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1
Tyagi, Ashok K. "Jet to jet impingement in a confined space." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30117.pdf.
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Webb, Stephen David. "Jet impingement on porous surfaces." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/47117/.
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A series of experiments are described, documenting the flow resulting from the normal impingement of planar and axisymmetric jets onto a porous surface. Six different porous surfaces with open area ratios of 23, 26, 31, 37, 44 and 54% (β = 0.23, 0.26, 0.31, 0.37, 0.44 and 0.54) were placed in low speed (usually 40m/s exit velocity) air jets sufficiently far from the jet exit for the jet to be self similar. The β=0.31, 0.37, 0.44 and 0.54 surfaces were wove wire mesh. Exit Reynolds number based on jet exit diameter is 3x104 for the axisymmetric case and based on exit width from 0.5x104 to 2.1x104 for the planar case. For β=0.44 and β=0.54 the impingement of the jet for both planar and axisymmetric geometries can be summarised as a widening of the jet as it passes through the mesh, followed by a region of reduced entrainment. For β=0.37 and below, there is evidence of wall jets on the upstream side of the surface. For the β=0.31 mesh and β=0.26 perforated plate, there are marked differences between the axisymmetric and planar cases. For the planar cases the flow is turned downstream of the porous surface away from the centreline such that on the centreline the axial velocity falls to zero, whilst a clear jet remains in the axisymmetric cases. Downstream of the β=0.23 porous surface there is a clear bounded jet in both planar and axisymmetric cases. The presence of a counter-flow at some distance from the centreline, downstream of the surface inhibits entrainment into the downstream jet; its growth rate and velocity decay rate are reduced
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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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Skuriat, Robert. "Direct jet impingement cooling of power electronics." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/13982/.
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The aim of the work presented in this thesis is to improve the operational reliability of a power module and increase the efficiency of its associated cooling system by integrating the design of the cooler as part of the module. Power modules are increasingly used in a variety of applications ranging from aircraft and mass transport systems, to motor control and power conversion in the home. Reliability of the power module is very important in aerospace applications where the highest levels of safety and robustness are required while keeping the volume and mass of the module as low as possible. Certain parts of the power module such as the solder layer beneath the silicon device and the substrate are prone to failure with thermal cycling. The layer of thermal grease between the baseplate of the module and the heatsink significantly increases the thermal resistance between the electronic devices and the coolant fluid. The power module can be constructed so that some of the interfaces within the module which are prone to failure are improved or completely removed from the assembly greatly reducing the thermal resistance from junction to ambient. The research identified cooling methods which are able to cope with the increasingly high heat fluxes produced by power electronic devices. Jet impingement cooling was selected for testing and further development. An initial series of tests confirmed that liquid jet impingement can be used to generate high heat transfer coefficients for the efficient cooling of power modules. Results from experimental tests showed that directly cooling the substrate tile with jet impingement resulted in the devices being cooled more effectively compared to the commonly used serpentine coldplate and a direct-baseplate cooled jet impingement system. It was postulated that more efficient cooling can be achieved by targeting the hotspots on the substrate beneath each device with a carefully designed impingement array. A test apparatus was constructed to test a variety of jet impingement arrays to confirm the hypothesis. A second test apparatus was constructed to characterise the performance of the jet arrays in more detail using a thermal imaging camera to monitor the surface temperature of a single device. An optimal jet configuration was found for the efficient cooling of a single device. The work concluded that an improvement in efficiency and reliability can be gained by constructing power modules with integrated jet impingement arrays direct-substrate cooling the hotspots beneath the devices.
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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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Ashforth-Frost, Shirley. "Flow visualisation of semi-confined jet impingement." Thesis, Nottingham Trent University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385846.
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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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Stoddard, Jonathan Glenn. "Jet and Droplet Impingement on Superhydrophobic Surfaces." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6048.
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The effect of superhydrophobicity on liquid water impingement on a flat horizontal surface was explored. The surfaces combined a hydrophobic surface chemistry with a patterned microstucture in order to produce high contact angles with water. Three sets of experiments were performed, one for jet impingement and two for droplet impingement, which advance previous work in characterizing the interaction of water and superhydrophobic surfaces.Jet impingement experiments were performed to characterize a transitional regime between an unsubmerged and a completely submerged superhydrophobic surface by varying an imposed downstream depth. For low downstream depths, the surface remained unsubmerged and displayed only break up of the thin film, while at high downstream depths, the surface was completely submerged and only a hydraulic jump occurred. Within the transition, the surface was partially submerged and both thin film breakup and a hydraulic jump were observed. Experiments were performed for three Reynolds numbers, Re, ranging from 1.9 x 104 to 2.2 x 104 (based on the volume flow rate). For all Re, the transition was characterized by a reduction in the hydraulic jump radius as downstream depth increased. Also, as Re increased, the downstream depths over which the transition occurred was greater. When a droplet impinges on a surface covered with a liquid film, a thin liquid wall, or crown, forms and propagates outward. Here a comparison of this crown dynamic was made for smooth hydrophilic surfaces and superhydrophobic (SH) surfaces patterned with post or rib microfeatures. Due to the high contact angle of the SH surfaces, a relatively thick film (h ≈ 5 mm) of water was required to maintain a film. This resulted in negligible differences between the surfaces utilized. Droplet train impingement on the same post and rib SH surfaces was also investigated. When each individual droplet impinged on the surface, a crown formed which spread out radially until reaching a semi-stable or regularly oscillating breakup diameter. At this point, the water would either build up or breakup into droplets or filaments and then continue radially outward. In some cases the crown would break up, causing splashing. A comparison to previous experiments on hydrophilic surfaces shows a distinct difference in splashing at low frequency. The breakup diameter was measured over a Weber number range of 72-2800. The data was collapsed as a function of a combination of the Reynolds number (Re), Capillary number (Ca), and Strouhal number (St), resulting in Re0.7CaSt. The rib SH surface displayed an elongated breakup due to the anisotropic surface features. The breakup diameter for the droplet train was compared to the breakup diameter which has been shown to occur with a jet impinging on a SH surface.
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Tapanlis, Orpheas. "Turbine casing impingement cooling systems." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711623.
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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.
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Garcia, Robert Gordon. "CFD simulation of flow fields associated with high speed jet impingement on deflectors." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31675.
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Computational Fluid Dynamics is used to analyze the formation of under-expanded jets and to investigate the three-dimensional flow field associated with the impingement of free jets onto stationary deflectors. This investigation was performed to develop a verified modeling ability for such problems. Predictions were compared with the experimental results obtained by Donaldson and Snedeker [1]. Computational models for free and impinging jets were created according to the data provided in Ref. 1. Numerical results for each of the experiments performed in this benchmark report are presented.
<p> Three different turbulent free jets produced by a simple convergent nozzle were analyzed. These include a subsonic jet with p<sub>1</sub>/pâ =1 and M<sub>1</sub>=0.57, a moderately under-expanded jet with p<sub>1</sub>/pâ =1.42 and M<sub>1</sub>=1, and a highly under-expanded jet with p<sub>1</sub>/pâ =3.57 and M<sub>1</sub>=1. The reflecting shocks associated with the moderately under-expanded jet as well as the shock disk associated with the highly under-expanded jet were fully resolved. Velocity profile data predicted at locations downstream of the nozzle exit agreed very well with the experimental results.
<p>The impingement of a moderately under-expanded jet with p<sub>1</sub>/pâ =1.42 and M<sub>1</sub>=1 was also investigated. The interaction of the high speed jet with circular flat plates at angles of 60° and 45° relative to the center axis of the jet are presented. Wall jet velocity profiles on the surface of the flat plate are fully resolved and compare well with experimental results. The CFD solver controls and method used to obtain these results are summarized and justified.<br>Master of Science
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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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Rahmani, Hatef. "Particle-laden liquid jet impingement on a moving surface." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58208.
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In the railroad industry, coating of the rail with liquid changes the forces at the wheel-rail interface. Wet leaves on rail tracks can reduce the wheel-rail traction to dangerously low levels. To enhance wheel traction, railroads spray sand on the tracks. The sand may be applied in the form of a particle-laden jet. The impingement of high-speed liquid jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water-glycerin solutions. At the low concentration studied, the suspension has a Newtonian fluid viscosity. A variety of jet and surface velocities, liquid properties, mean particle sizes, and volume fractions were studied. It was observed that for jets with very small particles, the addition of solids to the jet enhances deposition. In contrast, jets with larger particles in suspensions were more prone to splash than single phase jets of the same viscosity. It is speculated that the non-monotonic dependence of the splash threshold on the particle size occurs when the particle diameter is comparable to the lamella thickness. Additionally, volume-of-fluid (VOF) CFD simulations were carried out to provide a full description of the flow field of a particle-free Newtonian jet spreading over a moving surface. The jet Reynolds number and Weber number of the simulations were in the range of 50-1000 and 100-8000, respectively. The simulations were generally in good agreement with experiments and they could successfully predict the lamella dimensions and velocity profiles.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate
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Mohajer, Behzad. "Flow characteristics of single and double liquid jet impingement." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/60142.
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In the past few decades, the increasing demands for superior cooling systems in various industries have shifted the focus onto impinging liquid jets as an efficient, powerful cooling technique. Although much has been done on the thermal aspects of jet impingement, the available knowledge still lacks an in-depth understanding of the fluid dynamics involved in the phenomena that dictate the associated transport mechanisms. The present thesis has been planned to study the fluid dynamics of the interaction between a liquid, free-surface impinging jet with a solid surface, and also with a neighboring jet. The circular hydraulic jump as a key feature of a free-surface jet impingement was analyzed. The focus was given to the influence of the target plate on the behavior of the hydraulic jump. Two conditions for the target plate were examined: large plates with capillary limit at the edge, and also small target plates. It was experimentally and theoretically discussed that the circular jumps with these two conditions exhibit different behaviors from those presented in the literature. Furthermore, a systematic Froude number analysis on circular hydraulic jumps was carried out and the significant differences between circular jumps and the open-channel jumps were Highlighted. It was shown that due to the significant influence of the surface tension in circular jumps, the critical Froude number differs from that observed in the classical jumps and could be larger than unity. Moreover, the interaction between the flow fields formed by two jets impinging on a solid surface was investigated in detail. Understanding of this interaction is of significant importance due to the promising potentials of multiple jets for high heat flux applications. Two different configurations were studied: two vertical jets, and two inclined jets. The fluid dynamics involved in the collision between two thin liquid films formed on the surface was theoretically analyzed. A systematic experimental study was also carried out to examine the effects of different parameters on the flow field interaction. The experimental results were then compared to the theoretical predictions to verify the presented models. Good agreements were observed between the presented theory and the experimental data.<br>Applied Science, Faculty of<br>Engineering, School of (Okanagan)<br>Graduate
15
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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Abdul, Husein Reyad Abdul Ameer. "Impingement cooling of gas turbine components." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255236.
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Nobari, Amir Hossein. "Mechanistic jet impingement model for cooling of hot steel plates." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/47099.
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Accelerated cooling on the run-out table of a hot rolling mill is a key technology to tailor microstructure and properties of advanced steels. Thus, it is crucial to develop accurate heat transfer models in order to predict the temperature history of the steel plates on run-out tables.
The present study describes a strategy to develop a mechanistic cooling model to simulate the temperature of the plate cooled by top water nozzles on a run-out table. Systematic experiments have been carried out on a pilot scale run-out table facility using two types of top nozzles: planar (curtain) and circular (axisymmetric) nozzles. Experimental results for cooling of stationary plates showed that the heat transfer rate depends strongly on the distance from the jet especially in the temperature range where the transition boiling regime occurs. Based on experimental results, a boiling curve model has been proposed that takes into account boiling heat transfer mechanisms and maps local boiling curves for cooling of stationary steel plates. The effects of water flow rate and water temperature on the heat extraction from the plate have been included in the model.
Then, systematic experimental heat transfer studies were conducted to investigate the effect of plate speed on the heat transfer rate. It was found that the plate motion influences the heat transfer rate in the film boiling and transition boiling regimes; however, it does not have an effect on the heat flux in the nucleate boiling regime. Moreover, for the circular nozzle system, it was found that the nucleate boiling heat flux does not change with lateral distance. However, heat flux in the film boiling and transition boiling regimes decreases with increasing distance from the longitudinal centerline of the plate. In the next step, a cooling model was proposed by accounting for the boiling curves of single nozzle cooling for moving plates. Transient heat conduction within the plate was analyzed and surface heat flux and temperature histories were predicted. The validity of the cooling model was examined with multiple nozzles experimental data from the literature. Very good agreement with experimental results has been obtained.<br>Applied Science, Faculty of<br>Materials Engineering, Department of<br>Graduate
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Guo, Yuchen. "Newtonian and viscoelastic liquid jet impingement on a moving surface." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/51123.
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Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement in railroad friction control applications, an experimental investigation into Newtonian and viscoelastic liquid jet impingement on moving surfaces is presented.
Seven PEO-glycerine-water solutions and three commercial liquid friction modifiers were tested with a variety of jet speeds, jet diameters, surface speeds and surface roughnesses. The effects of these test conditions on jet impingement splash behaviours as well as jet and lamella geometries were studied. High-speed imaging was employed to visualize the interaction between the impinging jet and the moving surface.
Experiments on the effect of modest surface roughness revealed that, while jet and surface speed were both important factors, splash was more likely to occur on surfaces with lower roughness levels. By analyzing experimental results for Newtonian liquids, a relation between lamella geometry and test conditions were found, which can be used to predict lamella dimensions. Three types of non-Newtonian behaviours were observed at high surface speed and low jet speed: jet necking, jet bending and jet stretching.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate
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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.
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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.<br>Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.
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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%.
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Park, Heungsup. "Drop impingement and interaction with a solid surface." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/8236.
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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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Karwa, Nitin. "Experimental Study of Water Jet Impingement Cooling of Hot Steel Plates." Phd thesis, tuprints, 2012. https://tuprints.ulb.tu-darmstadt.de/3041/1/PhD_Thesis_Karwa.pdf.
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Liquid jet impingement cooling is critical in many industrial applications. Principle applications include extracting large heat flux from metal parts, such as hot fuel bundle post-loss-of-coolant-accident in nuclear reactors, heat treatment of steel plates post-hot-processing, etc. The ability of liquid jets to extract high heat flux at controlled rates from metal parts, with temperatures as high as 800-1000 ºC, at moderate flow rates has made them indispensable in these applications. Due to the complexity of the process, the mechanism of flow boiling heat transfer during jet impingement cooling is not well understood. Resultantly, the presently used design approaches are based more on experience and rule of thumb than science. The principle challenge in the study of jet impingement cooling for these high temperature applications has been the lack of reliable instrumentation for measuring the cooling rates. To add to this, the conjugate nature of boiling heat transfer, especially on low conductivity metal like steel, makes this problem very complicated to understand. Thus, much of the state of art on this subject has been limited to experiments where either the conjugate problem has not been addressed or the tests have been performed at temperatures that are much lower than in the above mentioned applications.
The basic objective of the present work is to contribute to the understanding of the thermo-hydrodynamic phenomenon occurring during the cooling of a hot steel plate with an impinging water jet. This work also complements a parallel study being conducted at the Institute of Fluid Mechanics and Aerodynamics (Technische Universität Darmstadt), in which the complex transport processes are being treated theoretically and validated against the experimental results of this work.
To achieve the objective, transient cooling experiments have been performed on an instrumented stainless steel AISI-type 314 cylinder. To measure the temperature variation within the stainless steel cylinder during the transient cooling, fast-response thermocouples have been embedded within holes that are precisely drilled though its bottom flat face. The cylinder is induction heated to a homogeneous initial temperature of 900 ºC and is subsequently cooled by means of an axisymmetric subcooled free-surface water jet that impinges on its top flat face (impingement surface). During the cooling, each thermocouple output has been recorded at the rate of 100 samples per second. A two-dimensional axisymmetric inverse heat conduction analysis using these measured temperature data has been performed to estimate the temporospatial variation of temperature and heat flux on the impingement face. Both low and high speed images have been recorded to visualize the two-phase flow. These images and the estimated heat transfer distribution are used to understand the boiling mechanism. The effect of jet parameters, namely subcooling and impingement velocity, on the heat transfer process has been studied. Additionally, the effect of spent liquid accumulation over the impingement surface has been studied in few exploratory plunging jet experiments.
This study presents a systematic methodology for the measurement and estimation of the temporospatial variation of heat transfer on the impingement surface of a hot steel plate. Three distinct regions, with difference in the extent of liquid-wall contact, have been identified on the impingement surface from the recorded images.
i) A wetted region surrounds the jet stagnation region. Nucleate boiling is the principle heat transfer mode in this region. The outer periphery of this region is called the wetting front. No boiling activity has been observed in the high speed images, most likely because the bubbles were small and were unable to reach the liquid free-surface. The maximum heat flux position is determined to be within this region. As the wetted region grows in size with time, the maximum heat flux position also moves radially outwards. The wetting front and maximum heat flux position velocity reduce with increasing radial distance from the impingement point because the liquid velocity and subcooling reduce at the wetting front. Likewise, the wetting front velocity increases with jet velocity and subcooling.
ii) The liquid gets deflected at the wetting front due to the efflux of large vapor bubbles beyond the maximum heat flux position. A term ``wetting front region' has been coined in this thesis to describe this region. The width of this region could not be determined from the high speed images. Transition boiling within a thin superheated liquid film that is continuously replenished by the bulk flow is proposed to be the probable reason for the high heat flux in this region. Further, the radial heat conduction to the wetted region is also significant here.
iii) The impingement surface outside the wetting front region is dry. The dry surface slowly cools down due to film boiling and radial heat conduction to the wetting front region. The film boiling rate is very low in the impingement region. After deflecting away from the impingement surface in the wetting front region, the liquid film breaks into droplets over this region. Looking from the side, droplet deflection angle is observed to be small; still these droplets do not come into direct contact with the impingement surface, as has been confirmed by looking down from the top.
The velocity of the splashed droplets has been determined by analyzing the high speed images. It has been found that the drop velocity is much lower than the liquid film velocity calculated at the wetting front position using single-phase flow relations suggested by Watson. It has been hypothesized that the liquid film in the wetted region is decelerated by the bubbles growing on the impingement surface. Further, measurements reveal that the drop velocity increases with decreasing subcooling, which means that the film and the droplet are accelerated in the radial outward direction by the vapor released in the wetting front region.
It has been shown that the rewetting temperature (analogous to the Leidenfrost temperature for a sessile droplet), which refers here to the temperature below which the direct liquid-wall contact is re-established and the heat flux increases, in both the impingement and radial flow regions is significantly higher than that reported in the literature for pool boiling. Removal of bubbles by the flowing liquid in the early stages of their growth and then their rapid condensation within the subcooled liquid avoids the buildup of vapor near the hot wall, which is the likely reason for the enhancement of the rewetting temperature. This observation confirms that high heat fluxes can be removed at large wall superheats by impinging liquid jets, as practiced in the industry.
The boiling curve shifts to higher heat flux and superheat with the increase in the jet velocity and subcooling. The maximum heat flux and surface temperature at maximum heat flux increase with both the jet velocity and subcooling. Area-weighted average boiling curves have been determined, which clearly show the enhancement in the heat transfer with jet velocity over the average surface superheat of 100 to 800 K. The enhancement in jet subcooling is, however, noticeable only in the wall superheat range of 300 to 700 K. The maximum heat flux and surface temperature at maximum heat flux decrease with radial distance from the stagnation point before reaching a constant value. The radial distribution of maximum heat flux condition has been classified into three regions based on the relative size of the hydrodynamic/thermal boundary layer and the liquid film.
In the plunging jet impingement studies, it has been found that the wetting front growth slightly slows down due to accumulation of the spent liquid over the impingement surface. Area-weighted average boiling curves show that the heat transfer reduces due to accumulation.
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Salehi, Neyshabouri Seyed Ali Akbar. "Impingement of offset jets on rigid and movable beds." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233806.
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The present thesis describes an experimental and theoretical investigation of the flow field and scour action of an offset jet. The hydraulic characteristics of the offset jet and the resulting scour developed in the bed were investigated in the laboratory. Tests were carried out using a fixed bed and a single offset ratio (height of jet above bed / jet thickness). Three flow rates were used. Velocity measurements in two directions, especially in the recirculating zone, were of help in understanding the flow field and in providing the necessary data for comparison with the theoretical results. The development of scour, on a uniform sand, was monitored at set time intervals, in most cases until the asymptotic state was reached. A new effective and simple method for measuring the scour profile, while the experiment was running, was devised. The experiments were conducted using four different offset ratios and several flow-rates. Results showed dependency of the scour characteristics on Froude number, time and especially the offset ratio. The findings of each experiment were combined dimensionlessly to produce relationships which describe the development of scour characteristics for the tested range of parameters. Scour profiles were found to be similar for a given offset ratio, but differed from one offset ratio to another. The second part of the work was concerned with developing a general integral method capable of the prediction of velocity fields of different flow situations, including those of offset jet impinging on rigidand eroded beds. The combination of strip integral method in a curvilinear system with the k-E and algebraic stress turbulence models provided such a method. Application of this method to a variety of selected test cases revealed the ability of the model to capture the main features of the flow within the considered range of interest. The algebraic stress model was found to give better results in curved and wall effected flows.
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Toh, Hoong Thiam. "Large Eddy Simulation of Supersonic Twin-Jet Impingement Using a Fifth-Order WENO Scheme." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28992.
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A three-dimensional flow field produced by supersonic twin-jet impingement is studied using a large eddy simulation (LES). The numerical model consists of two parallel axisymmetric jets of diameter 𝐷*, 3𝐷* apart, issuing from a plane which is at a distance H*=4𝐷* above the ground. The jet diameter 𝐷*, mean velocity 𝑊ₒ*, mean density 𝜌ₒ* and mean temperature 𝑇ₒ* at the jet center in the exit plane are used as reference values. The Mach number and Reynolds number of the jets are M=1.5 and Re=550,000, respectively. This model is closely related to the experimental setup of Elavarasan <i>et al.</i>(Elavarasan <i>et al.</i>, 2000).
The three-dimensional time-dependent compressible Navier-Stokes equations are solved using the method of lines. The convective terms are discretized using a fifth-order WENO scheme, whereas the viscous terms are discretized using a fourth-order central-differencing scheme. A low-storage five-stage fourth-order Runge-Kutta scheme is used to advance the solution in time. Code verification is achieved by comparison with flat-plate boundary-layer linear stability analysis, and computational data by Bendiks <i>et al.</i> (Bendiks <i>et al.</i>, 1999). for a compressible turbulent round jet.
Instantaneous flow, mean flow and Reynolds stresses for the twin-jet impingement are presented and discussed. The results reveal the existence of flapping behavior in the fountain. The flapping fountain is the vortical structure formed by the alternating merging of a primary vortex tube with a secondary vortex tube induced by the neighboring primary vortex tube. The nondimensional period of flapping is found to be 7𝐷*/𝑊ₒ*. High unsteadiness and strong interaction between the fountain and the jets are also observed. Due to the high diffusion and spreading rate of the fountain, the interaction between the fountain and the jets is only significant up to a height which is less than 3𝐷*. It is found that the mean peak velocity in the fountain is 0.40406 𝑊ₒ* and it occurs at 0.536607𝐷* from the ground.
The suitability of the fifth-order WENO scheme to simulate turbulent flow field with embedded shocks is also demonstrated by its capability to capture unsteady shock waves in the impingement regions.<br>Ph. D.
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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.<br>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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Maghzian, Hamid. "Simulation of hydrodynamics of the jet impingement using Arbitrary Lagrangian Eulerian formulation." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/421.
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Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible.
Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary.
Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process.
Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields.
Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach.
This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application.
In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications.
After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application.
These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented.
The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model.
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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.<br>Master of Science
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Mehra, Deepak. "Effects of varying body forces on isothermal and non isothermal liquid jet impingement." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5106.
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Thesis (Ph. D.)--West Virginia University, 2007.<br>Title from document title page. Document formatted into pages; contains xiii, 131 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 129-130).
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Sterling, George Earl Grant. "An experimental study on jet impingement on a very high speed moving surface." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43074.
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Motivated by the need to improve transfer efficiencies of liquid coatings from jet impingement, an experimental investigation into jet impingement on very high speed moving surfaces is presented. Seven different Newtonian liquids with widely varying shear viscosities were made to impinge on a surface which could be made to move at speeds up to 350km/hr. Tests for the Newtonian liquids were done with several modified surfaces to study the effects of roughness and surface inconsistencies. Nozzle sizes and impingement angles were varied to interrogate their effects on the interaction of the impacting jet and moving surface while high speed photography was employed to capture these interactions. Spread radii and spread widths were measured for viscous fluids which deposited.
While it was observed that stable jets of fluids with sufficiently high viscosities almost always deposited, tests with water indicate that the effects of the impingement angle as well as jet diameter significantly alter the locations of boundaries between deposition, spatter and lamella lift-off. Impingement angles that result in jet velocities with large components of velocity parallel to the surface velocity are prone to deposit. Jets of smaller diameters are also prone to deposit. It was observed that both the jet velocity and surface velocity are important determining factors in the likelihood of deposition.
The deposition of viscous fluids demonstrated that it is possible to observe transitions from deposition to lift-off and vice versa through mechanisms that trigger random fluctuations in the lamella. The track distance covered before a transition from lift-off to deposition occurs is shown to be a Poisson Process.
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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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Landers, Brian D. "Mixing Characteristics of Turbulent Twin Impinging Axisymmetric Jets at Various Impingement Angles." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1467987856.
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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 transfer<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Mechanical Engineering
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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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Wilken, Nicolas John. "Experimental investigation of free-surface jet-impingement cooling by means of TiO2-water nanofluids." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/73456.
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The exponential advancements in the field of electronics and power generation have resulted in increased pressure on the thermal management of these systems where the desire for enhanced heat transfer is prevalent. A technique for enhancing heat transfer that has gained sufficient attention over the past two decades is to suspend nano-sized metallic particles in a base fluid in order to enhance its thermophysical properties. Fluids produced in such a manner are commonly termed nanofluids. Due to the promising heat transfer capabilities of nanofluids, many industrial applications are beginning to implement these fluids in their thermal practices. One of the potential applications where nanofluids may be used which has received a great deal of research attention is jet-impingement heat transfer. Concerning the existing publications on nanofluid jet impingement, most works within the steady state regime are limited to the cooling of Al2O3-water nanofluids, while transient studies do not account for cooling without the effects of boiling phenomena and for surfaces other than steel.
In this study, six particle volume fractions of TiO2-water ranging between 0.025 and 1% were prepared and characterised for appropriate cooling tests. The study was conducted within both the steady and transient state with the main objective of evaluating the thermal performance of the selected nanofluid and to determine the optimum particle concentration for jet-impingement cooling applications. Therefore, an experimental rig was designed and manufactured where a copper target surface of 42 mm was impinged upon by a 1.65 mm orifice nozzle at a non-dimensional nozzle-to-target height of 4. The results indicated that the use of nanofluids in impingement applications produced adverse effects, depending on the particle fraction considered.
With respect to the steady-state cooling tests, the copper surface was subjected to a constant heat flux of 145 watt and cooled by the different fluids at Reynolds numbers ranging between approximately 10 000 and 30 000. A maximum enhancement of 14.75% was observed in the measured Nusselt numbers, which occurred at a particle volume concentration of 0.05%. When increasing the volume fraction above 0.1%, unfavourable effects were observed for the heat transfer of the system in comparison with the base case tests of DI-water. Such trends were characterised by the trade-off between the enhancement in thermal conductivity and viscosity, both of which were increased with an increase in particle concentration. As for the effect of Reynolds number on the resulting thermal performance, a directly proportional relation was shown and could be described by the forced convection effect. The transient impingement tests showed that particle concentrations less than 0.1% produced an enhancement in cooling efficiency, while those of higher volume fractions showed negative effects. According to these tests the maximum enhancement was also obtained at a volume fraction of 0.05% and produced an average cooling efficiency enhancement of 16%.
The results of the investigation clearly showed that the use of TiO2-water nanofluids in jet-impingement cooling applications produced thermal enhancement depending on the selected particle concentration.<br>Dissertation (MEng)--University of Pretoria, 2019.<br>NRF<br>Mechanical and Aeronautical Engineering<br>MEng<br>Unrestricted
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Akhtar, Kareem. "A Numerical Study of Supersonic Rectangular Jet Impingement and Applications to Cold Spray Technology." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/71711.
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Particle-laden supersonic jets impinging on a flat surface are of interest to cold gas-dynamic spray technology. Solid particles are propelled to a high velocity through a convergent-divergent nozzle, and upon impact on a substrate surface, they undergo plastic deformation and adhere to the surface. For given particle and substrate materials, particle velocity and temperature at impact are the primary parameters that determine the success of particle deposition. Depending on the particle diameter and density, interactions of particles with the turbulent supersonic jet and the compressed gas region near the substrate surface can have significant effects on particle velocity and temperature. Unlike previous numerical simulations of cold spray, in this dissertation we track solid particles in the instantaneous turbulent fluctuating flow field from the nozzle exit to the substrate surface. Thus, we capture the effects of particle-turbulence interactions on particle velocity and temperature at impact.
The flow field is obtained by direct numerical simulations of a supersonic rectangular particle-laden air jet impinging on a flat substrate. An Eulerian-Lagrangian approach with two-way coupling between solid particles and gas phase is used. Unsteady three-dimensional Navier-Stokes equations are solved using a six-order compact scheme with a tenth-order compact filter combined with WENO dissipation, almost everywhere except in a region around the bow shock where a fifth-order WENO scheme is used. A fourth-order low-storage Runge-Kutta scheme is used for time integration of gas dynamics equations simultaneously with solid particles equations of motion and energy equation for particle temperature. Particles are tracked in instantaneous turbulent jet flow rather than in a mean flow that is commonly used in the previous studies. Supersonic jets for air and helium at Mach number 2.5 and 2.8, respectively, are simulated for two cases for the standoff distance between the nozzle exit and the substrate. Flow structures, mean flow properties, particles impact velocity and particles deposition efficiency on a flat substrate surface are presented. Different grid resolutions are tested using 2, 4 and 8 million points. Good agreement between DNS results and experimental data is obtained for the pressure distribution on the wall and the maximum Mach number profile in wall jet. Probability density functions for particle velocity and temperature at impact are presented. Deposition efficiency for aluminum and copper particles of diameter in the range 1 micron to 40 microns is calculated.
Instantaneous flow fields for the two standoff distances considered exhibit different flow characteristics. For large standoff distance, the jet is unsteady and flaps both for air (Mach number 2.5) and for helium (Mach number 2.8), in the direction normal to the large cross-section of the jet. Linear stability analysis of the mean jet profile validates the oscillation frequency observed in the present numerical study. Available experimental data also validate oscillation frequency. After impingement, the flow re-expands from the compressed gas region into a supersonic wall jet. The pressure on the wall in the expansion region is locally lower than ambient pressure. Strong bow shock only occurs for small standoff distance. For large standoff distance multiple/oblique shocks are observed due to the flapping of the jet.
The one-dimensional model based on isentropic flow calculations produces reliable results for particle velocity and temperature. It is found that the low efficiency in the low-pressure cold spray (LPCS) compared to high-pressure cold spray (HPCS) is mainly due to low temperature of the particles at the exit of the nozzle. Three-dimensional simulations show that small particles are readily influenced by the large-scale turbulent structures developing on jet shear layers, and they drift sideways. However, large particles are less influenced by the turbulent flow. Particles velocity and temperature are affected by the compressed gas layer and remain fairly constant in the jet region. With a small increase in the particles initial temperature, the deposition efficiency in LPCS can be maximized. There is an optimum particle diameter range for maximum deposition efficiency.<br>Ph. D.
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Geiger, Gabriel M. "Modeling Deposition and Erosion of Deposits in an Impingement Cooling Jet Using Mesh-Morphing." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1588953863722674.
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Searle, Matthew Clark. "Thermal Transport at Superhydrophobic Surfaces in Impinging Liquid Jets, Natural Convection, and Pool Boiling." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7065.
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This dissertation focuses on the effects of superhydrophobic (SHPo) surfaces on thermal transport. The work is divided into two main categories: thermal transport without phase change and thermal transport with phase change. Thermal transport without phase change is the topic of four stand-alone chapters. Three address jet impingement at SHPo surfaces and the fourth considers natural convection at a vertical, SHPo wall. Thermal transport with phase change is the topic of a single stand-alone chapter exploring pool boiling at SHPo surfaces. Two chapters examining jet impingement present analytical models for thermal transport; one considered an isothermal wall and the other considered an isoflux wall. The chapter considering the isothermal scenario has been archivally published. Conclusions are presented for both models. The models indicated that the Nusselt number decreased dramatically as the temperature jump length increased. Further, the influence of radial position, jet Reynolds number, Prandtl number and isoflux versus isothermal heating become negligible as temperature jump length increased. The final chapter concerning jet impingement reports an experimental exploration of jet impingement at post patterned SHPo surfaces with varying microfeature pitch and cavity fraction. The empirical results show a decrease in Nusselt number relative to smooth hydrophobic surfaces for small pitch and cavity fraction and the isoflux model agrees well with this data when the ratio of temperature jump length to slip length is 3.1. At larger pitch and cavity fractions, the empirical results have higher Nusselt numbers than the SHPo surfaces with small pitch and cavity fraction but remain smaller than the smooth hydrophobic surface. We attribute this to the influence of small wetting regions. The chapter addressing natural convection presents an analytical model for buoyant flow at a vertical SHPo surface. The Nusselt number decreased dramatically as temperature jump length increased, with greater decrease occurring near the lower edge and at higher Rayleigh number. Thermal transport with phase change is the topic of the final stand-alone chapter concerning pool boiling, which has been archivally published. Surface heat flux as a function of surface superheat was reported for SHPo surfaces with rib and post patterning at varying microfeature pitch, cavity fraction, and microfeature height. Nucleate boiling is more suppressed on post patterned surfaces than rib patterned surfaces. At rib patterned surfaces, transition superheat decreases as cavity fraction increases. Increasing microfeature height modestly increases the transition superheat. Once stable film boiling is achieved, changes in surface microstructure negligibly influence thermal transport.
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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.
Full textAbstract:
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.