MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

Passive techniques of enhanced heat transfer that create swirl flows inside tubes are useful in many applications in the process industry. Use of twisted inserts is one such type of swirl flow device. Steady, incompressible, laminar, constant property, fully developed flow and heat transfer has been computationally modeled in this study. Two cases, with 4 and 8 helically twisted fins inside a tube are considered, where the radial protrusions of the fins are highly conductive and have negligible thickness. The axial helical geometry of the fins of negligible thickness (δ=0) is defined by the twist ratio y (180° pitch H to tube inside diameter d). Using the vorticity and stream function formulation the governing equations for mass, momentum and energy transport are reduced in a helical coordinate system for the fully-developed swirl-flow condition. These are resolved in their conservative form and discretized using the control volume approach. For the heat transfer, both uniform wall temperature (T or UWT) and Uniform heat flux conditions (H1 or UHF) are considered. The diffusion terms are discretized using central-difference scheme and the power law scheme is used for the convective fluxes. Computed results highlight the effects of helical twist of the fin (3.0 ≤ y ≤ 12.0), number of fins N (4 and 8), flow Reynolds number (10 ≤ Re ≤ 1000), and fluid Prandtl number (1.0 ≤ Pr ≤ 25). The results show that effects of swirl flows, produced by the helical surface curvature of the fins, dominate in flows with Re > 100 and more so with decreasing y. Up to 1.1 to 2.8 times higher Nusselt numbers, relative to those in straight fin cases, and depending upon N, y, and Pr are obtained in this regime. The corresponding friction loss penalty is only 1.1 to 1.4 times that with straight fins, thereby making helical fin an attractive enhancement technique.

Committee: Milind Jog Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Raj Manglik Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2021, EMC - Aerospace Engineering

This study explores pool boiling of HFE-7100 on copper surfaces. The key objective of this study was to examine the effects that surface engineering has on nucleate boiling performance. The surface enhancements studied are roughness, artificial nucleation sites, and the combination of both. Data were gathered at Case Western Reserve University's Two-Phase Flow and Thermal Management Laboratory. Observing roughness between 0.480 μm to 7.564 μm shows that HTC improves with increasing roughness. Observing hole diameters from 1 mm to 3 mm and hole pitch, or spacing to diameter ratio, from 1.75 to 3.5; a configuration with hole diameter of 1 mm and pitch of 2.5 provides the best improvement to HTC compared to a bare surface with roughness of 0.480 μm, while the configuration with hole diameter of 1 mm and pitch of 3.5 provides worse HTC compared to a bare surface with roughness of 0.480 μm. Applying a roughness to a hole pattern also improves HTC with increasing roughness compared to both a bare surface with roughness of 0.480 μm, as well as to the hole pattern alone. The majority of the surface enhancement modes yields overall improvements in HTC. The introduction of surface enhancement generally decreases CHF.

Committee: Chirag Kharangate (Advisor); Chirag Kharangate (Committee Chair); Yasuhiro Kamotani (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

Gas turbine engines are an essential technology in aviation and power generation. One of the challenges associated with increasing the efficiency of gas turbines is the thermal loading experienced by the engine components downstream of the combustors especially the high-pressure turbine blades. High temperatures and rotational velocities can cause blade failures in numerous ways such as creep or stress rupture. Technologies like film cooling are implemented in these components to lower the thermal loading and reduce the risk of failure. However, these introduce complexities into the flow which in turn increases the difficulty of predicting the performance of film cooled turbines. Accurately predicting the capabilities of these components is essential to prevent failure in gas turbine engines. Engineers use a combination of experiments and computational simulations to understand how these technologies perform and predict the operating conditions and lifespan of these components. A combined experimental and numerical program is performed on a single stage high-pressure turbine to increase understanding of film cooling in gas turbines and improve computational methods used to predict their performance. The turbine studied is a contemporary production model from Honeywell Aerospace with both cooled and uncooled turbine blades. The experimental work is performed at The Ohio State University Gas Turbine Laboratory Turbine Test Facility, a short duration facility operating at engine corrected conditions. The experiments capture heat flux, temperature, and pressure data across the entire blade, but this work will focus on the turbine blade tip data. Tip temperature data are captured using a high-speed infrared camera providing a unique data set unseen in the current literature. In addition to the experiments, transient conjugate heat transfer simulations of a single turbine passage are performed to recreate the experiments and give insight into the flow field in the tip (open full item for complete abstract)

Committee: Randall Mathison (Advisor); Sandip Mazumder (Committee Member); Michael Dunn (Committee Member); Jeffrey Bons (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2020, Chemical Engineering

Coal Direct Chemical Looping (CDCL) is a novel coal process that removes carbon dioxide from coal combustion. This process makes use of multiple fluidized beds to cycle a metal oxide between a combustor and reducer. This process uses large particles and cannot fully recirculate air. Most existing heat transfer models for fluidized beds used recirculated air instead of cold flow and are based on results for smaller particles. They also only test immersed heater surfaces but being a moving bed reactor CDCL may have a heat exchanger in the freeboard region at times. Particles in fluidized beds are characterized by how readily they fluidize as a function of the particle and gas density and particle size. Three models, Molerus hmax, Xavier and Davidson, and an Bubble Wake model are tested. The cold flow heat transfer coefficient for three different particle sizes are experimentally determined in a bench-scale fluidized bed column. The gas convective heat transfer is very low in the experimental results relative to the expected values from the models. Gas film resistance, a significant component of the Bubble Wake and Xavier and Davidson models, is small and insignificant. The particle convective heat transfer for the Xavier and Davidson model correlates reasonably well with the experimental data. The heat transfer coefficient with the heater in the freeboard region is greater than that of an immersed heater. This is likely due to the geometry causing a small but significant increase in the gas convective heat transfer.

Committee: L.S. Fan (Advisor) Subjects: Chemical Engineering

Master of Science, The Ohio State University, 2020, Mechanical Engineering

In order to keep turbine blade surface temperature below melting point in gas turbine engines, internal passages in blades must be used to route cooler air through the blade. Design optimization of cooling passages necessitates an understanding of heat transfer patterns to minimize cooling mass flow. This project compares two approximations used to determine the heat transfer rate inside cooling channels in both computational and experimental investigations. The two approximations used in this project are constant surface temperature and transient heating. In an operating engine, the accuracy of both these conditions are not guaranteed. During steady state operation, the blade can cycle through many different flow paths which will impart different temperatures across the surface, and at no time will a blade be under completely uniform temperature except for the starting cycle. However, to make measurements of heat transfer easier, the two assumptions mentioned beforehand are utilized extensively. The constant surface temperature method uses a heater attached to the back of a thin copper plate to hold the surface temperature at a constant value in air flow. In the transient full-field method, thermochromic liquid crystals, which change colors with temperature, are applied to flat plate and turbulated geometries to capture the change in wall temperature during heating and cooling processes. Heat transfer rates are then derived from the transient temperature data using a semi-infinite solid model. The constant temperature approach is better established than the transient method and produces significantly higher Nusselt numbers, but the transient method provides better spatial resolution. A numerical conjugate heat transfer model is used to further investigate the discrepancy between the methods. The experimental geometry is replicated for both methods to gain an understanding of the fluid dynamics in each setup and how they differ.

Committee: Randall Mathison Ph.D (Advisor); Michael Dunn Ph.D (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science, Miami University, 2020, Mechanical and Manufacturing Engineering

In this study, air-side heat transfer enhancement via the introduction of hemispherical vortex generators (VGs) within a fin-and-tube heat exchanger was examined. A new technique for the deployment of hemispherical VGs utilizing the naturally-occurring condensation within the heat exchanger was employed. By using patterned surface wettability to collect condensate and encourage coalescence in predetermined locations, it was found that large frozen droplets can be formed in various configurations which can serve as VGs to enhance air-side heat transfer at airflow rates typical to domestic refrigeration (i.e. 1.0 to 2.0 m/s). These findings were then simulated numerically within ANSYS Fluent. Ten different configurations of VGs in channel flow were investigated using a fin spacing (5 FPI) typical to domestic refrigerator evaporators. Airflow of 1.0 to 2.0 m/s at 20°C was used for the flow through the channel where the walls and VGs were set to -9°C and the air-side heat transfer coefficient (h), pressure drop, and temperature changes were measured. Compared to a baseline configuration without VGs, h enhancements ranging from 14.0 – 75.9% were measured, with corresponding pressure drops ranging from 35.7 – 165.6%. The air-side temperature change within the test section ranged from 9.0 – 13.5°C between the inlet and outlet.

Committee: Andrew Sommers (Advisor); Ryan Clark (Committee Member); Edgar Caraballo (Committee Member); Carter Hamilton (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

Compact heat exchangers are employed in many different applications because of their high surface area density. Plate-fin heat exchangers in particular are well suited for gas-to-gas and air-to-air recuperators and heat recovery units, among many other applications. In this thesis, constant property, fully or periodically developed laminar flows of air (Pr = 0.72) inside a variety of different inter-fin channels of plate-fin heat exchangers are studied computationally, with the goal of achieving better understanding of plate-fin heat exchangers and providing new designs with superior performance to the existing ones. Majority of plate-fin channels have rectangular, trapezoidal or triangular cross-sectional shapes. Their convective behavior for air flows is investigated and solutions and polynomial equations to predict the Nusselt number are provided. Besides the limiting cases of a perfectly conducting and insulated fin, the actual conduction in the fin is also considered by applying a conjugate conduction-convection boundary condition at the fin surface between partition plates. For the latter, new sets of solutions and charts to determine the heat transfer coefficient based on the fin materials, channel aspect ratio, and fin density are presented. Furthermore, while large fin density increases the heat transfer surface area, the convection coefficient can be increased by geometrical modification of the fins. To this end, two different novel plate-fin configurations are proposed and their convective behavior investigated in this thesis. These include (1) slotted plate-fins with trapezoidal converging-diverging corrugations, and (2) offset-strip fins with in-phase sinusoidal corrugations. The enhanced heat transfer performance of the plate-fin compact core with perforated fin-walls of symmetric, trapezoidally profiled, converging-diverging corrugations is modeled computationally. Air flow rates in the range 10=Re=1000 are considered in a two dimensional duct geome (open full item for complete abstract)

Committee: Milind Jog PhD (Committee Chair); Raj Manglik PhD (Committee Chair); Shaaban Abdallah PhD (Committee Member); Manish Kumar PhD (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2010, Engineering and Applied Science: Mechanical Engineering

Periodically fully-developed swirling laminar flows in twisted tubes with elliptical cross sections are numerically simulated. The tubes are helically twisted along the axis perpendicular to their cross-section. The helical twist geometry is described by the 180 degree twist ratio and the elliptical cross-section is described by the ellipse aspect ratio. The geometries considered for this study have twist ratios with values {3,4.5,6} and ellipse aspect ratios with values {0.3, 0.5, 0.7}. Constant-property flow with a nominal Prandtl number of 3 (e.g. water at 60 degree Celsius) and Reynolds numbers in the range 10 ≤ Re ≤ 1000 was considered. The analysis quantifies the improvement in the Nusselt number as well as the increase in friction factor in order to map the effective heat transfer enhancement due to the twisted-tube-geometry-induced swirl flows. To this effect, the numerical results are compared, for a given aspect ratio, with the case of a straight elliptical tube (i.e. twist ratio tends to infinity) for which well established correlations are available. The results were also compared with those of circular tubes with twisted tape inserts for any given twist ratio. Numerical results show that the friction factor and the Nusselt number are strong functions of the twist ratio, aspect ratio and the Reynolds number. The increase in the friction factor and Nusselt number is higher for more tightly twisted tubes and for tubes with a lower ellipse aspect ratio. For Reynolds numbers below 100, the heat transfer results do not deviate significantly from the straight-tube values, but at higher values of Re, significant enhancement in heat transfer is evident for all twist ratios considered here. For example, for tubes with aspect ratio α = 0.3 and a twist ratio y = 3, the enhancement of the Nusselt number relative to the straight tube Nusselt number Nu/Nuy=∞ = 2.7. For the same aspect ratio, but with a twist ratio y=6, the enhancement Nu/Nuy=∞ = 2. On the other hand (open full item for complete abstract)

Committee: Milind Jog PhD (Committee Chair); Raj Manglik PhD (Committee Member); Shaaban Abdallah PhD (Committee Member) Subjects: Engineering

Master of Science, The Ohio State University, 1989, Food, Agricultural, and Biological Engineering

Heat transfer coefficients (h) between fluids and particles were determined for three situations: the first two involving natural convection of a mushroom-shaped particle immersed in Newtonian and non-Newtonian liquids, and the third involving continuous flow of a sphere within liquid in a tube. For natural convection studies, h was much higher for heating than for cooling, and decreased with time as equilibration occurred. For the continuous flow studies, h was found to increase with flow rate.

Committee: Sudhir Sastry (Advisor) Subjects:

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

In this work, the heat transfer performance of chemically functionalized, double growth silica nanospring coated aluminum tubes during methanol condensation experiments is investigated. Tube sets were coated in a fluorosilane compound via liquid immersion, and then a Krytox oil was used to create a slippery liquid infused porous surface (SLIPS). Heat transfer performance of each tube was evaluated by conducting condensation experiments in a vacuum chamber with saturated methanol. Experimental data were collected for methanol with each set of tubes for subcooling degrees of 0.5°C, 1.0°C, 1.5°C, 2.0°C, 2.5°C, 3.0°C, 4.0°C, 5.0°C, and 7.0°C with cooling water flowing at volumetric flow rates ranging from 1.5 LPM to 4.0 LPM. At 0.5°C subcooling and 1.5 LPM, the surface coating combination of the fluorosilane and Krytox GPL103 oil was found to outperform the baseline, bare uncoated tubes by 94.2% on average. Additionally, all SLIPS coatings maintained their dropwise condensation behavior without reverting back to filmwise condensation during the entire testing period (i.e. > 16 hours). While heat transfer performance showed a slight increase at low degrees of subcooling and low flow rates, further testing is still needed to test the long-term durability and efficacy of this coating technology at higher flow rates.

Committee: Andrew Sommers (Advisor); Edgar Caraballo (Committee Member); Mark Sidebottom (Committee Member); Giancarlo Corti (Advisor) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science, The Ohio State University, 1971, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1971, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science in Engineering, Youngstown State University, 2024, Department of Mechanical, Industrial and Manufacturing Engineering

With the constant innovation of technology and the need for more power generation, the need for improved methods of heat transfer are also needed. These innovations have always driven the research into new and improved methods of heat transfer. The topics covered in this research mainly being porous media, submerged two-phase jet impingement and boiling have all been seen to create improvements in cooling but have not been used in conjunction with each other. Using this combination to find the possible heat transfer improvement is the goal of this research. Experiments are done in both a non-boiling and boiling scenario. This allowed for verification that the two-phase flow had an effect on the surface before performing a boiling experiment. Two surfaces were tested, these were a plain surface and a columnar post-wick porous structure. For both sets of experiments, water flow rates were chosen from Reynolds numbers of 729 and 2929. The air flow rates were calculated using values of the volumetric quality (𝛽) that ranged from 0 ≤ 𝛽 ≤ 0.9 and the previously mentioned water flow rates. The results of this experiment were quantified by looking at the heat transfer coefficient (HTC) compared to the change in volumetric quality for both experiments. The non-boiling experiment showed that the added two-phase impinging jet created improvements in the HTC of porous media. An improvement of 81.94% over a single-phase jet was observed at a volumetric quality of 𝛽 = 0.9. The boiling experiment showed that the added two-phase impinging jet made minimal improvements on each surface. The plain surface saw an improvement of 9.50% over a single-phase jet at a volumetric quality of 𝛽 = 0.9. The post-wick surface saw a maximum improvement of only 2.94% at a volumetric quality of 𝛽 =

Committee: Kyosung Choo PhD (Advisor); Alexander Pesch PhD (Committee Member); Eric Haake M.S.E (Committee Member) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Continuous control and monitoring of the gas turbine combustor wall is essential for preventing combustor liner from overheating which may significantly damage structural integrity and reduce overall lifespan. In the past half century combustor outlet temperature has risen from 1100 to 1850 K. The continuous increase of severity of operating conditions inside combustor demands for a temperature determination method whose operation and accuracy are not affected by ever rising temperature. Conventional methods such as thermocouples and thermographic phosphor are not only intrusive, but their operation is also either restricted by an upper temperature limit (thermocouple) or measurement accuracy significantly decreases with increasing temperature beyond a certain threshold (thermographic phosphor). In this paper a multi-wavelength pyrometry system is developed which provides a fast, minimally intrusive temperature determination of the combustor wall. This method does not require any prior knowledge of exact emissivity but of the functional relationship between emissivity and wavelength over the spectral region of interest. One of major problems of wall temperature measurement using a pyrometry in combustor is that the emission from the combustor wall is interfered by the emissions from molecular radicals existing in the flame such as CH* (~431nm), OH* (~308nm), CO2* (400-600 nm) in the visible range and major species such as H2O (1.4,1.9,2.7,6.3 um) and CO2 (2.7,4.3,15 um) in the infrared region. In this report, a combustor that is made of stainless steel and runs on natural gas and the spectrum of flame emission is measured to identify a proper wavelength range (650-800 nm) over which there exists minimal or no interference from flame emission with thermal radiation. Thermal radiation is measured within the mentioned spectral range with a spectrometer and camera assembly from the target spot on the combustor wall with temperatures ranging from 1000 to 1300K. Thermal (open full item for complete abstract)

Committee: Jongguen Lee Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, Case Western Reserve University, 2024, EMC - Mechanical Engineering

The aim of this study is to understand the intricate flow physics and conditions leading to critical heat flux (CHF) inside a horizontally oriented rectangular channel. This study is divided into three parts: design of experimental setup, effect of inlet conditions on critical heat flux and two-phase heat transfer coefficient and understanding the effect of vapor generation on liquid-phase velocity using Particle Image Velocimetry (PIV). The experimental setup allows both upward and downward-facing single-sided heating configurations. Various inlet mass fluxes are examined, along with different levels of inlet sub-cooling. The impact of gravity is studied using flow visualization. During downward facing heating, vapor accumulates along the copper heater wall due to buoyancy effects resulting in notably low CHF and heat transfer values. In contrast, with upward facing heating, buoyancy assists in extraction of vapor from the copper heater wall, facilitating increased liquid contact and higher CHF and heat transfer values. CHF values begin to converge at high inlet mass flux for both orientations, which can be attributed to inertia dominating gravity. Inlet sub-cooling also influences CHF, with highly sub-cooled conditions yielding higher CHF. The impact of orientation and sub-cooled inlet on CHF and heat transfer coefficients are captured. Experimental CHF data was used to validate the Hydrodynamic Instability-Based Model for CHF prediction demonstrating a Mean Absolute Error of 10.8%. Effectively considering gravity forces, heated wall orientation, and flow regimes, the model demonstrates a proficiency in its comprehensive approach. Particle Image Velocimetry (PIV) is utilized to understand the flow physics and the impact of vapor phase on the liquid flow velocity. Four mass flow rates ranging from 5 – 20 g/s with sub-cooled inlet conditions are investigated in a rectangular channel with single-sided heating. Three regions of interest along the heated channel are (open full item for complete abstract)

Committee: Chirag Kharangate (Advisor); Donald Feke (Committee Member); Yasuhiro Kamotani (Committee Member); Steve Hostler (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Food, Agricultural and Biological Engineering

The smoking process for a food product involves the deposition and absorption of smoke on the product surface, followed by a drying step to reduce the product moisture content to a defined level. The uniformity of air velocity and temperature within a smokehouse significantly influences final product quality, including color, texture, and flavor. Additionally, process efficiency and production capacity depend on uniform heat and mass transfer at the surface for all products in the smokehouse. While Computational Fluid Dynamics (CFD) has been used to study airflow patterns, air velocity and temperature distributions due to ventilation systems, research on applications to airflow distribution in a smokehouse have been limited. The overall objective of this research was to develop and validate CFD simulations of a smokehouse ventilation system to investigate the applications to airflow uniformity within a smokehouse. A CFD simulation of airflow distribution in a smokehouse without product was developed and used to investigate the influence of smokehouse ventilation configuration on uniformity of air velocity. The ventilation system configuration with outlet vents positioned near the inlet vents at both sides of the smokehouse ceiling exhibited the highest air velocity uniformity index of 0.64. An investigation of three different outlet vent dimensions indicated that outlet vent size did not influence the uniformity of air velocity distribution within the empty smokehouse. The influence of model products in the smokehouse was investigated using the CFD simulation. The average air velocity at 20 locations decreased from 3.9 ±1.4 m/s to 2.7 ±0.90 m/s when the ratio of model product to smokehouse volume was increase from 0 to 0.047. The influence of ventilation configuration was also evaluated by comparing outlet vents positioned near the inlet vents at both sides of the smokehouse ceiling to the outlet vent located in the ceiling at the middle of the smokehouse. The ave (open full item for complete abstract)

Committee: Dennis Heldman (Advisor); Sudhir Sastry (Committee Member); Sandip Mazumder (Committee Member); Osvaldo Campanella (Committee Member) Subjects: Engineering; Fluid Dynamics; Food Science

Master of Science (M.S.), University of Dayton, 2023, Mechanical Engineering

Particle systems for concentrating solar applications present a non-trival challenge to adequately model with DEM software. A compiled modeling suite for radiative exchange, coined DEM+, is directly integrated into commercial software Aspherix®. A presentation of this modeling suite, advantages, and disadvantages is followed by an expanded look at the Distance Based Approximation (DBA) method for estimating particle-particle and particle-wall radiative exchange of more realistic particle size distributions and some simple binary mixtures. In addition, design, operation, and preliminary experimental results for a lab-scale multi-stage falling particle curtain are evaluated with particle image velocimetry (PIV) from two perspectives with discussion of the challenges therein. A room temperature DEM model of investigated particles is compared to experimental results with emphasis on future work for material calibration for DEM+.

Committee: Andrew Schrader (Committee Chair); Kevin Hallinan (Committee Member); Andrew Chiasson (Committee Member); Rydge Mulford (Committee Member) Subjects: Alternative Energy; Energy; Experiments; Mechanical Engineering; Sustainability

MS, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Wavy fin cores exhibit superior convective heat transfer performance over plain fins due to higher heat transfer surface area, waviness-induced swirl flow, and early inception of turbulence. There is an enhancement of heat transfer in both the laminar and turbulent regimes. In the continuous wavy channel, the waviness causes the flow to recirculate in the trough region, resulting in high local pressures at the flow reattachment locations. In the laminar regime, flow stagnation occurs at the recirculation zone in the trough region, which moderates the increase in heat transfer. In the turbulent regime, the heat transfer is improved because of flow recirculation, which aids in the turbulent mixing of the fluid. In continuous wavy fins, although the convective heat transfer is improved, the associated pressure drop penalty is also considerably higher than the plain fins. In the current study, modified wavy fins such as perforated and slotted wavy fins are investigated to better understand the potential to further improve the performance of wavy fins. The perforated wavy fins are produced through conventional methods of punching holes into aluminum sheet metal and then molding it into a wavy surface. In order to take full advantage of conventional manufacturing techniques, it is beneficial to invest time and resources to examine the performance of perforated wavy fins. A steady, periodically fully developed flow exposed to fin walls with uniform temperature is computationally modeled through perforated wavy fin cores. The computational model is validated by comparing numerical results for pressure drop and heat transfer for continuous wavy fins and perforated wavy fins with available experimental data where excellent agreement is observed. The model is then used to characterize the thermal-hydraulic performance of the air flows (Pr ≈ 0.71 and 50 ≤ Re ≤ 4000) in perforated wavy fin cores. The effect of the number of perforations on the performance of the perforated w (open full item for complete abstract)

Committee: Milind Jog Ph.D. (Committee Chair); Raj Manglik Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Akron, 2023, Mechanical Engineering

Recent advancements in polymer science and manufacturing have made market interest for Gradient Refractive Index (GRIN) lens technology grow exponentially. At the forefront of this field, Peak Nano is developing a process to engineer lenses for a variety of applications from medical to defense [1]. In the compression molding process step of manufacturing a GRIN lens, it is required to heat the polymer laminate above Glass Transition Temperature (Tg). This is currently achieved by conduction and convection heating of a charge inside the molding tool. Due to the poor thermal properties of polymers, a long transient is required for the charge to reach steady state. Additional difficulty is involved with GRIN laminates as the material properties are different for each layer. As stakeholder, Peak Nano would benefit from a shorter transient and improved thermal uniformity at steady state. Optical transmission data collected for the GRIN material blends indicated potential in heating via infrared (IR) radiation. A novel IR heating method was then developed for comparison to the conventional strategy. Results of this model gave improved heating time and uniformity over the current process. From there, a simulation matrix was generated, and the most successful setup was presented as a viable replacement to the conventional process.

Committee: Guo-Xiang Wang (Advisor); Ali Dhinojwala (Committee Member); Sadhan Jana (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Optics; Plastics