Showing papers in "Journal of Engineering for Power in 1976"

A Theory of Concentrators of Solar Energy on a Central Receiver for Electric Power Generation

Abstract: The modeling of the performance of large-area solar concentrators for central receiver power plants is formulated using a continuum field representation of ideal heliostat arrays that accounts for two governing factors: the law of reflection of light rays imposes steering constraints on mirror orientations; the proximity of mirrors creates shadow effects by blocking the incident and/or reflected solar radiation. The results of a steering analysis which develops the space-time characteristics of heliostats and of a shadow analysis which determines the local effectiveness of mirrors in reflecting solar energy to a central point are combined to obtain in closed analytical form the global characteristics of circular concentrators. These characteristics which appear as time profiles for mirror orientations, for effective concentration areas (i.e., reflected solar flux), and for concentration ratios, establish theoretical limits of performance against which actual or realistic solar power systems can be compared and assessed.

Three Dimensional Characteristics of Turbulent Wakes Behind Rotors of Axial Flow Turbomachinery

Abstract: Analytical and experimental investigations of the characteristics of three-dimensional turbulent wakes downstream of a turbomachinery rotor are reported in this paper. An approximate quasi-three-dimensional turbulent wake model for turbomachinery rotor is developed and compared with the cascade and isolated airfoil wake models. The rotor wake model is capable of predicting the decay of mean component of radial and streamwise velocities as a function of rotor geometry, speed of rotation, and the turbulence properties of the flow field. A rotation parameter based on similarity analysis is derived. The velocity profiles in both the radial and cylindrical planes are coupled together. Measurement of mean velocities (Un , Us , Ur ), turbulent intensities and stresses (un2, us2, ur2, usun, unur, usur) is carried out using a triple sensor hot wire probe in a stationary system at various axial and radial locations downstream of the rotor. Profiles of mean and turbulent quantities are obtained. Semi-theoretical expressions for the decay rates of the defect in mean velocity, turbulence intensity, and Reynolds stress (maximum values) with distance downstream of the rotor are derived. The experimental data on the rotor wake are compared with that of an isolated airfoil and cascade of airfoils. The investigation suggests that rotor wake decays much faster than the cascade or an isolated airfoil wake.

Experiments Concerning the Response of Supersonic Nozzles to Fluctuating Inlet Conditions

Abstract: The noise field produced by the passage of pressure and entropy fluctuations through a supersonic nozzle has been investigated in an experimental program. Magnitude and phase information for the disturbances produced within the nozzle are presented and are compared with numerical calculations.

The Effect of Water/Residual Oil Emulsions on Air Pollutant Emissions and Efficiency of Commercial Boilers

Abstract: Two commercially available water-in-oil emulsifiers were tested to determine the effect of water/residual oil emulsions on air pollutant emissions and thermal efficiency of a packaged boiler Of the two emulsifiers, one (Cottell reactor) utilized low pressure mechanical and ultrasonic energy and the other (total emulsifier) utilized high pressure mechanical energy Each emulsifier was tested at a constant oil flow rate with varying amounts of water over a range of stoichiometric ratios Water/residual oil emulsions from both emulsifiers significantly reduced particulate mass With the Cottrell reactor smoke emissions were significantly reduced, whereas with the total emulsifier smoke emissions increased and peaked with a 20 percent water emulsion, then decreased as water was increased to 30 percent Neither emulsifier had any significant effect on emissions of NO, SO/sub 2/, or HC when firing water/residual oil emulsions Both emulsifiers were capable of improving efficiency by approximately 2 percent under certain conditions

The Physical and Chemical Characteristics of Pyrites and Their Influence on Fireside Problems in Steam Generators

Abstract: With the increase in the boiler size, increase in heat release rates within the combustion zone and general degradation of the fossil fuel supply, fireside fouling and slagging problems have become more acute. Considerable efforts have been made in the past to define the mechanism responsible for these problems. Little has been done, however, to relate the problems to the manner in which the impurities appear in the fuel. Such an understanding should permit prediction of problems prior to combustion as well as assist in the development of means for modifying the fuel to suitable limits for successful firing in the steam generator. The influence of a single mineral impurity, pyrites, on fireside problems is examined. Several alternatives exist for the prevention of slagging problems caused by pyrites. These include reduction of the pyrites to levels which will insure complete combustion within the time allowed and simultaneous reduction of the potential for segregation of the ash within the boiler. Experimental work in the laboratory should continue to define accurately the combustion rates of pyrites, as well as the heat transfer properties of slag to permit further modeling of the deposit formation within the furnace. (RCK)

Combustion generated noise in gas turbine combustors

Abstract: Experiments were conducted to determine the noise power and spectra emitted from a gas turbine combustor can exhausting to the atmosphere. Limited hot wire measurements were made of the cold flow turbulence level and spectra within the can. The fuels used were JP-4, acetone and methyl alcohol burning with air at atmospheric pressure. The experimental results show that for a fixed fuel the noise output is dominated by the airflow rate and not the fuel/air ratio. The spectra are dominated by the spectra of the cold flow turbulence spectra which were invariant with airflow rate in the experiments. The effect of fuel type on the noise power output was primarily through the heat of combustion and not the reactivity. A theory of combustion noise based upon the flame radiating to open surroundings is able to reasonably explain the observed results. A thermoacoustic efficiency for noise radiation as high as .00003 was observed in this program for JP-4 fuel. Scaling rules are presented for installed configurations.

An Examination of the Relationship Between Ash Chemistry and Ash Fusion Temperatures in Various Coal Size and Gravity Fractions Using Polynomial Regression Analysis

Abstract: Fireside fouling and slagging properties of western subbituminous coals were studied. An examination of the relationship between the ash chemistry and ash fusion temperature indicates variation in softening temperature of individual species within the coal and may be important for those ashes whose bulk basicity is in the vicinity of 20 and 60 percent and whose ash softening temperature is approximately 1533/sup 0/K. Variations in melting temperatures of independent specie in ash whose composite softening temperature is greater than 1533/sup 0/K contribute little to the fouling problem. By including the determination of ash fusion temperature and ash chemistry in washability studies of coals with several different size distributions, fuel preparation can be evaluated as a means of modifying coals to meet air pollution prevention standards and to avoid fireside fouling and slagging problems. The regression analysis has indicated that a simple relationship exists between the ash softening temperature and the basic constituents, using the silica to alumina ratio as a parameter. The relationships appear to apply to all coals within a given rank. A generalization such as this, however, requires confirmation with many more analyses. A statistical examination of the data fit by the regression analysis indicates the standard errormore » is approximately 55/sup 0/K for data generated in a single laboratory, as well as for data generated in several laboratories. This points to a confidence limit of only 68.7 percent on a deviation in softening temperature twice the limits set by the ASTM procedure.« less

A Method of Measuring the Three-Dimensional Mean Flow and Turbulence Quantities Inside a Rotating Turbo-machinery Passage

Abstract: A method of measuring the three-dimensional components of mean velocity and turbulence quantities within a rotating turbomachinery passage is developed through the use of hot wire anemometry techniques. Equations are derived which, when solved simultaneously and in conjunction with the data obtained from the hot wire anemometer measurements, will provide values for the radial, axial and tangential components of mean velocity, turbulence intensity and turbulence stress within the rotating turbomachinery passage. A three-bladed rocket pump inducer model, operating in air, was used in the experimentation. The method is very accurate and provides very useful information on the characteristics of the flow inside rotor passages hitherto unexplored.

A One-Dimensional Variable Area Computer Simulation of Combustion in a Divided Chamber, Stratified Charge Engine

Abstract: A numerical simulation model of a divided chamber, stratified charge engine has been developed. The conservation equations of fluid mechanics, coupled to a single, global chemical reaction model have been solved by use of a generalized Eulerian-Lagrangian numerical technique for a one-dimensional, variable-area combustion volume. The simulation results in a prediction of the flame propagation dynamics which leads to temperatures, pressures, and species concentrations as functions of spatial location, time, and the various engine design parameters such as rpm and fuel/air ratio. The results indicate that both broad, turbulent flame fronts as well as detonations can occur, depending upon the rate of the oxidation reaction and the rate of heat release. The technique should be useful for calculating concentrations of pollutants as well as for investigating various design options such as fuel/air ratio and stratification function on pollution level and engine performance.

A Diffusion Limited Model That Accurately Predicts the NOx Emissions From Gas Turbine Combustors Including the Use of Nitrogen Containing Fuels

Abstract: A diffusion limited model has been described previously to simulate accurately the thermal NO/sub x/ emission processes in various gas turbine combustors for fuels containing negligible amounts of fuel bound nitrogen The application of this model to simulate accurately the water injection process has also been demonstrated It is currently proposed that any bound nitrogen in fuel is completely reacted to form nitric oxide during the hydrocarbon combustion process; the ultimate net conversion is determined subsequently based on the Zeldovich mechanisms With this additional assumption, this model was generalized to include the use of fuels containing significant amounts of bound nitrogen, such as crude or residual oils The predicted NO/sub x/ emissions from these nitrogen containing fuels are in excellent agreement with laboratory and field data including the effect of water injection Comprehensive understanding of the NO/sub x/ formation processes was gained from the current analytical study

The Vorbix Burner—A New Approach to Gas Turbine Combustors

Abstract: The vorbix burner (acronym for Vortex Burning and Mixing) represents a new approach to a practical gas turbine combustor design. The concept exploits the Rayleigh instability of swirling flows to enhance the mixing and combustion rates. The combination of a two-stage fuel system with a piloted combustor leads to a unique high rate technique for fuel prevaporization within the combustor proper. This paper presents the fundamental concepts in the definition of the vorbix combustor and the results of exploratory tests conducted on can (tubular) and annular vorbix combustors. The results indicate that this type of combustor has unique performance characteristics that include excellent stability and high combustion efficiency over wide excursions in operating fuel air ratios in addition to substantially reduced emission levels during high power operation.Copyright © 1975 by ASME