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(1 - 4 of 4)
- Title
- Experimental Investigation of Breakup and Coalescence Characteristics of a Hollow Cone Swirling Spray.
- Creator
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Lee, Joshua, Kumar, Ranganathan, Deng, Weiwei, Kapat, Jayanta, Basu, Saptarshi, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
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Atomization can be achieved by discharging liquid at relative high velocities into a slow moving environment (hydraulic nozzles) or by discharging liquid at low velocities into a fast moving gas flow (air-blast nozzles). These two types of injector nozzles are featured in majority of the industry applications such as power generation, food or pharmaceutical powder formation, spray painting, petroleum refining, and thermal sprays. The most common atomizer used in combustion engines is the...
Show moreAtomization can be achieved by discharging liquid at relative high velocities into a slow moving environment (hydraulic nozzles) or by discharging liquid at low velocities into a fast moving gas flow (air-blast nozzles). These two types of injector nozzles are featured in majority of the industry applications such as power generation, food or pharmaceutical powder formation, spray painting, petroleum refining, and thermal sprays. The most common atomizer used in combustion engines is the pressure-swirl nozzle (Simplex nozzle) to obtain a homogenous mixture at different equivalence ratios. The experimental studies performed with pressure-swirl nozzles have reported contradictory results over the last few years. Thus, the fundamentals of spray dynamics, such as spray formation, liquid breakup length, droplet breakup regimes, and coalescence still need to be understood for a pressure-swirl nozzle.An experimental study of the breakup characteristics of various liquids and fuels with different thermal physical properties emanating from hollow cone hydraulic injector nozzles induced by pressure-swirling was investigated. The experiments were conducted using two nozzles with different orifice diameters 0.3mm and 0.5mm and injection pressures (0.3-4MPa) which correspond to Rep = 7,000-31,000 depending on the liquids being tested. Three laser-based techniques, i.e., Shadowgraph, Particle Image Velocimetry (PIV) and Phase Doppler Particle Anemometry (PDPA) were utilized in this study. Although each technique had its limitation in different flow regimes, the results were cross-validated, and generally showed correct trends in axial and radial measurements of velocity and diameter for different nozzles, Weber and Reynolds numbers.The spatial variation of diameter and velocity arises principally due to primary breakup of liquid films and subsequent secondary breakup of large droplets due to aerodynamic shear. Downstream of the nozzle, coalescence of droplets due to collision is also found to be significant. Different types of liquid film break up was considered and found to match well with the theory. The spray is subdivided into three zones: near the nozzle, a zone consisting of film and ligament regime, where primary breakup and some secondary breakup take place; a second zone where the secondary breakup process continues, but weakens, and the centrifugal dispersion becomes dominant, and a third zone away from the spray where coalescence is dominant. Each regime has been analyzed in detail to understand the effect of surface tension and viscosity. Surface tension and viscosity were engineered to mimic fuels, which were then compared with real fuels such as Ethanol, Jet-A and Kerosene. Results show similarity in the diameter in the beginning stages of breakup but in the coalescence regime, the values deviate from each other, indicating that the vapor pressure also plays a major role in this regime.
Show less - Date Issued
- 2013
- Identifier
- CFE0005021, ucf:50014
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005021
- Title
- LOW REYNOLDS NUMBER WATER FLOW CHARACTERISTICS THROUGH RECTANGULAR MICRO DIFFUSERS/NOZZLES WITH A PRIMARY FOCUS ON MAJOR/MINOR PRESSURE LOSS, STATIC PRESSURE RECOVERY, AND FLOW SEPARATION.
- Creator
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Hallenbeck, Kyle, Chew, Larry, University of Central Florida
- Abstract / Description
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The field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS...
Show moreThe field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS soft lithography including 38 diffuser/nozzle channels a piece. Each nozzle and diffuser consisted of a throat dimension of 100μm x 50μm, leg lengths of 142μm, and half angles varying from 0o – 90o in increments of 5o. The flow speeds tested included throat Reynolds numbers of 8.9 – 89 in increments of 8.9 using distilled water as the fluid. The static pressure difference was measured from the entrance to the exit of both the diffusers and the nozzles and the collected data was plotted against a fully attached macro theory as well as Idelchik's approximations. Data for diffusers and nozzles up to HA = 50o hints at the idea that the flow is neither separating nor creating a vena contracta. In this region, static pressure recovery within diffuser flow is observed as less than macro theory would predict and the losses that occur within a nozzle are also less than macro theory would predict. Approaching a 50o HA and beyond shows evidence of unstable separation and vena contracta formation. In general, it appears that there is a micro scaled phenomenon happening in which flow gains available energy when the flow area is increased and looses available energy when the flow area decreases. These new micro scaled phenomenon observations seem to lead to a larger and smaller magnitude of pressure loss respectively.
Show less - Date Issued
- 2008
- Identifier
- CFE0002391, ucf:47772
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002391
- Title
- CONJUGATE HEAT TRANSFER ANALYSIS OF COMBINED REGENERATIVE AND DISCRETE FILM COOLING IN A ROCKET NOZZLE.
- Creator
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Pearce, Charlotte M, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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Conjugate heat transfer analysis has been carried out on an 89kN thrust chamber in order to evaluate whether combined discrete film cooling and regenerative cooling in a rocket nozzle is feasible. Several cooling configurations were tested against a baseline design of regenerative cooling only. New designs include combined cooling channels with one row of discrete film cooling holes near the throat of the nozzle, and turbulated cooling channels combined with a row of discrete film cooling...
Show moreConjugate heat transfer analysis has been carried out on an 89kN thrust chamber in order to evaluate whether combined discrete film cooling and regenerative cooling in a rocket nozzle is feasible. Several cooling configurations were tested against a baseline design of regenerative cooling only. New designs include combined cooling channels with one row of discrete film cooling holes near the throat of the nozzle, and turbulated cooling channels combined with a row of discrete film cooling holes. Blowing ratio and channel mass flow rate were both varied for each design. The effectiveness of each configuration was measured via the maximum hot gas-side nozzle wall temperature, which can be correlated to number of cycles to failure. A target maximum temperature of 613K was chosen. Combined film and regenerative cooling, when compared to the baseline regenerative cooling, reduced the hot gas side wall temperature from 667K to 638K. After adding turbulators to the cooling channels, combined film and regenerative cooling reduced the temperature to 592K. Analysis shows that combined regenerative and film cooling is feasible with significant consequences, however further improvements are possible with the use of turbulators in the regenerative cooling channels.
Show less - Date Issued
- 2016
- Identifier
- CFH2000138, ucf:45923
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000138
- Title
- SPRAY COOLING FOR LAND, SEA, AIR AND SPACE BASED APPLICATIONS,A FLUID MANAGEMENT SYSTEM FOR MULTIPLE NOZZLE SPRAY COOLING AND A GUIDE TO HIGH HEAT FLUX HEATER DESIGN.
- Creator
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Glassman, Brian, Chow, Louis, University of Central Florida
- Abstract / Description
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This thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore,...
Show moreThis thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore, this chapter outlines in detail the impact that land, air, sea, and space environments have on the cooling system and what technologies could be enabled in each environment with the aid of spray cooling. In particular, the heat exchanger, condenser and radiator are analyzed in their corresponding environments. Chapter three presents an experimental investigation of a fluid management system for a large area multiple nozzle spray cooler. A fluid management or suction system was used to control the liquid film layer thickness needed for effective heat transfer. An array of sixteen pressure atomized spray nozzles along with an imbedded fluid suction system was constructed. Two surfaces were spray tested one being a clear grooved Plexiglas plate used for visualization and the other being a bottom heated grooved 4.5 x 4.5 cm2 copper plate used to determine the heat flux. The suction system utilized an array of thin copper tubes to extract excess liquid from the cooled surface. Pure water was ejected from two spray nozzle configurations at flow rates of 0.7 L/min to 1 L/min per nozzle. It was found that the fluid management system provided fluid removal efficiencies of 98% with a 4-nozzle array, and 90% with the full 16-nozzle array for the downward spraying orientation. The corresponding heat fluxes for the 16 nozzle configuration were found with and without the aid of the fluid management system. It was found that the fluid management system increased heat fluxes on the average of 30 W/cm2 at similar values of superheat. Unfortunately, the effectiveness of this array at removing heat at full levels of suction is approximately 50% & 40% of a single nozzle at respective 10„aC & 15„aC values of superheat. The heat transfer data more closely resembled convective pooling boiling. Thus, it was concluded that the poor heat transfer was due to flooding occurring which made the heat transfer mechanism mainly forced convective boiling and not spray cooling. Finally, Chapter four gives a detailed guide for the design and construction of a high heat flux heater for experimental uses where accurate measurements of surface temperatures and heat fluxes are extremely important. The heater designs presented allow for different testing applications; however, an emphasis is placed on heaters designed for use with spray cooling.
Show less - Date Issued
- 2005
- Identifier
- CFE0000473, ucf:46351
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000473
