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IN MEMORIAM

J. Energy Resour. Technol. 1993;115(2):79. doi:10.1115/1.2905983.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Energy Resour. Technol. 1993;115(2):80-85. doi:10.1115/1.2905984.

This article presents the essential features of an integrated resource planning (IRP) process designed to provide energy for societal and industrial needs at least cost. Use of renewable energy sources and energy conservation measures, as well as consideration of social costs, are described. Available data of social costs and estimates for energy cost of conservation measures and renewable energy systems are included.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):86-92. doi:10.1115/1.2905985.

In this paper, the essential building blocks of a new formalism called Engineering Functional Analysis (EFA) are presented. This formalism results in higher degrees of decentralization for engineering system optimization than is otherwise possible. By decentralization , it is meant that the improvement or optimization of individual components by themselves (i.e., components which are isolated economically from the rest of the overall system), serves to improve or optimize the system as a whole (within some degree of error, which defines the degree of decentralization ). Higher degrees of decentralization are important in that they provide a more stable economic environment for individual components, thus permitting more rapid synthesis and greater system improvement than could otherwise be obtained.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):93-99. doi:10.1115/1.2905986.

In this paper, a new formalism called Engineering Functional Analysis (EFA) is presented. This formalism results in higher degrees of decentralization for engineering system optimization than is otherwise possible. By decentralization , it is meant that the improvement or optimization of individual components by themselves (i.e., components which are isolated economically from the rest of the overall system) serves to improve or optimize the system as a whole (within some degree of error, which defines the degree of decentralization ). Higher degrees of decentralization are important in that they provide a more stable economic environment for individual components, thus permitting more rapid synthesis and greater system improvement than could otherwise be obtained.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):100-104. doi:10.1115/1.2905975.

The ideal voltage of steady-flow fuel cells is usually expressed by Emf = −ΔG°/nF where ΔG° is the “Gibbs free energy of reaction” for the oxidation of the fuel at the supposed temperature of operation of the cell. Furthermore, the ideal power of the cell is expressed as the product of the fuel flow rate with this emf. Such viewpoints are flawed in several respects. While it is true that if a cell operates isothermally, the maximum conceivable electrical work output is equal to the difference between the Gibbs free energy of the incoming reactants and that of the leaving products; nevertheless, even if the cell operates isothermally, the use of the conventional ΔG° of reaction (a) assumes that the products of reaction leave separately from one another (and from any unused fuel); and (b) when ΔS of reaction is positive, it assumes that a free heat source exists at the operating temperature, whereas if ΔS is negative, it neglects the potential power which theoretically could be obtained from the heat released during oxidation. Moveover, (c) the usual cell does not operate isothermally, but (virtually) adiabatically. Comment (a) is often accounted for by employing the Nernst equation to correct for the dilution of reactants and/or products. Nevertheless, comments (b) and (c) remain pertinent. Rather than with emf, the proper starting place is with power output. The ideal power is that which would be obtained if the fuel were oxidized without irreversible entropy generation. Among other factors, this ideal power output depends upon the ratio of oxidant to fuel flow rate (e.g., air-fuel ratio) and the percentage of fuel oxidation. The ideal voltage is deduced from the ideal power, because it is defined as electrical work output per unit of charge delivered. It is a local characteristic which varies with the percent of fuel oxidized. Therefore, (d) ideal power is not equal to the product of emf with current (unless the amount of fuel utilized is infinitesimal). Examples are presented which illustrate such affects and their importance for the evaluation of ideal power and of efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):105-107. doi:10.1115/1.2905976.

Dunbar, Lior and Gaggioli (1991) proposed a configuration of a fuel-cell-topped electrical Rankine power generating station and analyzed its performance. That study revealed that the fuel-cell topping improved plant efficiency to values up to 62 percent, versus the conventional plant efficiency of 41.5 percent. This work lays the foundation for a thermoeconomic analysis of such systems by relating exergy consumption to fuel-cell unit size, as follows: 1) the relationship between system efficiency (and hence fuel consumption) and fuel-cell unit size is presented for a number of fuel-cell operating conditions; 2) the relationship between fuel flow rate and fuel-cell unit size is shown; and 3) the exergetic effects of the major plant components are discussed as a function of fuel-cell unit size. The results reveal that specific fuel consumption may be reduced by as much as 32 percent when incorporating fuel-cell units into electrical power plants.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):108-116. doi:10.1115/1.2905977.

This paper presents the first results of an experimental and theoretical investigation of the feasibility of using ultrasonic measurements in multiphase pipe flow. Extant downhole flow rate measurement technology used in the petroleum industry is not adequate in some multiphase flow regimes, particularly when the well is deviated from vertical. Ultrasonics offers Doppler velocity and imaging capabilities, both of which could be of great value in production logging. Some air-water measurements, both imaging and velocimetry, are presented, along with a discussion of pulsed Doppler theory.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):117-123. doi:10.1115/1.2905978.

Well K6-2 was drilled for geothermal production for the Kakkonda No. 2 Power Plant (to be built in 1995) at the Kakkonda geothermal field, northern Honshu Island, Japan from 1988 through 1989. The well was planned to be vertical and the target area was a 100-m radius of 2800 m. Mainly, because of the formation inclination, strong bit walk tendency was encountered below 1200 m. Even with packed-hole bottom-hole assemblies (BHA), the well inclination buildup rate was over 1 deg per 30 m. With this buildup rate, the well inclination would be over 50 deg at 2800 m, and not only miss the target area, but could not reach total depth because of severe rotation drag in the very abrasive formation (tertiary: shale, dacitic tuff and andesitic tuff-breccia; pre-tertiary: slate, sandstone and andesitic tuff). Because a pendulum BHA did not help to drop the inclination, downhole motors with bent subs were employed. Totals of six and seven downhole motors for 12 1/4 and 8 1/2-in. hole sections, respectively, were run. The estimated formation temperature was over 350°C below 1900 m, so two mud cooling towers and 500 m3 pit were used to cool the returned mud. These systems worked well, but at 2245 m the estimated mud circulation temperature on bottom went up to 150°C and the stator rubber of the downhole motors unbonded and broke up after a 1-h run. Below that depth, only a packed hole BHA was employed, and the inclination increased from 6 deg at 2300 m to 14 deg at 2800 m. At 2799 m, lost circulation was encountered and drilling terminated at 2818 m.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):124-132. doi:10.1115/1.2905979.

This paper presents a simulation study to evaluate the combined effect of cutting depth (drilling rate) and wear (bit dull) on the thermal response of polycrystalline diamond compact (PDC) cutters under downhole drilling conditions. A new understanding of frictionally generated heat between rock and PDC cutter is introduced from the analysis of forces active on the wearflat and the cutting (leading) surfaces of a cutter. Then this new concept is used to predict PDC bit performance with the controlled temperature of its cutters. Previous concepts, largely based on the laboratory drilling tests (with low drilling rate and under atmospheric conditions), recognize only one source of heat—the wearflat surface. However, this study, using field data, shows that the heat generated at the cutting surface may significantly contribute to the total heat flux in the cutter. As a result, the distribution of temperature within the cutter is changed, which particularly affects the maximum value of temperature at the cutting edge. A simplified 2-D finite difference numerical code is used to quantify the difference in cutter wearflat temperatures calculated with and without the additional heat flux generated at the cutting surface. The numerical analysis reveals that neglecting the cutting surface effect results in underestimation of the actual wearflat temperature by 10 to 530 percent, depending upon bit dull and downhole hydraulics. Also demonstrated is the actual impact of these findings on field drilling practices. The example comparison is made by calculating the optimal-control procedures for PDC bit with and without the effect of cutting surface. In these procedures, wearflat temperature becomes a mathematical constraint which limits weight on bit and rotational speed. The comparison includes calculation of the maximum bit performance curves which represent maximum drilling rate attainable for a bit to drill a predetermined length of a borehole (footage). The curves show an up to 18 percent reduction of drilling rate when the new and more rigorous temperature limitation is used. In addition, the example calculations show that the actual temperature of the bit cutters can be 460°C (860°F), and exceeds by almost 30 percent its maximum acceptable value of 350°C (660°F). For practical applications, the study reveals that many field failures of PDC bits may have been caused by lack of understanding of operational limits imposed by heat considerations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):133-141. doi:10.1115/1.2905980.
Abstract
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(2):142-147. doi:10.1115/1.2905981.

The blowout limits of a methane diffusion flame in a co-flowing air-fuel or air-diluent stream were determined for a range of surrounding co-flow stream velocities, both laminar and turbulent, up to ~ 1.50 m/s. Methane, ethylene, propane and hydrogen were used as the fuels in the surrounding co-flow stream while nitrogen and carbon dioxide were used as diluents. The experimental results show that the velocity of the surrounding stream affects the blowout phenomena significantly. An increase in the stream velocity has a detrimental effect on the blowout limits at very low velocities up to 0.30 m/s (essentially laminar flow) and at velocities higher than 1.50 m/s (turbulent flow). The addition of a fuel to the air stream in most cases enhances the blowout limit of a methane diffusion flame. However, different trends in the variation of the blowout limits with the surrounding fuel concentration were observed, depending on the type of fuel used and on whether the surrounding coflow stream was laminar or turbulent. The addition of nitrogen or carbon dioxide to the air stream results in decreasing the blowout limits. The effect is more severe at the higher velocities.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Energy Resour. Technol. 1993;115(2):148-150. doi:10.1115/1.2905982.
Commentary by Dr. Valentin Fuster

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