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Full-Text Articles in Mechanical Engineering

An Experimental Study Of The Thermal Performance Of R-134a And Refrigerant Blends In An Air Conditioning System , Stephen W. Crown Jan 1993

An Experimental Study Of The Thermal Performance Of R-134a And Refrigerant Blends In An Air Conditioning System , Stephen W. Crown

Retrospective Theses and Dissertations

This document presents the findings of an experimental study of the effects of changing refrigerants on the performance of a refrigeration system. The different refrigerants studied are considered to be less harmful to the environment than R-12 which is currently widely used. Environmentally harmful effects include global warming and ozone depletion. The findings are based on the results of over one hundred independent tests using four refrigerants, namely R-12, R-134a, and two R-22 blends;The test equipment consisted of a 3-ton vapor compression refrigeration system, an air flow loop used to control evaporator conditions, and a water flow loop used ...


Evaluation Of Multigrid Acceleration For A Coupled, Strongly Implicit Procedure For The Navier-Stokes Equations, Robert L. Cupples Jan 1993

Evaluation Of Multigrid Acceleration For A Coupled, Strongly Implicit Procedure For The Navier-Stokes Equations, Robert L. Cupples

Retrospective Theses and Dissertations

No abstract provided.


Nurbs Based Computer Interface For Rapid Prototyping, Janardhanan K. Varadachari Jan 1993

Nurbs Based Computer Interface For Rapid Prototyping, Janardhanan K. Varadachari

Retrospective Theses and Dissertations

No abstract provided.


In-Tube Evaporation And Condensation Of Hfc-134a And Cfc-12 With Various Lubricant Mixtures , Steven J. Eckels Jan 1993

In-Tube Evaporation And Condensation Of Hfc-134a And Cfc-12 With Various Lubricant Mixtures , Steven J. Eckels

Retrospective Theses and Dissertations

Mandates currently in place by the Environmental Protection Agency require use of new environmentally acceptable refrigerants by 1996. Implementation of these new refrigerants by refrigeration and air-conditioning manufactures requires design data for the various components of these systems. This study focused on obtaining design data for evaporators and condensers of vapor compression systems. Specifically, a new environmentally acceptable refrigerant HFC-134a, which is targeted as a replacement for refrigerant CFC-12, was tested in an instrumented evaporator and condenser and their performance measured;Heat transfer coefficients and pressure drops were measured during evaporation and condensation of HFC-134a and CFC-12 in smooth and ...


A Model Of Coal Combustion Dynamics In A Fluidized Bed Combustor , Kenneth William Junk Jan 1993

A Model Of Coal Combustion Dynamics In A Fluidized Bed Combustor , Kenneth William Junk

Retrospective Theses and Dissertations

A model of coal combustion dynamics in a fluidized bed is developed in this study. The model is carried out on the premise that the total combustion response can be decomposed into two distinct processes: volatile combustion and char combustion. For an impulse in the feed rate of coal, the transient response of volatile combustion is modeled as an exponential decay. In contrast with volatile combustion, the transient response of char combustion cannot be approximated by an exponential decay. Instead, the transient response of char combustion is based on a closed-form solution to a population balance equation. This solution is ...


Freezing Problem In Pipe Flows , Jong Suk Lee Jan 1993

Freezing Problem In Pipe Flows , Jong Suk Lee

Retrospective Theses and Dissertations

Problems with phase change have in common a characteristic nonlinearity resulting from the moving boundary (solid-liquid interface), which complicates their analyses and which also renders each problem somewhat different. Furthermore, they have one or more singularities due to the appearance or disappearance of one phase or another. The nonlinearity and the singularity of these problems make them intrinsically difficult to solve;This study examines the two-dimensional freezing problem in pipe flows. Analytical analysis and numerical methods are used to determine solutions of the equations which govern the process. The governing equations and boundary conditions for the pipe flow are obtained ...


Collision-Free Path Planning For Robots Using B-Splines And Simulated Annealing , Horacio Martínez-Alfaro Jan 1993

Collision-Free Path Planning For Robots Using B-Splines And Simulated Annealing , Horacio Martínez-Alfaro

Retrospective Theses and Dissertations

This thesis describes a technique to obtain an optimal collision-free path for an automated guided vehicle (AGV) and/or robot in two and three dimensions by synthesizing a B-spline curve under geometric and intrinsic constraints. The problem is formulated as a combinatorial optimization problem and solved by using simulated annealing. A two-link planar manipulator is included to show that the B-spline curve can also be synthesized by adding kinematic characteristics of the robot. A cost function, which includes obstacle proximity, excessive arc length, uneven parametric distribution and, possibly, link proximity costs, is developed for the simulated annealing algorithm. Three possible ...


Effects Of Gasket Heat Gain And An Alternative Refrigerant On Refrigerator/Freezer Performance , Majid Ghassemi Jan 1993

Effects Of Gasket Heat Gain And An Alternative Refrigerant On Refrigerator/Freezer Performance , Majid Ghassemi

Retrospective Theses and Dissertations

Home refrigerators are the largest consumers of electricity among household appliances, consuming an estimated 7% of the total electricity used in the United States;As a result of the NAECA and Montreal Protocol, refrigerator/freezer manufacturers and researchers are presently searching for more efficient refrigerator/freezer designs which utilize non-CFC refrigerants. Recent studies show that the gasket area heat gain may account for as much as 21% of the total thermal load in refrigerator/freezer. Also, study shows that HFC-134a, the most likely replacement of CFC-12, is immiscible with mineral oil and may result in slightly higher energy consumption as ...


Remote Robot Manipulator Coupled With Remote-Controlled Guide Vehicle For Soil Sampling In Hazardous Waste Sites , Kiho Kim Jan 1993

Remote Robot Manipulator Coupled With Remote-Controlled Guide Vehicle For Soil Sampling In Hazardous Waste Sites , Kiho Kim

Retrospective Theses and Dissertations

The important initial step for remediation of hazardous waste is contaminant analysis since the cleanup operation can not begin until the contaminants in hazardous waste sites have been clearly identified. Ames Laboratory, one of the U.S. Department of Energy sites, has developed a robotic sampling system for automation of real-time contaminant analysis in situ which will provide the advantage of lowering the cost per sample, eliminating personnel exposure to hazardous environments, and allowing quicker results. Successful accomplishment of real-time contaminant analysis will require a remote manipulator to perform the sampling tasks in remote and unstructured surroundings, and a remote-controlled ...


Determining Char Burning And Sulfur Sorption Rates From Dynamic Analysis Of Co2 And So2 Profiles , Nearchos J. Christofides Jan 1993

Determining Char Burning And Sulfur Sorption Rates From Dynamic Analysis Of Co2 And So2 Profiles , Nearchos J. Christofides

Retrospective Theses and Dissertations

This work introduces a method for determining coal devolatilization, char burning, limestone calcination, and sulfur sorption rates based on the analysis of CO[subscript]2 and SO[subscript]2 profiles from a fluidized bed combustor. The technique is non-intrusive and can be performed under realistic combustion conditions. The method involves batching coal or limestone samples in a fluidized bed heated with propane gas or other fuel. Carbon dioxide and sulfur dioxide profiles are analyzed with linear models to obtain characteristic time constants for coal devolatilization, char burning, and sulfur sorption. Time constants for coal devolatilization and char burning can be ...


Dynamic Modeling Of Multibody Flexible Structures , Jiechi Xu Jan 1993

Dynamic Modeling Of Multibody Flexible Structures , Jiechi Xu

Retrospective Theses and Dissertations

This dissertation presents research work on the dynamic modeling of a three-dimensional, multibody, flexible, structural system with mutually coupled multicoordinates of unknown large overall rigid body motion. The study includes theory development and mathematical modeling, time integration numerical technique investigation, computer simulation and results, and experimental measurements and verification. The specific structure under consideration is characterized as an open loop system with spherical unconstrained chains capable of three-dimensional rotation motion. The elastic deflections and rotations change the instantaneous body shape and energy level of each individual flexible member and consequently affect the rigid body motion of the system. In return ...


Carbon In Fly Ash Analysis Using Photoacoustic Spectroscopy , Jeffrey Raymond Dykstra Jan 1993

Carbon In Fly Ash Analysis Using Photoacoustic Spectroscopy , Jeffrey Raymond Dykstra

Retrospective Theses and Dissertations

Photoacoustic absorption spectroscopy (PAS) was investigated as a method for on-line monitoring of carbon in fly ash from coal-fired boilers. PAS is based on the periodic heating of a gas when amplitude-modulated radiation is absorbed by the gas or by particles suspended in the gas. This periodic heating produces an acoustical wave that can be detected by a microphone. Because the PAS signal is based solely on the absorption of radiation (by carbon) and not scattering of radiation (by mineral matter), it has the potential for distinguishing unburned carbon from mineral matter suspended in the flue gas. Two radiation sources ...


Study Of Melting And Freezing Processes Of Water For Application To Ice Thermal Energy Storage System , Liang Yong Jan 1993

Study Of Melting And Freezing Processes Of Water For Application To Ice Thermal Energy Storage System , Liang Yong

Retrospective Theses and Dissertations

This thesis presents the results of a study of the solid-liquid phase change process of water in a rectangular enclosure for application to thermal energy storage systems. The work performed combined experimental results with analytical and numerical methods to develop computer models of the system;Experiments were performed to obtain data to verify the models under various melting and freezing conditions. A connective heat transfer correlation, for melting of ice in a container confined by two horizontal plates, was obtained based on the experimental work. An analytical model based on heat conduction was developed to predict ice formation in an ...


Alternative Technologies For Refrigeration And Air Conditioning Applications , Don Carlyle Gauger Jan 1993

Alternative Technologies For Refrigeration And Air Conditioning Applications , Don Carlyle Gauger

Retrospective Theses and Dissertations

A study was conducted to assess refrigeration technologies which are alternatives to vapor-compression for use in five application categories: domestic air conditioning, commercial air conditioning, mobile air conditioning, domestic refrigeration, and commercial refrigeration. A fundamental criteria for the selection of the alternative refrigeration technologies to be assessed was that they are environmentally safe;The study was conducted in three phases: a survey of U.S. patents, system modeling, and a technology assessment;Each refrigeration application was defined by a set of thermal source and sink temperatures. The U.S. patent survey was conducted from 1918 to the present. A method ...


Dimensional Verification And Correction Of Five-Axis Numerically Controlled Milling Tool Paths , Yun-Ching Huang Jan 1993

Dimensional Verification And Correction Of Five-Axis Numerically Controlled Milling Tool Paths , Yun-Ching Huang

Retrospective Theses and Dissertations

A system of algorithms is presented for material removal simulation, automatic dimensional verification and integrated error correction of numerically controlled (NC) milling tool paths. Several different approaches to these problems have been proposed including direct solid modeling, discrete vector intersection, and spatial partitioning. However, each of these methods suffer inherent restrictions that limit their practical application. This dissertation presents a discrete dexel NC verification algorithm based on a spatial partitioning technique (dexel representation) which incorporates the advantages of the discrete vector intersection approach. Hence, real-time animated five-axis milling simulation is supported by efficient regularized Boolean set operations, and dimensional milling ...


Numerical Simulation Of Two And Three-Dimensional Viscous Free Surface Flows In Partially-Filled Containers Using A Surface Capturing Approach , Franklyn Joseph Kelecy Jan 1993

Numerical Simulation Of Two And Three-Dimensional Viscous Free Surface Flows In Partially-Filled Containers Using A Surface Capturing Approach , Franklyn Joseph Kelecy

Retrospective Theses and Dissertations

A new surface capturing method is developed for numerically simulating viscous free surface flows in partially-filled containers. The method is based on the idea that the flow of two immiscible fluids (specifically, a liquid and a gas) within a closed container is governed by the equations of motion for a laminar, incompressible, viscous, nonhomogeneous (variable density) fluid. By computing the flowfields in both the liquid and gas regions in a consistent manner, the free surface can be captured as a discontinuity in the density field, thereby eliminating the need for special free surface tracking procedures;The numerical algorithm is developed ...


Using Sensitivity Derivatives Of Resonant Response To Guide Structural Redesign , Tsung-Hsiun Li Jan 1993

Using Sensitivity Derivatives Of Resonant Response To Guide Structural Redesign , Tsung-Hsiun Li

Retrospective Theses and Dissertations

Finite element-based optimization techniques have emerged as useful tools to control the vibration of a structural or mechanical system. Effective use of these techniques depends on sensitivity calculations. In this dissertation, the resonant frequencies and amplitudes at resonance of a vibrational system are identified as functions of design variables. Based on these features, the variation of resonant frequency is considered in the derivations of sensitivity equations of steady state resonant response;This dissertation presents several methods to compute the sensitivities of steady state resonant response of damped vibrational systems with respect to design parameters and to estimate the resonant frequencies ...


The Aerodynamics Of A Baseline Supersonic Throughflow Fan Rotor , Daniel Lawrence Tweedt Jan 1993

The Aerodynamics Of A Baseline Supersonic Throughflow Fan Rotor , Daniel Lawrence Tweedt

Retrospective Theses and Dissertations

A baseline supersonic throughflow fan has been designed and tested at the NASA Lewis Research Center in order to demonstrate proof-of-concept and provide an experimental data base for this unique type of turbomachine. The aerodynamics of the rotor, which was tested in both an isolated and a stage configuration, is discussed in somewhat generic terms for conditions covering most of the practical operating range. Much detailed and quantitative information is also included. In addition to the experimental results, viscous computational fluid dynamics (CFD) results and simple analytical solutions are discussed, having been used extensively to understand and assess the aerodynamic ...