The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Peter J. Catto - One of the best experts on this subject based on the ideXlab platform.
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zonal Flow in a tokamak pedestal
Physics of Plasmas, 2009Co-Authors: Grigory Kagan, Peter J. CattoAbstract:Neoclassical shielding is the dominant mechanism reducing the collisionless zonal Flow in a tokamak. Previously, this phenomenon was analyzed in the case of an essentially homogeneous equilibrium since the wavelength of the zonal Flow Perturbation was assumed to be much less than the scale length of background plasma parameters. This assumption is not appropriate in a tokamak pedestal. Therefore the pedestal neoclassical polarization and the zonal Flow residual differ from the conventional results. This change is due to the strong electric field intrinsic to a subsonic pedestal that modifies neoclassical ion orbits so that their response to a zonal Flow Perturbation is qualitatively different from that in the core. In addition to orbit squeezing, we find a spatial phase shift between the initial and final zonal Flow potentials—an effect absent in previous works. Moreover, we demonstrate that because of orbit modification neoclassical phenomena disappear in the large electric field limit making the residual close to one.
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Zonal Flow in a tokamak pedestal
Physics of Plasmas, 2009Co-Authors: Grigory Kagan, Peter J. CattoAbstract:Neoclassical shielding is the dominant mechanism reducing the collisionless zonal Flow in a tokamak. Previously, this phenomenon was analyzed in the case of an essentially homogeneous equilibrium since the wavelength of the zonal Flow Perturbation was assumed to be much less than the scale length of background plasma parameters. This assumption is not appropriate in a tokamak pedestal. Therefore the pedestal neoclassical polarization and the zonal Flow residual differ from the conventional results. This change is due to the strong electric field intrinsic to a subsonic pedestal that modifies neoclassical ion orbits so that their response to a zonal Flow Perturbation is qualitatively different from that in the core. In addition to orbit squeezing, we find a spatial phase shift between the initial and final zonal Flow potentials—an effect absent in previous works. Moreover, we demonstrate that because of orbit modification neoclassical phenomena disappear in the large electric field limit making the residua...
Grigory Kagan - One of the best experts on this subject based on the ideXlab platform.
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zonal Flow in a tokamak pedestal
Physics of Plasmas, 2009Co-Authors: Grigory Kagan, Peter J. CattoAbstract:Neoclassical shielding is the dominant mechanism reducing the collisionless zonal Flow in a tokamak. Previously, this phenomenon was analyzed in the case of an essentially homogeneous equilibrium since the wavelength of the zonal Flow Perturbation was assumed to be much less than the scale length of background plasma parameters. This assumption is not appropriate in a tokamak pedestal. Therefore the pedestal neoclassical polarization and the zonal Flow residual differ from the conventional results. This change is due to the strong electric field intrinsic to a subsonic pedestal that modifies neoclassical ion orbits so that their response to a zonal Flow Perturbation is qualitatively different from that in the core. In addition to orbit squeezing, we find a spatial phase shift between the initial and final zonal Flow potentials—an effect absent in previous works. Moreover, we demonstrate that because of orbit modification neoclassical phenomena disappear in the large electric field limit making the residual close to one.
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Zonal Flow in a tokamak pedestal
Physics of Plasmas, 2009Co-Authors: Grigory Kagan, Peter J. CattoAbstract:Neoclassical shielding is the dominant mechanism reducing the collisionless zonal Flow in a tokamak. Previously, this phenomenon was analyzed in the case of an essentially homogeneous equilibrium since the wavelength of the zonal Flow Perturbation was assumed to be much less than the scale length of background plasma parameters. This assumption is not appropriate in a tokamak pedestal. Therefore the pedestal neoclassical polarization and the zonal Flow residual differ from the conventional results. This change is due to the strong electric field intrinsic to a subsonic pedestal that modifies neoclassical ion orbits so that their response to a zonal Flow Perturbation is qualitatively different from that in the core. In addition to orbit squeezing, we find a spatial phase shift between the initial and final zonal Flow potentials—an effect absent in previous works. Moreover, we demonstrate that because of orbit modification neoclassical phenomena disappear in the large electric field limit making the residua...
Christophe Andre - One of the best experts on this subject based on the ideXlab platform.
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Influence of Flow regime and thermal power on residence time distribution in tubular joule effect heaters
Journal of Food Engineering, 2009Co-Authors: Luc Fillaudeau, K. Le-nguyen, Christophe AndreAbstract:To improve treatment homogeneity in tubular Joule Effect Heater (JEH), geometric modifications could be used even in laminar regime inducing Flow Perturbation and mixing. As a response variable, residence time distribution (RTD) is an important parameter and it has been commonly used in determining the performances of industrial heat exchangers. In present work, our objectives were (i) to investigate the impact of processing conditions (Flow regime, heat flux) on RTD in an industrial JEH equipped with smooth and modified tubes, (ii) to contribute to the estimation of treatment homogeneity versus global energetic performances of heat exchanger and (iii) to validate a general reactor model.Analytical solution and systemic analysis of RTD signals were reported. The evolutions of mean reduced variance, beta(2) against efficiency number, Eff for smooth (beta(2) = 0.00129, Eff - 0.0300, R(2) = 0.992) and modified (beta(2) = 0.000547, Eff - 0.0169, R(2) = 0.979) tubes exhibited a similar and linear relationship. Under the conditions investigated (38 < Re < 10,000, 4 < Pr < 950 with Newtonian fluids), treatment homogeneity was significantly improved by modified geometry and strong interactions between heat transfer and hydrodynamics. A significant decrease in reduced variance under both laminar (beta(2)(ST) = 0.1054 . Exp(-0.00518.P/(rho.Q)), beta(2)(MT) = 0.0661 . Exp(-0.00342 . P/(rho.Q))) and turbulent (beta(2)(ST) = 0.00624 . Exp(-0.00447.P/(rho.Q)), beta(2)(MT) = 0.00108 . Exp(-0.00195.P/(rho.Q))) regimes was observed versus heat energy.However geometric modification and heat treatment affected the residence time distribution and specifically reduced variance, beta(2) within same order of magnitude. Systemic analysis of experimental data enabled to evaluate two reactor models: Dispersed Plug Flow (DPF) and Plug Flow (PF) + 2 Continuous Stirred Tank Reactor (CSTR) with and without convolution and with 1 or 2 degrees of freedom.Second model could be considered as the most accurate model to predict RTD in JEH with an accurate degree of confidence for residence time and reduced variance estimation (tau = 0.995 . t(s) R(2) = 0.64, error < 3% and beta(2) = 0.3119 . (beta(2)(exp))(0.73) R(2) = 0.98) and a simplified model with only 1 degree of freedom can be used.
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Residence time distribution in tubular joule effect heaters with and without geometric modifications
Chemical Engineering & Technology, 2006Co-Authors: Christophe Andre, Benjamin Boissier, Luc FillaudeauAbstract:In the food industry, heat treatment of highly viscous fluids in continuous processes is becoming more and more common, and the process should perform as a homogenous thermal treatment, in order to ensure quality and safety of the final product. To improve treatment homogeneity, geometric modifications can be used even in the laminar regime, to induce Flow Perturbation and mixing. The objectives of this work include: (i) Investigation of the residence time distribution (RTD) for industrial indirect Joule effect heaters (JEH), with smooth (ST) and modified (MT) tubes, (ii) Demonstration and quantification of the efficiency of the geometrical modifications, and (iii) Proposition of a single semi-empirical model including the Flow regime (10
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Modelling and measurement of residence time distribution in tubular Joule effect heaters with and without geometric modifications
2006Co-Authors: Christophe Andre, Benjamin Boissier, Luc FillaudeauAbstract:In food industry, heat treatment of highly viscous fluids in continuous process is more and more common and the process should perform homogenous thermal treatment in order to ensure quality and safety of the final product. To improve treatment homogeneity, geometric modifications could be used even in laminar regime inducing Flow Perturbation and mixing. In this work, our objectives were (i) to investigate residence time distribution (RTD) for industrial indirect Joule effect heaters (JEH) with smooth (ST) and modified (MT) tubes, (ii) to demonstrate and quantify the efficiency of geometrical modifications and (iii) to propose a general reactor model including Flow regime (10
Luc Fillaudeau - One of the best experts on this subject based on the ideXlab platform.
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Influence of Flow regime and thermal power on residence time distribution in tubular joule effect heaters
Journal of Food Engineering, 2009Co-Authors: Luc Fillaudeau, K. Le-nguyen, Christophe AndreAbstract:To improve treatment homogeneity in tubular Joule Effect Heater (JEH), geometric modifications could be used even in laminar regime inducing Flow Perturbation and mixing. As a response variable, residence time distribution (RTD) is an important parameter and it has been commonly used in determining the performances of industrial heat exchangers. In present work, our objectives were (i) to investigate the impact of processing conditions (Flow regime, heat flux) on RTD in an industrial JEH equipped with smooth and modified tubes, (ii) to contribute to the estimation of treatment homogeneity versus global energetic performances of heat exchanger and (iii) to validate a general reactor model.Analytical solution and systemic analysis of RTD signals were reported. The evolutions of mean reduced variance, beta(2) against efficiency number, Eff for smooth (beta(2) = 0.00129, Eff - 0.0300, R(2) = 0.992) and modified (beta(2) = 0.000547, Eff - 0.0169, R(2) = 0.979) tubes exhibited a similar and linear relationship. Under the conditions investigated (38 < Re < 10,000, 4 < Pr < 950 with Newtonian fluids), treatment homogeneity was significantly improved by modified geometry and strong interactions between heat transfer and hydrodynamics. A significant decrease in reduced variance under both laminar (beta(2)(ST) = 0.1054 . Exp(-0.00518.P/(rho.Q)), beta(2)(MT) = 0.0661 . Exp(-0.00342 . P/(rho.Q))) and turbulent (beta(2)(ST) = 0.00624 . Exp(-0.00447.P/(rho.Q)), beta(2)(MT) = 0.00108 . Exp(-0.00195.P/(rho.Q))) regimes was observed versus heat energy.However geometric modification and heat treatment affected the residence time distribution and specifically reduced variance, beta(2) within same order of magnitude. Systemic analysis of experimental data enabled to evaluate two reactor models: Dispersed Plug Flow (DPF) and Plug Flow (PF) + 2 Continuous Stirred Tank Reactor (CSTR) with and without convolution and with 1 or 2 degrees of freedom.Second model could be considered as the most accurate model to predict RTD in JEH with an accurate degree of confidence for residence time and reduced variance estimation (tau = 0.995 . t(s) R(2) = 0.64, error < 3% and beta(2) = 0.3119 . (beta(2)(exp))(0.73) R(2) = 0.98) and a simplified model with only 1 degree of freedom can be used.
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Residence time distribution in tubular joule effect heaters with and without geometric modifications
Chemical Engineering & Technology, 2006Co-Authors: Christophe Andre, Benjamin Boissier, Luc FillaudeauAbstract:In the food industry, heat treatment of highly viscous fluids in continuous processes is becoming more and more common, and the process should perform as a homogenous thermal treatment, in order to ensure quality and safety of the final product. To improve treatment homogeneity, geometric modifications can be used even in the laminar regime, to induce Flow Perturbation and mixing. The objectives of this work include: (i) Investigation of the residence time distribution (RTD) for industrial indirect Joule effect heaters (JEH), with smooth (ST) and modified (MT) tubes, (ii) Demonstration and quantification of the efficiency of the geometrical modifications, and (iii) Proposition of a single semi-empirical model including the Flow regime (10
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Modelling and measurement of residence time distribution in tubular Joule effect heaters with and without geometric modifications
2006Co-Authors: Christophe Andre, Benjamin Boissier, Luc FillaudeauAbstract:In food industry, heat treatment of highly viscous fluids in continuous process is more and more common and the process should perform homogenous thermal treatment in order to ensure quality and safety of the final product. To improve treatment homogeneity, geometric modifications could be used even in laminar regime inducing Flow Perturbation and mixing. In this work, our objectives were (i) to investigate residence time distribution (RTD) for industrial indirect Joule effect heaters (JEH) with smooth (ST) and modified (MT) tubes, (ii) to demonstrate and quantify the efficiency of geometrical modifications and (iii) to propose a general reactor model including Flow regime (10
Tilman Spohn - One of the best experts on this subject based on the ideXlab platform.
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interannual Perturbations of the martian surface heat Flow by atmospheric dust opacity variations
Journal of Geophysical Research, 2016Co-Authors: Anacatalina Plesa, M Grott, M T Lemmon, N Muller, S Piqueux, M A Siegler, S Smrekar, Tilman SpohnAbstract:The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission will perform the first Martian in situ heat Flow measurement by deploying the Heat Flow and Physical Properties Package (HP3) onto the Martian surface. In order to estimate the heat Flow coming from the planetary interior, HP3 will measure the local subsurface thermal gradient as well as the local thermal conductivity to a depth of up to 5 m. From these measurements, local heat Flow can be determined, but this will in general differ from the heat Flow emanating from the planetary interior due to atmosphere-induced Perturbations. Here we quantify heat Flow Perturbation induced by dust loading of the Martian atmosphere using dust opacity data obtained by the Mars Exploration Rover Opportunity. Dust opacity data span the time period between Mars year (MY) 27 and MY 32, thus incorporating the global dust storm event of MY 28 as a signal. We consider two end-member cases for the regolith thermal conductivity and find that the background planetary heat Flow is superposed by atmosphere-induced Perturbations of less than 1.5 mW m−2 at depths below 2 m if regolith thermal conductivity is low and around 0.025 W m−1 K−1 on average. If thermal conductivity is high and around 0.05 W m−1 K−1 on average, Perturbations are less than 2.5 mW m−2 at depths below 3 m. Overall, the influence of interannual variability on subsurface heat Flow is found to be moderate following a global dust storm. Considerably smaller Perturbations are introduced by regional dust storms, which are of shorter duration and smaller magnitude.