scholarly journals Two-phase change in CO2, Antarctic temperature and global climate during Termination II

2013 ◽  
Vol 6 (12) ◽  
pp. 1062-1065 ◽  
Author(s):  
A. Landais ◽  
G. Dreyfus ◽  
E. Capron ◽  
J. Jouzel ◽  
V. Masson-Delmotte ◽  
...  
Keyword(s):  
Phase Change ◽  
Global Climate ◽  
Two Phase

scholarly journals Numerical Study of a Cooling System Using Phase Change of a Refrigerant in a Thermosyphon

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3634
Author(s):  
Grzegorz Czerwiński ◽  
Jerzy Wołoszyn
Keyword(s):  
Mass Transfer ◽  
Phase Change ◽  
Heat Dissipation ◽  
Cooling System ◽  
Numerical Study ◽  
Relaxation Parameter ◽  
Phase Changes ◽  
Transfer Time ◽  
Two Phase ◽  
Time Relaxation

With the increasing trend toward the miniaturization of electronic devices, the issue of heat dissipation becomes essential. The use of phase changes in a two-phase closed thermosyphon (TPCT) enables a significant reduction in the heat generated even at high temperatures. In this paper, we propose a modification of the evaporation–condensation model implemented in ANSYS Fluent. The modification was to manipulate the value of the mass transfer time relaxation parameter for evaporation and condensation. The developed model in the form of a UDF script allowed the introduction of additional source equations, and the obtained solution is compared with the results available in the literature. The variable value of the mass transfer time relaxation parameter during condensation rc depending on the density of the liquid and vapour phase was taken into account in the calculations. However, compared to previous numerical studies, more accurate modelling of the phase change phenomenon of the medium in the thermosyphon was possible by adopting a mass transfer time relaxation parameter during evaporation re = 1. The assumption of ten-fold higher values resulted in overestimated temperature values in all sections of the thermosyphon. Hence, the coefficient re should be selected individually depending on the case under study. A too large value may cause difficulties in obtaining the convergence of solutions, which, in the case of numerical grids with many elements (especially three-dimensional), significantly increases the computation time.

Shock–like structure of phase-change flow in porous media

1981 ◽  
Vol 104 ◽  
pp. 467-482 ◽  
Author(s):  
L. A. Romero ◽  
R. H. Nilson
Keyword(s):  
Porous Media ◽  
Phase Change ◽  
Single Phase ◽  
Flow In Porous Media ◽  
Two Phase ◽  
Flows In Porous Media ◽  
Dissipative Effects ◽  
Condensing Flows ◽  
Self Similar ◽  
Phase Change Flows

Shock-like features of phase-change flows in porous media are explained, based on the generalized Darcy model. The flow field consists of two-phase zones of parabolic/hyperbolic type as well as adjacent or imbedded single-phase zones of either parabolic (superheated, compressible vapour) or elliptic (subcooled, incompressible liquid) type. Within the two-phase zones or at the two-phase/single-phase interfaces, there may be steep gradients in saturation and temperature approaching shock-like behaviour when the dissipative effects of capillarity and heat-conduction are negligible. Illustrative of these shocked, multizone flow-structures are the transient condensing flows in porous media, for which a self-similar, shock-preserving (Rankine–Hugoniot) analysis is presented.

Modeling of a two-phase system with phase change, applications in planetology: Earth's inner core and Transneptunian objects

2021 ◽  
Author(s):  
Robin Métayer ◽  
Renaud Deguen ◽  
Aurélie Guilbert-Lepoutre ◽  
Marine Lasbleis ◽  
Jenny Wong
Keyword(s):  
Phase Change ◽  
Inner Core ◽  
Phase System ◽  
Two Phase ◽  
Transneptunian Objects ◽  
Earth’S Inner Core

scholarly journals The role of a mid-air collision in drifting snow

2018 ◽  
Author(s):  
Shuming Jia ◽  
Zhengshi Wang ◽  
Shumin Li
Keyword(s):  
Friction Velocity ◽  
Global Climate ◽  
Three Dimensional ◽  
Particle Collision ◽  
High Concentration ◽  
Three Dimensional Model ◽  
Two Phase ◽  
Drifting Snow ◽  
Collision Mechanism

Abstract. Drifting snow, a common two-phase flow movement in high and cold areas, contributes greatly to the mass and energy balance of glacier and ice sheets and further affects the global climate system. Mid-air collisions occur frequently in high-concentration snow flows; however, this mechanism is rarely considered in current models of drifting snow. In this work, a three-dimensional model of drifting snow with consideration of inter-particle collisions is established; this model enables the investigation of the role of a mid-air collision mechanism in openly drifting snow. It is found that the particle collision frequency increases with the particle concentration and friction velocity, and the blown snow with a mid-air collision effect produces more realistic transport fluxes since inter-particle collision can enhance the particle activity under the same condition. However, the snow saltation mass flux basically shows a cubic dependency with friction velocity, which distinguishes it from the quadratic dependence of blown sand movement. Moreover, the snow saltation flux is found to be largely sensitive to the particle size distribution since the suspension snow may restrain the saltation movement. This research could improve our understanding of the role of the mid-air collision mechanism in natural drifting snow.

Binary two-phase flow with phase change in porous media

2001 ◽  
Vol 27 (3) ◽  
pp. 477-526 ◽  
Author(s):  
S. Békri ◽  
O. Vizika ◽  
J.-F. Thovert ◽  
P.M. Adler
Keyword(s):  
Porous Media ◽  
Phase Change ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase

Phase Change Process Inside a Small-radii Cylinder Subjected to Cyclic Convective Boundary Conditions: a Numerical Study

2021 ◽  
Author(s):  
Yousef Kanani ◽  
Avijit Karmakar ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Freezing Process ◽  
Fourier Number ◽  
Two Phase ◽  
Convective Boundary

Abstract We numerically investigate the melting and solidi?cation behavior of phase change materials encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square wave). Initially, we explore the effect of the Stefan and Biot numbers on the non-dimensionalized time required (i.e. reference Fourier number Tref ) for a PCM initially held at Tcold to melt and reach the cross?ow temperature Thot. The increase in either Stefan or Biot number decreases Tref and can be predicted accurately using a correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed for the above process. We further study the effect of the cyclic Fourier number on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates towards the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and higher overall heat transfer is achieved as the surface temperature oscillates in the vicinity of the melting temperature, which increases the effective temperature difference driving the convective heat transfer.

Development of a Phase-field Method for Phase Change Simulations Using a Conservative Allen-cahn Equation

2021 ◽  
Author(s):  
Akinori Tamura ◽  
Kenichi Katono
Keyword(s):  
Phase Change ◽  
Phase Field ◽  
Computational Efficiency ◽  
Power Plants ◽  
Field Method ◽  
Industrial Applications ◽  
Phase Field Method ◽  
Benchmark Problems ◽  
Two Phase ◽  
Cahn Equation

Abstract Two-phase flows including a phase change such as liquid-vapor flows play an important role in many industrial applications. A deeper understanding of the phase change phenomena is required to improve performance and safety of nuclear power plants. For this purpose, we developed a phase change simulation method based on the phase field method (PFM). Low computational efficiency of the conventional PFM based on the Cahn-Hilliard equation is an obstacle in practical simulations. To resolve this problem, we presented a new PFM based on the conservative Allen-Cahn equation including a phase change model. The wettability also needs to be considered in the phase change simulation. When we apply the conventional wetting boundary condition to the conservative Allen-Cahn equation, there is a problem that the mass of each phase is not conserved on the boundary. To resolve this issue, we developed the mass correction method which enables mass conservation in the wetting boundary. The proposed PFM was validated in benchmark problems. The results agreed well with the theoretical solution and other simulation results, and we confirmed that this PFM is applicable to the two-phase flow simulation including the phase change. We also investigated the computational efficiency of the PFM. In a comparison with the conventional PFM, we found that our proposed PFM was more than 100 times faster. Since computational efficiency is an important factor in practical simulations, the proposed PFM will be preferable in many industrial simulations.

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