Browsing by Subject "Cooling"
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Item An investigation of enhanced thermosolutal axial dispersion in a horizontal concentric annular enclosure(Texas Tech University, 2004-08) Leggett, William FFor the post-closure phase of waste package cooling in the proposed Yucca Mountain Repository. it is important to be able to predict possible regions in the drift enclosure where condensation may occur. During this post-closure phase, natural convection and radiation are the mechanisms by which heat is transported from the heated waste packages to the host rock. Material failure due to corrosion is a significant issue due to the hazardous materials being stored and the extensive project design life of 10.000 years. The objective of the experimental investigation is to quantify the axial dispersion of a secondary gas in a horizontal enclosure including heat sources similar to the YMP drift configuration. Test results showed that the aided mixing due to unheated concentration buoyancy effects enhanced the dispersion coefficient by 8 times. The heated tests in which a turbulent plume from the simulated heater packages aided in mixing, yielded an axial dispersion coefficient of 20 times molecular diffusion. The objective of the numerical investigation is to develop a 3-D computational fluid dynamics (CFD) model using Fluent based on the experimental mockup of a YMP configuration and to compare the steady-state mass-transport results of the simulations to the experimental data. In this study, interest is focused solely on quantifying the increased axial mass dispersion of a secondary gas due to buoyancy.Item Calculating the structure of protoplanetary disks within the first few AU using Pisco(2011-12) Harrold, Samuel Thomas; Lacy, John Howard; Jaffe, DanThe calculation of the physical conditions near the inner rim of a protoplanetary disk using the new computational model Pisco is described. Diagnostic plots illustrate solutions for disk structure, radiation field, chemical composition, and heating and cooling of the disk in a steady-state approximation for both disks with unsettled dust and with settled dust. Disks with unsettled dust are found to have hotter gas temperatures above the disk photosphere and a more pronounced temperature inversion at the disk photosphere. Recommendations are made for the development of Pisco. Pisco has the potential to explore what observed molecular emission can imply about disk structure.Item Design and evaluation of a micro-climate cooling system using a vest with ice bags(Texas Tech University, 1986-05) Tayyari, FariborzA microclimate cooling system was designed in this dissertation project. The system consists of a vest with 54 small ice bags inserted in the pockets sewn to the Inside of it. The system was tailored in such a way as to open and close in front (to be worn as a vest) and on both sides (to be worn as a poncho). The effectiveness of the designed cooling system with (DCSS) and without (DCSN) a slicker worn over it, and a South African cooling system (SACS) in reducing heat stress encountered by men working in hot environments was evaluated. Testing was conducted in an environmental control chamber to simulate hot-humid and warm-humid environmental conditions. Two workloads, moderate and heavy, were performed by the four subjects who participated in this project. Under the hot thermal condition the average tolerated exposure time by the subjects when not using a cooling system was 72.5 minutes when they performed the heavy workload, and 85 minutes when performing the moderate workload. But, when the cooling systems were utilized, all subjects completed the 95-minute work sessions. Under the warm condition the subjects were able to complete all work sessions even without a cooling system. The effectiveness of the cooling systems in reducing physiological strains and subjective responses (i.e., the feeling of discomfort and thermal sensation), especially under the hot condition, was statistically significant. It was concluded that both the cooling system designed for this study and the South African cooling system were effective in reducing the heat stress associated with working in the hot-humid condition investigated in this study. It was also concluded that the performance of the designed cooling system was better than that of the South African cooling system and the best results were achieved when a slicker was worn over the designed cooling system.Item Experimental investigation of film cooling and thermal barrier coatings on a gas turbine vane with conjugate heat transfer effects(2013-05) Kistenmacher, David Alan; Bogard, David G.In the United States, natural gas turbine generators account for approximately 7% of the total primary energy consumed. A one percent increase in gas turbine efficiency could result in savings of approximately 30 million dollars for operators and, subsequently, electricity end-users. The efficiency of a gas turbine engine is tied directly to the temperature at which the products of combustion enter the first stage, high-pressure turbine. The maximum operating temperature of the turbine components’ materials is the major limiting factor in increasing the turbine inlet temperature. In fact, current turbine inlet temperatures regularly exceed the melting temperature of the turbine vanes through advanced vane cooling techniques. These cooling techniques include vane surface film cooling, internal vane cooling, and the addition of a thermal barrier coating (TBC) to the exterior of the turbine vane. Typically, the performance of vane cooling techniques is evaluated using the adiabatic film effectiveness. However, the adiabatic film effectiveness, by definition, does not consider conjugate heat transfer effects. In order to evaluate the performance of internal vane cooling and a TBC it is necessary to consider conjugate heat transfer effects. The goal of this study was to provide insight into the conjugate heat transfer behavior of actual turbine vanes and various vane cooling techniques through experimental and analytical modeling in the pursuit of higher turbine inlet temperatures resulting in higher overall turbine efficiencies. The primary focus of this study was to experimentally characterize the combined effects of a TBC and film cooling. Vane model experiments were performed using a 10x scaled first stage inlet guide vane model that was designed using the Matched Biot Method to properly scale both the geometrical and thermal properties of an actual turbine vane. Two different TBC thicknesses were evaluated in this study. Along with the TBCs, six different film cooling configurations were evaluated which included pressure side round holes with a showerhead, round holes only, craters, a novel trench design called the modified trench, an ideal trench, and a realistic trench that takes manufacturing abilities into account. These film cooling geometries were created within the TBC layer. Each of the vane configurations was evaluated by monitoring a variety of temperatures, including the temperature of the exterior vane wall and the exterior surface of the TBC. This study found that the presence of a TBC decreased the sensitivity of the thermal barrier coating and vane wall interface temperature to changes in film coolant flow rates and changes in film cooling geometry. Therefore, research into improved film cooling geometries may not be valuable when a TBC is incorporated. This study also developed an analytical model which was used to predict the performance of the TBCs as a design tool. The analytical prediction model provided reasonable agreement with experimental data when using baseline data from an experiment with another TBC. However, the analytical prediction model performed poorly when predicting a TBC’s performance using baseline data collected from an experiment without a TBC.Item General ram correlations for automobiles(Texas Tech University, 2000-05) Verner, Debra G.The driving pressure required for the cooling system airflow comes from two sources: the pressure due to the forward motion of the vehicle known as ram pressure, and the radiator fan pressure rise. These internal and external flow fields interact at the cooling air inlets and at the underside of the engine bay. These flow fields are closely related and are considered together in this study. The primary focus of this study is to find general ram pressure correlations for automobiles. The principal test results consist of a set of correlation equations which describe the variation of the ram pressure coefficient with respect to the size and location of the openings, the freestream velocity, and the cooling air flow rate for individual and combinations of openings. These correlations are in a format suitable for use with streamtube cooling system models such as ttu Cool®.Item Massively-Parallel Direct Numerical Simulation of Gas Turbine Endwall Film-Cooling Conjugate Heat Transfer(2011-02-22) Meador, Charles MichaelImprovements to gas turbine efficiency depend closely on cooling technologies, as efficiency increases with turbine inlet temperature. To aid in this process, simulations that consider real engine conditions need to be considered. The first step towards this goal is a benchmark study using direct numerical simulations to consider a single periodic film cooling hole that characterizes the error in adiabatic boundary conditions, a common numerical simpliflication. Two cases are considered: an adiabatic case and a conjugate case. The adiabatic case is for validation to previous work conducted by Pietrzyk and Peet. The conjugate case considers heat transfer in the solid endwall in addition to the fluid, eliminating any simplified boundary conditions. It also includes an impinging jet and plenum, typical of actual endwall configurations. The numerical solver is NEK5000 and the two cases were run at 504 and 128 processors for the adiabatic and conjugate cases respectively. The approximate combined time is 100,000 CPU hours. In the adiabatic case, the results show good agreement for average velocity profiles but over prediction of the film cooling effectiveness. A convergence study suggests that there may be an area of unresolved flow, and the film cooling momentum flux may be too high. Preliminary conjugate results show agreement with velocity profiles, and significant differences in cooling effectiveness. Both cases will need to be refined near the cooling hole exit, and another convergence study done. The results from this study will be used in a larger case that considers an actual turbine vane and film cooling hole arrangement with real engine conditions.Item Modeling and optimization for energy efficient large scale cooling operation(2013-12) Kapoor, Kriti; Edgar, Thomas F.Optimal chiller loading (OCL) is described as a means to improve the energy efficiency of a chiller plant operation. It is formulated as a multi-period constrained mixed integer non-linear optimization problem to optimize the total cooling load distribution through accurate chiller models. OCL is solved as a set of quadratic programs using sequential programming algorithm (SQP) in MATLAB. Based on application of the methodology to chiller systems at UT Austin and a semiconductor manufacturing facility, OCL can result in an annual energy savings of about 8%. However, the savings may reduce considerably in case of additional physical constraints on overall plant operation. With the addition of thermal energy storage (TES) to the system, OCL can reduce the daily cooling costs in the case of time varying electricity prices by 13.45% on an average. The energy efficiency of a chiller plant as a function of its chiller arrangement is studied by using fitted chiller models. If all other variables are kept same, chillers operating in parallel consume up to 9.62% less power as compared to when they are operated in series. Otherwise, chillers may operate up to 12.26% more efficiently in series depending on their chilled water outlet temperature values. The answer to the optimal chiller arrangement can be straightforward in some cases or can be a complex optimization problem in others.Item Numerical simulation of flow and heat transfer of internal cooling passage in gas turbine blade(Texas A&M University, 2007-04-25) Su, GuoguangA computational study of three-dimensional turbulent flow and heat transfer was performed in four types of rotating channels. The first type is a rotating rectangular channel with V-shaped ribs. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio (e/Dh) is 0.078 and the rib pitch-to-height ratio (P/e) is 10. The rotation number and inlet coolant-to-wall density ratio were varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number was varied from 10,000 to 500,000. Three channel orientations (90 degrees, -135 degrees, and 135 degrees from the rotation direction) were also investigated. The second type is a rotating rectangular channel with staggered arrays of pinfins. The channel aspect ratio (AR) is 4:1, the pin length-to-diameter ratio is 2.0, and the pin spacing-to-diameter ratio is 2.0 in both the stream-wise and span-wise directions. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.20, respectively, while the Reynolds number varied from 10,000 to 100,000. For the rotating cases, the rectangular channel was oriented at 150 degrees with respect to the plane of rotation. In the rotating two-pass rectangular channel with 45-degree rib turbulators, three channels with different aspect ratios (AR=1:1; AR=1:2; AR=1:4) were investigated. Detailed predictions of mean velocity, mean temperature, and Nusselt number for two Reynolds numbers (Re=10,000 and Re=100,000) were carried out. The rib height is fixed as constant and the rib-pitch-to-height ratio (P/e) is 10, but the rib height-to-hydraulic diameter ratios (e/Dh) are 0.125, 0.094, and 0.078, for AR=1:1, AR=1:2, and AR=1:4 channels, respectively. The channel orientations are set as 90 degrees, the rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. The last type is the rotating two-pass smooth channel with three aspect ratios (AR=1:1; AR=1:2; AR=1:4). Detailed predictions of mean velocity, mean temperature and Nusselt number for two Reynolds numbers (Re=10,000 and Re=100,000) were carried out. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure.Item Temperature dependent refractive index of lipid tissue by optical coherence tomography imaging(2011-05) Lim, Hyunji; Milner, Thomas E.; Tunnell, JamesTemperature dependent optical properties of lipid tissue verify critical information of tissue dynamics which can be applied to tissue treatment and diagnosis of various pathological features. Current methods of treating lipid rich tissues via heating are associated with post operation complications. Recent studies shows potential of lipid rich tissue removal by cooling. For monitoring cooling procedure and physical and chemical changes in lipid tissue, temperature dependent optical properties in subzero cooling need to be verified. This study designed heat transfer system estimating heat flux by cooling and programmed codes for image and data processing to obtain refractive indices of rodent subcutaneous lipid tissue. Phase transition of lipid tissue was observed and finally verified temperature dependent refractive index coefficient of lipid tissue from 24°C to -10°C.