Applicability of Choking Flow Models for Subcooled Flashing Flow Through Tube Cracks

2011 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Mechanistic Model ◽  
Channel Length ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Flow Models ◽  
Model Predictions ◽  
Flow Through ◽  
The Difference ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. These data are used in assessing the key choking flow models. Based on this assessment a mechanistic choking model is developed. The model is used to predict the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values (∼5) to large values (100). Results are presented on the effects of thermal and mechanical non-equilibrium on the choking flow for small L/D channels. A mechanistic model was developed to model two-phase choking flow through slits. A comparison of model results to experimental data shows that the homogeneous equilibrium based models markedly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases.

Model for Choking of Subcooled Flashing Flow Through a Steam Generator Tube Crack

2012 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Steam Generator ◽  
Mechanistic Model ◽  
Channel Length ◽  
Saturation Curve ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Frictional Pressure Drop ◽  
Flow Through ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. A one dimensional mechanistic model was developed to model two-phase choking flow through slits from conservation principles. The model takes into account channel entrance loss as well as frictional pressure drop for single-phase subcooled liquid. Flashing criteria are defined and temperature and pressure of the fluid are assumed to follow the saturation curve. The two-phase mixture was treated as a quasi-fluid with mixture properties and both homogenous equilibrium (HE) and homogeneous non-equilibrium models were considered. The models were compared with the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values ( 5) to large values (100). Results are presented on the effects of thermal non-equilibrium on the choking flow for small L/D channels. A comparison of model results to experimental data shows that the HE based models grossly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases for HE case.

scholarly journals Numerical Simulation of Non-Equilibrium Two-Phase Wet Steam Flow through an Asymmetric Nozzle

Fluids ◽  
2017 ◽  
Vol 2 (4) ◽  
pp. 63
Author(s):  
Miah Alam ◽  
Manabu Takao ◽  
Toshiaki Setoguchi
Keyword(s):  
Numerical Simulation ◽  
Steam Flow ◽  
Wet Steam ◽  
Two Phase ◽  
Flow Through ◽  
Wet Steam Flow ◽  
Non Equilibrium

Numerical Solution of Wet Steam Flow through Blade Cascade

2016 ◽  
Vol 821 ◽  
pp. 31-38
Author(s):  
Vladimír Hric ◽  
Jan Halama
Keyword(s):  
Equations Of State ◽  
Suction Side ◽  
Steam Flow ◽  
Droplet Growth ◽  
Wet Steam ◽  
Two Phase ◽  
Blade Cascade ◽  
Flow Through ◽  
Wet Steam Flow ◽  
Non Equilibrium

The paper concerns with the numerical modeling of wet steam flow through a blade cascade in transonic regime with non-equilibrium condensation in 2D. Real thermodynamics of vapor phase is implemented in the way which mostly avoid iterations in order to calculate thermodynamic properties. This equation of state is represented by the function for non-dimensional entropy with independent variables scaled density and scaled internal energy. Other equations of state are used for comparison, namely special gas equation which comes from IAPWS-95 formulation and simple pseudo perfect gas relation. We applied simple homogeneous non-equilibrium approach to model two-phase flow. Laminar compressible Navier-Stokes system of equations is used for the mixture properties. Liquid phase is described by the standard method of moments of droplet number distribution function. We consider obtained numerical results to be in good agreement with the measured data. We note the fact that robust and accurate closure of supplementary liquid system (nucleation rate and droplet growth model) is still not available and most often ad-hoc corrections are proposed by the authors. Results show differences among used equations of state as well. This is apparent mainly in the vicinity of condensation shock region on the suction side.

Experimental Study of Entrance Effects on Laminar Gas Flow Through Silicon Orifices

2005 ◽  
Author(s):  
Aaron J. Knobloch ◽  
Joell R. Hibshman ◽  
George Wu ◽  
Rich Saia
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Flow Area ◽  
Fully Developed Flow ◽  
Flow Rates ◽  
Flow Models ◽  
Entry Length ◽  
Orifice Flow ◽  
Measured Flow ◽  
Flow Through

This study summarizes a fundamental investigation of flow through an array of silicon micromachined rectangular slots. The purpose of the study is to evaluate the effect of entrance pressure, flow area, orifice thickness, slot length, and slot width of the orifice on flow rate. These orifices were fabricated using a simple frontside through wafer DRIE process on a 385 μm thick wafer and wafer bonding to create thicker orifices. The dies were then packaged as part of a TO8 can and flow tested. To complement the results of this experimental work, two simple flow models were developed to predict the effect of geometrical and entrance conditions on the flow rate. These models were based on macroscale assumptions that were not necessarily true in the case of thin orifices. One relationship was based on Pouiselle flow which assumes fully developed flow conditions. Calculation of the entry length required for fully developed flow indicate that in the low Reynolds Number regime (32-550) evaluated, the entry flow development requires 2-8 times the thickness of the thickest orifices used for this study. Therefore, calculations of orifice flow based on a Pouiselle model are an overestimate of the actual measured flow rates. Another model examined typical orifice relationships using head loss at the entrance and exit of the slots did not accurately capture the particular flow rates since it overestimated the expansion or constriction losses. A series of experiments where the pressure was varied between 75 and 1000 Pa were performed. A comparison of the Pouiselle flow solution with experimental results was made which showed that the Pouiselle flow model overpredicts the flow rates and more specifically, the effect of width on the flow rates. The results of these tests were used to develop a transfer function which describes the dependence of flow rate on orifice width, thickness, length, and inlet pressure.

Steam-generator simulation with non-equilibrium two-phase flow models

1986 ◽  
Vol 13 (11) ◽  
pp. 617-621
Author(s):  
P. Munshi ◽  
K.S. Ram ◽  
M.S. Kalra ◽  
D.V. Rao
Keyword(s):  
Steam Generator ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Models ◽  
Non Equilibrium

Comparative Study of Loss-of-Coolant Accident Using MAAP4.03 and RELAP5/MOD3.2.2

2002 ◽  
Author(s):  
Chang Hwan Park ◽  
Doo Yong Lee ◽  
Ik Jeong ◽  
Un Chul Lee ◽  
Kune Y. Suh ◽  
...  
Keyword(s):  
Flow Model ◽  
Correction Term ◽  
Sensitivity Study ◽  
Severe Accident ◽  
Primary System ◽  
Two Phase ◽  
Flow Rates ◽  
Flow Models ◽  
Loss Of Coolant Accident ◽  
Loss Of Coolant

Analysis was performed for a large-break loss-of-coolant accident (LOCA) in the APR1400 (Advanced Power Reactor 1400 MWe) with the thermal-hydraulic analysis code RELAP5/ MOD3.2.2 and the severe accident analysis code MAAP4.03. The two codes predicted different sequences for essentially the same initiating condition. As for the break flow and the emergency core cooling (ECC) flow rates, MAAP4.03 predicted considerably higher values in the initial stage than RELAP5/ MOD3.2.2. It was considered that the differing break flow and ECC flow rates would cause the LOCA sequences to deviate from one another between the two codes. Hence, the break flow model in MAAP4.03 was modified with partly implementing the two-phase homogeneous critical flow model and adopting a correction term. The ECC flow model in MAAP4.03 was also varied by changing the hardwired friction factor through the sensitivity study. The modified break flow and ECC flow models yielded more consistent calculational results between RELAP5/MOD3.2.2 and MAAP4.03. It was, however, found that the resultant effect is rather limited unless more mechanistic treatments are done for the primary system in MAAP4.03.

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