16 Fuel science and technology (fundamental science, analysis, instrumentation)

Natural convection of fluid and solid conjugate problem inside a complex cavity is studied by using vorticity-stream function method. The influences of material character, geometrical shape and Rayleigh number on the heat transfer in overall concerned region have been investigated. The followings can be concluded under steady state: The flow and heat transfer increase with the increase of the thermal conductivity in solid region; Both geometric shape and Rayleigh number affect the overall flow and heat transfer greatly.

04/03098 Demonstration of plasma excited atomic resonance line spectroscopy for on-line measurement of alkali metals in a 20 kW bubbling fluidized bed Hfiyrinen, V. et al. Fuel, 2004, 83, (7-8), 791 797. An instrument based on Plasma Excited Atomic Resonance Line Spectroscopy (PEARLS) was applied to measurements of vapour and aerosol phase Na and K in atmospheric combustion conditions. The PEARLS method is based on dissociation of alkali compounds by a direct current plasma torch and subsequent determination of alkali concentration by atomic absorption spectroscopy. The measurements were carried out in a 20 kW bubbling fluidized bed reactor during co- combustion of biomass and coal. The capability of the instrument to operate under atmospheric high-ash conditions was demonstrated. The analysis was made directly from hot (880°C) particulate laden sample gas. The fuels were pine bark mixed with South African coal and Finnish forest residue mixed with Polish lignite. Thirty percent addition of coal or lignite to biomass reduced measured alkali concentrations by 44-64%. The reduction is explained by conversion of alkali chlorides and hydroxides to sulfates and silicates.

04•03099 Density, refractive index and speed of sound for mixtures of ethyl acetate with 2-butanol and 3-methyl-I- butanol Resa, J. M. et al. Fluid Phase Equilibria, 2004, 217, (2), 175-180. Densities, refractive indices and speeds of sound at 298.15, 303.15, and 308.15 K are reported for the binary mixtures ethyl acetate + 2-butanol and ethyl acetate + 3-methyl-l-butanol. Isobaric vapour-liquid equilibrium data at 101.3 kPa were determined for the ethyl acetate + 3-methyl-l-butanol system. Excess molar volumes, refractive index deviations and changes of speed of sound on mixing were calculated from experimental results and fitted with Redlich-Kister polynomials. VLE experimental data were satisfactorily tested for thermodynamic consistency by means of a modified Dechema test. The activity coefficients were correlated with the UNIQUAC, NRTL, and Wilson equations. The ASOG model was also used for prediction.

04103100 Development of a fundamental crack tip strain rate equation and its application to quantitative prediction of stress corrosion cracking of stainless steels in high temperature oxygenated water Peng, Q. J. et al. Journal o f Nuclear Materials, 2004, 324, (I), 52 61. A formulation for the quantitative calculation of the stress corrosion cracking (SCC) growth rate was proposed based on a fundamental- based crack tip strain rate (CTSR) equation that was derived from the time-based mathematical derivation of a continuum mechanics equation. The CTSR equation includes an uncertain parameter r0, the characteristic distance away from a growing crack tip, at which a representative strain rate should be defined. In this research, slow strain rate tensile tests on sensitized 304L stainless steel in oxygenated high temperature water were performed. By curve fitting the experimental results to the numerically calculated crack growth rate, the parameter r0 was determined. Then, the theoretical formulation was used to predict the SCC growth rates. The results indicate that r0 is on the order of several micrometers, and that the application of the theoretical equation in predicting the crack growth rate provides satisfactory agreement with the available data.

04/03101 Effects of pressure gradient on film cooling effectiveness from two rows of simple and compound angle holes in combination Maiteh, B. Y. and Jubran, B. A. Energy Conversion and Management, 2004, 45, (9 10), 1457-1469. This paper describes the results of an experimental investigation into the effect of pressure gradient on the film cooling effectiveness from compound angle holes at both injection rows or the combination of one row of simple angle holes and one row of compound angle holes. Two pressure gradients were used in the range from -1.11 x 10 6 to +1.11 x 10 -6. The presence of a favourable pressure gradient tends to increase the dilution of the injected coolant jets, which results in a reduction of the film cooling protection over the surface. The presence of an adverse pressure gradient at high blowing rate tends to dilute the film coolant even at a higher rate than that when zero or favourable pressure gradients are present.

04/03102 Efficient methods for calculations of compressibility, density and viscosity of natural gases Elsharkawy, A. M. Fluid Phase Equilibria, 2004, 218, (1), 1 13. This study presents two new methods for calculating properties of natural gases. The first is an efficient empirical model to calculate compressibility and density of natural gases containing high amount of heptane plus and none-hydrocarbon components. The model is derived from 2400 measurements of compressibility and density of various gases presented in this study. Accuracy of the model is compared to various equations of state (EOS), corresponding state, and empirical methods. The study shows that the new model is simpler and more efficient than EOS. It eliminates the numerous computations involved in EOS calculations. The new method also eliminates the character- ization of the heptane plus fraction and estimation of binary interaction parameters needed for EOS calculations. Experimentally measured density of several gases has been used to study the validity of the proposed method. These measurements indicate that the new method successfully capture the physical trend of changing gas density as a function of pressure, temperature, and composition. The second method is a modification of Lee-Gonzalez-Eakin gas viscosity correlation. The new method accounts for the presence of heptane plus, hydrogen sulfide, and carbon dioxide in natural gases. The proposed method is compared to other EOS-based viscosity model, corresponding state methods, and correlations. The comparison indicates the superiority of the new method over the other methods used to calculate viscosity of natural gases.

04•03103 Efficient numerical solution of the point kinetics equations in nuclear reactor dynamics Kinard, M. and Allen, E. J. Annals o f Nuclear Energy, 2004, 3 l, (9), 1039-1051. A numerical procedure to efficiently calculate the solution to the point kinetics equation in nuclear reactor dynamics is described and investigated. Piecewise constant approximations of the reactivity and source functions are made. The resulting system of linear differential equations is solved exactl~¢ over each time step. The method is proved to converge with order h ~ where h is the time step. The procedure is tested using a variety of initial conditions, data, and reactivity functions. The computational results indicate that the method is efficient and accurate.

04/03104 Evaporation of diesel fuel droplets: kinetic versus hydrodynamic models Kryukov, A. P. et al. International Journal o f Heat and Mass Transfer, 2004, 47, (12-13), 2541~549. A comparative analysis of hydrodynamic and kinetic approaches to the problem of diesel fuel droplet evaporation is presented. It is pointed out that the kinetic effects on droplet evaporation are always noticeable, despite the fact that this evaporation takes place at high pressures (up to 30 atm and even more). This shows the limitation of applying the hydrodynamic approach to modelling this process. The hydrodynamic approach is universally used in computational fluid dynamics (CFD) codes. Kinetic models predict longer evaporation time and higher droplet temperature compared with the hydrodynamic model. The kinetic effects are shown to be more pronounced for smaller droplets (5 gin) than for larger ones (20 ~m). The droplet evaporation time and droplet temperature increase with decreasing evaporation coefficient. It is recommended that kinetic effects are taken into account when modelling the evaporation process of diesel fuel droplets in realistic internal combustion engines.

04/03105 Faster on-line calculation of thermal stresses by time integration Zucca, S. et aL International Journal o f Pressure Vessels and Piping, 2004, 81, (5), 393-399. The Green's function technique (GFT) is largely used for on-line calculation of thermal stresses in machines and plants, because it allows turning parameters such as fluid temperatures, pressures and flow rates directly in thermal stresses. Recently the use of the GFT has been extended by the authors to thermo-meehanical models having variable convective coefficients. The novel methodology consists of two steps. First, boundary temperatures are evaluated by time integration of a reduced thermal model and then thermal stresses are calculated by means of the GFT using as inputs the boundary temperatures previously evaluated. The new approach implies a large number of convolution integrals to be solved for thermal stress calculation. In order to reduce computation time, it is here proposed that the convolution integrals that characterize the GFT are replaced with a reduced model of uncoupled first-order differential equations, whose coefficients are estimated fitting the Green's functions of the thermo- mechanical model with a sum of exponential terms. Thermal stresses are obtained by time integration of the model,

435 Fuel and Energy Abstracts November 2004