Showing papers in "Journal of Energy in 1983"

Aspects of Computer Simulation of Liquid-Fueled Combustors

Abstract: An existing ''discrete droplet'' model of liquid sprays has been extended to include a stochastic representation of turbulent dispersion effects. Applications to simple test cases, including the dispersion of single particles, produce reasonable agreement. However, two further applications involving volatile and combusting sprays show that the turbulent dispersion effects are small in comparison to those due to uncertainties about the initial conditions of the spray.

K-epsilon equation for compressible reciprocating engine flows

Abstract: An order-of-magnitude analysis has been applied to the basic equations for k and epsilon under engine running conditions with a view to identify important terms that appear during compression/expansion in engine cylinders. It has been found that some of the terms neglected in previous studies could be quite large, and modeling of these terms has been performed. Calculations have been carried out using the modified epsilon equation, and the results have been found to be more plausible physically than those obtained with an earlier version. It is noted that more experimental data are required for validation purposes.

Double multiple streamtube model with recent improvements

Abstract: The objective of the present paper is to show the new capabilities of the double multiple streamtube (DMS) model for predicting the aerodynamic loads and performance of the Darrieus vertical-axis turbine. The original DMS model has been improved (DMSV model) by considering the variation in the upwind and downwind induced velocities as a function of the azimuthal angle for each streamtube. A comparison is made of the rotor performance for several blade geometries (parabola, catenary, troposkien, and Sandia shape). A new formulation is given for an approximate troposkien shape by considering the effect of the gravitational field. The effects of three NACA symmetrical profiles, 0012, 0015 and 0018, on the aerodynamic performance of the turbine are shown. Finally, a semiempirical dynamic-stall model has been incorporated and a better approximation obtained for modeling the local aerodynamic forces and performance for a Darrieus rotor.

Optimization of Darrieus turbines with an upwind and downwind momentum model.

Abstract: This paper presents a theoretical inviscid aerodynamic optimization method for straight-bladed Darrieus wind turbines. First, a generalized Betz limit has been derived for an arbitrary number of actuator disks in series. Then a momentum-type velocity model is introduced with separate cosine-type interference coefficients for the upwind and downwind half of the rotor. The cosine-type velocity interference permits the rotor blades to become unloaded near the junction of the upwind and downwind rotor halves. A closed-form solution for the optimum and off-design value of the interference coefficients has been obtained by equating the jc component of force on each of the rotor halves to that on each of two semicylindrical actuators in series. The values for the optimum rotor efficiency, solidity, and corresponding interference coefficients have been obtained in a closed-form analytical solution by maximizing the power extracted from the downwind rotor half as well as from the entire rotor. The Betz limit for two uniformly loaded actuator disks in series is shown to equal CP = 0.64 and for two cosine loaded semicylindrical actuators in series Cp = 0.617 and for a straight-bladed Darrieus rotor CP = 0.610.

Stored Chemical Energy Propulsion System for Underwater Applications

Abstract: An underwater propulsion system that couples a lithium fueled boiler with a standard Rankine cycle has been developed and demonstrated in an ocean environment. Although the demonstration vehicle was a small diameter axisymmetric body, other configurations have been subjected to study and experimentation. Various fuel-oxidizer combinations have been considered for use in the system, and these are examined along with the necessary supporting technologies for future development efforts. A brief history of the system development is included. It is concluded that the described system has been shown to be a viable candidate for numerous underwater applications.

Experimental and Systems Studies of the Alkali Metal Thermoelectric Converter for Aerospace Power

Abstract: The alkali metal thermoelectric converter (AMTEC) is a thermally regenerative electrochemical device for the direct conversion of heat to electrical energy. It is characterized by high potential efficiencies and no moving parts, which makes it a candidate for space power applications. This paper presents a review of AMTEC operating principles and characteristics showing that device conversion efficiencies of 15-40% may be achievable. Experimental voltage vs current curves are presented where power densities of 0.7 W/cm are observed. Measured electrode efficiencies of up to 40% that confirm the high potential efficiencies of the AMTEC are presented. Also shown are the results of preliminary radiation heat-transfer measurements, data that can be utilized to study methods for reducing parasitic radiation losses in the AMTEC. Finally, the results of a preliminary design study are presented showing that by incorporating the AMTEC into existing space power system designs, conversion efficiencies of 15-20% may be achieved at specific powers of 14-17 We/kg in a small power system (800 W). Similar performance is also predicted for a much larger («360 kW) nuclear electric system.

Mathematical Model for the Analysis of Wind-Turbine Wakes

Abstract: The concept of wind farms with clustered wind turbines at a given site seems to offer an attractive means for extracting wind power on a large scale. Techniques for minimizing the effect of upstream wind-turbine wakes on downstream wind turbines are needed to optimize overall performance of the wind-turbine array. A numerical model for prediction of the interaction of the wind turbine with the prevailing wind flow is described. The model is based on a numerical solution of the three-dimensional Navier-Stokes equations for the planetary boundary layer with the hydrostatic approximation. Three different hypothetical wind-turbine configurations are analyzed to demonstrate the utility of this model. Model predictions from the present study compare favorably with the basic characteristics of measured wind-turbine wakes. Nomenclature a = axial interference factor D = turbine blade diameter / = Coriolis parameter k = von Karman constant KM = turbulent diffusion coefficient KM - dKM/dz, gradient of turbulent diffusion coefficient L = Monin-Obukov length P = atmospheric pressure t =time U = characteristic wind speed u = velocity component in x direction ur = velocity at reference height zr u* = friction velocity v = velocity component in y direction w = velocity component in z direction x,y,z = orthogonal Cartesian coordinates Z0 = aerodynamic surface roughness Z = height of the inversion base A = incremental change p = atmospheric density 6,\I/ = dimensionless functions Subscripts

Aerodynamic performance of a Wells air turbine

Abstract: Experiments were performed in a unidirectional flow rig to assess the performance of the Wells self-rectifying air turbine. Results indicated that the efficiency of the turbine was very sensitive to the Reynolds number based on blade chord. Increase in Reynolds number by a factor of three resulted in an increase in peak efficiency from 37 to 60%. Increases in the solidity of the blade produced increases in pressure drop and power output but decreases in efficiency. The hub-to-tip ratio had only a weak influence on the turbine performance but is critical for starting conditions. It is concluded that a hub-to-tip ratio of 0.6 and a solidity of 0.6 are are the most favorable values, taking into consideration both the starting and running performances.

Aerodynamic analysis of the Darrieus rotor including secondary effects

Abstract: An aerodynamic analysis is made of two variants of the two-actuator-disk theory for modeling the Darrieus wind turbine. The double-multiple-streamtube model with constant and variable interference factors, including secondary effects, is examined for a Darrieus rotor. The influence of the secondary effects, namely, the blade geometry and profile type, the rotating tower, and the presence of struts and aerodynamic spoilers, is relatively significant, especially at high tip-speed ratios. Variation of the induced velocity as a function of the aximuthal angle allows a more accurate calculation of the aerodynamic loads on the downwind zone of the rotor with respect to the assumed constant interference factors. The theoretical results were compared with available experimental data for the Magdalen Islands wind turbine and Sandia-type machines (straight-line/ circular-arc shape).

Fault Detection and Isolation in a Nuclear Reactor

Abstract: A fault detection and identification methodology has been developed for sensor and plant component validation, with special emphasis on applications to nuclear powerplants. The methodology is particularly suitable for on-line fault diagnostics and does not rely on detailed knowledge of sensor and plant noise statistics. The algorithm has been computer coded for real-time applications and validated by on-line demonstration in an operating nuclear reactor. ARIOUS methods for fault detection and identification (FDI) of sensors have been reported in the literature.1"4 However, current practice in the nuclear industry is restricted to a few rather rudimentary techniques such as like-sensor comparisons, limit checking, auctioneering, etc. Although these techniques generally serve to improve system safety, availability, and operability, some limitations, such as the inability to identify gradual drifts and to detect common mode failures, significantly curtail their effectiveness. (If two or more elements fail identically, due to a common cause, the failure is called common mode.) The above limitations can often be circumvented with the aid of advanced computer-aided diagnostic techniques that have been developed for aerospace systems. In addition to improvement of plant availability and operability, these techniques promise to aid plant operators in making valid and timely decisions, thereby enhancing plant safety. The FDI methodology reported in this paper is developed on the basis of the "parity space" concept,3 which takes into account inconsistencies among all data sources. Any malfunctioning sensors are isolated by sequential checking until a relative consistency among the remaining (normal) sensors is achieved. This methodology does not require a detailed knowledge of sensor and plant noise statistics. Error bounds that are allowed for normal operation of the sensors are sufficient for making decisions. Real-time computer codes have been developed for detection and identification of failed sensors and plant components. As a proof of concept, these codes were verified by demonstration of on-line detection and identification of sensor failures in the 5 MW(t) nuclear reactor presently in operation at MIT, Cambridge, Mass.

Comparison of NACA 6-series and 4-digit airfoils for Darrieus wind turbines

Abstract: The aerodynamic efficiency of Darrieus wind turbines as effected by blade airfoil geometry was investigated. Analysis was limited to curved-bladed machines having rotor solidities of 7 to 21% and operating at a Reynolds number of 3 X 10/sup 6/, Ten different airfoils, having thickness-to-chord ratios of 12, 15, and 18%, were studied. Performance estimates were made using a blade element/momentum theory approach. Results indicated that NACA 6-series airfoils yeild peak power coefficients as great as NACA 4-digit airfoils and have broader and flatter power coefficient-tip speed ratio curves. Sample calculations for an NACA 63/sub 2/-015 airfoil showed an annual energy output increase of 17-27%, depending on rotor solidity, compared to an NACA 0015 airfoil.

Pitch control system for large-scale wind turbines

Abstract: The purpose of this analysis is to study the design of a pitching blade segment control system for the NASA-DOE MOD 0 wind turbine to alleviate some of the problems associated with shear, tower shadow, and gravity phenomena, such as shortened lifetime and noise generation. The classical linear quadratic Gaussian optimal regulator approach is used in the control formulation. A quasisteady aerodynamic analysis incorporating wind shear and tower shadow is utilized. An equivalent hinge model describes the turbine structural dynamics. The study shows that the proposed control system can provide significant vibration and noise reduction as well as a cleaner power signal, better gust response, and increased annual energy output.

Correlation of Lean Blowoff of Gas Turbine Combustors Using Alternative Fuels

Abstract: Generalisation d'un modele de l'extinction de la flamme en melange pauvre, a la chambre de combustion en forme de pot d'une turbine a gaz

Analytic Redundancy for On-Line Fault Diagnosis in a Nuclear Reactor

Abstract: A computer-aided diagnostic technique has been applied to on-line signal validation in an operating nuclear reactor. To avoid installation of additional redundant sensors for the sole purpose of fault isolation, a real-time model of nuclear instrumentation and the thermal-hydraulic process in the primary coolant loop was developed and experimentally validated. The model provides analytically redundant information sufficient for isolation of failed sensors as well as for detection of abnormal plant operation and component malfunctioning. Nomenclature B =bias for sensor calibration b = error bound for measurement C = specific heat F = mass flow rate of primary coolant H = measurement matrix K = product of heat transfer coefficient and area £ = number of measurements M = thermal mass m = measurement p = parity vector Q = power or rate of energy flow S = scale factor for measurement T = temperature t = time V = projection matrix v = sensor output in volts w = weighting coefficient (0 < w < 1) x = true value of a measured variable e = measurement noise 77 = parameter associated with heat transfer £ = shim blade position r = time constant X = fraction of neutron power

Optimization of Dish Solar Collectors

Abstract: Methods for optimizing parabolic dish solar collectors and the consequent effects of various optical, thermal, mechanical, and cost variables are examined The most important performance optimization is adjusting the receiver aperture to maximize collector efficiency Other parameters that can be adjusted to optimize efficiency include focal length, and, if a heat engine is used, the receiver temperature The efficiency maxima associated with focal length and receiver temperature are relatively broad; it may, accordingly, be desirable to design somewhat away from the maxima Performance optimization is sensitive to the slope and specularity errors of the concentrator Other optical and thermal variables affecting optimization are the reflectance and blocking factor of the concentrator, the absorptance and losses of the receiver, and, if a heat engine is used, the shape of the engine efficiency versus temperature curve Performance may sometimes be improved by use of an additional optical element (a secondary concentrator) or a receiver window if the errors of the primary concentrator are large or the receiver temperature is high Previously announced in STAR as N83-19224

Dish Concentrators for Solar Thermal Energy

Abstract: A wide variety of point-focusing concentrators are under consideration for solar thermal energy use They are briefly reviewed in this paper These concentrators differ in such characteristics as optical configuration and materials, structure for support of the optical elements and receiver, mount, foundation, drive, and controls Point-focusing concentrators require good optical efficiency and, especially for high-temperature applications, high geometric concentration ratios Most important are low cost, as installed, and low lifetime cost Critical cost contributors for quantity production are the cost of materials and the cost of installation labor Field testing and performance measurements of concentrators, with receivers and controls, are badly needed

Predicted and experimental aerodynamic forces on the Darrieus rotor

Abstract: Comparaison des charges aerodynamiques calculees a l'aide d'un modele de tube d'ecoulement double-multiple et des charges mesurees en soufflerie pour un rotor Darrieus a pales rectilignes

The Performance of Biplane Wells Turbine

Abstract: Etude experimentale des performances d'une turbine a air de Wells a deux rotors de 0,2 m de diametre

Aerodynamic platform comparison for jet-stream electricity generation

Abstract: Wind-tunnel experiments to determine lift and power extraction capability and an economic analysis to determine the cost of electricity generation have been undertaken for four aerodynamic platform configurations: integrated diffuser augmented wind turbine (IDAWT), separated diffuser augmented wind turbine (SDAWT), separated unshrouded wind turbine (SUWT), and rotary-wing concept (RWC). For each configuration the capital and operating costs of a 22-MW jet-stream power station based on ten minimum-cost aerodynamic platforms and related ground equipment have been calculated. The IDAWT anrf SDAWT configurations would produce electricity at a capital cost of about $(Australian) 650/kW [in Feb. 1981 $(Australian)l = $(U.S.)1.15, approximately—all currency is in Australian dollars unless otherwise noted] and an operating cost of under 5C/kWh; potential improvements in diffuser performance could reduce these costs below $550/kW and 4C/kWh, respectively. The SUWT configuration would produce electricity at a capital cost of about $700/kW and an operating cost of about 5.4C/kWh, but with little prospect of further reduction. The RWC would produce electricity at a capital cost of about $800/kW and an operating cost of about 16C/kWh. The high operating cost makes the RWC unsuited to the task of generating electricity from jet-stream winds. Nomenclature A e = diffuser exit area A T = diffuser area at the turbine station CL = lift coefficient Cp = power coefficient = Pi 1/2pu30A T C*4 = pressure coefficient at diffuser exit plane D = total drag on the platform de = diffuser exit diameter k = loss parameter, Eq. (1) £ = total length of diffuser augmented wind turbine Pi = probability that the wind speed lies in the /th speed band PDi = average power density associated with the /th speed band

Sooting Tendency of Fuels Containing Polycyclic Aromatics in a Research Combustor

Abstract: Several jet fuel blends containing alkyl benzenes, methyl naphthalenes, tetralin, and indene were prepared with hydrogen contents ranging from 11.5 to 14.2%. The effects of burner inlet conditions on the sooting tendency of the test fuels were measured in a Phillips 5.08-cm (2-in.) diameter cylindrical combustor at inlet pressures and temperatures up to 1620 kPa (16 atm) and 1100 K, respectively. Both flame radiation and opacity measurements were used to determine the soot formed in the primary zone of the burner. Combustion efficiency and fuel/air ratio were determined from gaseous emissions. The sensitivity of the sooting tendency to the H/C ratio was determined from the correlation of flame radiation intensity with the H/C ratio. This sensitivity varied significantly with operating parameters such as burner inlet temperature and reference velocity. The effects of polycyclic aromatics were determined by comparing the sensitivity to the H/C ratio of fuels blended by adding methyl naphthalenes and tetralin with that of fuels blended by adding alkyl benzenes. The increased sooting tendency of those fuels containing polycyclic aromatics was most affected by the fuel/air ratio and reference velocity. Nomenclature F/A = fuel/air weight ratio H/C = hydrogen/carbon atom ratio R = flame radiation intensity, kW/m2 S = normalized sensitivity of sooting tendency to the H/C ratio 57V = smoke number T = burner inlet temperature, K V = reference velocity, m/s p = gas density, kg/m3

Correlation of gas-turbine-combustor efficiency

Abstract: A new model is proposed to correlate combustion efficiency from gas turbine combustors, including fuel type and atomization effects. The model includes two zones in which evaporation, mixing, and kinetic processes occur. Time scales are defined to model these processes, and an expression is written for combustion inefficiency in terms of these scales. Data for four combustors, and for fuels in the range from JP-4 to DF-2, are correlated. The model reproduces the primary empirical observations, and represents a significant extension of previously proposed correlations.

An overview of combustion noise

Abstract: Combustion noise was discussed as early as 1802 in a technical note on singing flames. Occasional papers followed this early work up to about 1950, when jet propulsion spurred interest. Since then there has been a continual broadening of the areas of interest: Now the phenomena related to combustion noise are considered in a host of specific uses of combustion. This review is based on the authors' observations of nonpropulsive combustion in the residential, commercial, and industrial fields, although it is realized that there are many parallels to specific propulsive applications. Three specific areas of combustion noise are discussed in some detail, namely, combustion roar, combustion-driven oscillations, and pulse combustion. Combustion roar, in the absence of acoustic distortion effects, is characterized by a smooth noise spectrum related to the reacting chemistry of the flame and the turbulence level of the combustion region. Combustion-driven oscillations are characterized by a discrete frequency and a feedback cycle to maintain the oscillation. Pulse combustion is the positive application of combustiondriven oscillations. In addition, some other combustion noise phenomena are discussed, such as the interaction with vortex shedding and the combustion amplification of flow phenomena.

Underground coal gasification cavity growth model

Abstract: A two-dimensional underground coal gasification cavity growth model has been developed from first principles. The model accounts for injected flow conditions, oxygen content, coal seam thickness, coal heating value, coal carbon content, and initial link zone cross-sectional area distribution between the injection and production wells. The model calculates as a function of space and time: cavity growth, gas and wall temperatures, heat lost to the surroundings, the oxygen content of the flow within the cavity, and the coal consumed. The model is used to predict the final cavity shape of a recent field test with good agreement. A parametric study is also presented which shows the effects of mass flow and injected oxygen concentration on reactor growth.

Coupled Three-Dimensional Flow and Electrical Calculations for Faraday MHD Generators

Abstract: A three-dimensio nal model fully incorporating the interaction between the flow and electrical fields in MHD channels is presented. The model consists of Navier-Stokes equations in parabolic form, Maxwell and Ohm's law equations as they apply to the MHD situation, and a two-equation turbulence model. The model predictions are first compared against the supersonic flow experimental data from the AEDC facility; these data reflect weak MHD interaction in that the flowfield is little affected by the electrical power extraction. The model is then applied to high-interact ion subsonic flow in the AEDC channel to show the emergence of velocity overshoots, secondary flow, and the asymmetries in flow and electrical fields. Nomenclature B = magnetic field CD = turbulence constant E = electric field G = generation h = enthalpy H = channel height / = current density k = kinetic energy of turbulence K — load factor p = pressure field p = average pressure Pt = electrode pitch q = heat flux R( = load resistance u = velocity in x direction v = velocity in y direction w = velocity in z direction W = channel width x = axial direction y = electrode direction Z — sidewall direction o = electrical conductivity o = Prandtl or Schmidt number 0 = Hall coefficient /x = viscosity e - dissipation rate of turbulence energy p = density T — shear stress = two-dimensional potential ^ = three-dimensional potential Subscripts eff = laminar plus turbulent k = turbulence energy £ = laminar / = turbulent e = dissipation x,y,z = directions A — ( ^

A Solar Pumped Gas Laser for the Direct Conversion of Solar Energy

Abstract: The first solar pumping of a gas laser scalable to high-power levels was achieved. The solar radiation was from a xenon arc solar simulator with a 4-kW beam power and a spectral distribution of air mass zero to an accuracy of about 20%. With the lasant n-heptafluoropropyl iodide (C/sub 3/F/sub 7/I), continuous lasing at 1.315 ..mu..m for over 10 ms and peak power output of 10 W were obtained for a single static fill. Numerical simulations based on the kinetics of the iodine laser match well the experimentally observed lasing features. The laser was also operated with quasisteady flow for up to 200 ms at a 30-Hz pulse rate indicating the feasibility of continual lasing by flowing the lasant. Since an equivalent pumping power is obtainable from a modest-sized collector only 2 m in diameter, this research indicates that solar energy can be transformed effectively directly into a continuous laser output which may be useful for extended space communications, powering deep space or near-Earth missions, and possibly even supplying energy to the Earth.

The Effect of Nonimiform Water Distribution on Cooling Tower Performance

Abstract: In the design of a counterflow cooling tower, computations are based on the total water flow so that uniform delivery at a mean value over the fill is assumed. The water is generally distributed by a manifold system of pipes and nozzles which produce radial patterns on the fill. Although the nozzles are spaced to provide overlap, the distribution of water on the fill is not uniform. A method for estimating the variation in thermal performance due to nonuniformity is presented. Several test cases based on simple nozzle patterns have been considered. The results of these studies have been correlated with nozzle spacing and energy required to produce the spray as a means of indicating optimum tower design.

Analysis of the Effect of Oxygen Addition on Minimum Ignition Energy

Abstract: The optimum minimum ignition energy for quiescent or flowing mixtures can be correlated by equations. Relative to a specific fuel-air ratio, only one oxygen addition is optimum. The optimum equivalence ratio /phi/ /SUB opt/ can be correlated by an equation against the oxygen fraction, and it is independent of pressure and flow condition. The thermal ignition theory can be used to predict the minimum ignition energy reduction by oxygen addition both for quiescent and flowing mixtures. Oxygen addition affects the minimum ignition energy by means of change of oxygen concentration and change of flame temperature; both increase the chemical reaction rates and thus flame speeds. Oxygen addition is a very useful method for improving low pressure ignition or ignition of alternative or heavy fuels.

Temperature and Species-Concentration Measurements in Turbulent Flames by the CARS Technique

Abstract: Simultaneous temperature and N/sub 2/-concentration data have been obtained employing a 10-Hz coherent anti-stokes Raman spectroscopy system on two propane-air turbulent-jet diffusion flames with Reynolds numbers of 2000 and 6000. Average values, probability density functions, and correlation plots show reasonable trends for both centerline and radial profiles of the turbulent flames.