The Experts below are selected from a list of 9864 Experts worldwide ranked by ideXlab platform
A. Baïri - One of the best experts on this subject based on the ideXlab platform.
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free convection in parallelogram shaped enclosures with isothermal active walls Viscous Shear Stress in active systems
Fluid Dynamics Research, 2012Co-Authors: A. Baïri, E Zarcopernia, Jm Garcia De Maria, Najib LaraqiAbstract:Thermocouples are often used for thermoregulation of active thermal systems. When the junctions of these sensors are under a natural convection flow, it is necessary to take into account the Viscous Stress that can affect the measurement of temperature and therefore the regulation set points. The main objective of this work is to study the Viscous Shear Stress taking place close to the active hot wall in closed air-filled cavities of parallelogrammic shape. The influence of Shear Stress is examined for different inclination angles of the cavity and large Rayleigh numbers which are usual in thermal applications. The local Stress distributions are presented for the steady state for all the geometric configurations considered. The Nusselt number at the hot wall as well as the temperature and stream function distributions in the cavities are also included. The findings obtained from the numerical simulation using the finite volume method are validated by thermal measurements on an experimental cavity. This study confirms the need to properly choose the location of thermocouples in the reference cell used for controlling the active system.
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effects of Viscous Shear Stress on thermoregulation of electronics transient free convection in diode enclosures induced by discrete heat bands under constant heat flux
Applied Thermal Engineering, 2011Co-Authors: A. BaïriAbstract:Abstract Thermal and dynamic phenomena that occur in the immediate vicinity of electronic components during operation generate Viscous Shear Stresses due to velocity gradients. When thermocouples used for thermal regulation of these assemblies are installed in this environment, temperature measurements may be erroneous. It is therefore essential to take into account Viscous effects in the boundary layer when dealing with thermal control of electronics subjected to natural convection. These phenomena are particularly pronounced and complex when generation of heat at the active wall is not uniform. That is the case for the real device treated in this work. The natural convective flow is generated by a vertical wall composed by alternated adiabatic and heated bands under constant heat flux, representing a working electronic equipment. The 2D transient boundary layer near the vertical active hot wall of parallelogram-shaped enclosures is treated in order to determine the Viscous Shear Stress. Results are obtained by numerical approach using the finite volume method and some measurements. Many geometrical configurations are treated while varying the inclination angle of the top and bottom passive adiabatic walls. The very different local distributions of Viscous Shear Stresses and vertical thermal gradients confirm the necessity to take them into account to properly install the sensors used for thermoregulation.
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Effects of Viscous Shear Stress on thermoregulation of electronics. Transient free convection in diode enclosures induced by discrete heat bands under constant heat flux
Applied Thermal Engineering, 2011Co-Authors: A. BaïriAbstract:Thermal and dynamic phenomena that occur in the immediate vicinity of electronic components during operation generate Viscous Shear Stresses due to velocity gradients. When thermocouples used for thermal regulation of these assemblies are installed in this environment, temperature measurements may be erroneous. It is therefore essential to take into account Viscous effects in the boundary layer when dealing with thermal control of electronics subjected to natural convection. These phenomena are particularly pronounced and complex when generation of heat at the active wall is not uniform. That is the case for the real device treated in this work. The natural convective flow is generated by a vertical wall composed by alternated adiabatic and heated bands under constant heat flux, representing a working electronic equipment. The 2D transient boundary layer near the vertical active hot wall of parallelogram-shaped enclosures is treated in order to determine the Viscous Shear Stress. Results are obtained by numerical approach using the finite volume method. Many geometrical configurations are treated while varying the inclination angle of the top and bottom passive adiabatic walls. The very different local distributions of Viscous Shear Stresses and vertical thermal gradients confirm the necessity to take them into account to properly install the sensors used for thermoregulation.
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thermoregulation of electronics inside diode enclosures Viscous Shear Stress in 2d natural convection generated by isothermal active walls
International Conference on Communications, 2011Co-Authors: A. Baïri, E Zarcopernia, Najib Laraqi, I Bairi, J Garcia M De Maria, Bravo A MaloAbstract:Correct operation of electronic assemblies is subject to their regulation in the temperature range recommended by manufacturers. It is therefore necessary to control the heat exchange phenomena that affect them. When thermoregulation of these assemblies is based on thermocouples, the effects of fluid flow on the junctions of these sensors must be considered, particularly the thermal and velocity gradients. This prevents measurement errors that can be detrimental to the proper functioning of the equipment. The main objective of this study concerns the examination of the Viscous Stresses that occur by natural convection in parallelogram-shaped cavities containing electronic equipments. These enclosures, called diode cavities in the convective heat transfer sense, lead to very different flows depending on the geometry. Many geometrical configurations are treated while varying the inclination angle of the top and bottom passive adiabatic walls. A detailed study of the boundary layer is used to find the distribution of Viscous Shear Stresses and the heat exchanged by natural convection through the Nusselt number. The numerical approach is made using the finite volume method. The results are confirmed by previous numerical and experimental works, and allow to better control thermoregulation of electronic assemblies by means of thermocouples.
F. Laadhari - One of the best experts on this subject based on the ideXlab platform.
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On the evolution of maximum turbulent kinetic energy production in a channel flow
Physics of Fluids, 2002Co-Authors: F. LaadhariAbstract:The Reynolds number effects on turbulent kinetic energy production and mean transport terms in near-wall turbulent channel flow are investigated analytically and with the help of direct numerical simulations ͑DNS͒. Using the momentum equation for turbulent channel flow, an analytical expression for the envelope of turbulent kinetic energy production curves is derived. It is shown that this envelope coincides with the wall-normal position at which the turbulent and Viscous Shear Stress are equal. The DNS results carried out corroborate this finding and assess other quantitative details, namely the evolution of the peak of kinetic energy production and of its wall-normal position in terms of the Reynolds number. Empirical relations for the envelopes of the mean momentum transport terms and for their extrema position are also derived.
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On the evolution of maximum turbulent kinetic energy production in a channel flow
Physics of Fluids, 2002Co-Authors: F. LaadhariAbstract:The Reynolds number effects on turbulent kinetic energy production and mean transport terms in near-wall turbulent channel flow are investigated analytically and with the help of direct numerical simulations (DNS). Using the momentum equation for turbulent channel flow, an analytical expression for the envelope of turbulent kinetic energy production curves is derived. It is shown that this envelope coincides with the wall-normal position at which the turbulent and Viscous Shear Stress are equal. The DNS results carried out corroborate this finding and assess other quantitative details, namely the evolution of the peak of kinetic energy production and of its wall-normal position in terms of the Reynolds number. Empirical relations for the envelopes of the mean momentum transport terms and for their extrema position are also derived.
Markus Bussmann - One of the best experts on this subject based on the ideXlab platform.
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oil particle separation in a falling sphere configuration effect of viscosity ratio interfacial tension
International Journal of Multiphase Flow, 2018Co-Authors: Sasan Mehrabian, Edgar Acosta, Markus BussmannAbstract:Abstract The separation of oil from a single oil-coated spherical particle falling through an aqueous solution is evaluated as a function of viscosity ratio and interfacial tension. A solvent was used to modify the viscosity of the oil and a surfactant was used to modify the interfacial tension. The separation process is characterized with respect to a capillary number (ratio of Viscous Shear Stress to interfacial tension) and the viscosity ratio (between the oil phase and the aqueous solution). The separation of oil from the falling sphere can be described as a two-stage process. The first stage is the deformation of the oil film coating the sphere, leading to the formation of a thread or “tail” downstream of the particle. The second stage involves the breakup of that tail as the sphere falls. The initial film deformation and tail formation is best described by a capillary number based on the Shear rate at the oil-water interface; and the tail breakup by the rate of elongation experienced by the tail. More oil is removed when thicker tails are formed, which are obtained at high viscosity ratios. However, high viscosity ratios require longer Shearing time for the tail to form. Our results indicate that maximum separation takes place when the viscosity ratio is between 0.1 and 1, with capillary numbers close to 1.
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Oil-particle separation in a falling sphere configuration: Effect of viscosity ratio & interfacial tension
International Journal of Multiphase Flow, 2017Co-Authors: Sasan Mehrabian, Edgar Acosta, Markus BussmannAbstract:Abstract The separation of oil from a single oil-coated spherical particle falling through an aqueous solution is evaluated as a function of viscosity ratio and interfacial tension. A solvent was used to modify the viscosity of the oil and a surfactant was used to modify the interfacial tension. The separation process is characterized with respect to a capillary number (ratio of Viscous Shear Stress to interfacial tension) and the viscosity ratio (between the oil phase and the aqueous solution). The separation of oil from the falling sphere can be described as a two-stage process. The first stage is the deformation of the oil film coating the sphere, leading to the formation of a thread or “tail” downstream of the particle. The second stage involves the breakup of that tail as the sphere falls. The initial film deformation and tail formation is best described by a capillary number based on the Shear rate at the oil-water interface; and the tail breakup by the rate of elongation experienced by the tail. More oil is removed when thicker tails are formed, which are obtained at high viscosity ratios. However, high viscosity ratios require longer Shearing time for the tail to form. Our results indicate that maximum separation takes place when the viscosity ratio is between 0.1 and 1, with capillary numbers close to 1.
Sasan Mehrabian - One of the best experts on this subject based on the ideXlab platform.
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oil particle separation in a falling sphere configuration effect of viscosity ratio interfacial tension
International Journal of Multiphase Flow, 2018Co-Authors: Sasan Mehrabian, Edgar Acosta, Markus BussmannAbstract:Abstract The separation of oil from a single oil-coated spherical particle falling through an aqueous solution is evaluated as a function of viscosity ratio and interfacial tension. A solvent was used to modify the viscosity of the oil and a surfactant was used to modify the interfacial tension. The separation process is characterized with respect to a capillary number (ratio of Viscous Shear Stress to interfacial tension) and the viscosity ratio (between the oil phase and the aqueous solution). The separation of oil from the falling sphere can be described as a two-stage process. The first stage is the deformation of the oil film coating the sphere, leading to the formation of a thread or “tail” downstream of the particle. The second stage involves the breakup of that tail as the sphere falls. The initial film deformation and tail formation is best described by a capillary number based on the Shear rate at the oil-water interface; and the tail breakup by the rate of elongation experienced by the tail. More oil is removed when thicker tails are formed, which are obtained at high viscosity ratios. However, high viscosity ratios require longer Shearing time for the tail to form. Our results indicate that maximum separation takes place when the viscosity ratio is between 0.1 and 1, with capillary numbers close to 1.
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Oil-particle separation in a falling sphere configuration: Effect of viscosity ratio & interfacial tension
International Journal of Multiphase Flow, 2017Co-Authors: Sasan Mehrabian, Edgar Acosta, Markus BussmannAbstract:Abstract The separation of oil from a single oil-coated spherical particle falling through an aqueous solution is evaluated as a function of viscosity ratio and interfacial tension. A solvent was used to modify the viscosity of the oil and a surfactant was used to modify the interfacial tension. The separation process is characterized with respect to a capillary number (ratio of Viscous Shear Stress to interfacial tension) and the viscosity ratio (between the oil phase and the aqueous solution). The separation of oil from the falling sphere can be described as a two-stage process. The first stage is the deformation of the oil film coating the sphere, leading to the formation of a thread or “tail” downstream of the particle. The second stage involves the breakup of that tail as the sphere falls. The initial film deformation and tail formation is best described by a capillary number based on the Shear rate at the oil-water interface; and the tail breakup by the rate of elongation experienced by the tail. More oil is removed when thicker tails are formed, which are obtained at high viscosity ratios. However, high viscosity ratios require longer Shearing time for the tail to form. Our results indicate that maximum separation takes place when the viscosity ratio is between 0.1 and 1, with capillary numbers close to 1.
Jau-wen Lin - One of the best experts on this subject based on the ideXlab platform.
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lubrication of journal bearings influence of Stress jump condition at the porous media fluid film interface
Tribology International, 2002Co-Authors: Ming-da Chen, Kuo-ming Chang, Jau-wen LinAbstract:In this study, the microstructure of bearing surface is modeled as a thin porous film press-fitted on an impermeable surface. On the basis of the Brinkman-extended Darcy model with Stress jump condition at the porous-media/fluid film interface, the effects of Viscous Shear Stress and Stress jump on the performance of finite journal bearings are examined. The Elrod algorithm as well as the successive over-relaxation method is utilized to solve the modified Reynolds equation and determine the accurate cavitation region. The results show that the increase in Stress jump parameter (β) provides a decrease in the load capacity, an increase in the attitude angle, and an increase in the coefficient of friction.
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Lubrication of journal bearings: influence of Stress jump condition at the porous-media/fluid film interface
Tribology International, 2002Co-Authors: Ming-da Chen, Kuo-ming Chang, Jau-wen LinAbstract:In this study, the microstructure of bearing surface is modeled as a thin porous film press-fitted on an impermeable surface. On the basis of the Brinkman-extended Darcy model with Stress jump condition at the porous-media/fluid film interface, the effects of Viscous Shear Stress and Stress jump on the performance of finite journal bearings are examined. The Elrod algorithm as well as the successive over-relaxation method is utilized to solve the modified Reynolds equation and determine the accurate cavitation region. The results show that the increase in Stress jump parameter (β) provides a decrease in the load capacity, an increase in the attitude angle, and an increase in the coefficient of friction.
