The Experts below are selected from a list of 117 Experts worldwide ranked by ideXlab platform

Taku Tsuchiya - One of the best experts on this subject based on the ideXlab platform.

  • Thermodynamic properties of (Mg,Fe2+)SiO3 perovskite at the lower-mantle pressures and temperatures: an internally consistent LSDA+U study
    Geophysical Journal International, 2012
    Co-Authors: Arnaud Metsue, Taku Tsuchiya
    Abstract:

    SUMMARY The thermodynamic properties of (Mg0.9375Fe2+0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions of the lower mantle by first-principles calculations where iron is incorporated in the high and low-spin states for the first time. The electronic structure of ferrous Fe-bearing perovskite is modelled within the internally consistent local spin density approximation with a Hubbard correction U. The thermodynamic properties are derived from the calculation of the Helmholtz free energy within the quasi-harmonic approximation, which requires the phonon frequencies determined by direct calculations of the dynamic matrices. Incorporation of iron, irrespective of its spin states, decreases the acoustic phonon mode frequencies, but less affects high-energy optic modes, leading to decreasing of the acoustic wave velocities in Fe-bearing MgSiO3 perovskite, consistent with previous studies on the elasticity of this phase. This study suggests that the thermodynamic properties of silicate perovskite, such as the equation of state and isothermal bulk modulus, are not largely modified by the incorporation of 6.25 per cent of ferrous iron. Calculations of the Static Enthalpy of the iron-bearing perovskite in the 0–150-GPa-pressure range demonstrate that low-spin ferrous iron is unstable at the pressure conditions of the lower mantle. Finally, we clarify the perovskite-to-post-perovskite phase transition boundary in an (Mg0.9375Fe0.0625)SiO3 composition. Ferrous iron is found to decrease the transition pressure between the two phases with a small binary phase loop of 3–4 GPa at the lowermost mantle conditions from 111 to 115 GPa at 2500 K and from 116 to 119 GPa at 3000 K.

  • lower-mantle pressures and temperatures: an internally consistent LSDA+U study
    2012
    Co-Authors: Arnaud Metsue, Taku Tsuchiya
    Abstract:

    SUMMARY The thermodynamic properties of (Mg0.9375Fe 2+ 0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions of the lower mantle by first-principles calculations where iron is incorporated in the high and low-spin states for the first time. The electronic structure of ferrous Fe-bearing perovskite is modelled within the internally consistent local spin density approximation with a Hubbard correction U. The thermodynamic properties are derived from the calculation of the Helmholtz free energy within the quasi-harmonic approximation,whichrequiresthephononfrequenciesdeterminedbydirectcalculationsofthe dynamic matrices. Incorporation of iron, irrespective of its spin states, decreases the acoustic phonon mode frequencies, but less affects high-energy optic modes, leading to decreasing of the acoustic wave velocities in Fe-bearing MgSiO3 perovskite, consistent with previous studies ontheelasticityofthisphase.Thisstudysuggeststhatthethermodynamicpropertiesofsilicate perovskite, such as the equation of state and isothermal bulk modulus, are not largely modified by the incorporation of 6.25 per cent of ferrous iron. Calculations of the Static Enthalpy of the iron-bearing perovskite in the 0–150-GPa-pressure range demonstrate that low-spin ferrous ironisunstableatthepressureconditionsofthelowermantle.Finally,weclarifytheperovskiteto-post-perovskitephasetransitionboundaryinan(Mg0.9375Fe0.0625)SiO3 composition.Ferrous iron is found to decrease the transition pressure between the two phases with a small binary phase loop of 3–4 GPa at the lowermost mantle conditions from 111 to 115 GPa at 2500 K and from 116 to 119 GPa at 3000 K.

Manoj Kumar - One of the best experts on this subject based on the ideXlab platform.

  • CFD Analysis to Envisage the Fluid Flow Inside a Turboexpander Operating at Cryogenic Temperature
    Advances in Air Conditioning and Refrigeration, 2020
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Debashis Panda, Suraj Kr Behera
    Abstract:

    The one-dimensional design methodology of radial turbine blade profile has a substantial role in the advancement of an efficient liquefaction cycle (cryogenic fluids) because of growing demand in research and various industrial applications. The main part of the current study is to obtain an optimum design of radial turboexpander. The CFD analysis of a turboexpander is carried out to characterize the flow filed inside it. The initial blade profile is generated using ANSYS Blade-Gen which is further modified based on CFD analysis. The pressure, temperature, velocity, Static Enthalpy and entropy at various cross sections are reported.

  • Rotational Effect on Flow Field and Thermal Characteristics of a Turboexpander for Helium Liquefaction System: A Numerical Perspective
    Journal of Heat Transfer, 2020
    Co-Authors: Manoj Kumar, Amitesh Kumar, Suraj K. Behera, Ranjit K. Sahoo
    Abstract:

    Abstract Cryogenic turboexpander is an essential component to produce the refrigeration effect in various helium liquefaction systems. The convergent nozzle and small-scale radial inflow turbine (turboexpander) are the important components that are responsible for increasing the performance of the cycle. In this paper, an optimum preliminary design approach of the turbine and nozzle is explained using real gas properties. Initially, the Sobol method is used to determine the sensitivity indices and optimized range of ten important nondimensional and geometrical variables for better performance of the radial turbine. Three turboexpanders of a modified Collins cycle-based helium liquefaction system have been designed considering the optimized ranges. The proposed method improves the isentropic efficiency and power output of the turbine up to 3.86% and 5.14%, respectively, as compared to the initial design. Hereafter, a comparative three-dimensional numerical analysis is conducted to characterize the flow physics and thermal properties of three turboexpander systems (16 bar and 40 K, 6 bar and 20 K, and 16 bar and 10 K). The thermal and fluid flow properties such as temperature, Prandtl number, Static Enthalpy, entropy, velocity vectors, Reynolds number, and turbulence kinetic energy are determined at different spans and streamwise locations. Moreover, the present numerical results are also verified with the experimental and numerical results obtained from the existing literature. The study highlights the optimal range of design variables for helium turbine, the methodology for helium liquefaction system, and the numerical analysis to understand the flow physics and thermal properties of helium near its boiling point.

  • Preliminary design, flow field, and thermal performance analysis of a helium turboexpander: a numerical approach
    SN Applied Sciences, 2019
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Amitesh Kumar, Debashis Panda, Suraj K. Behera
    Abstract:

    Most studies on cryogenic turboexpanders are focused on parametric studies and mean-line design to increase the performance of cryogenics liquefaction cycle without much attention to the splitter blades which are crucial for the stability of the flow field. This study focuses on a novel mean-line design methodology to develop the radial turbine and nozzle (hereafter renowned as turboexpander) to investigate the performance characteristics. Firstly, Sobol sensitivity analysis is performed to identify the effect of major non-dimensional design variables on isentropic efficiency of the turbine. Secondly, the non-dimensional design variables are optimized using artificial intelligence techniques. Thirdly, three turboexpander models with and without splitter blades are designed within the optimized range of non-dimensional variables. After that, the three-dimensional numerical analysis is carried out to visualize the effect of splitter blades on flow field and thermal characteristics of the turboexpander. It is noticed that the passage vortices and flow separation are minimized using the splitter blades. The numerical results are further validated with available data in the literature. A detailed comparative analysis of Mach number, pressure, temperature, velocity, Static Enthalpy, Static entropy, etc., is carried out at different operating conditions. The results reveal that the use of splitter blades has a tremendous effect on the performance and flow field characteristics of the radial turbine. The proposed methodology specifies the insights for an optimum turbine design methodology of a cryogenic turboexpander, Sobol sensitivity analysis, prediction capability of artificial intelligence methods, numerical techniques to simulate the assimilating performance of turboexpander, as it is the most crucial and expensive component of turboexpander-based cryogenic system.

  • A methodology for the performance prediction: flow field and thermal analysis of a helium turboexpander
    Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2019
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Amitesh Kumar, Debashis Panda, Suraj K. Behera
    Abstract:

    Helium liquefaction systems are widely used in nuclear fission, superconductivity, space industries, and other scientific instruments. However, the efficiency of these systems is quite low due to the cryogenic operating temperature. In this regard, the one-dimensional design methodology of the helium turbine and nozzle (hereafter, renowned as turboexpander) is important to increase the efficiency of the system. This paper demonstrates the sensitivity analysis and optimal range of non-dimensional design variables on which the radial inflow turbine has maximum efficiency, minimum losses, and maximum power output using artificial intelligence techniques. On this basis, three turboexpander models are developed within the optimal range of predicted non-dimensional variables. After that, a comparative numerical study is carried out to highlight the flow field and thermal characteristics of helium fluid. The standard two equations $$k{-}\omega $$ k - ω SST model is used to solve the three-dimensional incompressible flow inside the computational domain. The numerical results are validated with the available experimental data from the existing literature. The variation of Mach number, Reynolds number, Prandtl number, Static entropy, Static Enthalpy, temperature, and pressure inside the turboexpander is significantly affected by blade profile which is enormously affected by the design methodology. The study also demonstrates the flow separation region, vortex formation, tip leakage flow, secondary losses, and its reasons along with the spanwise location. The results highlight the importance of the design methodology, sensitivity analysis, the prediction capability of the artificial intelligence network, numerical methodology, and development of the helium turboexpander prototype models.

  • Design and numerical investigation to visualize the fluid flow and thermal characteristics of non-axisymmetric convergent nozzle
    Elsevier, 2019
    Co-Authors: Manoj Kumar, R.k. Sahoo, S.k. Behera
    Abstract:

    In this paper, numerical simulations are conducted to visualize the fluid flow and thermal characteristics of a non-axisymmetric convergent nozzle. The novel design methodology is based on curve-fitting approach. The curves used for designing the nozzle are based on a combination of fifth and third order polynomial at upper and lower surfaces respectively. The computations are performed using commercially available computational fluid dynamics (CFD) tool ANSYS CFX®. Firstly, mesh independence analysis are carried out. Then, numerical simulation is further validated for medium and low-pressure helium by comparing it with the available experimental data. Thereafter, an exhaustive analysis is carried out to compare the fluid flow behavior inside the nozzle for two cryogenic fluids, nitrogen and helium at three different inlet pressure and temperature. The fluid flow pattern, pressure, velocity, Prandtl number, Static Enthalpy, Reynolds number, eddy viscosity, etc. are identified at various positions. The Mach number and temperature at the outlet of the nozzle is the key feature of this analysis which satisfies the criteria for a nozzle which is used for the high, medium and low-pressure turbine. The analysis provides a better understanding of the further improvement of the design methodology or performed an experiment. The designed nozzle has a tremendous effect on the fluid flow behavior and suitable for impulse type turbine with a small amount of reaction used in a turboexpander. The work proposes a new design methodology for designing a non-axisymmetric airfoil convergent nozzle of rectangular cross-section. Keywords: Non-axisymmetric nozzle, Fluid flow, Thermal characteristics, Numerical analysi

Berend Van Wachem - One of the best experts on this subject based on the ideXlab platform.

  • conservative finite volume framework and pressure based algorithm for flows of incompressible ideal gas and real gas fluids at all speeds
    Journal of Computational Physics, 2020
    Co-Authors: Fabian Denner, Fabien Evrard, Berend Van Wachem
    Abstract:

    Abstract A conservative finite-volume framework, based on a collocated variable arrangement, for the simulation of flows at all speeds, applicable to incompressible, ideal-gas and real-gas fluids is proposed in conjunction with a fully-coupled pressure-based algorithm. The applied conservative discretisation and implementation of the governing conservation laws as well as the definition of the fluxes using a momentum-weighted interpolation are identical for incompressible and compressible fluids, and are suitable for complex geometries represented by unstructured meshes. Incompressible fluids are described by predefined constant fluid properties, while the properties of compressible fluids are described by the Noble-Abel-stiffened-gas model, with the definitions of density and specific Static Enthalpy of both incompressible and compressible fluids combined in a unified thermodynamic closure model. The discretised governing conservation laws are solved in a single linear system of equations for pressure, velocity and temperature. Together, the conservative finite-volume discretisation, the unified thermodynamic closure model and the pressure-based algorithm yield a conceptually simple, but versatile, numerical framework. The proposed numerical framework is validated thoroughly using a broad variety of test-cases, with Mach numbers ranging from 0 to 239, including viscous flows of incompressible fluids as well as the propagation of acoustic waves and transiently evolving supersonic flows with shock waves in ideal-gas and real-gas fluids. These results demonstrate the accuracy, robustness and the convergence, as well as the conservation of mass and energy, of the numerical framework for flows of incompressible and compressible fluids at all speeds, on structured and unstructured meshes. In particular, the precise recovery of a divergence-free velocity field in the incompressible limit, the accurate prediction of acoustic waves, and the convergence to the correct weak solution for strong shock waves with the same finite-volume discretisation and pressure-based algorithm are important features of the proposed numerical framework.

Suraj K. Behera - One of the best experts on this subject based on the ideXlab platform.

  • Rotational Effect on Flow Field and Thermal Characteristics of a Turboexpander for Helium Liquefaction System: A Numerical Perspective
    Journal of Heat Transfer, 2020
    Co-Authors: Manoj Kumar, Amitesh Kumar, Suraj K. Behera, Ranjit K. Sahoo
    Abstract:

    Abstract Cryogenic turboexpander is an essential component to produce the refrigeration effect in various helium liquefaction systems. The convergent nozzle and small-scale radial inflow turbine (turboexpander) are the important components that are responsible for increasing the performance of the cycle. In this paper, an optimum preliminary design approach of the turbine and nozzle is explained using real gas properties. Initially, the Sobol method is used to determine the sensitivity indices and optimized range of ten important nondimensional and geometrical variables for better performance of the radial turbine. Three turboexpanders of a modified Collins cycle-based helium liquefaction system have been designed considering the optimized ranges. The proposed method improves the isentropic efficiency and power output of the turbine up to 3.86% and 5.14%, respectively, as compared to the initial design. Hereafter, a comparative three-dimensional numerical analysis is conducted to characterize the flow physics and thermal properties of three turboexpander systems (16 bar and 40 K, 6 bar and 20 K, and 16 bar and 10 K). The thermal and fluid flow properties such as temperature, Prandtl number, Static Enthalpy, entropy, velocity vectors, Reynolds number, and turbulence kinetic energy are determined at different spans and streamwise locations. Moreover, the present numerical results are also verified with the experimental and numerical results obtained from the existing literature. The study highlights the optimal range of design variables for helium turbine, the methodology for helium liquefaction system, and the numerical analysis to understand the flow physics and thermal properties of helium near its boiling point.

  • Preliminary design, flow field, and thermal performance analysis of a helium turboexpander: a numerical approach
    SN Applied Sciences, 2019
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Amitesh Kumar, Debashis Panda, Suraj K. Behera
    Abstract:

    Most studies on cryogenic turboexpanders are focused on parametric studies and mean-line design to increase the performance of cryogenics liquefaction cycle without much attention to the splitter blades which are crucial for the stability of the flow field. This study focuses on a novel mean-line design methodology to develop the radial turbine and nozzle (hereafter renowned as turboexpander) to investigate the performance characteristics. Firstly, Sobol sensitivity analysis is performed to identify the effect of major non-dimensional design variables on isentropic efficiency of the turbine. Secondly, the non-dimensional design variables are optimized using artificial intelligence techniques. Thirdly, three turboexpander models with and without splitter blades are designed within the optimized range of non-dimensional variables. After that, the three-dimensional numerical analysis is carried out to visualize the effect of splitter blades on flow field and thermal characteristics of the turboexpander. It is noticed that the passage vortices and flow separation are minimized using the splitter blades. The numerical results are further validated with available data in the literature. A detailed comparative analysis of Mach number, pressure, temperature, velocity, Static Enthalpy, Static entropy, etc., is carried out at different operating conditions. The results reveal that the use of splitter blades has a tremendous effect on the performance and flow field characteristics of the radial turbine. The proposed methodology specifies the insights for an optimum turbine design methodology of a cryogenic turboexpander, Sobol sensitivity analysis, prediction capability of artificial intelligence methods, numerical techniques to simulate the assimilating performance of turboexpander, as it is the most crucial and expensive component of turboexpander-based cryogenic system.

  • A methodology for the performance prediction: flow field and thermal analysis of a helium turboexpander
    Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2019
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Amitesh Kumar, Debashis Panda, Suraj K. Behera
    Abstract:

    Helium liquefaction systems are widely used in nuclear fission, superconductivity, space industries, and other scientific instruments. However, the efficiency of these systems is quite low due to the cryogenic operating temperature. In this regard, the one-dimensional design methodology of the helium turbine and nozzle (hereafter, renowned as turboexpander) is important to increase the efficiency of the system. This paper demonstrates the sensitivity analysis and optimal range of non-dimensional design variables on which the radial inflow turbine has maximum efficiency, minimum losses, and maximum power output using artificial intelligence techniques. On this basis, three turboexpander models are developed within the optimal range of predicted non-dimensional variables. After that, a comparative numerical study is carried out to highlight the flow field and thermal characteristics of helium fluid. The standard two equations $$k{-}\omega $$ k - ω SST model is used to solve the three-dimensional incompressible flow inside the computational domain. The numerical results are validated with the available experimental data from the existing literature. The variation of Mach number, Reynolds number, Prandtl number, Static entropy, Static Enthalpy, temperature, and pressure inside the turboexpander is significantly affected by blade profile which is enormously affected by the design methodology. The study also demonstrates the flow separation region, vortex formation, tip leakage flow, secondary losses, and its reasons along with the spanwise location. The results highlight the importance of the design methodology, sensitivity analysis, the prediction capability of the artificial intelligence network, numerical methodology, and development of the helium turboexpander prototype models.

  • Design and numerical investigation to visualize the fluid flow and thermal characteristics of non-axisymmetric convergent nozzle
    Engineering Science and Technology an International Journal, 2019
    Co-Authors: Manoj Kumar, Ranjit K. Sahoo, Suraj K. Behera
    Abstract:

    Abstract In this paper, numerical simulations are conducted to visualize the fluid flow and thermal characteristics of a non-axisymmetric convergent nozzle. The novel design methodology is based on curve-fitting approach. The curves used for designing the nozzle are based on a combination of fifth and third order polynomial at upper and lower surfaces respectively. The computations are performed using commercially available computational fluid dynamics (CFD) tool ANSYS CFX®. Firstly, mesh independence analysis are carried out. Then, numerical simulation is further validated for medium and low-pressure helium by comparing it with the available experimental data. Thereafter, an exhaustive analysis is carried out to compare the fluid flow behavior inside the nozzle for two cryogenic fluids, nitrogen and helium at three different inlet pressure and temperature. The fluid flow pattern, pressure, velocity, Prandtl number, Static Enthalpy, Reynolds number, eddy viscosity, etc. are identified at various positions. The Mach number and temperature at the outlet of the nozzle is the key feature of this analysis which satisfies the criteria for a nozzle which is used for the high, medium and low-pressure turbine. The analysis provides a better understanding of the further improvement of the design methodology or performed an experiment. The designed nozzle has a tremendous effect on the fluid flow behavior and suitable for impulse type turbine with a small amount of reaction used in a turboexpander. The work proposes a new design methodology for designing a non-axisymmetric airfoil convergent nozzle of rectangular cross-section.

Arnaud Metsue - One of the best experts on this subject based on the ideXlab platform.

  • Thermodynamic properties of (Mg,Fe2+)SiO3 perovskite at the lower-mantle pressures and temperatures: an internally consistent LSDA+U study
    Geophysical Journal International, 2012
    Co-Authors: Arnaud Metsue, Taku Tsuchiya
    Abstract:

    SUMMARY The thermodynamic properties of (Mg0.9375Fe2+0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions of the lower mantle by first-principles calculations where iron is incorporated in the high and low-spin states for the first time. The electronic structure of ferrous Fe-bearing perovskite is modelled within the internally consistent local spin density approximation with a Hubbard correction U. The thermodynamic properties are derived from the calculation of the Helmholtz free energy within the quasi-harmonic approximation, which requires the phonon frequencies determined by direct calculations of the dynamic matrices. Incorporation of iron, irrespective of its spin states, decreases the acoustic phonon mode frequencies, but less affects high-energy optic modes, leading to decreasing of the acoustic wave velocities in Fe-bearing MgSiO3 perovskite, consistent with previous studies on the elasticity of this phase. This study suggests that the thermodynamic properties of silicate perovskite, such as the equation of state and isothermal bulk modulus, are not largely modified by the incorporation of 6.25 per cent of ferrous iron. Calculations of the Static Enthalpy of the iron-bearing perovskite in the 0–150-GPa-pressure range demonstrate that low-spin ferrous iron is unstable at the pressure conditions of the lower mantle. Finally, we clarify the perovskite-to-post-perovskite phase transition boundary in an (Mg0.9375Fe0.0625)SiO3 composition. Ferrous iron is found to decrease the transition pressure between the two phases with a small binary phase loop of 3–4 GPa at the lowermost mantle conditions from 111 to 115 GPa at 2500 K and from 116 to 119 GPa at 3000 K.

  • lower-mantle pressures and temperatures: an internally consistent LSDA+U study
    2012
    Co-Authors: Arnaud Metsue, Taku Tsuchiya
    Abstract:

    SUMMARY The thermodynamic properties of (Mg0.9375Fe 2+ 0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions of the lower mantle by first-principles calculations where iron is incorporated in the high and low-spin states for the first time. The electronic structure of ferrous Fe-bearing perovskite is modelled within the internally consistent local spin density approximation with a Hubbard correction U. The thermodynamic properties are derived from the calculation of the Helmholtz free energy within the quasi-harmonic approximation,whichrequiresthephononfrequenciesdeterminedbydirectcalculationsofthe dynamic matrices. Incorporation of iron, irrespective of its spin states, decreases the acoustic phonon mode frequencies, but less affects high-energy optic modes, leading to decreasing of the acoustic wave velocities in Fe-bearing MgSiO3 perovskite, consistent with previous studies ontheelasticityofthisphase.Thisstudysuggeststhatthethermodynamicpropertiesofsilicate perovskite, such as the equation of state and isothermal bulk modulus, are not largely modified by the incorporation of 6.25 per cent of ferrous iron. Calculations of the Static Enthalpy of the iron-bearing perovskite in the 0–150-GPa-pressure range demonstrate that low-spin ferrous ironisunstableatthepressureconditionsofthelowermantle.Finally,weclarifytheperovskiteto-post-perovskitephasetransitionboundaryinan(Mg0.9375Fe0.0625)SiO3 composition.Ferrous iron is found to decrease the transition pressure between the two phases with a small binary phase loop of 3–4 GPa at the lowermost mantle conditions from 111 to 115 GPa at 2500 K and from 116 to 119 GPa at 3000 K.