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Measurements of decompression wave speed in conventional and rich natural gas mixtures following rupture of a high-pressure pipe have been conducted A high-pressure stainless steel rupture tube (internal diameter = 38.1 mm and 42 m long) has been constructed and instrumented with 16 high frequency-response pressure transducers mounted very close to the rupture end and along the length of the tube to capture the pressure-time traces of the decompression wave. Tests were conducted for initial pressures of 33-37 MPa-a and a temperature range of 21-68[degrees]C. The experimentally determined decompression wave speeds were compared with both GASDECOM and PIPEDECOM predictions with and without nonequilibrium condensation delays at phase crossing. The interception points of the isentropes representing the decompression process with the corresponding phase envelope of each mixture were correlated with the respective plateaus observed in the decompression wave speed profiles. Additionally, speeds of sound in the undisturbed gas mixtures at the initial pressures and temperatures were compared with predictions by five equations of state, namely, BWRS, AGA-8, Peng--Robinson, Soave--Redlich--Kwong, and Groupe Europeen de Recherches Gazieres. The measured gas decompression curves were used to predict the fracture arrest toughness needed to assure fracture control in natural gas pipelines. The rupture tube test results have shown that the Charpy fracture arrest values predicted using GASEDCOM are within +7% (conservative) and -11% (nonconservative) of the rupture tube predicted values. Similarly, PIPEDECOM with no temperature delay provides fracture arrest values that are within +13% and -20% of the rupture tube predicted values, while PIPEDECOM with a 1[degrees]C temperature delay provides fracture arrest values that are within 0% and -20% of the rupture tube predicted values. Ideally, it would be better if the predicted values by the equations of state were above the rupture tube predicted values to make the predictions conservative but that was not always the case. [DOI: 10.1115/1.4001438] Keywords: gas pipelines, rupture, rich gas, decompression wave speed, GASDECOM, PIPEDECOM, expansion waves, dynamic pressure measurements

The gas-liquid two-phase slug flow regime phenomenon is commonly encountered in the chemical engineering industry, particularly in oil and gas production transportation pipelines. Slug flow regime normally occurs for a range of pipe inclinations, and gas and liquid flowrates. A pipeline operating in the slug flow regime creates high fluctuations in gas and liquid flowrates at the outlet. Therefore, the monitoring of slugs and the measurement of their characteristics, such as the gas void fraction, are necessary to minimize the disruption of downstream process facilities. In this paper, a correlation between gas void fraction, absolute acoustic emission energy, and slug velocities in a two-phase air/water flow regime was developed using an acoustic emission technique. It is demonstrated that the gas void fraction can be determined by measurement of acoustic emission. [DOI: 10.1115/1.4000463] Keywords: acoustic emission, slug flow, gas void fraction, slug velocity, process monitoring

Computational simulations of flow and heat transfer in heat recovery steam generators (HRSGs) of vertical-and horizontal-tube designs are reported. The main objective of the work was to obtain simple modifications of their internal configuration that render the flow of combustion gas more spatially uniform. The computational method was validated by comparing some of the simulation results for a scaled-down laboratory model with experimental measurements in the same. Simulations were then carried out for two plant HRSGs--without and with the proposed modifications. The results show significantly more uniform combustion gas flow in the modified configurations. Heat transfer calculations were performed for one superheater section of the vertical-tube HRSG to determine the effect of the configuration modification on heat transfer from the combustion gas to the steam flowing in the superheater tubes. [DOI: 10.1115/1.2751505]

A preconditioned numerical method for gas-liquid two-phase flows is applied to solve cavitating flow. The present method employs a finite-difference method of the dual time-stepping integration procedure and Roe's flux difference splitting approximation with the MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. The present density-based numerical method permits simple treatment of the whole gas-liquid two-phase flow field, including wave propagation, large density changes and incompressible flow characteristics at low Mach number. Two-dimensional internal flows through a backward-facing step duct, convergent-divergent nozzles and decelerating cascades are computed using this method. Comparisons of predicted and experimental results are provided and discussed. [DOI: 10.1115/1.1777230]

The application of pneumatic metrology to control dimensional accuracy on machined parts is based on the measurement of gas flow resistance through a restricted section formed by a jet orifice placed at a small distance away from a machined surface. The backpressure, which is sensed and indicated by a pressure gauge, is calibrated to measure dimensional variations. It has been found that in some typical industrial applications, the nozzles are subject to fouling, e.g., dirt and oil deposits accumulate on their frontal areas, thus requiring more frequent calibration of the apparatus for reliable service. In this paper, a numerical and experimental analysis of the flow behavior in the region between an injection nozzle and a flat surface is presented. The analysis is based on the steady-state axisymmetric flow of an incompressible fluid. The governing equations, coupled with the appropriate boundary conditions, are solved using the SIMPLER algorithm. Results have shown that for the standard nozzle geometry used in industrial applications, an annular low-pressure separated flow area was found to exist near the frontal surface of the nozzle. The existence of this area is believed to be the cause of the nozzle fouling problem. A study of various alternate nozzle geometries has shown that this low-pressure recirculation area can be eliminated quite readily. Well-designed chamfered, rounded, and reduced frontal area nozzles have all reduced or eliminated the separated recirculation flow area. It has been noted, however, that rounded nozzles may adversely cause a reduction in apparatus sensitivity. [DOI: 10.1115/1.1598991]

A new probe technique is introduced for the measurement of concentration in binary gas flows. The new technique is demonstrated through application of the probe in a Mach 4 nonreacting jet of hydrogen injected into a nominally quiescent air environment. Previous concentration probe devices have mostly used hot wires or hot films within an aspirating probe tip. However, the new technique relies on Pitot pressure and stagnation point transient thin film heat flux probe measurements. The transient thin film heat flux probes are operated at a number of different temperatures and thereby provide stagnation temperature and heat transfer coefficient measurements with an uncertainty of around [+ or -] 5 K and [+ or -] 4% respectively. When the heat transfer coefficient measurements are combined with the Pitot pressure measurements, it is demonstrated that the concentration of hydrogen within the mixing jet can be deduced. The estimated uncertainty of the reported concentration measurements is approximately [+ or -] 5% on a mass fraction basis. [DOI: 10.1115/1.1595671]

Studies of wavy stratified and stratified/atomization two-phase flow in horizontal pipes are outlined. Notable features of this flow regime include the appearance of disturbance waves, the atomization onset and the drastic change of the gas/liquid interface profile from flat to 'concave.' Liquid-to-wall shear stress tends to decrease circumferentially. A computational procedure for predicting main flow characteristics, which takes into account the above results in its design relations, is first assessed with detailed experimental data and is then combined with a CFD code, aiming at enhancing the predictive capability. [DOI: 10.1115/1.1576265] Keywords: Gas/Liquid Flow, Stratified Flow, Horizontal Pipes, Liquid Holdup, Pressure Drop, Shear Stress, Computational Method.

The mechanistic model of Taitel and Dukler [1] has previously been reported to exhibit a region in which three solutions exist for the height of the gas-liquid interface in the stratified/wave flow regime. Most laboratory studies have not dealt with flow rates in the ranges where the multiple solutions occur. An experimental study has been carried out at the University of Calgary to obtain such data. The object of this work is to review the relevant theory, investigate situations where theory suggests that multiple solutions should exist, and attempt to show whether or not such solutions do physically exist. [DOI: 10.1115/1.1521710]

Pressure drop experiments on natural gas flow in 150 mm pipes at 80 to 120 bar pressure and high Reynolds number were carried out for pipes smooth to rough surfaces. The roughness was measured with an accurate stylus instrument and analyzed using fractal methods. Using a similar approach to that of Nikuradse the measured friction factor was related to the measured roughness values. Taking the value of the relative roughness and dividing it by the slope of the power spectrum of the measured roughness, a greatly improved fit with the measured friction factor was obtained. Indeed, a new friction factor correlation was obtained, but now formulated in terms of direct measurement of roughness. [DOI: 10.1115/1.1576264] Keywords: Friction Factor, Turbulent Flow, Wall Roughness, Pressure Drop, Natural Gas

This paper deals with the numerical simulation of two-phase flows based on the solution of the Navier-Stokes equations with a k-[epsilon] turbulence model for the gas phase and a particle tracking model of the disperse phase fulfilling the framework of the Eulerian-Lagrangian (PSI-cell) approach. The numerical procedures for the two phases are based on multigrid and domain decomposition methods applied to a block-structured grid. Due to the enormous numerical effort of such flow simulations the entire solving procedure has been parallelized for computers of MIMD architecture. The paper gives a short description of the applied and developed numerical methods. Furthermore the numerical simulation of a particle laden gas flow through a flow splitter from the area of power engineering is presented as an example for a real world application of the numerical approach.

Research is conducted to examine turbulent heat fluxes in homogeneous curved shear flow. The measurements are performed far downstream of a thermal line source in both destabilized and stabilized curved shear flow. The curvature is observed to affect the heat fluxes due to its impact on the turbulence kinetic energy of the flow. Results are in good agreement with previous findings showing that momentum transport in curved boundary layers are more strongly affected by flow curvature than heat transport.

An instrument for the measurement of wall shear stress in two-phase flows is described. The device, termed a Laser Interferometer Skin Friction (LISF) meter, determines the wall shear by optically measuring the time rate of thinning of a thin oil film placed on the wall of the flow channel. The LISF meter has proven to be a valuable tool for measurement of wall shear in single-phase gaseous flows but, to date, had not been applied to liquid or gas-liquid flows. This paper describes modifications to the LISF meter developed to facilitate its use in two-phase flows. The instrument's configuration, governing theory, and data reduction procedure are described. Additionally, results of validation experiments for a single-phase water flow are presented, which demonstrate the instrument's ability to accurately measure wall shear. Measurements are also presented for two-phase, water-air flows in a duct of square cross section at various superficial gas and liquid velocities within the bubbly flow regime. Results of the measurements confirm previous observations that the addition of a very small amount of the gaseous phase increases the wall shear significantly over that in a single-phase water flow. The two-phase wall shear saturates to a maximum and then declines again as the superficial gas velocity is increased. The peak two-phase wall shear increases as the liquid superficial velocity is decreased. These trends are qualitatively in agreement with previous measurements obtained in pipes using an electrochemical technique.

An experimental procedure was developed for determining both the density and flow rate of a gas from measurements of pressure drops caused by an abrupt flow area contraction in a cylindrical pipe. Experiments were carried out by varying the density and flow rate of a light gas mixture of air and helium, spanning a Reynolds number range from 0.2 x [10.sup.4] to 3.4 x [10.sup.4]. From experimental results, a procedure was then proposed for evaluating the density from pressure change measurements in the scope of light gas extraction experiments. [DOI: 10.1115/1.2953294]

This paper describes a novel in-line sensor that measures the magnitude and direction of gas flow in a tube. The sensor possesses a unique set of performance characteristics: low detection limit, little resistance to flow, and directional sensitivity. The sensor consists of two hot wire anemometers mounted in a U-shaped tube. Differences in the signals between the two hot wires under low velocity conditions are used to determine the direction of the flow. Calibration curves of flow rate versus measured velocity are used to determine the magnitude of the flow. The sensor has applications in systems that are characterized by naturally driven oscillating flows.

This paper develops a liquid film symmetry correlation and a liquid film thickness distribution model for horizontal annular gas-liquid pipe flows. The symmetry correlation builds on the work of Williams et al. (1996) (Droplet Flux Distributions and Entrainment in Horizontal Gas-Liquid Flows,' Int. J. Multiphase Flow, Vol. 22, pp. 1-18). A new correlating parameter is presented. The liquid film thickness model is based on the work of Laurinat et al. (1985) (Film Thickness Distribution for Gas-Liquid Annular Flow in a Horizontal Pipe,' PhysicoChem. Hydrodynam., Vol. 6, pp. 179-195). The circumferential momentum equation is simplified to a balance between the normal Reynolds stress in the film's circumferential direction and the circumferential component of the weight of the film. A model for the normal Reynolds stress in the circumferential direction is proposed. The symmetry correlation is used to close the model equations. The model is valid for films with disturbance waves, and is shown to be applicable to air-water flows over a range of conditions from low velocity asymmetric to high velocity symmetric annular flows. [S0098-2202(00)02102-7] Keywords: Two-Phase Flow, Annular Flow, Horizontal Gas-Liquid Flow, Liquid Film Thickness Distribution

A direct simulation Monte Carlo method (DSMC) solver, adapted to the subsonic microflow, is developed under the object-conception language (c++). Some technical details critical in these DSMC computations are provided. The numerical simulations of gas flow in a microchannel are carried out using the developed DSMC solver. Streamwise velocity distributions in the slip flow regime are compared with the analytical solution based on the Navier-Stokes equations with the velocity slip boundary condition. Satisfactory agreements have been achieved. Furthermore, the domain of the validity of this continuum approach is discussed. Simulations are then extended to the transitional flow regime. Streamwise velocity distributions are also compared with the results of the numerical solutions of the linearized Boltzmann equation. We emphasize the influence of the accommodation coefficient on the velocity profiles and on the mass flow rate. The simulation results on the mass flow rate are compared with the experimental data, which allow us to validate the 'experimental' technique of the determination of the accommodation coefficient. [DOI: 10.1115/1.3026733]