Upendra S. Rohatgi

A simple model for predicting the release of a liquid-vapor mixture from a large break in a pressurized container

Abstract This paper presents a simple, accurate model for determining the amount and composition of a liquid-vapor release from a pressurized tank that develops a large break above the level of the liquid. Most models commonly used by the chemical industry assume that there is thermal- and mechanical-equilibrium between the liquid- and the vapor-phase (homogeneous equilibrium models, HEM). While this assumption is valid for releases though long pipes and nozzles, we found that it overestimates the total amount released during rapid discharges through large breaks in a vessel when there is insufficient time for the mixture to become homogeneous. We derived an analytical non-homogeneous, thermal equilibrium model that accurately determines the void fraction of the mixture at the time of the release, and the quantity of a release from a pressurized container. Our model is based on equations describing the transfer of interfacial momentum between the liquid- and the vapor- phases that develop during the quick depressurization of a vessel. The model’s predictions are verified by comparing them with actual measurements of the void fraction, and with the results of the RELAP5 model. Also, our model is used to determine emissions of nitrogen oxides and nitric acid in an actual rupture of a railcar tank. The results agreed with actual observations, whereas a homogeneous equilibrium model gave erroneous predictions.

Assessment of RAMONA-3B methodology with oscillatory flow tests

Abstract The instability event at the LaSalle County Plant (GE BWR-5) imposed a new challenge on the computer codes available for reactor transient analysis. While the codes were originally designed to predict non-oscillatory transients, the new requirement on the code is to model limit cycle oscillations with large amplitudes, where feed-back effects from the core and the balance of plant, and the nonlinear effects are significant. Two of the United States Nuclear Regulatory Commissions (USNRC) computer codes, namely RAMONA-3B/MODO [1] and HIPA-BWR of Engineering Plant Analyzer [2] were expected, and are shown in part in this paper, to meet the above demands. The RAMONA-3B/MOD1 has now been upgraded from the RAMONA-3B/MODO. It has a three dimensional neutron kinetics model, coupled to multi-channel nonequilibrium drift-flux formulation, and an explicit integration scheme for the thermal hydraulics. The accuracy of the thermohydraulics in the RAMONA-3B code was assessed for the new application by modelling oscillatory transients in the FR1GG test facilty. Nodalization studies showed that twenty-four axial nodes are sufficient for a converged solution; calculations with twelve axial nodes produce, in comparison to the 24-node calculation, the deviation of 4.4% in the peak gain of the power to flow transfer function. The code predicted correctly the effects of power and inlet subcooling on the transfer function gain and the system resonance frequency. For the six available tests modeled, the code-predicted peak gain differs from the experimentally obtained gain on the average by +7%, with the standard deviation of ±30%. The uncertainty in the experimental data lies between −11% and +12%. The difference between predicted and measured frequency at the peak gain on the average is −6%, with the standard deviation of ±14%.

Validation of the engineering plant analyzer methodology with peach bottom 2 stability tests

Abstract The Engineering Plant Analyzer (EPA) had been developed in 1984 at Brookhaven National Laboratory to simulate plant transients in boiling water reactors (BWR). Recently, the EPA with its High-Speed Interactive Plant Analyzer code for BWRs (HIPA-BWR) simulated for the first time oscillatory transients with large, non-linear power and flow amplitudes; transients which are centered around the March 9, 1988 instability at the LaSalle-2 BWR power plant. The EPAs capability to simulate oscillatory transients has been demonstrated first by comparing simulation results with LaSalle-2 plant data (Wulff et al., NUREG/CR-5816, BNL-NUREG-52312, Brookhaven National Laboratory, 1992). This paper presents an EPA assessment on the basis of the Peach Bottom 2 instability tests (Carmichael and Niemi, EPRI NP-564, Electric Power Research Institute, Palo Alto,CA, 1978). This assessment of the EPA appears to constitute the first validation of a time-domain reactor systems code on the basis of frequency-domain criteria, namely power spectral density, gain and phase shift of the pressure-to-power transfer function. The reactor system pressure was disturbed in the Peach Bottom 2 power plant tests, and in their EPA simulation, by a pseudo-random, binary sequence signal. The data comparison revealed that the EPA predicted for Peach Bottom tests PT1, PT2, and PT4 the gain of the power-to-pressure transfer function with the biases and standard deviations of (−10 ± 28)%, (−1 ± 40)% and (+28 ± 52)%, respectively. The respective frequencies at the peak gains were predicted with the errors of +6%, +3%, and −28%. The differences between the predicted and the measured phase shift increased with increasing frequency, but stayed within the margin of experimental uncertainty. The code assessment presented here is valid only for small-amplitude oscillations, but it encompasses neutron kinetics, fuel thermal response, coolant thermohydraulics and control-system dynamics. To our knowledge, this assessment of the time-domain HIPA-BWR code by frequency-domain methods and spectral plant data demonstrates for the first time the feasibility of such an assessment.

Computation of flow fields induced by water spraying of an unconfined gaseous plume

Flow fields induced by the interaction of water sprays and a gaseous plume have been studied in the context of absorbing and dispersing and accidental release of toxic gas in the air. The effectiveness of water sprays in absorbing highly water soluble gases was recently demonstrated in extended laboratory and field tests. In this paper, computer simulations are presented of the Hawk, Nevada Test Site, series of water spray/HF mitigation field tests. The model used, HFSPRAY, is a Eulerean/Lagrangian model which simulates the momentum, mass and energy interactions between a water spray and a turbulent plume of HF in air; the model can predict the flow velocities, temperature, water vapor,a nd HF concentration fields in two-dimensional large-geometries for spraying in any direction, (i.e, down-flow, inclined-down-flow, up-flow, and co-current horizontal flow). The model was validated against recent data on spraying of water on large releases of HF. It can provide a direct input to the design of water spray systems for HF mitigation.

Methods of reducing vehicle aerodynamic drag

A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.

Anticipated Transient Without Scram Analysis of the Simplified Boiling Water Reactor Following Main Steam Isolation Valve Closure with Boron Injection

The simplified boiling water reactor (SBWR) operating in natural circulation is designed with many passive safety features. An anticipated transient without scram (ATWS) initiated by inadvertent closure of the main steam isolation valve (MSIV) in an SBWR has been analyzed using the RAMONA-4B code of Brookhaven National Laboratory. This analysis demonstrates the predicted performance of the SBWR during an MSIV closure ATWS, followed by shutdown of the reactor through injection of boron into the reactor core from the standby liquid control system.

Evolution of a Cavitating Bubble in a Nonuniform Pressure Field

The cavitation erosion problem is not a new one; however, it is still important and even becomes more pressing. This is associated with requirements to justify and extend service life of power-generating plants while obviously seeking the maximum efficiency. Currently semiempirical correlation relations are typically used in pump designing for prediction of modes of operation that may be hazardous in terms of development of cavitation erosion [1, 2]. It appears, however, that a progress can be made in this field by introducing numerical modeling of flow with direct modeling of the cavitation erosion process. This optimism is based on an established fact that the major effect of erosion damage is observed in the mode of operation between the “NPSH-incipient” mode (mode of activation of vapor-phase formation centers) and the “NPSH-3%” mode (mode where a noticeable vapor volume content is produced in the near-wall layer), i.e. in the mode of operation where the vapor volume content is small and its effect on flow characteristics can be neglected.© 2007 ASME

Modeling the Operation Regimes in Ultra-High Temperature Continuous Reactors

The main advantage of carbon material treatment in electro-thermal furnaces with fluidized bed [EFFB] at 2000–3000C is that they allow producing graphite of high chemical purity, which is especially important in manufacture of ion-lithium batteries. The team conducted extensive research into hydraulic and heat modes of such units and developed a methodology for their design based on the concept of increase in electric resistance with fluidization. The choice of the working space configuration and the operation mode of EFFB are largely determined by the specific electrical resistance [SER] of the fluidized bed. This parameter is a complex function of a number of factors: fluidization character, uniformity of the bed and the temperature, nature and size of the material fractions, current density and furnace atmosphere composition. It is vital to take into account relationships between SER, working temperature T and current density i, which eventually define electrothermal mode of the unit operation. Thus, if graphite size is d = 130μm within temperature range T = 0–2500C and current density i = 0,004–1.0 A/cm2, SER varies in reverse proportion to these parameters Statistic processing of the experimental data allowed to obtain regressive function SER = f (i, t), which we used as the basis of mathematic modeling, heat balance calculation and predicting transitory and operation modes of EFFB with 10kg/hour productivity: Display FormulaSER=0.01.84.711-2.,593*10-2.T-46.854*i+1.205*10-2.T*i,Ω-m′Resulting volt-ampere characteristics (VACs) of the furnace have maximum values at constant temperature (T = const) which is explained by the non-linear character of the SER function. There exists a technological temperature limit of EFFB responsible for its stable operation. The furnace operation beyond the stability margin depends on the power source characteristics which may cause a sharp power drop or a shorting. The VAC characteristics are determined by the type of material, geometry of the furnace working space, electrode diameter, active zone height, the gap between the electrode and the lining, design of heat insulation and the cooling system. Taking these parameters into consideration, it is possible to conduct a preliminary analysis of the unit stable operation modes as early as during the design stage.Copyright

Investigation of Air Flow Cooling of Li-Ion Batteries

Lithium -ion batteries are used in electric cars, hybrid cars and Boeing 787 Dreamliner. There is an issue with heat generation in these batteries that may cause fire and reduce performance.An experimental chamber has been setup that provides dynamic and static cooling/heating regimes for Li-ion batteries. Air flow is produced by air station with maximum output of 80 m3/h. The maximum possible pressure drop is 7000 Pa. Air station can work both in pumping and exhausting mode. This test setup will be used to study various surface topology to enhance heat transfer without increase weight.Experimental setup contains two-stage temperature stabilization system. During the first stage we use the preliminary heating or cooling of the inlet air in the air buffer. The aim is to achieve the air temperature close to required inlet temperature. During the next stage air passes through the chamber with temperature controller where eventually the flow temperature is set. This approach provides flow temperature stabilization within −30°C to +50°C range with 0.2°C accuracy.For our studies we have designed and manufactured simulators of Li-ion battery power cells with the same thermal properties as the original ones. Each simulator contains 40 surface temperature sensors (20 per side). The data from sensors is transferred to computer by the NI-6225 PC card for control and further processing. The design of the simulators provides information about the placement of cooling surfaces with various surface elements and its efficiency — fins, triangles, wings, etc.In this paper, the characteristics of cooling surfaces with filleted pins will be reported. We have measured the surface temperature distributions and obtained the corresponding cooling diagrams for 10–40°C temperature range and 1 m/sec – 4 m/sec flow rates. The experimental results are compared to the computer simulation using SolidWorks Flow Simulation™ software.Copyright

Numerical Procedure for Assessment of Centrifugal Pump Cavitation Erosion

Currently the cavitation erosion damage becomes a critical issue that limits the centrifugal pump life cycle extension. Despite of a long history of studying the cavitation erosion phenomenon in centrifugal pumps there are still no reliable assessment methods except semi-empirical formula having rather limited application and accuracy. The paper is presenting a novel method for assessment of centrifugal pump cavitation erosion combining 3D unsteady flow CFD modeling and numerical analysis of cavitation bubbles behavior. The Navier-Stokes equations are solved by a splitting method with the implicit algorithm and high-order numerical scheme for convective transfer terms. The 3D numerical procedure is based on non-staggered Cartesian grid with adaptive local refinement and a sub-grid geometry resolution method for description of curvilinear complex boundaries like blade surfaces. Rotation is accounted with implementation of “sliding-grid” technology. The method considers evolution of the bubble in 3D flow from initial conditions until the disruption moment with determination of the erosion jet power impact. Validation of the method on model feed centrifugal pump stages is completed for two model centrifugal impellers Centrifugal impeller #1 is designed with a goal of through-passed shaft pump flow modeling. There are completed computations of cavitating bubbles’ evolution under non-uniform pressure field that show the non-uniform pressure distribution near the blade surface causes an essential influence on cavitation erosion. Computational prediction of the impeller #1 cavitation erosion damage is confirmed experimentally.© 2008 ASME