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- Title
- A Case Study of a Solar Augmented Heating System Versus A Solar Assisted Heat Pump.
- Creator
-
Braleski, Louis P., Klee, Harold, Engineering
- Abstract / Description
-
Florida Technological University College of Engineering Thesis; The usage and applications of solar energy are numerous; however, it's still in its infancy. The subject matter discusses two applications of solar energy, a "Solar Augmented Heated System" and a "Solar Assisted Heat Pump." The solar augmented system and the solar assisted system have the same components; however, the way they are used is of primary concern. A solar system in parallel with a heat pump is called "Solar Augmented...
Show moreFlorida Technological University College of Engineering Thesis; The usage and applications of solar energy are numerous; however, it's still in its infancy. The subject matter discusses two applications of solar energy, a "Solar Augmented Heated System" and a "Solar Assisted Heat Pump." The solar augmented system and the solar assisted system have the same components; however, the way they are used is of primary concern. A solar system in parallel with a heat pump is called "Solar Augmented Heating System" or in series with a heat pump is a "Solar Assisted Heat Pump" A 2000 ft2 house was utilized as the basis of the design. The heating load was calculated from the construction materials. With this information the collector area, tank volume and heat pump sizes were determined. Once the system size and design was completed, TRNSYS, a "Transient Simulation Program" was used to simulate the two systems. A comparison was made of the two systems for a 21 day period to determine which of the two systems is more advantageous to use.
Show less - Date Issued
- 1978
- Identifier
- CFR0008158, ucf:53079
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFR0008158
- Title
- EXPLORING ENVIRONMENTAL HEAT INJURIES IN THE PEDIATRIC POPULATION.
- Creator
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Bowman, Jennifer, Heglund, Stephen, University of Central Florida
- Abstract / Description
-
Children are considered a vulnerable population in society. While thermoregulation in children is similar to that of an adult, children are vulnerable to heat-related illness. Student athletes have been found to be particularly vulnerable to heat-related illness for numerous reasons, including intense outdoor play. Football players are perhaps the most at-risk population of student athletes due to the intense physical requirements, outdoor practice during the hottest months of the year, and...
Show moreChildren are considered a vulnerable population in society. While thermoregulation in children is similar to that of an adult, children are vulnerable to heat-related illness. Student athletes have been found to be particularly vulnerable to heat-related illness for numerous reasons, including intense outdoor play. Football players are perhaps the most at-risk population of student athletes due to the intense physical requirements, outdoor practice during the hottest months of the year, and the extensive protective equipment required. By conducting a literature review on the subject of pediatric heat illness, the purpose of this thesis is to explore evidenced based research and guidelines regarding heat-related illness prevention. This review of literature was conducted through the utilization of the University of Central Florida's online databases using the EBSCOhost platform of: CINAHL Plus with Full Text, Cochrane Database of Systematic Reviews, ERIC, Health Source: Nursing/Academic Edition, MEDLINE, PsycINFO and SPORTDiscus. This thesis is unique because it does not focus on an individual sport; rather, it focuses on pediatric athletes from various disciplines. The prevalence, pathophysiology, prevention, and treatment of heat-related injuries are complex phenomena requiring the attention of law makers, athletic associations, school officials, coaches, athletic trainers, parents, and students.
Show less - Date Issued
- 2019
- Identifier
- CFH2000568, ucf:45667
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000568
- Title
- CONJUGATE HEAT TRANSFER ON A GAS TURBINE BLADE.
- Creator
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Salazar, Santiago, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
Clearances between gas turbine casings and rotating blades is of quite importance on turbo machines since a significant loss of efficiency can occur if the clearances are not predicted accordingly. The radial thermal growths of the blade may be over or under predicted if poor assumptions are made on calculating the metal temperatures of the surfaces exposed to the fluid. The external surface of the blade is exposed to hot gas temperatures and it is internally cooled with air coming from the...
Show moreClearances between gas turbine casings and rotating blades is of quite importance on turbo machines since a significant loss of efficiency can occur if the clearances are not predicted accordingly. The radial thermal growths of the blade may be over or under predicted if poor assumptions are made on calculating the metal temperatures of the surfaces exposed to the fluid. The external surface of the blade is exposed to hot gas temperatures and it is internally cooled with air coming from the compressor. This cold air enters the radial channels at the root of the blade and then exists at the tip. To obtain close to realistic metal temperatures on the blade, the Conjugate Heat Transfer (CHT) approach would be utilized in this research. The radial thermal growth of the blade would be then compared to the initial guess. This work focuses on the interaction between the external boundary conditions obtained from the commercial Computational Fluid Dynamics software package CFX, the internal boundary conditions along the channels from a 1D flow solver proprietary to Siemens Energy, and the 3D metal temperatures and deformation of the blade predicted using the commercial Solid Mechanics software package ANSYS. An iterative technique to solve CHT problems is demonstrated and discussed. The results of this work help to highlight the importance of CHT in predicting metal temperatures and the implications it has in other aspect of the gas turbine design such as the tip clearances.
Show less - Date Issued
- 2010
- Identifier
- CFE0003398, ucf:48375
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003398
- Title
- THE EFFECT OF HEAT TRANSFER COEFFICIENT ON HIGH ASPECT RATIO CHANNEL ACCOMPANIED BY VARYING RIB ASPECT RATIO.
- Creator
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Le, An, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Heat transfer and pressure data were performed and reported on two different rigs. The first rig has an aspect ratio of (19:1) with two different inlet conditions and the second rig is composed of two different aspect ratio channels, (1:8) and (1:4). Rib turbulators were used as a flow disruptor scheme to enhance the heat transfer and friction factor. Rib aspect ratios ranging from (1:1) to (1:5) rib-height-to-width ratio were used. The first channel rib-width-to-pitch (Wr/P) ratio was kept...
Show moreHeat transfer and pressure data were performed and reported on two different rigs. The first rig has an aspect ratio of (19:1) with two different inlet conditions and the second rig is composed of two different aspect ratio channels, (1:8) and (1:4). Rib turbulators were used as a flow disruptor scheme to enhance the heat transfer and friction factor. Rib aspect ratios ranging from (1:1) to (1:5) rib-height-to-width ratio were used. The first channel rib-width-to-pitch (Wr/P) ratio was kept at 1/2 where flow was kept at relatively low Reynolds numbers, between 3000 and 13000. Results from the current tests showed that existing correlations could be used for high aspect ratio channels in predicting the effectiveness of the cooling scheme. Two different inlet conditions were tested; one was arranged so that the flow was hydrodynamically fully-developed at the entrance of the heated section, while the other uses an abrupt entrance from bleeding off mass flow from a horizontal channel. The heat transfer augmentation (compared to a well known and accepted correlation proposed by Dittus-Boelter) in these channels are extremely high with an average of 350% to 400%. However, this was accompanied by a substantial increase in the pressure drop, causing the overall thermal performance to increase between twenty to thirty percent. The second channel rib-width-to-pitch ratio (Wr/P) ranges from 0.1, 0.3, and 0.5; the flow conditions are tested from 20,000 to 40,000 Reynolds number. Correlations for heat transfer and friction augmentation of the test data was also given. The test shows large rib blockage ratio does not demonstrate the best thermal performance; however it does give a high heat transfer augmentation ranging from 200 to 300 percent for both aspect ratios depending on the width of the used ribs.
Show less - Date Issued
- 2009
- Identifier
- CFE0002782, ucf:48130
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002782
- Title
- Investigation of Heat Transfer Enhancement Within a Concentric Annulus.
- Creator
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Hanhold, Alexander, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
Effective heat exchange is key for many energy applications including heat exchangers, heat extraction from heat source, and heat rejection to ambient thermal sink. This study focuses on the investigation for a specific heat exchange configuration, namely heat removal within a concentric annular passage using helical turbulators and jet impingement. Numerical testing was used to see how the different geometric parameters affect the heat transfer and pressure drop within the annulus by using...
Show moreEffective heat exchange is key for many energy applications including heat exchangers, heat extraction from heat source, and heat rejection to ambient thermal sink. This study focuses on the investigation for a specific heat exchange configuration, namely heat removal within a concentric annular passage using helical turbulators and jet impingement. Numerical testing was used to see how the different geometric parameters affect the heat transfer and pressure drop within the annulus by using helicoil turbulators. A vast range of designs were studied by changing the turbulator shape, pitch, and blockage ratio while maintaining a constant Reynolds number of 25,000. CFD was performed in STARCCM+ using the realizable ?-? turbulence model. Results show that turbulence and heat transfer increase with a higher blockage ratio and smaller pitch but the pressure drop is subsequently increased as well. The square turbulator promoted higher heat transfer compared to the circle turbulator but the pressure drop was significantly increased when the helix angle was greater than 20(&)deg; and blockage ratio greater than 0.48.Experimental and numerical efforts were used to find the heat transfer due to impingement jets on the target surface. Multiple flows as a function of jet Reynolds number ranging from 16,000-33,000 were tested for two geometries. Temperature Sensitive Paint (TSP) was utilized to observe local heat transfer. It was observed that jet degradation occurs after the 6th row of stream-wise impingement jets for both cases experimentally and it was difficult to numerically capture the effect of the cross flow from previous jets but managed to follow the same trend. The numerical results showed that they can be used with good agreement to predict the surface averaged Nusselt number to be within the 12% uncertainty found from experimental efforts. Geometry B was determined to perform better in terms of heat transfer as opposed to Geometry A with the same pressure loss.
Show less - Date Issued
- 2017
- Identifier
- CFE0007286, ucf:52155
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007286
- Title
- DESIGNING OF ENERGY EFFICIENT INDOOR ENVIRONMENTS USING A LOCALIZED RADIAL BASIS FUNCTION MESHLESS METHOD.
- Creator
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Huayamave, Victor, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
Around the world, the energy over consumption issue has been one of the key socio-economic and political challenges, which has drastically worsened over the last few years. Over the years engineers and environmentalists have proposed several approaches to improve energy efficiency. One is to reduce energy demand by improving consumption habits and a second approach is to introduce the use of a "greener" concept by using biomaterials in a diverse and more efficient manner in engineering...
Show moreAround the world, the energy over consumption issue has been one of the key socio-economic and political challenges, which has drastically worsened over the last few years. Over the years engineers and environmentalists have proposed several approaches to improve energy efficiency. One is to reduce energy demand by improving consumption habits and a second approach is to introduce the use of a "greener" concept by using biomaterials in a diverse and more efficient manner in engineering construction to create energy efficient environments. This work will investigate the effects of using "green" stabilized earth materials to provide and enhance thermal regulation for indoor environments. This effects can be compared to what skin does to regulate body temperature in humans, animals, and plants. On this effort the thermal behavior of several biomaterials will be analyzed using a computational tool in order to test the mechanical properties of biomaterials and also several geometry configurations to minimize the energy needed for heating and cooling an environment. In this research a localized radial basis function (LRBF) meshless method, developed by the Computational Mechanics Lab (CML) at the University of Central Florida, has been implemented to test several wall geometrical configuration using known biomaterials such as clay. The advantage of using the LRBF meshless method in this particular research is based in the accuracy of the numerical method and also because it decreases computation time regardless of model complexity geometry without the need of mesh generation. This research includes a complete description of the LRBF meshless method, as well as a quantification of cooling methods that have been used by past civilizations and recent construction standards but have not been validated on scientific basis. Results are presented which will demonstrate the effectiveness of using integrated sheets of biomaterials in engineering construction to increase energy efficiency in indoor environments.
Show less - Date Issued
- 2010
- Identifier
- CFE0003335, ucf:48478
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003335
- Title
- SOUNDING ROCKET REDESIGN AND OPTIMIZATION FOR PAYLOAD EXPANSION AND IN FLIGHT TELEMETRY TRANSMITTAL.
- Creator
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Huffman, Matthew, Chew, Larry, University of Central Florida
- Abstract / Description
-
Due to renewed interest in the sub orbital rocket program of the Florida Space Authority and a surplus of Super Loki Sounding Rockets, an effort to improve the usefulness of this surplus is herein undertaken. Currently, the capacity of the payload compartment in the upper stage of the Super Loki system is very limited. A redesign of the upper stage will allow larger and more versatile payloads to be carried, assuming the appropriate design parameters are met. It has therefore been undertaken...
Show moreDue to renewed interest in the sub orbital rocket program of the Florida Space Authority and a surplus of Super Loki Sounding Rockets, an effort to improve the usefulness of this surplus is herein undertaken. Currently, the capacity of the payload compartment in the upper stage of the Super Loki system is very limited. A redesign of the upper stage will allow larger and more versatile payloads to be carried, assuming the appropriate design parameters are met. It has therefore been undertaken to create a design procedure that is comprehensive in scope in order to affect this redesign. This procedure includes five major components. These are the separation of the upper and lower stages, the stability of the vehicle, the altitude and velocity of the rocket, the mechanical loading and finally the aerodynamic heating. Semi-empirical methods were used whenever possible to allow comparison with experimental data. This procedure revealed that larger diameter upper stages might be used up to a reasonable maximum of four inches. The four-inch modification is found to be stable as were the smaller modifications considered. The altitude and velocity of the rocket were found via a simple Eulerian time stepping scheme resulting in an estimate of approximately 148,000ft for the four-inch dart. The mechanical loading analysis allowed for the material selection for the rocket components. Reinforced steel fins and carbon fiber tubing, for the payload section, are adequate to meet expected mechanical loads, those being, 16000psi for the fin section due to launcher forces, 22800psi for compressive plus torsion forces on the composite section and 18000psi for the ejection stresses. An ablative coating is considered necessary to counteract the 760ºF temperatures along the composite tube.
Show less - Date Issued
- 2005
- Identifier
- CFE0000546, ucf:46440
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000546
- Title
- DESIGN OF SEA WATER HEAT EXCHANGERFOR MINIATURE VAPOR COMPRESSION CYCLE.
- Creator
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Hughes, James, Chow, Louis, University of Central Florida
- Abstract / Description
-
Recent advances in the development of miniature vapor compression cycle components have created unique opportunities for heating and cooling applications, specifically to human physiological requirements that arise in extreme environments. Diving in very cold water between 1.7 and 5°C requires active heating because passive thermal insulation has proven inadequate for long durations. To maintain diver mobility and cognitive performance, it is desirable to provide 250 to 300 W of heat from...
Show moreRecent advances in the development of miniature vapor compression cycle components have created unique opportunities for heating and cooling applications, specifically to human physiological requirements that arise in extreme environments. Diving in very cold water between 1.7 and 5°C requires active heating because passive thermal insulation has proven inadequate for long durations. To maintain diver mobility and cognitive performance, it is desirable to provide 250 to 300 W of heat from an un-tethered power source. The use of a miniature vapor compression cycle reduces the amount of power (batteries or fuel cell) that the diver must carry by 2.5 times over a standard resistive heater. This study develops the compact evaporator used to extract heat from the sea water to provide heat to the diver. The performance is calculated through the application of traditional single-phase and two-phase heat transfer correlations using numerical methods. Fabrication methods were investigated and then a prototype was manufactured. A test stand was developed to fully characterize the evaporator at various conditions. The evaporator is then evaluated for the conditions of interest. Test results suggest the correlations applied over predict performance up to 20%. The evaporator tested meets the performance specifications and design criteria and is ready for system integration.
Show less - Date Issued
- 2009
- Identifier
- CFE0002917, ucf:48016
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002917
- Title
- Convective Heat Transfer in Nanofluids.
- Creator
-
Schraudner, Steven, Vajravelu, Kuppalapalle, Mohapatra, Ram, Rollins, David, University of Central Florida
- Abstract / Description
-
In recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we...
Show moreIn recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we study the effects of radiation on the heat and mass transfer characteristics of nanofluid flows over solid surfaces. In Chapter 2, an investigation is made into the effects of radiation on mixed convection over a wedge embedded in a saturated porous medium with nanofluids, while in Chapter 3 results are presented for the effects of radiation on convection heat transfer about a cone embedded in a saturated porous medium with nanofluids. The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results in the literature, and the results are found to be in very good agreement. The numerical results for the velocity, temperature, volume fraction, the local Nusselt number and the Sherwood number are presented graphically. The salient features of the results are analyzed and discussed for several sets of values of the pertinent parameters. Also, the effects of the Rosseland diffusion and the Brownian motion are discussed.
Show less - Date Issued
- 2012
- Identifier
- CFE0004214, ucf:49024
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004214
- Title
- ELL AND NON-ELL STUDENTSÂÂ' MISCONCEPTIONS ABOUT HEAT AND TEMPERATURE IN MIDDLE SCHOOL.
- Creator
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Weiss, Leah, Jeanpierre, Bobby, University of Central Florida
- Abstract / Description
-
ABSTRACT All students come to the classroom with their own ideas about a number of science phenomena. In the classroom setting, English language learners may have ideas about heat and temperature that present additional challenges for teachers. In fact, their ideas can stem from many different influences and English language learners (ELL), in particular, may have misconceptions about topics and language barriers, or misconceptions, that are culturally or language-based (Lee, 2001). This...
Show moreABSTRACT All students come to the classroom with their own ideas about a number of science phenomena. In the classroom setting, English language learners may have ideas about heat and temperature that present additional challenges for teachers. In fact, their ideas can stem from many different influences and English language learners (ELL), in particular, may have misconceptions about topics and language barriers, or misconceptions, that are culturally or language-based (Lee, 2001). This action research thesis was performed to explore the research questions: How did my use of formative assessment affect ELL studentsÂÂ' misconceptions about heat?, How did my use of formative assessment uncover studentsÂÂ' misconceptions about heat? Formative assessments were used in the classroom to uncover studentsÂÂ' misconceptions about heat and temperature. The students performed labs based on the formative assessment activity sheets. The students answer before and after questions related to the labs. Data were collected and analyzed to examine changes in ELL studentsÂÂ' conceptions of heat and temperature. Data showed that some ELL students changed their ideas about heat and temperature but other misconceptions remained. Time allotted to instruction and alignment of laboratory activities with formative assessments need to be further explored to address changing studentsÂÂ' ideas about heat and temperature.
Show less - Date Issued
- 2010
- Identifier
- CFE0003238, ucf:48534
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003238
- Title
- Study of High Efficiency Micro Thermoelectric Energy Harvesters.
- Creator
-
Pedrosa, Steven, Chen, Quanfang, Cho, Hyoung, Xu, Yunjun, University of Central Florida
- Abstract / Description
-
Thermal energy sources, including waste heat and thermal radiation from the sun, are important renewable energy resources. Thermal energy can be converted into electricity by thermoelectric phenomena; the thermoelectric phenomena can also be operated in reverse when provided an electric current, producing a temperature gradient across the device. Thermoelectric devices are scalable, renewable, and cost effective products that offer capabilities to harness waste heat or environmental heat...
Show moreThermal energy sources, including waste heat and thermal radiation from the sun, are important renewable energy resources. Thermal energy can be converted into electricity by thermoelectric phenomena; the thermoelectric phenomena can also be operated in reverse when provided an electric current, producing a temperature gradient across the device. Thermoelectric devices are scalable, renewable, and cost effective products that offer capabilities to harness waste heat or environmental heat sources, and convert the captured heat into usable electricity. The operating principle of a thermoelectric device requires that a temperature gradient be present across the device, which induces the flow of electrons from the hot side of the device to the cold side. Thermoelectric devices are currently hampered by the low conversion efficiencies and strict operating temperatures for certain materials. This study investigates the main factors affecting efficiencies of thermoelectric devices as energy harvesters and aims to optimize the devices for maximum efficiency and lower costs by using microfabrication processes and self-assembled materials for complete thermoelectric modules (TEMs). By first establishing operating conditions and a desired mode of operation, optimization equations have been established to determine device dimensions and performance parameters. Compact integration realized by microfabrication technologies that allow for multiple output voltages from a single chip was also investigated. Additionally, cost savings were found by reducing the number of fabrication processing steps and eliminating the need for precious metals during fabrication. The optimized design proposed in this study utilizes copper electrodes and requires fewer applications of photoresist than previous proposed designs. In fabrication of thin film based micro devices, the film quality and the composition of the film are essential elements for producing TEMs with desired efficiencies. Although Bi2Te3 has been investigated as thermoelectric material, this study determined that there was a possibility that both N-type and P-Type Bi2Te3 could be created from a single electrolyte solution by controlling the amount of Te present in the film. Films were produced with both AC and DC signals and varied composition of Te at.% of Bi2Te3 was achieved by controlling the average current density during electrochemical deposition. A linear relationship was established between the average current density and the resultant Te content. SEM and EDS were used to characterize the morphology and the composition of the thin films created. With the fabricated thermoelectric materials, analytical models could be developed using known material properties of thermoelectric films with a given Te content. The analytical results obtained by the developed optimization equations were comparable with the FEA models produced by using COMSOL, a multiphysics program with powerful solving algorithms that was used to evaluate designs. Further improvements to device performance can be achieved by designing a segmented thermoelectric device with multiple layers of thermoelectric material to allow the device to operate across a larger temperature gradient.
Show less - Date Issued
- 2011
- Identifier
- CFE0004486, ucf:49318
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004486
- Title
- Heat Transfer and Friction Augmentation in a Narrow Rectangular Duct with Symmetrical and Non-Symmetrical Wedge-Shaped Turbulators.
- Creator
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Valentino, Michelle, Kapat, Jayanta, Deng, Weiwei, Kassab, Alain, University of Central Florida
- Abstract / Description
-
The need for cleaner and more fuel efficient means to produce electricity is growing steadily. Advancements in cooling technologies contribute to the improvements in turbine efficiency and are used for gas turbines and for power generation in automotive, aviation, as well as in naval applications, and many more. Studies introducing turbulators on walls of internal cooling channels, which can be applied to hot gas components and in recuperative heat exchangers, have been reviewed for their...
Show moreThe need for cleaner and more fuel efficient means to produce electricity is growing steadily. Advancements in cooling technologies contribute to the improvements in turbine efficiency and are used for gas turbines and for power generation in automotive, aviation, as well as in naval applications, and many more. Studies introducing turbulators on walls of internal cooling channels, which can be applied to hot gas components and in recuperative heat exchangers, have been reviewed for their ability to promote heat transfer in the channel while observing pressure loss caused by adding the features. Several types of turbulators have been studied; ribs, pin fins, dimples, wedges, and scales are some examples of features that have been added to walls of internal cooling channels or heat exchangers to increase heat transfer. This study focuses on two types of wedge turbulator designs, a full symmetrical wedge and a half, or non-symmetrical right-triangular wedge for the purpose of disrupting the thermal boundary layer close to hot walls without causing large-scale mixing and pressure drops. There are two sizes of the wedges, the first set of full and half wedges have an e/Dh=0.10 with the second at e/Dh=0.40, a feature that fills the height of the boundary layer. There are six cases studied, two one-wall and four two-wall cases in a 2:1 aspect ratio channel at Reynolds numbers of 10,000, 20,000, 30,000, and 40,000. Two experimental setups are utilized: a segmented copper block and transient TLC, along with numerical simulation for computational flow visualization. Wall temperature data is collected from all four walls for the copper experimental setup and three walls on the transient TLC setup. The fourth wall of the acrylic test section for the transient TLC tests is utilized for pressure testing, where static pressure ports are placed along the side wall. Although the small features did not show large influence in heat transfer on the side walls as much as the larger features or as high of heat transfer on the featured walls, the minimal pressure loss in the channel kept overall thermal performance of the small two wall full wedge features very high. The case of the large half wedge on two walls also showed very high thermal performance, having pressure loss values nearly half of the same sized (length and height) full wedge feature while having the ability to incorporate side walls into the overall heat transfer enhancement. The results found in the experimental setups are supported by the visualization of flow characteristics from the numerical testing. Comparing the initial wedge study to recent full rib studies show the wedges have similar improvements in heat transfer to the full rib cases with friction augmentations 5 to 10 times lower than the full rib cases. Further improvements to wedge heat transfer and pressure drop can be done by determining optimal wedge size and orientation.
Show less - Date Issued
- 2011
- Identifier
- CFE0004489, ucf:49299
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004489
- Title
- A Full Coverage Film Cooling Study: The Effect of an Alternating Compound Angle.
- Creator
-
Hodges, Justin, Kapat, Jayanta, Gordon, Ali, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
This thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f...
Show moreThis thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f turbulence model predicted film cooling effectiveness throughout the array, as compared with experimental data. The two staggered arrays tested are different from one another through a compound angle shift after 12 rows of holes. The compound angle shifts from ?=-45(&)deg; to ?=+45(&)deg; at row 13. Each geometry had 22 rows of cylindrical film cooling holes with identical axial and lateral spacing (X/D=P/D=23). Levels of laterally averaged film cooling effectiveness for the superior geometry approach 0.20, where the compound angle shift causes a decrease in film cooling effectiveness. Levels of heat transfer augmentation maintain values of nearly h/h0=1.2. There is no effect of compound angle shift on heat transfer augmentation observed. The CFD results are used to investigate the detrimental effect of the compound angle shift, while the SST k-? turbulence model shows to provide the best agreement with experimental results.
Show less - Date Issued
- 2015
- Identifier
- CFE0005626, ucf:50228
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005626
- Title
- HIGH HEAT FLUX SPRAY COOLING WITH AMMONIA ON ENHANCED SURFACES.
- Creator
-
Bostanci, Huseyin, Chow, Louis, University of Central Florida
- Abstract / Description
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Many critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several oC across the...
Show moreMany critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several oC across the cooled device) aspects, as well as system mass, volume and power consumption, spray cooling appears to be the best choice. The current study focused on high heat flux spray cooling with ammonia on enhanced surfaces. Compared to some other commonly used coolants, ammonia possesses important advantages such as low saturation temperature, and high heat absorbing capability. Moreover, enhanced surfaces offer potential to greatly improve heat transfer performance. The main objectives of the study were to investigate the effect of surface enhancement on spray cooling performance, and contribute to the current understanding of spray cooling heat transfer mechanisms. These objectives were pursued through a two stage experimental study. While the first stage investigated enhanced surfaces for the highest heat transfer coefficient at heat fluxes of up to 500 W/cm2, the second stage investigated the optimized enhanced surfaces for critical heat flux (CHF). Surface modification techniques were utilized to obtain micro scale indentations and protrusions, and macro (mm) scale pyramidal, triangular, rectangular, and square pin fins. A third group, multi-scale structured surfaces, combined macro and micro scale structures. Experimental results indicated that micro- and macrostructured surfaces can provide heat transfer coefficients of up to 534,000 and 426,000 W/m2oC at 500 W/cm2, respectively. Multi-scale structured surfaces offered even a better performance, with heat transfer coefficients of up to 772,000 W/m2oC at 500 W/cm2, corresponding to a 161% increase over the reference smooth surface. In CHF tests, the optimized multi-scale structured surface helped increase maximum heat flux limit by 18%, to 910 W/cm2 at nominal liquid flow rate. During the additional CHF testing at higher flow rates, most heaters experienced failures before reaching CHF at heat fluxes above 950 W/cm2. However, the effect of flow rate was still characterized, suggesting that enhanced surfaces can achieve CHF values of up to 1,100 W/cm2 with 67% spray cooling efficiency. The results also helped shed some light on the current understanding of the spray cooling heat transfer mechanisms. Data clearly proved that in addition to fairly well established mechanisms of forced convection in the single phase regime, and free surface evaporation and boiling through secondary nucleation in the two phase regime, enhanced surfaces can substantially improve boiling through surface nucleation, which can also be supported by the concept of three phase contact lines, the regions where solid, liquid and vapor phases meet. Furthermore, enhanced surfaces are capable of retaining more liquid compared to a smooth surface, and efficiently spread the liquid film via capillary force within the structures. This unique advantage delays the occurrence of dry patches at high heat fluxes, and leads to higher CHF.
Show less - Date Issued
- 2010
- Identifier
- CFE0003290, ucf:48502
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003290
- Title
- Development of Full Surface Transient Thermochromic Liquid Crystal Technique for Internal Cooling Channels.
- Creator
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Tran, Lucky, Kapat, Jayanta, Kassab, Alain, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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Proper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used. For detailed design, local distributions are needed in addition to bulk quantities....
Show moreProper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used. For detailed design, local distributions are needed in addition to bulk quantities. Detailed local distributions require advanced experimental techniques whereas they are readily available using numerical tools. Numerical predictions using a computational fluid dynamics approach with popular turbulence models are benchmarked against a semi-empirical correlation for the friction in a circular channel with repeated-rib roughness to demonstrate some shortcomings of the models used. Numerical predictions varied widely depending on the turbulence modelling approach used. The need for a compatible experimental dataset to accompany numerical simulations was discussed.An exact, closed-form analytical solution to the enhanced lumped capacitance model is derived. The temperature evolution in a representative 2D turbulated surface is simulated using Fluent to validate the model and its exact solution. A case including an interface contact resistance was included as well as various rib sizes to test the validity of the model over a range of conditions. The analysis was extended to the inter-rib region to investigate the extent and magnitude of the influence of the metallic rib features on the apparent heat transfer coefficients in the inter-rib region. It was found that the thermal contamination is limited only to the regions closest to the base of the rib feature.An experimental setup was developed, capable of measuring the local heat transfer distributions on all four channel walls of a rectangular channel (with aspect ratios between 1 and 5) at Reynolds numbers up to 150,000. The setup utilizes a transient thermochromic liquid crystals technique using narrow band crystals and a four camera setup. The setup is used to test a square channel with ribs applied to one wall. Using the transient thermochromic liquid crystals technique and applying it underneath high conductivity, metallic surface features, it is possible to calculate the heat transfer coefficient using a lumped heat capacitance approach. The enhanced lumped capacitance model is used to account for heat conduction into the substrate material. Rohacell and aluminum ribs adhered to the surface were used to tandem to validate the hybrid technique against the standard technique. Local data was also used to investigate the effect of thermal contamination. Thermal contamination observed empirically was more optimistic than numerical predictions.Traditional transient thermochromic liquid crystals technique utilizes the time-to-arrival of the peak intensity of the green color signal. The technique has been extended to utilize both the red and green color signals, increasing the throughput by recovering unused data while also allowing for a reduction in the experimental uncertainty of the calculated heat transfer coefficient. The over-determined system was solved using an un-weighted least squares approach. Uncertainty analysis of the multi-color technique demonstrated its superior performance over the single-color technique. The multi-color technique has the advantage of improved experimental uncertainty while being easy to implement.
Show less - Date Issued
- 2014
- Identifier
- CFE0005430, ucf:50436
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005430
- Title
- COMPARISON OF SQUARE-HOLE AND ROUND-HOLE FILM COOLING: A COMPUTATIONAL STUDY.
- Creator
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Durham, Michael Glenn, Kapat, Jay, University of Central Florida
- Abstract / Description
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Film cooling is a method used to protect surfaces exposed to high-temperature flows such as those that exist in gas turbines. It involves the injection of secondary fluid (at a lower temperature than that of the main flow) that covers the surface to be protected. This injection is through holes that can have various shapes; simple shapes such as those with a straight circular (by drilling) or straight square (by EDM) cross-section are relatively easy and inexpensive to create. Immediately...
Show moreFilm cooling is a method used to protect surfaces exposed to high-temperature flows such as those that exist in gas turbines. It involves the injection of secondary fluid (at a lower temperature than that of the main flow) that covers the surface to be protected. This injection is through holes that can have various shapes; simple shapes such as those with a straight circular (by drilling) or straight square (by EDM) cross-section are relatively easy and inexpensive to create. Immediately downstream of the exit of a film cooling hole, a so-called horseshoe vortex structure consisting of a pair of counter-rotating vortices is formed. This vortex formation has an effect on the distribution of film coolant over the surface being protected. The fluid dynamics of these vortices is dependent upon the shape of the film cooling holes, and therefore so is the film coolant coverage which determines the film cooling effectiveness distribution and also has an effect on the heat transfer coefficient distribution. Differences in horseshoe vortex structures and in resultant effectiveness distributions are shown for circular and square hole cases for blowing ratios of 0.33, 0.50, 0.67, 1.00, and 1.33. The film cooling effectiveness values obtained are compared with experimental and computational data of Yuen and Martinez-Botas (2003a) and Walters and Leylek (1997). It was found that in the main flow portion of the domain immediately downstream of the cooling hole exit, there is greater lateral separation between the vortices in the horseshoe vortex pair for the case of the square hole. This was found to result in the square hole providing greater centerline film cooling effectiveness immediately downstream of the hole and better lateral film coolant coverage far downstream of the hole.
Show less - Date Issued
- 2004
- Identifier
- CFE0000044, ucf:46080
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000044
- Title
- EXPERIMENTS IN POOL BOILING HEAT TRANSFER AND NUCLEATIONDYNAMICS OF HIGH PRESSURE REFRIGERANTS.
- Creator
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Joo, Daniel, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
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A high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable...
Show moreA high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable of studying the physics and thermodynamics of refrigerants under nucleate pool boiling. The main objective of this experiment was the design of the experimental setup. Various designs were tested and validated, of which all incorporated a pressure resistant chamber constructed out of aluminum and glass viewing ports. Design parameters such as the heating element thickness were verified using a transient FEA thermal model. This model, which was developed in ANSYS, verified that this design would be able to capture the thermal response of the thermochromatic liquid crystals. This analysis concluded that a negligible error of 0.02°C is expected due to transient effects. Difficulties were encountered during early stages of development; most notable were imaging limitations such as low camera frame-rates and poor resolution. Since a TLC technique was used to measure the temperature of the boiling surface, a camera system fast enough to capture the thermal response was needed. At bubble frequencies of 30 nucleations per second, it was necessary for the camera to have much higher frame rates. Through the use of two synchronized cameras, the surface temperature, position, size and shape of the bubbles were recorded simultaneously. Two camera systems were designed and tested. The first system consisted of a high speed CMOS camera capable of capturing 1,000 frames per second, and an RBG CCD color camera capable of 30 Frames per second. However, this system was limited the slow frame rate and low resolution of the RBG camera. The second system used two high resolution and fast shutter speed cameras, which were able to capture fast bubble nucleations. This method required the assumption that under constant operating conditions, the path of one bubble was identical to the next. This method was tested utilizing the high speed camera, and was shown that there was less than a .04% deviation from the path any bubble to that of the next. Detailed analysis of nucleating surface temperatures using thermochromatic liquid crystal technique and temporal-temperature response under various heat flux and at 813.6kPa (118Psia) and 882.5kPa (128Psia) was performed. It is seen that temperature distribution is quite varied in each case. At high pressures the size of nucleation site decreases, giving rise to an increase in the surface temperature. Bubble growth is also analyzed through the use of high speed cameras and compared to temperature distributions. Simultaneous temperature and bubble size measurements provided a correlation between bubble growth and heat transfer. Boiling parameters such as bubble frequency, bubble size, and contact area are also analyzed. From the surface temperature plots, the local and average heat transfer coefficients were calculated as a function of time and bubble dynamics.
Show less - Date Issued
- 2006
- Identifier
- CFE0001489, ucf:47106
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001489
- Title
- Investigation of Flow Field Structures in a Rectangular Channel with a Pin Fin Array.
- Creator
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Tran, Patrick, Kapat, Jayanta, Bhattacharya, Samik, Huang, Helen, University of Central Florida
- Abstract / Description
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Pin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in...
Show morePin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in the wake region, where KV are dominate. These flow structures increase the local levels turbulence and generate eddies that promote flow mixing, which in turn allows for higher levels of heat transfer. Improvement in heat transfer can increase the efficiency of the heat exchanger by reducing the thermal load and stress on the components which can extended product life. A study of the vortex shedding using a Particle Image Velocimetry (PIV) technique is used to measure flow field using a closed loop vertical water tunnel. A Time Resolved Particle Image Velocimetry (TR-PIV) study for both steady and unsteady flow structures in the fully developed region of a pin fin array at multiple wall normal cross sections are performed. The pin fin array consists of circular pin fins with 8 rows of 7.5 pins in rectangular channel with Reynolds number varying from 10,000 to 20,000. The Pin array is in a staggered configuration with stream wise (Y/D) spacing of 2.5 and span wise (X/D) spacing of 2.5, and height to pin diameter (H/D) of 2. A supplemental computation fluid dynamic (CFD) study is also for comparison with the PIV flow field. The goal of the present study is to determine the major vortex structures that found the flow at different Z/D, quantify parameters that numerical methods are unable to solve, and provide a base line for other parameters that can be used to improve the accuracy of numerical models. The novelty of this work is to provide data and characterize the near the viscous sub layer of Z/D =0.
Show less - Date Issued
- 2019
- Identifier
- CFE0007736, ucf:52446
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007736
- Title
- Improving Turbine Performance: A Contribution to the Understanding of Heat Transfer and Vortical Structures in Staggered Pin Fin Arrays.
- Creator
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Otto, Marcel, Kapat, Jayanta, Ahmed, Kareem, Bhattacharya, Samik, Kinzel, Michael, Wiegand, Rudolf, University of Central Florida
- Abstract / Description
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Through the comparison of flow structures, velocity contours, turbulence statistics, and additional flow quantities, the error sources of RANS are qualitatively described. The findings in this work will help gas turbine design engineers to tweak their turbulence models and give guidance on the interpretation of their results. The novelty is the application of the transient TLC method on this type of geometry as well as the near-wall PIV measurements. The advancements in additive manufacturing...
Show moreThrough the comparison of flow structures, velocity contours, turbulence statistics, and additional flow quantities, the error sources of RANS are qualitatively described. The findings in this work will help gas turbine design engineers to tweak their turbulence models and give guidance on the interpretation of their results. The novelty is the application of the transient TLC method on this type of geometry as well as the near-wall PIV measurements. The advancements in additive manufacturing disrupt the classic turbine cooling development for casted airfoils. More and more complicated shapes and cooling schemes are possible. Nonetheless, a detailed physical understanding of fundamental cases - as provided in this study - is required for physics-based optimization of cooling designs.
Show less - Date Issued
- 2019
- Identifier
- CFE0007848, ucf:52803
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007848
- Title
- An experimental investigation on the dynamics of bubbles utilizing refrigerant R134a under pressurized flow boiling conditions.
- Creator
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Vereen, Keon, Kumar, Ranganathan, Chow, Louis, Deng, Weiwei, University of Central Florida
- Abstract / Description
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Flow boiling heat transfer allows for the dissipation of large amounts of heat. In this work, the effect of heat flux and pressure on flow boiling of liquid refrigerant R-134a is studied in a vertical thin channel. The experimental setup mimics a refrigeration cycle and specifically looks at the effect of pressure and wall heat flux on the departure size and bubble generation rate. The experimental setup consists of a closed loop which includes a vertical narrow rectangular channel and two...
Show moreFlow boiling heat transfer allows for the dissipation of large amounts of heat. In this work, the effect of heat flux and pressure on flow boiling of liquid refrigerant R-134a is studied in a vertical thin channel. The experimental setup mimics a refrigeration cycle and specifically looks at the effect of pressure and wall heat flux on the departure size and bubble generation rate. The experimental setup consists of a closed loop which includes a vertical narrow rectangular channel and two synchronized high speed cameras for optical measurements at either sides of the channel. The setup is built to employ an accurate measurement technique to define wall temperatures of the representative flow boiling process. Instead of using thermocouples on the surface channel, the thermochromic liquid crystallography (TLC) technique is used to determine non-invasively the heater surface temperature at high temporal and spatial resolution. The TLC interval range is 30-50(&)deg;C. The TLC is attached to a Fecralloy heating section. The high speed Prosilica cameras simultaneously capture, colored TLC images as well as bubble nucleation and departure at very high frame rates. Experiments on subcooled flow boiling heat transfer have been conducted with refrigerant R-134a under a mass flux range of 484.838 kg/m2s to 1212.1 kg/m2s. With the low mass flux, the wall heat flux ranged from 167.2 to 672.1 kW/m2, the inlet subcooling ranged from 0.35(&)deg;C to 16.55 (&)deg;C, the system pressure ranged from 621 kPa to 1034 kPa. At high mass flux, the wall heat flux ranged from 329.8 kW/m2 to 744 kW/m2, the inlet subcooling from 0.16(&)deg;C to 17.21 (&)deg;C, and the system pressure from 621 kPa to 1034 kPa. A parametric study was done by maintaining various input parameters constant.From the high speed images, bubble parameters such as size and frequency are calculated. Temperature contours are utilized to determine the surface wall temperature at specific points. Sequential wall temperatures are traced over a short period of time to understand the cooling effects. The bubble propagation and coalescence are also visualized. Results show that bubble size and frequency increased with heat flux at any particular pressure. At higher pressure, the trend would be for the bubble size to decrease; however, the inlet subcooling and heat flux also affect bubble size. The bubble frequency is also seen to be affected by the inlet subcooling and the heat flux. Even though the inlet subcooling is maintained approximately constant, any slight decrease in subcooling increased bubble growth rate. Another trend that is observed is that at higher the heat flux, the bubble generation frequency is faster; however no specific trend is observed for wall superheat. With an increase in heat flux, the wall superheats are expected to increase; however, the localized nature of the nucleation activity sites is seen to affect the results. The variables are non-dimensionalized to note trends in parameters. In summary, the data analysis demonstrates that both heat flux and pressure significantly influence the bubble generation rate, size, propagation and coalescence.
Show less - Date Issued
- 2011
- Identifier
- CFE0004175, ucf:49077
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004175
