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John W. Coleman - One of the best experts on this subject based on the ideXlab platform.

  • An Expermentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Journal of Fluids Engineering, 2003
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    We report the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m 2 -s and 750 kg/m 2 -s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included

  • Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Heat Transfer Volume 4, 2002
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2 s and 750 kg/m2 s. Results from previous work by the authors were used to select the data that correspond to the Intermittent Flow Regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. The model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubbles and slugs. Slug frequency was estimated using a simple correlation for non-dimensional unit-cell length. The model predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.Copyright © 2002 by ASME

  • An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels
    Journal of Fluids Engineering, 2001
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included. Empirical data from the literature for the relative length and velocity of the slugs and bubbles, and relationships from the literature for the pressure loss associated with the mixing that occurs between the slug and film were used with assumptions about individual phase friction factors, to estimate the total pressure drop in each unit cell. A simple correlation for non-dimensional unit-cell length based on slug Reynolds number was then used to estimate the total pressure drop. The results from this model were on average within ±13.4% of the measured data, with 88% of the predicted results within ±25% of the 77 measured data points.

Srinivas Garimella - One of the best experts on this subject based on the ideXlab platform.

  • Modeling of Pressure Drop During Condensation in Circular and Noncircular Microchannels
    Journal of Fluids Engineering, 2008
    Co-Authors: Akhil Agarwal, Srinivas Garimella
    Abstract:

    This paper presents a multiple Flow-Regime model for pressure drop during condensation of refrigerant R134a in horizontal microchannels. Condensation pressure drops measured in two circular and six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.8 mm are considered here. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from 100% vapor to 100% liquid for five different refrigerant mass fluxes between 150 kg/m 2 s and 750 kg/m 2 s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were used to assign the applicable Flow Regime to the data points. Garimella et al. (2005, "Condensation Pressure Drop in Circular Microchannels," Heat Transfer Eng., 26(3) pp. 1-8) reported a comprehensive model for circular tubes that addresses the progression of the condensation process from the vapor phase to the liquid phase by modifying and combining the pressure drop models for Intermittent (Garimella et al., 2002, "An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels," ASME J. Fluids Eng., 124(1), pp. 205-214) and annular (Garimella et al., 2003, "Two-Phase Pressure Drops in the Annular Flow Regime in Circular Microchannels," 21st IIR International Congress of Refrigeration, International Institute of Refrigeration, p. ICR0360) Flows reported earlier by them. This paper presents new condensation pressure drop data on six noncircular channels over the same Flow conditions as the previous work on circular channels. In addition, a multiple Flow-Regime model similar to that developed earlier by Garimella et al. for circular microchannels is developed here for these new cross sections. This combined model accurately predicts condensation pressure drops in the annular, disperse-wave, mist, discrete-wave, and Intermittent Flow Regimes for both circular and noncircular microchannels of similar hydraulic diameters. Overlap and transition regions between the respective Regimes are also addressed to yield relatively smooth transitions between the predicted pressure drops. The resulting model predicts 80% of the data within ±25%. The effect of tube shape on pressure drop is also demonstrated.

  • An Expermentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Journal of Fluids Engineering, 2003
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    We report the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m 2 -s and 750 kg/m 2 -s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included

  • Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Heat Transfer Volume 4, 2002
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2 s and 750 kg/m2 s. Results from previous work by the authors were used to select the data that correspond to the Intermittent Flow Regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. The model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubbles and slugs. Slug frequency was estimated using a simple correlation for non-dimensional unit-cell length. The model predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.Copyright © 2002 by ASME

  • An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels
    Journal of Fluids Engineering, 2001
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included. Empirical data from the literature for the relative length and velocity of the slugs and bubbles, and relationships from the literature for the pressure loss associated with the mixing that occurs between the slug and film were used with assumptions about individual phase friction factors, to estimate the total pressure drop in each unit cell. A simple correlation for non-dimensional unit-cell length based on slug Reynolds number was then used to estimate the total pressure drop. The results from this model were on average within ±13.4% of the measured data, with 88% of the predicted results within ±25% of the 77 measured data points.

Francesco Versino - One of the best experts on this subject based on the ideXlab platform.

  • Intermittent Flow Regime of water/gas emissions as sinkhole trigger in alluvial plains: a study case at S. Vittorino plain (Rieti, Italy)
    Environmental Earth Sciences, 2015
    Co-Authors: Mario Voltaggio, Massimo Spadoni, Francesco Versino
    Abstract:

    A case of natural Intermittent Flow Regime (slug/churn) of a CO_2-enriched spring water is discussed as an example of trigger process for the collapse of sinkholes. The hydrodynamic Regime of the spring, situated in the area of S. Vittorino alluvial plain (Rieti, Italy), was investigated by monitoring acoustic emission, carrying out geochemical analyses and installing a sedimentation trap during a long-lasting phase of slug Flow Regime followed by a churn Flow phase. The slug and churn Flows can erode and transport upward fine and medium size particles of sand, progressively removing them from some underground shallow sandy levels where the groundwater mixes with gas of deep crustal origin to form the Intermittent Flow that can be observed at the surface. The slug Flow Regime was characterized by a stable slugging frequency whose value is in agreement with the estimated superficial velocities of Taylor bubbles and liquid slugs. The transition from the slug to the churn Flow Regime, the latter characterized by an increase of gas flux and by more severe erosion, was also observed during our study. In a span of 15 years, the transport of sand upward could produce a collapse volume similar to those of the sinkholes that recently originated in the same area. The study of such multiphase Flows prolonged over time could help to monitor and prevent the sinkhole formation process.

  • Intermittent Flow Regime of water gas emissions as sinkhole trigger in alluvial plains a study case at s vittorino plain rieti italy
    Environmental Earth Sciences, 2015
    Co-Authors: Mario Voltaggio, Massimo Spadoni, Francesco Versino
    Abstract:

    A case of natural Intermittent Flow Regime (slug/churn) of a CO2-enriched spring water is discussed as an example of trigger process for the collapse of sinkholes. The hydrodynamic Regime of the spring, situated in the area of S. Vittorino alluvial plain (Rieti, Italy), was investigated by monitoring acoustic emission, carrying out geochemical analyses and installing a sedimentation trap during a long-lasting phase of slug Flow Regime followed by a churn Flow phase. The slug and churn Flows can erode and transport upward fine and medium size particles of sand, progressively removing them from some underground shallow sandy levels where the groundwater mixes with gas of deep crustal origin to form the Intermittent Flow that can be observed at the surface. The slug Flow Regime was characterized by a stable slugging frequency whose value is in agreement with the estimated superficial velocities of Taylor bubbles and liquid slugs. The transition from the slug to the churn Flow Regime, the latter characterized by an increase of gas flux and by more severe erosion, was also observed during our study. In a span of 15 years, the transport of sand upward could produce a collapse volume similar to those of the sinkholes that recently originated in the same area. The study of such multiphase Flows prolonged over time could help to monitor and prevent the sinkhole formation process.

Mario Voltaggio - One of the best experts on this subject based on the ideXlab platform.

  • Intermittent Flow Regime of water/gas emissions as sinkhole trigger in alluvial plains: a study case at S. Vittorino plain (Rieti, Italy)
    Environmental Earth Sciences, 2015
    Co-Authors: Mario Voltaggio, Massimo Spadoni, Francesco Versino
    Abstract:

    A case of natural Intermittent Flow Regime (slug/churn) of a CO_2-enriched spring water is discussed as an example of trigger process for the collapse of sinkholes. The hydrodynamic Regime of the spring, situated in the area of S. Vittorino alluvial plain (Rieti, Italy), was investigated by monitoring acoustic emission, carrying out geochemical analyses and installing a sedimentation trap during a long-lasting phase of slug Flow Regime followed by a churn Flow phase. The slug and churn Flows can erode and transport upward fine and medium size particles of sand, progressively removing them from some underground shallow sandy levels where the groundwater mixes with gas of deep crustal origin to form the Intermittent Flow that can be observed at the surface. The slug Flow Regime was characterized by a stable slugging frequency whose value is in agreement with the estimated superficial velocities of Taylor bubbles and liquid slugs. The transition from the slug to the churn Flow Regime, the latter characterized by an increase of gas flux and by more severe erosion, was also observed during our study. In a span of 15 years, the transport of sand upward could produce a collapse volume similar to those of the sinkholes that recently originated in the same area. The study of such multiphase Flows prolonged over time could help to monitor and prevent the sinkhole formation process.

  • Intermittent Flow Regime of water gas emissions as sinkhole trigger in alluvial plains a study case at s vittorino plain rieti italy
    Environmental Earth Sciences, 2015
    Co-Authors: Mario Voltaggio, Massimo Spadoni, Francesco Versino
    Abstract:

    A case of natural Intermittent Flow Regime (slug/churn) of a CO2-enriched spring water is discussed as an example of trigger process for the collapse of sinkholes. The hydrodynamic Regime of the spring, situated in the area of S. Vittorino alluvial plain (Rieti, Italy), was investigated by monitoring acoustic emission, carrying out geochemical analyses and installing a sedimentation trap during a long-lasting phase of slug Flow Regime followed by a churn Flow phase. The slug and churn Flows can erode and transport upward fine and medium size particles of sand, progressively removing them from some underground shallow sandy levels where the groundwater mixes with gas of deep crustal origin to form the Intermittent Flow that can be observed at the surface. The slug Flow Regime was characterized by a stable slugging frequency whose value is in agreement with the estimated superficial velocities of Taylor bubbles and liquid slugs. The transition from the slug to the churn Flow Regime, the latter characterized by an increase of gas flux and by more severe erosion, was also observed during our study. In a span of 15 years, the transport of sand upward could produce a collapse volume similar to those of the sinkholes that recently originated in the same area. The study of such multiphase Flows prolonged over time could help to monitor and prevent the sinkhole formation process.

Jesse D. Killion - One of the best experts on this subject based on the ideXlab platform.

  • An Expermentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Journal of Fluids Engineering, 2003
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    We report the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m 2 -s and 750 kg/m 2 -s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included

  • Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels
    Heat Transfer Volume 4, 2002
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2 s and 750 kg/m2 s. Results from previous work by the authors were used to select the data that correspond to the Intermittent Flow Regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. The model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubbles and slugs. Slug frequency was estimated using a simple correlation for non-dimensional unit-cell length. The model predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.Copyright © 2002 by ASME

  • An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels
    Journal of Fluids Engineering, 2001
    Co-Authors: Srinivas Garimella, Jesse D. Killion, John W. Coleman
    Abstract:

    This paper reports the development of an experimentally validated model for pressure drop during Intermittent Flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the authors on condensation Flow mechanisms in microchannel geometries were then used to identify data that corresponded to the Intermittent Flow Regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble Flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the Flow of liquid between the film and slug to the pressure drop were included. Empirical data from the literature for the relative length and velocity of the slugs and bubbles, and relationships from the literature for the pressure loss associated with the mixing that occurs between the slug and film were used with assumptions about individual phase friction factors, to estimate the total pressure drop in each unit cell. A simple correlation for non-dimensional unit-cell length based on slug Reynolds number was then used to estimate the total pressure drop. The results from this model were on average within ±13.4% of the measured data, with 88% of the predicted results within ±25% of the 77 measured data points.