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- Title
- Simulation of Heat/Mass Transfer of a Three-Layer Impingement/Effusion Cooling System.
- Creator
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Smith, Brandon, Chow, Louis, Wu, Xinzhang, Deng, Weiwei, University of Central Florida
- Abstract / Description
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Cooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 (-) 100 W/cm2. While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer...
Show moreCooling techniques for high density electrical components and electronic devices have been studied heavily in recent years. The advancements in the electrical/electronic industry have required methods of high heat flux removal. Many of the current electrical components and electronic devices produce a range of heat fluxes from 20 W/cm2 (-) 100 W/cm2. While parallel flow cooling systems have been used in the past, jet impingement is now more desirable for its potential to have a heat transfer coefficient 3-5 times greater than that of parallel flow at the same flow rate. Problems do arise when the jet impingement is confined and a cross flow develops that interacts with impinging jets downstream leading to a decrease in heat transfer coefficient. For long heated surfaces, such as an aircraft generator rotor, span wise fluid management is important in keeping the temperature distribution uniform along the length of the surface. A detailed simulation of the heat/mass transfer on a three-layer impingement/effusion cooling system has been conducted. The impingement jet fluid enters from the top layer into the bottom layer to impinge on the heated surface. The spent fluid is removed from the effusion holes and exits through the middle layer. Three different effusion configurations were used with effusion diameters ranging from 0.5 mm to 2 mm. Temperature uniformity, heat transfer coefficients, and pressure drops were compared for each effusion diameter arrangement, jet to target spacing (H/d), and rib configuration. A Shear Stress Transport (SST) turbulence fluid model was used within ANSYS CFX to simulate all design models. Three-layer configurations were also set in series for long, rectangular heated surfaces and compared against traditional cooling methods such as parallel internal flow and traditional jet impingement models. The results show that the three-layer design compared to a traditional impingement cooling scheme over an elongated heated surface can increase the average heat transfer coefficient by 75% and reduce the temperature difference on the surface by 75%. It was shown that for a three layer design under the same impingement geometry, the average heat transfer coefficient increases when H/d is small. The inclusion of ribs always provided better heat transfer and centralized the cooling areas. The heat transfer was increased by as much as 25% when ribs were used. The effusion hole arrangement showed minimal correlation to heat transfer other than a large array provides better results. The effusion holes' greatest impact was found in the pressure drop of the cooling model. The pressure losses were minimal when the effective area of effusion holes was large. This minimizes the losses due to contraction and expansion.
Show less - Date Issued
- 2012
- Identifier
- CFE0004795, ucf:49720
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004795
- Title
- AN EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER FOR ARRAYS OF IMPINGEMENT JETS ONTO THE FEATURED SURFACES WITH CYLINDRICAL AND ELLIPTICAL RAISED SURFACES.
- Creator
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Medina, Marc A, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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This study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries...
Show moreThis study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries for multi-jet impingement. An experimental was taken for this study to extend the current knowledge of multi-jet impingement geometries and to further understand the heat transfer performance. A temperature sensitive paint (TSP) technique was used to measure the heat transfer on the target surface, in which the local temperature was measured to estimate area averaged heat transfer coefficient (HTC) and row averaged HTC. In order stay consistent with literature, non-dimensional parameters were used for geometry locations and boundaries. For this study, the Reynolds number range, based on jet diameter and mass flux, is 10-15k. The X/D (streamwise direction), Y/D (spanwise direction), Z/D (channel height direction), L/D (thickness of the jet plate) constraints for this study are 5, 6, 3, and 1 respectively. From the local heat transfer distributions of the different roughness elements, it is concluded that the inclusion of these elements increases heat transfer by 2-12% as compared to a flat/smooth target plate. It is therefore recommended from this study, that elements, elliptical in shape, provide favorability in heat transfer for gas turbine configurations.
Show less - Date Issued
- 2016
- Identifier
- CFH2000131, ucf:46021
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000131
- Title
- STUDY OF HEAT TRANSFER CHARACTERISTICS OF IMPINGING AIR JET USING PRESSURE ANDN TEMPERATURE SENSITIVE LUMINESCENT PAINT.
- Creator
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Liu, Quan, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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Luminescent coating measurement system is a relatively new technology for quantitative pressure and temperature measurement. Usually referred to as Pressure Sensitive Paint (PSP) and Temperature Sensitive Paint (TSP), luminescent coatings contain sensor molecules, which undergoes a luminescent transition when excited with light of proper wavelength. The reaction is pressure and/or temperature sensitive. The image of TSP or PSP coated model surface can be captured with a scientific grade...
Show moreLuminescent coating measurement system is a relatively new technology for quantitative pressure and temperature measurement. Usually referred to as Pressure Sensitive Paint (PSP) and Temperature Sensitive Paint (TSP), luminescent coatings contain sensor molecules, which undergoes a luminescent transition when excited with light of proper wavelength. The reaction is pressure and/or temperature sensitive. The image of TSP or PSP coated model surface can be captured with a scientific grade camera and then processed to obtain full field temperature and pressure distribution with very high fidelity. The preparation time of the technique is short. The measurement system offers an economic alternative to conventional testing methods using large number of pressure taps and thermocouples. The purpose of the experiment in this thesis is to take the benefits of the TSP and PSP technique, develop a well-controlled process and then apply the technique for a fundamental study on jet impingement heat transfer. First, Uni-Coat TSP and Binary-FIB PSP purchased from ISSI Inc. are calibrated to high accuracy. The calibration uncertainty of TSP and PSP are found to be ±0.93 °C and ±0.12 psi over temperature and pressure ranges of 22 to 90 ° C and 5 to 14.7 psia, respectively. The photodegradation of TSP is then investigated with the same calibration system. The photodegradation refers to the phenomenon of decreasing emission intensity as the luminescent paint is exposed to the illumination light during testing. It was found that photodegradation rate is a strong function of temperature and the optical power of illumination lighting. The correlation developed in this work is expected to compensate the degradation of TSP to achieve high measurement accuracy. Both TSP and PSP were then applied in the flow and heat transfer measurement of single round impinging air jet. Various separation distance (Z/D) and jet Reynolds number are tested. Pressure measurement on the jet impinged target surface using PSP clearly shows the boundary of jet impingement zone, which broadens with separation distance. In heat transfer experiment using TSP, the "second peak" in local heat transfer occurring at radial distance r/D around 2 is clearly observed when the separation distance Z/D is shorter than the length of jet potential core. The slight variation in radial location and the amplitude of the "second peak" are captured as Z/D and jet Reynolds number change. The optimum Z/D of stagnation point heat transfer is found to be around 5. The effect of jet nozzle configuration is investigated. It is found that the heat transfer rate associated with "tube jet" is generally higher than that of "plate jet". The difference in heat transfer between the two jet configurations is related to the weaker entrainment effect associated with "plate jet", where the entrainment of surrounding air is confined by the injection plate, especially under small Z/D circumstances. When compared with the benchmark data in the literature, the averaged heat transfer data of "tube jet" matches the empirical data better than those of "plate jet". The maximum difference is 3.3% for tube jet versus 15.4% for plate jet at Reynolds number of 60000 and Z/D of 5. The effect of surface roughness on jet impingement heat transfer is also studied. Heat transfer can be significantly increased by the enhanced roughness of the target surface. The largest roughness effect is achieved near stagnation point at high jet Reynolds number. Compared to the heat transfer to a smooth plate, as high as 30.9% increase in area-averaged Nusselt number is observed over a rough surface at r/D=1.5 and jet Reynolds number of 60000. The most significant advance of the present work is that both temperature and pressure measurement be obtained with the same measurement system and with accuracy comparable to traditional testing methods. The procedures that were employed in this work should be easy to apply in any university or industrial testing facility. It provides a rapid testing tool that can help solve complex problems in aerodynamics and heat transfer
Show less - Date Issued
- 2006
- Identifier
- CFE0000960, ucf:46747
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000960
- Title
- Heat Transfer and Pressure Measurements from Jet Array Impingement onto a Large Radius Curved Surface.
- Creator
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Harrington, John, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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This study investigates the heat transfer and pressure drop characteristics of jet array impingement in two distinct parts. In the first part, the performance of a uniform array of jets on both a flat and a large radius curved target surface are compared. This comparison was done at average jet Reynolds number ranging from 55,000 to 125,000. In the second part, the characteristics of a non-uniform array of jets, more typical of geometries used in actual gas turbine combustors, are...
Show moreThis study investigates the heat transfer and pressure drop characteristics of jet array impingement in two distinct parts. In the first part, the performance of a uniform array of jets on both a flat and a large radius curved target surface are compared. This comparison was done at average jet Reynolds number ranging from 55,000 to 125,000. In the second part, the characteristics of a non-uniform array of jets, more typical of geometries used in actual gas turbine combustors, are investigated, including the effects of the removal of downstream rows and the placement of rib features onto the target surface. The non-uniform configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behavior. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. A steady-state measurement technique utilizing temperature sensitive paint (TSP) was used on the target surface to obtain heat transfer coefficients, while pressure taps placed on the sidewall and jet plate were used to evaluate the pressure and flow distribution in the impingement channel. Alongside the experimental work, CFD simulations were performed utilizing the v^2-f eddy viscosity turbulence model. The results from the uniform array impingement onto a curved surface comparison show that the large radius curvature of the current geometry has little to no effect on the flow distribution and heat transfer of the array.The non-uniform array results illustrate the applicability of tuning a jet impingement array using varying jet diameters and spacing. However, there are some difficulties in obtaining streamwise pitch resolved heat transfer predictions for non-uniform arrays as current open literature correlations for uniform arrays are shown to be not applicable. The computational results from this study show that simulations can be used to obtain initial predictions, with streamwise pitch averaged Nu values found to be within 20% of experimental results. The use of ribs downstream in place of several jet rows was shown to yield similar heat transfer results at lower pressure drop levels.
Show less - Date Issued
- 2016
- Identifier
- CFE0006317, ucf:51547
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006317
- Title
- Investigation of the Flow Field and Associated Heat Transfer within an Asymmetrical Leading Edge Jet Impingement Array.
- Creator
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Torres, Jorge, Kapat, Jayanta, Bhattacharya, Samik, Fernandez, Erik, University of Central Florida
- Abstract / Description
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This thesis investigates the turbulent flow features present in asymmetrical leading edge jet impingement and their effects from a fluid and heat transfer prospective using both numerical and experimental techniques. The jet-centerline plane flow field was quantified experimentally through the non-intrusive experimental method of Particle Image Velocimetry (PIV), while an area average heat transfer was acquired via a traditional copper block method. The numerical element served to investigate...
Show moreThis thesis investigates the turbulent flow features present in asymmetrical leading edge jet impingement and their effects from a fluid and heat transfer prospective using both numerical and experimental techniques. The jet-centerline plane flow field was quantified experimentally through the non-intrusive experimental method of Particle Image Velocimetry (PIV), while an area average heat transfer was acquired via a traditional copper block method. The numerical element served to investigate how well the Reynolds Averaged Navier-Stokes (RANS) k-? SST turbulence model predicts the flow field and heat transfer within the leading edge and further investigate the results outside of the experimental scope.Two different geometries, varied by H/d, were investigated at various Reynolds numbers ranging from 20,000 to 80,000. The geometry consisted of an array of 9 identical jets impinging on a leading edge of diameter D/d = 2, with an asymmetrical sidewall configuration to better represent the pressure side (PS) and suction side (SS) of a turbine blade. Several vortices were identified within the flow field of the leading edge geometry. These vortices were larger for the H/d = 4 configuration but did not contribute to any increased or decreased heat transfer compared to that of the H/d = 2.7 configuration. The most influential aspect to both the flow field and heat transfer was the change in crossflow velocity between the two geometries. The smaller cross sectional area of the H/d = 2.7 configuration saw an increase in crossflow velocity and jet bending, tending to also decrease the heat transfer. The numerical results also reflected these results and in both area averaged heat transfer and localized heat transfer contour plots.
Show less - Date Issued
- 2019
- Identifier
- CFE0007734, ucf:52431
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007734
- Title
- The Study of an Impinging Unsteady Jet - Fluid Mechanics and Heat Transfer Analysis.
- Creator
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Osorio, Andrea, Kapat, Jayanta, Kinzel, Michael, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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The high heat transfer capabilities of impinging jets have led to their widespread use in industrial applications, such as gas turbine cooling. These impinging jets are usually manufactured on the walls of super-alloy metals and are influenced by being positioned with a confined setting. Studies have been shown to enhance the heat transfer of impinging jets by fluctuating the flow which will be analyzed in this project with two designs. The first design is a self-sustaining stationary fluidic...
Show moreThe high heat transfer capabilities of impinging jets have led to their widespread use in industrial applications, such as gas turbine cooling. These impinging jets are usually manufactured on the walls of super-alloy metals and are influenced by being positioned with a confined setting. Studies have been shown to enhance the heat transfer of impinging jets by fluctuating the flow which will be analyzed in this project with two designs. The first design is a self-sustaining stationary fluidic oscillator that causes a sweeping motion jet to impinge on the surface. This is investigated using Particle Image Velocimetry (PIV) to study the flow field as well as copper- block heated surface to study the heat transfer. The second design involves pulsating the jet through a rotating disk that opens and closes the jet hole, providing a pulsing impingement on the surface. This is examined using hot-wire anemometry for understanding the fluid mechanics and copper-block heated surface to study the heat transfer. Both configurations are tested at a constant Reynolds number of 30,000 with the oscillator tested at normalized jet-to-surface spacings of 3, 4, 6 and the pulsing mechanism tested at jet-to-surface spacing of 3. The results for the fluidic oscillator indicate: Reynolds stress profiles of the jet demonstrated elevated levels of mixing for the fluidic oscillator; heat transfer enhancement was seen in some cases; a confined jet does worse than an unconfined case; and the oscillator's heat removal performed best at lower jet-to- surface spacings. The results for the pulsing mechanism indicate: lower frequencies displayed high turbulence right at the exit of the jet as well as the jet-to-surface spacing of 3; the duty cycle parameter strongly influences the heat transfer results; and heat transfer enhancement was seen for a variation of frequencies.
Show less - Date Issued
- 2018
- Identifier
- CFE0007353, ucf:52102
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007353