J. Energy Resour. Technol. 1992;114(1):1-13. doi:10.1115/1.2905917.

Upward gas-liquid flow through vertical concentric and fully eccentric annuli was studied both experimentally and theoretically. A flow system was designed and constructed for this study. The system consists of a 16-m long vertical annulus with 76.2-mm i.d. casing and 42.2-mm o.d. tubing. A comprehensive experimental investigation was conducted for both concentric and fully eccentric annuli configurations, using air-water and air-kerosene mixtures as the flowing fluids. Included were definition and classification of the existing flow patterns and development of flow pattern maps. Measurements of volumetric average liquid holdup and average total pressure gradient were made for each flow pattern for a wide range of flow conditions. Additional data include single-phase friction factor values and Taylor bubble rise velocities in a stagnant liquid column. Data analysis revealed that application of the hydraulic diameter concept for annuli configurations is not always adequate, especially at low Reynolds number flow conditions. A more rigorous approach was thus required for accurate prediction of the flow behavior, especially for two-phase flow. Part I of the study includes experimental data and analyses of single-phase friction factor, Taylor bubble rise velocity, and flow pattern transition boundaries.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):14-30. doi:10.1115/1.2905916.

Mechanistic models have been developed for each of the existing two-phase flow patterns in an annulus, namely bubble flow, dispersed bubble flow, slug flow, and annular flow. These models are based on two-phase flow physical phenomena and incorporate annulus characteristics such as casing and tubing diameters and degree of eccentricity. The models also apply the new predictive means for friction factor and Taylor bubble rise velocity presented in Part I. Given a set of flow conditions, the existing flow pattern in the system can be predicted. The developed models are applied next for predicting the flow behavior, including the average volumetric liquid holdup and the average total pressure gradient for the existing flow pattern. In general, good agreement was observed between the experimental data and model predictions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):31-37. doi:10.1115/1.2905918.

In the previous paper on this subject it was found that the oil-water interface at the retention boom becomes unstable under certain conditions permitting an oil escape under the boom. In the absence of waves, the experimental results were in fair agreement with predictions; but, when the waves were present, the instability occurred much earlier than predicted. In this paper the behavior of waves is studied both analytically and experimentally. It is found that the waves consist of a combination of stationary and progressive waves which is confirmed by the experiment, but the oil thickness variation on waves is found from experiment to be much greater than predicted. With certain modifications to the theory, the predicted onset of instability falls closely to experimental value.

Topics: Waves , Thickness , Water
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):38-45. doi:10.1115/1.2905919.

The problems associated with engineering tasks are often too large and complex for application of conventional software methods, but are suitable to application of expert system methods. Development of custom expert system applications is expensive and difficult, but expert system development tools provide the basic components needed to construct an expert system. Such tools enable engineers to implement expert system applications by entering knowledge specific to the particular problem they are attempting to solve. Because the choice of a development tool can determine the success of the resulting expert system application, the characteristics of these tools and of the target problem must be clearly understood before a selection is made. An overview of expert systems and development tools is given, characteristics of some common engineering problems are discussed, and selection criteria for tools well suited to these problems are presented. Implementation of a rule-based advisor to assist with tool selection is discussed briefly.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):46-53. doi:10.1115/1.2905920.

In this study a technique is provided for determining formation pore pressure and flow properties based upon analysis of shut-in drill pipe pressure. Both radial and spherical transient flow of slightly compressible fluid are considered. Solutions are provided in dimensionless forms. A newly developed concept of effective (equivalent) flowing rate and time is applied to replace the unknown variable flow rate which takes place prior to shutting-in the well. Two numerical examples show how to utilize the information on pit gain, approximate flow-in time and the shut-in drill pipe pressure to determine formation fluid pressure. Fluid mobility (spherical flow) and formation transmissibility (radial flow) can also be determined from knowledge of shut-in drill pipe pressure as a function of time. Application of the proposed method is simple, and therefore, useful on the rig floor.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):54-64. doi:10.1115/1.2905921.

As part of a combined experimental and computational study of erosion for gas and oil production conditions, a semi-empirical model has been developed to predict erosion ratio behaviors of metals due to solid particle impingement. One use of the model will be to reduce the total number of experiments needed to characterize erosion behavior. The model represents material property information associated with both the target material and the impinging particles, as well as impingement speed. Five different models are examined in terms of ability to predict erosion ratio behavior as a function of impingement speed. The model selected is based on a conservation of energy formulation and fracture mechanics considerations to predict the amount of material removed due to solid particle impingement. The resulting equation to predict the erosion ratio for a given particle size contains one unknown coefficient which is determined through comparison with experimental data. Illustrative examples are presented for data for two different sizes of glass bead solid particles in an oil carrier fluid impinging on an API (American Petroleum Institute) N80 grade steel target at an impingement angle 90 deg to the target surface. Using erosion data at one impingement speed to determine the unknown coefficient, the model was used to predict erosion behavior at a range of other speeds. Good agreement between the erosion ratio data and the values predicted by the model were found for two solid particle sizes. Recommendations for expanding the capabilities of the model are pointed out.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):65-69. doi:10.1115/1.2905922.

The effects of two processes used to treat coal on the flammability characteristics of the coal are presented. Experiments were conducted on an Entrained Dust Flow Facility which supports a stationary premixed coal dust and air flame. The facility is designed to provide access for thermocouples so that detailed axial and radial temperature profiles of the coal flames can be used to investigate the flame structure. Flame speeds of the coal and air mixtures were determined based on the inlet velocity of the flow and the temperature maps. Flame speed increases of over 35 percent were observed as a direct result of an aggregate flotation process which reduced the ash content and the average size of the coal and increased the volatile content and heating value. Partially devolatilized chars were burned to simulate the use of a low-volatile solid by-product of a gasification process. Under most conditions either methane addition or inlet air heating was required to establish a flame. Both methane addition and inlet air heating with the low-volatile chars resulted in improved flame stability and higher flame speeds. Relatively modest amounts (2.2 percent by volume) of methane addition with the parent coal increased the flame speed by a factor of 2 to 3.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):70-74. doi:10.1115/1.2905923.

Numerical studies have been made to evaluate the interdependence of drop size characteristics and evaporation histories of an atomized liquid spray in a convective medium of uniform free stream at high temperature. With the help of a discrete droplet evaporation model, both the actual drop size distribution and the apparent one, that could have been obtained in practice by light-scattering technique, have been determined numerically at different downstream locations perpendicular to the spray axis. Variations of actual and apparent mass mean diameter and the evaporation rate with the axial distance of the spray have been established. Finally, the influences of pertinent input parameters, namely, the initial Reynolds number of the spray, the ratio of free stream to initial drop temperature and the ratio of free stream to initial drop velocity on the mean diameter and evaporation histories have been recognized.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):75-83. doi:10.1115/1.2905924.

Energy conversion processes inherently have associated irreversibility. A better understanding of energy conversion will motivate intuition to create new energy-conversion and energy-utilization technology. In the present article, such understanding is further enhanced by decomposing the equations of energy and exergy (availability, available energy, useful energy) to reveal the reversible and irreversible parts of energy transformations. New definitions of thermal, strain, chemical, mechanical and thermochemical forms of energy/exergy are justified and expressions for these properties and their changes are rigorously developed. In the resulting equations, terms appear which explicitly reveal the interconversions between the different forms of energy/exergy, including the breakdown into reversible and irreversible conversions. The equations are valid for chemically reacting or non-reacting inelastic fluids, with or without diffusion.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):84-90. doi:10.1115/1.2905925.

This paper documents the relative merits of using more than one type of phase-change material for energy storage. In the case of two phase-change systems in series, which are melted by the same stream of hot fluid, there exists an optimal melting point for each of the two materials. The first (upstream) system has the higher of the two melting points. The second part of the paper addresses the theoretical limit in which the melting point can vary continuously along the source stream, i.e., when an infinite number of different (and small) phase-change systems are being heated in series. It is shown that the performance of this scheme is equivalent to that which uses an optimum single phase-change material, in which the hot stream remains unmixed during the melting process. The time dependence, finite thickness and longitudinal variation of the melt layer caused by an unmixed stream are considered in the third part of the paper. It is shown that these features have a negligible effect on the optimal melting temperature, which is slightly higher than (T∞ T e )1/2 .

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):91-94. doi:10.1115/1.2905926.

Power generation, especially that of electricity, must simultaneously meet the requirements of being able to satisfy peak demands and being easily modulable, even over short periods. The combined use of hydraulic and thermal energy can contribute to satisfy energy demands by increasing the amount of peak power generated, while modulating power to fit users’ needs. The hydraulic-gas plant described in this paper features a hydraulic turbine positioned directly on the compressor shaft, with the compressor mechanically connected to the gas turbine.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(1):95-99. doi:10.1115/1.2905927.

Taking strain as the independent variable, the strain space plasticity theory introduced by Naghdi and Trapp is applied to the problem of interpreting strain gage readings for load paths that involve inelastic deformation. Equations developed herein permit the straightforward decomposition of the total measured strain into elastic and plastic components. Further, the strain space formulation leads naturally to the prediction of stress components, both the strain decomposition and the stress calculation requiring information on uniaxial stress-strain behavior obtained from a simple tension test.

Commentary by Dr. Valentin Fuster

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