Numerical Analysis of a Novel Two-Phase Turbine using Thermal Non-Equilibrium, Homogeneous Nucleation Phase Change

2020 ◽  
pp. 100827
Author(s):  
Sham Rane ◽  
Li He
Keyword(s):  
Numerical Analysis ◽  
Phase Change ◽  
Homogeneous Nucleation ◽  
Two Phase ◽  
Nucleation Phase ◽  
Non Equilibrium

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.

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.

A Study of Non-Equilibrium Two-Phase Pressure Drop in Converging Channels Supplied With Atomized Liquid

2006 ◽  
Author(s):  
J. D. Schwarzkopf ◽  
C. T. Crowe ◽  
B. Q. Li
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Phase Change ◽  
Heat Fluxes ◽  
Two Phase ◽  
Converging Channel ◽  
Mini Channels ◽  
Phase Pressure ◽  
Good Agreement ◽  
Non Equilibrium

Two-phase pressure drop measurements are very difficult to make while the fluid is in non-equilibrium condition (i.e. while phase change is occurring). This is further complicated by the fact that supplying the channels with an initial quality comprised of atomized liquid and entrained gas changes the presupposed trends. The purpose of this paper is to present methods of measurement for fluctuating two-phase pressure drop in converging mini-channels with phase change (i.e. in the heat acquisition zone), an initial quality, and varying heat fluxes. The inlet and exit hydraulic diameters of the converging channel are 1.55mm and 1.17mm respectively and the fluid was PF5050. A numerical model was developed to understand the parameters contributing to the trends identified in the data. The numerical model includes the momentum effects of droplets from entrainment and atomization. The model shows good agreement with the experimental data.

On the Analysis of Critical Flow Discharged From a Pressurized Pipe System Using a HEM

2009 ◽  
Author(s):  
Moon-Sun Chung ◽  
Sung-Jae Lee
Keyword(s):  
Phase Change ◽  
Equilibrium Model ◽  
Critical Flow ◽  
Vapor Generation ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Pipe System ◽  
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 have not been 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.

Exsolution and inversion in pigeonite from the Whin Sill, Northern England

1978 ◽  
Vol 36 (1) ◽  
pp. 474-475
Author(s):  
P.P.K. Smith
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Homogeneous Nucleation ◽  
Silicate Mineral ◽  
Antiphase Boundaries ◽  
Two Phase ◽  
Primitive Form ◽  
The Core ◽  
Nucleation Mechanisms ◽  
And Inversion

Grains of pigeonite, a calcium-poor silicate mineral of the pyroxene group, from the Whin Sill dolerite have been ion-thinned and examined by TEM. The pigeonite is strongly zoned chemically from the composition Wo8En64FS28 in the core to Wo13En34FS53 at the rim. Two phase transformations have occurred during the cooling of this pigeonite:- exsolution of augite, a more calcic pyroxene, and inversion of the pigeonite from the high- temperature C face-centred form to the low-temperature primitive form, with the formation of antiphase boundaries (APB's). Different sequences of these exsolution and inversion reactions, together with different nucleation mechanisms of the augite, have created three distinct microstructures depending on the position in the grain.In the core of the grains small platelets of augite about 0.02μm thick have farmed parallel to the (001) plane (Fig. 1). These are thought to have exsolved by homogeneous nucleation. Subsequently the inversion of the pigeonite has led to the creation of APB's.

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