Demos T Tsahalis | University of Patras (original) (raw)
Papers by Demos T Tsahalis
A one-dimensional, water dispersion model for rivers, RIDIS, i.e., River Dispersion, has been dev... more A one-dimensional, water dispersion model for rivers, RIDIS, i.e., River Dispersion, has been developed and is presented in this paper. It requires a minimum of input data and predicts the temporal and spatial distribution of the concentration of a soluble product accidentally discharged to a river. The model has been coded in FORTAN IV PLUS designed to run on Shell’s Information Center IBM 370/158 computer accessed through the Time Sharing Computer System, CMS. A user with basic knowledge of operating the CMS remote, portable terminal can successfully operate the model, written in conversational mode, and interpret the resulting output data.
Active Control in Mechanical Engineering, 2021
Anemia in pregnancy is a condition of pregnant woman with hemoglobin (Hb) <11 gr% in the first an... more Anemia in pregnancy is a condition of pregnant woman with hemoglobin (Hb) <11 gr% in the first and third trimesters while in the second trimester hemoglobin level <10,5 gr%. This study aims to determined the factors of the occurrence of anemia in third trimester pregnant women in Kampung Melayu sub-district Bengkulu City 2017.This research uses Analytical Survey design with Cross Sectional Approach. Population in this research is third trimester pregnant woman in Kampung Melayu sub-district as many as 106 people, using sample total sampling technique. The analysis used Chi square test with significance level p <0,05.The results of this study indicate that there is a relationship between adherence of Fe (p = 0,000) and knowledge (p = 0,000) with anemia occurrence in third trimester pregnant women, no relationship between age (p = 0,346), parity (p = 0,949) , Education (p = 0.198), occupation (p = 1,000) with anemia and the most dominant factor with anemia was the consumption of Fe tablet (OR = 78,803).Health workers are expected to provide routine counseling on the causes, symptoms, and effects of anemia for pregnant women and screening anemia by checking Hb at least twice during pregnancy.
International Journal of Low-Carbon Technologies, 2007
The objective of this paper is to present a theoretical investigation of the operational characte... more The objective of this paper is to present a theoretical investigation of the operational characteristics on a small-scale Capillary Pump Loop (CPL), focused on the CPL capacity to create flow in addition to its heat transfer capacity. A typical design of a CPL is composed of a capillary evaporator, a condenser, a two-phase reservoir, liquid and vapour lines. The capillary evaporator generates the required pressure pumping for moving the working fluid from the condenser to the evaporator section. The fundamental principles of the proposed modelling are: The overall pressure drop in the loop must be less than the maximum capillary pressure in order to ensure that the system will operate continuously. The major components of the CPL pressure drop are related to the flow in the wick structure, condenser, vapour and liquid lines. The wick structure present in the evaporator causes a flow restriction that affects the CPL performance, which is dependent on the wick permeability, a property of the porous material that describes its ability to transport the liquid under an applied pressure gradient. An experimental lab-scale installation is used for the validation of the theoretical analysis. The results showed that the proposed CPL modelling is able to describe the CPL performance very well.
ABSTRACT This article is focused on the development of a finite element model for capturing the f... more ABSTRACT This article is focused on the development of a finite element model for capturing the fluid-structure interactions in a hybrid electro-hydraulic pump system. The system under study consists of a piezo-actuated piston and two passive poppet valves. A Finite Element Model has been developed which simulates the oscillatory fluid motion (compressible Navier–Stokes equations with standard k-e turbulence extensions) and incorporates an Arbitrary Lagrangian–Eulerian formulation to allow a deforming moving mesh. Through this moving mesh the fluid is capable of tracking the motion of the piston and valves, while a two-way interaction is applied to the surrounding rigid structure. The fluid pressure profile surrounding the solid regions is applied as a force load to the solid and the solid motion is transferred to the fluid domain as a mesh deformation. The simulation results offer useful insight on the pump’s performance caused by changes in the: a) valves’ spring stiffness and mass, and b) piston’s operating frequency. A careful parametric optimization on certain pump’s parameters yields a twofold increase in its performance at high frequencies (500 Hz)
Aircraft Engineering and Aerospace Technology, 2000
In order to achieve maximum noise reduction inside an aircraft cabin through the use of an active... more In order to achieve maximum noise reduction inside an aircraft cabin through the use of an active noise control system (ANCS), it is important that the number and positions of the sensors for monitoring the noise field; the control system for driving the actuators; and the number and positions of the actuators that generate the secondary noise field, which partially cancels the primary noise field, must be optimally determined. An optimization strategy for the positioning of the actuators, based on genetic algorithms (GA), is presented, assuming a fixed sensor configuration and a given control system. The application of the developed GA to a propeller aircraft is also discussed. The work presented was performed under the CEC BRITE/EURAM‐Aeronautics project “ASANCA”, in which a demonstrator ANCS was developed.
International Journal of Low-Carbon Technologies, 2014
6th Fluid and PlasmaDynamics Conference, 1973
14th Mediterranean Conference on Control and Automation, MED'06, 2006
In this article, an adaptive width/phase differential modulated controller is designed for an act... more In this article, an adaptive width/phase differential modulated controller is designed for an active electro-hydraulic pump (AehP) system consisting of a single straight cylinder. This controller adjusts the duty cycle and relative phase between the incoming and outgoing valve. The adjustment relies on the maximization of a cost function that characterizes the net outflow rate. The developed model relies on
International Journal of Low-Carbon Technologies, 2013
Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for... more Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
In this article, an adaptive width/phase differential modulated controller is designed for an act... more In this article, an adaptive width/phase differential modulated controller is designed for an active electro-hydraulic pump (AehP) system. The controller adjusts the duty cycle and relative phase between the incoming and outgoing valve. The adjustment relies on the maximization of a multiparametric cost function which is comprised of the net outflow rate, the energy delivered by the piston to the fluid and the maximum pressure evaluated on the piston surface. The developed model relies on computational fluid dynamics (CFD). Transient CFD analysis shows that the pressure propagation causes the pump performance to be highly dependent to the overall dimensions of the hydraulic system, the fluid's properties and the operating conditions, thus constraining and complicating the controller design process. The controller's adaptation mechanism relies on the cyclic coordinate method, which adjusts each parameter in a periodic manner. Simulation studies are used to investigate the e...
International Journal of Low-Carbon Technologies, 2007
This paper describes the development of an experimental setup to investigate the performance of h... more This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a brief description of the experimental setup that was constructed and a description of the experimental procedure that was followed will be given together with some results that were obtained for various configurations.
International Journal of Low-Carbon Technologies, 2013
Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for... more Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
This paper describes the development of an experimental setup to investigate the performance of h... more This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a...
The SEATTLER solar power plant, consisting of a tall tower where the atmospheric air is heated by... more The SEATTLER solar power plant, consisting of a tall tower where the atmospheric air is heated by a heliostat array through a solar receiver and drives an air turbine by the new mechanism of cold air gravity draught, is modeled into a mathematical integral equivalent. The all-air working fluid principle is proposed as the result of an encouraging previous, small scale research sponsored by the CNCSIS Grant No. 27642 of 14 March 2005 in Romania. The presented numerical investigation on the model is targeted towards demonstrating the feasibility and efficiency of the all-air system at full scale. The natural peculiarities of the solar tower systems are connected to their small working pressures and, in the present case, to the medium working temperatures in particular. At the same time, air enthalpy capture efficiencies between 65% and 80% are known within the SOLAIR project in Spain, while the SEATTLER efficiency could go much further. The alternative here evoked is focused on prelim...
A one-dimensional, water dispersion model for rivers, RIDIS, i.e., River Dispersion, has been dev... more A one-dimensional, water dispersion model for rivers, RIDIS, i.e., River Dispersion, has been developed and is presented in this paper. It requires a minimum of input data and predicts the temporal and spatial distribution of the concentration of a soluble product accidentally discharged to a river. The model has been coded in FORTAN IV PLUS designed to run on Shell’s Information Center IBM 370/158 computer accessed through the Time Sharing Computer System, CMS. A user with basic knowledge of operating the CMS remote, portable terminal can successfully operate the model, written in conversational mode, and interpret the resulting output data.
Active Control in Mechanical Engineering, 2021
Anemia in pregnancy is a condition of pregnant woman with hemoglobin (Hb) <11 gr% in the first an... more Anemia in pregnancy is a condition of pregnant woman with hemoglobin (Hb) <11 gr% in the first and third trimesters while in the second trimester hemoglobin level <10,5 gr%. This study aims to determined the factors of the occurrence of anemia in third trimester pregnant women in Kampung Melayu sub-district Bengkulu City 2017.This research uses Analytical Survey design with Cross Sectional Approach. Population in this research is third trimester pregnant woman in Kampung Melayu sub-district as many as 106 people, using sample total sampling technique. The analysis used Chi square test with significance level p <0,05.The results of this study indicate that there is a relationship between adherence of Fe (p = 0,000) and knowledge (p = 0,000) with anemia occurrence in third trimester pregnant women, no relationship between age (p = 0,346), parity (p = 0,949) , Education (p = 0.198), occupation (p = 1,000) with anemia and the most dominant factor with anemia was the consumption of Fe tablet (OR = 78,803).Health workers are expected to provide routine counseling on the causes, symptoms, and effects of anemia for pregnant women and screening anemia by checking Hb at least twice during pregnancy.
International Journal of Low-Carbon Technologies, 2007
The objective of this paper is to present a theoretical investigation of the operational characte... more The objective of this paper is to present a theoretical investigation of the operational characteristics on a small-scale Capillary Pump Loop (CPL), focused on the CPL capacity to create flow in addition to its heat transfer capacity. A typical design of a CPL is composed of a capillary evaporator, a condenser, a two-phase reservoir, liquid and vapour lines. The capillary evaporator generates the required pressure pumping for moving the working fluid from the condenser to the evaporator section. The fundamental principles of the proposed modelling are: The overall pressure drop in the loop must be less than the maximum capillary pressure in order to ensure that the system will operate continuously. The major components of the CPL pressure drop are related to the flow in the wick structure, condenser, vapour and liquid lines. The wick structure present in the evaporator causes a flow restriction that affects the CPL performance, which is dependent on the wick permeability, a property of the porous material that describes its ability to transport the liquid under an applied pressure gradient. An experimental lab-scale installation is used for the validation of the theoretical analysis. The results showed that the proposed CPL modelling is able to describe the CPL performance very well.
ABSTRACT This article is focused on the development of a finite element model for capturing the f... more ABSTRACT This article is focused on the development of a finite element model for capturing the fluid-structure interactions in a hybrid electro-hydraulic pump system. The system under study consists of a piezo-actuated piston and two passive poppet valves. A Finite Element Model has been developed which simulates the oscillatory fluid motion (compressible Navier–Stokes equations with standard k-e turbulence extensions) and incorporates an Arbitrary Lagrangian–Eulerian formulation to allow a deforming moving mesh. Through this moving mesh the fluid is capable of tracking the motion of the piston and valves, while a two-way interaction is applied to the surrounding rigid structure. The fluid pressure profile surrounding the solid regions is applied as a force load to the solid and the solid motion is transferred to the fluid domain as a mesh deformation. The simulation results offer useful insight on the pump’s performance caused by changes in the: a) valves’ spring stiffness and mass, and b) piston’s operating frequency. A careful parametric optimization on certain pump’s parameters yields a twofold increase in its performance at high frequencies (500 Hz)
Aircraft Engineering and Aerospace Technology, 2000
In order to achieve maximum noise reduction inside an aircraft cabin through the use of an active... more In order to achieve maximum noise reduction inside an aircraft cabin through the use of an active noise control system (ANCS), it is important that the number and positions of the sensors for monitoring the noise field; the control system for driving the actuators; and the number and positions of the actuators that generate the secondary noise field, which partially cancels the primary noise field, must be optimally determined. An optimization strategy for the positioning of the actuators, based on genetic algorithms (GA), is presented, assuming a fixed sensor configuration and a given control system. The application of the developed GA to a propeller aircraft is also discussed. The work presented was performed under the CEC BRITE/EURAM‐Aeronautics project “ASANCA”, in which a demonstrator ANCS was developed.
International Journal of Low-Carbon Technologies, 2014
6th Fluid and PlasmaDynamics Conference, 1973
14th Mediterranean Conference on Control and Automation, MED'06, 2006
In this article, an adaptive width/phase differential modulated controller is designed for an act... more In this article, an adaptive width/phase differential modulated controller is designed for an active electro-hydraulic pump (AehP) system consisting of a single straight cylinder. This controller adjusts the duty cycle and relative phase between the incoming and outgoing valve. The adjustment relies on the maximization of a cost function that characterizes the net outflow rate. The developed model relies on
International Journal of Low-Carbon Technologies, 2013
Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for... more Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
In this article, an adaptive width/phase differential modulated controller is designed for an act... more In this article, an adaptive width/phase differential modulated controller is designed for an active electro-hydraulic pump (AehP) system. The controller adjusts the duty cycle and relative phase between the incoming and outgoing valve. The adjustment relies on the maximization of a multiparametric cost function which is comprised of the net outflow rate, the energy delivered by the piston to the fluid and the maximum pressure evaluated on the piston surface. The developed model relies on computational fluid dynamics (CFD). Transient CFD analysis shows that the pressure propagation causes the pump performance to be highly dependent to the overall dimensions of the hydraulic system, the fluid's properties and the operating conditions, thus constraining and complicating the controller design process. The controller's adaptation mechanism relies on the cyclic coordinate method, which adjusts each parameter in a periodic manner. Simulation studies are used to investigate the e...
International Journal of Low-Carbon Technologies, 2007
This paper describes the development of an experimental setup to investigate the performance of h... more This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a brief description of the experimental setup that was constructed and a description of the experimental procedure that was followed will be given together with some results that were obtained for various configurations.
International Journal of Low-Carbon Technologies, 2013
Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for... more Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
This paper describes the development of an experimental setup to investigate the performance of h... more This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a...
The SEATTLER solar power plant, consisting of a tall tower where the atmospheric air is heated by... more The SEATTLER solar power plant, consisting of a tall tower where the atmospheric air is heated by a heliostat array through a solar receiver and drives an air turbine by the new mechanism of cold air gravity draught, is modeled into a mathematical integral equivalent. The all-air working fluid principle is proposed as the result of an encouraging previous, small scale research sponsored by the CNCSIS Grant No. 27642 of 14 March 2005 in Romania. The presented numerical investigation on the model is targeted towards demonstrating the feasibility and efficiency of the all-air system at full scale. The natural peculiarities of the solar tower systems are connected to their small working pressures and, in the present case, to the medium working temperatures in particular. At the same time, air enthalpy capture efficiencies between 65% and 80% are known within the SOLAIR project in Spain, while the SEATTLER efficiency could go much further. The alternative here evoked is focused on prelim...