bluuebunny/crossref_metadata_2025 huggingface dataset:
An Elastoplastic Beam Model for Column-Grid-Array Solder Interconnects
Authors: Swanson J. A. , Heinrich S. M. , Lee P. S.
Published: February 2008

An analytical model is developed and implemented to analyze the deformation of solder columns in column-grid-array(CGA) assemblies. Each solder column is modeled as a prismatic beam of circular cross section subjected to end shearing deflections caused by thermal mismatch between the module and the circuit board. The solder is idealized as an elastic-perfectly plastic material whose yielding is governed by the von Mises criterion. Since the columns are relatively short by beam standards, transverse shear deformation has been incorporated into the beam model. The results generated with the model indicate the following: 1. Yielding is governed by bending for slenderness ratios (height-to-diameter) of h/d ≥ 1/3. 2. The nonlinear stiffness relationship for a sheared column, presented in dimensionless form, reduces to a single curve, which is valid for arbitrary values of slenderness ratio (≥1/3) and material parameters. 3. The normalized relationship between maximum shear strain (in the Tresca sense) and the relative end deflection depends on Poisson’s ratio but is independent of the other material parameters and the slenderness ratio. The peak shear strain can easily be decomposed into elastic and plastic portions. 4. The maximum value of the total or the plastic shear strain in the solder column can be expressed in terms of a correction factor to be applied to the nominal shear strain (shear displacement divided by the column height). The correction factors are quite sensitive to the column slenderness and the load level. Since correction factors less than unity are possible, one should not interpret the nominal shear strain as the “average” shear strain in the column. Regardless of the load level, the nominal strain underestimates the peak strain by the greatest amount at a slenderness ratio (height/diameter) of 1.7. The nonlinear stiffness results presented in the paper may be used to create more efficient finite element models of entire assemblies by replacing each column with a single nonlinear spring element. When used in conjunction with an appropriate Coffin-Manson relationship, the maximum shear strain results presented herein may be utilized to increase column fatigue life.
JP-8+100: The Development of High-Thermal-Stability Jet Fuel
Authors: Heneghan S. P. , Zabarnick S. , Ballal D. R. , Harrison W. E.
Published: February 2008

Jet fuel requirements have evolved over the years as a balance of the demands placed by advanced aircraft performance (technological need), fuel cost (economic factors), and fuel availability (strategic factors). In a modern aircraft, the jet fuel not only provides the propulsive energy for flight, but also is the primary coolant for aircraft and engine subsystems. To meet the evolving challenge of improving the cooling potential of jet fuel while maintaining the current availability at a minimal price increase, the U.S. Air Force, industry, and academia have teamed to develop an additive package for JP-8 fuels. This paper describes the development of an additive package for JP-8, to produce “JP-8+100.” This new fuel offers a 55°C (100°F) increase in the bulk maximum temperature (from 325°F to 425°F) and improves the heat sink capability by 50 percent. Major advances made during the development of JP-8+100 fuel include the development of several new quantitative fuel analysis tests, a free radical theory of autooxidation, adaptation of new chemistry models to computational fluid dynamics programs, and a nonparametric statistical analysis to evaluate thermal stability. Hundreds of additives were tested for effectiveness, and a package of additives was then formulated for JP-8 fuel. This package has been tested for fuel system materials compatibility and general fuel applicability. To date, the flight testing has shown an improvement in thermal stability of JP-8 fuel. This improvement has resulted in a significant reduction in fuel-related maintenance costs and a threefold increase in mean time between fuel-related failures. In this manner, a novel high-thermal-stability jet fuel for the 21st century has been successfully developed.
Combustion Technology for Low-Emissions Gas-Turbines:Selected Phenomena Beyond NOx
Authors: Correa S. M. , Dean A. J. , Hu I. Z.
Published: February 2008

Since recent reviews cover the issues in NOx formation under gas-turbine canditions, and since regulations essentially dictate use of the premixed mode of combustion for minimum NOx, this review concentrates on phenomena that can arise in premixed combustion. Specifically, 1) the initial unmixedness in a fuel-air premixer has been shown to make overall lean mixtures autoignite sooner than might be expected based on the overall fuel-air ratio, because the richer portions of the mixture lead the process;2) combustion pressure oscillations caused by the interplay between acoustic waves and unsteady heat release in a one-dimensional system can be calculated in good accordance with measured data, and set the stage for multi-dimensional CFD;3) carbon deposition arising from the flow of liquid fuel over metal surfaces such as found in fuel injectors and swirl cups has been described as a function of temperature and of surface composition; and 4) quenching and subsequent emissions of carbon monoxide can be minimized by preservation of a boundary-layer rather than an impingement type of flow over combustor liners.
Storage of Fuel in Hydrates for Natural Gas Vehicles (NGVs)
Authors: Yevi G. Y. , Rogers R. E.
Published: February 2008

The need for alternative fuels to replace liquid petroleum-based fuels has been accelerated in recent years by environmental concerns, concerns of shortage of imported liquid hydrocarbon, and congressional prompting. The fact is accepted that natural gas is the cheapest, most domestically abundant, and cleanest burning of fossil fuels. However, socio-economical and technical handicaps associated with the safety and efficiency of on-board fuel storage inhibit its practical use in vehicles as an alternative fuel. A concept is presented for safely storing fuel at low pressures in the form of hydrates in natural gas vehicles. Experimental results lead to gas storage capacities of 143 to 159 volumes/volume. Vehicle travel range could be up to 204 mi. Controlled decomposition rate of hydrates is possible for feeding an automotive vehicle. Upon sudden pressure decrease in the event of a vehicle accident, the rate of release of hydrocarbons from the hydrates at constant temperature is 2.63 to 12.50 percent per min, slow enough to prevent an explosion or a fireball. A model is given for predicting the rates of gas release from hydrates in a vehicle wreck. A storage tank design is proposed and a process is suggested for forming and decomposing hydrates on-board vehicles. A consistent fuel composition is obtained with hydrates.
Application of Deterministic Chaos Theory to Local Instantaneous Temperature, Pressure, and Heat Transfer Coefficients in a Gas Fluidized Bed
Authors: Karamavruc¸ A. I. , Clark N. N.
Published: February 2008

The local instantaneous temperature, heat transfer coefficient, and pressure data, gathered around a horizontal tube in a fluidized bed, have been analyzed using the deterministic chaos theory. A stainless steel heat transfer tube, carrying a hot water flow, was placed in a cold bubbling fluidized bed. The tube was instrumented in the circumferential direction with five fast-responding surface thermocouples and a vertical pressure differential sensor. The local temperature and pressure data were measured simultaneously at a frequency of 120 Hz. Additionally, the local instantaneous heat transfer coefficient was evaluated by solving the transient two-dimensional heat conduction equation across the tube wall numerically. The mutual information function (MIF) has been applied to the signals to observe the relationship between points separated in time. MIF was also used to provide the most appropriate time delay constant τ to reconstruct an m-dimensional phase portrait of the one-dimensional time series. The distinct variation of MIF around the tube indicates the variations of solid-surface contact in the circumferential direction. The correlation coefficient was evaluated to calculate the correlation exponentv, which is closely related to the fractal dimension. The correlation exponent is a measure of the strange attractor. The minimum embedding dimension as well as the degrees of freedom of the system were evaluated via the correlation coefficient. Kolmogorov entropies of the signals were approximated by using the correlation coefficient. Kolmogorov entropy considers the inherent multi-dimensional nature of chaotic data. A positive estimation of Kolmogorov entropy is an indication of the chaotic nature of the signal. The Kolmogorov entropies of the temperature data around the tube were found to be between 10 bits/s and 24 bits/s. A comparison between the signals has shown that the local instantaneous heat transfer coefficient exhibits a higher degree of chaos than the local temperature and pressure signals.
Latent Heat Effects in Thermoelectric Air Conditioners and Heat Pumps Equipped With a Heat Exchanger
Authors: Chen K. , Suphasith S.
Published: February 2008

The effects of moisture on the performance of thermoelectric air conditioning systems and heat pumps equipped with a heat exchanger were studied. Coefficients of performance and fluid temperature variations were calculated for heat capacity ratios from 1 to 10 and relative humidities ranging from 0 to 100 percent at the cold fluid inlet. Only the energy effects of the water condensation are considered as it is assumed that the heat transfer coefficients are those of a dry heat exchanger. It was found that different flow arrangements and the energy associated with condensation on the cold fluid side have no strong effects on the variation of the hot fluid temperature. The coefficient of performance decreases and the cold fluid exit temperature increases when condensation occurs. When the moisture content at the cold fluid inlet increases most of the cases studied show a decrease in the difference between the optimum and uniform current results. The difference among different flow arrangements also becomes smaller as more water vapor condenses in the cold flow.
Second Law Analysis of Adsorption Cycles With Thermal Regeneration
Authors: Pons M.
Published: February 2008

Adsorption processes can be used for operating environment-friendly refrigeration cycles. When combined with the thermal regeneration process, these cycles can have quite high performance. The second law analysis of the adsorption cycles with thermal regeneration is fully developed. The different heat transports between heat transfer fluid and adsorbent, between adsorbate and condenser/evaporator heat sources, and between heat transfer fluid and heat sources are analyzed. The entropy balance is then completely established. Consistency between the first law and second law analysis is verified by the numerical values of the entropy productions. The optimal Operation of an adsorber is then described, and the study of those optimal conditions lead to some correlation between the different internal entropy productions.
Exergetic Analysis of Energy Storage using Multiple Phase-Change Materials
Authors: Gong Z.-X. , Mujumdar A. S.
Published: February 2008

This paper presents an exergetic analysis of the charge process in energy storage using multiple phase-change materials (PCMs). Thermal storage using two, three, five, as well as an infinite number of PCMs is analyzed with a distributed model for the heat transfer fluid. Analytical results show the relative merits of using multiple PCMs compared with a single PCM for thermal energy storage. Sample results are presented and discussed.
Reliability-Based Maintenance Strategies for Heat Exchangers Subject to Fouling
Authors: Sheikh A. K. , Zubair S. M. , Haq M. U. , Budair M. O.
Published: February 2008

Fouling in heat exchangers is an unavoidable by-product of the heat transfer process. The decision regarding periodic maintenance (cleaning) of the exchangers subject to fouling is generally based on thermal and economic behavior of the process. In this paper, a reliability-based maintenance strategy is discussed by incorporating the risk and scatter parameters of the linear random fouling growth model. In addition, the dimensionless cost-objective function is formulated by considering various cost elements for a heat exchanger used in a crude oil preheat train. The variation in the dimensionless cost Γ with reduced time tp/(tp + tdown) is presented for different values of unit cost parameters γ1, γ2, and γ3 representing additional fuel cost, antifoulant cost, and miscellaneous costs, respectively. Furthermore, the optimal cleaning cycle of the heat exchanger recently investigated by Casado (1990) is demonstrated to be a special case of the results presented in the paper.
Thermal Stress Analysis of a Subsurface Inclined Crack Subjected to a Point Heat Source
Authors: Chao C. K. , Wang J. W.
Published: February 2008

The thermoelastic response of a subsurface inclined crack under the application of a point heat source is studied in this paper. Based on the complex variable theory and the method of analytical continuation, the problem is formulated by two stress functions and a temprature function which are enforced to satisfy the interface condition. The singular integral equations for both the temperature field and thermoelastic field are derived by taking dislocation functions along the crack border such that both the insulated condition and traction-free condition are satisfied on the crack surface. Numerical results of the thermal stress intensity factors for different geometric configurations are discussed in detail and provided in graphical form. The results obtained in this study will be helpful in understanding the problems of seismology generated by thermal loading in a cracked body.
Lift-Off Stability of n-Heptane Jet Diffusion Flames in Homogeneous Environments of Fuel and Air
Authors: Samuel P. , Karim G. A.
Published: February 2008

The lift-off of jet diffusion flames of a liquid fuel in coflowing streams of air was established experimentally for a range of jet discharge and stream velocities. The improvement in the lift-off stability of the flame due to the presence of a small concentration of an auxiliary gaseous fuel in the surrounding air was established. Liquid n-heptane was the jet fuel while methane, ethylene, propane, and hydrogen were employed individually in small concentrations as the auxiliary fuels. It is shown that the lift-off distance and the corresponding ignition delay of the jet flame can be correlated for all the observations made in terms of derived dimensionless grouping of the main parameters varied, which included the jet discharge velocity, the surrounding stream velocity, and the concentration of the fuel added to the surroundings of the flame.
A Numerical Study of Droplet Evaporation and Combustion in the Presence of an Oscillating Flow
Authors: Ha M. Y.
Published: February 2008

The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy, and species transport in the gas phase are solved numerically in spherical coordinates in order to study heat and mass transfer, and combustion around a single spherical droplet. The droplet mass, momentum, and energy equations are also solved simultaneously with the gas phase equations in order to investigate the effects of droplet entrainment and heating in the oscillating flow with and without a steady velocity. The numerical solution for the case of single droplet combustion gives the droplet diameter and temperature variation as well as the gas phase velocity, temperature, and species concentrations as a function of time. The effects of frequency, amplitude of oscillating flow, and velocity ratio of oscillating flow amplitude to the steady velocity on droplet combustion are also investigated. The droplet burning history is not governed by the d2-law in the presence of oscillating flow, unlike the case of quiescent ambient conditions.
The Deformation of O-Rings Compressed by Smooth Rigid Plates
Authors: Warren W. E. , Weese J. A.
Published: February 2008

Three-dimensional effects of symmetrically compressing an O-ring with rigid plates are investigated. The O-ring is assumed to be an incompressible elastic material and the mixed boundary value problem is formulated within the framework of classical the linear elasticity theory. Transversely compressing the O-ring between flat rigid plates increases the toroidal radius and induces a reduction in the O-ring cross-sectional radius. This reduction depends strongly on the conditions of contact between plate and O-ring, and the reduced contact pressure may threaten the integrity of the seal. For O-rings compressed radially inward compressed radially inward or outward, most of the radial displacement is accommodated by a change in the toroidal radius with very little actual compression of the ring material. If this effect is not accounted for in the design of the seal, the contact pressure may not be sufficient to secure the seal.
Study of Hydration During Curing of Residues From Coal Combustion With Limestone Addition
Authors: Anthony E. J. , Iribarne A. P. , Iribarne J. V.
Published: February 2008

The hydration reactions that occur with CFBC materials treated via the CERCHAR hydration process and combined with PFA have been examined and compared with materials produced via the LIFAC (limestone injection into the furnace and activation of unreacted calcium) process. A wide range of chemical and physical techniques have been used to differentiate the actual speciation of cubes treated for up to 150 days. The two materials behave very differently, with FBC-derived ashes being dominated by sulphate chemistry, i.e., the formation of gypsum and ettringite. The CERCHAR-treated ashes appear to “make” portlandite available for “sulpho-pozzolanic” reactions, and this seems to be the key to understanding why these materials display superior performance in applications with PFA or cement substitution. The LIFAC materials, with much less sulphate and Fe2O3 and more Al2O3, still produces ettringite, but no gypsum, and hydrated tetracalcium aluminate appears as the major hydration product.
High Heat Flux Absorption Utilizing Porous Materials With Two-Phase Heat Transfer
Authors: Dickey J. T. , Peterson G. P.
Published: February 2008

By combining two-phase heat transfer with forced convective flow through a porous material, a new heat transfer scheme emerges with the ability to absorb high heat fluxes without the corresponding temperature increase encountered in single-phase systems. In general, flow-through sintered metals are characterized by high thermal conductivity due to the metallic media, and a fluid flow which on the macro scale can be described as slug flow in nature. These same characteristics are exhibited by liquid metal flow cooling systems. To predict the heat transfer attributes of this two-phase flow process, a semi-analytical model was developed using the conservation equations of mass, momentum, and energy along with the apparent physical properties of the composite material. The results indicate that when a heat flux is applied to one side of the bounding surface and adiabatic conditions exist on the remaining sides, the surface temperature asymptotically approaches the same value regardless of the mass flow rate. In addition to the analytical results, definitions for the convection coefficient and Nusselt number for flow-through porous materials with phase change are presented.
The Influence of Orifice Size on the Mass Flow During Flash Boiling of HCFC-22 From a Small Vessel
Authors: Nutter D. W. , O’Neal D. L.
Published: February 2008

An experimental investigation was conducted to study the flash boiling process and the influence of the exiting restriction (orifice) size on the mass flow during flash boiling of HCFC-22 in a glass pressure vessel. An apparatus was built and a combination of tests were run with three interchangeable exiting orifices (1.59, 3.18, and 5.56 mm diameters). The flashed vapor was vented from a 1110-mL vessel to a large “semi-infinite” tank initially set at 120 kPa. Calculations revealed that the refrigerant flow exiting the vessel was choked, depending on the orifice size. Smaller orifices were choked longer, had slower depressurization rates, and reduced mass flow rates. The depressurization rates were greater for tests large offices which enabled the liquid to become more highly superheated, up to 41°C for one test case, and ultimately vaporize more refrigerant.
Sectoral Energy and Exergy Modeling of Turkey
Authors: Rosen M. A. , Dincer I.
Published: February 2008

A modeling technique for analyzing sectoral energy use of a country, by considering the flows of energy and exergy through the four major economic sectors (residential/commercial, industrial, transporation, and utility), is applied to Turkish sectoral energy utilization. Energy and exergy efficiencies for the four main sectors of the Turkish economy and for Turkey as a whole are obtained. The results provide insights into Turkish energy use that may assist in energy planning for that country.
Chaotic and Random Whirling Motion of Drillstrings
Authors: Kotsonis S. J. , Spanos P. D.
Published: February 2008

Lateral vibrations of stabilized bottomhole assemblies of drillstrings often exhibit quite complicated patterns. Previous work has taken into account nonlinearities due to fluid damping, wall contact, eccentric collars, and initial curvature of the collar. This paper addresses the effects of these forces, along with linear and parametric excitation of the lateral motion due to an applied dynamic weight on bit (WOB). Four state-space nonlinear ordinary differential equations in two-dimensional space are used to describe the model. A time variant zero-mean axial WOB is considered and described as a stationary random process. Random and chaotic whirling characteristics of drillstrings are investigated using the minimum phase-volume deconvolution technique. The reported study serves to point out that even in ordinary engineering practice problems, rather complex phenomena can appear, and should thus be taken into consideration in the design and operation stages.
Sanding: An Expert-System Approach for Assessment and Control in Wells
Authors: Kanj M. , Zaman M. , Roegiers J.-C.
Published: February 2008

The sand production problem is plaguing the petroleum industry by its adverse effects on thousands of oil and gas fields throughout the world. A tremendous amount of money is spent each year on attempts to predict and control sand influx and/or repair wells and equipment damaged by sand. Sand inflow into the well during production leads to casing abrasion and failure, formation damage and distortion, and frequent sand removal and cleaning. The sand control process has a major influence on the type of the well completion design and it influences the guidelines for the completion process. In addition, many wells are currently being produced below their potential in order to restrict sand influx or erosion, and/or as a result of poorly designed or installed sand control methods. Evidently, the sand prediction and control problem is exceedingly complex and suggests the use of heuristics and the appropriateness of the expert systems technology. An automated sand control consultant and expert system has been developed. The system is aimed at assisting users in predicting sand occurrence during production and in selecting and designing the proper sand-exclusion treatments. The knowledge base of the system is based on an easy upgrade, easy expand format and involves four primary modules, thus giving the end-user greater flexibility to tentatively access and evaluate different scenarios of knowledge processing. Input data can range from “not known” formation characteristics and/or well stimulation requirements, for which the system gives conservative recommendations based on the remaining known facts, completion characteristics of the hole, well history, and geological probability; to cases with detailed information available, in which case very elaborate and precise recommendations are prescribed. This paper describes the knowledge involved in various modules of the sanding system, as well as future plans and further developments.
Absorption Heat Pump Performance Improvement Through Ground Coupling
Authors: Garimella S.
Published: February 2008

The present study investigates the improvement in the performance of an absorption heat pump for residential space-conditioning due to the use of the ground as the heat source in the heating mode and the heat sink in the cooling mode. A baseline air-coupled single-effect ammonia-water heat pump is first designed to deliver 10.55 kW (36,000 Btu/h) of cooling load at the ARI rating conditions. Particular attention is paid to incorporating many realistic details of an operating system such as fuel combustion efficiencies of the burner, nonequilibrium conditions, and moist air processes in the air-coupled heat exchangers. A range of parametric studies is also conducted to investigate the variation in performance of this system with ambient conditions in the heating and cooling modes. The same system is then analyzed in a ground-coupled configuration. The instantaneous COP for the ground-coupled system is compared with the COP of the air-coupled system as a function of the time of the year and the corresponding variations in ambient and ground temperatures using 30-yr average climate data for various locations from the National Weather Service. Improvements in COP of up to 20 percent over the air-coupled system values (cooling mode COP of 0.495 at 35°C (95°F) and heating mode COP of 1.20 at 8.33°C (47°F)) are demonstrated in diverse geographic locations with widely varying heating and cooling loads. These improvements indicate that an efficient ground-coupled heat pump could be developed for residential space-conditioning applications using simple thermodynamic cycles and existing technology for the heat and mass exchange components.
Numerical Simulation of Hydrate Transport in Natural Gas Pipeline
Authors: Ibraheem S. O. , Adewumi M. A. , Savidge J. L.
Published: February 2008

Accurate modeling of hydrate transportation in natural gas pipelines is becoming increasingly important in the design and operation of offshore production facilities. The dynamics involved in the formation of hydrate particles and in its transportation are governed by the multiphase hydrodynamics equations ensuing from the balance of mass, momentum, and energy. In this study, a two-fluid model is solved to characterize particulate transportation. The numerical algorithm employed is stable and robust and it is based on higher-order schemes. This is necessary since the governing equations describing the simultaneous flow of gas and solid particles are hyperbolic and, thus, admit discontinuities. Specialized higher-order schemes provide a viable approach for efficient frontal tracking of continuity waves in particular. Several simulation experiments that can facilitate thorough understanding of the design and maintenance of pipelines susceptible to hydrate formation are presented.
Predicting Single-Phase and Two-Phase Non-Newtonian Flow Behavior in Pipes
Authors: Kaminsky R. D.
Published: February 2008

Improved and novel prediction methods are described for single-phase and two-phase flow of non-Newtonian fluids in pipes. Good predictions are achieved for pressure drop, liquid holdup fraction, and two-phase flow regime. The methods are applicable to any visco-inelastic non-Newtonian fluid and include the effect of surface roughness. The methods utilize a reference fluid for which validated models exist. For single-phase flow, the use of Newtonian and power-law reference fluids are illustrated. For two-phase flow, a Newtonian reference fluid is used. Focus is given to shear-thinning fluids. The approach is theoretically based and is expected to be more accurate for large, high-pressure pipelines than present correlation methods, which are all primarily based on low-pressure, small-diameter pipe experimental data.
Numerical Simulation of the Gas-Liquid Flow in a Rotary Gas Separator
Authors: Lackner G. , Alhanati F. J. S. , Shirazi S. A. , Doty D. R. , Schmidt Z.
Published: February 2008

The presence of free gas at the pump intake adversely affects the performance of an electrical submersible pump (ESP) system, often resulting in low efficiency and causing operational problems. One method of reducing the amount of free gas that the pump has to process is to install a rotary gas separator. The gas-liquid flow associated with the down hole installation of a rotary separator has been investigated to address its overall phase segregation performance. A mathematical model was developed to investigate factors contributing to gas-liquid separation and to determine the efficiency of the separator. The drift-flux approach was used to formulate this complex two-phase flow problem. The turbulent diffusivity was modeled by a two-layer mixing-length model and the relative velocity between phases was formulated based on published correlations for flows with similar characteristics. The well-known numerical procedure of Patankar-Spalding for single-phase flow computations was extended to this two-phase flow situation. Special discretization techniques were developed to obtain consistent results. Special under relaxation procedures were also developed to keep the gas void fraction in the interval [0, 1]. Predicted mixture velocity vectors and gas void fraction distribution for the two-phase flow inside the centrifuge are presented. The model’s predictions are compared to data gathered on a field scale experimental facility to support its invaluable capabilities as a design tool for ESP installations.
A New Look at Measurement Uncertainty of Multiphase Flow Meters
Authors: Kouba G. E.
Published: February 2008

At present, no standard of presenting multiphase flow meter (MPFM) uncertainties has been accepted by industry. Consequently, vendors’ specifications may only indicate velocity and component fraction uncertainties, while customers will typically need to know the overall uncertainty of the hydrocarbon (gas or oil) flow rate. Moreover, comparisons between different meters, meter locations, and metering strategies are difficult without the combined uncertainties of the hydrocarbon measurement. A simple uncertainty analysis (UA) is presented as a means of combining individual measurement uncertainties to determine an overall uncertainty for one of the mixture components, e.g., oil rate. The results are displayed as contour lines of constant oil rate uncertainty on plots of gas fraction versus water cut. Examples illustrate how the uncertainty of oil rate measurement might be reduced by operating the meter at higher pressure, or employing partial separation strategies, and limitations of such strategies.
Multiphase Flow-Enhanced Corrosion Mechanisms in Horizontal Pipelines
Authors: Jiang L. , Gopal M.
Published: February 2008

Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of gas bubbles (Gopal et al., 1997). Corrosion rate measurements have been made at pressures up to 0.79 MPa and temperatures up to 90°C, and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude number. This paper describes mass transfer measurements under multiphase slug and annular flows using the limiting current density technique. The experiments are carried out in a 10-cm-dia pipe using a 0.01-M potassium ferro/ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6, and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The results show instantaneous peaks in the mass transfer rates corresponding to the pulses of bubbles in slug flow. Instantaneous increases of 10–100 times the average values in multiphase flow are seen. Peaks are also seen in instantaneous mass transfer rates in some annular flows.
Drill String Safety Valve Reliability: Experimental Measurements of Actuating Torque
Authors: Stephens L. S. , Coleman E. D. , Casemore M. A. , Core T. T.
Published: February 2008

Drill string safety valves (DSSVs) are used to prevent blowouts up the drillpipe when unexpected subsurface pressures are encountered in oil and gas drilling. Several case history reviews of well control events have recently shown evidence of poor reliability with DSSVs. Of the problems reported, valve lock-up was most significant, resulting in failure to open or close due to high actuation torque. This paper describes an experimental apparatus and experimental procedures used to quantify the actuating torque of DSSVs under a variety of common operating conditions. Experimentally obtained torque curves are presented for both commercially available and prototype DSSVs, and the results are discussed. Results show the benefit of using special low-torque DSSV designs under certain operating conditions.
Investigation of Holdup and Pressure Drop Behavior for Oil-Water Flow in Vertical and Deviated Wells
Authors: Flores J. G. , Sarica C. , Chen T. X. , Brill J. P.
Published: February 2008

Two-phase flow of oil and water is commonly observed in wellbores, and its behavior under a wide range of flow conditions and inclination angles constitutes a relevant unresolved issue for the petroleum industry. Among the most significant applications of oil-water flow in wellbores are production optimization, production string selection, production logging interpretation, down-hole metering, and artificial lift design and modeling. In this study, oil-water flow in vertical and inclined pipes has been investigated theoretically and experimentally. The data are acquired in a transparent test section (0.0508 m i.d., 15.3 m long) using a mineral oil and water (ρo/ρw = 0.85, μo/μw = 20.0 & σo−w = 33.5 dyne/cm at 32.22°C). The tests covered inclination angles of 90, 75, 60, and 45 deg from horizontal. The holdup and pressure drop behaviors are strongly affected by oil-water flow patterns and inclination angle. Oil-water flows have been grouped into two major categories based on the status of the continuous phase, including water-dominated and oil-dominated flow patterns. Water-dominated flow patterns generally showed significant slippage, but relatively low frictional pressure gradients. In contrast, oil-dominated flow patterns showed negligible slippage, but significantly large frictional pressure gradients. A new mechanistic model is proposed to predict the water holdup in vertical wellbores based on a drift-flux approach. The drift flux model was found to be adequate to calculate the holdup for high slippage flow patterns. New closure relationships for the two-phase friction factor for oil-dominated and water-dominated flow patterns are also proposed.
An Analysis of the Design Loads Placed on a Well by a Diverter System
Authors: Beck F. E. , Langlinais J. P. , Bourgoyne A. T.
Published: February 2008

Diverter systems, used as a means of well control while drilling surface hole, have a history of occasional failure. This paper addresses excessive back pressure, which can result in mechanical failure of surface equipment or foundation collapse. Flows at critical rates are shown both experimentally and theoretically to have a significant effect on back pressure. Critical flow is modeled by quantifying exit pressures and by including fluid acceleration pressure losses in back-pressure calculations. Experiments were then conducted in 1-in., 2-in., and 5-in. pipes to verify these mathematical models. A “systems analysis” approach was used for the diverter design, which allowed for consideration of wellbore and reservoir performance effects. This procedure allows the relationship of diverter vent line diameter, conductor depth, and drilling depth to be better identified, yielding improved design criteria.
The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part II: Modeling Results
Authors: Gopal M. , Jepson W. P.
Published: February 2008

A definition is given for a Froude number in the liquid film ahead of the slug and it is seen that slug characteristics are strongly influenced by the Froude number. The mechanisms in the mixing zone of the slug are described in detail and are shown to be a function of the film Froude number. It is shown that the Hubbard and Dukler model for mixing length is inadequate. A new expression is proposed for the slug mixing length as a function of the film Froude number.
Thermodynamics of Insulated Pressure Vessels for Vehicular Hydrogen Storage
Authors: Aceves S. M. , Berry G. D.
Published: February 2008

This paper studies the application of insulated pressure vessels for hydrogen-fueled light-duty vehicles. Insulated pressure vessels are cryogenic-capable pressure vessels that can be fueled with liquid hydrogen (LH2); low-temperature (46 K) compressed hydrogen (CH2); or ambient-temperature CH2. In this analysis, hydrogen temperatures, pressures, and venting losses are calculated for insulated pressure vessels fueled with LH2 or with low-temperature CH2, and the results are compared to those obtained in low-pressure LH2 tanks. Hydrogen losses are calculated as a function of daily driving distance during normal operation; as a function of time during long periods of vehicle inactivity; and as a function of initial vessel temperature during fueling. The results show that insulated pressure vessels have packaging characteristics comparable or better than those of conventional, low-pressure LH2 tanks, with greatly improved dormancy and much lower boil-off, and therefore appear to be a good alternative for vehicular hydrogen storage.
Dispersion—An Entropy Generator of Diffusion
Authors: Call F. W.
Published: February 2008

In multicomponent gaseous flows with chemical reactions, diffusion is usually considered to be a single-source entropy generator. Introducing the concept of dispersion, where the atom balance is dominant rather than the molecular, shows in an ideal setting that, even when there is diffusion, the dispersion part of entropy generation can be reduced to zero by proper choice of species flow velocities. Fuel cells and methane reformers are employed as examples to illustrate these concepts.
Prediction and Validation of Blowout Limits of Co-Flowing Jet Diffusion Flames—Effect of Dilution
Authors: Karbasi M. , Wierzba I.
Published: February 2008

The blowout limits of a co-flowing turbulent methane jet diffusion flame with addition of diluent in either jet fuel or surrounding air stream is studied both analytically and experimentally. Helium, nitrogen, and carbon dioxide were employed as the diluents. Experiments indicated that an addition of diluents to the jet fuel or surrounding air stream decreased the stability limit of the jet diffusion flames. The strongest effect was observed with carbon dioxide as the diluent followed by nitrogen and then by helium. A model of extinction based on recognized criterion of the mixing time scale to characteristic combustion time scale ratio using experimentally derived correlations is proposed. It is capable of predicting the large reduction of the jet blowout velocity due to a relatively small increase in the co-flow stream velocity along with an increase in the concentration of diluent in either the jet fuel or surrounding air stream. Experiments were carried out to validate the model. The predicted blowout velocities of turbulent jet diffusion flames obtained using this model are in good agreement with the corresponding experimental data.
The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation Rate for Refrigeration Cycles
Authors: Klein S. A. , Reindl D. T.
Published: February 2008

This paper investigates the effect of heat exchanger allocation on overall system performance using both reverse Carnot and vapor compression refrigeration cycle models to calculate system performance and entropy generation rate. The algebraically simple constraints applied in previous studies are shown to be justifiable. The vapor compression model considers nonideal compressor performance, compressor volumetric efficiency, refrigerant properties, and throttling, in addition to mechanistic heat exchanger models. The results support the conclusions of previous studies in that maximum performance is observed when the condenser and evaporator thermal sizes are approximately equal. For air-to-air systems, this result indicates that the areas of the heat exchangers should be approximately equal. However, it is found that minimizing the entropy generation rate does not always result in the same design as maximizing the system performance unless the refrigeration capacity is fixed. Minimizing the entropy generation rate per unit capacity is found to always correspond to maximizing the coefficient of performance of refrigeration systems.
Incorporating a District Heating/Cooling System Into an Existing Geothermal Power Plant
Authors: Kanog˘lu M. , C¸engel Y. A. , Turner R. H.
Published: February 2008

Geothermal energy has been used for power generation, space and process heating, and to a lesser extent, space cooling. However, it is rarely used for cogeneration. This paper shows how a district heating/cooling system can be incorporated into an existing geothermal power plant to make the best use of extracted hot brine. In the power plant analysis, exergy destruction throughout the plant is quantified and illustrated using an exergy cascade. The primary source of exergy destruction in the plant is determined to be the reinjection of used brine into the ground, which accounts for 48.1 percent of the total exergy destruction. The overall first and the second law efficiencies of the plant are calculated to be 5.6 and 28.3 percent, respectively, based on the exergy of the geothermal fluid at downwell, and 5.7 and 28.6 percent, respectively, based on the exergy of the geothermal fluid at wellhead. A binary system is considered for the heating/cooling district to avoid corrosion and scaling problems. The heating system, as designed, has the capability to meet the entire needs of the Reno Industrial Park under peak load conditions, and has 30 percent reserve for future expansion. An absorption system will be used for the cooling of the intended 40 percent floor space of the industrial park. An economic analysis shows that the incorporation of the district heating/cooling system with 2,785,000 m2 of floor space connected to the geothermal grid appears to be feasible, and financially very attractive. Further, using the returning freshwater from the district heating/cooling system for partial cooling of the binary fluid of the power plant can save up to 15 percent of the fan work.
Mechanisms of Bed Material Agglomeration in a Petroleum Coke-Fired Circulating Fluidized Bed Boiler
Authors: Skrifvars B.-J. , Hupa M. , Anthony E. J.
Published: February 2008

Petroleum coke firing in a circulating fluidized bed boiler has sometimes been reported to be associated with cyclone deposit problems and return leg plugging. In this paper, we present data which indicate that some of these problems may be due to the calcium-rich bed material used during the firing. We have earlier shown that calcium oxide may react with the flue gas components SO2 or CO2, causing neck growth between the solid particles. This neck growth between particles may lead to both deposits in the cyclone and plugging of the cyclone return leg. In this study we made use of a sintering testing method, based on compressive strength tests of heat-treated cylindrical pellets. Laboratory-prepared petroleum coke ash was mixed with two potential bed materials, limestone and dolomite, and sintering tests were performed in three different gas atmospheres. Significant differences were found between the mixtures as a function of both the gas atmosphere and temperature. We also performed thermogravimetric analyses on one of the bed materials, the limestone. Based on these results a mechanism for the formation of cyclone deposits and bed material agglomeration in the return leg was suggested.
Application of the First and Second Laws to Fuel Minimization in a Batch Furnace
Authors: von Spakovsky M. R. , Geskin E. S.
Published: February 2008

This paper presents results for the minimization of fuel consumption in a batch furnace. Several different criteria are used and minimized with respect to time-dependent process and control variables. As would be expected, the results show that globally there is no significant difference between the solutions found (i.e., the same minimum fuel consumption results) when the choice of criterion is either energy, exergy, exergy destruction, entropy creation of the system and entropy creation of the system plus environment. However, the specific details or local results of each solution (i.e., the heating strategies) are, in fact, quite different. These differences cannot simply be attributed to numerical error (round-off and truncation). What they show is that multiple optimum strategies satisfy the same global optimum. The advantage of one over the other may simply be that from a practical standpoint some are easier to implement than others. Nonetheless, regardless of the strategy used, employing an optimum one raises the possibility of significant reductions in overall fuel consumption in these and other types of furnaces.
Entropy Generation in Multicomponent Reacting Flows
Authors: Teng H. , Kinoshita C. M. , Masutani S. M. , Zhou J.
Published: February 2008

A comprehensive equation to determine the rate of local entropy generation in multicomponent, reacting, laminar fluid flow involving heat and mass transfer is formulated based on species-average velocity in a multicomponent continuum. The entropy-generation equation developed in this study suggests that species diffusion induces a diffusive-viscous effect, heretofore not reported in the literature, which could contribute significantly to entropy generation in multicomponent fluid systems, and that entropy generation in a multicomponent system exceeds that in a single-component fluid system having similar velocity and temperature distributions because a greater number of irreversible processes, such as species diffusion, chemical reaction, and the Soret and Dufour effects, are involved. Under appropriate conditions, if the diffusive-viscous effect is neglected, the entropy-generation equation of this study reduces to those reported in the literature for simpler fluid systems based on mean flow.
Using Genetic Algorithms and the Exergonomic Approach to Optimize District Heating Networks
Authors: Cammarata G. , Fichera A. , Marletta L.
Published: February 2008

This paper discusses the application of exergy analysis to a district heating network (DHN) currently in operation in Brescia (Italy). The purpose is to compare the existing system design with that resulting from an exergonomic analysis. To this aim a general mathematical model is formulated to account for irreversibilities due to the temperature and pressure losses as well as for the assessment of exergy costs for each stream. The objective function is stated as the sum of capital, operational, and maintenance costs of the whole DHN. Such a function is minimized by using two different approaches: an iterative procedure and a genetic algorithm; the latter proves to be particularly suited for this type of problem. Both methods lead to comparable outcomes in terms of minimum cost and plant arrangement. Finally, the optimum configuration is compared with the existing one and shows that the actual network is far from an optimum design both from a thermodynamic and an economic standpoint. Such a procedure could be used profitably in the design of any future DHN.