J. Energy Resour. Technol. 1992;114(3):175-180. doi:10.1115/1.2905938.

This paper gives a method of analysis for determining drill string weight required to develop a given bit force while drilling through and out of high-curvature well bores. The analysis is directed at medium radius well bores having radii of curvature ranging between 286 ft (87 m) and 955 ft (291 m), which are typically found in horizontal drilling. Sample calculations show how friction within the angle building portion of the well affect bit force.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):181-186. doi:10.1115/1.2905939.

Evaporative coolers consist of two main types: (a) the direct evaporative cooler in which water mixes with the air to be cooled; and (b) the indirect evaporative cooler in which water is sprayed into alternate passages cooling the secondary airflow, which in turns cools the primary flow which then passes to the building to be cooled. A three-dimensional numerical evaluation of the indirect cooler is given. Energy and mass balance equations are derived for the primary and secondary flows and the effectiveness is calculated for different variable inlet velocities and compared with experimental values.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):187-196. doi:10.1115/1.2905940.

A mechanistic model was developed for the thermal-hydraulic processes in the spout flash evaporator of an OC-OTEC plant. Nonequilibrium, two-fluid, conservation equations were solved for the two-phase flow in the spout, accounting for evaporation at the gas-liquid interface, and using a two-phase flow regime map consisting of bubbly, churn-turbulent and dispersed droplet flow patterns. Solution of the two-phase conservation equations provided the flow conditions at the spout exit, which were used in modeling the fluid mechanics and heat transfer in the evaporator, where the liquid was assumed to shatter into a spray with a log-normal size distribution. Droplet size distribution was approximated by using 30 discrete droplet size groups. Droplet momentum conservation equations were numerically solved to obtain the residence time of various droplet size groups in the evaporator. Evaporative cooling of droplets was modeled by solving the 1-D heat conduction equation in spheres, and accounting for droplet internal circulation by an empirical thermal diffusivity multiplier. The model was shown to favorably predict the available single-spout experimental data.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):197-203. doi:10.1115/1.2905941.

This investigation employs the techniques of second law analysis to show that significant improvements in performance are possible through the use of “perfectly stratified” thermal energy storage systems. Although the possibility of such improvements has been widely acknowledged in the literature, previous studies have not quantified the maximum possible performance gains attainable through the use of thermally stratified systems, nor have they established the viability of these optimal systems in actual practice. Thus, the present study was performed to achieve these two goals. This work is presented in two parts. In Part I, the specific class of systems to be examined is defined and the development of the basic analytical model is carried out. The completion of the analytical model and the presentation and interpretation of the results of an optimization study are given in Part II.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):204-208. doi:10.1115/1.2905942.

This investigation is presented in two parts. The basic analytical model is developed in Part I. Part II includes the completion of the analytical model and the results of an optimization study performed with this model. The results show that: 1) Significant performance gains, that is, reductions in the entropy generation number on the order of 10 percent, are possible by employing perfectly stratified thermal energy storage systems that are designed on the basis of the second law of thermodynamics. 2) These performance gains are mainly due to the complete elimination of the entropy generation due to heat transfer through finite temperature differences within the storage element. 3) In general, the optimum design of a perfectly stratified thermal energy storage system requires the use of a very large heat exchanger; however, it is possible to employ a much smaller than optimum heat exchanger without seriously degrading the superior performance of the system. 4) The operation of a stratified system is quite flexible because it has no optimum storage time. 5) The optimum values of the capacity rate ratios, (φR )opt and (φR )opt , for a perfectly stratified thermal energy storage system are in general not equal to unity; however, this finding is shown to be in concert with Bejan’s theory of “remanent” irreversibilities for a heat exchanger.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):209-215. doi:10.1115/1.2905943.

An experimental study of the effects of diluent gas injection on the structure and pollutant emissions of a kerosene spray from a twin fluid atomizer is presented. Nitrogen and carbon dioxide were used as the diluents. Flame length, radiation emission, axial and radial temperature profiles, and the radial profiles of carbon monoxide, oxygen, nitric oxide, and soot in flame gas samples were studied. The emission index, defined as the mass ratio of the rate of the species emitted to the fuel input rate, was determined from the experimental data. Results show, at a diluent injection rate approximately equal to the atomizing air flow rate, nitrogen was more effective than carbon dioxide in reducing flame length, flame radiation, and the emission indices of carbon monoxide and soot. Although both diluents increased nitric oxide emission, the effect of carbon dioxide was weaker.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):216-220. doi:10.1115/1.2905944.

Flame propagation within confined, stratified gaseous environments were investigated experimentally. The diluents nitrogen and helium were used in turn to overlay initially combustible methane-air or hydrogen-air mixtures. Gas stratification was achieved by allowing the two initially homogeneous gases to interdiffuse for a certain period of time at constant temperature and pressure within a long, vertical, smooth, closed, circular tube. Upward flame propagation was examined following spark ignition while the tube was closed at the top but open at the bottom. Near-extinction flame speeds, lower than those predicted according to Davies and Taylor (1950), were obtained with helium dilution. Moreover, estimated reactant concentrations at the observed location of flame extinction indicated, in specific instances, that mixture stratification appears to slightly enhance locally the lean flammability limit. Nonuniform, stratified combustible gaseous mixtures and flame propagation within such mixtures are found in many situations, including in numerous technical applications, as well as in various potentially hazardous circumstances. The leakage of a fuel from storage tanks or pipelines, the formation of layered combustible mixtures within rooms, corridors, or elevator shafts of buildings, the formation of gas pockets in coal mine galleries, and the inerting of flammable mixtures through diluent gas addition are some examples. Some relevant information about the stratification process and the flame propagation characteristics in these specific circumstances has already been reported in the literature by Bakke and Leach (1962), James and Purdy (1962), Girard et al. (1979), Karim and Lam (1986) and Karim et al. (1987). This investigation considers some aspects of flame propagation and mass transfer within confined, stratified gaseous environment. The diluents nitrogen and helium were used in turn to overlay initially combustible methane-air or hydrogen-air mixtures. Mixture stratification was produced by permitting the two initially homogeneous gaseous systems to interdiffuse at constant temperature within a long, vertical, smooth, closed, circular tube. Only upward flame propagation was examined, as this mode is expected to involve the widest flammability limits and the fastest propagation for both homogeneous and stratified methane-air mixtures when confined in tubes (Liebman et al., 1971).

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):221-226. doi:10.1115/1.2905945.

A system to reduce carbon dioxide emissions from combustion power plants is described. Unlike earlier proposals based on flue gas treatment, the problem is addressed prior to combustion by reforming the hydrocarbon fuel into H2 and CO2 . Following separation, H2 is burned in place of the original fuel and the captured CO2 is liquefied and injected into the deep ocean at a depth sufficient to ensure effective containment, and to minimize damage to the marine environment. Calculations indicate moderate plant thermal efficiency and power cost penalties. In addition, the H2 production potential of this system may be exploited as a means to facilitate the transition from fossil fuels to future hydrogen energy systems.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):227-234. doi:10.1115/1.2905946.

A thermochemical nuclear hydrogen producing process has been developed and evaluated from thermodynamics and engineering points of view. The cycle is based on sulfuric acid decomposition process developed earlier, which produces mechanical power using additional primary energy as well as excess process heat generated within the cycle. The sulfuric acid decomposition process has been closed using a sulfur dioxide electrochemical oxidizer cell and feasibility of its energy self-sufficient operation has been demonstrated. The first law efficiency of the cycle has been determined as 34.14 percent and the second law efficiency as 43.32 percent. It is found that the modified sulfuric acid decomposition section is improved by 14.8 percent compared to the basic process used in the sulfur family cycles. For a plant size producing 8.94 × 106 GJ H2 per year, the typical levelized costs of hydrogen are $20.15(1988) per GJ energy and $24.47(1988) per GJ exergy.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):235-243. doi:10.1115/1.2905947.

A new constitutive model for interface shear in concrete is presented. The composite is treated as a single-phase medium with no distinction in the strength difference between the matrix and the inclusions. The model consists of an assemblage of springs and a triangular asperity as a statistically equivalent replacement of the rough crack surfaces. The constitutive model relates the normal and shearing stresses and displacements in terms of the interface strength, contact areas, the contact angle of the rough crack surface, and the crack closing pressure. Using the concepts of critical state soil mechanics, conditions were stipulated for dilation and contraction of the rough crack, in terms of the intensity of the applied constant normal stresses. The deformability of the asperity was mathematically described in terms of the initial angle of contact and a progression of this angle to a minimum by means of an exponential model. Using idealized test results, a mathematical model was developed for contact area as a function of the crack width and tangential displacement. The performance of the constitutive model was verified by predicting the experimental results. The comparisons appear to be very satisfactory.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):244-249. doi:10.1115/1.2905948.

Various anisotropic damage models are investigated to take into account the nonlinear behavior of a ceramic matrix composite. A critical analysis of classical strain metrology results proves that it is unfeasible to evaluate the damage in a direction orthogonal to the stress one, because the nine elasticity constants of an orthotropic material are independent and Poisson’s ratios are strain’s second order, whereas Young’s modulus are first-order ones. An ultrasonic method provides the necessary stiffness variations, inaccessible by classical strain measurements, required to identify the anisotropic damage.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):250-254. doi:10.1115/1.2905949.

The analytical solution to the natural convection problem in a rotating rectangular porous domain is presented for a small aspect ratio of the domain. The convection results from differential heating of the horizontal walls leading to temperature gradients orthogonal to the centrifugal body force. The solution to the nonlinear set of partial differential equations was obtained through an asymptotic expansion of the dependent variables in terms of a small parameter representing the aspect ratio of the domain. The convection regime is apparent in the results, although it has a weak effect on the mean heat flux.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1992;114(3):255-260. doi:10.1115/1.2905950.

Intercooling of compressors is necessary for an efficient process. Among the optimal criteria required, minimizing the compression-specific work is one of the more commonly used. Upon ideal conditions, such a criterion leads to an isothermal compression whose importance is purely theoretical, since it requires an infinite number of intercoolers. In this paper the evaluation of correction factors to the well-known relations of the optimal location of intercoolers in a compression process and its corresponding work of compression was performed for a general compression process which accounts for pressure losses and other irreversibilities as well. As a result of including the pressure losses in the equations, a finite number of intercoolers is evaluated as optimum. The results, although qualitatively expected, show a quantitative nonempirical figure of the optimal number of intercoolers as a function of the terminal pressure ratio and as a function of the relative pressure losses . The ideal conditions are evaluated and verified as a particular case by assuming no pressure losses. In practice, these results can be used as an upper limit for technoeconomical optimization processes.

Commentary by Dr. Valentin Fuster

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