Master of Science, The Ohio State University, 2016, Nuclear Engineering

Coupling the s-CO2 Brayton cycle to the advanced nuclear reactors generally requires an intermediate heat exchanger (IHX). From an economic viewpoint, it is important to reduce the size and cost of IHX, but at the same time, the thermal hydraulic performances should not be deteriorated. Printed-circuit heat exchanger (PCHE), one of advanced compact heat exchangers, has been demonstrated as a competitive candidate. This thesis mainly focuses on designing a PCHE-type advanced IHX with innovative surface geometry with thermal, economic and mechanical consideration. Among the four outstanding surface geometries, zigzag and S-shaped fin channels are selected for a helium-to-s-CO2 IHX. Since the thermal-hydraulic correlations of the zigzag channel with a variety of geometrical parameters are available, a thermal-economic optimization is carried out to optimize the design of zigzag channel. For such multi-objective optimization problem, the annual total cost and heat exchanger thermal effectiveness are selected as two objectives functions. NSGA-II (a fast and elitist non-dominated sorting genetic algorithm), one of the widely used multi-objective genetic algorithms, is used for searching a group of Pareto-optimal designs. It is found that among the Pareto-optimal solutions, the total cost gradually increases with the thermal effectiveness between 88 and 95% while rises rapidly after the heat exchanger effectiveness exceeds around 95%. The sensitivity study shows that for the solutions with thermal effectiveness below around 95% the heat exchanger core physical length is the dominant factor that causes conflict between the total cost and thermal effectiveness. A similar trend can be observed from both the basic and extended design space. The final selection of the optimal designs obtained from the thermal-economic optimization requires a structural evaluation of surface geometry, especially for high-temperature high-pressure applications. S-shaped fin channels are ch (open full item for complete abstract)

Committee: Xiaodong Sun (Advisor); Tunc Aldemir (Committee Member); Richard Christensen (Committee Member) Subjects: Nuclear Engineering

Master of Science, The Ohio State University, 2009, Nuclear Engineering

Very High Temperature Reactors (VHTRs) operate at high temperatures (1,173-1,223 K) and require intermediate heat exchangers to transfer thermal energy to a hydrogen production plant or power conversion system. A promising plate-type compact heat exchanger for these applications is the Printed Circuit Heat Exchanger (PCHE). The objective of this study is to numerically model an Alloy 617 PCHE core with Helium as the working fluid using Fluent™ computational fluid dynamics software. The PCHE dimensions and operating conditions are those of a high-temperature helium test facility under construction at The Ohio State University. The test conditions considered are based upon the nominal design conditions of the test facility: operating pressure up to 3 MPa, mass flow rates of 10 to 80 kg/h, and hot and cold side inlet temperatures of 1,173 and 813 K, respectively. These operating conditions correspond to laminar and laminar-to-turbulent transitional flows within the fluid passages of the PCHEs being fabricated and modeled. The overall heat transfer coefficient ranges from 563-1697 W/m2K. The maximum effectiveness achieved is 85%. The maximum pressure drop of this PCHE is found to be approximately 1.5% of the operating pressure. The thermal duty of the heat exchanger ranges from 4.45 to 28.73 kW. The critical Reynolds number is found to be approximately 2800 for the semicircular channel as opposed to 2300 for a circular channel. CFD simulations carried out for laminar flow operating conditions are within good agreement with the predictions made using published correlations and empirical data. CFD simulations carried out for low Reynolds number laminar-to-turbulent transition cases are not accurately predicted by the correlations recommended in the published literature.

Committee: Xiaodong Sun (Advisor); Brian Hajek (Advisor); Richard Christensen (Committee Member) Subjects: Energy; Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2008, Nuclear Engineering

The U.S. Department of Energy's Generation IV Program has generated considerable interest for High-Temperature Gas-Cooled Reactors (HTGR), in particular, the Very-High-Temperature Reactor (VHTR). VHTR is one of the six reactor concepts selected by the Generation IV International Forum and is anticipated to be reactor type for the Next Generation Nuclear Plant (NGNP). The VHTR concept, with a projected plant design service life of 60 years, is being actively researched not only due to its near-term deployment potential but also because it offers a broad range of process heat applications ranging from electricity generation to hydrogen co-generation. To efficiently and reliably transfer the thermal output from the reactor core, VHTRs require high temperature (900-950 °C) and high integrity heat exchangers with high effectiveness during normal and off-normal conditions. A class of compact plate-type heat exchangers, namely, Printed Circuit Heat Exchangers (PCHEs), made of high-temperature materials and found to have these above characteristics are being increasingly pursued for heavy duty applications. The current thesis work is a part of a larger research project aimed at investigating the design, fabrication, testing, modeling, and optimization of PCHEs at operating temperatures proposed to be realized in VHTRs. In the present work, two PCHEs were designed and fabricated. In addition, a detailed design of a high-temperature helium test facility to test the thermal-hydraulic performance of these PCHEs was completed. Owing to the high operating temperatures and pressures, a detailed investigation on various high-temperature materials was carried out to aid in the design of the test facility and the heat exchangers. The study showed that Alloys 617 and 230 are the leading candidate materials for high-temperature applications. However, economics and material availability in the required form dictated the final design operating conditions. The helium test facility is of A (open full item for complete abstract)

Committee: Xiaodong Sun PhD (Advisor); Richard Christensen PhD (Other) Subjects: Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2009, EMC - Mechanical Engineering

The damping force and the self-excited force, which are a part of Heat Exchanger tube vibrations, act in the same (transverse) direction. The wedging process introduces alternating longitudinal coulomb forces that act at double the frequency of transverse vibrations and is defined by the wave equation. The transverse vibrations and the alternating longitudinal coulomb forces are coupled and act orthogonal to each other. Physical observations show that the transverse vibrations cannot exist without longitudinal vibrations. The governing constitutive equations for coupling can be shown theoretically through material non-linearities by considering higher order terms for the elastic energy, and geometric non-linearities by considering non-linear strain displacement relations. This non-linear constitutive equation when used in the equation of motion for transverse vibrations, the Gol'dberg tensorial result emerges. Energy reorganization due to this coupling results in reduced transverse vibration amplitudes. A simple experimental setup simulating this wedging process validates that transverse vibrations cannot occur without longitudinal vibrations.

Committee: Joseph Mansour (Advisor); Winston Perera (Committee Co-Chair); Vassilis Panoskaltsis (Advisor); Joseph Prahl (Committee Member); Roger Quinn (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2020, Engineering and Applied Science: Mechanical Engineering

Regulation of brain temperature is critical for managing heat stress-related adverse events. It can be achieved by external cooling of the head. Head cooling systems that are lightweight, portable, and suitable for active work scenarios, such as firefighting, mining, and construction work, are currently unavailable on the market. This study proposes a novel active head cooling system that a) uses phase change material for thermal storage and b) can be designed for portability. The closed-loop bench-top system consists of two heat exchangers: a water-cooled heat exchanger with an attached heater, mimicking heat generated from the head, and a helical tube heat exchanger surrounded with ice as a heat sink. These heat exchanges are interconnected by tubing for water circulation. The system performance is assessed by the cooling duration that depends on the mass of ice used and the heat transfer rate. The system was evaluated for different heat loads varying from rest to exercise condition (20 W – 40 W) and flowrates (0.25 l/min – 0.65 l/min). The results show that the system can handle a heat generation rate of 40 W from the head for 100 min (for the flowrate of 0.25 l/min), which is about 3 times the safe duration of firefighting drills. The cooling time increases linearly with decreasing heat load: 138 min for 30 W and 190 min for 20 W, an increase of 38%, and 90%, respectively. It also increases with a decreasing flow rate. The range of Nusselt number for helical coil flow is about 4.4 – 6.8 times higher when compared to that of a straight pipe flow. The helical design of the heat exchanger leads to enhanced heat transfer owing to the formation of Dean's vortical flow. The results suggest that the head cooling system, having possible features of being portable, cost-effective, lightweight, and easy to use, can assist in the thermoregulation of brain temperature for workers during elevated thermal stress conditions.

Committee: Rupak Banerjee Ph.D (Committee Chair); Marwan Al-Rjoub Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member); Amit Bhattacharya Ph.D. (Committee Member); Michael Kazmierczak Ph.D. (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Mechanical Engineering

The pressure drop and heat transfer performance for airflows (Pr ~ 0.71 and 50 = Re = 4000) in sinusoidal wavy plate-fin heat exchangers have been studied both experimentally and computationally. Compared with the widely used plain plate-fins, the heat transfer enhancement from wavy fin surfaces stems not only from their corrugated and enlarged surface areas, but more significantly, from swirl flow effects and early trigger of turbulence. To characterize and scale the surface-curvature-induced swirl or vortical recirculation, Swirl number (Sw) is introduced from balancing viscous, inertial, and centrifugal forces. The measured Fanning friction factor f and Colburn j factor from experiments show the onset of transition from laminar (Sw < 300) to turbulent regime (Sw > 800) occurs at approximately the same Sw for fin cores with different wavy corrugations and inter-fin spacings. After analyzing the effects of Sw and fin geometries on the local friction and convective heat transfer, a new set of generalized correlations are developed based on the fully developed behavior in plain plate-fin cores and a supposition of corrugation-induced-convection enhancement. The former can be scaled by fin cross-section aspect ratio (?) and Re, respectively, in the laminar and turbulent regime. The latter is shown to be described or scaled by the surface-area enlargement ratio (?) and swirl flow effects (Ff (or j)) as a function of Sw, corrugation aspect ratio (?), and inter-fin spacing (?). The new correlations predicted f and j factors, respectively, within ± 20% and ± 15% of the experimental data from this study and in the literature. Subsequently, the overall thermal-hydraulic performance is evaluated, and wavy plate-fin cores generally require larger frontal area but much smaller core volume and surface heat transfer area compared with plain plate-fins. To optimize the fin geometries and heat exchanger sizes, a systematic approach based on Genetic Algorithm (GA) is established (open full item for complete abstract)

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

Master of Science, Miami University, 2019, Mechanical and Manufacturing Engineering

In this work, the condensation heat transfer performance of silica nanospring-coated horizontal aluminum tubes is assessed. Coated samples with varying nanospring mat thicknesses, dependent on growth time, were evaluated against a baseline aluminum sample. Condensation heat transfer testing with water was performed in an evacuated environmentally controlled chamber at flowrates ranging from 1.5 to 5.5 LPM and subcooling temperatures of 1.5, 5.5, and 9.5℃ (Tsat ≈ 20℃). During this testing, the nanospring-coated samples exhibited similar condensation heat transfer coefficients to the baseline sample and the SN15 sample (15-min. growth) increased the heat transferred to the cooling fluid by 60% as compared to the baseline. A patterned sample with alternating hydrophobic and hydrophilic rings was created with 15 minutes of growth, which offered similar heat transfer performance to the SN15 sample. Video analysis determined that the SN15 and SN20 (20-min. growth) experienced an 84% increase in the condensate removal rate over the baseline, while the patterned sample experiences a 96% increase. SEM imaging revealed that the coating withstood the condensation environment. Additional work needs to be performed to further evaluate the coating, but these findings suggest that the coating may be capable of improving condensation heat transfer performance.

Committee: Andrew Sommers Dr. (Advisor); Giancarlo Corti Dr. (Advisor); Carter Hamilton Dr. (Committee Member); Edgar Caraballo Dr. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2018, Mechanical Engineering

This research presents engineering models that simulate steady-state and transient operations of air-cooled condensing units and an automatic commercial ice making machines ACIM, respectively. The models use easily-obtainable inputs and strategies that promote quick computations. Packaged, air-cooled condensing units include a compressor, condensing coil, tubing, and fans, fastened to a base or installed within an enclosure. A steady-state standard condensing unit system simulation model is assembled from conventional, physics-based component equations. Specifically, a four-section, lumped-parameter approach is used to represent the condenser, while well-established equations model compressor mass flow and power. To increase capacity and efficiency, enhanced condensing units include an economizer loop, configured in either upstream or downstream extraction schemes. The economizer loop uses an injection valve, brazed-plate heat exchanger (BPHE) and scroll compressor adapted for vapor injection. An artificial neural network is used to simulate the performance of the BPHE, as physics-based equations provided insufficient accuracy. The capacity and power results from the condensing unit model are generally within 5% when compared to the experimental data. A transient ice machine model calculates time-varying changes in the system properties and aggregates performance results as a function of machine capacity and environmental conditions. Rapid "what if" analyses can be readily completed, enabling engineers to quickly evaluate the impact of a variety of system design options, including the size of the air-cooled heat exchanger, finned surfaces, air flow rate, ambient air and inlet water temperatures, compressor capacity and/or efficiency for freeze and harvest modes, refrigerants, suction/liquid line heat exchanger and thermal expansion valve properties. Simulation results from the ACIM model were compared with the experimental data of a fully instrumented, standar (open full item for complete abstract)

Committee: David Myszka (Advisor); Kevin Hallinan (Committee Member); Andrew Chiasson (Committee Member); Rajan Rajendran (Committee Member) Subjects: Computer Engineering; Condensation; Conservation; Design; Endocrinology; Energy; Engineering; Environmental Economics; Environmental Education; Environmental Engineering; Environmental Science; Mechanical Engineering

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2016, Renewable and Clean Energy

Most applications of flat plate, low-temperature solar thermal panels are for water heating, such as producing domestic hot water or raising the temperature of swimming pools. This is reasonable given that the large masses of water present in these systems inherently provide built-in thermal energy storage so that a separate energy storage tank does not have to be purchased. For a space heating system, extra thermal energy storage generally has to be purchased and is a detriment to the economics of these systems. Despite the economic drawbacks of solar thermal space heating, this thesis focuses on the size of thermal systems required to heat an average size home in Minneapolis, MN and Dayton, OH. For these two locations and for a standard test case, this thesis studies the effect of solar panel size and orientation, heat exchanger size, and operation parameters including flow rates through the solar panels and heat exchanger. Liquid, flat plate collectors are one of the simplest methods for collecting solar energy. These panels are generally inexpensive and can have collection efficiencies above 50%. This makes solar thermal panels more efficient than solar photovoltaic panels, which generally have efficiencies less than 20%. Since the solar thermal panels chosen for study in this work heat a liquid with the sun's energy and the fluid being heated in the building is air, a heat exchanger has to be included in the model. Lastly, because solar thermal systems are inherently unsteady, thermal energy storage must be included in the model. These components of a solar thermal space heating system are modeled by writing and adding routines to the Wright State developed simulation program called Solar_PVHFC. Solar_PVHFC is a simulation program which models solar photovoltaic panels coupled with fuel cells and hydrogen storage tanks. Because of this work, Solar_PVHFC is now capable of modeling a solar thermal system. The advantage of coupling this solar thermal work to So (open full item for complete abstract)

Committee: James Menart Ph.D. (Advisor); Allen Jackson Ph.D. (Committee Member); Amir Farajian Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, Miami University, 2016, Mechanical and Manufacturing Engineering

Heat exchangers have seen widespread use in aerospace applications to properly manage aircraft and propulsion system heat loads. However, these heat exchangers are typically non-conformal, costly to implement, and large in terms of their volume and weight relative to the flowrate. There is motivation therefore for heat exchangers to be better integrated into the existing flow paths of the engine, both for packaging and performance improvements. Recent advances in additive manufacturing have presented the potential to create highly conformal and better optimized heat exchangers. In this work, a reduced-order computational tool was developed to predict the thermal-hydraulic performance of an annular two-pass, cross-counterflow heat exchanger. Area ruling was used to keep the velocities nearly constant in the heat exchanger core. The outputs of the model include heat transfer rate, outlet temperature, pressure loss, heat exchanger weight and volume, and heat exchanger effectiveness as a function of the user-supplied geometry and fluid inlet conditions. Various geometries were then simulated and analyzed using the computational tool, and based on these results, a prototype heat exchanger was created using additive manufacturing for future experimental testing. Computational fluid dynamics (CFD) simulations were also performed to assess the overall accuracy of the reduced-order model.

Committee: Andrew Sommers Dr. (Committee Chair); Amit Shukla Dr. (Committee Member); Edgar Caraballo Dr. (Committee Member); Todd Bailie Dr. (Advisor) Subjects: Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2016, Mechanical Engineering

The primary objective of this research is to study the performance of a heat exchanger system with a bypass valve. At first a simplified double-pipe heat exchanger is considered and a computational fluid dynamic (CFD) code FluentTM 15.0 is used to analyze the heat exchanger performance. The geometry of the double-pipe heat exchanger is scaled down based on the prototypic heat exchanger design provided by Tenneco. Numerical computations are carried out for different inlet conditions provided by Tenneco. The results, including the pressure drop, thermal entrance length, and heat transfer coefficient are benchmarked against correlations available in the literature. Furthermore the performance of the heat exchanger system with a bypass valve is studied. In order to simplify the model, the heat exchanger is modeled using the porous media approach. In addition, the mal-distribution of the flow within the heat exchanger is investigated. The simulations are performed for a range of mass flow rate with both closed and open bypass valve positions. The results are compared with the values obtained using the in-house heat exchanger light tool. The ultimate goal of the thesis is to improve the performance of the overall heat exchanger system to minimize pressure losses and maximize the heat transfer efficiency. This goal could be achieved by optimizing the geometries of the bypass leg to improve the flow uniformity into the heat exchanger and optimizing the flow response dynamics for the open/closed valve positions.

Committee: Mei Zhuang (Advisor); Xiaodong Sun (Committee Member) Subjects: Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2015, Washkewicz College of Engineering

Design of the fluid flow and heat transfer components utilizing the Computational Fluid Dynamics (CFD) is relatively new yet cheaper and accurate method that becomes popular and reliable today. In this thesis, design of a heat exchanger using CFD analysis technique is considered. A key investigation of this devise is the selection of the tubes and connection them to inlet and outlet manifolds. Correctly selected tube size and tube cross section impacts the heat exchanger performance. Thermal and hydrodynamic performance of the flow in circular and elliptic tubes connected to the inlet and outlet manifolds have been computationally investigated for maximum Figure of Merit. The tube with high Figure of Merit is the one with high heat transfer rate and low pressure drop. The tube has four different configurations of the cross section: a circular tube and three elliptic tubes with aspect ratios = 0.75, 0.50, and 0.25. All tubes are constrained to have the same wetted perimeter and the length, thus have the same heat transfer area. The tube is a smooth straight tube that has the length of 0.3048 m (12 in.) and wetted perimeter of 0.0798 m (3.1416 in.). The tube wall thickness is negligible. The contribution of the inlet and outlet manifolds is examined. A wide range of Reynolds numbers is covered, Re =100 (laminar flow), 10,000 (transitional flow), and 20,000 (turbulent flow). ANSYS FLUENT commercial code has been utilized in this investigation. The code was validated matching with experimental correlations (for developing hydrodynamic and thermal flow) available in the literature. The CFD simulation results were in agreement with the experimental correlation within 5%. This investigation started with simulating 12 different flow conditions inside the tubes without manifolds: three sets with four different tube options (as stated above) in each set. Each set represents the different flow regime: laminar transitional and turbulent with set Reynold number value, as n (open full item for complete abstract)

Committee: Mounir Ibrahim PhD (Committee Chair); Majid Rashidi PhD (Committee Member); Asuquo Ebiana PhD (Committee Member) Subjects: Aerospace Engineering; Automotive Engineering; Mechanical Engineering; Nuclear Engineering; Petroleum 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

The increasing heat generation rates produced by very large scale integration (VLSI) devices require more sophisticated heat removal systems to replace the macroscopic fin-array heat sinks. The goal of this research is to design, fabricate, and test an actively cooled micro-channel heat sink device that can achieve high-heat dissipation rate with a reduced chip-backside volume. An experimental setup was assembled and Electro-Osmotic Flow (EOF) was used. An increase in the cooling fluid (buffer) temperature of 3.7 °C, 11.4 °C, and 20.7 °C was achieved for 315.8 W/m2, 1008.8 W/m2, and 1842.1 W/m2 heat flux values, respectively. A flow rate of 82 µL/ min was achieved at 400 V of applied EOF voltage. The maximum increase in the cooling fluid temperature due to the joule heating was 4.5 °C for 400 V of applied EOF voltage. Heat transfer coefficient (h) was plotted along the non-dimensional length of the channel; it reached a maximum of 292 W/m2.K at the channel inlet and decreased to reach 92 W/m2.K at the channel outlet. Numerical calculations of temperatures and flow were conducted and the results were compared to experimental data. It was found that using a shorter channel length and an EOF voltage in the range of 400 – 600 V allows application of a heat flux in the order of 104 W/m2. For elevated voltages, the velocity due to EOF increased, leading to an increase in total heat transfer for a fixed duration of time; however, the joule heating also got elevated with increase in voltage.

Committee: Rupak Banerjee PhD, PE (Committee Chair); Teik Lim PhD (Committee Member); Ajit Roy PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 2009, Mechanical Engineering (Engineering and Technology)

The purpose of this work was to use copper micro-channel tube to design, construct and analyze the performance of a loop thermosyphon prototype. The design stage included a pressure loss analysis to ensure working fluid circulation. Analytical, numerical and experimental analyses were performed to calculate the heat transfer coefficient and heat transfer and to compare the results. The analytical analyses consisted of estimations of the heat transfer coefficient and heat transfer with the fin theory, and flow over a flat surface. The numerical analysis was performed using the computational fluid dynamics software Fluent. The experimental work was conducted on a small-scale wind tunnel under constant air flow, 0.5 and 1.0 m/s, and different operating temperatures, ~50°C and ~70°C. Propane was chosen as the working fluid for the system due to its relatively low global warming potential, saturation temperature range, availability, ease of storage, and non toxic properties. This work confirmed the concept of a loop thermosyphon by providing an isothermal surface throughout the prototype. The isothermal fins increased the heat transfer by a maximum of 63% compared to the classical fin mode.

Committee: Khairul Alam (Committee Chair) Subjects: Mechanical Engineering

Master of Sciences, Case Western Reserve University, 2011, Materials Science and Engineering

A brazing method is developed for high efficiency microchannel heat plate heat exchangers for waste heat recovery. Prototype elements for these heat exchangers are fabricated by laser machining 316 stainless steel, and bonding with AMS 4777 brazing alloy. Specifications require that the heat exchangers withstand in excess of 5000psi of fluid pressure, tested with a high pressure water system that was developed for this project. Due to the costly nature of the pressure test, a model is developed to correlate braze performance in the heat exchanger with data from inexpensive mechanical tensile and peel tests. The model predicts that the maximum peel load per specimen width will be 342lbs/in and a maximum pressure of 7200psi in the heat exchanger. The highest value from the experiments is 330lbs/in for peel load and 6467psi in the pressure test, 97% and 90% of their respective theoretical values.

Committee: David Schwam PhD (Advisor); John Lewandowski PhD (Committee Member); Gerhard Welsch PhD (Committee Member) Subjects: Energy; Materials Science; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2013, Materials Science and Engineering

Recent advances in minimally invasive surgical techniques and an increasing need to miniaturize medical devices has led to a surge in developing advanced manufacturing techniques. In order to meet the functional needs of such small devices as cardiovascular stents, guide wires, and needles, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. Some applications often include fine details that are impossible to achieve with rotary tool machining. Laser machining is one tool harnessing an enormous potential for the manufacture of such finely detailed devices as well as providing a means for improving the local material effects as a result of processing. However, thermal damage caused by laser machining can affect the performance of the components. As devices continue shrinking in size, there is a greater need for “athermal” manufacturing methods that have no adverse effect on performance. In this study, Nd:YAG and femtosecond lasers with different pulse widths were used to machine AISI 316LVM biomedical grade wires. The mechanical behavior of these materials were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a flex tester operated to provide fully reversed bending fatigue. All the fatigue testing was conducted in air over a range of cyclic strains to determine both the high-cycle and low-cycle fatigue regimes. The effects of laser input energy and pulse width on surface quality, heat affected zone (HAZ), and subsequent mechanical response are reported Baseline fatigue data on 316LVM wires in the annealed and hard conditions revealed that the hard wires exhibited better high cycle fatigue behavior than exhibited by the annealed wires. However, the low cycle fatigue behavior of the annealed wires was better than that obtained on the hard wires. This was successfully modeled using the Coffin-Manson-Basquin approach. Mixed results were obtained on the fatigue (open full item for complete abstract)

Committee: John J. Lewandowski PhD (Committee Chair); David Schwam PhD (Committee Member); Gerhard Welsch PhD (Committee Member); Malcolm Cooke PhD (Committee Member) Subjects: Materials Science

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

Storage technologies play a significant role in managing temporal fluctuations in energy supply and demand, which is key to transition towards a renewable and sustainable energy infrastructure. Thermal energy storage (TES) systems, in particular, have different applications across numerous industries to improve thermal management, reliability and reduce operation cost. This study focuses on investigating its novel use in enhancing the performance of an air-cooled condenser in thermal power plants. Despite numerous investigations, the large-scale adoption of Phase Change Material (PCM) based TES Systems (which are relatively compact and cost-effective) has been limited due to frequent reports of low PCM reliability, poor TES performance and the lack of relevant experimental data in the literature. This dissertation aims to address such issues to develop and test novel TES designs for high performance and reliability. To select the PCM to be used in the TES, in Chapter 2, the salt hydrate PCM- lithium nitrate trihydrate (Tsf= 30°C, hsf= 274 kJ/kg)- is identified and evaluated by subjecting it to extended thermal cycling to ascertain its long-term performance. Additionally, the material compatibility of the PCM with metals is also evaluated. The results suggest negligible loss of capacity and subcooling indicating the superior performance of the PCM with self-seeding compared to the traditional methods where nucleating agents are used. Additionally, the low thermal conductivity of PCM has typically limited the heat transfer performance in a TES. While a large section of the literature addresses the issue by designing high thermal conductivity PCM composites, the current study looks at a simpler alternative by reducing the length scale of the PCM encasement, thereby avoiding limitations and complications associated with the former method. Experimental and numerical work was carried out to identify the optimal l (open full item for complete abstract)

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

Master of Science, The Ohio State University, 2022, Mechanical Engineering

Truck drivers idle their trucks for their comfort in the Cab. They might need air conditioning to maintain a comfortable temperature and use the onboard appliances like TV, radio, etc. while they rest during their long journeys. On average idling requires 0.8 gallons of diesel per hour for an engine and up to 0.5 gallons per hour for a diesel APU. For a journey greater than 500 miles, a driver rests for 10 hours for every 11 hours of driving. Drivers tend to leave the truck idling throughout the 10 hours. With today's cost of diesel in the US, for one 10-hour period, the average cost incurred by the owner only on idling is $32. About a million truck drivers idle their trucks overnight for more than 300 days a year. Super Truck II is a 48V mild hybrid class 8 truck with all auxiliary loads powered purely by the battery pack. This offers an opportunity to reduce the idling from the whole 10 hours to whatever is necessary to charge the battery enough to power the auxiliaries. To quantify this “necessary idling” during the hoteling period we need to predict what the power load requirement in the future would be. The total power estimation is divided into two portions, (1) Cabin Hotel loads except HVAC and (2) HVAC load. A physics-based grey box models are developed for components in the vapor compression cycle and cabin using system dynamics which is used to estimate the HVAC power consumption. A special kind of Recurrent Neural Network (RNN) called Long, and Short Term Memory (LSTM) is used to predict the cabin hotel loads by user activity tracking. Synthetic load profiles are synthesized to overcome the limitation of lack of availability of data, about the user activity inside the cabin for training the LSTM algorithm, using rules and observations derived from the existing load profile for the hotel period from a survey conducted for SuperTruck project and literature survey on driver sleeping behavior. Dynamic Time Warping along with pointwise Euclidian distance is us (open full item for complete abstract)

Committee: Qadeer Ahmed Dr (Advisor); Marcello Canova Dr (Committee Member); Athar Hanif Dr (Other) Subjects: Artificial Intelligence; Automotive Engineering; Engineering; Mechanical Engineering; Statistics; Sustainability; Systems Design; Transportation