J. Energy Resour. Technol. 1993;115(4):239-246. doi:10.1115/1.2906428.

This paper presents an advanced concept in drilling optimization—the dynamic drilling strategy. The dynamic drilling strategy is a new methodology of drilling process planning and control; it combines theory of single-bit control with an optimal multi-bit drilling program for a well. In the simulation study, the dynamic drilling strategy was compared to conventional drilling optimization and typical field practices; the considerable cost-saving potential of 25 and 60 percent, respectively, was estimated. The method also appeared to be the most cost-effective for expensive and long-lasting PDC bits through better utilization of their performance and reduction in the number of bits needed for the hole.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):247-256. doi:10.1115/1.2906429.

An analytical development of a new mechanistic drilling model for polycrystalline diamond compact (PDC) bits is presented. The derivation accounts for static balance of forces acting on a single PDC cutter and is based on assumed similarity between bit and cutter. The model is fully explicit with physical meanings given to all constants and functions. Three equations constitute the mathematical model: torque, drilling rate, and bit life. The equations comprise cutter’s geometry, rock properties drilling parameters, and four empirical constants. The constants are used to match the model to a PDC drilling process. Also presented are qualitative and predictive verifications of the model. Qualitative verification shows that the model’s response to drilling process variables is similar to the behavior of full-size PDC bits. However, accuracy of the model’s predictions of PDC bit performance is limited primarily by imprecision of bit-dull evaluation. The verification study is based upon the reported laboratory drilling and field drilling tests as well as field data collected by the authors.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):257-263. doi:10.1115/1.2906430.

This paper explores some of the basic thermodynamic and technical considerations involved in using water as a working fluid for refrigeration and heat pump cycles down to its freezing point of 0°C. It is first shown how the integration of the functions of refrigerant and heat transfer fluid can lead to energy savings, especially for the case of ice production. Next, the two fundamental requirements that the compressor must fulfill—handling a very large volume flow and achieving a large compression ratio—are described. A thermodynamic analysis of multistage compression follows to investigate the adiabatic head requirements and the large desuperheating irreversibility. It is concluded that a radically new type of vacuum compressor must be developed in order for water to be used as working fluid in vapor compression refrigeration cycles.

Topics: Refrigerants , Water
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):264-271. doi:10.1115/1.2906431.

Energy efficiency and source air pollutant emission factors of gas heaters, gas engine heat pumps, and electric heat pumps for domestic heating have been evaluated and compared. The analysis shows that with the present state of technology, gas engine heat pumps have the highest energy efficiency followed by electric heat pumps and then gas heaters. Electric heat pumps produce more than twice as much NOx , and comparable CO2 and CO per unit of useful heating energy compared to natural gas heaters. CO production per unit of useful heating energy from gas engine heat pumps without any emission control is substantially higher than electric heat pumps and natural gas heaters. NOx production per unit of useful heating energy from natural gas engine heat pumps (using lean burn technology) without any emission control is about the same as effective NOx production from electric heat pumps. Gas engine heat pumps produce about one-half CO2 compared to electric heat pumps.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):272-277. doi:10.1115/1.2906432.

The radiator and its vulnerability to damage is one of the main criteria in automotive design. This study employed heat pipes in simulated radiators to transfer waste heat to the surrounding environment. A small-scale heat-pipe radiator module was designed using a computer program. Experimental tests were performed on this module to validate the design methodology and to study the vulnerability characteristics. The tests were conducted for a wide range of operating parameters such as air velocity, coolant flow rates, and the number of heat pipes damaged. The study indicated that a heat-pipe radiator may provide the necessary “limp home” capability to a vehicle, even with 50 percent of the pipes damaged. Also, with the radiators operating at less than peak load (slower vehicle speed), the undamaged heat pipes substantially compensated for the damaged heat pipes, adding to the reliability of the system.

Topics: Heat pipes
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):278-286. doi:10.1115/1.2906433.

Analytical and experimental investigations were conducted to identify and better understand the parameters that govern the entrainment of liquid droplets in high-velocity gas streams flowing over capillary wicking structures. Using a flow visualization technique, two modes of entrainment were identified and described for high-velocity gas flows over an intermittently interrupted liquid surface. These two modes, roll-wave entrainment and stripping entrainment, were found to correspond to the lower and upper critical gas velocities, respectively. Measurements of the critical gas velocities and the droplet size distribution (Sauter mean diameter) of the entrained sprays were made as a function of the capillary pore size for three different mesh sizes and were compared with several analytical models developed in previous investigations. The flow visualization results indicate that the upper critical velocity is insensitive to variations in the capillary pumping rate provided the capillary pores are properly primed. The experimental results also indicate that the critical velocity for a given mesh is strongly influenced by the mesh dimensions, but that the previously developed criteria for estimating the critical velocity results in an underestimation of the upper critical velocity for all but very small pore sizes. Finally, to resolve this problem a new analytical model for predicting the critical velocity was developed and shown to be accurate for a wide range of capillary pore sizes.

Topics: Structures
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):287-290. doi:10.1115/1.2906434.

Equations that predict the dependence of regenerator effectiveness on heat conduction in the matrix both parallel to and perpendicular to the fluid flow are derived from numerical simulations. The equations developed use Biot numbers parallel to the direction of fluid flow (Bix ) and perpendicular to the fluid flow direction (Biy ), the ratio of heat capacity rates (C*), the heat capacity rate ratio (C*Γ ), and the overall number of transfer units (NTUo ) to characterize the regenerator performance. Comparison of numerical predictions with those obtained using the equations developed in this paper show excellent agreement. These equations enable designers to accurately account for two-dimensional conduction effects when regenerators are designed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):291-300. doi:10.1115/1.2906435.

A theoretical model for simulation of conventional steam-heated cylinder dryers is developed by considering the heat and mass transfer in a porous sheet during drying. Expressions for sheet shrinkage as a function of mass of water removed and for reductions in sheet porosity are derived for inclusion in the model. The interface thermal contact conductance of moist paper handsheet/metal interfaces has been experimentally investigated. A resulting empirical correlation, representing the thermal contact conductance between the cast iron dryer surface and paper web, is incorporated into the drying simulation model to reflect reductions in heat input to the sheet during drying. Finite difference techniques are used to obtain the numerical solutions. Average sheet moisture content and temperature along the length of the dryer section as well as average evaporation rates per cylinder are predicted by the model. Consideration of the internal dynamics of the drying process allows profiles of sheet moisture content, temperature, liquid flux, and vapor flux through the sheet thickness to be developed throughout the dryer section. Drying results are consistent with actual production cases. The model can be used to design dryer sections, study changes in operating conditions or in layout of a multi-cylinder dryer, or simulate the application of enhanced drying devices to a conventional drying section. The effect of the drum/paper contact conductance on drying rates and resultant dryer section requirements is provided as an example application of the model.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):301-306. doi:10.1115/1.2906436.

The thermodynamics and chemical kinetics of the combustion in air of methane when containing varying concentrations of the common diluents CO2 , N2 , and H2 O are considered over a wide range of composition, temperature and pressure. Some approaches are then suggested towards enhancing the combustion rate of such mixtures in air.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):307-313. doi:10.1115/1.2906437.

The combustion of rich mixtures of methane representing natural gas in air or oxygenated air involving the uncatalyzed partial oxidation of methane is examined analytically with the view of hydrogen and/or synthesis gas (carbon monoxide and hydrogen) production from natural gas. This is carried out in turn for isothermal, constant pressure and constant volume combustion processes over the feed temperature range of 800–2000K and equivalence ratio of up to 3.5. The role of various operating parameters in establishing the yield of hydrogen is presented and discussed. The effectiveness of the controlled recirculation of combustion gases to the feed for enhancing the reaction and conversion rates of methane into hydrogen is examined. It is shown that there are some conditions that can be employed for such recirculation to yield significant increases in the conversion rate.

Topics: Hydrogen , Methane , oxidation
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1993;115(4):314-322. doi:10.1115/1.2906438.

The optimal lamination arrangements of laminated composite plates with maximum shear buckling loads are studied via a multi-start global optimization technique. A previously proposed shear deformable finite element is used to evaluate the positive and negative shear buckling loads of laminated composite plates in the optimal design process. Optimal lay-ups of thin as well as moderately thick composite plates with global maximum positive or negative shear buckling loads are determined utilizing the multi-start global optimal design technique. A number of examples of the optimal shear buckling design of symmetrically and antisymmetrically laminated composite plates with various material properties, length-to-thickness ratios, aspect ratios and different numbers of layer gorups are given to illustrate the trends of optimal layer orientations of the plates. Since the existence of in-plane axial forces is possible, the effects of axial compressive load on the optimal layer orientations for maximum shear buckling load are also investigated.

Commentary by Dr. Valentin Fuster

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