Numerical Modeling and Validation of Supersonic Two-Phase Flow of CO2 in Converging-Diverging Nozzles

2011 ◽  
Author(s):  
Miad Yazdani ◽  
Thomas D. Radcliff ◽  
Abbas A. Alahyari ◽  
Mohsen Farzad
Keyword(s):  
Phase Change ◽  
Equilibrium Phase ◽  
Velocity Model ◽  
Attractive Alternative ◽  
Sonic Velocity ◽  
Shock Train ◽  
Alternative Refrigerants ◽  
Two Phase ◽  
Expansion Waves ◽  
Non Equilibrium

CO2 is an attractive alternative to conventional refrigerants due to its low direct global warming effects. Unfortunately, CO2 and many alternative refrigerants have lower thermodynamic performance resulting in larger indirect emissions. Effective use of ejectors to recover part of the lost expansion work, which occurs in throttling devices can close this performance gap and enable the use of CO2. In an ejector, the pressure of the motive fluid is converted into momentum through a choked converging-diverging nozzle, which then entrains and raises the energy of a lower-momentum suction flow. In a two-phase ejector, the motive nozzle flow is complicated by non-equilibrium phase change affecting local sonic velocity and leading to various types of shockwaves, pseudo shocks, and expansion waves inside or outside the exit of the nozzle. Since the characteristics of the jet leaving the motive nozzle greatly affect the performance of the ejector, this paper focuses on the details of flow development and shockwave interaction within and just outside the nozzle. The analysis is based on a high-fidelity model that incorporates real-fluid properties of CO2, local mass and energy transfer between phases, and a two-phase sonic velocity model in the presence of finite-rate phase change. The model has been validated against literature data for two-phase supersonic nozzles as well as overall ejector performance data. The results show that due to non-equilibrium effects and delayed phase change, the flow can choke well downstream of the minimum-area throat. Also, Mach number profiles show that, although phase change is at a maximum near the boundaries, the flow first becomes supersonic in the interior of the flow where sound speed is lowest. Shock waves occurring within the nozzle can interact with the boundary layer flow and result in a ‘shock train’ and a sequence of subsonic and supersonic flow observed previously in single-phase nozzles. In cases with lower nozzle back pressure, the flow continues to accelerate through the nozzle and the exit pressure adjusts in a series of supersonic expansion waves.

Numerical Modeling and Validation of Supersonic Two-Phase Flow of CO2 in Converging-Diverging Nozzles

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Miad Yazdani ◽  
Abbas A. Alahyari ◽  
Thomas D. Radcliff
Keyword(s):  
Phase Change ◽  
Velocity Model ◽  
Attractive Alternative ◽  
Sonic Velocity ◽  
Shock Train ◽  
Alternative Refrigerants ◽  
Two Phase ◽  
Expansion Waves ◽  
Fluid Properties ◽  
Layer Flow

Carbon dioxide is an attractive alternative to conventional refrigerants due to its low direct global warming effects. Unfortunately, CO2 and many alternative refrigerants have lower thermodynamic performance resulting in larger indirect emissions. The effective use of ejectors to recover part of the lost expansion work, which occurs in throttling devices, can close this performance gap and enable the use of CO2. In an ejector, the pressure of the motive fluid is converted into momentum through a choked converging-diverging nozzle, which then entrains and raises the energy of a lower-momentum suction flow. In a two-phase ejector, the motive nozzle flow is complicated by the nonequilibrium phase change affecting local sonic velocity and leading to various types of shockwaves, pseudo shocks, and expansion waves inside or outside the exit of the nozzle. Since the characteristics of the jet leaving the motive nozzle greatly affect the performance of the ejector, this paper focuses on the details of flow development and shockwave interaction within and just outside the nozzle. The analysis is based on a high-fidelity model that incorporates real-fluid properties of CO2, local mass and energy transfer between phases, and a two-phase sonic velocity model in the presence of finite-rate phase change. The model has been validated against the literature data for two-phase supersonic nozzles and overall ejector performance data. The results show that due to nonequilibrium effects and delayed phase change, the flow can choke well downstream of the minimum-area throat. In addition, Mach number profiles show that, although phase change is at a maximum near the boundaries, the flow first becomes supersonic in the interior of the flow where sound speed is lowest. Shock waves occurring within the nozzle can interact with the boundary layer flow and result in a ‘shock train’ and a sequence of subsonic and supersonic flow previously observed in single-phase nozzles. In cases with lower nozzle back pressure, the flow continues to accelerate through the nozzle and the exit pressure adjusts in a series of supersonic expansion waves.

Hydrogen Solubility in Inhomogeneous PD Alloys

1998 ◽  
Vol 513 ◽  
Author(s):  
Ted B. Flanagan ◽  
D. Wang ◽  
J. D. Clewley
Keyword(s):  
Phase Change ◽  
Equilibrium Phase ◽  
Hydrogen Solubility ◽  
Two Phase ◽  
Ni Alloys

ABSTRACTAs-cast, arc-melted Pd-Ni alloys are inhomogeneous and the H2 isotherms for these differ from their homogeneous counterparts in the two phase, (dilute + hydride), regions but not in the dilute phase regions. Pd-Ni alloys, which become inhomogeneous via a ternary (Pd + Ni + H) equilibrium phase change, have H2 isotherms which differ from those of the homogeneous alloy in both the two-phase and the dilute phase regions. These results are discussed with respect to the expected type of inhomogeneities.

scholarly journals Analysis of Non-Equilibrium Phase Change in Transfers at Low Water Content by Considering the Film Flow

2021 ◽  
Vol 17 (1) ◽  
pp. 1-13
Author(s):  
Marcel Bawindsom Kébré ◽  
François Ouédraogo ◽  
Bétaboalé Naon ◽  
Fabien Cherblanc ◽  
François Zougmoré
Keyword(s):  
Phase Change ◽  
Water Content ◽  
Film Flow ◽  
Equilibrium Phase ◽  
Non Equilibrium

Non-Equilibrium Phase Change in a Proton Exchange Membrane Fuel Cell

2010 ◽  
Author(s):  
N. Khajeh-Hosseini-Dalasm ◽  
Kazuyoshi Fushinobu ◽  
Ken Okazaki
Keyword(s):  
Fuel Cell ◽  
Phase Change ◽  
Proton Exchange Membrane ◽  
Equilibrium Phase ◽  
Proton Exchange ◽  
Isothermal Model ◽  
Change Rate ◽  
Liquid Saturation ◽  
Exchange Membrane ◽  
Non Equilibrium

A three-dimensional steady-state two-phase non-isothermal model which couples the water and thermal management has been developed in order to numerically investigate the spatial distribution of the interfacial mass transfer phase-change rate in the cathode side of a proton exchange membrane fuel cell (PEMFC). A non-equilibrium evaporation-condensation phase change rate is incorporated in the model which allows a supersaturation and undersaturation take place. The differences of non-equilibrium phase and equilibrium assumption inside the gas diffusion layer (GDL) has been addressed by comparing the corresponding liquid saturation and temperature distributions. Regarding water management, the assumption of isothermal model versus the non-isothermal model has been investigated. A parametric study has been also carried out to investigate the effects of operation conditions namely as the channel inlet humidity, cell operating temperature and inlet mass flow rate on the phase-change rate. Since the exact values of the phase change constants for the hydrophobic GDL has not been specified yet, the effects of the phase-change constant on the liquid saturation distribution are demonstrated.

Non-Equilibrium Phase Change in Metal Induced by Nanosecond Pulsed Laser Irradiation

2001 ◽  
Vol 124 (2) ◽  
pp. 293-298 ◽  
Author(s):  
Xianfan Xu ◽  
David A. Willis
Keyword(s):  
Phase Change ◽  
Laser Irradiation ◽  
Rapid Heating ◽  
Equilibrium Phase ◽  
Saturation Pressure ◽  
Pulsed Laser ◽  
Superheated Liquid ◽  
Phase Explosion ◽  
Nanosecond Pulsed Laser ◽  
Non Equilibrium

Materials processing using high power pulsed lasers involves complex phenomena including rapid heating, superheating of the laser-melted material, rapid nucleation, and phase explosion. With a heating rate on the order of 109K/s or higher, the surface layer melted by laser irradiation can reach a temperature higher than the normal boiling point. On the other hand, the vapor pressure does not build up as fast and thus falls below the saturation pressure at the surface temperature, resulting in a superheated, metastable state. As the temperature of the melt approaches the thermodynamic critical point, the liquid undergoes a phase explosion that turns the melt into a mixture of liquid and vapor. This article describes heat transfer and phase change phenomena during nanosecond pulsed laser ablation of a metal, with an emphasis on phase explosion and non-equilibrium phase change. The time required for nucleation in a superheated liquid, which determines the time needed for phase explosion to occur, is also investigated from both theoretical and experimental viewpoints.

Two-Phase Critical Flow Simulations by Using a New Non-Equilibrium Model and a Modified Equilibrium Model

2010 ◽  
Author(s):  
Moon-Sun Chung ◽  
Sung-Jae Yi ◽  
Keun-Shik Chang
Keyword(s):  
Phase Change ◽  
Equilibrium Model ◽  
Phase Changes ◽  
Critical Flow ◽  
Vapor Generation ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Equilibrium Parameter ◽  
Phase Mixture ◽  
Non Equilibrium

An accurate prediction of a critical flow discharged from a pressurized pipe system is of most importance in such a safety analysis of nuclear power plants, since it provides the transient boundary conditions during the depressurization transients initiated by a pipe break in primary or secondary systems and during the over-pressurization transients resulting in a relief of coolant through valves. Mass and energy discharge through the opening of pressure boundary affects the system thermal hydraulic responses, that is, phase changes and flow distribution in the system, and the mass inventory remaining in the system necessary to remove core decay heat of a nuclear reactor. Therefore, the safety significance relating to the critical flow led to a development of various empirical and mechanistic critical flow models. However, the accuracies of these models are still in question especially during two-phase critical flow condition. A good example of that is a homogeneous equilibrium model (HEM). The HEM is the basis of several system codes, such as early versions of RELAP, for nuclear loss-of-coolant accident (LOCA). The major non-equilibrium phenomena that are ignored in the HEM are vapor bubble nucleation and interface heat, mass, and momentum transfer. Henry-Fauske empirically handled non-equilibrium vapor generation by introducing a non-equilibrium parameter that allows only a fraction of the equilibrium vapor generation to occur. This approach boils down in essence to a correlation of the deviation between the measured flow rate and the prediction from the HEM: The details of the flow path do not have to be worked out and only needs to know the upstream conditions. However, if we treat non-equilibrium phenomena with this model, it requires an empirical database of the non-equilibrium parameters or their correlations that are so far unknown. Further, because the coefficients are not applied separately to the subcooled liquid and two-phase mixture, we have not been able to treat the non-equilibrium phenomena with the phase change properly. For this reason, we propose the non-equilibrium parameters for subcooled liquid and two-phase mixture, respectively, and then we adopt their combinations according to the flow conditions through the phase change process using the RELAP5/MOD3 code. In addition, we discuss the assessment results of Marviken LBLOCA tests using these non-equilibrium parameter sets with those from the non-equilibrium model by Trapp-Ransom and Chung et al.

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