the metal industry. One of the important areas of laser application is surface treatment of engineering metals. To improve the process parameters in the laser heating process, an exploration of the heating mechanism is fruitful. The present study is carried out to develop a three-dimensional model for a laser pulsed heating process using the electron kinetic theory approach. The heating model introduced relies on successive electronphonon collisions; therefore, it is this process that describes the heat conduction mechanism. This study is limited to heat conduction only. Consequently, the phase change process is not taken into account. To validate the theoretical predictions, an experiment is conducted to measure the surface temperature using an optical method. Moreover, a one-dimensional heating model developed previously is also considered and the predictions of three- and one-dimensional heating models as well as experimental results ar...
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
The laser processing of engineering materials requires an in-depth analysis of the applicable hea... more The laser processing of engineering materials requires an in-depth analysis of the applicable heating mechanism. The modelling of the laser heating process offers improved understanding of the machining mechanism. In the present study, a closed-form solution for a step input laser heating pulse is obtained and a numerical scheme solving a three-dimensional heat transfer equation is introduced. The numerical solution provides a comparison of temperature profiles with those obtained from the analytical approach. To validate the analytical and numerical solutions, an experiment is conducted to measure the surface temperature and evaporating front velocity during the Nd—YAG laser heating process. It is found that the temperature profiles resulting from both theory and experiment are in a good agreement. However, a small discrepancy in temperatures at the upper end of the profiles occurs. This may be due to the assumptions made in both the numerical and the analytical approaches. In addi...
ARCHIVE: Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 1989-1996 (vols 203-210), 1996
Laser drilling may improve by proper selection of the laser parameters. One of the important para... more Laser drilling may improve by proper selection of the laser parameters. One of the important parameters in laser hole drilling is the focus setting of the focusing lens. In the present study, the effect of the beam waist position on the resulting hole exit/entry diameter ratio is investigated experimentally. An Nd-YAG laser is used to drill the holes in stainless steel and mild steel sheets at different thicknesses. The study was conducted to include the physical processes involved at different beam waist positions during the drilling operations. It is shown that altering the beam waist positions tends to produce converging and diverging hole walls for negative and positive positions respectively. The drilling improves at a certain beam waist position for a given workpiece thickness.
... NOTATION A, B Constants Cp Specific heat capacity (J/kg K) I Power intensity (W/m2) k Thermal... more ... NOTATION A, B Constants Cp Specific heat capacity (J/kg K) I Power intensity (W/m2) k Thermal conductivity (W/mK) ky Boltzmann's constant L Enthalpy of evaporation (kJ/kg) 53 54 Bekir S. Yilbas et al. ... Int. Commun. Heat Mass Transfer, 20 (1993), 545-55. ...
Lasers find wide applications in industry due to their precision operation and low cost. Laser ma... more Lasers find wide applications in industry due to their precision operation and low cost. Laser machining processes exhibit common characteristics such as heating, melting and evaporation. Modelling of the heating process may enhance understanding of the laser machining process, which in turn minimizes the optimization cost. This study is conducted to explore the laser heating process including evaporation through the
The present study examines the entropy generation during cooling and heating cycles of repetitive... more The present study examines the entropy generation during cooling and heating cycles of repetitive pulsed-laser heating. Two repetitive pulses are introduced in the analysis. The possible thermal integration occurring at the workpiece surface due to repetitive pulse heating is then related to the second-law efficiency of the heating process. It is found that the cooling periods and low intensity decay
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