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

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

Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical, Industrial and Manufacturing Engineering

Impinging jets have been studied in great depth due to their high rates of heat transfer and wide range of application. Some applications of impinging jets include electronic equipment cooling, metal annealing, furnace heating, and many others. The goal of this research was to understand the effects of the nozzle-to-plate spacing and volumetric quality on the Nusselt number of two-phase, free surface impinging jets and submerged impinging jets. The Nusselt number of two-phase, free surface and submerged impinging jets were obtained at several nozzle-to-plate spacings and the trends of the stagnation pressure and Nusselt number were compared. The Nusselt number of the submerged jet was also compared to that of the free surface jets with the same conditions. The two working fluids of the jet were water and air. The nozzle-to-plate spacing ranged from H/d = 0.03 - 8.5 and the experiment was done at five volumetric qualities. The Nusselt number and stagnation pressure decreased exponentially in both free surface and submerged jets for all volumetric qualities in Region I, the jet deflection region. In Region II, the transition region, the Nusselt number and stagnation pressure of the free surface jet remained constant with some fluctuation. The Nusselt number and stagnation pressure of the submerged jet continued to decrease linearly. In Region III, the free jet region, the Nusselt number and stagnation pressure increased linearly in the free surface jet and decreased linearly in the submerged jet. Comparing the values of the free surface and submerged jet, the submerged jet had a higher Nusselt number for low nozzle-to-plate spacings, and a lower Nusselt number for higher nozzle-to-plate spacings.

Committee: Kyosung Choo PhD (Advisor); Hazel Marie PhD (Committee Member); Kevin Disotell PhD (Committee Member) Subjects: Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical, Industrial and Manufacturing Engineering

This study expands upon the current knowledge of the relationship between the heat transfer and fluid flow characteristics of air-assisted water impingement jets. Fluid flow and heat transfer characteristics of air-assisted water jet impingement were experimentally investigated under a fixed water flow rate condition with varying relative height (H/d). The test fluids were water and air. The effects of nozzle-to-plate spacing at volumetric qualities ß =0.3, 0.5, 0.7, and 0.8 where ß is the ratio of the volume of air to the total volume of the two-phase mixture on the hydraulic jump diameter, stagnation pressure, and stagnation Nusselt number were considered. The results showed that stagnation Nusselt number, hydraulic jump diameter, and stagnation pressure increased as the relative height decreased and the volumetric quality increased with the maximum values occurring at H/d of 0.02 and a volumetric quality of 0.8. This research is most applicable in the use of cooling of industrial applications such as cooling of electronics and processing of materials.

Committee: Kyosung Choo PhD (Advisor); Stefan Moldovan PhD (Committee Member); Kevin Disotell PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2017, EMC - Mechanical Engineering

In the present research an innovative space thermal management system is developed utilizing an integral planar variable conductance heat pipe (VCPHP) radiator, which can function reliably over a wide range of environmental conditions. The condenser (or radiator) of this planar shaped heat pipe is self-adjustable, and the evaporator temperature can be stabilized within a tolerable range even when the sink temperature changes significantly. This research includes the design, fabrication and test of four prototype planar heat pipe radiators, which are made with a metallic material and a thermally conductive polymer. The corresponding thermal performance of prototype VCPHPs were measured and analyzed through a benchtop heat pipe-based heat rejection system. To further support the concept, a multi-scale, steady-state heat pipe operation model (SSHPOM), which is able to capture both the thermal and hydrodynamic characteristics of the developed VCPHP radiator was developed. The mathematical model combines a theoretical thin-film evaporation model, a NCG expansion model and 2D steady-state heat transfer analysis. After validation, a feasibility of a large scale VCPHP designed for the Altair Lunar lander mission is predicted via numerical simulations with radiation cooling boundary conditions. Using the mathematical model, the influence of several design parameters can be identified and a maximum heat rejection turn-down ratio of 11.0 is achievable. Furthermore, the vapor-NCG topology within the integral planar heat pipe with a non-uniform heat load is simulated through a volume of fluid (VOF)-based approach.

Committee: Yasuhiro Kamotani (Advisor); Jaikrishnan Kadambi (Advisor); James T'ien (Committee Member); Chung-Chiun Liu (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science in Engineering, Youngstown State University, 2016, Department of Mechanical, Industrial and Manufacturing Engineering

This study further expands the current knowledge of the relationship between heat transfer and fluid mechanics. Fluid flow and heat transfer characteristics of air-assisted water jet impingement was experimentally investigated under a fixed water flow rate condition. Water and air were the test fluids. The effects of volumetric quality (ß = 0 – 0.9) on the Nusselt number, hydraulic jump diameter, and pressure were considered. The results showed that stagnation Nusselt number, hydraulic jump diameter, and stagnation pressure increased with volumetric quality to a maximum value at 0.8 of the volumetric quality, and then decreased. The stagnation Nusselt number and hydraulic jump diameter of the air assisted water jet impingement are governed by the stagnation pressure. Based on the experimental results, a new correlation for the normalized stagnation Nusselt number and hydraulic jump are developed as a function of the normalized stagnation pressure alone. This research can be applied to further enhance the cooling of industrial applications, such as, cooling of electronics and processing of materials.

Committee: Kyosung Choo PhD (Advisor); Guha Manogharan PhD (Committee Member); Jae Joong Ryu PhD (Committee Member) Subjects: Experiments; Fluid Dynamics; Mechanical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2008, Mechanical Engineering

The objective of this thesis was to investigate the cooling performance of a 16-nozzle spray array, using FC-72 as the working fluid, in variable gravity conditions with additional emphasis on fluid management and flow stability. A flight test experiment was modified to accommodate a 16-nozzle spray array, which was then tested in the parabolic flight trajectory environment of NASA's C-9 reduced gravity aircraft. The 16-nozzle array was designed to cool a 25.4 x 25.4 [mm] area on a thick film resistive heater used to simulate electronic components. Data was taken and reduced as a result of flight tests conducted over the course of two flight weeks (each week consisting of four flights, each flight consisting of 40 to 60 parabolas). The flight tests were conducted in order to examine gravity effects on spray cooling performance and to evaluate a novel liquid-vapor separator design. The mass flow rate through the 16-nozzle spray array ranged from 13.1 < m < 21.3 [g/s] for the spray cooling analysis and 14 < m < 35 [g/s] for the separator evaluation. The heat flux at the thick film resistor ranged from 2.9 < q" < 25 [W/cm2], the subcooling of the working fluid ranged from 1.6 < Tsc < 18.4 [C], the saturation temperature ranged from 37.4 < Tsat < 47.2 [C] and the absorbed air content in the working fluid was C = 10.1%, 14.3%, and 16.8% by volume. The spray chamber pressure ranged from 42 < P < 78 [kPa] while the acceleration ranged from -0.02 < a < -2.02 [g]. Two-phase cooling was emphasized, but some single-phase data was also collected. A one-dimensional model was used to predict the heater surface temperature from the heat input and mean heater base temperature.It was found that the cooling performance was enhanced in micro-gravity over terrestrial and elevated gravity. In addition, a sudden degradation in performance was found at high mass flow rates in micro-gravity, possibly due to liquid buildup on the surface between the nozzle impact zones. A high degree of sub (open full item for complete abstract)

Committee: Scott K. Thomas Ph.D. (Committee Chair); James A. Menart Ph.D. (Committee Member); J. Mitch Wolff Ph.D. (Committee Member); Kirk L. Yerkes Ph.D. (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering

PhD, University of Cincinnati, 2007, Engineering : Electrical Engineering

This dissertation describes the complete development of a very novel micro loop heat pipe. The activities described include the proof of concept research and convenes at the transition into commercial development. The proof of concept devices consisted of a small 1x1 cm. MEMS (micro electro mechanical systems) based silicon LHP cell that was developed and tested, which is intended as a pre-prototype for arbitrary lateral planar expansion in multiple cells for cooling electronic chips and other systems, in terrestrial and space applications (e.g. solar cell farms for energy beaming back to earth). The author as a member of a team of MEMS researchers and thermal science researchers, concentrated mainly on physical development, and measurement issues. The micro loop heat pipe is unique in that the wick is planar, is made of semiconductor grade silicon and is fabricated by the unique application of a photon pumped electrochemical etching (developed elsewhere for other applications but refined in this lab), locally referred to as “coherent porous silicon”. The resulting micro-capillary arrays were in the low micron range, with up to several million such through-capillaries per square centimeter. Also “quartz wool” has been demonstrated to serve well as a secondary or even primary wick with multi-micron effective pore size and porosity in the range of 95 percent. The author's major research contribution to this work was the refinement of the coherent porous silicon fabrication. A number of cps wicks were fabricated to act as the central component of the aforementioned LHP systems. The author also reveled and resolved multiple materials issues associated with the controlled micropatterening of the CPS wicks. This controlled micropatterening made it possible to carry out micro bonding of thermal pads/rails necessary for proper device operation. Cooling has been demonstrated up to about 60Watts/cm2, while maintaining top cap temperatures well below military specifications (open full item for complete abstract)

Committee: Dr. H. Henderson (Committee Chair); Dr. Frank Gerner (Other); Dr. Joseph Nevin (Other); Dr. Punit Boolchand (Other); Dr. Neville Pinto (Other); Dr. Charles Matthews (Other) Subjects: