Mechanical Engineering
http://hdl.handle.net/10125/2095
Mon, 02 Mar 2015 19:43:15 GMT2015-03-02T19:43:15ZOrganic solar cells enhanced by cadmium sulfide nanoparticles and a carbon buckyball derivative (PCBM)
http://hdl.handle.net/10125/20702
Organic solar cells (a.k.a. organic photovoltaic cells, OPVs, polymer solar cells) offer a promising approach to inexpensive, lightweight, flexible, and environmentally friendly devices that can convert sunlight into useable electrical power. Major challenges in developing organic cells at the current stage include low power conversion efficiency (standing laboratory record a maximum of 6% in literature compared to a typical 15% efficiency of commercial polycrystalline Silicon solar cells), polymer degradation especially in ambient air and humidity in the presence of light, and relatively low mechanical durability. My research focuses on the fabrication and characterization of conjugated polymer solar cells incorporated with nanoscale structures, such as Carbon nanotubes, Cadmium Sulfide nanoparticles and Carbon Buckyballs (e.g. PCBM). The incorporation of certain nanostructures has proven to enhance exciton dissociation and charge transport utilizing their high surface-area and unique electrical properties (Le. high mobility, semiconductivity). Key factors including the type of nanomaterials, treatments, geometry, and concentration in the polymer matrix were studied. Relationships between these factors were established in terms of different facets of cell performance (e.g. power conversion efficiency, fill factor, Voc, Jsc, internal losses). Results showed that Cadmium Sulfide nanoparticles independently enhance Voc, and PCBM nanoparticles enhance Jsc. It was also shown, however, that these two materials cannot work together to augment both values in tandem. They do, in fact, impede each other's abilities to enhance organic solar cells. I will be presenting background information on organic photovoltaics, current status of the field, and my research at the Hawaii Nanotechnology Laboratory and Hawaii Natural Energy Institute's (HNEI) Thin Films Lab on improving specific aspects of performance of bulk-heterojunction solar cells based on poly(3-hexylthiophene) (P3HT), a conjugated polymer, embedded with nanomaterials like Carbon nanotubes, Cadmium Sulfide nanoparticles and Carbon Buckyballs.
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 56-58).; viii, 58 leaves, bound 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/207022008-01-01T00:00:00ZKaneshiro, Jess Masao MakanaFabrication and mechanical analysis of polymer-nanocomposite monofilaments
http://hdl.handle.net/10125/20701
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 87-92).; xiii, 92 leaves, bound 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/207012008-01-01T00:00:00ZHashiro, Garret MinoruNumerical modeling of mass and ionic transport in corrosion processes
http://hdl.handle.net/10125/20700
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 81-83).; xv, 83 leaves, bound 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/207002007-01-01T00:00:00ZKaya, Jasen DPhoto-realistic graphical representation of helical cable structure
http://hdl.handle.net/10125/20699
Cables and wire ropes frequently incorporate strands consisting of double and triple helical wires. Stranded conductors are helically wrapped into larger units that again are helically laid into cables. A structural analysis of such complex geometries requires knowledge of the net elongation, bending and twist of the individual wires in these strands. Equations that describe the centerlines of these wires and the wire surface areas are derived in this paper. These equations are useful in the development of structural models as well as accurate three-dimensional plots of the cable geometry. Three parametric equations are used to describe the center line of the double and triple helical wires. A companion parametric equation, using two parameters, describes the double and triple helical wire surfaces. These equations are used to produce plots of the three-dimensional shape of individual helical wires and second, third degree helical cable. Such plots are useful in designing cables where geometrical interrelationships are easily understood.
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references.; xi, 91 leaves, bound 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206992007-01-01T00:00:00ZHuang, ChangKinetic and radiative extinctions of spherical diffusion flames
http://hdl.handle.net/10125/20698
In this thesis, the effect of radiative heat loss on extinction of spherical diffusion flame stabilized by a spherical porous burner was investigated by activation energy asymptotics. The flow field was developed by issuing a reactant flow from the burner into a quiescent ambient filled with the other reactant. A one-step, overall and irreversible reaction that follows an Arrhenius kinetics with high activation energy was adopted to model the combustion reaction. The radiative heat loss rate was described by an optically thin model. Based on which reactant is supplied from the burner and how the inert gas is distributed, four model flames, namely the flames with fuel issuing into air, diluted fuel issuing into oxygen, air issuing into fuel, and oxygen issuing into diluted fuel were studied to understand the effects of stoichiometric mixture fraction and flow direction. Results show that when the flow rates fixed, only the conventional kinetic extinction limit at low Damköhler number (low residence times) was observed. The effect of radiative heat loss was to promote extinction such that it is easier to occur. By keeping the radiation intensity constant while varying the flow rate, both the kinetic and radiative extinction limits, representing the smallest and largest flow rates between which steady burning is possible, were exhibited. For flames with low radiation intensity, extinction was primarily characterized by the residence time such that the high-flow rate flames were easier to be quenched. As to the flames suffering strong radiative heat loss, extinction was dominated by the energy loss so the flame with larger size is weaker and easier to extinguish.
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 59-63).; x, 63 leaves, bound ill. 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206982007-01-01T00:00:00ZWang, QianThermal and hydraulic performance of single-phase and two-phase micro-channel heat sinks
http://hdl.handle.net/10125/20697
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 136-139).; xx, 139 leaves, bound ill. 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206972007-01-01T00:00:00ZLee, Scott W. C. HDesign of a smart composite telescope with stabilization and precision pointing capabilities
http://hdl.handle.net/10125/20696
Thesis (M.S.)--University of Hawaii at Manoa, 207.; Includes bibliographical references (leaves 82-84).; x, 84 leaves, bound ill. 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206962007-01-01T00:00:00ZBritton, Shawn RDesign of a mechanical stimulator for the promotion of osteoblast proliferation
http://hdl.handle.net/10125/20695
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 92-95).; ix, 95 leaves, bound ill. (some col.) 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206952007-01-01T00:00:00ZPuri, Neil SStructure and extinction of spherical diffusion flames in microgravity
http://hdl.handle.net/10125/20694
Spherical diffusion flames in microgravity were studied both numerically and experimentally. The flames are supported on a porous spherical burner which Issues a constant flowrate into a quiescent atmosphere. Experiments were performed in the NASA Glenn 2.2 sand 5.2 s drop facilities. The experiments involved flames burning ethylene and propane at 0.98 bar. The numerical simulations incorporate a one-dimensional flame code with detailed chemistry and transport and an optically thick radiation model. The microgravity environment eliminates the effect of buoyancy resulting In spherically symmetric flames and increased residence times. The increased residence times inflate the Lewis number effect and radiative heat loss In the flames. Comparisons between the model and experiments reveal the model consistently over predicts the flame sizes. One explanation for the over prediction of the flame size in the model could be attributed to the fact that the thermal and mass diffusion in the code is too low. Good agreement between the experiments and model, with respect to flame size, is achieved by increasing the diffusion properties in the code by 30%. The experimental and numerical results show that when pure oxygen is Issued from the burner the flame temperature Is lower than the cases where fuel Is Issued from the burner. The lower flame temperature for the case when diluted fuel Is in the ambient Is expected to be a consequence of a higher than unity Lewis number. In the experiments it is hard to prove this hypothesis since the radiation for each flame Is different. However, in the numerical model the radiation was turned off and the steady state flame temperatures indicate a 200 K reduction in flame temperature from adiabatic for the case with diluted fuel in the ambient. Aside from the Lewis number effect radiative extinction was also investigated. The results indicate that at high flowrates (above 5.1 mg/s) radiative extinction occurs. At high flowrates it was found that extinction time and flame temperature became independent of flowrate.
Thesis (M.S.)--University of Hawaii at Manoa, 2006.; Includes bibliographical references (leaves 43-46).; vii, 46 leaves, bound ill. (some col.) 29 cm
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10125/206942006-01-01T00:00:00ZSanta, Karl JModeling aspects of vocal fold oscillations with validation to clinical data
http://hdl.handle.net/10125/20693
Thesis (M.S.)--University of Hawaii at Manoa, 2006.; Includes bibliographical references (leaves 108-110).; x, 110 leaves, bound ill. (some col.) 29 cm
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10125/206932006-01-01T00:00:00ZBentil, Sarah AFinite element analysis design and optimization of an adaptive circular composite panel for vibration suppression
http://hdl.handle.net/10125/20692
The objective of this work is to design a circular adaptive composite panel with optimized embedded piezoelectric sensor and actuator patches in terms of their location and configuration for active vibration suppression application. Piezoelectric sensors and actuators embedded in the composite panel create a lightweight smart structure with increased structural efficiency and thermal stability. in addition to the ability to monitor and respond to external stimuli to control shape, properties, and dynamic responses of the structure. The panel is designed to be the mounting surface for an active composite platform to be used in intelligent thruster vector control applications for satellites. A triangular piece, made of steel, with three circular-shape connections at the three vertices, simulating the base of the thruster, is attached to the circular adaptive composite panel to provide a more realistic boundary condition. The developed finite element model is employed to determine the optimum number of composite layers based on the voltage required to deliver maximum possible vibration suppression for the plate. A direct approach using Control Design Charts is employed for active vibration suppression. The vibration suppression techniques used in this work are the direct Constant Voltage (CV) and direct Corresponding Voltage (COV) schemes.
Thesis (M.S.)--University of Hawaii at Manoa, 2006.; Includes bibliographical references (leaves 92-93).; x, 93 leaves, bound ill. 29 cm
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10125/206922006-01-01T00:00:00ZSakagawa, RandyIgnition behavior and air delivery requirements observed during the carbonization of pressurized packed beds of biomass
http://hdl.handle.net/10125/20691
Flash Carbonization ™ (FC) is a novel procedure by which biomass is converted to bio-carbon (i.e. charcoal) quickly and efficiently. To begin this process, a canister containing a packed bed of feedstock is placed within a pressure vessel, compressed air is used to charge the system to an initial pressure of ~1-2 MPa, and a flash fire is ignited at the bottom of the bed. After approximately two minutes, air is delivered to the top of the bed and the biomass is converted to a high-yield bio-carbon. This technology has progressed to the point that a commercial-scale demonstration reactor is currently being assembled on the campus of the University of Hawaii, Manoa. The adaptation of the technology from the lab-scale reactor to the larger pilot plant is the underlying theme of this thesis. Specifically, the subjects of ignition behavior and air delivery are explored in detail. In lab-scale tests of the FC process, some fuel have been observed to ignite violently, resulting in a sudden drastic pressure rise (ΔP~1 MPa within 2-3 seconds). Because this event could be potentially hazardous, a study of this phenomenon was undertaken in preparation for the scale-up of the FC process. The influence of initial pressure, feed moisture content, and ignition heater power were examined following a 23 full factorial experimental design approach. It was determined that the violence of the ignition is related to the moisture content of the feedstock and the operating pressure of the process. The information gained from this study was used to size the emergency venting components of the pilot plant. Additionally, this work details the impact of compressibility effects on previously published air-to-biomass ratios (ABRs)-a value used to indicate the optimum level of air delivery for an individual biomass feedstock. As a result of this study, the accuracy of the ABR values were improved for all feedstock types.
Thesis (M.S.)--University of Hawaii at Manoa, 2005.; Includes bibliographical references (leaves 99-105).; xvi, 105 leaves, bound ill. 29 cm
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10125/206912005-01-01T00:00:00ZWade, Samuel RProcessing and characterization of continuous fiber ceramic nanocomposites by preceramic polymer pyrolysis
http://hdl.handle.net/10125/20690
In this work, two types of Continuous Fiber Ceramic Composites (CFCCs) were manufactured using preceramic polymer pyrolysis method for corrosion and mechanical testing. The two types of fiber reinforcements were Nicalon™ and Carbon fibers, and KiON CERASET® preceramic polymer was used as the matrix in this study. Further, the effects of nanoparticles on processing and flexural mechanical performance of Nicalon/KiON CERASET® continuous fiber ceramic composites by preceramic polymer pyrolysis method have been investigated. Five different nanoparticles varying in size from 15-55 nanometers were used. These nanoparticles were: titanium oxide, yttrium oxide, zinc oxide, silicon carbide, and carbon. Nicalon™ ceramic fiber was used as the reinforcement. KiON preceramic polymer was mixed with nano size fillers in the presence of a surfactant agent to give a good dispersion of the particles and was used as the matrix. Initial work from nanoparticle reinforced CFCCs led to further investigations in the effects of using varying weight percentage of nanoparticle inclusions on mechanical performance of continuous fiber ceramic nanocomposites. Yttrium oxide nanoparticles with an average size of 29 nm was used as the inclusion with varying weight percentages of 5, 10, 15, and 20. Two different types of nanoparticle filled composites were manufactured through different processing routes. Characterization analysis and dispersion studies of the samples using scanning electron microscopy were reported. Four-point bending test was also conducted to evaluate the flexural mechanical performance of the ceramic nanocomposites samples at room temperature. Nanoparticle filled samples consistently showed significant improvement in flexural strength compared to their counterparts without nanoparticle reinforcement.
Thesis (M.S.)--University of Hawaii at Manoa, 2005.; Includes bibliographical references (leaves 56-61).; xi, 61 leaves, bound ill. 29 cm
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10125/206902005-01-01T00:00:00ZGudapati, Vamshi MohanDevelopment of catalyst and gas diffusion layers using nanotechnology for proton exchange membrane fuel cells
http://hdl.handle.net/10125/20689
Nanotechnology in Proton Exchange Membrane Fuel Cells (PEMFCs), the topic of this thesis, encompasses a large array of subjects. It is important to understand the market demand for fuel cells and then realize the types of changes and improvements of the technology needed to bring it to the marketplace. By integrating nanotechnology into fuel cells, their performances will be greatly increased. Nanotechnology will be able to provide the profound material properties of nanoscaled materials and structures needed to make fuel cells a desired technology. Novel gas diffusion layers (GDLs) and catalyst layers (CLs) have been developed for PEMFCs in this work. Carbon nanotubes (CNTs) are grown directly and in-situ on carbon papers to develop high performance durable GDLs that can operate at high temperature and low humidity during fuel cell testing. Platinum nanopartic1es are combined with CNTs using a new chemical processing route to develop efficient and lower cost CLs confirmed by fuel cell testing. In addition, platinum nanowires were employed for the development of catalyst layers; however, due to the manufacturing of platinum nanowires and their substrate, necessary to hold them vertically, the fuel cell tests did not show promising results and further work is recommended for future studies to utilize the full potentials of platinum nanowires.
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 58-60).; viii, 60 leaves, bound ill. 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206892008-01-01T00:00:00ZStuckey, Philip AHigh pressure autothermal reforming in low oxygen environments
http://hdl.handle.net/10125/20688
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 95-99).; ix, 104 leaves, bound 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206882008-01-01T00:00:00ZReese, Mark AActive vibration suppression and precision pointing for a space-based laser communications smart composite telescope
http://hdl.handle.net/10125/20687
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 90-92).; xii, 92 leaves, bound ill. 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206872008-01-01T00:00:00ZLeong, Aaron DAn experimental investigation employing combined calorimetry and raman spectroscopy of thermodynamic inhibitors used to decompose methane hydrates
http://hdl.handle.net/10125/20686
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 92-96).; xii, 96 leaves, bound 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206862008-01-01T00:00:00ZKinoshita, Christopher KDesign and analysis of a secondary mirror adaptive nano-platform with structural nano-positioning for a space based laser communications smart composite telescope
http://hdl.handle.net/10125/20685
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 106-107).; ix, 108 leaves, bound ill. 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206852008-01-01T00:00:00ZJurasek, Nicholas JA comprehensive methodology to define appropriate regulating criteria for solar domestic hot water systems
http://hdl.handle.net/10125/20684
Thesis (M.S.)--University of Hawaii at Manoa, 2008.; Includes bibliographical references (leaves 97-103).; xvii, 103 leaves, bound 29 cm
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10125/206842008-01-01T00:00:00ZGoorskey, Sarah SMethodology to measure impulses in the micro-newton range for a novel micro-thruster concept
http://hdl.handle.net/10125/20683
The concept of small Low-Earth Orbit (LEO) satellites for educational and scientific applications is becoming increasingly popular because of their relatively low cost and short developmental period. However as programs evolve and attempt more diverse and complex missions. the need for attitude control and/or orbital maneuvers from micropropulsion systems often emerges as a bottleneck technology. These micro-thruster systems arc therefore one of the core enabling technologies for the next generation of small satellites. The design for a novel sublimating micro-thruster is presented and analyzed. This micro-thruster attempts to retain the advantageous qualities of previous sublimating solid micro-thrusters while addressing their shortcomings. The performed analysis included determining the general trends of modifying certain design parameters on the expected performance. It is shown that the micro-thruster requirements suggested by Mueller (2000) arc attainable by manipulating the discussed design parameters. The design and development of a testbed capable of accommodating test measurements of the novel sublimating micro-thruster is also presented. The components included in this discussion arc the thrust stand, vacuum chamber system. and the calibration system. The testbed was assembled and initial calibration tests were conducted and arc analyzed.
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 56-59).; xi, 59 leaves, bound 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206832007-01-01T00:00:00ZYoneshige, Lance KMiltiphase micro-pin-fin heat sink : pressure drop and heat transfer
http://hdl.handle.net/10125/20682
This paper is a study concerning the thermal and hydrodynamic characteristics of a liquid single-phase flow and flow boiling in an array of micro-pin-fins. An array of 1950 staggered square micro-pin-fins with 200 x 200 µm2 cross-section by 670 µm height were fabricated into a copper heat sink test section. The ratios of longitudinal pitch (SL) and transverse pitch (ST) to pin-fin equivalent diameter (de) are equal to 2. Deionized water was used as the cooling liquid. Two coolant inlet temperatures of 30•C and 60•C, and six maximum mass velocities for each inlet temperature, ranging from 183 to 420 kg/m2s, were tested. The corresponding inlet Reynolds number ranged from 45.9 to 179.6. For single-phase flow, the measured pressure drop was used to calculate the average friction factor, and the measured temperature distribution was used to evaluate single-phase heat transfer coefficient and Nusselt number. Predictions of the previous friction factor and heat transfer correlations that were developed for low Reynolds number (Re < 1000) single-phase flow in pin-fin arrays were compared to the present micro-pin-fin single-phase pressure drop and Nusselt number data, respectively. Most predictions of other friction factor and heat transfer correlations were significantly different from the experimental data collected in this study. Two new heat transfer correlations were proposed for average heat transfer based on the present data, in which average Nusselt number is correlated to the average Reynolds number by power law. Also, there is indication of a strong dependence of Nusselt number on Reynolds number in micro-pin-fin arrays. A new power-law type of correlation was proposed base on the present pressure drop data too. Last, micro-pin-fin heat sink was tested at high temperatures in which pressure drop and temperature were measured and boiling curves were obtained.
Thesis (M.S.)--University of Hawaii at Manoa, 2007.; Includes bibliographical references (leaves 74-76).; xvii, 76 leaves, bound 29 cm
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10125/206822007-01-01T00:00:00ZHo, Abel SiuAdvanced control of autonomous underwater vehicles
http://hdl.handle.net/10125/11729
Thesis (Ph. D.)--University of Hawaii at Manoa, 2004.; Includes bibliographical references (leaves 140-155).; Also available by subscription via World Wide Web; xiii, 155 leaves, bound ill. 29 cm
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10125/117292004-01-01T00:00:00ZZhao, SideCorrosion Studies Between Ceramics And 6061-T6 Aluminum
http://hdl.handle.net/10125/10498
Mon, 01 Aug 2005 00:00:00 GMThttp://hdl.handle.net/10125/104982005-08-01T00:00:00ZSrinivasan, RaghuOn The Modeling Of The Hydrodynamic Force Acting On A Spherical Particle
http://hdl.handle.net/10125/10497
A new model of the hydrodynamic force acting on a particle under an oscillating viscous fluid flow, at finite Reynolds and Strouhal numbers in the range of 0.01 to 25 is developed. This drag model is based on the novel concept of variable-order calculus, where the order of derivative can vary with the dynamics of the flow. A numerical simulation, based on a fourth-order compact scheme in space and a implicit third-order time-marching scheme has been used to compute the time-dependent, axisymmetric viscous flow past the rigid sphere. The solution is used to determine the appropriate differential operator (constant or variable) in the drag model for the several cases simulated. Also, it is determined: (i) the region of validity of the creeping flow equation for an oscillatory flow, (ii) the region where the order of the derivative is fractional, but constant and (iii) the region where the strong nonlinearity of the flow requires a variable-order derivative to account for the increased complexity of the drag force behavior. The proposed drag model is able to accurately predict the hydrodynamic force acting on the sphere within the parameter range investigated. For moderate values of the Reynolds numbers, the constant-order model provides an accurate description of the drag. Increasing the Reynolds number or decreasing the product of the Reynolds and Strouhal numbers leads to non-linear effects, which require a variable-order differential operator to model accurately the history effects on the drag.
Tue, 01 Aug 2006 00:00:00 GMThttp://hdl.handle.net/10125/104972006-08-01T00:00:00ZPedro, Hugo T. C.Mechanical Design Of A Reactionless Telescope Pointing Mechanism For Intersatellite Laser Communication
http://hdl.handle.net/10125/10496
Mon, 01 Aug 2005 00:00:00 GMThttp://hdl.handle.net/10125/104962005-08-01T00:00:00ZMitchell, Chad F.Corrosion Initiation Sites Of Particle Reinforced 6092 Aluminum Metal Matrix Composites
http://hdl.handle.net/10125/10495
Mon, 01 Aug 2005 00:00:00 GMThttp://hdl.handle.net/10125/104952005-08-01T00:00:00ZDevarajan, Thamarai SelviDynamics With Variable-Order Operators
http://hdl.handle.net/10125/10494
In this work, the novel concept of Variable-Order (VO) Calculus is explored. VO Calculus extends the notion of Constant-Order (CO) Calculus by allowing the order of differentiation or integration to be a function of pertinent variables. VO Calculus is a powerful tool to model history-dependent processes and may allow solutions of CO partial differential equations to be reduced to simple VO expressions. Such expressions are extremely useful for parametric studies of complex systems such as fuel cells. Following a review of fractional calculus, the behavior of proposed Variable-Order Differential Operators (VODOs) is analyzed and it is shown that these operators must interpolate between integer-order derivatives. A VODO that returns the associated CO derivative at any instant in time is identified. The selected VODO is used to formulate a VO Differential Equation (VODE) of motion for a variable viscoelasticity oscillator. The damping force in the oscillator varies continuously between the elastic and viscous regimes depending on the position of the mass. The oscillator is composed of a linear spring of stiffness k that inputs a restitutive force Fk = -kx(t), a VO damper of order q(x(t)) that generates a damping force Fq = -cq1Ji(x(t)) x(t), and a mass m. A Runge-Kutta method is used in conjunction with a product-trapezoidal numerical integration technique to yield a second-order accurate method for the solution of the VODE. The VO oscillator also is modeled using a CO formulation where a number of CO fractional derivatives are weighted to simulate the VO behavior. The CO formulation asymptotically approaches the VO results when a relatively large number of weights is used. For the viscoelastic range of 0< q < 1, the dynamics of the oscillator is well approximated by the CO formulation when 5 or more fractional terms are included (e.g., 0, 1/4, 1/2, 3/4, and 1).
Sun, 01 May 2005 00:00:00 GMThttp://hdl.handle.net/10125/104942005-05-01T00:00:00ZSoon, Cory M.Corrosion Protection Of Aluminum - A Ceramic Barrier Coating
http://hdl.handle.net/10125/10493
Sun, 01 May 2005 00:00:00 GMThttp://hdl.handle.net/10125/104932005-05-01T00:00:00ZNiemi, Alexander E.Dynamics Of A Spherical Particle In A Model Clinostat Or Bioreactor
http://hdl.handle.net/10125/10492
The dynamics of a spherical particle in a fast clinostat or rotating bioreactor is analyzed. The model clinostat environment consists of purely rotational flow that is perpendicular to a gravitational field. The Lagrangian equation of motion is written in terms of dimensionless parameters and solved exactly for small particle and shear Reynolds numbers. The solution shows that lift effects considerably alter the position of the equilibrium point reached by the particles in the (vertical) direction collinear to the gravitational field, and that the inertial lift effect is negligible in the (horizontal) direction perpendicular to the gravitational field. These results are applicable for all practical rotation rates and small shear and particle Reynolds numbers that are characteristic of realistic experimental conditions. For light (heavy) particles, inclusion of lift in the formulation forces the equilibrium position to be below (above) the horizontal plane that contains the axis of rotation. The equilibrium point for light particles is stable and therefore is observable experimentally, however, the equilibrium point for heavy particles is unstable. The stress level applied to the particle is estimated and an algebraic expression is derived that indicates that the stress level acting on the particle decreases with increasing shear Reynolds number. Finally, the practicality of using the solution to design an experiment to show the vertical displacement of a particle in its equilibrium position is demonstrated.
Wed, 01 Dec 2004 00:00:00 GMThttp://hdl.handle.net/10125/104922004-12-01T00:00:00ZRamirez, Lynnette E. S.Geometric Transformation For Double Helical Wire Rods
http://hdl.handle.net/10125/10491
The true shape of a double-helical geometry in a rope cross-section is needed for the design of ropes to predict the interstitial voids that need to be filled with water-blocking material. Commercially-available software such as AutoCAD, Inventor, Ideas, Mechanical Desktop, etc. are unable to develop this geometry. Thus, the objective of this study is to develop the parametric equations needed to produce scaled rope cross-section plots. Two fundamental mathematical tools are used to describe the cross-section of helical wire rods. The premier tool is the equation of the "Pencil of Spheres" where coordinates of the second helix centerline in a global coordinate system is found. To establish the centerline, coordinates of the helical path geometric transformations are developed. The equation of the "Pencil of Spheres" for the second helix is then intersected with a plane perpendicular to the rope axis. This results in the true shape of the helical round rods. The objective of this research is to derive a mathematical model that describes the exact geometry of double-helical round rods in a plane perpendicular to the rope axis. Using this model, a computer program is developed to plot the rope cross-section to a true scale.
Wed, 01 Dec 2004 00:00:00 GMThttp://hdl.handle.net/10125/104912004-12-01T00:00:00ZHardy, Manuel MunozNumerical Controlled Electrochemical Machining Of Silicon Carbide/Aluminum Metal Matrix Composites
http://hdl.handle.net/10125/10490
Wed, 01 Dec 2004 00:00:00 GMThttp://hdl.handle.net/10125/104902004-12-01T00:00:00ZSugadev, Prasath MungunduAcoustic Technique In The Diagnosis Of Voice Disorders
http://hdl.handle.net/10125/10489
Wed, 01 Dec 2004 00:00:00 GMThttp://hdl.handle.net/10125/104892004-12-01T00:00:00ZKulinski, ChristinaCable Vibration Considering Internal Friction
http://hdl.handle.net/10125/10488
The cable consists of an assemblage of wires laid helically around a core. The cable is widely used as an efficient structure for use in cable-stayed structures, for signal transmission and for power transmission. For overhead power transmission cables, both strength and dynamic characteristics are critical design parameters. Due to the inherently low damping characteristics of long span cables, vibration can result in damage to transmission cables and shorten their useful life. Moreover, for cable-stayed structures, vibrations can lead to a decrease in the cable load-carrying capacity. In addition, agreement on helical cable designs is difficult. Cable design choices include jacket materials, water blocking techniques, and the number of fibers to place within the cable. The cable design chosen depends on the cable's intended application. Each different application may require a slightly different cable design. The cable must meet minimal levels of performance in safety and durability (able to withstand shock, vibration, etc.). These current design concerns suggest that the dynamic behavior of cables need to be better understood. Determination of various mechanical characteristics of helical cables has never been an easy task. Substantial work has been accomplished over the past twenty years to model the structural behavior of such cables. The most important dynamical property of cables is wire slippage that creates large variations in flexural rigidity. Various flexural rigidities have been predicted by a number of previously developed models. In addition, the static and dynamic behavior of cables also have been predicted by previously reported models. The main focus of recent research has been the response of the cable under dynamic loading conditions. The primary dynamic response of cables includes free vibration and forced vibration. Gutzer, Seemann and Hagedorn (1995) applied a MASING model for a steel cable damping vibration system, in which the cable was analyzed as a collection of discrete and continuous systems of bonded layers. Each of the different layers consists of one or more parallel JENKIN or PRANDTL elements. The stick-slip behavior between the structural parts was simulated as a special case of static hysteresis. The slowly varying amplitude method and the phase method were used in the simulation to identify the damping parameters of the physical cable. Gatti-Bono and Perkins (2003) conducted an analysis of a two-dimensional towed cable in an attempt to cover all aspects of cable under tension, torsion, and two-axis bending. A numerical algorithm based on separate finite differencing in time and in space is described. Seabed contact forces are added by modeling the seabed as an elastic foundation with a prescribed profile. In deriving the motion of the cable, the cable was treated as a one-dimensional dynamic elastic inextensible continuum. An alternative approach of cable analysis was suggested by Zhong (2003). The cable is modeled as a one-dimensional continuum with varying flexural rigidity. A simplified cable vibration model, the frictional bending model (FBM), was developed to estimate cable damping due to internal friction. Her study showed that the numerical solution can be derived by directly integrating the equation of motion of the cable. The results of her study showed some agreement with experimental data. All of these investigations address the improvements of dynamic analyses of the cable, and that the effects of internal dry friction between helical wire layers of a cable playa significant role in the dynamic behavior of the cable. Although these research studies illustrate different applications of the cable, the major focus has been the dynamic response of these cables to external load and internal frictions. Their results provide methods for cable dynamic analyses, and are very helpful for the design of cable systems. Some of these analyses have resulted in rather complex stiffness matrixes, while others have focused on individual wires of cable layers, which may not be easily applied to other types of cables. The objective of this study is to develop a mathematical cable model to predict cable vibration and the attendant reduction in vibration amplitude due to internal friction caused by relative wire slippage, which allows a faster identification of the vibration nature of the cable. In addition, a computer program is to be developed to investigate cable free vibration cases using the mathematical cable model. Finally, the validity of this model is to be verified by experimental data for forced vibration.
Sun, 01 Aug 2004 00:00:00 GMThttp://hdl.handle.net/10125/104882004-08-01T00:00:00ZLiu, XinOutdoor & Laboratory Corrosion Studies Of Aluminum Metal - Matrix Composites
http://hdl.handle.net/10125/10487
Sun, 01 Aug 2004 00:00:00 GMThttp://hdl.handle.net/10125/104872004-08-01T00:00:00ZHawthorn, George A.Systematic Testing And Analysis Of Corrosion At Organic Matrix Composite And 6061-T6 Aluminum Interfaces
http://hdl.handle.net/10125/10486
Sun, 01 Aug 2004 00:00:00 GMThttp://hdl.handle.net/10125/104862004-08-01T00:00:00ZGovindaraju, Thanigai ArasuDesign And Analysis Of An Intelligent Composite Platform For Thrust Vector Control
http://hdl.handle.net/10125/10485
Sun, 01 Aug 2004 00:00:00 GMThttp://hdl.handle.net/10125/104852004-08-01T00:00:00ZAntin, NicolasA dual state variable formulation for ordinary differential equations
http://hdl.handle.net/10125/9970
This dissertation defines a new state variable formulation for ordinary differential equations. The formulation allows the systematic identification of eigenvalues for any ordinary differential equation, and leads to parallels with other concepts from linear algebra as well. Furthermore, the eigenvalues described here are generally defined by ordinary differential equations, and as such, the proposed state variable formulation can be reapplied to them. This results in the identification of nested, subsidiary eigenvalues. As a simple example of its utility, the formulation is applied to the oscillatory motion of the nonlinear pendulum. By modeling the behavior of the eigenvalues for this equation, an approximate solution can be obtained for the period of the pendulum and for its motion. The results are excellent when compared to those of other non-numerical approximation methods.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1996.; Includes bibliographical references (leaves 175).; Microfiche.; x, 175 leaves, bound ill. 29 cm
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/10125/99701996-01-01T00:00:00ZPost, Alvin MOscillatory flow and heat transfer characteristics in a pipe and a packed column
http://hdl.handle.net/10125/9969
The fluid flow and heat transfer characteristics in a pipe subjected to a periodically oscillatory and reversing flow have been investigated numerically and experimentally. An examination of the governing equations and boundary conditions shows that the governing similarity parameters for the oscillatory flow in a pipe of finite length are the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the pipe. An experimental study on the onset of turbulence found that the changes in the sign of the pressure gradient are directly responsible for the occurrence of instability in an oscillatory and reversing pipe flow. Friction coefficients of a fully developed laminar oscillating and reversing pipe flow were investigated analytically and experimentally. The numerical simulation of a sinusoidally oscillatory and reversing flow in a pipe of finite length shows that, at any instant of time, there exist three flow regimes in the pipe: an entrance regime, a fully developed regime, and an exit regime. Based on the numerical results, a correlation equation of the space-cycle averaged friction coefficient was obtained. For forced heat convection in an oscillatory flow, it was found that the Prandtl number is the additional similarity parameter, besides the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the heated pipe. The numerical results of the associated heat transfer problem reveal that annular effects also exist in the temperature profiles of an oscillatory flow at high kinetic Reynolds numbers near the entrance and exit locations of the pipe. The space-cycle averaged Nusselt numbers of air oscillating in a pipe heated at constant temperature and uniform heat flux were obtained based on either the numerical results or the experimental data. The related problem of pressure drop in an oscillatory flow through a woven-screen packed column has also been investigated experimentally.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1995.; Includes bibliographical references (leaves 147-152).; Microfiche.; xviii, 152 leaves, bound ill. 29 cm
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10125/99691995-01-01T00:00:00ZZhao, TianshouRange determination from translational motion blur
http://hdl.handle.net/10125/9968
A survey is carried out and the principles of various range sensing techniques are described. A method to determine range from a translationally blurred and a sharp image is presented. To decode the length of blur in the translationally blurred image, three decoding methods; minimization approach, Fourier transform approach, and method-of-slopes, were tested on various images. The results were found to be favorable for the minimization approach and the method-of-slopes. Ringing was encountered with the Fourier transform approach. The minimization approach is iterative and slow. The method-of-slopes was investigated further for the case of inclined plane surfaces and the results were found to be favorable. The method-of slopes can also determine disparity for cylindrical surfaces. A rotating mirror system is described, which simulates camera translation in order to produce a linearly blurred image, in real-time.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1993.; Microfiche.; ix, 109 leaves, bound 29 cm
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/10125/99681993-01-01T00:00:00ZMakkad, SatwinderpalMechanism and kinetics of the autocatalytic dehydration of tert-butanol in near-critical water
http://hdl.handle.net/10125/9967
This work describes studies of the kinetics and mechanism for the autocatalytic dehydration of tert-butanol in near-critical water at 225°C, 34.5 MPa and 250°C, 34.5 MPa. Two tasks were performed in this study. First, to identify the mechanism for the autocatalytic dehydration of tert-butanol; second, to study the temperature effect to verify the mechanism. Experiments were conducted on two flow reactors which perform as plug flow reactors. At 225°C, 34.5 MPa and 250°C, 34.5 MPa, tert-butanol undergoes rapid and selective dehydration to isobutene without any catalyst in near-critical water. Four different models were postulated and tested. The kinetics of the dehydration reaction are consistent with an autocatalytic E1 mechanism with ether formation and decomposition. In this mechanism, tert-butanol plays three different roles: 1) dissociates as Arrhenius acid with catalytic acid/conjugate base pair H3O+/H2O; 2) acts as Bronsted acid with catalytic acid/conjugate base pair (CH3)3COH/(CH3)3CO;3) acts as alcohol which suffers dehydration. The autocatalytic E2 model with ether formation and decomposition, water catalytic E1 model with ether formation and decomposition, and a simplified autocatalytic E1 model without ether formation and decomposition are not consistent with the experiment measurements. The dissociation of tert-butanol as an acid in water is an endothermic reaction. The standard enthalpy and entropy associated with this reaction were found to be: ΔH°=142 kJ/mol, ΔS°=82 J/moI.K. The dehydration of tert-butanol is also an endothermic reaction, high temperature favors the conversion of tert-butanol to isobutene. The values of the standard entropy of activation associated with the elementary rate constant of the autocatalytic E1 model with ether formation and decomposition are also presented.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1992.; Includes bibliographical references (leaves 180-189).; Microfiche.; xix, 189 leaves, bound ill. 29 cm
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/10125/99671992-01-01T00:00:00ZXu, XiaodongFinite element modeling of nonsymmetrical cable cross-sections considering nonuniform radial loadings
http://hdl.handle.net/10125/9966
A new two-dimensional finite element model, named the REMCC (ring element model with contact constraint), is proposed for the analysis of radial deformations in an umbilical cable. This model accounts for material orthotropy and unsymmetrical geometry and loads. Each component of the cable is assumed to possess a circular cross-section and is modeled as a REMCC element having nodal degrees-of-freedom at all contacting points with adjacent components. A new numerical scheme is developed for forming the stiffness matrices of the REMCC elements. Axisymmetric two-dimensional ring elements are used to form the geometrical configuration of the REMCC element. with the aid of the penalty method for imposing displacement constraints, the unit displacement theorem is applied numerically for obtaining the stiffness matrix of the REMCC element with respect to its contact nodal points. Once the stiffness matrices of all the REMCC elements are generated, the normal global coordinate transformations and assembly procedures of the finite element method are applied to form the system of equations for the entire cable cross-section. Loads are then applied and the system equations are solved for the unknown displacements of the contact nodal points. The model is verified by several examples involving exact classical solutions and the test results obtained for an as-built cable.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1992.; Includes bibliographical references (leaves 164-170); Microfiche.; xvi, 170 leaves, bound ill. 29 cm
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/10125/99661992-01-01T00:00:00ZLe, Tung TuanA numerical study of mixed and forced convection in a vertical packed tube and a packed channel
http://hdl.handle.net/10125/9965
A detailed numerical investigation has been performed for forced and mixed convection in a vertical channel and a cylindrical tube filled with a fluid-saturated porous medium, with particular emphasis on the developing region. The uniform wall temperature boundary condition has been assumed. The full momentum equations derived by Hsu and Cheng have been used, which accounts for variable porosity and permeability as well as viscous and inertia effects. A modification has been proposed to the dispersion conductivity model given by Hsu and Cheng, to take into account the ratio of the particle diameter to the characteristic length of the problem. An expression that accounts for the variation of porosity in the streamwise and cross-stream directions has been introduced to take into account the variation of porosity near the walls, entrance and the exit sections. The empirical constants N, C1 and φa, in the porosity function, and the Ergun constants A and B, in the permeability expression, have been determined by a comparison of the numerical and observed data for the pressure drop in a packed tube. The predicted hydrodynamic entrance length has been found to be 10 to 20 particle diameters long for 0.024 ≤ γ ≤ 0.097 and 1 ≤ ReD ≤ 10^3 (where γ is the ratio of the particle to the tube diameter and Red is the Reynolds number based on the particle diameter, dp) , with the shorter length corresponding to the smaller particle size. For all practical purpose the entrance length can be considered to be about the size of the diameter of the tube (or the plate separation distance). The empirical constants Cd and CJ)in the proposed dispersion model have been determined by comparing the predicted and observed heat flux data. The proposed porosity function with the present dispersion model have been found to predict the observed heat flux data of the air/glass sphere system to within 10% for 0.06 ≤ γ ≤ 0.12 and 10^3 ≤ Red≤2 x 10^4 (where ReD is the Reynolds number based on the tube diameter, D) for the packed tube. For the air/chrome steel sphere system (γ = 0.12 and 0.14, 10^3 ≤ ReD ≤ 2 x 104) the agreement was within 19%. The higher error in this case has been attributed to the large difference between the thermal conductivities of air and chrome steel, in which case the thermal equilibrium assumption invoked in the derivation of the energy equation may not be applicable. For the packed channel geometry (γ=0.06 and 0.12 for the Freon/glass sphere system and γ =0.125 for the 3 4 Freon/chrome steel sphere system, 2 x 10 ≤ ReD ≤ 2 x 10^4) the agreement between the observed and calculated heat flux was within 20%, the discrepancy being due to improper experimentation and variable property effects of the fluid next to the heated surface which was not taken into account in the numerical simulation. The volume averaged method that is used to derive the governing equations has been found to be applicable to problems in which γ≤0.15. The effect of using a fluid with a higher Prandlt number or a solid with a larger thermal conductivity has been observed to enhance heat transfer at high and low flow rates respectively. The exact values of the Reynolds number at which the above mentioned enhancement takes place was found to be dependent on the Prandlt number of the saturating fluid. Finally, it has been predicted in this study that the buoyancy force would play an important role in the heat transfer process for the air/glass sphere system with γ =0.06, if GrD/ReD > 9 x 10^5 for the packed tube and GrH/ReH > 9 x 10^4 for the packed channel configuration.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1992.; Includes bibliographical references (leaves 167-179); Microfiche.; xxii, 179 leaves, bound ill. 29 cm
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/10125/99651992-01-01T00:00:00ZChowdhury, AshrafuddinSolar sailcraft motion in sun-earth-moon space with application to lunar transfer from geosynchronous orbit
http://hdl.handle.net/10125/9964
A three dimensional model of the dynamics of a solar sailcraft in the earth-sun-moon system is developed. The model includes the following features: (1) a development of the physics of radiation pressure; (2) the derivation of a unit vector describing the direction of the resultant radiation pressure force for two types of sails; (3) the derivation of equations of motion for the sailcraft and the moon in spherical coordinates; (4) the derivation of generalized equations for the initial conditions of the sailcraft in terms of orbit parameters; (5) the development of attitude control equations for the sail; (6) an analytical criterion to account for the periodic eclipsing of the sun by the earth, and (7) an analysis of reflection of solar radiation by planetary bodies. A computer program based on the above model and including a search routine is developed and described. The program is used, together with a search strategy for searching through a four dimensional parametric space of initial orbit parameters, to investigate the problems of transfer to the moon (impact or close flybys) from a geosynchronous orbit. Results are obtained for three types of lunar encounters and three values of the sailcraft's area to mass ratio. Results are presented for the orbits of the sailcraft and the moon for the lunar encounter and the post encounter sailcraft trajectories when applicable. It is found that a lunar impact or close flyby can take place in 63 to 67 days for an area to mass ratio of 100 and that the type of lunar encounter can result in significantly different post encounter sailcraft trajectories.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1991.; Includes bibliographical references (leaves 152-154); Microfiche.; xvi,154 leaves, bound ill. 29 cm
Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/10125/99641991-01-01T00:00:00ZSalvail, James RonaldDynamic analysis of cables with variable flexural rigidity
http://hdl.handle.net/10125/6990
In general the governing equation for cable dynamics is a nonlinear partial differential equation with the fourth-order derivative in the space domain and the second-order derivative in the time domain. Analytical solutions are impossible by current available methods, and numerical methods are needed. In this research, several approaches are examined to simplify this type of nonlinear equation. The nonlinear properties of cables are mostly caused by internal damping. According to experiments[3] at least two sources of internal losses can be identified in a vibrating cable: (1) those due to dry friction between the wires; and (2) those due to viscous damping of the material of which the wires are made [9]. The former is amplitude-dependent but frequency-independent, whereas the latter is amplitude-independent and frequency dependent. The combination of these two mechanisms of losses results in hysteretic loop shapes, which are amplitude and frequency dependent. In this study, viscous damping is neglected in comparison with the large dry friction effects. Since dry friction is frequency-independent, its effect can be studied on the basis of a static approach. As is well known, an undamped cable can be modeled as a BERNOULLI-EULER beam under strong tension, with the bending moment at each point is proportional to the local curvature. But for cables where internal friction exists, the relation between an instantaneous bending moment and curvature is no longer linear but is described by hysteresis loops. The CableCAD®' [lO] software can predict the moment curvature relationship (hysteretic loop shape) based on a static approach. By using this relationship, the value of moment at any point along the deflected cable can be calculated. In this study, the cable is modeled as a continuous beam, and instead of adding extra damping term to the governing equation, only the moment-curvature relationship predicted by the CableCAD® software is used to calculate the value of flexural rigidity and bending moment. This frictional bending model (FBM) appears to be a reasonable approach because there are no external dampers attached to vibrating cables. In this approach, the fourth-order derivative partial differential equation can be reduced to second-order derivative partial differential equation, and solved by the finite difference method (FDM).
viii, 45 leaves
Thu, 01 May 2003 00:00:00 GMThttp://hdl.handle.net/10125/69902003-05-01T00:00:00ZZhong, MinExtended film theory for transpiration boundary layer flow at high mass transfer rates
http://hdl.handle.net/10125/6984
Mass transfer is of interest to understand a wide variety of applications ranging from natural systems to technological processes, from biological metabolic rates to mass exchanger and catalytic converters, from pollution control to transpiration cooling, etc. Moreover, mass transfer processes playa critical role in the regulation of climate at both local and global levels. For example, in Oahu, trade winds pick up moisture as they blow from the ocean to the windward coast of the island. As the moist air reaches the mountain range and is forced to move up (and cool off), water vapor is condensed. The inertia of the flow is sufficient to make the condensing vapors pass the mountain ridge, delivering high rates of precipitation to the Manoa valley. The main mechanism in the rain formation in this case is a mass transfer-controlled process. The evaporation rate of water vapor from the surface of the ocean and the amount of condensation formed during the cool-off process directly impact the yearly levels of precipitation in the Manoa valley. Despite its relevance to natural and technological processes, there are still much not known in the process of evaporation and the combined effects of convective flow, heat and mass transfer. In order to estimate mass transfer rates in boundary layer flows, two approaches are currently available: 1. To solve numerically the boundary layer equations. 2. To use appropriate graphs in textbooks to estimate the mass transfer rate, based on solutions given by the methods described in item (1). Both methods described above have shortcomings. The first is not practical because it requires a considerable amount of effort and time to yield a comprehensive understanding of the phenomena involved for each case under study. The second is limited in accuracy and leaves the mass transfer analyst with little flexibility beyond the results available in the literature. Ideally one would like to have reliable correlations that are valid for a wide range of parameters such as blowing factors, Schmidt numbers, Reynolds numbers, etc. The goal of the present study is to provide one such correlation based on a detailed analysis of the boundary layer equations and results of film theory applied to a porous plate. To pursue our goal for mass transfer rates in the boundary layer flow, in the present study, we will consider an inert binary mixture where one of the species is transferred (evaporated) through a porous (or wet) flat plate. A laminar boundary layer is formed over the plate, and we will focus on high mass transfer in the blowing (evaporation) regime, such as water evaporating at high temperatures (when the vapor pressure at the liquid-vapor interface is relatively high and therefore the mass fraction at the interface is not negligibly small). We will develop the functional form for a correlation that gives the mass transfer rate as a function of the relevant parameters. As it is usual in heat and mass transfer problems, a correlation is formed by collapsing the information contained in the boundary value problem (the combination of differential governing equations and boundary conditions) into an algebraic expression that involves only the boundary conditions and the properties of the medium. In our case, the Schmidt number (the ratio of momentum to mass diffusion coefficients), the flow conditions (free stream velocity, viscosity and length scale, or the Reynolds number), and vapor concentrations at the liquid-vapor interface and at the free-stream conditions are the dependent variables. The mass transfer (or evaporation) rate is therefore correlated in terms of the Reynolds and Schmidt numbers and the boundary conditions for mass concentrations. The boundary conditions are lumped into a dimensionless number referred to as the mass transfer potential, which is given by Bm =(m1,s -m1,e)/(1-m1.s), where 'm1' is the mass fraction of species 1 and the subscripts 's' and 'e' referred to "surface" and "external".
vi, 45 leaves
Thu, 01 May 2003 00:00:00 GMThttp://hdl.handle.net/10125/69842003-05-01T00:00:00ZNakamura, Fuminori