J. Energy Resour. Technol. 1999;121(1):1-8. doi:10.1115/1.2795055.

A comprehensive mechanistic model is formulated to predict flow patterns, pressure drop, and liquid holdup in vertical upward two-phase flow. The model identifies five flow patterns: bubble, dispersed bubble, slug, churn, and annular. The flow pattern prediction models are the Ansari et al. (1994) model for dispersed bubble and annular flows, the Chokshi (1994) model for bubbly flow, and a new model for churn flow. Separate hydrodynamic models for each flow pattern are proposed. A new hydrodynamic model for churn flow has been developed, while Chokshi’s slug flow model has been modified. The Chokshi and Ansari et al. models have been adopted for bubbly and annular flows, respectively. The model is evaluated using the expanded Tulsa University Fluid Flow Projects (TUFFP) well data bank of 2052 well cases covering a wide range of field data. The model is also compared with the Ansari et al., (1994), Chokshi (1994), Hasan and Kabir (1994), Aziz et al. (1972), and Hagedorn and Brown (1964) methods. The comparison results show that the proposed model performs the best and agrees well with the data.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):9-14. doi:10.1115/1.2795063.

Several mechanistic models have been already developed for predicting the onset of liquid carryover in gas-liquid cylindrical cyclone (GLCC) separators. However, currently no model is available to predict gas carryunder. A bubble trajectory model has been developed that can be used to determine the initiation of gas carryunder in the GLCC and to design GLCC for field applications. The bubble trajectory model uses a predicted flow field in GLCC that is based on swirl intensity. This paper describes the development of a general correlation to predict the decay of the swirl intensity. The correlation accounts for the effects of fluid properties (Reynolds number) as well as inlet geometry. Available experimental data as well as computational fluid dynamics (CFD) simulations were used to validate the correlation. The swirl intensity is used to calculate the local axial and tangential velocities. The flow model and improved bubble trajectory results agree with experimental observation and CFD results. Examples are provided to show how the bubble trajectory model can be used to design GLCC.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):15-23. doi:10.1115/1.2795054.

The petroleum industry has recently shown interest in the development of innovative alternatives to the conventional vessel-type separator. One such alternative is the gas-liquid cylindrical cyclone (GLCC) separator, which is simple, compact, and low weight, and has low capital and operational costs. A new mechanistic model is proposed, for the first time, to predict the aspect ratio of the GLCC, based on its complex hydrodynamic multiphase flow behavior. This model incorporates an analytical solution for the gas-liquid vortex interface shape, and a unified particle trajectory model for bubbles and droplets. A simplified GLCC design methodology, based on the foregoing mechanistic model, is developed and specific design criteria are proposed as user guidelines for GLCC design. A summary of four actual field application designs is provided to demonstrate the capability of the aspect ratio modeling and the impact the GLCC technology may have on the petroleum industry.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):24-30. doi:10.1115/1.2795056.

The performance of oil wells producing during boundary-dominated flow was investigated to develop a better understanding of multiphase flow and its effects on single well performance. This understanding can assist the petroleum engineer in predicting the pressure-production behavior of oil wells producing under boundary-dominated flow conditions. An analytical inflow performance relationship (IPR) was developed from the multiphase flow equations. This relationship is based on the physical nature of the multiphase flow system and contributes to a better understanding of the pressure-production behavior of an individual well. The analytical IPR was verified using simulator information and provides a method for the petroleum engineer to develop individual IPRs for each reservoir.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):31-39. doi:10.1115/1.2795057.

This paper presents time-dependent poroelastic failure analyses of boreholes drilled in directions inclined to the far-field stress principal axes in fluid-saturated isotropic porous formations. The work is based on a recently derived analytical solution. The analyses include collapse as well as fracturing failures. The time-dependent failures in relation to borehole inclination, azimuth, and mud pressure are presented. The critical roles of poroelastic constants in borehole stability are also demonstrated.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):40-44. doi:10.1115/1.2795058.

A laboratory study has been conducted on the use of chemical plugs, instead of conventional mechanical packers, to isolate water and gas-producing zones in horizontal wells. Results of experiments using horizontal wellbore models, consisting of PVC pipes internally lined with sand, indicate that slumping of the chemical plug could be avoided if the plug were spotted in a viscous brine pill. Of the three chemicals tested, a monomer, a polyacrylamide, and a plastic, only the plastic plug had a sufficiently high holding pressure. Research is being continued using a full-scale horizontal wellbore model.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):45-50. doi:10.1115/1.2795059.

A simple model has been developed to estimate the sensible thermodynamic properties such as Gibbs free energy, enthalpy, heat capacity, and entropy of unbranched hydrocarbons over a wide range of temperatures. The model is based on statistical thermodynamic expressions incorporating translational, rotational, and vibrational motions of the atoms. A relatively small number of parameters are needed to calculate the thermodynamic properties of a wide range of molecules. The calculated results are in good agreement with the available experimental data for unbranched hydrocarbons. The model can be used to make estimates for molecules whose properties have not been measured and is simple enough to be easily programmed as a subroutine for on-line kinetic calculations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):51-59. doi:10.1115/1.2795060.

Solid sorption heat pumps can improve the effectiveness with which energy resources are used for heating and cooling. These systems operate by alternately heating and cooling beds of adsorbent material to produce a flow of refrigerant. The research presented here evaluates the effects of adsorbent thermal conductivity and permeability on the performance of a thermal wave solid sorption heat pump. In order to evaluate these effects, a numerical model of the thermal wave heat pump is developed. This model incorporates not only the effects of the conductivity and permeability, but also the effects of the adsorption equilibrium properties, refrigerant properties, application parameters, operating parameters, and bed geometry. For a typical air conditioning application, the model is used to study the influence of conductivity and permeability on the COP for systems using ammonia as a refrigerant. The results indicate that for the geometry considered, increasing the thermal conductivity of the adsorbent to 1 W/m-K can improve the COP to approximately 0.75. Further increases in conductivity do not yield improved performance. Furthermore, the reduced permeability associated with high conductivity adsorbents can impair vapor flow and lead to decreased performance.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):60-65. doi:10.1115/1.2795061.

This paper shows the development and use of a transient model for evaluating frost formation on a parallel-plate heat pump evaporator. A frost formation model is derived by applying the equations of conservation of mass, momentum, and energy, as well as empirical correlations, to calculate the growth and densification of the frost layer. The frost formation model is validated by comparison with experimental results. The frost formation model is then incorporated into the evaporator subroutine of an existing heat pump model to calculate performance losses due to frosting as a function of weather conditions and time of operation since the last evaporator defrost. Performance loss calculation includes the effect of air pressure drop through the evaporator and the reduction in evaporator temperature caused by the growth of the frost layer. The results show frost formation parameters and heat pump COP as a function of time and ambient conditions. It is determined that there is a range of ambient temperatures and humidities in which frosting effects are most severe, and this range is explored to calculate heat pump operating conditions. The heat pump analysis results are expected to be useful in predicting optimum defrosting conditions, and to evaluate alternative methods for defrosting.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1999;121(1):66-72. doi:10.1115/1.2795062.

Partial premixing can be induced by design in combustors, occurs inadvertently during turbulent nonpremixed combustion, or arises through inadequate fuel-air mixing. Therefore, it is of interest to investigate the effect of partial premixing in a burner that mimics conditions that might occur under practice. In this investigation, we report on similitude of partially premixed flames encountered in practical complex and multi-dimensional burners with simpler, less complex flames, such as counterflow flamelets. A burner is designed to simulate the more complex multi-dimensional flows that might be encountered in practice, and includes the effects of staging, swirl, and possible quenching by introduction of secondary air. The measurements indicate that the structure of partially premixed flames in complex, practical devices can be analyzed in a manner similar to that of flamelets, even if substantial heat transfer occurs. In particular, the flame structure can be characterized in terms of a modified mixture fraction that differentiates the lean and rich zones, and identifies the spatial location of the flame.

Commentary by Dr. Valentin Fuster

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