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Papers by Iskender Gokalp

32nd Aerospace Sciences Meeting and Exhibit, Jan 10, 1994

Journal of the Energy Institute, 2020

Canada has the third-largest oil sand reserves in the world as a result of which, it generates co... more Canada has the third-largest oil sand reserves in the world as a result of which, it generates considerable amounts of light gas oil and heavy gas oil through petroleum distillation. With the escalating energy demands, it has become essential to explore alternative fuel resources from biomass and petrochemical residues. This study explores the potential of supercritical water gasification to transform light and heavy gas oils to hydrogen-rich syngas through the optimization of process conditions such as temperature (375e675 C), feed concentration (20e35 wt%) and reaction time (30e75 min). Nickel-supported functionalized carbon nanotubes (10%Ni/FCNT) were synthesized for application in catalytic supercritical water gasification. The functionalization of carbon nanotubes resulted in an increase in their surface area from 108 m 2 /g (in pristine CNT) to 127 m 2 /g (in FCNT) and 122 m 2 /g (in 10%Ni/FCNT). The impregnation of catalytic nickel particles onto carbon nanotubes was confirmed through X-ray diffraction (XDR) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Fouriertransform infrared (FTIR) spectroscopy of both gas oils revealed the presence of aliphatics, alkyl-aryl ethers and sulfur-containing compounds among several other aromatics. Light gas oil revealed higher hydrogen yields of 3.32 mol/kg compared to that of heavy gas oil (2.79 mol/kg) at optimal process conditions, i.e. 675 C and 75 min, 20 wt% feed concentration. However, 10%Ni/FCNT enhanced hydrogen yields (4.46 mol/kg), total gas yield (9.22 mol/kg), hydrogen selectivity (94%) and lower heating value (1685 MJ/kg) of product gases obtained from light gas oil in contrast to heavy gas oil. This study indicates a tremendous potential of gas oils for hydrogen generation via hydrothermal gasification.

HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2020

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Journal of water process engineering, Apr 1, 2021

The main aim of this study is to investigate the usability of the process water obtained from the... more The main aim of this study is to investigate the usability of the process water obtained from the hydrothermal carbonization (HTC) of two different types of biomass waste for microalgae production. In this context, the process waters released as a result of hydrothermal carbonization of olive and orange pomace were diluted in different proportions (50×, 100×, 200×, and 400×) and used in the cultivation of Chlorella minutissima and Botryococcus braunii microalgae. It was observed that the growth rates were higher and the doubling times were shorter at low dilution rates for both microalgae species. The highest growth rate and the shortest doubling time values were found as 0.130 g/L/day and 5.33 day, respectively, for Chlorella minutissima microalgae cultivated in the HTC process water of olive pomace. It was also observed that the process water dilution rate had no specific effect on microalgae biochemical characteristics. It can be concluded that the aqueous phases from HTC of orange and olive pomaces can be a good source of nutrients for different types of microalgae, opening a sustainable, cost effective and environmentally friendly approach for microalgae cultivation and, at the same time, for the cleaning of the otherwise biochemically toxic HTC process waters.

HAL (Le Centre pour la Communication Scientifique Directe), Apr 11, 2007

The aim of the present work is to reduce the burning time of aluminum particles with the ultimate... more The aim of the present work is to reduce the burning time of aluminum particles with the ultimate goal to improve the performances of solid propellants. Aluminium nanoparticles have gained importance because of their increased reactivity as compared with traditional micro-sized particle. Decreasing the size of Al particles increases their specific surface area, and hence decreases the burning time of the same mass of particles. Nevertheless another consequence of decreasing the particle size is an increase of alumina mass fraction in the reactant powders passivated in air. An experimental program is initiated to determine flame propagation velocities of micro-sized (around 6 µm) and nano-sized (around 250 nm) aluminum particle clouds. Another goal of this study is to estimate the gas phase temperature from AlO molecular spectra and the temperature of condensed phase emitters in the flame using emission spectroscopy. To this end, an experimental setup is developed to investigate the flame characteristics of particle clouds ignited by an electric spark in a glass tube. The present results show that nano-sized Al particle clouds burn faster than micro-sized particle clouds for the same global particle mass concentration in air. The cloud flame propagation velocity depends also on the particle concentration. The temperature measurements indicate a consistent value around 2900 K for all nano-Al particle burning clouds and 3300 K for micro-Al particle clouds. The results of the condensed phase temperature show, first a stable temperature and then a decreasing trend along the axis of the flame.

Comptes rendus, Apr 6, 2023

Investigation of cellular instabilities and local extinction for two-phase flames under micrograv... more Investigation of cellular instabilities and local extinction for two-phase flames under microgravity conditions

HAL (Le Centre pour la Communication Scientifique Directe), Sep 4, 2016

This paper reports fundamental studies of two-phase combustion carried out with mono-sized ethano... more This paper reports fundamental studies of two-phase combustion carried out with mono-sized ethanol droplets aerosol generated with rapid expansion under microgravity conditions. Innovative diagnostics consisting of a coupling laser tomography with a high speed ILIDS technique was successfully applied for aerosol combustion. The droplet diameter reduction together with the radial droplet displacement ahead the flame front has been accurately measured. It was found that the fuel droplets evaporate by following a d 2 law which confirms the validity of this model in an aerosol configuration. Average temperatures of the surrounding gas have been extracted from the ILIDS measurements and were found to be near constant, usually in the range of 600−700 K, for any aerosol conditions. The laser tomography technique allows the identification of droplets which cross the flame front and then remain in the burnt gases. An experimental diagram has been built using relevant non-dimensional parameters of two-phase combustion to exhibit the observations of droplets passage. The results demonstrated that the droplet size and the droplet interdistance are the most important parameter which control the possibility for the droplet to enter in the burnt gases. Moreover, it was observed that typical topologies of flames in terms of size and number of cells are related to the number density of droplets.

HAL (Le Centre pour la Communication Scientifique Directe), Jul 2, 2018

arXiv (Cornell University), Dec 28, 2014

We propose a model for assessing the unresolved wrinkling factor in LES of turbulent premixed com... more We propose a model for assessing the unresolved wrinkling factor in LES of turbulent premixed combustion. It relies essentially on a power-law dependence of the wrinkling factor to the filter size and an original expression for the 'active' corrugating strain rate. The latter is written as a product of an efficiency function which accounts for viscous effects and the kinematic constraint of Peters 1 , by a recent expression for the turbulent strain intensity. Yields functional expressions for the fractal dimension and the inner cutoff length scale, the latter being (i) filter-size independent and (ii) consistent with the Damköhler asymptotic behaviours at both large and small Karlovitz numbers. A new expression for the wrinkling factor which incorporates finite Reynolds numbers effects is further proposed. Finally, the model is successfully assessed on an experimental filtered database.

Proceedings of the Combustion Institute, 2017

This paper reports experimental studies of two-phase combustion carried out with an aerosol of mo... more This paper reports experimental studies of two-phase combustion carried out with an aerosol of monosized ethanol droplets generated by rapid expansion under microgravity conditions. Optical diagnostics consisting of coupling laser tomography with the high-speed ILIDS technique are successfully applied for the aerosol combustion study. Droplet diameter reduction together with the radial droplet displacement ahead of the flame front is accurately measured. It is found that fuel droplets evaporate by following the d 2 law which confirms the validity of this model in an aerosol configuration. The laser tomography technique allows the identification of droplets which are present in the burnt gases. A regime diagram has been built using relevant non-dimensional parameters of two-phase combustion to exhibit the observations of droplets crossing. The results demonstrate that the droplet size and the droplet interdistance are the most important parameters which control the possibility for the droplet to penetrate the burnt gases. Moreover, it is observed that typical topologies of flames in terms of size and number of cells are related to the droplet number density.

Combustion and Flame, Jun 1, 1992

An experimental apparatus and strategy have been developed to investigate the influence of turbul... more An experimental apparatus and strategy have been developed to investigate the influence of turbulence on the global mass transfer rates from fuel droplets. Heptane and decane droplets suspended in grid-induced turbulent flows have been investigated in the regime where the integral length scales of turbulence are, on average, 5 times larger than the initial droplet diameter. The turbulence intensity has been increased up to 44%. A new mass transfer parameter that distinguishes between the influences of the mean relative velocity and those of turbulence structure has been introduced. Mass transfer from heptane droplets has been found to be insensitive to turbulence. The same turbulence conditions, however, exert a significant influence on the mass transfer from decane droplets. It is shown that the influence of turbulence on the mass transfer from decane droplets can be correlated by a turbulence Reynolds number. The Fr/Jssling coefficient is found to increase with the turbulence intensity. The differences in the sensitivity of heptane and decane droplets to the turbulence influence on mass transfer are tentatively explained by introducing a "vaporization Damk6hler number." The present experimental results suggest that turbulence enhances the mass transfer from liquid droplets only for low values of this number.

34th Aerospace Sciences Meeting and Exhibit, 1996

Optimised combustion in atmospheric induction burners of gas stove units is determined by the qua... more Optimised combustion in atmospheric induction burners of gas stove units is determined by the quality of the mixing and the structure of the dynamic field. These parameters are fixed by the geometry of the burner and also the excess momentum of the jet which creates an entrainment force. Velocity measurements (LDA and PIV) are performed on different jet configurations, from free to confined impinging jets. The effect of the confinement ratio, impinging distance, and of the density ratio are discussed and compared with the real domestic burner configuration. The flow field inside an atmospheric induction burner was found to be well described by a confined impinging axisymmetric jet, either turbulent or laminar, depending on the flow rate injected. The main parameters influencing the entrainment process are the density ratio and the distance to the stagnation plate. An optimum is deduced for a distance around ten jet diameters and light jets appear to drive more air than isodensity je...

Symposium (International) on Combustion, 1992

ABSTRACT

32nd Aerospace Sciences Meeting and Exhibit, Jan 10, 1994

Journal of the Energy Institute, 2020

Canada has the third-largest oil sand reserves in the world as a result of which, it generates co... more Canada has the third-largest oil sand reserves in the world as a result of which, it generates considerable amounts of light gas oil and heavy gas oil through petroleum distillation. With the escalating energy demands, it has become essential to explore alternative fuel resources from biomass and petrochemical residues. This study explores the potential of supercritical water gasification to transform light and heavy gas oils to hydrogen-rich syngas through the optimization of process conditions such as temperature (375e675 C), feed concentration (20e35 wt%) and reaction time (30e75 min). Nickel-supported functionalized carbon nanotubes (10%Ni/FCNT) were synthesized for application in catalytic supercritical water gasification. The functionalization of carbon nanotubes resulted in an increase in their surface area from 108 m 2 /g (in pristine CNT) to 127 m 2 /g (in FCNT) and 122 m 2 /g (in 10%Ni/FCNT). The impregnation of catalytic nickel particles onto carbon nanotubes was confirmed through X-ray diffraction (XDR) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Fouriertransform infrared (FTIR) spectroscopy of both gas oils revealed the presence of aliphatics, alkyl-aryl ethers and sulfur-containing compounds among several other aromatics. Light gas oil revealed higher hydrogen yields of 3.32 mol/kg compared to that of heavy gas oil (2.79 mol/kg) at optimal process conditions, i.e. 675 C and 75 min, 20 wt% feed concentration. However, 10%Ni/FCNT enhanced hydrogen yields (4.46 mol/kg), total gas yield (9.22 mol/kg), hydrogen selectivity (94%) and lower heating value (1685 MJ/kg) of product gases obtained from light gas oil in contrast to heavy gas oil. This study indicates a tremendous potential of gas oils for hydrogen generation via hydrothermal gasification.

HAL (Le Centre pour la Communication Scientifique Directe), Jun 5, 2020

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Journal of water process engineering, Apr 1, 2021

The main aim of this study is to investigate the usability of the process water obtained from the... more The main aim of this study is to investigate the usability of the process water obtained from the hydrothermal carbonization (HTC) of two different types of biomass waste for microalgae production. In this context, the process waters released as a result of hydrothermal carbonization of olive and orange pomace were diluted in different proportions (50×, 100×, 200×, and 400×) and used in the cultivation of Chlorella minutissima and Botryococcus braunii microalgae. It was observed that the growth rates were higher and the doubling times were shorter at low dilution rates for both microalgae species. The highest growth rate and the shortest doubling time values were found as 0.130 g/L/day and 5.33 day, respectively, for Chlorella minutissima microalgae cultivated in the HTC process water of olive pomace. It was also observed that the process water dilution rate had no specific effect on microalgae biochemical characteristics. It can be concluded that the aqueous phases from HTC of orange and olive pomaces can be a good source of nutrients for different types of microalgae, opening a sustainable, cost effective and environmentally friendly approach for microalgae cultivation and, at the same time, for the cleaning of the otherwise biochemically toxic HTC process waters.

HAL (Le Centre pour la Communication Scientifique Directe), Apr 11, 2007

The aim of the present work is to reduce the burning time of aluminum particles with the ultimate... more The aim of the present work is to reduce the burning time of aluminum particles with the ultimate goal to improve the performances of solid propellants. Aluminium nanoparticles have gained importance because of their increased reactivity as compared with traditional micro-sized particle. Decreasing the size of Al particles increases their specific surface area, and hence decreases the burning time of the same mass of particles. Nevertheless another consequence of decreasing the particle size is an increase of alumina mass fraction in the reactant powders passivated in air. An experimental program is initiated to determine flame propagation velocities of micro-sized (around 6 µm) and nano-sized (around 250 nm) aluminum particle clouds. Another goal of this study is to estimate the gas phase temperature from AlO molecular spectra and the temperature of condensed phase emitters in the flame using emission spectroscopy. To this end, an experimental setup is developed to investigate the flame characteristics of particle clouds ignited by an electric spark in a glass tube. The present results show that nano-sized Al particle clouds burn faster than micro-sized particle clouds for the same global particle mass concentration in air. The cloud flame propagation velocity depends also on the particle concentration. The temperature measurements indicate a consistent value around 2900 K for all nano-Al particle burning clouds and 3300 K for micro-Al particle clouds. The results of the condensed phase temperature show, first a stable temperature and then a decreasing trend along the axis of the flame.

Comptes rendus, Apr 6, 2023

Investigation of cellular instabilities and local extinction for two-phase flames under micrograv... more Investigation of cellular instabilities and local extinction for two-phase flames under microgravity conditions

HAL (Le Centre pour la Communication Scientifique Directe), Sep 4, 2016

This paper reports fundamental studies of two-phase combustion carried out with mono-sized ethano... more This paper reports fundamental studies of two-phase combustion carried out with mono-sized ethanol droplets aerosol generated with rapid expansion under microgravity conditions. Innovative diagnostics consisting of a coupling laser tomography with a high speed ILIDS technique was successfully applied for aerosol combustion. The droplet diameter reduction together with the radial droplet displacement ahead the flame front has been accurately measured. It was found that the fuel droplets evaporate by following a d 2 law which confirms the validity of this model in an aerosol configuration. Average temperatures of the surrounding gas have been extracted from the ILIDS measurements and were found to be near constant, usually in the range of 600−700 K, for any aerosol conditions. The laser tomography technique allows the identification of droplets which cross the flame front and then remain in the burnt gases. An experimental diagram has been built using relevant non-dimensional parameters of two-phase combustion to exhibit the observations of droplets passage. The results demonstrated that the droplet size and the droplet interdistance are the most important parameter which control the possibility for the droplet to enter in the burnt gases. Moreover, it was observed that typical topologies of flames in terms of size and number of cells are related to the number density of droplets.

HAL (Le Centre pour la Communication Scientifique Directe), Jul 2, 2018

arXiv (Cornell University), Dec 28, 2014

We propose a model for assessing the unresolved wrinkling factor in LES of turbulent premixed com... more We propose a model for assessing the unresolved wrinkling factor in LES of turbulent premixed combustion. It relies essentially on a power-law dependence of the wrinkling factor to the filter size and an original expression for the 'active' corrugating strain rate. The latter is written as a product of an efficiency function which accounts for viscous effects and the kinematic constraint of Peters 1 , by a recent expression for the turbulent strain intensity. Yields functional expressions for the fractal dimension and the inner cutoff length scale, the latter being (i) filter-size independent and (ii) consistent with the Damköhler asymptotic behaviours at both large and small Karlovitz numbers. A new expression for the wrinkling factor which incorporates finite Reynolds numbers effects is further proposed. Finally, the model is successfully assessed on an experimental filtered database.

Proceedings of the Combustion Institute, 2017

This paper reports experimental studies of two-phase combustion carried out with an aerosol of mo... more This paper reports experimental studies of two-phase combustion carried out with an aerosol of monosized ethanol droplets generated by rapid expansion under microgravity conditions. Optical diagnostics consisting of coupling laser tomography with the high-speed ILIDS technique are successfully applied for the aerosol combustion study. Droplet diameter reduction together with the radial droplet displacement ahead of the flame front is accurately measured. It is found that fuel droplets evaporate by following the d 2 law which confirms the validity of this model in an aerosol configuration. The laser tomography technique allows the identification of droplets which are present in the burnt gases. A regime diagram has been built using relevant non-dimensional parameters of two-phase combustion to exhibit the observations of droplets crossing. The results demonstrate that the droplet size and the droplet interdistance are the most important parameters which control the possibility for the droplet to penetrate the burnt gases. Moreover, it is observed that typical topologies of flames in terms of size and number of cells are related to the droplet number density.

Combustion and Flame, Jun 1, 1992

An experimental apparatus and strategy have been developed to investigate the influence of turbul... more An experimental apparatus and strategy have been developed to investigate the influence of turbulence on the global mass transfer rates from fuel droplets. Heptane and decane droplets suspended in grid-induced turbulent flows have been investigated in the regime where the integral length scales of turbulence are, on average, 5 times larger than the initial droplet diameter. The turbulence intensity has been increased up to 44%. A new mass transfer parameter that distinguishes between the influences of the mean relative velocity and those of turbulence structure has been introduced. Mass transfer from heptane droplets has been found to be insensitive to turbulence. The same turbulence conditions, however, exert a significant influence on the mass transfer from decane droplets. It is shown that the influence of turbulence on the mass transfer from decane droplets can be correlated by a turbulence Reynolds number. The Fr/Jssling coefficient is found to increase with the turbulence intensity. The differences in the sensitivity of heptane and decane droplets to the turbulence influence on mass transfer are tentatively explained by introducing a "vaporization Damk6hler number." The present experimental results suggest that turbulence enhances the mass transfer from liquid droplets only for low values of this number.

34th Aerospace Sciences Meeting and Exhibit, 1996

Optimised combustion in atmospheric induction burners of gas stove units is determined by the qua... more Optimised combustion in atmospheric induction burners of gas stove units is determined by the quality of the mixing and the structure of the dynamic field. These parameters are fixed by the geometry of the burner and also the excess momentum of the jet which creates an entrainment force. Velocity measurements (LDA and PIV) are performed on different jet configurations, from free to confined impinging jets. The effect of the confinement ratio, impinging distance, and of the density ratio are discussed and compared with the real domestic burner configuration. The flow field inside an atmospheric induction burner was found to be well described by a confined impinging axisymmetric jet, either turbulent or laminar, depending on the flow rate injected. The main parameters influencing the entrainment process are the density ratio and the distance to the stagnation plate. An optimum is deduced for a distance around ten jet diameters and light jets appear to drive more air than isodensity je...

Symposium (International) on Combustion, 1992

ABSTRACT