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COMPARISON OF SQUARE-HOLE AND ROUND-HOLE FILM COOLING: A COMPUTATIONAL STUDY
Title
COMPARISON OF SQUARE-HOLE AND ROUND-HOLE FILM COOLING: A COMPUTATIONAL STUDY.
Creator
Durham, Michael Glenn, Kapat, Jay, University of Central Florida
Abstract / Description
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.
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Date Issued
2004
Identifier
CFE0000044, ucf:46080
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000044
NOVEL CONCEPTUAL DESIGN AND ANLYSIS OF POLYMER DERIVED CERAMIC MEMS SENSORS FOR GAS TURBINE ENVIRONMENT
Title
NOVEL CONCEPTUAL DESIGN AND ANLYSIS OF POLYMER DERIVED CERAMIC MEMS SENSORS FOR GAS TURBINE ENVIRONMENT.
Creator
Nagaiah, Narasimha, Kapat, Jay, University of Central Florida
Abstract / Description
Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are...
Show moreTechnical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology. However, these nondirective measuring technologies lack the necessary accuracy, at least at present state. An alternative way to measure these parameters without disturbing the working environments is using MEMS type sensors. Currently, the techniques under development for such harsh environment applications are silicon carbide (SiC) and silicon nitrite (Si3N4) –based ceramic MEMS sensors. But those technologies present some limitation such as narrow processing method, high cost (materials and processing cost), and limited using temperatures (typically < 800 C). In this research we propose to develop two sensors based on recently developed polymer-derived ceramics (PDCs): Constant Temperature Hot wire Anemometer, temperature/heat-flux sensor for turbine applications. PDC is a new class of high temperature ceramics. As we shall describe below, many unique features of PDCs make them particularly suitable for the proposed sensors, including: excellent thermo-mechanical properties at high temperatures, enable high temperature operation of the devices; various well-developed processing technologies, such as injection molding,photolithography, embossing, DRIE etching and precise machining, can be used for the fabrication of the devices; and tunable electric conductivity, enable the proposed sensors fabricated from similar materials, thus reliability considerations associated with thermal mismatch, which is a big concern when using MEMS-based sensors at elevated temperatures, will be minimized.
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Date Issued
2006
Identifier
CFE0001285, ucf:46892
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001285
EFFECT OF RIB ASPECT RATIO ON HEAT TRANSFER AND FRICTION IN RECTANGULAR CHANNELS
Title
EFFECT OF RIB ASPECT RATIO ON HEAT TRANSFER AND FRICTION IN RECTANGULAR CHANNELS.
Creator
Tran, Lucky, kapat, Jay, University of Central Florida
Abstract / Description
The heat transfer and friction augmentation in the fully developed portion of a 2:1 aspect ratio rectangular channel with orthogonal ribs at channel Reynolds numbers of 20,000, 30,000, and 40,000 is studied both experimentally and computationally. Ribs are applied to the two opposite wide walls. The rib aspect ratio is varied systematically at 1, 3, and 5, with a constant rib height and constant rib pitch (rib-pitch-to-rib-height ratio of 10). The purpose of the study is to extend the...
Show moreThe heat transfer and friction augmentation in the fully developed portion of a 2:1 aspect ratio rectangular channel with orthogonal ribs at channel Reynolds numbers of 20,000, 30,000, and 40,000 is studied both experimentally and computationally. Ribs are applied to the two opposite wide walls. The rib aspect ratio is varied systematically at 1, 3, and 5, with a constant rib height and constant rib pitch (rib-pitch-to-rib-height ratio of 10). The purpose of the study is to extend the knowledge of the performance of rectangular channels with ribs to include high aspect ratio ribs. The experimental investigation is performed using transient Thermochromic Liquid Crystals technique to measure the distribution of the local Nusselt numbers on the ribbed walls. Overall channel pressure drop and friction factor augmentation is also obtained with the experimental setup. A numerical simulation is also performed by solving the 3-D Reynolds-averaged Navier-Stokes equations using the realizable-k-[episilon] turbulence model for closure. Flow visualization is obtained from the computational results as well as numerical predictions of local distributions of Nusselt numbers and overal channel pressure drop. Results indicate that with increasing rib width, the heat transfer augmentation of the ribbed walls decreases with a corresponding reduction in channel pressure drop.
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Date Issued
2011
Identifier
CFH0004103, ucf:44890
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0004103
PRESSURE DROP AND ENDWALL HEAT TRANSFER EFFECTS OF POROUS TURBULATORS IN A RECTANGULAR CHANNEL
Title
PRESSURE DROP AND ENDWALL HEAT TRANSFER EFFECTS OF POROUS TURBULATORS IN A RECTANGULAR CHANNEL.
Creator
Pent, Jared, Kapat, Jay, University of Central Florida
Abstract / Description
This study examines the local and averaged endwall heat transfer effects of a staggered array of porous pin fins within a rectangular channel. The porous pin fins were made from aluminum and had a pore density of 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates and presented in terms of the friction factor. Local heat transfer coefficients on the endwall were measured using Thermochromic Liquid Crystal (TLC) sheets recorded with a...
Show moreThis study examines the local and averaged endwall heat transfer effects of a staggered array of porous pin fins within a rectangular channel. The porous pin fins were made from aluminum and had a pore density of 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates and presented in terms of the friction factor. Local heat transfer coefficients on the endwall were measured using Thermochromic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. Results are presented for Reynolds numbers between 25000 and 130000 and a blockage ratio (blocked channel area divided by open channel area) of 50%. All results were compared to the corresponding results obtained using solid pins. All experiments were carried out in a 150 mm by 500 mm channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72 for the porous pins. It was found that for the range of Reynold's numbers tested in this study, the porous pin array consistently resulted in a larger friction factor, and therefore greater losses than a geometrically similar array of solid pins. The friction factors for the solid pin array were between 9.5 and 10.5, similar to the results found in the literature. For the porous pins, however, the friction factors were significantly increased as the Reynold's number increased, reaching as high as 15.3 at the highest Reynold's number tested. The heat transfer enhancement for the porous pins was found to be between 150 and 170% while the solid pins resulted in a heat transfer enhancement between 190 and 230%.
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Date Issued
2009
Identifier
CFE0002819, ucf:48085
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002819
EFFECT OF CORIOLIS AND CENTRIFUGAL FORCES ON TURBULENCE AND TRANSPORT AT HIGH ROTATION AND BUOYANCY NUMBERS
Title
EFFECT OF CORIOLIS AND CENTRIFUGAL FORCES ON TURBULENCE AND TRANSPORT AT HIGH ROTATION AND BUOYANCY NUMBERS.
Creator
Sleiti, Ahmad Khalaf, Kapat, Jay, University of Central Florida
Abstract / Description
This study attempts to understand one of the most fundamental and challenging problems in fluid flow and heat transfer for rotating machines. The study focuses on gas turbines and electric generators for high temperature and high energy density applications, respectively, both which employ rotating cooling channels so that materials do not fail under high temperature and high stress environment.Prediction of fluid flow and heat transfer inside internal cooling channels that rotate at high...
Show moreThis study attempts to understand one of the most fundamental and challenging problems in fluid flow and heat transfer for rotating machines. The study focuses on gas turbines and electric generators for high temperature and high energy density applications, respectively, both which employ rotating cooling channels so that materials do not fail under high temperature and high stress environment.Prediction of fluid flow and heat transfer inside internal cooling channels that rotate at high rotation number and high density ratio similar to those that are existing in turbine blades and generator rotors is the main focus of this study. Both smooth-wall and rib-roughened channels are considered here. Rotation, buoyancy, bends, ribs and boundary conditions affect the flow inside theses channels. Introducing ribs inside internal cooling channel can enhance the heat transfer rate. As the introduction of ribs approach causes rapid increase in the severely limited pressure drop and requires high cost, other means of achieving high heat transfer rate are desired. Another approach to increase heat transfer rate to a values that are comparable to those achieved by introduction of ribs is to increase rotation number. One objective of this research is to study and compare theses two approaches in order to decide the optimum range of application and a possible replacement of the high-cost and complex ribs by increasing rotation number.A fully computational approach is employed in this study. On the basis of comparison between two-equation (k-e and k-w) and RSM turbulence models, it is concluded that the two-equation turbulence models cannot predict the flow field and heat transfer correctly, while RSM showed improved prediction. For the near wall region, two approaches with standard wall functions and enhanced near wall treatment were investigated. The enhanced near wall approach showed superior results to the standard wall functions approach. Thus RSM with enhanced near wall treatment is validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention is given to how turbulence intensity, Reynolds stresses and transport are affected by Coriolis and buoyancy/centrifugal forces caused by high levels of rotation and density ratio. The results obtained are explained in view of physical interpretation of Coriolis and centrifugal forces. Investigation of channels with smooth and with rib-roughened walls that are rotating about an orthogonal axis showed that increasing rotation number always enhances turbulence and the heat transfer rate, while at high rotation numbers, increasing density ratio although causes higher turbulence activity but dose not increase Nu and in some locations even decreases Nu. The increasing thermal boundary layer thickness near walls is the possible reason for this behavior of Nu. The heat transfer enhancement correlates linearly with rotation number and hence it is possible to derive linear correlation for the increase in Nu as a function of Ro. Investigation of channels with rib-roughened walls that rotate about orthogonal axis showed that 4-side-average Nur correlates with Ro linearly, where a linear correlation for Nur/Nus as a function of rotation number is derived. It is also observed that the heat transfer rate on smooth-wall channel can be enhanced rapidly by increasing Ro to values that are comparable to the enhancement due to the introduction of ribs inside internal cooling channels. This observation suggests that ribs may be unnecessary in high-speed machines, and has tremendous implications for possible cost savings in these turbines.In square channels that are rotating about parallel axis, the heat transfer rate enhances by increasing Ro on three surfaces of the square channel and decreases on the fourth surface. Th
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Date Issued
2004
Identifier
CFE0000014, ucf:52854
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000014
ANALYSIS AND OPTIMIZATION OF A SOLAR THERMAL COLLECTOR WITH INTEGRATED STORAGE
Title
ANALYSIS AND OPTIMIZATION OF A SOLAR THERMAL COLLECTOR WITH INTEGRATED STORAGE.
Creator
Bonadies, Monica, Kapat, Jay, University of Central Florida
Abstract / Description
Solar energy, a topic popular in the United States during the oil embargo of the 1970ÂÂ's, has become a relevant topic once more with the current focus on reducing greenhouse emissions. Solar thermal energy in particular has become popular as it uses existing steam turbine technology to produce electricity, with the benefit of using solar energy to produce steam rather than coal or nuclear heat sources. Solar thermal can also be used at lower temperatures to heat water...
Show moreSolar energy, a topic popular in the United States during the oil embargo of the 1970ÂÂ's, has become a relevant topic once more with the current focus on reducing greenhouse emissions. Solar thermal energy in particular has become popular as it uses existing steam turbine technology to produce electricity, with the benefit of using solar energy to produce steam rather than coal or nuclear heat sources. Solar thermal can also be used at lower temperatures to heat water for pools or for residential use. While this energy source has its benefits, it has the problem of being opportunistic – the energy must be used as it is captured. With the integration of storage, a solar thermal system becomes more viable for use. In this work, a low temperature (50-70o C) thermal storage unit with a solar thermal collector is experimentally run then studied using both analytical and numerical methods. With these methods, suggestions for future developments of the storage unit are made. The prototype collector and storage combination tested worked best during the winter months, when there was low humidity. Furthermore, the heat exchanger design within the storage unit was found to work well for charging (heating) the unit, but not for discharging the storage to heat water. The best modeling method for the storage unit was the use of FLUENT, which would allow for the suggested changes to the prototype to be simulated before the next prototype was constructed.
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Date Issued
2010
Identifier
CFE0003260, ucf:48548
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003260