bluuebunny/crossref_metadata_2025 huggingface dataset:
Addition of Highly Efficient Bottoming Cycles for the Nth-Generation Molten Carbonate Fuel Cell Power Plant
Authors: Lobachyov K. V. , Richter H. J.
Published: February 2008

An intermediate scale (2.0 MW gross) molten carbonate fuel cell (MCFC) power plant recently began operating in Santa Clara, California. The goal of the project is to demonstrate the possibility of long-term operation of MCFC stacks. The fuel cell stacks are the only source of electricity, which means a simple power plant system, and relatively low capital costs. This, however, results in substantial work losses in the plant, most of which come from the hot exhaust gas discharge. The predicted efficiency is a respectable 50 percent. In this paper, an exergy analysis is performed in order to study if a future plant’s efficiency can be improved. It is shown that for the future plant of this type it would be worthwhile to consider the addition of a steam bottoming cycle as well as changing the configuration of the top cycle. This can lead to improving the efficiency to close to 70 percent. The modified power plant requires additional equipment, such as steam turbines, heat exchangers, condensers; thus, the capital cost of the plant changes substantially. A cost analysis of the modified plant was performed, and a comparison of the cost of electricity between the two cycles is made. Finally, a Kalina cycle as one option for a bottoming cycle is considered as well.
Effect of Air Distribution on Solid Fuel Bed Combustion
Authors: Kuo J. T. , Hsu W.-S. , Yo T.-C.
Published: February 2008

One important aspect of refuse mass-burn combustion control is the manipulation of combustion air. Proper air manipulation is key to the achievement of good combustion efficiency and reduction of pollutant emissions. Experiments, using a small fix-grate laboratory furnace with cylindrical combustion chamber, were performed to investigate the influence of undergrate/sidewall air distribution on the combustion of beds of wood cubes. Wood cubes were used as a convenient laboratory surrogate of solid refuse. Specifically, for different bed configurations (e.g., bed height, bed voidage, bed fuel size, etc.), burning rates and combustion temperatures at different bed locations were measured under various air supply and distribution conditions. One of the significant results of the experimental investigation is that combustion, with air injected from side walls and no undergrate air, has the maximum combustion efficiency. On the other hand, combustion with undergrate air achieves higher combustion rates but with higher CO emissions. A simple one-dimensional model was constructed to derive correlation of combustion rate as a function of flue gas temperature and oxygen concentration. Despite the fact that the model is one-dimensional and many detailed chemical and physical processes of combustion are not considered, comparisons of the model predictions and the experimental results indicate that the model is appropriate for quantitative evaluation of bed-burning rates.
Relating Burning Rate and NO Formation to Pressure Development in Two-Stroke Diesel Engines
Authors: Hill P. G. , Douville B.
Published: February 2008

A multizone thermodynamic method has been developed to determine combustion rate and NO formation from measured cylinder pressures and performance of two-stroke diesel engines. Integral to the analytical method is a nonlinear fit to the combustion chamber heat loss; the fit is consistent with the overall energy balance and with measured fuel consumption rate and exhaust temperature. The method assumes equilibrium combustion properties except for NO, whose relatively slow formation is estimated using the extended Zeldovich mechanism in the post-flame gas during a period of one mixing time. Application of the method to a 2-stroke diesel engine indicates a post-flame mixing time of 0.55 ms or 4 deg crank angle at 1250 rpm, yielding exhaust concentrations of NO considerably less than what would have been expected from equilibrium-then-sudden-freezing considerations.
Structure of the Flow Field of a Nonpremixed Gas Jet Flame in Cross-Flow
Authors: Savas O. , Huang R. F. , Gollahalli S. R.
Published: February 2008

Experimental studies on nonpremixed turbulent flames in cross flow are necessary as the current analytical and numerical tools are unable to provide acceptable quantitative information about their complex flow fields. This study, which complements the results of a previous study by the authors on the flame structure in the stabilization region of a partially lifted turbulent diffussion flame in cross-flow (TDFCF), presents the measured turbulence quantities in the flow field of the same flame. Results include mean velocities in the cross-stream and spanwise directions, the vertical and horizontal components of fluctuating components of velocity, Reynolds stress, power spectra, and autocorrelations useful for developing and validating theoretical models of TDFCF in the moderate momentum flux ratio range
Numerical/Experimental Analysis of an API 8-Round Connection
Authors: Assanelli A. P. , Xu Q. , Benedetto F. , Johnson D. H. , Dvorkin E. N.
Published: February 2008

The objective of the research reported in this paper is to investigate in depth the performance properties of the 5 1/2-in. 14-lb/ft J-55 API 8-round short thread casing connection under different load cases, via experimental tests and finite element analyses. The FEA models are validated by comparing the numerical results with full-scale tests. The validated models are afterwards used to perform parametric studies on the connection behavior.
Petroleum Coke and Coal Start-Up Testing in Bubbling Fluidized Bed Combustors
Authors: Anthony E. J. , Anderson K. , Carson R. , Lau I. T.
Published: February 2008

Bench-scale and 160 MWe demonstration tests were conducted for petroleum coke and high volatile bituminous coal blends. The bench-scale apparatus was a 100-mm-dia reactor located at the Canada Centre for Mineral and Energy Technology (CANMET), Energy Research Laboratories. The demonstration tests were conducted on the Tennessee Valley Authority’s (TVA) 160 MWe Shawnee Atmospheric Fluidized Bed Combustion (AFBC) Unit located at Paducah, Kentucky. Five and ten percent nominal volatile petroleum cokes were tested in the bench-scale unit. In addition, for the five-percent petroleum coke blends of 25, 50, and 75-percent petroleum coke, with the balance coal, were also examined at the bench scale. Eight start-up tests have been conducted with 50 percent blend of green delayed petroleum coke at the Shawnee AFBC unit. The bench-scale tests revealed that the volatile content in the petroleum coke was the primary factor affecting start-up. The tests showed that the volatile content from the coke and coal ignited at similar times; the char required longer to ignite. Bench-scale tests showed adequate start-up performance with blends up to 75 percent petroleum coke. Cold start-ups were conducted at the Shawnee AFBC Unit with 7 to 10 percent volatile green delayed petroleum coke. In all the start-ups, the operating temperature of 816°C was reached within 15 min of introducing the petroleum coke blend; this is similar to when high volatile bituminous coal was used. One start-up required a longer time because limestone had to be used to generate the bed. Local hot spots (982°C) were noticed in several start-ups for short periods, but subsided when additional air was supplied. Although more difficult to control, TVA routinely starts the Shawnee AFBC Unit with 50 percent shot petroleum coke and 50 percent high volatile bituminous coal.
Bottom-Hole Assembly Modeling and Dynamic Response Determination
Authors: Spanos P. D. , Payne M. L. , Secora C. K.
Published: February 2008

Understanding bottom-hole assembly (BHA) dynamic phenomena remains a critical drilling systems issue due to the cost of potential failures. Many studies have provided useful insight into drillstring dynamics. This study extends previous efforts by providing a novel BHA model which accounts for several critical response factors and can be augmented to address a variety of other effects; new data from an experimental study regarding damping are presented. The proposed model represents the transfer function of the drillstring in terms of its natural modes and properly incorporates several factors critical to BHA dynamic response prediction, including frequency-dependent fluid added mass, and nonlinear wellbore constraints. Results from pertinent numerical studies are presented.
Effect of Downhole Assembly and Polycrystalline Diamond Compact (PDC) Bit Geometry on Stability of Drillstrings
Authors: Elsayed M. A. , Dareing D. W. , Dupuy C. A.
Published: February 2008

Stability of drillstrings equipped with PDC bits depends on many factors such as the design of the drillstring, design of the bit, and formation type. In this paper, we show that the drill pipe plays a minor role in stability in comparison with that of the drill collars. We also show that the number of bit blades affects the location of the stability pockets, while their spacing affects the size of these pockets. Using this data, a combination of drill collar and bit design can be used to provide operating speeds resulting in maximum stability of the drillstring.
Dynamic Stress Behavior in Catalytic Combustors
Authors: Boehman A. L. , Simons J. W. , Niksa S. J. , McCarty J. G.
Published: February 2008

Dynamic stress behavior during catalytic combustion of methane has been simulated under transient warm-up, cool-down, and cyclic conditions. The numerical model combines a two-dimensional solution to the transport equations, solution of an energy balance on the monolith wall, and the NIKE3D structural analysis code to predict thermal stresses. The model also includes a detailed heterogeneous kinetics model for a proprietary palladium oxide (PdO) catalyst, but the model ignores gas-phase reactions. Results illustrate that thermal stresses as high as 630 MPa can form during transient operating modes, which risks structural failure of the ceramic monolith. The maximum computed thermal stress concentrations occur near the inlet of the monolith. Peak transverse stresses (which act to form axial cracks) typically form near the inlet and centerline of the monolith structure, while peak axial stresses form near the edges of the flat plate that represents the monolith structure. Increasing the preheat temperature of the incoming fuel and air mixture lessens the peak thermal stress. To a first approximation, the magnitude of the peak transverse stress during any transient cycle considered with our model can be estimated from the maximum value of the gradient in the computed temperature profiles.
Breakup of Viscous Liquid Sheets Subjected to Symmetric and Asymmetric Gas Flow
Authors: Witherspoon W. , Parthasarathy R. N.
Published: February 2008

A study of the breakup of planar viscous liquid sheets subjected to gas flow on both sides was conducted. A linear spatial stability analysis was used to determine the instability wave characteristics. The analysis included the effects of liquid properties such as viscosity, density, and surface tension; the gas was treated as inviscid. Dispersion relations were obtained relating the wave growth rates to the frequency and other flow variables. The wave characteristics were determined by numerical solution of the governing dispersion relations for a wide range of operating conditions. In all cases, the gas velocity was found to be destabilizing; increases in the liquid density, viscosity, and surface tension were all found to have stabilizing effects. When the liquid sheet was exposed to unequal gas velocities, the wave propagation characteristics were found to be altered from the case of equal gas velocities.
Foundations of the State Principle
Authors: Schaefer L. A.
Published: February 2008

The state principle is an important and fundamental thermodynamic concept. Having only recently been formally stated, however, there is still some disagreement as to the basis of the principle’s derivation. An examination of various state principle presentations leads to the conclusion that the state principle must be based on the first and second laws, and, additionally, that the energy, the amounts of the constituents, and the parameters solely determine property. Microscopic properties and non-equilibrium states are not inherently governed by the state principle, but extensions have been formulated to incorporate these areas.
Modeling the Transient Formation of Flammable Atmospheres Due to Convective Diffusion
Authors: Bunama R. , Karim G. A.
Published: February 2008

A one-dimensional computational model based on a finite difference scheme has been developed to model the transient formation of flammable atmospheres upon the diffusion of fuel vapor following the exposure of liquid fuel surfaces to air within containers at constant pressure. Two fuels were modeled, namely n-pentane and methanol. The effects of convection and temperature gradients produced by the extraction of the latent heat of evaporation from the liquid surface were taken into account. The thermodynamic and transport properties were taken to be variable. The model predictions for the variation with time of the location of the lean flammability limit concentration compared favorably with the corresponding experimental values. The width of the flammable region bounded between the lower and upper flammability limits concentrations was calculated for both fuels along with the associated temperature and concentration profiles. The role of ambient temperature on the formation of the flammable zone was also investigated and presented for different typical cases. The results show that a detailed parametric study is required individually for each fuel in order to assess the trends of the flammable regions development with changes in different operating parameters.
Evaluation of the Backpressure Technique for Blockage Detection in Gas Flowlines
Authors: Scott S. L. , Satterwhite L. A.
Published: February 2008

As longer, full well-stream flowlines are utilized to reduce the costs of deepwater and satellite developments, routine production monitoring attains a new level of importance. Of particular interest is the operational impact that blocking agents such as paraffins, asphaltenes, hydrates, and scale can have on the flowlines. Because blockages can reduce and even disrupt production, monitoring flowline performance becomes an economic necessity. This paper considers the application of the backpressure technique as a means of monitoring the growth of blockages in gas flowlines. Using only routine production data, this method quantifies partial blockages by comparing production data to a baseline performance curve. Experimental verification was performed using the LSU 9460-ft flowloop of 4 1/2-in. drillpipe. Multirate tests were conducted using methane at 250–620 psig with partial blockages placed in the flowloop. Good agreement with the backpressure model was observed.
Transients in Gas-Condensate Natural Gas Pipelines
Authors: Zhou J. , Adewumi M. A.
Published: February 2008

Liquid condensation in natural gas transmission pipelines commonly occurs due to the thermodynamic and hydrodynamic imperatives. Condensation subjects the gas pipeline to two-phase transport. Neither the point along the pipeline at which the condensate is formed nor the quantity formed is known a priori. Hence, compositional multiphase hydrodynamic modeling, which couples the multiphase hydrodynamic model with the natural gas phase behavior model, is necessary to predict fluid dynamic behavior in gas/condensate pipelines. A transient compositional multiphase hydrodynamic model for transient gas-condensate two-phase flow in pipelines is presented. This model consists of our newly developed well-posed modified Soo’s partial pressure model in conservative form which serves as the transient multiphase hydrodynamic model, and the phase behavior model for natural gas mixtures.
Velocity Guidelines for Avoiding Erosion-Corrosion Damage in Sweet Production With Sand
Authors: Shadley J. R. , Rybicki E. F. , Shirazi S. A. , Dayalan E.
Published: February 2008

CO2 corrosion in carbon steel piping systems can be severe depending on a number of factors including CO2 content, water chemistry, temperature, and percent water cut. For many oil and gas production conditions, corrosion products can form a protective scale on interior surfaces of the piping. In these situations, metal loss rates can reduce to below design allowances. But, if sand is entrained in the flow, sand particles impinging on pipe surfaces can remove the scale or prevent it from forming at localized areas of particle impingement. This process is referred to as “erosion-corrosion” and can lead to high metal loss rates. In some cases, penetration rates can be extremely high due to pitting. This paper combines laboratory test data on erosion-corrosion with an erosion prediction computational model to compute flow velocity limits (“threshold velocities”) for avoiding erosion-corrosion in carbon steel piping. Also discussed is how threshold velocities can be shifted upward by using a corrosion inhibitor.
Sizing Wet-Gas Pipelines and Slug Catchers With Steady-State Multiphase Flow Simulations
Authors: Xiao J. J. , Shoup G.
Published: February 2008

The design of wet-gas pipelines and slug catchers requires multiphase flow simulations, both steady-state and transient. However, steady-state simulation is often inadequately conducted and its potential not fully utilized. This paper shows how mechanistic steady-state simulation models can be used to obtain not only pressure drop, liquid holdup and flow regime, but also to extract important operational information such as pig transit time, pig exit speed, liquid buildup rate behind the pig, and the time for the pipeline to return to a steady-state after pigging. A well-designed set of steady-state simulations helps to determine pipeline size, slug catcher size, and pigging frequency. It also serves as a starting point for subsequent transient multiphase flow simulations.
Retractable Bits Development and Application
Authors: Gelfgat M. , Alikin R.
Published: February 2008

This paper presents a historical view and present status of retractable bit design and drilling results. Despite the significant improvements in cone-sealed bearing rock bits, the special features of retractable bits provides a wider range of field applications. Scientific drilling, both continental and offshore and stratigraphic offshore boreholes, is an area for profitable application of retractable bits with a downhole motor. Another promising application is drilling and simultaneous casing where some prototypes have been successfully tested. Other applications such as horizontal and geothermal drilling look promising for future developments.
Efficiency Optimizations of an Irreversible Brayton Heat Engine
Authors: Cheng C.-Y. , Chen C.-K.
Published: February 2008

A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.
The Study of Dynamic Slug Flow Characteristics Using Digital Image Analysis—Part I: Flow Visualization
Authors: Gopal M. , Jepson W. P.
Published: February 2008

This paper reports the application of novel, digital image analysis techniques in the study of slug flow characteristics, under dynamic conditions in two-phase gas-liquid mixtures. Water and an oil of viscosity 18 cP were used for the liquid phase and carbon dioxide was used for the gas phase. Flow in a 75-mm i.d., 10-m long acrylic pipeline system was studied. Images of slugs were recorded on video by S-VHS cameras, using an audio-visual mixer. Each image was then digitized frame-by-frame and analyzed on a SGI™ workstation. Detailed slug characteristics, including liquid film heights, slug translational velocity, mixing length, and, slug length, were obtained.
Liquid Holdup in Large-Diameter Horizontal Multiphase Pipelines
Authors: Maley L. C. , Jepson W. P.
Published: February 2008

This paper studies the liquid holdup within the mixing zone of the slug. The results of the study show that the liquid holdup begins at the liquid holdup of the liquid film before the slug and then increases until the end of the mixing zone is reached. Once past the mixing zone of the slug, the average liquid holdup becomes constant. As the height of the liquid film and/or viscosity increases, so does the liquid holdup at any given film Froude number. Since the liquid holdup becomes constant once past the mixing zone of the slug, the mixing zone length was determined for the film Froude numbers studied. The results show that the mixing zone length increases linearly with film Froude number and is independent of the viscosity of the liquid in the slug for a viscosity range of 1 to 16.6 cP.
Analysis of Yield-Power-Law Fluid Flow in Irregular Eccentric Annuli
Authors: Hussain Q. E. , Sharif M. A. R.
Published: February 2008

Fully developed laminar axial flow of yield-power-law fluids in eccentric annuli has been investigated numerically. The annuli may be fully open or partially blocked. General nonorthogonal, boundary-fitted curvilinear coordinates have been used to accurately model the irregular annular geometry due to the presence of a flow blockage. A computer code has been developed using a second-order finite-difference scheme. An exponential model for the shear stress, valid for both yielded and un-yielded regions of the flow, is used in the computation. The effects of pressure gradient, eccentricity, and blockage height on the flow rate have been studied and the results are presented. The flow rate is found to increase with increasing eccentricity for eccentric annuli without any blockage. For partially blocked eccentric annuli, the flow rate at a particular eccentricity decreases as the blockage height is increased.
Geochemical Partitioning of Metals in Spent Drilling Fluid Solids
Authors: Deuel L. E. , Holliday G. H.
Published: February 2008

Metals in oil and gas fluids have been of concern to the environmental and industrial communities since 1976. As a result, metals in 31 spent drilling fluids representative of the major oil and gas production provinces in the Continental United States, were fractionated into exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual forms using a sequential extraction (summation of fractions) technique. Bioavailability and mobility of metals in solid matrices follow in sequence of the operational defined fractions with chemical reactivity decreasing in the order of exchangeable > bound to carbonate > bound to Fe-Mn oxide > bound to organic matter > residual fractions. Metals evaluated in this study include arsenic, barium, cadmium, chromium, lead, and zinc. The summation of fractions was compared to independent total metals analysis using the United States Environmental Protection Agency (USEPA) SW-846 Method 3050 digest procedure to evaluate metal recoveries. No difference was observed in the summation of fractions and EPA Method 3050 total metal values for arsenic, barium, and cadmium. EPA Method 3050 digest was about 28 percent lower in chromium, and about 19 percent lower in lead and 16 percent lower in zinc than the total by summation of fractions. Almost all of the barium (95.6 percent) was recovered in the residual fraction. Arsenic was recovered primarily in the residual fraction (74.3 percent) and the Fe-Mn oxide fraction (16.1 percent). The highest quantity of cadmium was recovered in the residual fraction (43.3 percent), followed by the bound to organic (27.9 percent), and bound to Fe-Mn oxide (21.1 percent) fractions. Chromium was observed primarily in the residual (40.4 percent) and bound to Fe-Mn oxide (34 percent) fractions. Lead was distributed primarily in the bound to Fe-Mn oxide (49.3 percent), and residual (27 percent) fractions. Zinc was almost equally distributed in the bound to organic (36.2 percent), and bound to Fe-Mn oxide (33.1 percent) fractions. Cadmium (3.9 percent) and arsenic (2.7 percent) were the only metals with an exchangeable fraction >1 percent of the total. Low total and/or low exchangeable metal concentrations ultimately control the bioavailability and mobility of metals in spent drilling solids and limit the potential for an adverse impact on the environment.
Thermodynamic Optimization of a Gas Turbine Power Plant With Pressure Drop Irreversibilities
Authors: Radcenco V. , Vargas J. V. C. , Bejan A.
Published: February 2008

In this paper we show that the thermodynamic performance of a gas turbine power plant can be optimized by adjusting the flow rate and the distribution of pressure losses along the flow path. Specifically, we show that the power output has a maximum with respect to the fuel flow rate or any of the pressure drops. The maximized power output has additional maxima with respect to the overall pressure ratio and overall temperature ratio. When the optimization is performed subject to a fixed fuel flow rate, and the power plant size is constrained, the power output and efficiency can be maximized again by properly allocating the fixed total flow area among the compressor inlet and the turbine outlet.
Oilwell Cement Pulsing to Maintain Hydrostatic Pressure—A Search for Design Model
Authors: Manowski W. M. , Wojtanowicz A. K.
Published: February 2008

Presented are theoretical and experimental results from a project supporting development of a new method for cement vibration in well’s annulus to prevent gas migration. In this method, cyclic pressure pulses are applied at the wellhead and transmitted down the annulus. These pulses cause reciprocation and shear within cement column—a process delaying the loss of hydrostatic pressure and preventing the inflow of gas into the well’s annulus. Field tests in real wells conducted to observe transmission of a single pressure pulse and to measure compressibility of setting cement showed that application of pressure pulses of 100 psi amplitude and 0.1 Hz frequency may be an effective and inexpensive way of preventing gas flow after cementing. The paper presents development of a cement pulsation design method based upon the analytical model of pressure propagation in Bingham plastic fluid and experimental data on rheology of cement slurries subjected to continuous shear. The primary objective of the method is to minimize the likelihood of gas invasion into the cement-filled annulus.
Analysis of Offshore Guyed Tower Platforms to Wind and Wave Forces
Authors: Bisht R. S. , Datta T. K. , Jain A. K.
Published: February 2008

The fundamental frequency of guyed tower platforms is designed to be low, and, therefore, it is susceptible to low-frequency excitation caused by fluctuating components of the wind velocity. The dynamic response of a simplified model of the Lena guyed tower is obtained for the fluctuating component of the wind force and the wave force. Both wind velocity and water particle kinematics due to wave motion are modeled as stationary random processes and are simulated from their respective power spectral density functions. The response analysis is performed by an iterative frequency domain procedure which duly considers the nonlinearities produced due to the drag effect and the nonlinear guyline resistance. The responses are also obtained in the presence of current. A parametric study is conducted to evaluate the relative contribution to the responses made by the wind force. The parametric study also illustrates how the current modifies the overall dynamic response. It is shown that the wind force significantly influences the first mode displacement response of the tower; the bending moment and shear force are not much affected by it. The current velocity tends to modify the peaks of the power spectral density function of the displacement response.
Transport to a Chemically Active Thin Liquid Film Over a Spinning Disk
Authors: Rahman M. M.
Published: February 2008

An analytical solution for the process of mass transfer from a spinning disk to a chemically active thin liquid film flowing over the disk is presented. By analogy, the results are also applicable to heat transfer to the film with temperature-dependent heat generation. The process is modeled by establishing equations for the conservation of mass, momentum, and species concentration, and solving them analytically. The partial differential equation for species concentration is solved using the separation of variables technique along with the application of the Duhamel’s theorem. Tables for eigenvalues and eigenfunctions are presented for a number of reaction rate constants. A parametric study was performed using Reynolds number, Ekman number, and chemical reaction rate as parameters. It was found that Sherwood number increases with Reynolds number (flow rate) as well as inverse of Ekman number (rate of rotation). These fundamental results will be useful to design advanced energy transport processes for a low-gravity space environment.
Overall Efficiency of a Radial Fin Assembly Under Dehumidifying Conditions
Authors: Rosario L. , Rahman M. M.
Published: February 2008

The aim of this paper is the analysis of heat transfer in a radial fin assembly during the process of dehumidification. An individual finned tube geometry is a reasonable representation of heat exchangers used in air conditioning. The condensation process involves both heat and mass transfer and the cooling takes place by the removal of sensible as well as latent heat. The ratio of sensible to total heat is an important quantity that defines the heat transfer process during a dehumidifier operation. A one-dimensional model for heat transfer in the fin and the heat exchanger block is developed to study the effects of condensation on the fin surface. The combined heat and mass transfer process is modeled by incorporating the ratio of sensible to total heat in the formulation. The augmentation of heat transfer due to fin was established by comparing the heat transfer rate with and without fins under the same operating conditions. Calculations were carried out to study the effects of relative humidity and dry bulb temperature of the incoming air, and cold fluid temperature inside the coil on the performance of the heat exchanger. An analysis of the overall efficiency for the assembly was also done. Results were compared to those under dry conditions, wherever appropriate. Comparison between present results and those published for rectangular as well as radial fins under fully wet conditions were made. These comparisons established the validity of the present model. It was found that the heat transfer rate increased with increment in both dry bulb temperature and relative humidity of the air. The augmentation factor, however, decreased with increment in relative humidity and the dry bulb temperature. The fin efficiency decreased with relative humidity.
Performance Characteristics of a Compressor-Driven Metal Hydride Refrigerator
Authors: Lloyd G. M. , Razani A. , Kim K. J.
Published: February 2008

Thermodynamic analyses of compressor-driven metal hydride refrigerators predict a high coefficient of performance. Comparison with the results from a computational model indicates that the coefficient of performance attainable from an actual system operating under transient conditions can indeed be significant. Parametric calculations are given which illustrate the ideal power-efficiency operating characteristics of the system. The computed efficiency approaches the thermodynamic efficiency as the operating power tends to zero.
Analytical Inflow Performance Relationships
Authors: Wiggins M. L.
Published: February 2008

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.
Estimation of the Thermodynamic Properties of Unbranched Hydrocarbons
Authors: He H. , Metghalchi M. , Keck J. C.
Published: February 2008

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.
Effects of Evaporator Frosting on the Performance of an Air-to-Air Heat Pump
Authors: Marti´nez-Fri´as J. , Aceves S. M.
Published: February 2008

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.
Stator Life of a Positive Displacement Downhole Drilling Motor
Authors: Delpassand M. S.
Published: February 2008

The power section of a positive displacement drill motor (PDM) consists of a steel rotor and a tube with a molded elastomeric lining (stator). Power section failures are typically due to the failure of the stator elastomer. Stator life depends on many factors such as design, materials of construction, and downhole operating conditions. This paper focuses on the stator failure mechanisms and factors affecting stator life. An analytical method for predicting the effect of various design and operating parameters on the strain state and heat build-up within elastomers is discussed. The effect of parameters such as rotor/stator design, downhole temperature, drilling fluid, stator elastomer properties, motor speed, and motor differential pressure on the stator life is discussed. Nonlinear finite element analysis is used to perform thermal and structural analysis on the stator elastomer. Data from laboratory accelerated life tests on power section stators is presented to demonstrate the effect of operating conditions on stator life.
Efficiency Comparisons for a Centrifugal Separator Using Hydrocarbon Fluids and Steam and Water
Authors: Birmingham D. P. , Hall W. H.
Published: February 2008

During 1996 and 1997, a steam and water separator used in the nuclear power industry was tested with hydrocarbon fluids to evaluate its potential for use in the hydrocarbon production industry. Prior to testing with hydrocarbon fluids, a nondimensional parameter was developed from a simple model of the second-stage centrifugal separator to correlate existing liquid separation efficiency data for this separator using steam and water. This paper outlines the development of the nondimensional correlating parameter and presents comparisons of liquid separation efficiency with steam and water and hydrocarbon fluids using this parameter.
The Relative Importance of Radicals on the N2O and NO Formation and Destruction Paths in a Quartz CFBC
Authors: Winter F. , Wartha C. , Hofbouer H.
Published: February 2008

In a laboratory-scale circulating fluidized bed combustor (CFBC), which mainly consists of quartz-glass, the relative importance of the radicals, generated by the combustion process, on the N2O and NO formation and destruction paths are studied. The CFBC unit is electrically heated and operating conditions can be nearly independently changed over a wide range; e.g., the bed temperature was varied between 700 and 900°C. The radicals’ importance on the destruction reactions of N2O has been investigated under CFBC conditions by a recently developed iodine-addition technique to suppress the radical concentrations. Additionally, CO, CH4 and H2O have been added to study their influence and to change the pool of radicals. Time-resolved concentration changes at the top of the riser have been measured by using a high-performance FT-IR spectrometer in combination with a low-volume, long-path gas cell. The FT-IR analysis is focused on the carbon-containing species, viz., CO2 CO, CH4 NO2 and other hydrocarbons, as well as on the nitrogen-containing species, viz., NO, NO2, N2O, and HCN. In the continuous combustion tests, petroleum coke has been burned in the CFBC. Concentration profiles and concentration changes at the top of the riser have been measured. Iodine has been added and the bed temperature and the initial fuel particle size are varied. With the knowledge of the N2O destruction reactions, the relative importance of the radicals on N2O and NO formation reactions has been identified and is discussed.
Estimation of Two-Phase Flow Heat Transfer in Pipes
Authors: Kaminsky R. D.
Published: February 2008

Heat transfer can be of importance in the design of multiphase petroleum flowlines. However, heat transfer data for gas-liquid flows are available only for small-diameter pipes at low pressures. Moreover, existing prediction methods are largely not suited to petroleum pipeline conditions due to implicit use of simplistic two-phase flow models. In this work heat transfer estimation methods are derived for nonboiling gas-liquid flow in pipes of high Prandtl number liquids, such as crude oil. The methods are readily evaluated for engineering applications and are applicable to all flow regimes, except those with low liquid holdup. Comparison is made with literature data. Accuracies of ±33 percent are obtained in general. The methods explicitly couple with arbitrary prediction methods for two-phase flow pressure drop and liquid holdup. This explicit coupling makes plausible the hypothesis that predictions will be robust at conditions well beyond the range of the existing experimental data.
Influence of Non-Newtonian Behavior of Blood on Flow in an Elastic Artery Model
Authors: Dutta A. , Tarbell J. M.
Published: February 2008

Two different non-Newtonian models for blood, one a simple power law model exhibiting shear thinning viscosity, and another a generalized Maxwell model displaying both shear thining viscosity and oscillatory flow viscoelasticity, were used along with a Newtonian model to simulate sinusoidal flow of blood in rigid and elastic straight arteries. When the spring elements were removed from the viscoelastic model resulting in a purely viscous shear thinning fluid, the predictions of flow rate and WSS were virtually unaltered. Hence, elasticity of blood does not appear to influence its flow behavior under physiological conditions in large arteries, and a purely viscous shear thinning model should be quite realistic for simulating blood flow under these conditions. When a power law model with a high shear rate Newtonian cutoff was used for sinusoidal flow simulation in elastic arteries, the mean and amplitude of the flow rate were found to be lower for a power law fluid compared to a Newtonian fluid experiencing the same pressure gradient. The wall shear stress was found to be relatively insensitive to fluid rheology but strongly dependent on vessel wall motion for flows driven by the same pressure gradient. The effect of wall motion on wall shear stress could be greatly reduced by matching flow rate rather than pressure gradient. For physiological flow simulation in the aorta, an increase in mean WSS but a reduction in peak WSS were observed for the power law model compared to a Newtonian fluid model for a matched flow rate waveform.
A Counter Current Vascular Network Model of Heat Transfer in Tissues
Authors: Huang H. W. , Chen Z. P. , Roemer R. B.
Published: February 2008

A fully conjugated blood vessel network model (FCBVNM) for calculating tissue temperatures has been developed, tested, and studied. This type of model represents a more fundamental approach to modeling temperatures in tissues than do the generally used approximate equations such as the Pennes’ BHTE or effective thermal conductivity equations. As such, this type of model can be used to study many important questions at a more basic level. For example, in the particular hyperthermia application studied herein, a simple vessel network model predicts that the role of counter current veins is minimal and that their presence does not significantly affect the tissue temperature profiles: the arteries, however, removed a significant fraction of the power deposited in the tissue. These more fundamental models can also be used to check the validity of approximate equations. For example, using the present simple model, when the temperatures calculated by the FCBVNM are used for comparing predictions from two approximation equations (a simple effective thermal conductivity and a simple Pennes’ bio-heat transfer equation formulation of the same problem) it is found that the Pennes’ equation better approximates the FCBVNM temperatures than does the keff model. These results also show that the “perfusion” value (W˙) in the Pennes’ BHTE is not necessarily equal to the “true” tissue perfusion (P˙) as calculated from mass flow rate considerations, but can be greater than, equal to, or less than that value depending on (1) how many vessel levels are modeled by the BHTE, and (2) the “true” tissue perfusion magnitude. This study uses a simple, generic vessel network model to demonstrate the potential usefulness of such fully conjugated vessel network models, and the associated need for developing and applying more complicated and realistic vascular network models. As more realistic vascular models (vessel sizes, orientations, and flow rates) are developed, the predictions of the fully conjugated models should more closely model and approach the true tissue temperature distributions, thus making these fully conjugated models more accurate and valuable tools for studying tissue heat transfer processes.
Importance of Soft Tissue Integrity on Biomechanical Studies of the Patella After TKA
Authors: Luo Zong-Ping , Hsu Horng-Chaung , Rand James A. , An Kai-Nan
Published: February 2008

This study evaluated the effects of soft tissue integrity on patellar tracking and patellofemoral joint force after total knee arthroplasty. The results indicate that partial dissection of the soft tissue integrity in the in vitro biomechanical studies of the patellofemoral joint can alter patellar tracking and joint force significantly, leading to improper conclusions.
Atomic Force Microscope Measurements of the Hardness and Elasticity of Peritubular and Intertubular Human Dentin
Authors: Kinney J. H. , Balooch M. , Marshall S. J. , Marshall G. W. , Weihs T. P.
Published: February 2008

An atomic force microscope was used to measure the hardness and elasticity of fully-hydrated peritubular and intertubular human dentin. The standard silicon nitride AFM tip and silicon cantilever assembly were replaced with a diamond tip and stainless steel cantilever having significantly higher stiffness. Hardness was measured as the ratio of the applied force to the projected indentation area for indentations with depths from 10–20 nm. The sample stiffness was measured by imaging specimens in a force-modulated mode. Hardness values of 2.3 ± 0.3 GPa and 0.5 ± 0.1 GPa were measured for the peritubular and intertubular dentin, respectively. Stiffness imaging revealed that the elastic modulus of the peritubular dentin was spatially homogeneous; whereas, there was considerable spatial variation in the elasticity of the intertubular dentin. The atomic force microscope can be used to measure the mechanical properties of fully hydrated calcified tissues at the submicron level of spatial resolution, thus augmenting more traditional depth sensing probes.
Stabilizing Role of Moments and Pelvic Rotation on the Human Spine in Compression
Authors: Shirazi-Adl A. , Parnianpour M.
Published: February 2008

The mechanisms by which the human spinal column in neutral postures can resist relatively large axial compression forces with no abnormal motions or instabilities remain yet unknown. A nonlinear finite element study of the ligamentous thoracolumbar spine was performed to investigate the stabilizing role of two plausible mechanisms of combined moments and pelvic rotation on the human spine in axial compression. The passive system, by itself was able to carry only a negligible fraction of physiological compression loads without exhibiting large motions. The unconstrained spine was most flexible in the sagittal plane (least stiff plane). The existence of combined moments and pelvic rotation significantly increased the load-bearing capacity of the spine so that the free standing passive thoracolumbar spine resisted the axial compression forces of more than 1000 N with minimal displacements. The former mechanism is much more effective in stabilizing the spine in compression than is the latter one. It is postulated that the pelvic rotation and the off-centered anterior placement of the gravity force are exploited to partially stabilize the passive spine in compression and relieve the musculature. Previous and on-going studies support the validity of the proposed mechanisms.