Heat Transfer, Combustion Commons^™

Floating Tube Heat Exchangers, Patrick Harris, Christina Gedeon, Leonel Medrano, George Milam

Mechanical Engineering

With the slowly diminishing supply of fossil fuels across the world and the heightened risk of carbon dioxide pollution leading to global warming, a shift towards renewable energy is gaining momentum. Recent advances in wind and solar power technology have increased the power density of alternative sources while decreasing the cost per kilowatt-hour, but the technology has not become advanced enough yet for large scale deployment. Combined Power Cooperative has developed a revolutionary design for a concentrated solar power plant that utilizes Fresnel reflectors and a large body of water in which to install them. In addition to being low-cost, …

Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans

Graduate Theses and Dissertations

The thermal demands of modern day electronic systems require innovative thermal solutions. Spray cooling has proven to be able to cool heat fluxes orders of magnitude higher than traditional cooling methodologies. This work includes a comparison of spray cooling to standard thermal management methodologies. Key system parameters and considerations are discussed. The properties of available packaging materials and their effect on the reliability of a spray cooled system are presented. Parameters such as fluid temperature, droplet size, fluid velocity and flow rate all directly impact performance and are detailed in this work. Finally, results from of a wide range of …

Rational Efficiency Of A Heat Exchanger, Jim Mcgovern, Brian P. Smyth

Articles

The authors propose a new and unique definition for the rational efficiency of a heat exchanger. This new rational efficiency is defined in terms of its sub-rational efficiencies: a heat transfer rational efficiency and a friction rational efficiency for each of the fluid systems comprising the heat exchanger. The heat transfer rational efficiency is based on the definition of a mean temperature for the heat source and a mean temperature for the heat sink and reflects the exergy supplied and the exergy received, due to heat transfer only. The friction rational efficiency for each fluid system of the heat exchanger …

Development Of Analytic Tools For Computational Flame Diagnostics, Mehrnaz Rouhi Youssefi

Master's Theses

No abstract provided.

An Optical Analysis Of The Blowoff Behavior For Bluff Body-Stabilized Flames In Vitiated Flow, Trevor Jensen

Master's Theses

In bluff body-stabilized flames, a variety of physical phenomena contribute to the flame destabilization as lean blowoff is approached. These effects include increased strain on the flame shear layers, decreased attenuation of Bénard-von Kármán vortex shedding, and the presence of thermoacoustic instabilities. Lean, bluff body-stabilized flames were studied in an enclosed rectangular-duct, turbulent combustion rig with a triangular flame holder under vitiated conditions with both symmetric and asymmetric fuel distributions. Air and fuel flows within the rig were characterized using a PIV system and a continuous emissions gas analyzer, respectively.

High-speed videos of these flames undergoing blowoff were taken to …

Experimental And Numerical Investigations Of Tubular-Shaped Direct Methanol Fuel Cells (Dmfcs), Travis R. Ward

Master's Theses

This study focuses on both the numerical and experimental investigations of the novel, passively operated, tubular-shaped, Direct Methanol Fuel Cell (DMFC) as an alternative geometry to the traditional planar-shaped fuel cell. The benefit of the tubular geometry compared to the planar geometry is the higher instantaneous volumetric power density provided by the larger active area, which could be beneficial in applications that require a high instantaneous power while occupying a small volume. First, a two-dimensional, two-phase, non-isothermal model was developed to investigate the steady-state performance and design characteristics of a tubular-shaped, passive DMFC. It was found that a higher ambient …

Characteristics Of The Hydrogen Electrode In High Temperature Steam Electrolysis Process, Chao Jin, Chenghao Yang, Fanglin Chen

Faculty Publications

YSZ-electrolyte supported solid oxide electrolyzer cells (SOECs) using LSM-YSZ oxygen electrode but with three types of hydrogen electrode, Ni–SDC, Ni–YSZ and LSCM–YSZ have been fabricated and characterized under different steam contents in the feeding gas at 850°C. Electrochemical impedance spectra results show that cell resistances increase with the increase in steam concentrations under both open circuit voltage and electrolysis conditions, suggesting that electrolysis reaction becomes more difficult in high steam content. Pt reference electrode was applied to evaluate the contributions of the hydrogen electrode and oxygen electrode in the electrolysis process. Electrochemical impedance spectra and over potential of both electrodes …

Time-Dependent Crack Growth Behavior Of Alloy 617 And Alloy 230 At Elevated Temperatures, Shawoon Kumar Roy

UNLV Theses, Dissertations, Professional Papers, and Capstones

Two Ni-base solid-solution-strengthened superalloys: INCONEL 617 and HAYNES 230 were studied to check sustained loading crack growth (SLCG) behavior at elevated temperatures appropriate for Next Generation Nuclear Plant (NGNP) applictaions with constant stress intensity factor (K _max = 27.75 MPa[checkmark]m) in air. The results indicate a time-dependent rate controlling process which can be characterized by a linear elastic fracture mechanics (LEFM) parameter - stress intensity factor (K). At elevated temperatures, the crack growth mechanism was best described using a damage zone concept. Based on results and study, SAGBOE (stress accelerated grain boundary oxidation embrittlement) is considered the primary reason for …

Immersion Cooling Of Photovoltaic Cells In Highly Concentrated Solar Beams, Ahmed Darwish

UNLV Theses, Dissertations, Professional Papers, and Capstones

Concentrated solar radiation can be utilized to generate electrical power from photovoltaic cells, but concentrated solar radiation increases the photovoltaic cell’s temperature. This increase in temperature can lead to degradation of the cell efficiency, and too high of a temperature can damage the cell’s integrity. This is particularly important in dish and tower systems where a maximum uniform flux may be difficult to achieve. While a variety of approaches have been used to the keep the cells cool, most are based upon removal of heat from the back (opposite surface of the incident flux exposed surface) of the cell. This …

The Transfer Of Laser-Machined Micro-Structured Patterns From Silicon To Polymethyl Methacrylate, Warren E. Withrow

Mechanical & Aerospace Engineering Theses & Dissertations

This research project's purpose was transferring a micro-scaled pattern from a silicon wafer to a polymethyl methacrylate (PMMA), or acrylic, substrate through light absorption generated heat. The secondary objective was to determine if the pattern on the silicon wafer could then be transferred to silica (i.e. a microscope glass slide) through light absorption generated heat. Once this pattern-transfer technique is developed for the micro scale, it could be instituted on the nano scale. The experiment was designed to find an alternate method to that currently being used to mass-produce compact discs (CDs). The most popular method employs a stamping process …

Thrust-Vector Control, Dane Larkin, Harsimran Singh

Mechanical Engineering

Mission Statement

The purpose of this project is to design, build, and test a thrust-vectoring rocket nozzle which will aid in controlling the trajectory of a solid-booster rocket. The system prototype must meet the requirements set forth by the sponsoring enterprise.

The Enterprise

Stellar Exploration is a small space systems technology company located in San Luis Obispo, CA. Stellar Exploration is currently seeking a thrust-vectoring system for its Silver Sword rocket.

Project Scope

The design and analysis portion of this project accounted for a system that would be mounted on to a rocket for operational flight. Therefore, this team has …

Rayleigh Test Apparatus Design Report, Josef Duller, Owen Raybould, James Nicovich

Mechanical Engineering

The Rayleigh Test Apparatus is a device that will be used to test the thermodynamic properties of Nitrous Oxide to assess the feasibility of using this fluid as a coolant for a hybrid rocket aero spike. The aero spike is intended to redirect the propulsion flow as it leaves the engine to create a more efficient flow pattern at low and high altitudes. However, there are issues of overheating which leads to melting of the aero spike. For this reason, the use of nitrous oxide (N2O) as a coolant is being explored. N20 is being considered because it is already …

Analyse Du Comportement Réel Et De L'Optimisation Structurelle Des Cycles De Turbines À Gaz, Alexandru Dobrovicescu, Michel Feidt, Lavinia Grosu, Jim Mcgovern, Georgiana Tirca-Dragomirescu

Conference Papers

L’article présente une étude comparative, basée sur l’analyse exégétique, de l’effet de non prise en considération du comportement réel de l’agent thermique et de l’utilisation des modèles simplifiés pour calculer les performances des cycles de turbines à gaz avec et sans récupération de chaleur. Un intérêt spécial a été réservé au processus de combustion et au transfert de chaleur dans le préchauffeur d’air. La variation des destructions et des pertes d’exergie par rapport à la variation des paramètres fonctionnels est présentée.

Heat Transfer Through A Rotating Ball Bearing At Low Angular Velocities, Sarah Isert

All Graduate Plan B and other Reports, Spring 1920 to Spring 2023

Bearings are commonly used in mechanical systems when there are rotating parts in the system. For bearings that run at speeds above about 1000 revolutions per minute, such as those used in aircraft turbines, machining tools, and automotive engines, it is important to take into account the heat transfer through the bearing system due to friction. Heat transfer is generally not considered for applications where the bearing is rotating at low speeds, such as clocks and bicycles. However, for certain aerospace applications, such as precision instruments or wind turbines, the heat transfer through the bearing becomes relevant. The case where …

Modeling And Numerical Investigation Of Hot Gas Defrost On A Finned Tube Evaporator Using Computational Fluid Dynamics, Oai The Ha

Master's Theses

Defrosting in the refrigeration industry is used to remove the frost layer accumulated on the evaporators after a period of running time. It is one way to improve the energy efficiency of refrigeration systems. There are many studies about the defrosting process but none of them use computational fluid dynamics (CFD) simulation. The purpose of this thesis is (1) to develop a defrost model using the commercial CFD solver FLUENT to simulate numerically the melting of frost coupled with the heat and mass transfer taking place during defrosting, and (2) to investigate the thermal response of the evaporator and the …

Irrigation Leak Detection: Using Flow Rate Sensors To Detect Breaks In An Irrigation System, Adam Openshaw, Kalvin Vu

Computer Engineering

This report details the exploration and invention of a mechanism that can detect breaks in an irrigation system. With the ultimate goal of conserving water, we have designed an inexpensive, self sustaining flow rate monitor that can be used to identify anomalies in an irrigation system and wirelessly communicate the status of the system to a base station. Our implementation can also determine the direction of the anomaly based on the nature of the anomaly itself. This means that multiple monitors can be used to pinpoint the location of a break within the system in addition to merely detecting its …

Pg&E Flow Loop Simulator, Cole Brooks, Seth Berger, Ben Thacker

Mechanical Engineering

PG&E’s Diablo Canyon Power Plant requested a full-sized Flow Loop Simulator to train technicians by giving them hands-on experience. The basic design requirements were established to determine the scope of the project and develop the specific characteristics of the system. The detailed system design is composed of a piping schematic, a three-dimensional layout of the system components and piping, and a skid structure for the support and transportation of the system. Heat transfer and fluid mechanics were used to analyze the system to size components.

Design And Analysis Of A Low Temperature Co-Fired Ceramic Micro Combustor, Matthew H. Mccrink

Boise State University Theses and Dissertations

This thesis details the design and construction of a Low Temperature Co-Fired Ceramic (LTCC) micro combustion system. The design of the combustor requires a detailed analysis of the flame’s operational properties and stability. To this end, an analytic model was created to address these concerns. These results were used in conjunction with a detailed numerical analysis to determine the stable operating range of the combustors. The combustion of gaseous fuels requires a device with a lower bound on the channel feature size. This lower limit for combustion corresponds to the minimum quenching distance of the specific fuel being used and …

Development Of Hydrogen Direct Injection For Conversion Of Internal Combustion Engines, Maxwell A. Wilson

UNLV Theses, Dissertations, Professional Papers, and Capstones

The trend toward usage of vehicles that operate on alternative, renewable forms of energy storage has generated areas for development of new products that will facilitate implementation of new automotive fuel systems. As the reality of a hydrogen-fueled economy emerges, intermediate technologies may be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. The University of Nevada Las Vegas Center for Energy Research has developed a method for converting the common hydrocarbon fueled internal combustion engine to hydrogen direct injected fueling. This thesis describes the second phase of development and involves the design, fabrication …

Numerical Investigation Of Pre-Detonator Geometries For Pde Applications, Robert T. Fievisohn

Theses and Dissertations

A parametric study was performed to determine optimal geometries to allow the successful transition of a detonation from a pre-detonator into the thrust tube of a pulse detonation engine. The study was performed using a two-dimensional Euler solver with progress variables to model the chemistry. The geometrical configurations for the simulations look at the effect of shock reflections, flow obstructions, and detonation diffraction to determine successful geometries. It was observed that there are success and failure rates associated with pre-detonators. These success rates appear to be determined by the transverse wave structure of a stably propagating detonation wave and must …