The Experts below are selected from a list of 8061 Experts worldwide ranked by ideXlab platform

Philippe Coussot - One of the best experts on this subject based on the ideXlab platform.

  • Measuring the surface tension of yield stress fluids
    Soft Matter, 2013
    Co-Authors: Jalila Boujlel, Philippe Coussot
    Abstract:

    With the aim of studying the impact of capillary forces on the flow of yield stress fluids we investigate the properties of a film formed by withdrawing a Blade from a bath of such a material. We show that before a progressive breakage of the film, the force amplitude reaches a maximum which is independent of the initial depth of penetration and the timing for Blade lifting, but increases with the material yield stress and the Blade Thickness. This critical force is shown to reflect both capillary and viscous effects, even at vanishing Blade velocity. We demonstrate that the ratio of this force to the Blade perimeter provides the surface tension of the yield stress fluid in the limit of a low (≪1) capillary number (ratio of yield stress times the Blade Thickness to surface tension). Moreover we show that all our data for the force to perimeter ratio fall along a master curve which may be used to deduce the surface tension from measurements obtained at a capillary number up to 1, even if viscous effects are significant. Finally Carbopol gels appear to have almost the same value of surface tension whatever their yield stress, but this value is almost 10% smaller than that of pure water.

  • Measuring the surface tension of yield stress fluids
    Soft Matter, 2013
    Co-Authors: Jalila Boujlel, Philippe Coussot
    Abstract:

    With the aim of studying the impact of capillary forces on the flow of yield stress fluids we investigate the properties of a film formed by withdrawing a Blade from a bath of such a material. We show that before a progressive breakage of the film, the force amplitude reaches a maximum which is independent of the initial depth of penetration and the timing for Blade lifting, but increases with the material yield stress and the Blade Thickness. This critical force is shown to reflect both capillary and viscous effects, even at vanishing Blade velocity. We demonstrate that the ratio of this force to the Blade perimeter provides the surface tension of the yield stress fluid in the limit of a low ("1) capillary number (ratio of yield stress times the Blade Thickness to surface tension). Moreover we show that all our data for the force to perimeter ratio fall along a master curve which may be used to deduce the surface tension from measurements obtained at a capillary number up to 1, even if viscous effects are significant. Finally Carbopol gels appear to have almost the same value of surface tension whatever their yield stress, but this value is almost 10% smaller than that of pure water. © 2013 The Royal Society of Chemistry.

Farid Bakir - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of Blade Thickness effects on the overall and local performances of a controlled vortex designed axial flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The overall performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus flow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity fields downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. Moreover, the thick Blades fan maintains an axial exit-flow on a wider range of flow-rates. The main differences concern local properties of the flow: phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.

  • Experimental study of Blade Thickness effects on the global and local performances of a Controlled Vortex Designed axial-flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The global performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity field downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. The thick Blades fan moreover maintains an axial exit-flow on a wider range of flow-rates. The main dierences concern local properties of the flow: Phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.

Jalila Boujlel - One of the best experts on this subject based on the ideXlab platform.

  • Measuring the surface tension of yield stress fluids
    Soft Matter, 2013
    Co-Authors: Jalila Boujlel, Philippe Coussot
    Abstract:

    With the aim of studying the impact of capillary forces on the flow of yield stress fluids we investigate the properties of a film formed by withdrawing a Blade from a bath of such a material. We show that before a progressive breakage of the film, the force amplitude reaches a maximum which is independent of the initial depth of penetration and the timing for Blade lifting, but increases with the material yield stress and the Blade Thickness. This critical force is shown to reflect both capillary and viscous effects, even at vanishing Blade velocity. We demonstrate that the ratio of this force to the Blade perimeter provides the surface tension of the yield stress fluid in the limit of a low (≪1) capillary number (ratio of yield stress times the Blade Thickness to surface tension). Moreover we show that all our data for the force to perimeter ratio fall along a master curve which may be used to deduce the surface tension from measurements obtained at a capillary number up to 1, even if viscous effects are significant. Finally Carbopol gels appear to have almost the same value of surface tension whatever their yield stress, but this value is almost 10% smaller than that of pure water.

  • Measuring the surface tension of yield stress fluids
    Soft Matter, 2013
    Co-Authors: Jalila Boujlel, Philippe Coussot
    Abstract:

    With the aim of studying the impact of capillary forces on the flow of yield stress fluids we investigate the properties of a film formed by withdrawing a Blade from a bath of such a material. We show that before a progressive breakage of the film, the force amplitude reaches a maximum which is independent of the initial depth of penetration and the timing for Blade lifting, but increases with the material yield stress and the Blade Thickness. This critical force is shown to reflect both capillary and viscous effects, even at vanishing Blade velocity. We demonstrate that the ratio of this force to the Blade perimeter provides the surface tension of the yield stress fluid in the limit of a low ("1) capillary number (ratio of yield stress times the Blade Thickness to surface tension). Moreover we show that all our data for the force to perimeter ratio fall along a master curve which may be used to deduce the surface tension from measurements obtained at a capillary number up to 1, even if viscous effects are significant. Finally Carbopol gels appear to have almost the same value of surface tension whatever their yield stress, but this value is almost 10% smaller than that of pure water. © 2013 The Royal Society of Chemistry.

Christophe Sarraf - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of Blade Thickness effects on the overall and local performances of a controlled vortex designed axial flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The overall performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus flow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity fields downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. Moreover, the thick Blades fan maintains an axial exit-flow on a wider range of flow-rates. The main differences concern local properties of the flow: phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.

  • Experimental study of Blade Thickness effects on the global and local performances of a Controlled Vortex Designed axial-flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The global performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity field downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. The thick Blades fan moreover maintains an axial exit-flow on a wider range of flow-rates. The main dierences concern local properties of the flow: Phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.

Hussain Nouri - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of Blade Thickness effects on the overall and local performances of a controlled vortex designed axial flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The overall performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus flow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity fields downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. Moreover, the thick Blades fan maintains an axial exit-flow on a wider range of flow-rates. The main differences concern local properties of the flow: phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.

  • Experimental study of Blade Thickness effects on the global and local performances of a Controlled Vortex Designed axial-flow fan
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: Christophe Sarraf, Hussain Nouri, Florent Ravelet, Farid Bakir
    Abstract:

    The purpose of this work is to study the effects of Blade Thickness on the performances of an axial-flow fan. Two fans that differ only in the Thickness of their Blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin Blades. The second fan has much thicker Blades compatible with the rotomoulding conception process. The global performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ow-rate) is slightly steeper for the fan with thick Blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick Blades fan is lower than the efficiency of the fan with thin Blades but remains high on a wider flow-rate range. The mean velocity field downstream of the rotors are very similar at nominal points with less centrifugation for the thick Blades fan. The thick Blades fan moreover maintains an axial exit-flow on a wider range of flow-rates. The main dierences concern local properties of the flow: Phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick Blades fan that for the thin Blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick Blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick Blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.