Experimental and Numerical Investigation of Evaporative Spray Cooling for a 45 Degree Bend Near a Gas Turbine Exhaust PDF Download
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Author: Grant Armitage Publisher: ISBN: Category : Languages : en Pages : 292
Book Description
The research performed in this work investigated evaporative spray cooling systems using water near a 45 degree bends in gas turbine exhaust piping systems. Both experimental data and numerical data were generated with the goal of evaluating the ability of Fluent 6.3.26 to predict the performance of these systems for the purpose of design using only modest computational resources. Three cases were investigated in this research: single phase exhaust flow with no water injection, injecting water before the bend and injecting water after the bend. Various probes were used to measure dry bulb temperature, total pressure and water mass flux of the two phase flow at the exit of the pipe. Seven hole probes and pitot static probes were used to measure single phase flow properties. Numerical simulations were performed using mass flow boundary conditions which were generated from experimental results. A turbulence model was selected for the simulations based on comparisons of single phase simulations with experimental data and convergence ability. Using Fluent's discrete phase model, different wall boundary conditions for the discrete phase were used in order to find the model which would best match the evaporation rates of the experimental data. Mass flux values through the exit plane of the pipe were found to be the most reliable of all the two phase data collected. Results from numerical simulations revealed the shortcomings of the available discrete phase wall boundary conditions to accurately predict the interaction of the liquid phase with the wall. Experimental results for both cases showed extensive areas of the wall which had liquid film layers running down the length of the pipe. Simulations resulted in particles either failing to impact the wall and create a liquid film, or creating a liquid film which was much smaller than the film present in experimental results. This led to 8% and 15% discrepancy in evaporation amounts between numerical and experimental results for water injection upstream and downstream of the bend respectively. Under-prediction of areas wetted with a wall film in the simulations also led to gross over predictions of wall temperature in numerical results.
Author: Grant Armitage Publisher: ISBN: Category : Languages : en Pages : 292
Book Description
The research performed in this work investigated evaporative spray cooling systems using water near a 45 degree bends in gas turbine exhaust piping systems. Both experimental data and numerical data were generated with the goal of evaluating the ability of Fluent 6.3.26 to predict the performance of these systems for the purpose of design using only modest computational resources. Three cases were investigated in this research: single phase exhaust flow with no water injection, injecting water before the bend and injecting water after the bend. Various probes were used to measure dry bulb temperature, total pressure and water mass flux of the two phase flow at the exit of the pipe. Seven hole probes and pitot static probes were used to measure single phase flow properties. Numerical simulations were performed using mass flow boundary conditions which were generated from experimental results. A turbulence model was selected for the simulations based on comparisons of single phase simulations with experimental data and convergence ability. Using Fluent's discrete phase model, different wall boundary conditions for the discrete phase were used in order to find the model which would best match the evaporation rates of the experimental data. Mass flux values through the exit plane of the pipe were found to be the most reliable of all the two phase data collected. Results from numerical simulations revealed the shortcomings of the available discrete phase wall boundary conditions to accurately predict the interaction of the liquid phase with the wall. Experimental results for both cases showed extensive areas of the wall which had liquid film layers running down the length of the pipe. Simulations resulted in particles either failing to impact the wall and create a liquid film, or creating a liquid film which was much smaller than the film present in experimental results. This led to 8% and 15% discrepancy in evaporation amounts between numerical and experimental results for water injection upstream and downstream of the bend respectively. Under-prediction of areas wetted with a wall film in the simulations also led to gross over predictions of wall temperature in numerical results.
Author: Nathon Begg Publisher: ISBN: Category : Languages : en Pages : 346
Book Description
This research studied the effects of evaporative spray cooling on air-air ejector performance. Experimental data was collected for the purpose of validating computational simulations. This was done by modifying an existing air-air ejector to accommodate four spray flow nozzles which were used to atomize cooling water. The only parameter that was varied throughout the study was the mass flow rate of cooling water. One single phase (air) case and four spray flow cases where performed and analyzed. The purpose of the single phase experiment was to have a baseline for the air-air ejector performance and isolate the sources of experimental error contributed by spray flow. Three specialized multiphase flow instruments were designed and fabricated by the author to measure, gas phase temperatures, spray mass flow rates, and mixture total pressures. A computational study was performed using the collected experimental data for inlet continuous phase and spray mass flow as boundary conditions for equivalent simulations. A temperature gradient modified turbulence model was written by the author to better predict the mixing rates found experimentally which was used for the duration of this research. Secondary droplet breakup was modeled by the author using empirical correlations following preliminary simulations recognizing the deficiencies of commercially available breakup models. Comparison of experimental and computational cases produced mixed results. It was found that the experimental gas temperature instrument performed poorly for the local droplet fluxes encountered during testing. The spray sampling probe showed more promising results with two integrated mass flows agreeing within 6% of computational simulations. The total pressure probe solved the issue of pressure port clogging, but measurements were representative of mixture density which made an inferred velocity calculation difficult. It was found that evaporation of spray flow before the nozzle exit plane caused a reduction in dynamic pressure and a reduction in back pressure. A full scale simulation was performed to determine the effects of scaling on evaporative spray cooling performance. It was found that for the geometrically similar full scale model, the total droplet surface area and particle residence times scaled up with the model which increased cooling performance.
Author: Vladimir Novak Publisher: ISBN: Category : Atomization Languages : en Pages :
Book Description
An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness. A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters. Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.
Author: Gerard Scheepers Publisher: ISBN: Category : Languages : en Pages :
Book Description
Developments regarding internal cooling techniques have allowed the operation of modern gas turbine engines at turbine inlet temperatures which exceed the metallurgical capability of the turbine blade. This has allowed the operation of engines at a higher thermal efficiency and lower specific fuel consumption. Modern turbine blade-cooling techniques rely on external film cooling to protect the outer surface of the blade from the hot gas path and internal cooling to remove thermal energy from the blade. Optimization of coolant performance and blade-life estimation require knowledge regarding the influence of cooling application on the blade inner and outer surface heat transfer. The following study describes a combined experimental and computational study of heat transfer augmentation near the entrance to a film-cooling hole. Steady-state heat transfer results were acquired by using a transient measurement technique in an 80 x actual rectangular channel, representing an internal cooling channel of a turbine blade. Platinum thin-film gauges were used to measure the inner surface heat transfer augmentation as a result of thermal boundary layer renewal and impingement near the entrance of a film-cooling hole. Measurements were taken at various suction ratios, extraction angles and wall temperature ratios with a main duct Reynolds number of 25? 103. A numerical technique, based on the resolution of the unsteady conduction equation, using a Crank-Nicholson scheme, was used to obtain the surface heat flux from the measured surface temperature history. Computational data was generated with the use of a commercial CFD solver.
Author: Kerri Michelle Baysinger Publisher: ISBN: Category : Cooling Languages : en Pages : 116
Book Description
Baseline tests were performed for a spray cooling system using subcooled fluid under terrestrial gravity conditions, and a steady state numerical model of the glass heater pedestal assembly was built using ANSYS finite element software. A parametric study was performed to study the effects of volumetric flow rate, heat transfer rate, and orientation with respect to gravity on the experimental system. The numerical model data was compared with the experimental data in order to determine the spray heat transfer coefficient along the top of the heated surface. For a volumetric flow range gal/hr and a heat load range of W, the estimated spray heat transfer coefficient was on the order of W/(m2-K), regardless of heater orientation. In addition, the heat lost due to conduction in the upward-facing heater pedestal was estimated using both experimental and numerical results, and was found to be 1.0 greater or less than (percent of heat loss due to conduction in glass heater pedestal assembly) greater or less than 2.5%.
Author: Grant Armitage
Author: Grant Armitage
Author: Grant Armitage
Author: Nathon Begg
Author: Andrea C. Ashwood
Author: Roy A. McKinnon
Author: Vladimir Novak
Author: Gerard Scheepers
Author: Marion John Balcerzak
Author: Dieter E. Bohn
Author: Kerri Michelle Baysinger