Showing papers in "Journal of Energy Resources Technology-transactions of The Asme in 1998"

The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation Rate for Refrigeration Cycles

Abstract: 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 algebrai­ cally 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 corre­ spond to maximizing the coefficient of performance of refrigeration systems.

Thermodynamic Optimization of a Gas Turbine Power Plant With Pressure Drop Irreversibilities

Abstract: In this paper we show that the thermodynamic performance of a gas turbine power plant can he optimized by adjusting the flow rate and the distribution of pressure losses along the flow path. Specifically, we show that the power output has a maximum with respect to the fuel flow rate or any of the pressure drops. The maximized power output has additional maxima with respect to the overall pressure ratio and overall temperature ratio. When the optimization is performed subject to a fixed fuel flow rate, and the power plant size is constrained, the power output and efficiency can be maximized again by properly allocating the fixed total flow area among the compres­ sor inlet and the turbine outlet.

Efficiency Optimizations of an Irreversible Brayton Heat Engine

Abstract: A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.

Thermodynamics of Insulated Pressure Vessels for Vehicular Hydrogen Storage

Abstract: 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 (LH 2 ); low-temperature (46 K) compressed hydrogen (CH 2 ), or ambient-temperature CH 2 . In this analysis, hydrogen temperatures, pressures, and venting losses are calculated for insulated pressure vessels fueled with LH 2 or with low-temperature CH 2 , and the results are compared to those obtained in low-pressure LH 2 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 LH 2 tanks, with greatly improved dormancy and much lower boil-off, and therefore appear to be a good alternative for vehicular hydrogen storage.

Investigation of Holdup and Pressure Drop Behavior for Oil-Water Flow in Vertical and Deviated Wells

Abstract: 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-waterflow 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 (00508 m id, 153 m long) using a mineral oil and water (ρ ο /ρ w = 085, μ o /μ w = 200 & σ o-w = 335 dyne/cm at 3222°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 drill flux model was found to be adequate to calculate the holdup for high slippage flow patterns New closure relationships for the two-phase friction factorfor oil-dominated and water-dominated flow patterns are also proposed

Numerical Simulations of Highly Preheated Air Combustion in an Industrial Furnace

Abstract: The numerical simulations of reactive turbulent flows and heat transfer in an industrial slab reheat furnace in which the combustion air is highly preheated have been carried out. The influence of the ratio of the air and fuel injection velocities on the NO x production rate in the furnace has also been studied numerically. A moment closure method with the assumed β probability density function (PDF) for mixture fraction was used in the present work to model the turbulent non-premixed combustion process in the furnace. The combustion model was based on the assumption of instantaneous full chemical equilibrium. The turbulence was modeled by the standard k-e model with a wall function The numerical simulations have provided complete information on the flow, heat, and mass transfer in the furnace. The results also indicate that a low NO, emission and high heating efficiency can be achieved in the slab reheat furnace by using low NO x regenerative burners. It is found that the air/ fuel injection velocity ratio has a strong influence on the NO, production rate in the furnace.

Retractable Bits Development and Application

Abstract: This paper presents a historical view and present status on the retractable bits design and drilling results. Despite the significant improvements in a cone sealed bearings rock bits the special features of retractable bits provides wide range of fields of application. Scientific drilling both continental and offshore and stratigraphic offshore boreholes were an area for profitable retractable bits with down hole motor application. Other promising field of application is drilling with simultaneous casing run where some prototypes have been successfully tested. Other areas such as horizontal and geothermal drilling looks promising for further developments.

Entropy Generation in Multicomponent Reacting Flows

Abstract: 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.

Evaluation of the Backpressure Technique for Blockage Detection in Gas Flowlines

Abstract: As longer, full well-stream flowlines are utilized to reduce the costs of deep water and satellite developments, routine production monitoring attains a new level of importance. Of particular interest is the operational impact that blocking agents such as paraffins, asphaltenes, hydrates, and scale can have on the flowlines. Because blockages can reduce and even disrupt production, monitoring flowline performance becomes an economic necessity. This paper considers the application of the backpressure technique as a means of monitoring the growth of blockages in gas flowlines. Using only routine production data, this method quantifies partial blockages by comparing production data to a baseline performance curve. Experimental verification was performed using the LSU 9,460 ft. flowloop of 4-1/2 inch drillpipe. Multirates tests were conducted using methane at 450--610 psig with partial blockages placed in the flowloop. Good agreement with the backpressure model was observed.

Overall Efficiency of a Radial Fin Assembly Under Dehumidifying Conditions

Abstract: The aim of this paper is the analysis of heat transfer in a radial fin assembly during the process of dehumidification. An individual finned tube geometry is a reasonable representation of heat exchangers used in air conditioning. The condensation process involves both heat and mass transfer and the cooling takes place by the removal of sensible as well as latent heat. The ratio of sensible to total heat is an important quantity that defines the heat transfer process during a dehumidifier operation. A one-dimensional model for heat transfer in the fin and the heat exchanger block is developed to study the effects of condensation on the fin surface. The combined heat and mass transfer process is modeled by incorporating the ratio of sensible to total heat in the formulation. The augmentation of heat transfer due to fin was established by comparing the heat transfer rate with and without fins under the same operating conditions. Calculations were carried out to study the effects of relative humidity and dry bulb temperature of the incoming air, and cold fluid temperature inside the coil on the performance of the heat exchanger. An analysis of the overall efficiency for the assembly was also done, Results were compared to those under dry conditions, wherever appropriate. Comparison between present results and those published for rectangular as well as radial fins under fully wet conditions were made. These comparisons established the validity of the present model. It was found that the heat transfer rate increased with increment in both dry bulb temperature and relative humidity of the air. The augmentation factor, however, decreased with increment in relative humidity and the dry bulb temperature. The fin efficiency decreased with relative humidity.

Using Genetic Algorithms and the Exergonomic Approach to Optimize District Heating Networks

Abstract: 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.

Design and Performance of Passive Control System for Gas-Liquid Cylindrical Cyclone Separators

Abstract: The performance of gas-liquid cylindrical cyclone (GLCC) separators can be improved by reducing or eliminating liquid carryover into the gas stream or gas carryunder through the liquid stream, utilizing a suitable liquid level control. In this study, a new passive control system has been developed for the GLCC, in which the control is achieved by utilizing only the liquid flow energy. A passive control system is highly desirable for remote, unmanned locations operated with no external power source. Salient features of this design are presented here. Detailed experimental and modeling studies have been conducted to evaluate the improvement in the GLCC operational envelope for liquid carryover with the passive control system. The results demonstrate that a passive control system is feasible for operation in normal slug flow conditions. The advantage of a dual inlet configuration of the GLCC is quantified for comparative evaluation of the passive control system. The results of this study could form the basis for future development of active control systems using a classical control approach.

Agglomeration and Fouling in Petroleum Coke-Fired FBC Boilers

Abstract: Experiments have been done subjecting ashes from industrial-scale FBC boilers to sulphating conditions in an oven for up to 105 days. These show that sulphation by itself causes agglomeration in the virtual absence of V, K, and Na, the elements normally associated with ash softening and classical fouling. In addition, it has been demonstrated that sulphation goes to completion over long periods of time and, at a specific level which differs from one ash to another, results in agglomeration. These experiments have also shown that there is a size range (75-300 μm) in which the agglomeration is worst, and particles that are smaller or larger either do not agglomerate or agglomerate more weakly. Added inert coal-derived ash decreases or prevent s the agglomeration. However, this ash does not appear to chemically combine with the sulphate, but acts by mechanically separating the sulphating particles. Finally, if alkali metals are present they can cause agglomeration at levels lower than those at which either the alkalis or sulphation separately cause agglomeration, i.e., they operate synergistically to cause fouling. Current work is being directed at examining these phenomena at higher temperatures (900°C and above).

Effect of Drag-Reducing Agents in Multiphase Flow Pipelines

Abstract: The effect of drag reducing agents (DRA) on pressure gradient and flow regime has been studied in horizontal and 2-deg upward inclined pipes. Experiments were conducted for different flow regimes in a JO-cm i.d., 18-m long plexiglass system. The effectiveness of DRA was examined for concentrations ranging from 0 to 75 ppm. Studies were done for superficial liquid velocities between 0.03 and 1.5 mls and superficial gas velocities between I and 14 mls. The results indicate that DRA was effective in reducing the pressure gradients in single and multiphase flow. The DRA was more effective for lower superficial liquid and gas velocities for both single and multiphase flow. Pressure gradient reductions of upto 42 percent for full pipe flow, 81 percent for stratified flow, and 35 percent for annular flow were achieved ill horizontal pipes. In 2 deg upward inclination, the pressure gradient reduction for slug flow, with a concentration of 50 ppm DRA, was found to be 28 and 38 percent at superficial gas velocities of 2 and 6 mis, respectively. Flow regimes maps with DRA were constructed in horizontal pipes. Transition to slug flow with addition of DRA was observed to occur at higher superficial liquid velocities.

Mechanisms of bed material agglomeration in a petroleum coke-fired circulating fluidized bed boiler

Abstract: 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 SO 2 or CO 2 , 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.

Evaluation of Several Turbulence Models for Turbulent Flow in Concentric and Eccentric Annuli

Abstract: Turbulent flow in concentric and eccentric annuli is numerically simulated as part of an investigation aimed at modeling drilled cuttings transport in wellbores. A numerical code is developed to solve the time-averaged momentum equation wherein the Reynolds stresses are modeled using the eddy viscosity approach. A nonorthogonal curvilinear, boundary-fitted coordinate system is used to facilitate the implementation of boundary conditions. Several turbulence models, including a one-layer mixing length model developed as part of this study, a two-layer mixing-length model, and a low Reynolds number, two-equation (k -τ) model are used to simulate turbulent flow in several concentric and eccentric annuli. Performance of these turbulence models is evaluated by comparing numerical predictions to experimental data obtained from several sources. Results show that the proposed one-layer mixing length model performs as well as the two-layer mixing length model and the two-equation model while avoiding some of the difficulties associated with the implementation of these models.

Prediction and Validation of Blowout Limits of Co-Flowing Jet Diffusion Flames—Effect of Dilution

Abstract: 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.

Incorporating a District Heating/Cooling System Into an Existing Geothermal Power Plant

Abstract: 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 56 and 283 percent, respectively, based on the exergy of the geothermal fluid at downwell, and 5 7 and 286 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 m 2 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

Analysis of Yield-Power-Law Fluid Flow in Irregular Eccentric Annuli

Abstract: Fully developed laminar axial flow of yield-power-law fluids in eccentric annuli has been investigated numerically. The annuli may be fully open or partially blocked. General nonorthogonal, boundary-fitted curvilinear coordinates have been used to accurately model the irregular annular geometry due to the presence of a flow blockage. A computer code has been developed using a second-order finite-difference scheme. An exponential model for the shear stress, valid for both yielded and unyielded regions of the flow, is used in the computation. The effects of pressure gradient, eccentricity, and blockage height on the flow rate have been studied and the results are presented. The flow rate is found to increase with increasing eccentricity for eccentric annuli without any blockage. For partially blocked eccentric annuli, the flow rate at a particular eccentricity decreases as the blockage height is increased.

Predicting Single-Phase and Two-Phase Non-Newtonian Flow Behavior in Pipes

Abstract: 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.

The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part I: Flow Visualization

Abstract: This paper reports the application of novel, digital image analysis techniques in the study of slug flow characteristics, under dynamic conditions in two-phase gas-liquid mixtures. Water and an oil of viscosity 18 cP were used for the liquid phase and carbon dioxide was used for the gas phase. Flow in a 75-mm i.d., 10-m long acrylic pipeline system was studied. Images of slugs were recorded on video by S-VHS cameras, using an audio-visual mixer. Each image was then digitized frame -by-frame and analyzed on a SGI workstation. Detailed slug characteristics, including liquid film heights, slug translational velocity, mixing length, and, slug length, were obtained.

The effect of drillpipe rotation on annular frictional pressure loss

Abstract: Accurate predictions of annular frictional pressure losses (AFPL) are important for optimal hydraulic program design of both vertical and horizontal wells. In this study the effects of drillpipe rotation on AFPL for laminar, helical flow of power law fluids are investigated through theoretical, experimental and field data studies. In the theoretical study flow models were developed for concentric and eccentric pipe configurations assuming that pipe rotates about its axis. A hybrid-analytical solution is developed for calculating AFPL in eccentric pipe configuration. Computer simulations indicate that the shear-thinning effect induced by pipe rotation results in reduction of AFPL in both concentric and eccentric pipe configurations. The pressure reduction is most significant for concentric pipe configuration. For conventional rotary drilling geometry and pipe rotary speeds the reduction in AFPL is small. A number of laboratory experiments conducted on the full-scale TUDRP flow loop are generally in good agreement with the results of modeling. Available field data, however, consistently show an increase in AFPL. This behavior is explained by pipe lateral movement (swirling), which causes turbulence and eventually an increase in AFPL.

Multiphase Flow-Enhanced Corrosion Mechanisms in Horizontal Pipelines

Abstract: 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 079 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 001-M potassium ferro/ferricyanide solution in 13 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

Liquid Holdup in Large-Diameter Horizontal Multiphase Pipelines

Abstract: This paper studies the liquid holdup within the mixing zone of the slug. The results of the study show that the liquid holdup begins at the liquid holdup of the liquid film before the slug and then increases until the end of the mixing zone is reached. Once past the mixing zone of the slug, the average liquid holdup becomes constant. As the height of the liquid film and/or viscosity increases, so does the liquid holdup at any given film Froude number. Since the liquid holdup becomes constant once past the mixing zone of the slug, the mixing zone length was determined for the film Froude numbers studied. The results show that the mixing zone length increases linearly with film Froude number and is independent of the viscosity of the liquid in the slug for a viscosity range of 1 to 16.6 cP.

Disturbed flow and flow-accelerated corrosion in oil and gas production

Abstract: The effect of fluid flow on corrosion of steel in oil and gas environments involves a complex interaction of physical and chemical parameters. The basic requirement for any corrosion to occur is the existence of liquid water contacting the pipe wall, which is primarily controlled by the flow regime. The effect of flow on corrosion, or flow-accelerated corrosion, is defined by the mass transfer and wall shear stress parameters existing in the water phase that contacts the pipe wall. While existing fluid flow equations for mass transfer and wall shear stress relate to equilibrium conditions, disturbed flow introduces nonequilibrium, steady-state conditions not addressed by these equations, and corrosion testing in equilibrium conditions cannot be effectively related to corrosion in disturbed flow. The problem in relating flow effects to corrosion is that steel corrosion failures in oil and gas environments are normally associated with disturbed flow conditions as a result of weld beads, pre-existing pits, bends, flanges, valves, tubing connections, etc. Steady-state mass transfer and wall shear stress relationships to steel corrosion and corrosion testing are required for their application to corrosion of steel under disturbed flow conditions. A procedure is described to relate the results ofa corrosion test directly to corrosion in an operation system where disturbed flow conditions are expected, or must be considered.

Dynamic Differential Pressure Effects on Drilling of Permeable Formations

Abstract: In the mathematical modeling of bit penetration rate for tri-cone roller bits in permeable formations, virtually all of the current techniques assume that the differential pressure between the bottom-hole wellbore pressure and the formation is a “static” value. This work shows that the appropriate differential pressure is a dynamic quantity, because for overbalanced drilling, fluid filtrate from the wellbore requires a finite time to flow into the formation, producing a changing pressure gradient ahead of the bit. Moreover, this dynamic gradient is directly dependent upon the rate of drill bit penetration, which is in turn dependent upon the dynamic gradient itself. Accordingly, coupled penetration rate and dynamic gradient equations must be solved, which frequently result in the prediction of higher drilling penetration rates than when the static gradient is used. The appropriate dynamic differential pressure equations are developed and applied to an example drilling situation. It is shown that with water-based drilling fluids, for rock with permeability greater than a few microdarcies at virtually all penetration rates, and for penetration rates less than 3 m/h (9.84 ft/h) at permeabilities greater than 1 μd (microdarcy), the dynamic differential pressure is significantly less than the static differential pressure. Accordingly, using the conventional static differential pressure results in the prediction of penetration rates that are much too low. Moreover, using measured penetration rates from the field, the conventional approach yields predicted in-situ rock strength that is much too high.

Effects of Flame Lift-Off on the Differences Between the Diffusion Flames From Circular and Elliptic Burners

Abstract: An experimental study conducted to determine the effects of lifting the flame base off the burner rim on the differences between the flame characteristics of diffusion flames from circular and elliptic burners is presented. The in-flame profiles of temperature, concentrations offuel and combustion product species, and the mean and fluctuating components of axial velocity are presented. This study has shown that the effects of burner geometry in turbulent lifted flames are considerable only in the near-burner region. In the midflame and far-burner regions, the effects traceable to burner geometry are much weaker, contrary to those observed in the attached flame configuration. The observations are attributed to the turbulence and additional air entrainment into the jet prior to the flame base accompanying the lift-off process, which mitigate the effects of burner geometry.

Borehole Failure Resulting From Formation Integrity (Leak-Off) Testing in Upper Marine Sediments Offshore

Abstract: This paper presents the results ofa theoretical study, supported with the finite element analysis, into potential loss of external integrity around a casing shoe resulting from leak-off testing (LOT) in upper marine sediments (UMS). Three types of possible failures from LOTs were considered: vertical fracture, horizontal fracture, and a channel outside cemented annulus. It is proved in the paper that vertical fracture is the most unlikely failure of the three. The other two types offailure can be distinguished by different values of propagation pressures. Although horizontal fractures are initiated at low pressure in the plastic zone around the wellbore, they cannot propagate beyond the plastic zone until wellbore pressures exceed overburden pressures. Annular channels, on the other hand, may propagate upwards at pressures lower than overburden pressure. The paper shows that these channels are initiated at pressures equal to the contact stress between cement and rock and their propagation pressures are on average 3.5-fold greater than contact stress. It is also explained how to identify the UMS with high risk of annular channeling during LOTs.

Transients in gas-condensate natural gas pipelines

Abstract: Liquid condensation in natural gas transmission pipelines commonly occurs due to the thermodynamic and hydrodynamic imperatives. Condensation subjects the gas pipeline to two-phase transport. Neither the point along the pipeline at which the condensate is formed nor the quantity formed is known a priori. Hence, compositional multiphase hydrodynamic modeling, which couples the multiphase hydrodynamic model with the natural gas phase behavior model, is necessary to predict fluid dynamic behavior in gas/condensate pipelines. A transient compositional multiphase hydrodynamic model for transient gas-condensate two-phase flow in pipelines is presented. This model consists of our newly developed well-posed modified Soo's partial pressure model in conservative form which serves as the transient multiphase hydrodynamic model, and the phase behavior model for natural gas mixtures.

Thermodynamic Definition and Quantum-Theoretic Pictorial Illustration of Entropy

Abstract: Carnot analyzed an engine operating between two reservoirs. Through a peculiar mode of reasoning, he found the correct optimum shaft work done during a cyclic change of state of the engine. Clausius justified Carnot's result by enunciating two laws of thermodynamics, and introducing the concept of entropy as a ratio of heat and temperature of a thermodynamic equilibrium state. In this paper, we accomplish five purposes: (i) We consider a Carnot engine. By appropriate algebraic manipulations we express Carnot's optimum shaft work in terms of available energies or exergies of the end states of one reservoir with respect to the other, and Clausius' entropy S in terms of the energies and available energies of the same end states. (ii) We consider the optimum shaft work done during a cyclic change of state of an engine operating between a reservoir, and a system with fixed amounts of constituents and fixed volume, but variable temperature. We express the optimum shaft work in terms of the available energies of the end states of the system, and Clausius' entropy in terms of the energies and available energies of the same end states. Formally, the entropy expression is identical to that found for the Carnot engine, except that here the change of state of the system is not isothermal. (iii) We consider the optimum shaft work done during a cyclic change of state of a general engine operating between a reservoir R and system A which initially is in any state A 1 , stable or thermodynamic equilibrium or not stable equilibrium, In state A 1 , the values of the amounts of constituents are n 1 , and the value of the volume is V 1 whereas, in the final state A 0 , no ¬= n 1 and V 0 ¬= V 1 . Using the laws of thermodynamics presented by Gyftopoulos and Beretta, we prove that such an optimum exists, call it generalized available energy with respect to R, and use it together with the energy to define a new property Σ 1 . We note that the expression for Σ is formally identical to and satisfies the same criteria as Clausius' entropy S. The only difference is that Σ applies to all states, whereas Clausius' S applies only to stable equilibrium states. So we call Σ entropy and denote it by S. (iv) We use the unified quantum theory of mechanics and thermodynamics developed by Hatsopoulos and Gyftopoulos, and find a quantum theoretic expression for S in terms of the density operator ρ that yields all the probabilities associated with measurement results. (v) We note that the quantum-theoretic expression for S can be interpreted as a measure of the shape of an atom, molecule, or other system because ρ can be thought of as such a shape, and provide pictorial illustrations of this interpretation. For given values of energy E, amounts of constituents n, and volume V, the value of the measure is zero for all shapes that correspond to projectors (wave functions), positive for density operators that are not projectors, and the largest for the ρ that corresponds to the unique stable equilibrium state determined by the given E, n, and V. Accordingly, spontaneous entropy generation occurs as a system adapts its shape to conform to the internal and external forces. Beginning with an arbitrary initial ρ, this adaptation continues only until no further spontaneous change of shape can occur, that is, only until a stable equilibrium state is reached.