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Nicky Eshtiaghi - One of the best experts on this subject based on the ideXlab platform.

  • impact of gas injection on the Apparent Viscosity and viscoelastic property of waste activated sewage sludge
    Water Research, 2017
    Co-Authors: Veena Bobade, Jeanchristophe Baudez, Geoffery Evans, Nicky Eshtiaghi
    Abstract:

    Gas injection is known to play a major role on the particle size of the sludge, the oxygen transfer rate, as well as the mixing efficiency of membrane bioreactors and aeration basins in the waste water treatment plants. The rheological characteristics of sludge are closely related to the particle size of the sludge floc. However, particle size of sludge floc depends partly on the shear induced in the sludge and partly on physico-chemical nature of the sludge. The objective of this work is to determine the impact of gas injection on both the Apparent Viscosity and viscoelastic property of sludge. The Apparent Viscosity of sludge was investigated by two methods: in-situ and after sparging. Viscosity curves obtained by in-situ measurement showed that the Apparent Viscosity decreases significantly from 4000 Pa s to 10 Pa s at low shear rate range (below 10 s-1) with an increase in gas flow rate (0.5LPM to 3LPM); however the after sparging flow curve analysis showed that the reduction in Apparent Viscosity throughout the shear rate range is negligible to be displayed. Torque and displacement data at low shear rate range revealed that the obtained lower Apparent Viscosity in the in-situ method is not the material characteristics, but the slippage effect due to a preferred location of the bubbles close to the bob, causing an inconsistent decrease of torque and increase of displacement at low shear rate range. In linear viscoelastic regime, the elastic and viscous modulus of sludge was reduced by 33% & 25%, respectively, due to gas injection because of induced shear. The amount of induced shear measured through two different tests (creep and time sweep) were the same. The impact of this induced shear on sludge structure was also verified by microscopic images.

  • predicting the Apparent Viscosity and yield stress of digested and secondary sludge mixtures
    Water Research, 2016
    Co-Authors: Nicky Eshtiaghi, Flora Markis, Dwen Zain, Kiet Hung Mai
    Abstract:

    Abstract The legal banning of conventional sludge disposal methods such as landfill has led to a global movement towards achieving a sustainable sludge management strategy. Reusing sludge for energy production (biogas production) through the anaerobic digestion of sludge can provide a sustainable solution. However, for the optimum performance of digesters with minimal use of energy input, operating conditions must be regulated in accordance with the rheological characteristics of the sludge. If it is assumed that only secondary sludge enters the anaerobic digesters, an impact of variations to the solids concentration and volume fraction of each sludge type must be investigated to understand how the Apparent Viscosity and yield stress of the secondary and digested sludge mixture inside the digesters changes. In this study, five different total solids concentration of secondary and digested sludge were mixed at different digested sludge volume fractions ranging from 0 to 1. It was found that if secondary sludge was mixed with digested sludge at the same total solids concentration, the Apparent Viscosity and the yield stress of the mixture increased exponentially by increasing the volume fraction of digested sludge. However, if secondary sludge was added to digested sludge with a different solids concentration, the Apparent Viscosity and yield stress of the resulting mixed sludge was controlled by the concentrated sludge regardless of its type. Semi – empirical correlations were proposed to predict the Apparent Viscosity and yield stress of the mixed digested and secondary sludge. A master curve was also developed to predict the flow behaviour of sludge mixtures regardless of the total solid concentration and volume fraction of each sludge type within the studied solids concentration range of 1.4 and 7%TS. This model can be used for digesters optimization and design by predicting the rheology of sludge mixture inside digester.

  • Predicting the Apparent Viscosity and yield stress of mixtures of primary, secondary and anaerobically digested sewage sludge: Simulating anaerobic digesters
    Water Research, 2016
    Co-Authors: Flora Markis, J.c. Baudez, R. Parthasarathy, Nicky Eshtiaghi
    Abstract:

    Predicting the flow behaviour, most notably, the Apparent Viscosity and yield stress of sludge mixtures inside the anaerobic digester is essential because it helps optimize the mixing system in digesters. This paper investigates the rheology of sludge mixtures as a function of digested sludge volume fraction. Sludge mixtures exhibited non-Newtonian, shear thinning, yield stress behaviour. The Apparent Viscosity and yield stress of sludge mixtures prepared at the same total solids concentration was influenced by the interactions within the digested sludge and increased with the volume fraction of digested sludge – highlighted using shear compliance and shear modulus of sludge mixtures. However, when a thickened primary – secondary sludge mixture was mixed with dilute digested sludge, the Apparent Viscosity and yield stress decreased with increasing the volume fraction of digested sludge. This was caused by the dilution effect leading to a reduction in the hydrodynamic and non-hydrodynamic interactions when dilute digested sludge was added.Correlations were developed to predict the Apparent Viscosity and yield stress of the mixtures as a function of the digested sludge volume fraction and total solids concentration of the mixtures. The parameters of correlations can be estimated using pH of sludge. The shear and complex modulus were also modelled and they followed an exponential relationship with increasing digested sludge volume fraction

  • The Apparent Viscosity and yield stress of mixtures of primary and secondary sludge: Impact of volume fraction of secondary sludge and total solids concentration
    Chemical Engineering Journal, 2016
    Co-Authors: Flora Markis, J.c. Baudez, R. Parthasarathy, P. Slatter, Nicky Eshtiaghi
    Abstract:

    Sludge rheology plays an important role in the design and optimization of anaerobic digesters. Organic matter such as primary and secondary sludge or a mixture of the two sludges enters the digesters for further digestion and stabilization. However, there is little information available on how the rheology of the mixed sludge changes. This paper investigates how the rheology of mixed primary and secondary sludge changes when the volume fraction of secondary sludge is altered. This will help predict the rheology of mixed sludge which is required for the design and optimization of pumping and mixing systems. Mixtures of primary and secondary sludge between 2.5 and 7%TS behave as non-Newtonian, shear thinning, yield stress materials whereby the Apparent Viscosity and yield stress of the mixed sludge depends on the volume fraction of secondary sludge and total solids concentration. The Apparent Viscosity of primary–secondary sludge mixtures (with same total solids concentration) increases with increasing secondary sludge volume fraction. This suggests that the weak flocs of primary sludge collapse such that the colloidal like particles of primary sludge become trapped and entangled in the gel-like network structure of secondary sludge. However, when dilute primary sludge is mixed with concentrated secondary sludge (and vice-versa), the Apparent Viscosity and yield stress of the primary–secondary sludge mixture increases with increasing volume fraction of the concentrated sludge regardless of sludge type. This is due to the strengthening of hydrodynamic and non-hydrodynamic interactions within concentrated sludge. A master curve was developed to predict the flow behaviour of sludge mixtures. Consequently, correlations were developed to predict the Apparent Viscosity and a yield stress of sludge mixtures as a function of volume fraction and total solids concentration.

Amirfarhang Mehdizadeh - One of the best experts on this subject based on the ideXlab platform.

  • a discrete model for the Apparent Viscosity of polydisperse suspensions including maximum packing fraction
    Journal of Rheology, 2013
    Co-Authors: Aaron Dorr, A Sadiki, Amirfarhang Mehdizadeh
    Abstract:

    Based on the notion of a construction process consisting of the stepwise addition of particles to the pure fluid, a discrete model for the Apparent Viscosity as well as for the maximum packing fraction of polydisperse suspensions of spherical, noncolloidal particles is derived. The model connects the approaches by Bruggeman and Farris and is valid for large size ratios of consecutive particle classes during the construction process, appearing to be the first model consistently describing polydisperse volume fractions and maximum packing fraction within a single approach. In that context, the consistent inclusion of the maximum packing fraction into effective medium models is discussed. Furthermore, new generalized forms of the well-known Quemada and Krieger–Dougherty equations allowing for the choice of a second-order Taylor coefficient for the volume fraction (ϕ2-coefficient), found by asymptotic matching, are proposed. The model for the maximum packing fraction as well as the complete Viscosity model is...

  • a discrete model for the Apparent Viscosity of polydisperse suspensions including maximum packing fraction
    arXiv: Fluid Dynamics, 2012
    Co-Authors: Aaron Dorr, A Sadiki, Amirfarhang Mehdizadeh
    Abstract:

    Based on the notion of a construction process consisting of the stepwise addition of particles to the pure fluid, a discrete model for the Apparent Viscosity as well as for the maximum packing fraction of polydisperse suspensions of spherical, non-colloidal particles is derived. The model connects the approaches by Bruggeman and Farris and is valid for large size ratios of consecutive particle classes during the construction process, appearing to be the first model consistently describing polydisperse volume fractions and maximum packing fraction within a single approach. In that context, the consistent inclusion of the maximum packing fraction into effective medium models is discussed. Furthermore, new generalized forms of the well-known Quemada and Krieger equations allowing for the choice of a second-order Taylor coefficient for the volume fraction ($\phi^2$-coefficient), found by asymptotic matching, are proposed. The model for the maximum packing fraction as well as the complete Viscosity model are compared to experimental data from the literature showing good agreement. As a result, the new model is shown to replace the empirical Sudduth model for large diameter ratios. The extension of the model to the case of small size ratios is left for future work.

Flora Markis - One of the best experts on this subject based on the ideXlab platform.

  • predicting the Apparent Viscosity and yield stress of digested and secondary sludge mixtures
    Water Research, 2016
    Co-Authors: Nicky Eshtiaghi, Flora Markis, Dwen Zain, Kiet Hung Mai
    Abstract:

    Abstract The legal banning of conventional sludge disposal methods such as landfill has led to a global movement towards achieving a sustainable sludge management strategy. Reusing sludge for energy production (biogas production) through the anaerobic digestion of sludge can provide a sustainable solution. However, for the optimum performance of digesters with minimal use of energy input, operating conditions must be regulated in accordance with the rheological characteristics of the sludge. If it is assumed that only secondary sludge enters the anaerobic digesters, an impact of variations to the solids concentration and volume fraction of each sludge type must be investigated to understand how the Apparent Viscosity and yield stress of the secondary and digested sludge mixture inside the digesters changes. In this study, five different total solids concentration of secondary and digested sludge were mixed at different digested sludge volume fractions ranging from 0 to 1. It was found that if secondary sludge was mixed with digested sludge at the same total solids concentration, the Apparent Viscosity and the yield stress of the mixture increased exponentially by increasing the volume fraction of digested sludge. However, if secondary sludge was added to digested sludge with a different solids concentration, the Apparent Viscosity and yield stress of the resulting mixed sludge was controlled by the concentrated sludge regardless of its type. Semi – empirical correlations were proposed to predict the Apparent Viscosity and yield stress of the mixed digested and secondary sludge. A master curve was also developed to predict the flow behaviour of sludge mixtures regardless of the total solid concentration and volume fraction of each sludge type within the studied solids concentration range of 1.4 and 7%TS. This model can be used for digesters optimization and design by predicting the rheology of sludge mixture inside digester.

  • Predicting the Apparent Viscosity and yield stress of mixtures of primary, secondary and anaerobically digested sewage sludge: Simulating anaerobic digesters
    Water Research, 2016
    Co-Authors: Flora Markis, J.c. Baudez, R. Parthasarathy, Nicky Eshtiaghi
    Abstract:

    Predicting the flow behaviour, most notably, the Apparent Viscosity and yield stress of sludge mixtures inside the anaerobic digester is essential because it helps optimize the mixing system in digesters. This paper investigates the rheology of sludge mixtures as a function of digested sludge volume fraction. Sludge mixtures exhibited non-Newtonian, shear thinning, yield stress behaviour. The Apparent Viscosity and yield stress of sludge mixtures prepared at the same total solids concentration was influenced by the interactions within the digested sludge and increased with the volume fraction of digested sludge – highlighted using shear compliance and shear modulus of sludge mixtures. However, when a thickened primary – secondary sludge mixture was mixed with dilute digested sludge, the Apparent Viscosity and yield stress decreased with increasing the volume fraction of digested sludge. This was caused by the dilution effect leading to a reduction in the hydrodynamic and non-hydrodynamic interactions when dilute digested sludge was added.Correlations were developed to predict the Apparent Viscosity and yield stress of the mixtures as a function of the digested sludge volume fraction and total solids concentration of the mixtures. The parameters of correlations can be estimated using pH of sludge. The shear and complex modulus were also modelled and they followed an exponential relationship with increasing digested sludge volume fraction

  • The Apparent Viscosity and yield stress of mixtures of primary and secondary sludge: Impact of volume fraction of secondary sludge and total solids concentration
    Chemical Engineering Journal, 2016
    Co-Authors: Flora Markis, J.c. Baudez, R. Parthasarathy, P. Slatter, Nicky Eshtiaghi
    Abstract:

    Sludge rheology plays an important role in the design and optimization of anaerobic digesters. Organic matter such as primary and secondary sludge or a mixture of the two sludges enters the digesters for further digestion and stabilization. However, there is little information available on how the rheology of the mixed sludge changes. This paper investigates how the rheology of mixed primary and secondary sludge changes when the volume fraction of secondary sludge is altered. This will help predict the rheology of mixed sludge which is required for the design and optimization of pumping and mixing systems. Mixtures of primary and secondary sludge between 2.5 and 7%TS behave as non-Newtonian, shear thinning, yield stress materials whereby the Apparent Viscosity and yield stress of the mixed sludge depends on the volume fraction of secondary sludge and total solids concentration. The Apparent Viscosity of primary–secondary sludge mixtures (with same total solids concentration) increases with increasing secondary sludge volume fraction. This suggests that the weak flocs of primary sludge collapse such that the colloidal like particles of primary sludge become trapped and entangled in the gel-like network structure of secondary sludge. However, when dilute primary sludge is mixed with concentrated secondary sludge (and vice-versa), the Apparent Viscosity and yield stress of the primary–secondary sludge mixture increases with increasing volume fraction of the concentrated sludge regardless of sludge type. This is due to the strengthening of hydrodynamic and non-hydrodynamic interactions within concentrated sludge. A master curve was developed to predict the flow behaviour of sludge mixtures. Consequently, correlations were developed to predict the Apparent Viscosity and a yield stress of sludge mixtures as a function of volume fraction and total solids concentration.

Aaron Dorr - One of the best experts on this subject based on the ideXlab platform.

  • a discrete model for the Apparent Viscosity of polydisperse suspensions including maximum packing fraction
    Journal of Rheology, 2013
    Co-Authors: Aaron Dorr, A Sadiki, Amirfarhang Mehdizadeh
    Abstract:

    Based on the notion of a construction process consisting of the stepwise addition of particles to the pure fluid, a discrete model for the Apparent Viscosity as well as for the maximum packing fraction of polydisperse suspensions of spherical, noncolloidal particles is derived. The model connects the approaches by Bruggeman and Farris and is valid for large size ratios of consecutive particle classes during the construction process, appearing to be the first model consistently describing polydisperse volume fractions and maximum packing fraction within a single approach. In that context, the consistent inclusion of the maximum packing fraction into effective medium models is discussed. Furthermore, new generalized forms of the well-known Quemada and Krieger–Dougherty equations allowing for the choice of a second-order Taylor coefficient for the volume fraction (ϕ2-coefficient), found by asymptotic matching, are proposed. The model for the maximum packing fraction as well as the complete Viscosity model is...

  • a discrete model for the Apparent Viscosity of polydisperse suspensions including maximum packing fraction
    arXiv: Fluid Dynamics, 2012
    Co-Authors: Aaron Dorr, A Sadiki, Amirfarhang Mehdizadeh
    Abstract:

    Based on the notion of a construction process consisting of the stepwise addition of particles to the pure fluid, a discrete model for the Apparent Viscosity as well as for the maximum packing fraction of polydisperse suspensions of spherical, non-colloidal particles is derived. The model connects the approaches by Bruggeman and Farris and is valid for large size ratios of consecutive particle classes during the construction process, appearing to be the first model consistently describing polydisperse volume fractions and maximum packing fraction within a single approach. In that context, the consistent inclusion of the maximum packing fraction into effective medium models is discussed. Furthermore, new generalized forms of the well-known Quemada and Krieger equations allowing for the choice of a second-order Taylor coefficient for the volume fraction ($\phi^2$-coefficient), found by asymptotic matching, are proposed. The model for the maximum packing fraction as well as the complete Viscosity model are compared to experimental data from the literature showing good agreement. As a result, the new model is shown to replace the empirical Sudduth model for large diameter ratios. The extension of the model to the case of small size ratios is left for future work.

Zhuoqing An - One of the best experts on this subject based on the ideXlab platform.

  • correlating the Apparent Viscosity with gas solid suspension flow in straight pipelines
    Powder Technology, 2019
    Co-Authors: Zhuoqing An
    Abstract:

    Abstract The Apparent Viscosity of dilute solids suspension flows has been inferred from the experimentally measured frictional pressure drop in a specially designed downflow straight pipeline. The results indicate that the Apparent Viscosity of gas-solid suspension flow increases with the increment of the solids holdup, and is, in the transition region only, inversely proportional to the gas velocity. As the influence of gas velocity to the gas-solid suspension flow becomes negligible in the turbulent region, the Apparent Viscosity can be linearly correlated with the solids holdup. New correlations for the Apparent Viscosity of the gas-solid suspension flow in straight pipelines were proposed.