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1
Whitney, Christopher Francis. "Heat transfer characteristics of slot jet impingement." Thesis, Nottingham Trent University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320599.
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Butterfield, David Jacob. "Jet Impingement Heat Transfer from Superheated, Superhydrophobic Surfaces." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9167.
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Liquid jet impingement is a technique ubiquitously used to rapidly remove large amounts of heat from a surface. Several different regions of heat transfer spanning from forced convection to nucleate, transition, and film boiling can occur very near to one other both temporally and spatially in quenching or high wall heat flux scenarios. Heat transfer involving jet impingement has previously shown dependency both on jet characteristics such as flow rate and temperature as well as surface material properties. Water droplets are known to bead up upon contact with superhydrophobic (SH) surfaces. This is due to reduced surface attraction caused by micro- or nanostructures that, combined with a natively hydrophobic surface chemistry, reduce liquid-solid contact area and attraction, promoting droplet mobility. This remarkable capability possessed by SH surfaces has been studied in depth due to its potential for self-cleaning and shear reduction, but previous research regarding heat transfer on such surfaces shows that it has varying effects on thermal transport. This thesis investigates the effect that quenching initially hot SH surfaces by water jet impingement has on heat transfer, particularly regarding phase change. Two comparative studies are presented. The first examines differences in transient heat transfer from hydrophilic, hydrophobic, and SH surfaces over a range of initial surface temperatures and with jets of varying Reynolds number (ReD), modified by adjusting flow rate. Comparisons of instantaneous local heat flux from the surfaces are made by performing an energy balance over differential control volumes across the surfaces. General trends show increased heat flux, jet spreading velocity and maximum jet spread radius when ReD is increased. An increase in inital surface temperature resulted in increased heat flux across all surfaces, but slowed jet spreading. The local heat flux, average heat rate, and total thermal energy transfer from the surface all confirmed that SH surfaces allow significantly less heat to transfer to the jet compared to hydrophilic surfaces, due to the enhanced Leidenfrost condition and reduced liquid-solid contact on SH surfaces which augments thermal resistance. The second study compares jet impingement heat transfer from SH surfaces of varying microstructures. Similar thermal effects due to modified jet ReD and initial surface temperature were observed. Modifying geometric pattern from microposts to microholes, altering cavity fraction, and changing feature pitch and width had little impact on heat transfer. However, reducing feature height on the post surfaces facilitated water penetration within the microstructure, slightly enhancing thermal transport.
3
Spring, Sebastian [Verfasser]. "Numerical Prediction of Jet Impingement Heat Transfer / Sebastian Spring." München : Verlag Dr. Hut, 2011. http://d-nb.info/1011441330/34.
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Chan, Phillip. "Jet impingement boiling heat transfer at low coiling temperatures." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/401.
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The production of advanced high strength steels (AHSS) for use in the automotive and construction industries requires complex control of runout table (ROT) cooling. Advanced high strength steels require coiling at temperatures below 500 °C in order to produce a complex multi-phase microstructure. The research described here will investigate the boiling conditions that occur for moving plate experiments when steel is cooled towards low coiling temperatures.
Experiments were performed on a pilot-scale ROT located at the University of British Columbia using industrially supplied steel plates. Tests were performed for four different speeds (0.3, 0.6, 1.0 and 1.3 m/s) and three different initial plate temperatures(350, 500 and 600 °C). Each plate was instrumented with thermocouples in order to record the thermal history of the plate.
The results show that cooling is more effective at slower speeds within the stagnation zone for surface temperatures over 200 °C. Outside the stagnation zone regardless of speed cooling is primarily governed by air convection and radiation with minor effects from latent heat caused by splashing water. The maximum peak heat flux value increases with decreasing speed and occurs at a surface temperature of approximately 200 °C, regardless of speed. Below a surface temperature of 200 °C, speed has a negligible effect on peak heat flux. The maximum integrated heat flux seems to vary with speed according to a second order polynomial.
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Kanokjaruvijit, Koonlaya. "Heat transfer investigation of jet impingement coupled with dimples." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415327.
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Ball, Stephen. "Near wall flow characteristics in jet impingement heat transfer." Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388866.
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Schroder, Andrew Urban. "Experimental and Numerical Study of Impingement Jet Heat Transfer." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1305897623.
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Alshatti, Rashid Ali. "Heat Transfer Analysis of Slot Jet Impingement onto Roughened Surfaces." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5898.
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The effect of surface roughness on jet impingement heat transfer was investigated in this research. A numerical analysis was conducted for free surface slot jet impinging normally onto a heated plate. Six different geometries and three different plate materials were investigated. The cooling fluid used for the analysis was water, and the flow was laminar with a range of Reynolds number (Re) from 500 to 1000. Temperature distribution, local and average heat transfer coefficient, and local and average Nusselt number were presented for each case.
The steady state heat transfer results show that the increase in Reynolds number (Re) increases the local heat transfer coefficient and the local Nusselt number. Impinging the jet nozzle directly onto a step has a better heat transfer enhancement than impinging the jet nozzle in between steps. Materials with low thermal conductivity exhibit large variation in temperature along the solid-fluid interface. The variations of the interface temperature become smaller between all cases when applying the isothermal boundary condition.
The transient heat transfer results show that the temperature of the interface increases with time until steady state condition is met. Materials with high thermal diffusivity reach the steady state condition with less time. The increase in surface roughness increases the time required to reach the steady state condition. The highest rates of heat transfer were found at locations where no fluid recirculation occurs. It takes less time to reach steady state condition when applying the isothermal boundary condition at the bottom surface of the plate.
9
Lombara, James S. (James Stewart). "An experimental investigation of liquid jet impingement heat transfer theories." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14286.
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Liewkongsataporn, Wichit. "A numerical study of pulse-combustor jet impingement heat transfer." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22651.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.
11
Hernandez-Ontiveros, Cesar F. "Numerical analysis of heat transfer during jet impingement on curved surfaces." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002123.
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Dobbertean, Mark Michael. "Steady and Transient Heat Transfer for Jet Impingement on Patterned Surfaces." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3076.
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Free liquid-jet impingement is well researched due to its high heat transfer ability and ease of implementation. This study considers both the steady state and transient heating of a patterned plate under slot-free-liquid jet impingement. The primary working fluid was water (H2O) and the plate material considered was silicon. Calculations were done for Reynolds number (Re) ranging from 500 to 1000 and indentation depths from 0.000125 to 0.0005 m for three different surface configurations. The effect of using different plate materials and R-134a as the working fluid were explored for the rectangular step case. The distributions of the local and average heat-transfer coefficient and the local and average Nusselt number were calculated for each case. A numerical model based in the FIDAP computer code was created to solve the conjugate heat transfer problem. The model used was developed for Cartesian coordinates for both steady state and transient conditions.
Results show that the addition of surface geometry alters the fluid flow and heat transfer values. The highest heat-transfer coefficients occur at points where the fluid flow interacts with the surface geometry. The lowest heat-transfer coefficients are found in the indentations between the changes in geometry. The jet velocity has a large impact on the heat transfer values for all cases, with increasing jet velocity showing increased local heat-transfer coefficients and Nusselt number. It is observed that increasing the indentation depth for the rectangular and sinusoidal surfaces leads to a decrease in local heat transfer whereas for triangular patterns, a higher depth results in higher heat-transfer coefficient. The transient analysis showed that changing surface geometry had little effect on the time required to reach steady state. The selection of plate material has an impact on both the final maximum temperatures and the time required to reach steady state, with both traits being tied to the thermal diffusivity (α) of the material.
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Moss, Michael Andrew. "A knowledge based database system for jet impingement heat transfer correlations." Thesis, Nottingham Trent University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334747.
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Kapasi, Shabir F. "A study of heat and mass transfer characteristics of jet impingement." Thesis, Nottingham Trent University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385932.
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Liu, Xin. "Liquid jet impingement heat transfer and its potential applications at extremely high heat fluxes." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13066.
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Van, Treuren Kenneth W. "Impingement flow heat transfer measurements of turbine blades using a jet array." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386660.
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Schaeffler, Norman W. "Heat transfer from a spherical surface by jet impingement: an experimental study." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53183.
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Methods for the removal of heat from a sphere, via jet impingement by single and multiple jets was documented experimentally. Average heat transfer rates from a sphere maintained at constant temperature, by means of an internal electronic heater, and subjected to single or multiple jet impingements were obtained and related to the exit conditions of the impinging air jet(s) and to geometric parameters. The heat transfer rate was found to be insensitive to small changes in geometry. The heat transfer rate was found to increase with an increase in mass flow rate. The impingement of two jets was found not to be as efficient as a single jet using the same mass flow rate. Compressibility was found to decrease the heat transfer rate at high values of the Mach number. Attempts to increase the heat transfer rate by increasing the entrainment of the jet by acoustic or mechanical excitation or by the use of an elliptic orifice meet with no success. The decrease in velocity due to the increase in entrainment cancelled any benefit that was gained by increasing the entrainment of the jet.Master of Science
18
Agricola, Lucas. "Nozzle Guide Vane Sweeping Jet Impingement Cooling." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525436077557298.
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Chan, Tat Leung. "Application of liquid crystal thermography in heat transfer characteristics of slot jet impingement." Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267018.
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Sridhar, Abishek. "Single phase and boiling heat transfer under steady and pulsating confined jet impingement." Thesis, Curtin University, 2013. http://hdl.handle.net/20.500.11937/2570.
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Computational and experimental investigations are carried out on steady and pulsating jet impingement heat transfer. The studies focus on the fundamental investigation of heat transfer with and without boiling phenomena, applicable in the area of electronic cooling. The novelty of the research is the exploration of the relative significance of the contributing fluid and heat transport mechanisms under different parametric conditions.
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Shevade, Shantanu S. "Simulation of Turbulent Air Jet Impingement for Commercial Cooking Applications." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7362.
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The research work in this dissertation focuses on turbulent air jet heat transfer for commercial cooking applications.
As a part of this study, convective heat transfer coefficient and its interdependency with various key parameters is analyzed for single nozzle turbulent jet impingement. Air is used as the working fluid impinging on the flat surface. A thorough investigation of velocity and temperature distributions is performed by varying nozzle velocity and height over diameter ratio (H/D). Nusselt number and Turbulent Energy are presented for the impingement surface. It was found that for H/D ratios ranging between 6 and 8, nozzle velocities over 20 m/s provide a large percentage increase in heat transfer.
Single nozzle jet impingement is followed by study of turbulent multi-jet impingement. Along with parameters mentioned above, spacing over diameter ratio (S/D) is varied. Convective heat transfer coefficient, average impingement surface temperature and heat transfer rate are calculated over the impingement surface. It was found that higher S/D ratios result in higher local heat transfer coefficient values near stagnation point. However, increased spacing between the neighboring jets results in reduced coverage of the impingement surface lowering the average heat transfer. Lower H/D ratios result in higher heat transfer coefficient peaks. The peaks for all three nozzles are more uniform for H/D ratios between 6 and 8. For a fixed nozzle velocity, heat transfer coefficient values are directly proportional to nozzle diameter. For a fixed H/D and S/D ratio, heat transfer rate and average impingement surface temperature increases as the nozzle velocity increases until it reaches a limiting value. Further increase in nozzle velocity causes drop in heat transfer rate due to ingress of large amounts of cold ambient air in the control volume.
The final part of this dissertation focuses on case study of conveyor oven. Lessons learned from analysis of single and multi-jet impingement are implemented in the case study. A systematic approach is used to arrive to an optimal configuration of the oven. As compared to starting configuration, for optimized configuration the improvement in average heat transfer coefficient was 22.7%, improvement in average surface heat flux was 24.7% and improvement in leakage air mass flow rate was 59.1%.
22
Ojada, Ejiro Stephen. "Analysis of mass transfer by jet impingement and study of heat transfer in a trapezoidal microchannel." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003297.
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Virk, Akashdeep Singh. "Heat Transfer Characterization in Jet Flames Impinging on Flat Plates." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52985.
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The experimental work involves calculation of radial distribution of heat transfer coefficient at the surface of a flat Aluminium plate being impinged by a turbulent flame jet. Heat transfer coefficient distribution at the surface is computed from the measured heat flux and temperature data using a reference method and a slope method. The heat transfer coefficient (h) has a nearly bell shaped radial distribution at the plate surface for H/d =3.3. The value of h drops by 37 % from r/d =0 to r/d= 2. Upon increasing the axial distance to H/d = 5, the stagnation point h decreased by 15%. Adiabatic surface temperature (AST) distribution at the plate surface was computed from the measured heat flux and temperature. AST values were found to be lower than the measured gas temperature values at the stagnation point. Radial distribution of gas temperature at the surface was estimated by least squares linear curve fitting through the convection dominated region of net heat flux data and was validated by experimental measurements with an aspirated thermocouple. For low axial distances (H/d =3.3), the gas temperature dropped by only 15 % from r/d = 0 to r/d = 2. Total heat flux distribution is separated into radiative and convective components with the use of calculated heat transfer coefficient and estimated gas temperatures. At H/d = 3.3, the radiation was found to be less than 25 % of the net heat flux for r/d ≤ 2.Master of Science
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Liu, Quan. "STUDY OF HEAT TRANSFER CHARACTERISTICS OF IMPINGING AIR JET USING PRESSURE ANDN TEMPERATURE SENSITIVE LUMINESCENT PAINT." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2261.
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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 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 transferPh.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Onstad, Andrew J. "Additions to compact heat exchanger technology : jet impingement cooling & flow & heat transfer in metal foam-fins /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Psimas, Michael J. "Experimental and numerical investigation of heat and mass transfer due to pulse combustor jet impingement." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33863.
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Under certain circumstances pulse combustors have been shown to improve both heat transfer and drying rate when compared to steady flow impingement. Despite this potential, there have been few investigations into the use of pulse combustor driven impingement jets for industrial drying applications. The research presented here utilized experimental and numerical techniques to study the heat transfer characteristics of these types of oscillating jets when impinging on solid surfaces and the heat and mass transfer when drying porous media. The numerical methods were extensively validated using laboratory heat flux and drying data, as well as correlations from literature. As a result, the numerical techniques and methods that were developed and employed in this work were found to be well suited for the current application. It was found that the pulsating flows yielded elevated heat and mass transfer compared to similar steady flow jets. However, the numerical simulations were used to analyze not just the heat flux or drying, but also the details of the fluid flow in the impingement zone that resulted in said heat and mass transport. It was found that the key mechanisms of the enhanced transfer were the vortices produced by the oscillating flow. The characteristics of these vortices such as the size, strength, location, duration, and temperature, determined the extent of the improvement. The effects of five parameters were studied: the velocity amplitude ratio, oscillation frequency, the time-averaged bulk fluid velocity at the tailpipe exit, the hydraulic diameter of the tailpipe, and the impingement surface velocity. Analysis of the resulting fluid flow revealed three distinct flow types as characterized by the vortices in the impingement zone, each with unique heat transfer characteristics. These flow types were: a single strong vortex that dissipated before the start of the next oscillation cycle, a single persistent vortex that remained relatively strong at the end of the cycle, and a strong primary vortex coupled with a short-lived, weaker secondary vortex. It was found that the range over which each flow type was observed could be classified into distinct flow regimes. The secondary vortex and persistent vortex regimes were found to enhance heat transfer. Subsequently, transition criteria dividing these regimes were formed based on dimensionless parameters. The critical dimensionless parameters appeared to be the Strouhal number, a modified Strouhal number, the Reynolds number, the velocity amplitude ratio, and the H/Dh ratio. Further study would be required to determine if these parameters offer similar significance for other configurations.
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Jondhale, Kailas Valu. "Heat transfer during multiple jet impingement on the top surface of hot rolled steel strip." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31402.
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The cooling which occurs on the runout table (ROT) is a key processing step for hot
rolled steel strip. It determines the final microstructure and thus mechanical properties as
well as flatness of the hot band. The use of multiple jets during ROT cooling results in
interactions between neighboring water jets which can affect the overall heat transfer rate.
The heat transfer which takes place during cooling with multiple jets is fairly complex and
the available knowledge is limited. The research work described was done to obtain an
understanding of the effect of varying nozzle-to-nozzle distance, plate speed and flow rate
of the impinging water on the heat transfer taking place on the ROT.
Experiments were performed on the pilot scale runout table available at UBC, using
instrumented test samples of steel. Each sample was instrumented with twenty
thermocouples which measured the internal thermal history. This data was then used in
conjunction with an Inverse Heat Conduction (IHC) model to calculate surface heat fluxes
and temperatures. Some of the variables examined included: speed of movement of the test
plate (0.22 m/s and 1 m/s), nozzle spacing (114.3, 76.2 and 38.1 mm) and water flow rate
(15 1/min and 30 1/min). These experimental results provide important information for the
development of improved runout table cooling models.
The results indicated that, during multiple jet cooling, high heat extraction takes
place directly below the nozzles and adjacent to them due to direct impact of water. Lower
heat extraction occurs at the locations between the nozzles, i.e. the interaction region.
Visual observations of the tests-indicate that, when the water jets hit the strip, a small
darkened zone can be observed at the impingement point below each nozzle. In the interaction region, the water flowing from the two adjacent jets interacts with each other
and large splashing of the water is observed in this region. The dark zones below all three
nozzles expand with cooling of the strip, indicating that the water front is progressing
outwards from the stagnation line and more water solid contact is taking place. The boiling
curves below each nozzle are similar to each other and clearly show the different boiling
regimes while the boiling curve for the interaction region does not show these regimes as
clearly. In the interaction region, heat transfer remains relatively low until the water
completely wets the strip. The investigation of the effect of strip speed indicated that the
heat fluxes are higher for lower strip speeds as the strip spends a longer time under the
nozzle. This effect was seen both below the nozzle and in the interaction region. In general,
increase in water flow rate increases heat fluxes at all measuring locations due to higher
amount of water impinged on the strip surface. The nozzle configuration having two
adjacent nozzles at 38.1 mm apart has more cooling capacity than the other two
configurations indicating that, having two nozzles close to each other enhances heat
transfer.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Alsaiari, Abdulmohsen Omar. "Augmentation of Jet Impingement Heat Transfer on a Grooved Surface Under Wet and Dry Conditions." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/98502.
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Array jet impingement cooling experiments were performed on flat and grooved surfaces with the surface at a constant temperature. For the flat surface, power and temperature measurements were performed to obtain convection coefficients under a wide range of operating conditions such as jet speed, orifice to surface stand-of distance, and open area percentage. Cooling performance (CP) was calculated as the ratio between heat transfer and fan power. An empirical model was developed to predict jet impingement heat transfer taking into account the entrainment effects. Experimental results showed that jet impingement can provide high transfer rates with lower rates of cooling cost in comparison to contemporary conventional techniques in the industry. CP values over 279 were measured which are significantly higher than the standard values of 70 to 95 in current technology. The model enhanced prediction accuracy by taking into account the entrainment effects; an effect that is rarely considered in the literature. Experiments on the grooved surfaces were performed at dry and wet surface conditions. Under dry conditions, results showed 10%~55% improvement in heat transfer when compared to the flat surface. Improvement percentage tends to be higher at wider gaps between the array of orifices and the grooved surface. An improvement of 30%~40% was observed when increasing Re either by increasing orifice diameter or jet speed. Similar improvement was observed at higher flow open area percentages. No significant improvement in heat transfer resulted from decreasing the size of the grooves from 3.56mm to 2.54mm. Similarly, no noticeable change in heat transfer resulted from changing the relative position of the jets striking the surface at the top of the grooves to the bottom of the grooves. Deeper grooves with twice the depth gave statistically similar average heat transfer coefficients as shallower grooves. Under wet conditions, a hybrid cooling technique approach was proposed by using air jets impinging on a grooved surface with the grooves containing water. The approached is proposed and evaluated experimentally for its feasibility as an alternative for cooling towers of thermoelectric power plants. Convection heat and mass transfer coefficients were measured experimentally using the heat mass transfer analogy. Results showed that hybrid jet impingement provided high magnitudes of heat flux at low jet speeds and flow rates. High coefficients of performance CP > 3000, and heat fluxes > 8,000W/m2 were observed. Hybrid jet impingement showed 500% improvement as compared to jet impingement on a dry flat surface. CP values of hybrid jet impingement is 600% to 1,500% more as compared to performance of air-cooled condensers and wet cooling towers. Water use for hybrid jet impingement cooling is efficient since evaporation energy is absorbed from the surface directly instead of cooling air to near wet-bulb temperature.PHD
29
Smith, Brandon. "Simulation of Heat/Mass Transfer of a Three-Layer Impingement/Effusion Cooling System." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5509.
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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 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.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermofluids
30
King, Andrew James Campbell. "Thermal enhancement strategies for fluid jets impinging on a heated surface." Curtin University of Technology, Dept. of Mechanical Engineering, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17743.
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This research investigation examines the thermal behaviour of single and arrays of fluid jets impinging at heated surfaces, and formulates enhancement schemes for the jet impingement heat transfer processes for high-intensity cooling applications. The proposed techniques are numerically modelled and analysed over a wide parametric range to identify flow characteristics leading to thermal enhancement and optimum performance. The first scheme applies to a single fluid jet and incorporates a protruding object at the impingement surface to improve heat transfer. In this, a conical protrusion of high thermal conductivity is attached to the heated surface directly beneath the jet. Three different aspect ratios of 0.5, 1 and 2 are investigated for the protrusion while the inclusion of a fillet at the base of the cone is also studied. Jet Reynolds numbers between 100 and 30,000 are modelled. The observed thermal performance is compared with a reference case having no surface attachment. With this arrangement, the heat transfer rate typically varies between 10 and 40 percent above the reference case although depending on certain parametric combinations, the heat transfer may increase above or decrease below the reference performance. The highest indicated increase in heat transfer is about 90 percent while 15 percent below is the lowest. Careful selection of cone surface profile creates potential for further thermal enhancement.The second scheme applies to a single fluid jet and incorporates a recess in the impingement surface to improve heat transfer. In this, a cylindrical cavity is introduced to the surface beneath the jet into which the fluid jet impinges. The effects of the cavity on heat transfer are examined for a number of different cavity diameters, cavity depths and jet discharge heights wherein a surface without a cavity is taken as the reference surface. Cavity diameters of 2, 3 and 4 times the jet diameter are investigated at cavity depths between zero and 4 times the jet diameter. Jet discharge heights range between 2 jet diameters above the reference surface to 2 jet diameters below the reference surface. The jet Reynolds number is varied between 100 and 30,000. With this enhancement technique, increases in heat transfer rates of up to 45 percent are observed when compared to the reference performance. The thermal performance of fluid jet arrays is examined by altering square or hexagonal array configurations to identify flow characteristics leading to optimal heat transfer rates. For this, the jet to jet spacing is varied between 1.5 and 7 times the jet diameter while the jet to surface height is varied between 2 and 6 times the jet diameter. Jet Reynolds numbers between 100 and 30,000 are investigated. For each configuration, a critical jet-to-jet spacing is identified below which the heat transfer is observed to reduce significantly. Correlations for the expected heat transfer for a square or hexagonal array are presented in terms of the jet to jet spacing, jet height and jet Reynolds number.
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King, Andrew. "Thermal enhancement strategies for fluid jets impinging on a heated surface." Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/815.
Full textAbstract:
This research investigation examines the thermal behaviour of single and arrays of fluid jets impinging at heated surfaces, and formulates enhancement schemes for the jet impingement heat transfer processes for high-intensity cooling applications. The proposed techniques are numerically modelled and analysed over a wide parametric range to identify flow characteristics leading to thermal enhancement and optimum performance. The first scheme applies to a single fluid jet and incorporates a protruding object at the impingement surface to improve heat transfer. In this, a conical protrusion of high thermal conductivity is attached to the heated surface directly beneath the jet. Three different aspect ratios of 0.5, 1 and 2 are investigated for the protrusion while the inclusion of a fillet at the base of the cone is also studied. Jet Reynolds numbers between 100 and 30,000 are modelled. The observed thermal performance is compared with a reference case having no surface attachment. With this arrangement, the heat transfer rate typically varies between 10 and 40 percent above the reference case although depending on certain parametric combinations, the heat transfer may increase above or decrease below the reference performance. The highest indicated increase in heat transfer is about 90 percent while 15 percent below is the lowest. Careful selection of cone surface profile creates potential for further thermal enhancement.The second scheme applies to a single fluid jet and incorporates a recess in the impingement surface to improve heat transfer. In this, a cylindrical cavity is introduced to the surface beneath the jet into which the fluid jet impinges. The effects of the cavity on heat transfer are examined for a number of different cavity diameters, cavity depths and jet discharge heights wherein a surface without a cavity is taken as the reference surface. Cavity diameters of 2, 3 and 4 times the jet diameter are investigated at cavity depths between zero and 4 times the jet diameter. Jet discharge heights range between 2 jet diameters above the reference surface to 2 jet diameters below the reference surface. The jet Reynolds number is varied between 100 and 30,000. With this enhancement technique, increases in heat transfer rates of up to 45 percent are observed when compared to the reference performance. The thermal performance of fluid jet arrays is examined by altering square or hexagonal array configurations to identify flow characteristics leading to optimal heat transfer rates. For this, the jet to jet spacing is varied between 1.5 and 7 times the jet diameter while the jet to surface height is varied between 2 and 6 times the jet diameter. Jet Reynolds numbers between 100 and 30,000 are investigated. For each configuration, a critical jet-to-jet spacing is identified below which the heat transfer is observed to reduce significantly. Correlations for the expected heat transfer for a square or hexagonal array are presented in terms of the jet to jet spacing, jet height and jet Reynolds number.
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Ajith, N. P. Shenoy Shyam Krishna Shenoy. "Heat Flux Measurements from a Human Forearm under Natural Convection and Isothermal Jets." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/87705.
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This work is an experimental study on heat transfer from a human arm and a model cylinder. Heat transfer from a human forearm to a large jet, representative of a building HVAC vent/outlet was studied using both an IR camera and a heat flux sensor. The isothermal jet was discharged horizontally from a wind tunnel, at the same temperature as the ambient air.
The model cylinder was used to validate the heat transfer results with results from previous studies, using both the IR camera and heat flux sensors. Further, a study on heat transfer to impingement jets from a human forearm at various Reynolds numbers (Re = 9500-41000) and impinging distances of four and eight jet diameters was done. Heat transfer from a human arm to such impingement jets were then compared with heat transfer due to natural convection under both open and controlled environments. A significant increase in convection heat transfer with Reynolds number and distance from the jet outlet was observed. A nearly four-fold increase in convection heat transfer coefficient was obtained when a jet with Reynolds number of 9500 was impinged on a human arm when compared to that obtained under natural convection in an open environment. Empirical correlations for predicting the stagnation and average Nusselt number from a human arm were also developed with high values of correlation coefficients for future studies. Impingement jets were found to be an effective means to transfer heat from human bodies and could potentially be used for creating thermally conditioned microenvironments.M. S.
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Mukka, Santosh Kumar. "Computation of fluid circulation in a cryogenic storage tank and heat transfer analysis during jet impingement." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001103.
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Glaspell, Aspen W. "Heat Transfer and Fluid Flow Characteristics of Two-Phase Jet Impingement at LowNozzle-to-Plate Spacing." Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1534357333244428.
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Natarajan, Thangam. "Large-eddy simulations of flow and heat transfer for jet impingement on static and vibrating surfaces." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/54046.
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The present numerical work serves to understand the flow and thermal characteristics of a turbulent impinging air jet under dynamic flow and geometric conditions using Large-eddy Simulations (LES). A clear relationship between the large-scale structures and resulting heat transfer on the impingement surface exists and was demonstrated through highly-resolved LES of both static and dynamic surface configurations.
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Rouse, Victoria J. "Comparison of heat transfer and fluid flow characteristics between submerged and free surface jet impingement for two-phase flow." Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1546428292091476.
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Balligand, Maxime. "Transferts de chaleur et de masse par impact de jets : application au refroidissement de machines électriques." Thesis, Valenciennes, 2017. http://www.theses.fr/2017VALE0014/document.
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Ces travaux s'inscrivent dans le cadre du projet ESSENCYELE, projet visant à développer un nouveau modèle de véhicule hybride. L'étude thermique présentée porte sur le refroidissement de machines électriques par jets impactant. Afin d'optimiser le refroidissement des bobinages de la partie fixe de la machine (stator), des travaux ont été menés dans le but d'étudier localement les échanges de chaleur lors de l'impact d'un jet. Deux fluides ont été considérés, l'air et l'huile. Le dispositif expérimental, associé à un programme de post-traitement par méthode inverse, permet de relever la température à la surface d'un cylindre lisse lors de l'impact d'un jet. L'influence de la distance jet/surface, de la géométrie de l'injecteur ou encore des propriétés du fluide ont été testées. Des travaux numériques ont permis de donner des informations supplémentaires sur l'évolution de l'écoulement au sein des injecteurs. Pour terminer, les configurations les plus intéressantes obtenues pour l'air et pour l'huile ont été testées sur le refroidissement des bobinages de statorThe present work is a part of an industrial project named ESSENCYELE. The main objective of this project is to develop a new hybrid vehicle. The present study is about the electrical machine cooling system by impinging jets. To improve the end winding cooling, experiments has been made to study the local heat transfers during a jet impingement. Two fluids were considered, air and oil. The experimental device, with an inverse method post-processing program, allowed to estimate the temperature at the surface of a smooth cylinder. The influence of the jet/surface distance, the nozzle geometry or the fluid properties were tested. Numerical studies have provided additional information on the fluid flow evolution inside the nozzle. Finally, the most interesting configuration obtained with air jet and oil jet were tested
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Pandit, Jaideep. "Numerical and Experimental Design of High Performance Heat Exchanger System for A Thermoelectric Power Generator for Implementation in Automobile Exhaust Gas Waste Heat Recovery." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/47919.
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The effects of greenhouse gases have seen a significant rise in recent years due to the use of fossil fuels like gasoline and diesel. Conversion of the energy stored in these fossil fuels to mechanical work is an extremely inefficient process which results in a high amount of energy rejected in the form of waste heat. Thermoelectric materials are able to harness this waste heat energy and convert it to electrical power.
Thermoelectric devices work on the principle of the Seebeck effect, which states that if two junctions of dissimilar materials are at different temperatures, an electrical potential is developed across them. Even though these devices have small efficiencies, they are still an extremely effective way of converting low grade waste heat to usable electrical power. These devices have the added advantage of having no moving parts (solid state) which contributes to a long life of the device without needing much maintenance. The performance of thermoelectric generators is dependent on a non-dimensional figure of merit, ZT. Extensive research, both past and ongoing, is focused on improving the thermoelectric generator's (TEG's) performance by improving this figure of merit, ZT, by way of controlling the material properties. This research is usually incremental and the high performance materials developed can be cost prohibitive.
The focus of this study has been to improve the performance of thermoelectric generator by way of improving the heat transfer from the exhaust gases to the TEG and also the heat transfer from TEG to the coolant. Apart from the figure of merit ZT, the performance of the TEG is also a function of the temperature difference across it, By improving the heat transfer between the TEG and the working fluid, a higher temperature gradient can be achieved across it, resulting in higher heat flux and improved efficiency from the system. This area has been largely neglected as a source of improvement in past research and has immense potential to be a low cost performance enhancer in such systems. Improvements made through this avenue, also have the advantage of being applicable regardless of the material in the system. Thus these high performance heat exchangers can be coupled with high performance materials to supplement the gains made by improved figure of merits.
The heat exchanger designs developed and studied in this work have taken into account several considerations, like pressure drop, varying engine speeds, location of the system along the fuel path, system stability etc. A comprehensive treatment is presented here which includes 3D conjugate heat transfer modeling with RANS based turbulence models on such a system. Various heat transfer enhancement features are implemented in the system and studied numerically as well as experimentally. The entire system is also studied experimentally in a scaled down setup which provided data for validation of numerical studies. With the help of measured and calculated data like temperature, ZT etc, predictions are also presented about key metrics of system performance.Ph. D.
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Li, Lifeng. "Numerical study of surface heat transfer enhancement in an impinging solar receiver." Thesis, Uppsala universitet, Fasta tillståndets fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-237365.
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During the impinging heat transfer, a jet of working fluid, either gas or liquid, will besprayed onto the heat transfer surface. Due to the high turbulence of the fluid, the heat transfer coefficient between the wall and the fluid will be largely enhanced. Previously, an impinging type solar receiver with a cylindrical cavity absorber was designed for solar dish system. However, non-uniform temperature distribution in the circumferential direction was found on absorber surface from the numerical model, which will greatly limit receiver's working temperature and finally affect receiver's efficiency. One of the possible alternatives to solve the problem is through modifying the roughness of the target wall surface. This thesis work aims to evaluate the possibility and is focusing on the study of heat transfer characteristics. The simulation results will be used for future experimental impinging solar receiver optimization work. Computational Fluid Dynamics (CFD) is used to model the conjugate heat transfer phenomenon of atypical air impinging system. The simulation is divided into two parts. The first simulation was conducted with one rib arranged on the target surface where heat transfer coefficient is relatively low to demonstrate the effects of rib shape (triangular,rectangular, and semi-circular) and rib height (2.5mm, 1.5mm, and 0.5mm). The circular rib with 1.5mm height is proved to be most effective among all to acquirerelatively uniform temperature distribution. In the second part, the amount of ribs is taken into consideration in order to reach more uniform surface heat flux. The target wall thickness is also varied to assess its influence.
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Jagannatha, Deepak. "Heat transfer and fluid flow characteristics of synthetic jets." Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/2437.
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This thesis presents a fundamental research investigation that examines the thermal and fluid flow behaviour of a special pulsating fluid jet mechanism called synthetic jet. It is envisaged that this novel heat transfer enhancement strategy can be developed for high-performance heat sinks in electronic cooling applications.The study considers a unique arrangement of a periodic jet induced by diaphragm motion within a cavity and mounted on a confined flow channel with a heated wall upon which the jet impingement occurs. The operation of this jet mechanism is examined as two special cases for unravelling its parametric influences. In Case (a), the jet impingement is analysed in a channel with stagnant fluid permitting clear view of the pure synthetic jet process and its controlling variables. In Case (b), jet impingement is considered with fluid flow in the channel to establish the nature of synthetic jet and cross-flow interaction.The unsteady flow of this jet mechanism is simulated as a time-dependant two-dimensional numerical model with air as the working fluid. The current model considers a solution domain in its entirety, comprising the confined flow regions of the jet impinging surface, the cavity and the orifice. With a User Defined Function (UDF), the model accounts for the bulk fluid temperature variations during jet operation, which has been grossly ignored in all published work. Overcoming previous modelling limitations, the current simulation includes flow turbulence for realistic representation of pulsed jet characteristics and cross-flow interference.Computations are performed with applicable boundary conditions to obtain the heat transfer and fluid flow characteristics of the synthetic jet along with cross-flow interaction for the diaphragm amplitude ranging from 0.5 mm to 2 mm and the diaphragm frequency varying from 250 Hz to 1000 Hz. The numerical simulation yields stable solutions and aptly predicts the sequential formation of synthetic jet and its intrinsic vortex shedding process while accurately portraying the flow within the cavity.It is identified that the diaphragm amplitude primarily determines the jet velocity while the diaphragm frequency governs the rate of vortex ejection and the fluid circulation in the vicinity of the heater. The synthetic jet thermal performance is improved with high amplitude that gives rise to stronger jet impingement and reduced bulk fluid temperature arising from high frequency leading to better fluid circulation. The fluid flow in the channel or cross flow drags the jet downstream affecting jet’s ability to reach the heated wall. The relative strengths of jet velocity and channel flow determine the combined thermal performance. The fluid compressibility is seen to have insignificant effect on the synthetic jet behaviour within the examined range of parameters. As for geometrical parameters, reduced orifice width increases jet velocity improving heat transfer rates while the optima is identified for the heater -to- orifice distance within 6 to 10 times the orifice width.Results conclusively show that in a stagnant fluid medium, the proposed synthetic jet mechanism delivers 40 percent higher heat transfer rates than an equivalent continuous jet. It also thermally outperforms pure natural convection at the heated channel wall by up to 120 times within the parametric range. Under cross-flow conditions, the synthetic jet can provide 2-fold improvement in heat transfer compared to an equivalent continuous jet. By adding this synthetic jet mechanism to a flow channel, the overall thermal performance of the hybrid system is enhanced up to about 18 times the pure forced convection heat transfer rates in a channel without this jet mechanism.The observed outstanding thermal performance of the pulsed jet-cross flow hybrid mechanism surpasses the heat removal potential of current conventional techniques for electronic component cooling. It operates with a unique ability of not causing flow pressure drop increases and not requiring additional fluid circuits, which are recognised as key advantages that set this method apart from other techniques. Thus, the proposed synthetic jet-cross flow hybrid mechanism is envisaged to be potentially regarded as an outstanding thermal enhancement strategy in the development of heat sinks for future high-capacity electronic cooling needs.
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Xu, Haoxin. "Numerical Study on the Thermal Performance of a Novel Impinging Type Solar Receiver for Solar Dish-Brayton System." Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-137091.
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An impinging type solar receiver has been designed for potential applications in a future Brayton Solar Dish System. The EuroDish system is employed as the collector, and an externally fired micro gas turbine (EFMGT) has been chosen as the power conversion unit. In order to reduce the risks caused by the quartz glass window, which is widely used in traditional air receiver designs, a cylinder cavity absorber without a quartz window has been adopted. Additionally, an impinging design has been chosen as the heat exchange system due to its high heat transfer coefficient compared to other single-phase heat exchange mechanisms. This thesis work introduces the design of an solar air receiver without a glass window, which features jet impingement to maximize the heat transfer rate. A detailed study of the thermal performance of the designed solar receiver has been conducted using numerical tools from the ANSYS FLUENT package. Concerning receiver performance, an overall thermal efficiency of 72.9% is attained and an output air temperature of 1100 K can be achieved, according to the numerical results. The total thermal power output is 38.05 kW, enough to satisfy the input requirements of the targeted micro gas turbine. A preliminary design layout is presented and potential optimization approaches for future enhancement of the receiver are proposed, regarding local thermal stress and pressure loss reduction. This thesis project also introduces a ray-thermal coupled numerical design method, which combines ray tracing techniques (using FRED®), with thermal performance analysis (using ANSYS Workbench).
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Elsheikh, Mutasim Mohamed Sarour. "Numerical Simulations of Heat Transfer Processes in a Dehumidifying Wavy Fin and a Confined Liquid Jet Impingement on Various Surfaces." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3090.
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This thesis consists of two different research problems. In the first one, the heat transfer characteristic of wavy fin assembly with dehumidification is carried out. In general, fin tube heat exchangers are employed in a wide variety of engineering applications, such as cooling coils for air conditioning, air pre-heaters in power plants and for heat dissipation from engine coolants in automobile radiators. In these heat exchangers, a heat transfer fluid such as water, oil, or refrigerant, flows through a parallel tube bank, while a second heat transfer fluid, such as air, is directed across the tubes. Since the principal resistance is much greater on the air side than on the tube side, enhanced surfaces in the form of wavy fins are used in air-cooled heat exchangers to improve the overall heat transfer performance. In heating, ventilation, and air conditioning systems (HVAC), the air stream is cooled and dehumidified as it passes through the cooling coils, circulating the refrigerant. Heat and mass transfer take place when the coil surface temperature in most cooling coils is below the dew point temperature of the air being cooled. This thesis presents a simplified analysis of combined heat and mass transfer in wavy-finned cooling coils by considering condensing water film resistance for a fully wet fin in dehumidifier coil operation during air condition. The effects of variation of the cold fluid temperature (-5˚C - 5˚C), air side temperature (25˚C - 35˚C), and relative humidity (50% - 70%) on the dimensionless temperature distribution and the augmentation factor are investigated and compared with those under dry conditions. In addition, comparison of the wavy fin with straight radial or rectangular fin under the same conditions were investigated and the results show that the wavy fin has better heat dissipation because of the greater area. The results demonstrate that the overall fin efficiency is dependent on the relative humidity of the surrounding air and the total surface area of the fin. In addition, the findings of the present work are in good agreement with experimental data.
The second problem investigated is the heat transfer analysis of confined liquid jet impingement on various surfaces. The objective of this computational study is to characterize the convective heat transfer of a confined liquid jet impinging on a curved surface of a solid body, while the body is being supplied with a uniform heat flux at its opposite flat surface. Both convex and concave configurations of the curved surface are investigated. The confinement plate has the same shape as the curved surface. Calculations were done for various solid materials, namely copper, aluminum, Constantan, and silicon; at two-dimensional jet. For this research, Reynolds numbers ranging from 750 to 2000 for various nozzle widths channel spacing, radii of curvature, and base thicknesses of the solid body, were used. Results are presented in terms of dimensionless solid-fluid interface temperature, heat transfer coefficient, and local and average Nusselt numbers. The increments of Reynolds numbers increase local Nusselt numbers over the entire solid-fluid interface. Decreasing the nozzle width, channel spacing, plate thickness or curved surface radius of curvature all enhanced the local Nusselt number. Results show that a convex surface is more effective compared to a flat or concave surface. Numerical simulation results are validated by comparing them with experimental data for flat and concave surfaces.
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Lallave-Cortes, Jorge C. "Numerical heat transfer during partially-confined, confined, and free liquid jet impingement with rotation and chemical mechanical planarization process modeling." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002968.
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Slabaugh, Carson D. "Heat transfer augmentation in a rectangular duct characterized by an impinging jet inlet : design of experiment." Honors in the Major Thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1329.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering and Computer Science
Mechanical Engineering
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Friedrich, Brian Karl II. "An Experimental Study of Volumetric Quality on Fluid Flow and Heat Transfer Characteristics for Two Phase Impinging Jets." Youngstown State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1463935537.
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Gabour, Laurette A. "The effects of surface roughness on stagnation-point heat transfer during impingement of turbulent liquid jets." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/38725.
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Tabrizi, Seyed Pariviz Alavi. "Jet impingement onto a circular cylinder." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263841.
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Chen, Guohua 1963. "Impingement heat transfer with re-entry channel nozzles." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59261.
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Intensity of axial turbulence at the nozzle exit and impingement heat transfer rate were measured for the re-entry slot channel nozzle, with nozzle length, L, nozzle width, w, and jet Reynolds number, Re, as parameters. With increasing Reynolds number over the range 5000-20000 the turbulence intensity decreases, but only slightly. For the shortest nozzles, i.e. orifices, turbulence varies greatly across the nozzle width, from 0% near the nozzle walls. A nozzle length of 3w-4w is sufficient to produce relatively flat profiles. Turbulence intensity is better characterized at the mid-plane, I$ sb{ rm jmp}$, than at the center line, I$ sb{ rm jcL}$. By varying w between 6 and 11 mm, and L from 13w down to an orifice, I$ sb{ rm jmp}$ varies between 4% and 9%.Impingement heat transfer is not significantly influenced by L/w.
This geometry of nozzle operated at spacings, H/w of 3 and 6, gives heat transfer rates that match the maximum obtained with the ASME standard contoured entry nozzle at H/w precisely of 8.
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Claretti, Roberto. "Heat transfer study of a triple row impingement channel at large impingement heights." Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/358.
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Advanced cooling techniques are required to increase the Brayton cycle temperature ratio necessary for the increase of the overall cycle's efficiency. Current turbine components are cooled with an array of internal cooling channels in the midchord section of the blade, pin fin arrays at the trailing edge and impingement channels in the leading edge. Impingement channels provide the designer with high convective coefficients on the target surface. Increasing the heat transfer coefficient of these channels has been a subject of research for the past 20 years. In the current study, a triple row impingement channel is studied with a jet to target spacing of 6, 8 and 10. The effects of sidewalls are also analyzed. Temperature sensitive paint alongside thin foil heaters are used to obtain heat transfer distributions throughout the target and side walls of the three different channels. Thermal performances were also calculated for the two largest channels. It was found that the side walls provide a significant amount of cooling especially when the channels are mounted side by side so that their sidewalls behave as fins. Similar to literature it was found that an increase in Z/D decreases heat transfer coefficient and provides a more uniform profile. It was also found that the Z/D = 6 and 8 target wall heat transfer profiles are very similar, hinting to the fact that successful potential core impingement may have occurred at height of eight diameters. A Computational Fluid Dynamics, or CFD, study was also performed to provide better insight into the flow field that creates such characteristic heat transfer profiles. The Realizable k-µ solution with enhanced wall functions gave surface heat transfer coefficients 30% off from the experimental data.B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical Engineering
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El-Jummah, Abubakar Mohammed. "Impingement and impingement/effusion cooling of gas turbine components : conjugate heat transfer predictions." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/9025/.
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Conjugate heat transfer (CHT) and computational fluid dynamics (CFD) were combined in this work using ICEM meshing and ANSYS Fluent software. Block-structured grids with hexahedral elements were used to investigates the key features of impingement cooling of gas turbine metal surfaces, with applications to combustor wall, nozzle and turbine blade cooling. Only flat wall cooling was investigated and not any influence of surface curvature. Combustor wall and turbine blade flank cooling both approximate to a flat wall as the hole diameter and pitch are all small in relation to the combustor or blade curvature. Also the experimental data base on impingement cooling predominantly uses a flat wall. The aim was to validate the computations against experimental data from hot metal wall research facilities and then to use the validated computational methodology to predict improved cooling geometries. Experimental investigations that used hot wall rigs at 770 K cross-flow temperature and 293 K coolant were modelled to predict the overall cooling effectiveness for impingement cooling. The impingement cooling of the metal surface with an equivalent heat flux was modelled, at a hot gas value equals to 100 kW/m2 and is an input relevant to real gas turbine combustor applications of 250 kW/m2K heat transfer coefficient (HTC). Much of the experimental data base with metal walls used electrically heated metal wall experiments with relatively low wall temperatures. These were also modelled using a constant hot gas side temperature and the thermal gradient through the thickness and between impingement and effusion holes were predicted. The work was confined to the internal wall heat transfer and did not investigate the combined film effusion cooling that is often used in combination with impingement cooling. However, the interaction of internal wall effusion cooling with impingement cooling was investigated, so that the whole internal wall cooling could be predicted. The heat transfer in a metal wall with a square array of 90o holes is a subcomponent of impingement and effusion cooling and was part of this study, which was used to evaluate the impact of the CFD turbulence models. The standard k - ɛ turbulence model with standard wall function (WF) for y+ values in the range 30 - 45 showed better agreement with the measured data, where all the flow features were predicted correctly. Also enhanced wall treatment approaches (EWT) were used for y+ values from 1 - 5, but there was no significant improvement in the predictions compared with the standard wall function approach. All the turbulence models available in Fluent were investigated for an array of holes in a metal wall, which involves only a computation of one hole that is classic short hole or pipe entry length heat transfer. Many of the models could not predict the flow separation and reattachment within a hole L/D of ~1 and as this was fundamental to both effusion and impingement heat transfer, indicating that these models were all poor at the predictions of impingement and impingement/effusions cooling. The experimental data base in impingement heat transfer has results that would not normally be expected and the CHT computations enabled the reason for the experimental trends to be explained. This includes the reduction in heat transfer along the impingement gap influenced by cross-flow, which would be expected to increase the heat transfer. The relatively low effect of turbulence enhancing obstacles in the impingement gap was also predicted. The influence of the number of impingement holes, which leads to methodology to choose a particular hole size has been predicted based on thermal gradients in the metal wall, this helps the designer in choosing optimum number of holes. For impingement cooling with single sided coolant exit from the cross-flow duct, it was shown that the deflection of the cross-flow onto the impingement jet wall surface was a major reason for the deterioration in the impingement target surface heat transfer along the gap. The very limited experimental database for heat transfer to the impingement jet wall surface was well predicted, thus showing that both wall surfaces were important in the overall impingement heat transfer. The design configurations investigated were the hole length, pitch, gap, height and depth to diameter ratios L/D, X/D, Z/D, H/D and E/D respectively. The range of L/D investigated was 0.78 - 4.85, by varying the hole diameter for a fixed metal wall thickness (length) of 6.35 mm. This heat transfer was dominated by thermal and aerodynamic entry length effects including the heat transfer on the hole approach surface. The X/D range investigated was 1.86 - 21.02 by varying D at constant X and also by varying X at constant D, which varies the number of holes per surface area, n. The range of Z/D investigated was from 0.76 - 7.65 at varied and also at a constant Z. The main coolant flow parameter varied was the mass flux G, which is equals to G*/P (kg/sm2bar) in this Ph. D thesis. The requirements for each G with a fixed hole geometry, is a new CHT computation, which is time consuming compared with fairly rapid experimental determinations of the effect of G. The literature survey showed that there were no available detailed flow dynamics investigations of multi-hole impingement cooling. The key experimental measurement that indicates the correctness of the aerodynamic predictions was the pressure loss, which was as a result of the air feed to the impingement gap or effusion hole discharge. The results showed, for the range of geometries, reasonable agreement with the experimental measurements. For heat transfer the experimental measurements were all surface averaged, either for the whole wall or for each row of holes. The predictions were shown to give excellent agreement with surface average heat transfer, which also gave the surface distribution of the heat transfer. It was shown that the surface distribution of heat transfer was directly related to the surface distribution of the turbulence kinetic energy. The experimental influence of turbulence enhancing obstacles in the impingement gap was well predicted. The experimental data base was for one obstacle per impingement hole using two flow configurations: flow parallel to the obstacles, so that the action was to increase the surface area for heat transfer at low blockage increase and flow across the obstacles, so that the action was to increase turbulence and surface area, but at the expense of higher pressure loss. Two obstacles shapes were investigated experimentally, simple continuous ribs and slotted ribs which gave rectangular pin fins relative to the cross-flow, with both turbulence generation and surface area increased. The predictions agreed with the experiments that showed the main effect of the obstacles, for which the deterioration of heat transfer with distance was reduced, but to only have a relatively small (~ 20%) increase in the surface averaged heat transfer. The validated computational procedures were used to investigate other obstacle geometries for the same impingement configuration: surface dimples, round pin-fins and inclined ribs in a zig-zag of ‘W’ format. The zig-zag design predicted an improvement in overall heat transfer compared with the other designs. Impingement/effusion internal wall heat transfer was modelled with one effusion hole per impingement hole and a fixed 8 mm gap. It was shown that the key interaction effect was to remove any cross-flow from the gap, provided all the impingement air flow went through the effusion holes. This geometry is then only viable for low coolant mass flow rates and thus the modelling was confined to low G. This limitation of coolant flow was because effusion cooling improves if the hole velocity is low relative to the cross-flow, which occurs at low mass flow rates.