Browsing by Subject "Pressure"
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Item A computational model to calculate the flow-induced pressure fluctuations on a bluff body(Texas Tech University, 2002-08) Senthooran, SivapalanPressure fluctuations on buildings cause vibrations in moderate winds and structural damage under severe winds. They also play an important role in determining the noise level inside buildings and automobiles. Therefore, knowledge on pressure fluctuations is desired for improved design of buildings and automobiles. This knowledge can be obtained by experimental studies or computational studies. In recent years, computational methods have become more popular because they are less expensive compared to the field and wind tunnel experiments in most cases and they predict the parameters of interest with comparable accuracy. In the current study, a computational technique is developed based on Reynolds Averaged Navier Stokes modeling (RANS), to predict the pressure fluctuation on a bluff body placed in turbulent flows. This technique has three main components: prediction of mean flow quantities, synthetic generation of velocity fluctuations, and prediction of pressure fluctuations. The mean flow calculations are performed using the standard K-s model with Kato and Launder modification, the fluctuating velocity field is synthesized from a stochastic description of the three dimensional turbulent motion, and the fluctuating pressure field calculations are performed by solving the Poisson equation for pressure fluctuation. Flow around the low-rise experimental building at Texas Tech and the flow around an automobile in the A-Pillar region are analyzed using the developed technique. Two different wind angles of attack are considered for flow around the low-rise experimental building and two different A-Pillar geometries are considered for flow around an automobile. Computational results obtained using the developed technique, show good agreement with the experimental results.Item Analysis of a low pressure p-v-t apparatus(Texas Tech University, 1965-05) Vidaurri, Fernando C.This investigation was concerned with the development of a workable low pressure pressure-volume-temperature (P-V-T) apparatus and possible forms of correlation of data obtained from such an apparatus. An apparatus of this type would be particularly suitable to use in the investigation of properties of mixtures. In an effort to obtain a more precise approximation of zero pressure data (from which second virlal coefficients may be obtained), an apparatus was specially constructed to get data from atmospheric pressure down to 100 mm. Hg.Item Developing two-phase flow with periodic longitudinal heat flux asymmetry(Texas Tech University, 1979-08) Lee, Yung FengNot availableItem Effect of pressure-dependent permeability on tight gas wells(Texas A&M University, 2005-08-29) Franquet Barbara, MarielaTight gas reservoirs are those reservoirs where the matrix has a low permeability range (k < 0.1 md). The literature documents laboratory experiments under restressed conditions that show stress dependent rock properties are more significant in tighter rocks. For gas reservoirs, real gas properties are also sensitive to variations of pressure, and the correct description of gas flow must include pressure-dependent gas properties. Under these circumstances the resulting equation for real gas flow is a second order, non-linear, partial differential equation. Non-linearities include pressure-dependence of gas viscosity, gas compressibility, reservoir permeability and reservoir porosity. This paper investigates dynamic permeability change as a function of net overburden stress in tight gas reservoirs. The gas reservoir simulator used for this work included pressure-dependent reservoir permeability. Radial flow cases are analyzed using this simulator. During this study we found that from analysis of production data alone, it is impossible to determine the correct permeability value for tight gas reservoirs with pressure-dependent permeability. For the cases studied, the transient performance was similar for both constant permeability and pressure-dependent permeability. This similarity causes constant permeability and pressure-dependent permeability to be indistinguishable, based on analysis of transient performance data. It was found that the productivity index decreases when pressure-dependent permeability is more significant. Finally, this study verified that the method of Ibrahim et al.28 under estimates original gas in place (OGIP) for tight gas reservoirs with pressure-dependent permeability.Item Flammability Characteristics of Hydrogen and Its Mixtures with Light Hydrocarbons at Atmospheric and Sub-atmospheric Pressures(2013-07-13) Le, Thuy Minh HaiKnowledge of flammability limits is essential in the prevention of fire and explosion. There are two limits of flammability, upper flammability limit (UFL) and lower flammability limit (LFL), which define the flammable region of a combustible gas/vapor. This research focuses on the flammability limits of hydrogen and its binary mixtures with light hydrocarbons (methane, ethane, n-butane, and ethylene) at sub-atmospheric pressures. The flammability limits of hydrogen, light hydrocarbons, and binary mixtures of hydrogen and each hydrocarbon were determined experimentally at room temperature (20?C) and initial pressures ranging from 1.0 atm to 0.1 atm. The experiments were conducted in a closed cylindrical stainless steel vessel with upward flame propagation. It was found that the flammable region of hydrogen initially widens when the pressure decreases from 1.0 atm to 0.3 atm, then narrows with the further decrease of pressure. In contrast, the flammable regions of the hydrocarbons narrow when the pressure decreases. For hydrogen and the hydrocarbons, pressure has a much greater impact on the UFLs than on the LFLs. For binary mixtures of hydrogen and the hydrocarbons, the flammable regions of all mixtures widen when the fraction of hydrogen in the mixture increases. When the pressure decreases, the flammable regions of all mixtures narrow. The applications of Le Chatelier?s rule and the Calculated Adiabatic Flame Temperature (CAFT) model to the flammability limits of the mixtures were verified. It was found that Le Chatelier?s rule could predict the flammability limits much better than the CAFT model. The adiabatic flame temperatures (AFTs), an important parameter in the risk assessment of fire and explosion, of hydrogen and the hydrocarbons were also calculated. The influence of sub-atmospheric pressures on the AFTs was investigated. A linear relationship between the AFT and the corresponding flammability limit is derived. Furthermore, the consequence of fire relating to hydrogen and the hydrocarbons is discussed based on the AFTs of the chemicals.Item Flow of fine particle suspensions in bends, fittings and valves(Texas Tech University, 1981-12) Hsu, Feng-lungThe results of extensive experimental studies to determine the head losses for flow of fine-particle suspensions in bends, fittings, valves and pipes are presented in this thesis. Methods of determining losses in fine-particle suspensions flowing through pipes and fittings are discussed, as well as methods of expressing these losses in a form useful for design purposes. Glass beads with dsO=12.5µ and with d5O=44.5µ were used in this work. This work was restricted to the transport of fine particles and the particle volume concentration of suspensions up to 32.5% were studied. Furthermore, in this work, only the practical important case of transport at fluid velocities above the saltation velocity has been considered. For homogeneous flow conditions, effects of particle size and concentration are negligible and the loss coefficients for carrier fluid can be used for fine-particle suspensions. Hence, practical prediction of pressure drop in pipelines can be carried out.Item Flow of Fine Particle Suspensions in Horizontal Pipelines(Texas Tech University, 1981-12) Ma, Tzu-wang WarrenA pressure drop correlation for the flow of fine particle suspensions (d < 75M) in horizontal pipelines was developed. A total number of 57I data points, comprised of 138 collected from the published literature together with 433 taken using our own test pipelines were used as the basis for this correlation. The correlation provides superior predictive capability for both uniformly and nonuniformly sized fine particle suspensions. Data for the deposit velocity of uniformly sized fine particle suspensions were determined from the minima in the pressure drop-velocity curves of our flow experiments. These data, which totalled 12 points were used to develop a deposit velocity correlation for uniformly sized fine particle suspensions. Deposit velocities from the SRC data on suspensions with broad particle size distributions consisted of 24 data points. These data were also used to develop a deposit velocity correlation for nonuniformly sized fine particle suspensions. Both correlations pertain to high solids concentrations (C > 10?J by volume) and provide an improved predictive capability over previously published correlations.Item Flow patterns and instabilities in two-phase down flow in packed beds(Texas Tech University, 1978-12) Halfacre, GlennNot availableItem High pressure study of spinel chromite(2005-05) White, Allen D. C.; Ma, Yanzhang; Levitas, Valery; Ertas, AtilaChromite has one of the most important crystal structures, the spinel structure; therefore its high pressure behavior has significant implications to the foundation of a wide range of materials. It is also found throughout our Earth's interior. These facts make its high pressure studies important to materials science, physics, geosciences, and crystallography. Synchrotron X-ray diffraction measurements of chromite were performed using a symmetrical diamond anvil cell to 41.2 GPa. The data was fit using the third order Birch-Murnaghan equation of state, and the bulk modulus KOT was determined to be 197±19 GPa with K'ot=66±12when fitting data to 16 GPa. Further investigation revealed a pressure induced phase transformation at 28.2 GPa.Item Impedance measurement of an orifice exposed to a turbulent boundary layer with pressure gradient(Texas Tech University, 1980-08) Chung, Chang-hwaNot availableItem Interactions between global and local performance incentives on decision-making and categorization(2010-08) Worthy, Darrell Andrew; Maddox, W. Todd; Markman, Arthur B.; Love, Bradley C.; Beer, Jennifer S.; Loewenstein, JeffreyRecent work has shown that the regulatory fit between global approach/avoidance goals and the local approach/avoidance mechanisms of goal pursuit influence cognition and behavior in predictable ways. A regulatory fit leads to an increase in motivation and engagement relative to a regulatory mismatch. The increase in engagement can lead to an increase in cognitive flexibility on cognitively demanding tasks. This work is composed of three inter-related studies that examine how the fit between global performance incentives and local mechanisms of goal pursuit influence decision-making and categorization. In Study 1 I examine how the interaction between global performance incentives and local goal pursuit mechanisms influences decision-making strategies in an experience-based decision-making paradigm. In this paradigm decision-making strategies can be classified as more exploratory or more exploitative. I find that participants in a regulatory fit would exhibit more exploratory decision-making patterns than participants in a regulatory mismatch. In Study 2 I examine how social pressure is related to approach and avoidance-based performance incentives using two types of category-learning tasks. I test the hypothesis that increasing performance pressure will induce an avoidance-based prevention focus which then interacts with the local mechanism of goal pursuit employed in the task (maximizing points gained or minimizing points lost). Participants either perform an explicit, rule-based category-learning task, or an implicit information-integration category-learning task. Behavioral and model-based analyses support the hypothesis that social pressure induces a prevention focus. When the pressure-induced prevention focus aligns with the local goal-pursuit mechanism participants perform better on the rule-based task, but worse on the information-integration task. Study 3 examines the effects of social pressure on categorization in highly-trained participants. Participants performed over 2500 training trials of either a rule-based or an information-integration category-learning task, and then performed another 640 trials after half received a manipulation designed to raise social pressure. Performance was worse on both the rule-based and information-integration task for participants who were under high social pressure compared to participants under low social pressure. The results from all three projects suggest that motivational incentives have a large effect on cognitively demanding tasks.Item Interpreting Horizontal Well Flow Profiles and Optimizing Well Performance by Downhole Temperature and Pressure Data(2011-02-22) Li, ZhuoyiHorizontal well temperature and pressure distributions can be measured by production logging or downhole permanent sensors, such as fiber optic distributed temperature sensors (DTS). Correct interpretation of temperature and pressure data can be used to obtain downhole flow conditions, which is key information to control and optimize horizontal well production. However, the fluid flow in the reservoir is often multiphase and complex, which makes temperature and pressure interpretation very difficult. In addition, the continuous measurement provides transient temperature behavior which increases the complexity of the problem. To interpret these measured data correctly, a comprehensive model is required. In this study, an interpretation model is developed to predict flow profile of a horizontal well from downhole temperature and pressure measurement. The model consists of a wellbore model and a reservoir model. The reservoir model can handle transient, multiphase flow and it includes a flow model and a thermal model. The calculation of the reservoir flow model is based on the streamline simulation and the calculation of reservoir thermal model is based on the finite difference method. The reservoir thermal model includes thermal expansion and viscous dissipation heating which can reflect small temperature changes caused by pressure difference. We combine the reservoir model with a horizontal well flow and temperature model as the forward model. Based on this forward model, by making the forward calculated temperature and pressure match the observed data, we can inverse temperature and pressure data to downhole flow rate profiles. Two commonly used inversion methods, Levenberg- Marquardt method and Marcov chain Monte Carlo method, are discussed in the study. Field applications illustrate the feasibility of using this model to interpret the field measured data and assist production optimization. The reservoir model also reveals the relationship between temperature behavior and reservoir permeability characteristic. The measured temperature information can help us to characterize a reservoir when the reservoir modeling is done only with limited information. The transient temperature information can be used in horizontal well optimization by controlling the flow rate until favorite temperature distribution is achieved. With temperature feedback and inflow control valves (ICVs), we developed a procedure of using DTS data to optimize horizontal well performance. The synthetic examples show that this method is useful at a certain level of temperature resolution and data noise.Item Prediction of the pressure drop during forced circulation of the helical flow(Texas Tech University, 1979-08) Tsai, Shyan SThe purpose of this investigation was to perform an experimental evaluation of the pressure drop characteristics for helical flows and compare the results to correlations available in the literature. The results for single-phase turbulent flow yielded a correlation of the form fc/fs = [Re (d/D)^2] which was found to be a good correlation formula in the superheated steam region for a ratio of the coil diameter to the tube diameter of 9.48. The author also proposed several correlation formulas for the pressure drop of a two-phase flow in a helical tube. Although these correlations lack experimental verification, they are shown to be reasonably located between the lower limit data for compressed liquid and upper limit data for superheated steam.Item Pressure transient test analysis of vuggy naturally fractured carbonate reservoir: field case study(2009-06-02) Ajayi, Babatunde TolulopeWell pressure transient analysis is widely used in reservoir management to obtain reservoir information needed for reservoir simulation, damage identification, well optimization and stimulation evaluation. The main objective of this project is to analyze, interpret and categorize the pressure transient responses obtained from 22 wells in a vuggy naturally fractured carbonate reservoir in an attempt to understand the heterogeneities of the porosity system. Different modeling techniques useful in simulating well behavior in vuggy naturally fractured reservoirs were developed and categorized. The research focused on pressure transient analysis using homogeneous, radial composite, single fracture, dual porosity and triple porosity reservoir models along with conventional boundary models which show boundary limits including single and double sealing boundary, closure and constant pressure boundary. A triple porosity model was developed, and it proved to be very effective for use in the analysis of the pressure responses obtained from this field. For some wells, the need for new models to characterize the pressure responses in more complex reservoirs was highlighted as conventional models failed.Item Stochastic modeling of the variation of velocity and permeability as a function of effective pressure using the Bed-of-Nails asperity-deformation model(2009-05-15) Genova Barazarte, EzequielThe mechanical and transport properties of porous and cracked media, such as velocity and permeability, are sensitive to the effects of effective pressure, which itself is a function of the confining pressure and the pore-fluid pressure. The dependence of permeability and velocity on effective pressure has previously been modeled using the Bed-of-Nails asperity-deformation model. The main objective of this research was to explore the sensitivity of the Bed-of-Nails and effective-pressure models to random, Gaussian errors, by using an inverse approach. To achieve this, numerical modeling of pre-existing velocity and permeability experimental data sets was done. Extrapolation to 600 MPa was performed using an epidosite data set of compressional velocity as a function of confining pressure, only using measurements in the range 0-100 MPa. The results showed that, given sufficient data and considering random error only, extrapolation can be done with a level of error of less than 1.5%. Model error can also be significant in this type of exercise because it can give rise to systematic misfit, although in this case it was shown that the effects of model error were not considerable. Modeling the variation of compressional velocities as a function of confining and pore-fluid pressures in a deep-sea chalk showed that the best-fitting asperity-deformation model is sensitive to the effective-pressure model. Measurements of permeability in a Navajo-sandstone specimen as a function of confining pressure were numerically modeled, and the results showed that measurements made at low pressures, specifically near Pe = 0, are very important to constrain the model. The same result was found in the case of permeability as a function of confining and pore-fluid pressure in a Wilcox-shale where the lack of measurements near Pe = 0 caused the error in the model parameters to be overestimated. This occurs because the rate of change of permeability as a function of effective pressure is very high at low pressures. The lack of sufficient data near Pe = 0 overestimates the curvature matrix and, therefore, the errors in the model parameters.Item Structural and functional characterization of a lymphatic system using computational and experimental approaches(2009-05-15) Madabushi Venugopal, ArunThe lymphatic system returns interstitial fluid back to the blood circulation. They have a network of vessels with numerous lymphangions, the segment of lymphatic vessel between two unidirectional valves. The valves aid in transporting lymph against a pressure gradient, in addition to the lymphangion pump which exhibit cyclical variations in diameter. Like blood vessels, baseline lymphatic tone is regulated with changes in transmural pressure; however, the transient response of lymphatic diastolic diameter following changes in transmural pressure has not been studied. The lymphangion pump is often described using cardiac analogies. However, since an active system empties into another active system in a lymphatic vessel, the analogy cannot characterize the principles governing optimal lymphatic vessel function. Furthermore, to optimize lymph flow there is also a need to characterize the lymphatic network structure. To characterize the transient diameter response of lymphatic segment, we used post-nodal bovine mesenteric lymphangions in an isobaric preparation and measured the diameter response to a step change in pressure. An immediate active reduction in enddiastolic diameter with each incremental increase in pressure was observed. To identify the principles governing optimal lymphatic vessel function, we applied the result obtained from optimizing the interaction of the heart-arterial system to measured lymphangion pressure-volume relationships. We assumed that the slope of end systolic pressure-volume relationship (Emax) is equal to the slope of end-diastolic relationship (Emin) above a cutoff pressure and Emax>Emin below the cutoff pressure. Unlike the heart, we found that stroke work is not optimized when Emax = Emin. However, there is a region where lymph flow is insensitive to changes in transmural pressure. To characterize the lymphatic network structure, we used an approximation of time-varying elastance model. We found there is an optimal length for the lymphangion when it produces maximal flow. To develop a fractal network model, we determined the ratio of radius and ratio of length of lymphangion at a confluence. Using conservation of mass and certain simplifying assumptions, we showed that the ratio of radius, as well as ratio of length of upstream lymphangion, to the downstream lymphangion at confluences is 1.26.