The Experts below are selected from a list of 24321 Experts worldwide ranked by ideXlab platform
Balasubramanian Sankaran - One of the best experts on this subject based on the ideXlab platform.
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internal length and time scales in a simple Shear granular flow
Physical Review E, 2004Co-Authors: Hayley H Shen, Balasubramanian SankaranAbstract:Kinetic theory has been successfully applied to mathematically model the constitutive relations for flowing granular materials. However, the basis for kinetic theory is the assumption of binary collisions between particles. Both physical and numerical experiments of granular flows have questioned the validity of this assumption. It is known that when solid concentration or Shear-Rate Increase, collision contact time becomes long relative to free-flight duration. Multiple collisions begin to prevail. Interactions between groups of particles may dominate the dynamics of the flow. This paper addresses both the size and lifetime of multiple collision groups in a granular flow. Computer simulations of a simple Shear two-dimensional assembly of visco-elastic particles with or without friction are performed. It is found that as the Shear-Rate or solid concentration Increase the Shearing particles begin to form distinct groups within each group particles collide simultaneously. The group size grows with further Increase of Shear-Rate or solid concentration to the extent that force chains spanning the whole Shearing assembly may form. Concomitantly the collision duration also Increases far beyond that of a binary collision. The evolution of the group size and the collision duration are associated with the change of the constitutive behavior of the granular materials. The existence of additional length and time scales demands new formulation for granular flows.
Hayley H Shen - One of the best experts on this subject based on the ideXlab platform.
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internal length and time scales in a simple Shear granular flow
Physical Review E, 2004Co-Authors: Hayley H Shen, Balasubramanian SankaranAbstract:Kinetic theory has been successfully applied to mathematically model the constitutive relations for flowing granular materials. However, the basis for kinetic theory is the assumption of binary collisions between particles. Both physical and numerical experiments of granular flows have questioned the validity of this assumption. It is known that when solid concentration or Shear-Rate Increase, collision contact time becomes long relative to free-flight duration. Multiple collisions begin to prevail. Interactions between groups of particles may dominate the dynamics of the flow. This paper addresses both the size and lifetime of multiple collision groups in a granular flow. Computer simulations of a simple Shear two-dimensional assembly of visco-elastic particles with or without friction are performed. It is found that as the Shear-Rate or solid concentration Increase the Shearing particles begin to form distinct groups within each group particles collide simultaneously. The group size grows with further Increase of Shear-Rate or solid concentration to the extent that force chains spanning the whole Shearing assembly may form. Concomitantly the collision duration also Increases far beyond that of a binary collision. The evolution of the group size and the collision duration are associated with the change of the constitutive behavior of the granular materials. The existence of additional length and time scales demands new formulation for granular flows.
Jukka Seppala - One of the best experts on this subject based on the ideXlab platform.
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flocculated flow of microfibrillated cellulose water suspensions an imaging approach for characterisation of rheological behaviour
Cellulose, 2012Co-Authors: Eve Saarikoski, Tapio Saarinen, Juha Salmela, Jukka SeppalaAbstract:Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing Shear Rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With Shearing, the network sepaRated first into chain-like floc formations and, upon further Shear Rate Increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the Shear Rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured Shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.
Eve Saarikoski - One of the best experts on this subject based on the ideXlab platform.
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flocculated flow of microfibrillated cellulose water suspensions an imaging approach for characterisation of rheological behaviour
Cellulose, 2012Co-Authors: Eve Saarikoski, Tapio Saarinen, Juha Salmela, Jukka SeppalaAbstract:Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing Shear Rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With Shearing, the network sepaRated first into chain-like floc formations and, upon further Shear Rate Increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the Shear Rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured Shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.
A C Badino - One of the best experts on this subject based on the ideXlab platform.
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Shear conditions in clavulanic acid production by streptomyces clavuligerus in stirred tank and airlift bioreactors
Bioprocess and Biosystems Engineering, 2012Co-Authors: Marcel Otavio Cerri, A C BadinoAbstract:In biochemical processes involving filamentous microorganisms, the high Shear Rate may damage suspended cells leading to viability loss and cell disruption. In this work, the influence of the Shear conditions in clavulanic acid (CA) production by Streptomyces clavuligerus was evaluated in a 4-dm3 conventional stirred tank (STB) and in 6-dm3 concentric-tube airlift (ALB) bioreactors. Batch cultivations were performed in a STB at 600 and 800 rpm and 0.5 vvm (cultivations B1 and B2) and in ALB at 3.0 and 4.1 vvm (cultivations A1 and A2) to define two initial oxygen transfer conditions in both bioreactors. The average Shear Rate (\( \dot{\gamma }_{\rm {av}} \)) of the cultivations was estimated using correlations of recent literature based on experimental data of rheological properties of the broth (consistency index, K, and flow index, n) and operating conditions, impeller speed (N) for STB and superficial gas velocity in the riser (UGR) for ALB. In the same oxygen transfer condition, the \( \dot{\gamma }_{\rm {av}} \) values for ALB were higher than those obtained in STB. The maximum \( \dot{\gamma }_{\rm {av}} \) presented a strong correlation with a maximum consistency index (Kmax) of the broth. Close values of maximum CA production were obtained in cultivations A1 and A2 (454 and 442 mg L−1) with similar maximum \( \dot{\gamma }_{\rm {av}} \) values of 4,247 and 4,225 s−1. In cultivations B1 and B2, the maximum CA production of 269 and 402 mg L−1 were reached with a maximum \( \dot{\gamma }_{\rm {av}} \) of 904 and 1,786 s−1. The results show that high values of average Shear Rate Increase the CA production regardless of the oxygen transfer condition and bioreactor model.