Engineering Commons^™

Modeling Thermosyphon And Heat Pipe Performance For Mold Cooling Applications, Dwaipayan Sarkar

Electronic Thesis and Dissertation Repository

Thermosyphons are enhanced heat transfer devices that can continuously transfer very large amounts of heat rapidly over long distances with small temperature differences. The high heat transfer rate is achieved through simultaneous boiling and condensation of the working fluid and the continuous heat transfer is achieved through recirculation of the working fluid in its liquid and vapor phase. A potentially important application of the thermosyphons has been towards reducing the cycle times of the mold cooling processes which would provide economic incentives to the automotive industry.

Different operational and geometrical parameters such as the input heating power, fill ratio (FR), …

Study Of Multi-Dimensional Transfer Effects In Applied Smouldering Systems, Seyed Ziaedin Miry Mr

Electronic Thesis and Dissertation Repository

Smouldering is a flameless form of combustion that is driven by oxygen directly diffusing into the surface of condensed phase fuel (liquid or solid) and involves a complex interplay between heat and mass transfer through porous media, chemical reactions, and multiphase flow. Applied smouldering systems have been gaining popularity for a variety of applications including (i) energy and resource recovery, (ii) waste-to-energy, (iii) pyrolysis and gasification, and (iv) applied smouldering of organic liquids/solids for environmental benefits. In all contexts, smouldering is a complicated oxygen-limited phenomenon where multi-dimensional transfer effects (i.e., non-uniformities in …

An Investigation Into Computational Modelling Of Melting And Solidification Of Phase Change Materials, Maryam Hemmat

Electronic Thesis and Dissertation Repository

This thesis evaluates the effectiveness of the enthalpy-porosity approach in simulating melting and solidification of phase change materials within latent heat thermal energy storage systems. It systematically investigates the sensitivity of the computational model to four adjustable parameters: mushy zone coefficient, thermal expansion coefficient, solidus/liquidus temperatures, and latent heat. The study includes individual and combined analyses of these factors in simulations of the melting process by comparing outcomes with extensive experimental data, resulting in a calibrated melting model. The calibrated model is validated across various heating conditions in the cylindrical cavity, and then in a rectangular cavity, confirming its reliability …

Experimental Investigation Of The Phase Change Process Within Circular Geometries, Kyle Teather

Electronic Thesis and Dissertation Repository

Latent heat thermal energy storage systems have many advantages over sensible-heat-based thermal storage systems, such as an increased energy density with a narrower range of operating temperatures. The main barrier to implementing latent heat storage systems is the low thermal conductivity of typical storage materials, called phase change materials (PCMs). Furthermore, the heat transfer mode in the liquid phase is natural convection, which is influenced by the geometry and orientation of the heat source and sink, thus impacting the phase change pattern and heat transfer. It is critical to have a good understanding of the underlying fundamental physics over the …

Pressure Drop And Heat Transfer In Flow Over An Array Of Blocks Of Varying Heights: A Statistical And Ai Analysis On The Effect Of Block Height Variation, Ali Navidi

Electronic Thesis and Dissertation Repository

The presence of a stiff obstruction in the path of fluid causes the creation of a boundary layer over and around the obstruction. The flow over an idealized, two-dimensional series of blocks is numerically investigated to determine how statistical blocks height variation, such as standard deviation, mean, and skewness, influence pressure drop and heat flux. These data sets serve as a foundation for developing models for estimating the heat transfer coefficient of each block using machine learning (ML) methods. The results show that the pressure drop increased by 60% when the standard deviation of heights of blocks increased from 0.1 …

Numerical Investigation Of Flow And Thermal Behavior In Channels With Pcm-Filled Thermal Energy Storage Columns For Potential Application In Photobioreactors, Sameed Akber

Electronic Thesis and Dissertation Repository

Microalgae has been identified as a potential source in the production of biofuel. Photobioreactors, which are used for microalgae production, normally experience temperature variations over the diurnal cycle due to changes in ambient conditions. The thermal regulation of photobioreactors to minimize temperature variations will result in a higher yield of microalgae, which are sensitive to such variations. The present research is aimed to investigate a novel approach to thermally regulate photobioreactors using phase change materials (PCM) where the latent heat of the material is exploited as the energy storage. The present research uses a numerical approach to study the flow …

Cooling Systems Analysis For Plastic Mold Injection Tools, Veronica Flores Quijada

Electronic Thesis and Dissertation Repository

The Plastic Injection Mold (PIM) industry has been searching for new technologies that improve the manufacturing of parts by reducing the production time and cost as well as increasing the quality of the product. The cooling systems in the PIM are designed initially to be straight-drilled into the mold, but this manufacturing process has traditionally not been very effective, since for molded parts with complex geometries, the cooling channels are not able to reach certain areas. This limitation has led the industry to develop conformal cooling channels that use the additive manufacturing technology, which allows the cooling channels to conform …

An Investigation Of Porous Materials For The Capture Of Concentrated Solar Energy, Elizabeth Blokker

Electronic Thesis and Dissertation Repository

Fossil fuel usage is resulting in climate change. There is a need to switch to renewable energies, but existing technologies lack the efficiency for wide-scale adoption. Concentrating solar energy to a receiver using a parabolic reflector is an efficient method of converting sunlight into thermal energy at a high efficiency. Current receivers suffer efficiency challenges due to significant re-radiation losses as they reach a high temperature at the front surface. This project is focused on the creation of a computational model to simulate the radiation heat transfer in porous geometries, which can be used to optimize the geometric properties of …

Characterization For Spray Droplet Behaviour In Afterburner-Like Flow Conditions, Matthew D. Mahaffy

Electronic Thesis and Dissertation Repository

Fuel injection processes can contribute to combustion instability in highly energetic combustion systems. In gas turbine engine afterburners, jet-in-crossflow (JIX) injection is used. Part one of the thesis study investigates the interaction between spray droplets and turbulent flow properties of a JIX. Jet-in-counterflow (JIC) configuration was also investigated. Part two of the investigation examined the behaviour of JIX droplets around a bluff body. Droplet size and flow turbulence was characterized simultaneously using particle image velocimetry and image processing techniques. Turbulence and droplet size were correlated, particularly at momentum flux ratios ≥ 60. High speed imaging was used to identify droplet …

Sustainable Smouldering For Waste-To-Energy: Scale, Heat Losses, And Energy Efficiency, Tarek L. Rashwan

Electronic Thesis and Dissertation Repository

Applied smouldering combustion is emerging as a highly energy efficient approach towards waste-to-energy. This thesis aims to better understand this potential by addressing a critical knowledge gap between laboratory scale smouldering research and large-scale applications. Altogether, new understanding in provided on the complex and dynamic interactions between the reaction zone (smouldering front) and the cooling zone (treated inert porous media) by integrating theory, experiments, analytical modelling, and global energy balance calculations. The experiments spanned a range of reactor sizes and smouldering conditions (from weak to robust) with dry (carbon) and wet (sludge) fuels mixed in sand. This work revealed that …

Energy Modelling To Evaluate The Thermal Regulation Of Aquaculture Raceways Using Geothermal Heat Exchange, Mitchell H. Kuska

Electronic Thesis and Dissertation Repository

Raceways are used in the aquaculture industry to farm fish species that swim against an upstream current. Raceways often draw water from a large waterbody and hence, their temperature changes due to seasonal variation, which directly affect the production yield. This study investigates a novel approach to regulate the raceway water temperature in a sustainable way by utilizing geothermal energy exchange. Energy models were developed to simulate heat transfer in a geothermal borehole heat exchange system and in the raceway system. The two models were then coupled to simulate the thermal regulation of the raceway water via borehole heat exchangers. …

Numerical And Semi-Analytical Estimation Of Convective Heat Transfer Coefficient For Buildings In An Urban-Like Setting, Anwar Demsis Awol

Electronic Thesis and Dissertation Repository

Urban building arrangements such as packing density, orientation and size are known to influence the microclimate surrounding each building. Studies on the impact of urban microclimatic changes on convective heat transfer coefficient (CHTC) from a stock of buildings, however, have been rare in surveyed literature. The present study focuses on numerical and analytical investigation of CHTC from building-like models with homogeneous set of equal and unequal planar and frontal densities. Consequently, the study discusses the CHTC response in relation to broader changes in the urban surface form. Part of the process involves the development of a simplified one-dimensional semi-analytical CHTC …

Validation Of Rhocentralfoam For Engineering Applications Of Under-Expanded Impinging Free Jets, Peter Nielsen

Electronic Thesis and Dissertation Repository

A numerical validation study of under-expanded impinging jet is conducted using OpenFOAM, an open-source computational fluid dynamics (CFD) library. RhoCentralFoam, a density based, compressible flow solver with a two-equation shear stress transport (SST) turbulence model is used on an axisymmetric model to reduce the computation cost. Major features of the flow were compared to an experimental study by Henderson et al., with a nozzle pressure ratio (NPR) of 4.0 and nozzle to plate spacing between 1.65-4.16. Of the features measured, the Mach diamond spacing, super-sonic core, and shear layer are all accurately predicted, while the recirculation bubble in the impingement …

Experimental Investigation Of The Heat Source Orientation On The Transient Flow And Thermal Behaviour Of Phase Change Material During Phase Transition, Steven Jevnikar

Electronic Thesis and Dissertation Repository

The present study reports the characterization of transient flow and transient thermal behavior of phase change material (PCM) during solid-liquid phase change (melting) through experimental investigation. Two specific aspects of the current work, both important in the field of latent heat thermal energy storage, are to investigate the influence of the flow behavior within liquid PCM on the melting and heat transfer processes, and the impact of heat source orientation on the underlying melting and heat transfer processes. A relationship between heat source orientation and the Nusselt number was discussed. The results show that the fluid velocity is critical for …

Fundamentals Of Applied Smouldering Combustion, Marco Zanoni

Electronic Thesis and Dissertation Repository

Smouldering combustion is defined as a flameless oxidation reaction occurring on the surface of the condensed phase (i.e., solid or liquid). Traditional research on smouldering was related to economic damages, fire risk, and death, due to the release of toxic gases and slow propagation rates. Recently, smouldering has been applied as an intentional, engineering technology (e.g., waste and contaminant destruction). Smouldering involves the transport of heat, mass, and momentum in the solid and fluid phases along with different chemical reactions. Therefore, numerical models are essential for the fundamental understanding of the process. Smouldering models either neglected heat transfer between phases …

On The Reduction Of The Driving Force In Shear-Driven Flows, Sakib Shadman

Electronic Thesis and Dissertation Repository

In shear-driven flows, an external driving force is needed to maintain the relative movement of horizontal plates. This thesis presents a systematic analysis on using spatially periodic heating and grooved surfaces to control this force. It is found that the use of periodic heating creates a buoyancy-driven effect that always reduces this force. The use of proper heating may even lead to the complete elimination of this force. It is further found that the use of isothermal grooved surfaces always enhances flow resistance, resulting in an increase of this force. When grooves and heating are applied together, their interaction induces …

The Development And Numerical Modelling Of A Representative Elemental Volume For Packed Sand, Ashraf Thabet

Electronic Thesis and Dissertation Repository

The motivation of this thesis is the development of simple microscopic-scale model (representative elemental volume; REV) that can be used to conduct flow and heat transfer simulations from which closure coefficients can be established for the volume-averaged transport equations for porous media (packed bed). The thesis provides a brief introduction to the computational technique adopted for the geometric generation of the REV (YADE), followed by a parametric study undertaken to reveal the minimum number of particles inside the REV that are required to mimic the appropriate physics. Additional analysis was conducted with the goal of determining the influence of deviation …

The Onset Of Convection In Rarefied Gases, Md Asif Zobaer

Electronic Thesis and Dissertation Repository

The onset of convection in the Rayleigh-Bénard problem for a monatomic rarefied gas at small Knudsen number has been investigated. Compressibility-induced density variations have been considered without imposing any restriction on the magnitude of temperature difference. A linear temporal stability analysis has been conducted for a compressible slip-flow model considering a Maxwellian gas and the dispersion relation is calculated using a Chebyshev collocation method. A neutral stability curve obtained in the Froude-Knudsen number plane marks transition to convection from a pure conduction state. The critical wave number observed for the onset of convection is in good agreement with the existing …

Convection In Corrugated Slots, Seyed Arman Abtahi

Electronic Thesis and Dissertation Repository

This thesis consists of two parts. The first part deals with the development of proper methodology, i.e. a spectrally accurate algorithm suitable for analysis of convection problems in corrugated slots. The second part is devoted to the study of natural convection in corrugated slots.

The algorithm uses the immersed boundary conditions (IBC) concept to deal with the irregular form of the solution domain associated with the presence of corrugated plates. The field equations are discretized on a regular domain surrounding the flow domain using Fourier expansions in the horizontal direction and Chebyshev expansions in the vertical direction. The boundary conditions …

The Effect Of Mesh-Type Bubble Breakers On Two-Phase Vertical Co-Flow, Alan Kalbfleisch

Electronic Thesis and Dissertation Repository

It is proposed that mesh-type bubble breakers can be used in two-phase gas-liquid vertical cocurrent pipe flow to enhance the heat and mass transfer rates. Two experimental studies were performed to investigate the effect of mesh-type bubble breakers with varying geometries on two-phase flow behaviour. The first used highspeed imaging to measure bubble size and observe the resulting flow regime for two-phase vertical co-flow consisting of air and water. A Froude number correlation that can be used to predict the bubble size generated by mesh-type bubble breakers is proposed. Flow regime maps for two-phase flow in the presence of bubble …

Numerical Investigation Of Full Scale Thunderstorm Downbursts: A Parametric Study And Comparison To Meteorological Model, Christopher Oreskovic

Electronic Thesis and Dissertation Repository

A series of Large Eddy Simulations using an atmospheric meteorological cloud model have been used to investigate the important geometric and thermal parameters that influence a thunderstorm downburst outflow, as it pertains specifically to the idealized cooling source model. A separate set of Large Eddy Simulations make use of the same idealized cooling source model, in a realistic atmospheric base state using real field sounding data, in an attempt to make a quantifiable comparison to a downburst from a full cloud simulation. Randomness has been added to the cooling source forcing function to mimic the thermal variation in a real …

A Model For Complex Heat And Mass Transport Involving Porous Media With Related Applications, Furqan A. Khan

Electronic Thesis and Dissertation Repository

Heat and mass transfer involving porous media is prevalent in, for example, air-conditioning, drying, food storage, and chemical processing. Such applications require non-equilibrium heat and mass (or moisture) transfer modeling inside porous media in conjugate fluid/porous/solid framework. Moreover, modeling of turbulence and turbulent heat and mass transfer becomes essential for many applications. A comprehensive literature review shows a scarcity of models having such capabilities. In this respect, the objectives of the present thesis are to: i) develop a formulation that simulates non-equilibrium heat and mass transfer in conjugate fluid/porous/solid framework, ii) demonstrate the capabilities of the developed formulation by simulating …

Application Of Natural Convection For Photovoltaic Cooling And Photocatalytic Disinfection, Usman J. Rajput

Electronic Thesis and Dissertation Repository

Two investigations for improving renewable technologies are engaged. First is the examination of the enhancement of heat transfer at the rear of a hot photovoltaic panel by natural convection using various configurations and the other is analyzing a new photocatalytic collector for water heating and cleaning. A 20 Watt polycrystalline panel is exposed to indoor simulated solar light, under constant ambient temperature and stagnant wind conditions. Three configurations are considered: a partial heat sink, a water cavity and a water channel. The experimentally obtained convective heat transfer coefficients are 4.4 W•m^-2•K^-1 at the rear of the bare …

Investigation Of Flow And Thermal Behaviour In A Pipe Submerged In A Hot Fluid, Ben S. Steen

Electronic Thesis and Dissertation Repository

Convection heat transfer through a pipe immersed in a stagnant fluid is used in various applications such as water heaters, chemical and food industry, etc. In this study, the effect of mixed convection on the flow and thermal structure of a fluid immersed inside a hotter, stagnant fluid was experimentally investigated. Temperature and velocity fields were obtained for a Reynolds number range of 330-6670, and a Grashof number range of 14000-95000 (0.6 < Gr/Re² < 0.0003). It was found that the buoyancy-induced wall-normal velocity component altered the streamwise velocity structure and the temperature profiles. The mean streamwise velocity profile was skewed towards the bottom of the pipe for initially laminar flow only. A vertical temperature gradient was also observed in the internal fluid under these conditions, where the hotter fluid resided in the top region of the pipe. The Nusselt number was found to moderately follow the predictive Gnielinski correlation, with an additional dependence on the bottom wall temperature. This showed that an increase in the Grashof number tended to dampen the turbulent convective heat transfer. The influence of natural convection on the mean and turbulent velocity profiles was found to be almost negligible in the high Reynolds number range.

Self-Sustaining Smouldering Combustion As A Novel Disposal Destruction Method For Waste Water Biosolids, Tarek L. Rashwan

Electronic Thesis and Dissertation Repository

Managing biosolids, the major by-product from wastewater treatment plants (WWTPs), persists as a major global challenge that often constitutes the majority of WWTP operating costs. Self-sustained smouldering is a new approach for organic waste treatment, in which the waste (i.e., the fuel) is destroyed in an energy efficient manner after mixing it with sand. Smouldering has never been applied to biosolids. Column experiments, using biosolids obtained from a WWTP, were employed to identify if - and under what conditions - smouldering could be used for treating biosolids. The parameter space in which smouldering was self-sustaining was mapped as a function …

Thermal Convection In Non-Fourier Fluids And Application To Liquid Helium Ii, Mohammad Niknami Esfahani

Electronic Thesis and Dissertation Repository

This thesis examines different conditions for which non-Fourier effects can be significant in the flow of fluids. Non-Fourier fluids of dual-phase-lagging type (DPL) possess a relaxation time and a retardation time, reflecting the delay in the response of the heat flux and the temperature gradient with respect to one another. For non-Fourier fluids of single-phase-lagging type (SPL) the retardation time is zero. Non-Fourier fluids span a wide range of applications, including liquid helium, nanofluids and rarefied gases. The parallels between non-Fourier fluids and polymeric solutions are established.

The instability of steady natural convection of a thin layer of non-Fourier fluid …

Wind And Thermal Effects On Ground Mounted Photovoltaic (Pv) Panels, Chowdhury Mohammad Jubayer

Electronic Thesis and Dissertation Repository

A combination of Computational Fluid Dynamics (CFD) simulations and wind tunnel experiments are carried out to investigate the effects of wind on the aerodynamic loading and heat transfer of a ground mounted stand-alone photovoltaic (PV) panel with tilt angle of 25^o in open country atmospheric boundary layer. Several azimuthal wind directions are considered: Southern 0^o, Southwest 45^o, Northwest 135^o and Northern 180^o. Three dimensional Reynolds-Averaged Navier-Stokes (RANS) approaches with an unsteady solver using Shear Stress Transport (SST) k-ω turbulence closure are employed for the CFD simulations, whereas Particle Image Velocimetry (PIV) and …

Thermal Convection Of Non-Fourier Fluids, Rahim Mohammadhasani Khorasany

Electronic Thesis and Dissertation Repository

The natural convection of non-Fourier fluids of the dual-phase-lagging (DPL) type is examined. These fluids possess a relaxation time and a retardation time, reflecting the delay in the response of the heat flux and the temperature gradient with respect to one another. DPL fluids span a wide range of applications, including low-temperature liquids, fluids subjected to fast heat transfer processes, and nanofluids (NFs), for which both the relaxation and retardation times are expressed in terms of nanoparticle concentration and solution properties. Both stationary and oscillatory convection become equally probable as the relaxation time increases. A nonlinear spectral approach is also …

Numerical Analysis Of Two Phase Flow And Heat Transfer In Condensers, Pooya Mirzabeygi

Electronic Thesis and Dissertation Repository

Steam surface condensers are commonly used in the power generation industry and their performance significantly affects the efficiency of the power plant. Therefore, it is vital to acquire a better understanding of the complex phenomena occurring inside condensers. A general three-dimensional numerical model is developed in this study to simulate the two-phase flow and heat transfer inside full-scale industrial condensers with irregular tube bundle shapes. The Eulerian-Eulerian two-phase model is selected to simulate gas and liquid flows and the interaction between them. A porous media approach is adopted to model the presence of large number of tubes in the condenser. …

A Cfd Assisted Control System Design For Supercritical Water Cooled Reactor, Rohit V. Maitri

Electronic Thesis and Dissertation Repository

In this study, the methodology to construct a control system based on computational fluid dynamics (CFD) simulations is developed for supercritical water cooled reactor (SCWR). The CFD model using Reynolds Stress Model (RSM) and k-w SST model is validated with the experimental cases of steady state and vertically up flowing supercritical water in circular tubes for normal heat transfer and deteriorated heat transfer (DHT) cases. This model is extended to simulate the transient thermal-hydraulic behaviour of supercritical fluid flow and heat transfer, and the results are also compared with the 1-D numerical model, THRUST. The DHT phenomenon is investigated using …