M. Christolis - Academia.edu (original) (raw)
Papers by M. Christolis
Emissions trading is a scheme whereby companies are allocated allowances for their emissions acco... more Emissions trading is a scheme whereby companies are allocated allowances for their emissions according to the overall environmental ambitions of their governments or authorities-allowances that the companies can subsequently trade with each other. These emission allowances are sometimes called quotas, credits, rights, permits or caps. The sum of all such allowances allocated to all the companies included in the scheme represents the overall limit on emissions allowed by the scheme. It is this overall limit that provides the environmental benefit of the scheme. Trading of emission/discharge limits between polluting facilities is said to be beneficial to the environment, industrial facilities, and to the administration. The trading program
Journal of Loss Prevention in the Process Industries, 2012
This paper presents a systematic hazards identification methodology for liquid hydrocarbon fuel s... more This paper presents a systematic hazards identification methodology for liquid hydrocarbon fuel storage tanks, by applying a checklist technique on the accident causes and the relevant protection measures, in the framework of the SEVESO Directive series. A forum discussion with Greek industrial safety experts has been also organised by the authors in order to locate any lack of the methodology. Results are presented and discussed, and it is concluded that the present hazards assessment methodology helps to identify the major contributors to risk, to improve safety measures and to assist the analysis in these aspects.
International Journal of Heat and Mass Transfer, 2009
The paper presents a Computational Fluid Dynamics (CFD) approach to major – hazard studies, by ap... more The paper presents a Computational Fluid Dynamics (CFD) approach to major – hazard studies, by applying a finite-domain technique to predict the dispersion of combustion products (CO, SO2, smoke, Volatile Organic Compounds, VOC, Polycyclic Aromatic Hydrocarbons, PAH, etc.) from fuel-tank fires, as well as the toxic plume rise.Furthermore, a methodology is presented for the identification of risk zones for the
permitting, Environmental or permit or discharge conditions.
Journal of Hazardous Materials, 2002
The most important characteristic of major chemical industrial accidents is that they have off-si... more The most important characteristic of major chemical industrial accidents is that they have off-site effects from their original location. As a result, the extent and severity of the accident may significantly affect the population of the adjacent areas. In this case, appropriate actions to protect the affected population should be based on rational and quantitative information that would lead to appropriate and efficient decisions. A computer-integrated tool for managing large-scale industrial accidents is an important facility that provides quantitative estimation of the accident consequences and proposes, under the circumstances, a reliable course of actions to be undertaken automatically. On this basis, an operational center for managing largescale industrial accidents is developed. Its architecture involves an integrated framework of GIS and RDBMS technology systems equipped with interactive communication capabilities between peripheral software tools. The operational center was developed in distributed software fashion technology for Windows 98 platforms, focusing to the region of Thriasion Pedion of Attika, where the concentration of industrial activity and storage of toxic chemicals is immense within areas of high population density. An appropriate case study is given in order to illuminate the use and necessity of the operational center.
A k-e turbulence model that accounts for buoyancy effects is used to predict flow and concentrati... more A k-e turbulence model that accounts for buoyancy effects is used to predict flow and concentration fields around a warehouse on fire. A parametric study of the effect of the buoyancy and momentum flux number was made to examine the influence of wind speed on plume lift-off and consequently, on ground clearing. It was found that lift-off occurs at F/U L=0.1 in agreement with the values reported in the literature. The parametric analysis shows the significance of the effect of the inlet boundary conditions on flow and concentration fields.
Journal of Biomechanics, 2006
Petrochemical industries normally use storage tanks containing large amounts of flammable and haz... more Petrochemical industries normally use storage tanks containing large amounts of flammable and hazardous substances. Therefore, the occurrence of a tank fire, such as the large industrial accident on 11th December 2005 at Buncefield Oil Storage Depots, is possible and usually leads to fire and explosions. Experience has shown that the continuous production of black smoke from these fires due to the toxic gases from the combustion process, presents a potential environmental and health problem that is difficult to assess. The goals of the present effort are to estimate the height of the smoke plume, the ground-level concentrations of the toxic pollutants (smoke, SO 2 , CO, PAHs, VOCs) and to characterize risk zones by comparing the ground-level concentrations with existing safety limits. For the application of the numerical procedure developed, an external floating-roof tank has been selected with dimensions of 85 m diameter and 20 m height. Results are presented and discussed. It is concluded that for all scenarios considered, the ground-level concentrations of smoke, SO 2 , CO, PAHs and VOCs do not exceed the safety limit of IDLH and there are no "death zones" due to the pollutant concentrations.
An operational center equipped with a powerful Spatial Information System (SIS ) for managing lar... more An operational center equipped with a powerful Spatial Information System (SIS ) for managing large-scale industrial accidents is an important tool that provides quantitative estimation of the accident consequences and proposes, under the certain circumstances, a reliable course of actions to be undertaken automatically. The heart of the operational center is a central Data Base connected to a cartographic representation
Fire Safety Science, 1994
V = volumetric flow rate (m3s-') w = vertical velocity component (m s-') p = density (kg m-3)
Journal of Biomechanics, 2008
In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably ... more In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably alter blood flow dynamics. CACGs aim at revascularizing pathological arteries according to the human anatomy. However, the exact mechanisms causing the failure of coronary bypass grafting are not yet well elucidated. In the present study, computational fluid dynamics (CFD) techniques are applied for the simulation of multi-branched CACGs under physiologically realistic inflow waveforms. The numerical solution is obtained by a finite-volume method formulated in non-orthogonal, curvilinear coordinates and a multi-grid approach. The geometrical models, consisting of idealized and rigid vessels, include the typical T-and a rather new P-graft configuration. The stenotic effect is also investigated by comparing computational results for three different degrees of area constriction, namely 25%, 50% and 75%, as well as the case without stenosis. Different grafting distances and various inflow rate ratios are imposed, to give an insight into haemodynamical alterations of CACGs and to study the process of restenosis. The results focus on the interaction between the grafts and coronary flows in terms of spatial and temporal variations of velocity and wall shear stress (WSS) distribution. Prominent variations among the different geometries, concerning the velocity profiles and secondary flow motion, are shown. Moreover, the residual flow emerging from different degrees of area constriction shows that low and oscillating shear stresses may arise for even moderate stenotic fields.
Journal of Loss Prevention in The Process Industries - J LOSS PREVENT PROC IND, 2006
This paper deals with the consequence assessment of an open fire incident in a Pesticides Storage... more This paper deals with the consequence assessment of an open fire incident in a Pesticides Storage Facility. Consequences are mainly caused by the atmospheric dispersion of toxic substances produced during the fire and transported downwind to considerable distance. An integrated methodology, based on Computational fluid Dynamics (CFD) techniques and the dimensionless buoyancy flux number, F/U3L, a parameter that can be associated with the flow characteristics, taking advantage of the dynamic similarity of the flow domain, is presented and used for the simulation of the plume dispersion.Rise to the present study gave a real incident, which happened in northern Greece in the beginning of 2004 and constituted the basis for the development of the accident scenarios eventually studied. Owing to the uncertainty in the estimation of source term strength and specifically of the magnitude of the heat released during the incident together with the variation in wind velocity, a parameterization...
Journal of Biomechanics, 2007
This paper presents a comparative study of simulated blood flow in different configurations of si... more This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD)
Journal of Biomechanics, 2008
In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably ... more In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably alter blood flow dynamics. CACGs aim at revascularizing pathological arteries according to the human anatomy. However, the exact mechanisms causing the failure of coronary bypass grafting are not yet well elucidated. In the present study, computational fluid dynamics (CFD) techniques are applied for the simulation of multi-branched CACGs under physiologically realistic inflow waveforms. The numerical solution is obtained by a finite-volume method formulated in non-orthogonal, curvilinear coordinates and a multi-grid approach. The geometrical models, consisting of idealized and rigid vessels, include the typical T-and a rather new P-graft configuration. The stenotic effect is also investigated by comparing computational results for three different degrees of area constriction, namely 25%, 50% and 75%, as well as the case without stenosis. Different grafting distances and various inflow rate ratios are imposed, to give an insight into haemodynamical alterations of CACGs and to study the process of restenosis. The results focus on the interaction between the grafts and coronary flows in terms of spatial and temporal variations of velocity and wall shear stress (WSS) distribution. Prominent variations among the different geometries, concerning the velocity profiles and secondary flow motion, are shown. Moreover, the residual flow emerging from different degrees of area constriction shows that low and oscillating shear stresses may arise for even moderate stenotic fields. r
Journal of Biomechanics, 2007
This paper presents a comparative study of simulated blood flow in different configurations of si... more This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD) model was developed to conduct computer-based studies of simulated blood flow in four different geometric configurations of CACGs, corresponding to routinely used networks in cardiac surgery coronary grafts (T, Y, P and sequential). The flow was assumed three-dimensional, laminar and steady and the fluid as Newtonian, while the vessel walls were considered as inelastic and impermeable. It was concluded that local haemodynamics, practically described by velocity, pressure drop, wall shear stress (WSS) and flow rates, may be strongly influenced by the local geometry, especially at the anastomotic sites. The computations were made at mean flow rates of 37.5, 75 and 150 ml/min. The side-branch outflow rates, computed for each bypass graft, showed noticeable differences. The results, which were found both qualitatively and quantitatively consistent with other studies, indicate that the P-graft exhibits significantly less uniform distribution of outflow rates than the other geometric configurations. Moreover, prominent variations in WSS and velocity distribution among the assessed CACGs were predicted, showing remarkable flow interactions among the arterial branches. The lowest shear stress regions were found on the lateral walls of bifurcations, which are predominantly susceptible to the occurrence of coronary artery disease (CAD). In contrast, the highest WSS were observed at the turn of the arterial branches. r
1 Ακαδημία Αθηνών, Κέντρον Ερεύνης Φυσικής της Ατμοσφαίρας και Κλιματολογίας 2 ΕΜΠ, Σχολή Χημικών... more 1 Ακαδημία Αθηνών, Κέντρον Ερεύνης Φυσικής της Ατμοσφαίρας και Κλιματολογίας 2 ΕΜΠ, Σχολή Χημικών Μηχανικών, Μονάδα Υπολογιστικής Ρευστομηχανικής KEY WORDS: Αστική ατμοσφαιρική ρύπανση, Μετρήσεις αερίων ρύπων, Βόλος Περίληψη Για την αξιολόγηση της ποιότητας του ατμοσφαιρικού αέρα στο Βόλο πραγματοποιήθηκε συστηματική ανάλυση των συνεχών μετρήσεων αερίων ρύπων που κατεγράφησαν κατά τη διάρκεια της διετίας 2001-2002 από τον σταθμό που είναι εγκατεστημένος στο κέντρο του Βόλου. Οι μετρούμενοι αέριοι ρύποι είναι: διοξείδιο του θείου (SΟ2), μονοξείδιο του άνθρακα (CO), διοξείδιο του αζώτου , όζον (O3) και αιωρούμενα σωματίδια (PM10). Εξετάσθηκαν οι ημερήσιες και οι εποχικές διακυμάνσεις καθώς και οι παρατηρούμενες διακυμάνσεις που προέρχονται από τις μεταβολές των ανεμολογικών παραμέτρων (διεύθυνση και ταχύτητα ανέμου). Από την εξέταση προκύπτει ότι αυξημένες τιμές και υπερβάσεις ορίων παρουσιάζουν το όζον και τα αιωρούμενα σωματίδια.
Emissions trading is a scheme whereby companies are allocated allowances for their emissions acco... more Emissions trading is a scheme whereby companies are allocated allowances for their emissions according to the overall environmental ambitions of their governments or authorities-allowances that the companies can subsequently trade with each other. These emission allowances are sometimes called quotas, credits, rights, permits or caps. The sum of all such allowances allocated to all the companies included in the scheme represents the overall limit on emissions allowed by the scheme. It is this overall limit that provides the environmental benefit of the scheme. Trading of emission/discharge limits between polluting facilities is said to be beneficial to the environment, industrial facilities, and to the administration. The trading program
Journal of Loss Prevention in the Process Industries, 2012
This paper presents a systematic hazards identification methodology for liquid hydrocarbon fuel s... more This paper presents a systematic hazards identification methodology for liquid hydrocarbon fuel storage tanks, by applying a checklist technique on the accident causes and the relevant protection measures, in the framework of the SEVESO Directive series. A forum discussion with Greek industrial safety experts has been also organised by the authors in order to locate any lack of the methodology. Results are presented and discussed, and it is concluded that the present hazards assessment methodology helps to identify the major contributors to risk, to improve safety measures and to assist the analysis in these aspects.
International Journal of Heat and Mass Transfer, 2009
The paper presents a Computational Fluid Dynamics (CFD) approach to major – hazard studies, by ap... more The paper presents a Computational Fluid Dynamics (CFD) approach to major – hazard studies, by applying a finite-domain technique to predict the dispersion of combustion products (CO, SO2, smoke, Volatile Organic Compounds, VOC, Polycyclic Aromatic Hydrocarbons, PAH, etc.) from fuel-tank fires, as well as the toxic plume rise.Furthermore, a methodology is presented for the identification of risk zones for the
permitting, Environmental or permit or discharge conditions.
Journal of Hazardous Materials, 2002
The most important characteristic of major chemical industrial accidents is that they have off-si... more The most important characteristic of major chemical industrial accidents is that they have off-site effects from their original location. As a result, the extent and severity of the accident may significantly affect the population of the adjacent areas. In this case, appropriate actions to protect the affected population should be based on rational and quantitative information that would lead to appropriate and efficient decisions. A computer-integrated tool for managing large-scale industrial accidents is an important facility that provides quantitative estimation of the accident consequences and proposes, under the circumstances, a reliable course of actions to be undertaken automatically. On this basis, an operational center for managing largescale industrial accidents is developed. Its architecture involves an integrated framework of GIS and RDBMS technology systems equipped with interactive communication capabilities between peripheral software tools. The operational center was developed in distributed software fashion technology for Windows 98 platforms, focusing to the region of Thriasion Pedion of Attika, where the concentration of industrial activity and storage of toxic chemicals is immense within areas of high population density. An appropriate case study is given in order to illuminate the use and necessity of the operational center.
A k-e turbulence model that accounts for buoyancy effects is used to predict flow and concentrati... more A k-e turbulence model that accounts for buoyancy effects is used to predict flow and concentration fields around a warehouse on fire. A parametric study of the effect of the buoyancy and momentum flux number was made to examine the influence of wind speed on plume lift-off and consequently, on ground clearing. It was found that lift-off occurs at F/U L=0.1 in agreement with the values reported in the literature. The parametric analysis shows the significance of the effect of the inlet boundary conditions on flow and concentration fields.
Journal of Biomechanics, 2006
Petrochemical industries normally use storage tanks containing large amounts of flammable and haz... more Petrochemical industries normally use storage tanks containing large amounts of flammable and hazardous substances. Therefore, the occurrence of a tank fire, such as the large industrial accident on 11th December 2005 at Buncefield Oil Storage Depots, is possible and usually leads to fire and explosions. Experience has shown that the continuous production of black smoke from these fires due to the toxic gases from the combustion process, presents a potential environmental and health problem that is difficult to assess. The goals of the present effort are to estimate the height of the smoke plume, the ground-level concentrations of the toxic pollutants (smoke, SO 2 , CO, PAHs, VOCs) and to characterize risk zones by comparing the ground-level concentrations with existing safety limits. For the application of the numerical procedure developed, an external floating-roof tank has been selected with dimensions of 85 m diameter and 20 m height. Results are presented and discussed. It is concluded that for all scenarios considered, the ground-level concentrations of smoke, SO 2 , CO, PAHs and VOCs do not exceed the safety limit of IDLH and there are no "death zones" due to the pollutant concentrations.
An operational center equipped with a powerful Spatial Information System (SIS ) for managing lar... more An operational center equipped with a powerful Spatial Information System (SIS ) for managing large-scale industrial accidents is an important tool that provides quantitative estimation of the accident consequences and proposes, under the certain circumstances, a reliable course of actions to be undertaken automatically. The heart of the operational center is a central Data Base connected to a cartographic representation
Fire Safety Science, 1994
V = volumetric flow rate (m3s-') w = vertical velocity component (m s-') p = density (kg m-3)
Journal of Biomechanics, 2008
In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably ... more In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably alter blood flow dynamics. CACGs aim at revascularizing pathological arteries according to the human anatomy. However, the exact mechanisms causing the failure of coronary bypass grafting are not yet well elucidated. In the present study, computational fluid dynamics (CFD) techniques are applied for the simulation of multi-branched CACGs under physiologically realistic inflow waveforms. The numerical solution is obtained by a finite-volume method formulated in non-orthogonal, curvilinear coordinates and a multi-grid approach. The geometrical models, consisting of idealized and rigid vessels, include the typical T-and a rather new P-graft configuration. The stenotic effect is also investigated by comparing computational results for three different degrees of area constriction, namely 25%, 50% and 75%, as well as the case without stenosis. Different grafting distances and various inflow rate ratios are imposed, to give an insight into haemodynamical alterations of CACGs and to study the process of restenosis. The results focus on the interaction between the grafts and coronary flows in terms of spatial and temporal variations of velocity and wall shear stress (WSS) distribution. Prominent variations among the different geometries, concerning the velocity profiles and secondary flow motion, are shown. Moreover, the residual flow emerging from different degrees of area constriction shows that low and oscillating shear stresses may arise for even moderate stenotic fields.
Journal of Loss Prevention in The Process Industries - J LOSS PREVENT PROC IND, 2006
This paper deals with the consequence assessment of an open fire incident in a Pesticides Storage... more This paper deals with the consequence assessment of an open fire incident in a Pesticides Storage Facility. Consequences are mainly caused by the atmospheric dispersion of toxic substances produced during the fire and transported downwind to considerable distance. An integrated methodology, based on Computational fluid Dynamics (CFD) techniques and the dimensionless buoyancy flux number, F/U3L, a parameter that can be associated with the flow characteristics, taking advantage of the dynamic similarity of the flow domain, is presented and used for the simulation of the plume dispersion.Rise to the present study gave a real incident, which happened in northern Greece in the beginning of 2004 and constituted the basis for the development of the accident scenarios eventually studied. Owing to the uncertainty in the estimation of source term strength and specifically of the magnitude of the heat released during the incident together with the variation in wind velocity, a parameterization...
Journal of Biomechanics, 2007
This paper presents a comparative study of simulated blood flow in different configurations of si... more This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD)
Journal of Biomechanics, 2008
In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably ... more In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably alter blood flow dynamics. CACGs aim at revascularizing pathological arteries according to the human anatomy. However, the exact mechanisms causing the failure of coronary bypass grafting are not yet well elucidated. In the present study, computational fluid dynamics (CFD) techniques are applied for the simulation of multi-branched CACGs under physiologically realistic inflow waveforms. The numerical solution is obtained by a finite-volume method formulated in non-orthogonal, curvilinear coordinates and a multi-grid approach. The geometrical models, consisting of idealized and rigid vessels, include the typical T-and a rather new P-graft configuration. The stenotic effect is also investigated by comparing computational results for three different degrees of area constriction, namely 25%, 50% and 75%, as well as the case without stenosis. Different grafting distances and various inflow rate ratios are imposed, to give an insight into haemodynamical alterations of CACGs and to study the process of restenosis. The results focus on the interaction between the grafts and coronary flows in terms of spatial and temporal variations of velocity and wall shear stress (WSS) distribution. Prominent variations among the different geometries, concerning the velocity profiles and secondary flow motion, are shown. Moreover, the residual flow emerging from different degrees of area constriction shows that low and oscillating shear stresses may arise for even moderate stenotic fields. r
Journal of Biomechanics, 2007
This paper presents a comparative study of simulated blood flow in different configurations of si... more This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD) model was developed to conduct computer-based studies of simulated blood flow in four different geometric configurations of CACGs, corresponding to routinely used networks in cardiac surgery coronary grafts (T, Y, P and sequential). The flow was assumed three-dimensional, laminar and steady and the fluid as Newtonian, while the vessel walls were considered as inelastic and impermeable. It was concluded that local haemodynamics, practically described by velocity, pressure drop, wall shear stress (WSS) and flow rates, may be strongly influenced by the local geometry, especially at the anastomotic sites. The computations were made at mean flow rates of 37.5, 75 and 150 ml/min. The side-branch outflow rates, computed for each bypass graft, showed noticeable differences. The results, which were found both qualitatively and quantitatively consistent with other studies, indicate that the P-graft exhibits significantly less uniform distribution of outflow rates than the other geometric configurations. Moreover, prominent variations in WSS and velocity distribution among the assessed CACGs were predicted, showing remarkable flow interactions among the arterial branches. The lowest shear stress regions were found on the lateral walls of bifurcations, which are predominantly susceptible to the occurrence of coronary artery disease (CAD). In contrast, the highest WSS were observed at the turn of the arterial branches. r
1 Ακαδημία Αθηνών, Κέντρον Ερεύνης Φυσικής της Ατμοσφαίρας και Κλιματολογίας 2 ΕΜΠ, Σχολή Χημικών... more 1 Ακαδημία Αθηνών, Κέντρον Ερεύνης Φυσικής της Ατμοσφαίρας και Κλιματολογίας 2 ΕΜΠ, Σχολή Χημικών Μηχανικών, Μονάδα Υπολογιστικής Ρευστομηχανικής KEY WORDS: Αστική ατμοσφαιρική ρύπανση, Μετρήσεις αερίων ρύπων, Βόλος Περίληψη Για την αξιολόγηση της ποιότητας του ατμοσφαιρικού αέρα στο Βόλο πραγματοποιήθηκε συστηματική ανάλυση των συνεχών μετρήσεων αερίων ρύπων που κατεγράφησαν κατά τη διάρκεια της διετίας 2001-2002 από τον σταθμό που είναι εγκατεστημένος στο κέντρο του Βόλου. Οι μετρούμενοι αέριοι ρύποι είναι: διοξείδιο του θείου (SΟ2), μονοξείδιο του άνθρακα (CO), διοξείδιο του αζώτου , όζον (O3) και αιωρούμενα σωματίδια (PM10). Εξετάσθηκαν οι ημερήσιες και οι εποχικές διακυμάνσεις καθώς και οι παρατηρούμενες διακυμάνσεις που προέρχονται από τις μεταβολές των ανεμολογικών παραμέτρων (διεύθυνση και ταχύτητα ανέμου). Από την εξέταση προκύπτει ότι αυξημένες τιμές και υπερβάσεις ορίων παρουσιάζουν το όζον και τα αιωρούμενα σωματίδια.