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

  • thermal expansivity and equation of state up to transition pressure and melting temperature nacl as an example
    Solid State Communications, 1994
    Co-Authors: Munish Kumar
    Abstract:

    Abstract The Thermodynamic Relation recently proposed by Kumar for thermal expansivity is used to compute the coefficient of volume thermal expansion for NaCl from atmospheric pressure upto the structural transition pressure at the temperatures ranging from room temperature upto the melting temperature. The formula requires the values of interatomic separations as a function of pressure and temperature which are evaluated from the theory of interionic potential recently developed in the field of high pressure and high temperature physics. The results obtained are in good agreement with the available experimental

Ezio Spessa - One of the best experts on this subject based on the ideXlab platform.

  • a comprehensive Thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous two phase barotropic flow model
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2006
    Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio Spessa
    Abstract:

    A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive Thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase barotropic flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a Thermodynamic Relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the flow discontinuities induced by them were numerically predicted and analyzed.

  • a comprehensive Thermodynamic approach to acoustic cavitation simulation in high pressure injection systems by a conservative homogeneous barotropic flow model
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2003
    Co-Authors: Andrea Catania, Alessandro Ferrari, Michele Manno, Ezio Spessa
    Abstract:

    A general conservative numerical model for the simulation of transmission-line unsteady fluid dynamics has been developed and applied to high-pressure injection systems. A comprehensive Thermodynamic approach for modeling acoustic cavitation, i.e., cavitation induced by wave propagation, was proposed on the basis of a conservative homogeneous two-phase barotropic flow model of a pure liquid, its vapor, and a gas, both dissolved and undissolved. A physically consistent sound speed equation was set in a closed analytical form of wide application. For the pure-liquid flow simulation outside the cavitation regions, or in the absence of these, temperature variations due to compressibility effects were taken into account, for the first time in injection system simulation, through a Thermodynamic Relation derived from the energy equation. Nevertheless, in the cavitating regions, an isothermal flow was retained consistently with negligible macroscopic thermal effects due to vaporization or condensation, because of the tiny amounts of liquid involved. A novel implicit, conservative, one-step, symmetrical, and trapezoidal scheme of second-order accuracy was employed to solve the partial differential equations governing the pipe flow. It can also be enhanced at a high-resolution level. The numerical model was applied to wave propagation and cavitation simulation in a high-pressure injection system of the pump-line-nozzle type for light and medium duty vehicles. The system was relevant to model assessment because, at part loads, it presented cavitating flow conditions that can be considered as severe, at least for a diesel injection system. The predicted time histories of pressure at two pipe locations and of injector needle lift were compared to experimental results, substantiating the validity and robustness of the developed conservative model in simulating acoustic cavitation inception and desinence with great accuracy degree. Cavitation transients and the flow discontinuities induced by them were numerically predicted and analyzed.

Qinjun Kang - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann modeling of pool boiling with large liquid gas density ratio
    International Journal of Thermal Sciences, 2017
    Co-Authors: Wenzhen Fang, Li Chen, Qinjun Kang
    Abstract:

    Abstract In the present paper, a 2D multiple-relaxation-time pseudopotential lattice Boltzmann model combined with the modified thermal lattice Boltzmann method is adopted to simulate the bubble nucleation, growth and departures process on a heated plate. It is a direct numerical simulation of boiling heat transfer determined by the local temperature and Thermodynamic Relation given by the equation of state. By using a smaller value of a in the P-R equation of state, a thicker liquid-vapor interface is formed and a better numerical stability at a large liquid/vapor density ratio is obtained. Furthermore, the conjugated boundary of heated plate and fluids is specially dealt with to avoid the rapid change of heat flux at the interface. The boiling heat transfer at a density ratio around 200 can be simulated. The results show that: the boiling heat flux decreases during the bubble expansion process while increases during the rewetting process; the average heat flux of boiling at Ts = 0.68Tc is much larger than that at Ts = 0.86Tc; bubble occurs earlier on a hydrophobic surface than a hydrophilic one; there exists a remained vapor on a hydrophobic surface after bubble departure, while it is not observed for hydrophilic surface; for the simulated boiling curve, the maximum (critical) heat flux decreases with the decreasing wettability of surfaces; there exists an optimal width of the rectangular cavity making the best heat transfer performance of surfaces; in this study, the roughness surface with a circle cavity has the best heat transfer performance.

Michal Pavelka - One of the best experts on this subject based on the ideXlab platform.

  • gradient and generic time evolution towards reduced dynamics
    Philosophical Transactions of the Royal Society A, 2020
    Co-Authors: Miroslav Grmela, Vaclav Klika, Michal Pavelka
    Abstract:

    Reduction of a mesoscopic dynamical theory to equilibrium Thermodynamics brings to the latter theory the fundamental Thermodynamic Relation (i.e. entropy as a function of the Thermodynamic state va...

  • gradient and generic evolution towards reduced dynamics
    arXiv: Mathematical Physics, 2019
    Co-Authors: Miroslav Grmela, Vaclav Klika, Michal Pavelka
    Abstract:

    Let (M,J) be a dynamical model of macroscopic systems and (N,K) a less microscopic model (i.e. a model involving less details) of the same macroscopic systems; M and N are manifolds, J are vector fields on M, and K are vector fields on N. Let P be the phase portrait corresponding to (M,J) (i.e. P is the set of all trajectories in M generated by a family of vector fields in J), and R the phase portrait corresponding to (N,K). Thermodynamics in its general sense is a pattern recognition process in which R is recognized as a pattern in P. In particular, the classical (both equilibrium and nonequilibrium) Thermodynamics arises in the investigation of Relations between models (M,J) and models without time evolution, i.e. models with K= 0. In such case R is a submanifold of M composed of fixed points. Let Su mapping M to R be a potential, called an upper entropy, generating the vector field J. The equilibrium Thermodynamic Relation in N is the lower entropy Sd(y) defined by Sd(y)=Su(x=y), where x is in M,y in N, and y is given by a final destination (i.e. when the time goes to infinity) of x in the time evolution generated by the vector field J. In this paper we show that if K is not zero (e.g. in externally forced or, in other words, open systems), then the reduction also provides Thermodynamics (we call it flux-Thermodynamics). If certain conditions are satisfied, then the lower entropy Ss, that arises in the investigation of the approach of J to K, is the time derivative of the lower entropy Sd arising in the investigation of the approach of M to N as t goes to infinity.

Jorge Vinals - One of the best experts on this subject based on the ideXlab platform.

  • phase field model for a weakly compressible soft layered material morphological transitions on smectic isotropic interfaces
    Soft Matter, 2021
    Co-Authors: Eduardo Vitral, Perry H Leo, Jorge Vinals
    Abstract:

    A coupled phase-field and hydrodynamic model is introduced to describe a two-phase, weakly compressible smectic (layered phase) in contact with an isotropic fluid of different density. A non-conserved smectic order parameter is coupled to a conserved mass density in order to accommodate non-solenoidal flows near the smectic–isotropic boundary arising from density contrast between the two phases. The model aims to describe morphological transitions in smectic thin films under heat treatment, in which arrays of focal conic defects evolve into conical pyramids and concentric rings through curvature dependent evaporation of smectic layers. The model leads to an extended Thermodynamic Relation at a curved surface that includes its Gaussian curvature, non-classical stresses at the boundary and flows arising from density gradients. The temporal evolution given by the model conserves the overall mass of the liquid crystal while still allowing for the modulated smectic structure to grow or shrink. A numerical solution of the governing equations reveals that pyramidal domains are sculpted at the center of focal conics upon a temperature increase, which display tangential flows at their surface. Other cases investigated include the possible coalescence of two cylindrical stacks of smectic layers, formation of droplets, and the interactions between focal conic domains through flow.

  • phase field model for a weakly compressible soft layered material morphological transitions on smectic isotropic interfaces
    arXiv: Soft Condensed Matter, 2021
    Co-Authors: Eduardo Vitral, Perry H Leo, Jorge Vinals
    Abstract:

    A coupled phase-field and hydrodynamic model is introduced to describe a two-phase, weakly compressible smectic (layered phase) in contact with an isotropic fluid of different density. A non-conserved smectic order parameter is coupled to a conserved mass density in order to accommodate non-solenoidal flows near the smectic-isotropic boundary arising from density contrast between the two phases. The model aims to describe morphological transitions in smectic thin films under heat treatment, in which arrays of focal conic defects lead to conical pyramids and concentric rings through curvature dependent evaporation of smectic layers. The model leads to an extended Thermodynamic Relation at a curved surface that includes its Gaussian curvature, non-classical stresses at the boundary and flows arising from density gradients. The temporal evolution given by the model conserves the overall mass of the liquid crystal while still allowing for the modulated smectic structure to grow or shrink. A numerical solution of the governing equations reveals that pyramidal domains are sculpted at the center of focal conics upon a temperature increase, which display tangential flows at their surface. Other cases investigated include the possible coalescence of two cylindrical stacks of smectic layers, formation of droplets, and the interactions between focal conic domains through flow.