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IN MEMORIAM

J. Energy Resour. Technol. 1994;116(1):1. doi:10.1115/1.2906004.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Energy Resour. Technol. 1994;116(1):2-9. doi:10.1115/1.2906006.

A three-dimensional hydraulic fracture simulator (HYFFIX) is reformulated using finite element methodology and a newly adapted fixed grid. The numerical procedures for the coupled equations governing the fracture width, fluid pressure, and evolution of equilibrium planar crack in layered media are summarized. Fixed grid mesh control algorithms for the efficient tracking of the moving crack/fracture fluid front are detailed. The introduction of these novel algorithms in the simulator makes it numerically efficient and stable, in comparison to previously reported models which utilize migrating mesh techniques. Due to the enhanced numerical efficiency and compactness of the refined code, the model can also be readily implemented on a workstation or microcomputer.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):10-15. doi:10.1115/1.2906002.

A drag force measurement method is presented which makes it possible to study the settling of particles in transparent and opaque fluids. A dimensionless treatment that takes into account the shear thinning effects of fluids was applied to normalize the measured drag force data. A wide range of particle Reynolds numbers can be covered by this method and a profile of friction factor versus Reynolds number can be established by the proposed dimensionless treatment. An algorithm for the prediction of settling of particles in non-Newtonian fluids was introduced. It can be executed by a computer program. With a good set of experimental data, the settling velocities predicted by the computer model are very close to the measured ones in the fluids tested. This method can be used to study the suspension properties of drilling and fracturing fluids, transparent or opaque. The wide coverage of Reynolds number range simplifies the experiment.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):16-21. doi:10.1115/1.2906003.

Aqueous solutions of different concentrations of three polymers: a synthetic high molecular weight polymer, partially hydrolyzed polyacrylamide (PHPA), a xanthantype biopolymer (Xanvis), and a cellulose-type polymer (HEC) were investigated in this study. It was found that the steric arrangement of molecules or interactions between molecules can be detected by a systematically designed strain and frequency sweep measurement, and is reflected by the different relaxation times of the solutions. The degree of elasticity can be quantified by G′/|G*| in linear viscoelastic range. The responses of the fluids to frequency sweeps are displayed in a normalized moduli versus normalized frequency pattern derived from the Maxwell model. Results show that within the tested concentration ranges, PHPA solutions are highly elastic with moderate relaxation times that are strain and concentration insensitive. Xanvis solutions are also highly elastic, but with high relaxation times that are both strain and concentration sensitive, indicating a different mechanism of elasticity compared to PHPA solutions. HEC (cellulose derivatives) are mostly viscous shear thinning fluids with weak elasticity and short relaxation times that are insensitive to strain, but sensitive to concentration.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):22-32. doi:10.1115/1.2906005.

Measurements of pressure drop, temperture, and average void fraction are presented for adiabatic, vertical-upwards, two-phase flow of Refrigerant 114 in a pipe. An experimental method has been developed according to which the evolution of flow states occurring in long pipes can be realized in a test section of limited length. The experiments cover the range of the flow from flashing to near choking. The measurements indicate existence of macroscopic thermodynamic equilibrium, except in the immediate neighborhood of flashing. Compressibility due to phase change is shown to play a very important role in the development of the flow. Three regions are recognized based on the measured energetics of the flow. Each region is dominated by potential energy changes, dissipation, and kinetic energy changes, respectively. The evolution of the flow is governed by hydrostatic effects in the initial region after flashing and by high, phase-change-induced kinetic energy increases far downstream as the flow approaches choking. In the intermediate region, viscous, inertial and gravitational effects play a role of comparable importance. The interfacial and wall shear forces have also been calculated from the measurements. The former dominate the initial regions of the flow, while the latter are strongest at high vapor contents.

Topics: Pipes , Two-phase flow
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):33-37. doi:10.1115/1.2906007.
Abstract
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):38-48. doi:10.1115/1.2906008.

Numerical modeling of the rock-bit interaction process in laminated formation has been performed using a finite element approach. A finite element program was developed with the assumption of plane strain. Anisotropic elements, dynamic, loading, progressive failure, and variable stiffness were used to represent the actual penetration process. The Hoek and Brown failure criterion was used in the failure analysis. An interation method, using an incremental approach, has been applied for the continuous tooth penetration process where displacements, axial loads, strength and stiffness of elements are modified after each iteration. The program provides quantitative information on stress, displacement, and rock failure for each iteration. Furthermore, deviation due to laminated formation can be inferred and the effects of changing bit geometry can be assessed. The model also shows good quantitative agreement with laboratory wedge indentation tests.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):49-55. doi:10.1115/1.2906009.

Flex joints in risers introduce abrupt directional changes along the drillstring. High drillstring stresses and flex joint wear rates are introduced, particularly when the drillstring tension is high. An analysis procedure is presented which finds the drillstring/flex joint contact loads in the vicinity of the flex joint as a function of the tension in the drillstring at the flex joint. The tensile and contact loads of the drillstring at the riser are used to estimate the wear rate on the flex joint and the axial and bending stresses in the drillstring. This example shows the value of the procedure in estimating maximum allowable angles for the flex joint.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):56-64. doi:10.1115/1.2906010.

An operational problem is discussed for a gas turbine cogeneration plant in combination with a heat pump/thermal storage system that utilizes time-of-use pricing of the electrical utility. An optimal planning method is presented by which the operational policy of constituent equipment is determined so as to minimize the daily operational cost. An algorithm is proposed to solve this optimization problem efficiently by combining the dynamic programming method with the mixed-integer programming one. A case study is carried out to investigate the effect of introducing a heat pump system into a cogeneration plant.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):65-71. doi:10.1115/1.2906011.

An optimal operational advisory system is proposed to operate rationally a brewery’s energy supply plant from the economical viewpoint. A mixed-integer linear programming problem is formulated so as to minimize the daily operational cost subject to constraints such as equipment performance characteristics, energy supply-demand relations, and some practical operational restrictions. This problem includes lots of unknown variables and a hierarchical approach is adopted to derive numerical solutions. The optimal solution obtained by this method is indicated to the plant operators so as to support their decision making. Through the numerical study for a real brewery plant, the possibility of saving operational cost is ascertained.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):72-78. doi:10.1115/1.2906012.

Experimental testing was performed on a prototype postcombustor fueled by pure oxygen and designed to treat exhaust gases from industrial waste incineration. The tests validated the technical feasibility of the small-size oxycombustion incinerator, which not only proved to be more flexible and compact than conventional systems of the same rating, but also faster in reaching operating conditions. The thermoeconomic analysis which followed was based on an exergy balance developed from the system’s operating conditions measured in the previous experimental phase. A subsequent comparison with conventional air-fueled solutions has shown that oxycombustion offers considerable energy savings and, as a result, economic benefits.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1994;116(1):79-86. doi:10.1115/1.2906013.

This paper presents an analysis of a class of latent heat storage systems (LHSS). The analysis is based on a lumped model (the basic model) that allows a broad class of LHSSs to be completely specified, with only two parameters and a set of operating temperatures, while still retaining the main thermodynamic aspects associated with its operation. Characterization of the performance in this manner permits the broad base application potential of such systems to be viewed. This modeling is in contrast to most studies to date, which employ many parameters to include details of specific systems, and therefore obscure, to a great extent, this broad-based application potential. The basic model is later modified in three ways to analyze operating conditions that either occur in practical units or are desirable for an improved operation of the units. The modifications include, first, the consideration of the LHSS as being formed by many independent phase-change material (PCM) capsules. Second, the possibility of having PCMs with different phase change temperatures filling the capsules. Third, the case when the PCM melts over a temperature range. The results indicate that the efficiency of the basic model represents a higher bound for the efficient operation of LHSSs with negligible sensible storage capacity, and a single PCM. Using multiple PCMs within a LHSS results in higher efficiencies. These efficiencies set higher bounds for efficiency of any sensible or latent heat storage system, and also represent the only possibility for reversible operation of LHSS.

Commentary by Dr. Valentin Fuster

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