Flow Choking Research Articles

Estimation of flow coefficient for subsonic natural gas flow through orifice-type chokes using a simple method

Abstract Choke valves are critical elements in gas production facilities. Malfunction or failure of a choke valve can seriously affect safety, the environment and production rates. Choke is a device installed at wellhead or down hole to control the flow rate for maintaining sufficient back pressure to prevent formation damage, to prevent water/gas coning, to stabilize the flow rate and to produce the reservoir at the most efficient possible rate. In this work a simple-to-use method is developed to estimate the choke flow coefficient for natural gas subsonic flow through orifice-type chokes as a function of Reynolds number and the ratio of choke diameter to pipe diameter. The results can be used in follow-up calculations for rapid estimating gas passage through a choke under subsonic flow conditions. Estimations are found to be in excellent agreement with reported data in the literature with average absolute deviation being less than 0.4%.

Hysteresis phenomenon in supersonic flow past a system of cylinders

The interaction between the bow shocks ahead of a system of bodies in a supersonic flow is numerically investigated. Flow past cylinders with parallel axes lying in the plane perpendicular to the flow direction is calculated. Three different shock interaction patterns are obtained in modeling flow past an infinite periodic lattice, namely, the regular and Mach-type regimes and a regime with flow choking. In the case of two bodies a collective bow shock is formed. Transition between the flow patterns with variation in the freestream Mach number and the spacing between the cylinders is studied. Regular-to-Mach-configuration transition and vice versa occurs at particular angles of inclination of the bow shock at the interaction point determined by the criterion of a maximum flow deflection angle and the von Neumann criterion, respectively.

Tapered-Bean Steam Chokes Revisited

This paper (SPE 144615) was accepted for presentation at the SPE Western North American Regional Meeting, Anchorage, 7–11 May 2011, and revised for publication. Original manuscript received for review 5 July 2011. Paper peer approved 31 August 2011. Summary Controlling and monitoring flow rates at continuousand cyclicsteam-injection wells are important elements of reservoir-heat management. For nearly 30 years, critical flow chokes have proven to be the most reliable and cost-effective means of controlling steam injection into heavy-oil reservoirs. Flow-control efficiency has been further improved with tapered-bore bean inserts to achieve critical flow, with only 10 to 15% pressure loss across the choke. For the past 10 years, the standard steam-choke assembly has consisted of a 1-in.-outer-diameter (OD) and 6-in.-long bean with a 6° tapered bore inserted inside a 2-in.-OD cage nipple or housing. Larger-diameter cage nipples and bean inserts have been required for steam-injection rates exceeding 500 B/D. More recently, a costcutting practice has been employed using shorter tapered beans inserted in standard choke assemblies. This paper presents the results of field tests conducted to evaluate the effectiveness of shorter tapered-bean length for controlling steam-injection rates. Transition from subcritical to critical flow and overall pressure loss for different tapered-bean lengths are presented. A modified Thornhill-Craver flow-rate equation is provided for criticaland subcritical-flow regions. Calculated and measured rates are compared, and their relative uncertainties are assessed.

A simple predictive tool to estimate flow coefficient for subsonic natural gas flow through nozzle-type chokes

Abstract In this work a simple-to-use method is developed to estimate the choke flow coefficient for natural gas subsonic flow through nozzle-type chokes as a function of Reynolds number and the ratio of choke diameter to pipe diameter. The results can be used in follow-up calculations for rapid estimation of gas passage through a choke under subsonic flow conditions for Reynolds number and the ratio of choke diameter to pipe diameter between 0.4 and 0.75. Estimations are found to be in excellent agreement with reported data in the literature with average absolute deviation being less than 0.3%. The tool developed in this study can be of immense practical value for petroleum engineers to have a quick check of gas flow through chokes at various conditions without opting for any field trials. In particular, engineers would find the approach to be user-friendly with transparent calculations involving no complex expressions.

A contribution to the understanding of cavitation effects in Diesel injector nozzles through a combined experimental and computational investigation

Abstract In this paper a combined experimental and computational study was carried out in order to assess the ability of a homogeneous equilibrium model in predicting the experimental behaviour observed from the hydraulical characterization of a nozzle. The nozzle used was a six-orifice microsac nozzle, with cylindrical holes, and therefore inclined to cavitate. The experimental results available for the validation purpose comprised measurements of mass flow rate and spray momentum flux, which correctly combined provide also fundamental information such as discharge coefficient, nozzle exit effective velocity and area contraction. The model was proved to be able of reproducing the experimental results with high degree of confidence and, through the exploration of the internal flow, allowed the explanation of widely reported experimental findings related to cavitation phenomena: the mass flow choking induced by cavitation and the increment of effective injection velocity.

Analysis of Heat Loadings in the Forced Cooled Electronic Chassis or Cold Plate

The forced cooled electronic chassis is revisited and, because of recent developments, changes which amend the design procedure are proposed. These considerations involve the thickness of the cover and splitter plates dictated by the Murray–Gardner assumptions, the impact of the so-called heat flow choke, and the development of a new concept involving the equivalent height of a fin. The current literature is reviewed and summarized, so that the new concept proposed here can be clearly apparent.

Aerodynamic analysis and design of Busemann biplane: towards efficient supersonic flight

Aiming to realize a low-drag supersonic transport, Busemann biplane concept was adopted in this study. Two- and three-dimensional (2D and 3D) biplanes were analysed and designed to improve their aerodynamic performance using computational fluid dynamics. It was confirmed that 3D biplane wings have better aerodynamic-performance areas than 2D biplane airfoils. A winglet is also useful for improvement of their aerodynamic performance. Aerodynamic characteristics of these biplanes at their off-design conditions were also analysed. In 3D wings, a flow choking and its attendant hysteresis as starting problems, which arise when the biplanes accelerate from low Mach numbers, disappear at lower Mach numbers than those in 2D airfoils. It was confirmed that hinged slats and flaps are effective to settle these issues. Finally, interference effects of a body with the biplanes were investigated. When the biplane wings are affected by the expansion waves from the body, their aerodynamic performance at the design Mach number and the starting Mach number are better and lower than those of their isolated wings, respectively. A 3D biplane wing obtained by an inverse-design method was applied to the body. The wing of this wing–body configuration achieves higher aerodynamic performance than the 2D flat-plate airfoil at sufficient lift conditions, which is the almost identical performance of 2D biplane airfoils.

Advanced approach to build the design space for the primary drying of a pharmaceutical freeze‐drying process

This paper deals with the design space of a pharmaceutical freeze-drying process. Mathematical modeling is used to investigate the effect of the operating conditions [shelf temperature (T(shelf)) and chamber pressure (P(c))] on product temperature (that has to remain below a limit value) and sublimation flux (that has to be lower than a level that would cause choked flow). The algorithm takes into account the variation of the design space with time due to the increase in the dried layer thickness. Besides T(shelf) and P(c), the dried layer thickness is used as the third coordinate of the diagram, thus resulting in just one graph that can be used to build recipes with variable operating conditions, as well as to analyze the effect of process failures. Such results are compared with those obtained when the variation of the design space with time is not accounted for; in this case, the design space comprises those operating conditions that fulfill the operation constraints throughout primary drying, thus giving a much more conservative recipe when designing the process or potentially misleading results when analyzing process failures. Finally, the proposed method has been used to design, and experimentally validate, a recipe for a pharmaceutical formulation.

Overtip Choking and Its Implications on Turbine Blade-Tip Aerodynamic Performance

At engine representative flow conditions a significant portion of flow over a high pressure turbine blade tip is transonic. In the present work, the choking flow behavior and its implications on over-tip leakage flow loss generation are computationally analyzed. An extensively developed RANS code (HYDRA) is adopted. Firstly a high speed linear cascade validation case is introduced, and the computations are compared with the experimental data to identify and establish the capability of the code in predicting the aerodynamics losses for a transonic turbine blade tip. The computational studies are then carried out for the blading configuration at different flow conditions ranging from a nearly incompressible to a nominal transonic one, enabling to establish a qualitatively consistent trend of the tip leakage losses in relation to the exit Mach number conditions. The results clearly show that the local choking sets a limiter for the over tip leakage mass flow, leading to a different leakage flow structure compared to that in a low speed and/or unchoked condition. The existence of tip choking effectively blocks the influence of the suction surface side on the over-tip flow, and hence leads to a breakdown of the pressure-driven mechanism, conventionally used in tip treatment and designs. The decoupling between blade loading and over tip leakage mass flow is clearly identified and highlighted. Furthermore, the realization of the loading-leakage flow decoupling indicates a possibility of a high-load blading design with a relatively low tip leakage loss. A high load blading is generated and analyzed to demonstrate the feasibility of such designs with a reduced tip leakage loss.

Investigation of the Behavior of Ventilated Supercavities

A study has been carried out to determine various aspects of the flow physics of a supercavitating vehicle at the Saint Anthony Falls Laboratory (SAFL). For the experimental work presented here, artificial supercavitation behind a sharp-edged disk was investigated for various model configurations. Results regarding supercavity shape, closure, and ventilation requirements versus Froude number are presented. Conducting experiments in water tunnels introduces blockage effects that are not present in nature. As a result, effects related to flow choking must also be considered. Two methods for computing ventilated cavitation number were compared, the first based on direct measurement of pressure and velocity, and the second technique based on measured cavity geometry and the use of previous numerical results. The results obtained are similar in character to previously reported data, but differ in measured numerical values. An attempt is made to correlate results from water tunnel experiments, where blockage has a significant effect, to an unbounded open flow. Supercavitation parameters, especially the minimum obtainable cavitation number are strongly affected by tunnel blockage.

Analysis of Unsteady Tip and Endwall Heat Transfer in a Highly Loaded Transonic Turbine Stage

In a previous study, vane-rotor shock interactions and heat transfer on the rotor blade of a highly loaded transonic turbine stage were simulated. The geometry consists of a high pressure turbine vane and a downstream rotor blade. This study focuses on the physics of flow and heat transfer in the rotor tip, casing, and hub regions. The simulation was performed using the unsteady Reynolds-averaged Navier–Stokes code MSU-TURBO. A low Reynolds number k-ε model was utilized to model turbulence. The rotor blade in question has a tip gap height of 2.1% of the blade height. The Reynolds number of the flow is approximately 3×106/m. Unsteadiness was observed at the tip surface that results in intermittent “hot spots.” It is demonstrated that unsteadiness in the tip gap is governed by inviscid effects due to high speed flow and is not strongly dependent on pressure ratio across the tip gap contrary to published observations that have primarily dealt with subsonic tip flows. The high relative Mach numbers in the tip gap lead to a choking of the leakage flow that translates to a relative attenuation of losses at higher loading. The efficacy of new tip geometry is discussed to minimize heat flux at the tip while maintaining choked conditions. In addition, an explanation is provided that shows the mechanism behind the rise in stagnation temperature on the casing to values above the absolute total temperature at the inlet. It is concluded that even in steady (in a computational sense) mode, work transfer to the near tip fluid occurs due to relative shearing by the casing. This is believed to be the first such explanation of the work transfer phenomenon in the open literature. The difference in pattern between steady and time-averaged heat fluxes at the hub is also explained.

Numerical Calculation of Throttle Nozzle Diameter Influence on Downhole Choke Flow Field

With calculation results comparison of different throttle nozzle diameter value, This article analyses the flow field with throttle nozzle diameter variety of 1.0mm, 2.0mm, 2.4mm, 2.6mm, 2.8mm, 4.0mm, while the other parameters take same value (such as the inlet pressure is 20mpa, the outlet pressure is 10MPa, the temperature is 333k, and the well depth is about 2000m). the results present the influence upon downhole choke flow field including pressure, velocity, temperature distribution. The pressure field composed by minimum on the axis shows the pressure dropping change at the throttle nozzle outlet. Velocity field gives the maximum value of velocity and Mach number, which determines the flow field is subsonic or supersonic flow. With hydrate formation conditions, temperature field formed by minimum on the axis gives the existing judgment of hydrate formation under a certain condition. With the throttle nozzle diameter increasing, the outlet flow maximum velocity increases, and the differential pressure before and after nozzle becomes larger, which means the pressure drop effect is better. The downhole choke design of throttle nozzle needs to consider the combination effects of pressure drop and temperature drop. These parameters provide reference for downhole choke structure design and operating performance improvement.

Numerical Calculation and Simulation Research on Natural Gas Downhole Choke Flow Field

Natural gas downhole choke process inlet is high temperature and high pressure. Usually it can achieves 10~30MPa, while it will be higher in high pressure drilling well. It is installing thousands of meters underground. It is difficult carrying on field test during working process. These special situations make the choke outlet flow being complex, which includes expansion wave, compression wave, and energy transformation. The physical experiment is difficult. To be more accurately analyzing the compressible viscous turbulent motion of downhole choke internal flow field, this article uses RNG − model for three dimensional numerical simulation. It analyzes the result of flow field streamlines, velocity, Mach number, pressure, and temperature distribution. It analyzes the influence on hydrate formation of choke working process. Numerical calculation can provide useful reference for the prevention of natural gas hydrate formation and optimization design of downhole choke.

Thermal crisis of a vortex source

The effect of circulation in the field of a bulk vortex source on thermal crisis (flow choking induced by energy supply in a layer in accordance with a known law) is studied. Substantial changes in the value of energy supply parameter and slight variations in the coordinate of the critical cross section in which the velocity of sound is attained are revealed, and the dependence of these parameters on the location and width of the heat-supply region is noted. The possibility of transition to a supersonic flow when the heat release region is near the minimal cross section of the vortex source is analyzed. The difference between the cases of polyatomic and monatomic gases is demonstrated. Distinguishing features of the vortex sink are considered.

Aerothermal Performance of a Winglet at Engine Representative Mach and Reynolds Numbers

This paper presents an experimental and numerical investigation of the aerothermal performance of an uncooled winglet tip, under transonic conditions. Spatially resolved heat transfer data, including winglet tip surface and near-tip side-walls, are obtained using the transient infrared thermography technique within the Oxford high speed linear cascade test facility. Computational fluid dynamics (CFD) predictions are also conducted using the Rolls-Royce HYDRA suite. Most of the spatial heat transfer variations on the tip surface are well-captured by the CFD solver. The transonic flow pattern and its influence on heat transfer are analyzed, which shows that the turbine blade tip heat transfer is greatly influenced by the shock wave structure inside the tip gap. The effect of the casing relative motion is also numerically investigated. The CFD results indicate that the local heat transfer distribution on the tip is affected by the relative casing motion but the tip flow choking and shock wave structure within the tip gap still exist in the aft region of the blade.

ICONE19-43676 Assessment of Choking Flow Models for Subcooled Flashing Flow through Steam Generator Tube Cracks

The state-of-the-art modeling of leak rates through individual pipe stress corrosion cracks is based on regression analysis of experimentally determined leak rates and defects size. This has relatively large uncertainties. Accurate leak rate predictions require two key parameters, crack area and choking flow rate. The thermalhydraulics models employed in the leak rate calculations are generally based on the Henry-Fauske model of two-phase flow through long channels. For small length to diameter ratio (L/D) channels such as in steam generator tube cracks both mechanical and thermal nonequilibrium must be accounted. Another very important problem in verifying the model of the critical flow through cracks is the limited data on the crack geometry. 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.

Effect of CO2 Hydrate on Flow Behavior of Liquid CO2 in Porous Media

In the sea around Japan, there is the region of sufficient environment of CO2 hydrate generation. When liquid CO2 is injected in those regions, choking of liquid CO2 flow is expected to occur due to CO2 hydrate generation in pipe arrangement or seabed. The purpose of the present study is to evaluate the influence of CO2 hydrate on the flow of liquid CO2 when liquid CO2 injected in a porous media as simulating seabed. In order to reveal the influence of CO2 hydrate, differential pressure is measured under both condition of CO2 hydrate generated and not generated. As the results, in the case of the hydrate generation environment, it is identified that differential pressure became large compared with the case of no-hydrate generation. In the upstream part, the differential pressure became large compared with the downstream region. It is suggested that flow resistance occurred due to choking of CO2 hydrate membrane on the porous media. Friction factor is also compared with the Ergun's equation which is proposed for single-phase flow in a porous media. The measured friction factor is larger than the value from Ergun's equation.

On the Use of Mathematical Models to Build the Design Space for the Primary Drying Phase of a Pharmaceutical Lyophilization Process

The aim of this article is to show a procedure to build the design space for the primary drying of a pharmaceuticals lyophilization process. Mathematical simulation of the process is used to identify the operating conditions that allow preserving product quality and meeting operating constraints posed by the equipment. In fact, product temperature has to be maintained below a limit value throughout the operation, and the sublimation flux has to be lower than the maximum value allowed by the capacity of the condenser, besides avoiding choking flow in the duct connecting the drying chamber to the condenser. Few experimental runs are required to get the values of the parameters of the model: the dynamic parameters estimation algorithm, an advanced tool based on the pressure rise test, is used to this purpose. A simple procedure is proposed to take into account parameters uncertainty and, thus, it is possible to find the recipes that allow fulfilling the process constraints within the required uncertainty range. The same approach can be effective to take into account the heterogeneity of the batch when designing the freeze-drying recipe.

Ski jump design

This paper is concerned with ski jump design for overflow dams and chute spillways. Despite the vast scope of literature on this subject, research in this field is still needed. Three important issues are addressed: take-off angle, length of the jet trajectory and choking flow. The aim is to summarise existing experience, present new formulae for convenient design and propose directions for future research.

Experimental and Numerical Investigation of a Non-Axisymmetric Strut Based Ejector

Tests were performed in a non-axisymmetric, single nozzle, strut-based ejector to investigate mass flow entrainment, choking mechanisms and stream mixing as a function of primary (strut nozzle) to secondary (duct inlet) flow stagnation pressure ratio. Experimental results show a mass flow choke in the mixing duct rather than a traditional aerodynamic choke in the strut gap. The stream mixing length was constant for lower primary flow pressures, whereas mixing length varied with pressure at higher values. A companion numerical study was performed using Reynolds Averaged Navier-Stokes solutions to investigate several turbulence models. Based on both 2-D and 3-D simulation results, compressibility correction to conventional incompressible twoequation models was required for capturing the supersonic ejector mixing phenomena. The Baldwin-Lomax and the SST two-equation models were capable of capturing the essential flow features. Even with compressibility correction, the k-Σ model could not reproduce wall-domin...