04/02604 development of a 2-d 2-group neutron noisesimulator: demazière, c. et al. annals of...

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

    reservoir on the optimal power and the corresponding efficiency and corresponding inter-cooling pressure ratio, as well as the optimal efficiency and the corresponding power and corresponding intercooling pressure-ratio are analysed by detailed numerical examples.

    0402602 Computer methods for performance prediction in fuel cells Beale, S. B. et al. Journal of Power Sources, 2003, 118, (1-2), 79-85. Several transport models for fuel ceils have been developed. The models are compared and tested for single fuel cells and multi-cell stacks of planar solid-oxide fuel cells, the three main approaches considered are (a) a detailed numerical model (DNM) of flow, heat and mass transfer and electrochemistry, (b) a flow-based methodology based on a distributed resistance analogy (DRA), and (c) a presumed- flow methodology (PFM). The results from each of the above approaches are compared in detail, and merits and drawbacks discussed. It is shown that, under certain circumstances, the simpler approaches have the potential to supplant or complement the direct numerical me~_hod in the analysis of fuel cells.

    0402606 Distribution of activation energy model applied to the rapid pyrolysis of coal blends Ulloa, C. et al. Journal of Analytical and Applied Pyrolysis, 2004, 71. (2), 465-483. A multiple reaction model (MRM) was used to characterize the kinetics of pyrolysis of single coals and binary blends; the MRM represents the kinetics through a continuous distribution of the activation energies of the individual reactions (DAEM). Kinetic parameters were assessed from experiments performed in a drop-tube reactor at high temperatures (1000-1300C) and low residence times (60-320 ms). Results are given for three single coals and two binary blends. Volatile yields are generally greater than the ASTM standard values due to fewer secondary reactions under the experimental conditions. The proposed model satisfactorily reproduces devolatiliza- tion curves as a function of activation energy distribution and a parameter that depends on the liptinite, vitrinite and ash content of the coal or blend. A defined 'Pyrolysis Yield Index' (PYI) that combines the maceral composition and ash content, appears to correlate well with a parameter of the kinetic model. Blends constituted by petrographically similar coals show no significant deviation from the expected weighted average of the single coals.

    0402603 Design approach for a biomass fed fluidized bed gasifier using the simulation software CSFB van den Enden, P. J. and Silva Lora, E. Biomass and Bioenergy, 2004, 26, (3), 281-287. In the paper a design approach for a biomass fluidized bed gasifier using the comprehensive simulator for fluidized bed equipment (CSFB) is proposed. Performance parameters such as air factor, feeding point position and bed height are determined looking for a maximum gasifier efficiency and gas heating value and a minimum tar content in the gas. Other parameters optimized by using the CSFB software are the pressure drop, the bubble diameter and the gas velocities in the bed.

    04102604 Development of a 2-D 2-group neutron noise simulator Demazi~re, C. et al. Annals of Nuclear Energy, 2004, 31, (6), 647-680 In this paper, the development of a so-called neutron noise simulator is reported. This simulator calculates both the direct and the adjoint reactor transfer function between a stationary noise source and its induced neutron noise for any two-dimensional heterogeneous critical system. The main advantage of this neutron noise simulator is that any realistic core can be modelled, since the simulator is designed to rely on a set of material constants corresponding to the actual reactor operating conditions. The calculations are performed in the two-group diffusion approximation and in the frequency domain. The spatial discretization is carried out with respect to the finite difference scheme. The noise source, expressed as an 'absorber of variable strength' type, is defined directly from the fluctuations of the macroscopic cross-sections and can be spatially distributed over the core or concentrated in a few discrete nodes. If the noise source is a point-source, the simulator actually estimates the two-dimensional two- group diseretized Green's function of the system. From the calculated Green's function, the neutron noise induced by a 'vibrating absorber' type of noise source can also be determined. Different benchmark cases show that this neutron noise simulator works satisfactorily.

    04/02605 Development of a radiant heating and cooling model for building energy simulation software Laouadi, A. Building and Environment, 2004, 39, (4), 421-431 Efficient radiant heating and cooling systems are promising technol- ogies in slashing energy bills and improving occupant thermal comfort in buildings with low-energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modelling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit- tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.

    0402607 Effect of varying dead-state properties on energy and exergy analyses of thermal systems Rosen, M. A. and Dincer, I. International Journal of Thermal Sciences, 2004, 43, (2), 121-133. This study deals with the effects on the results of energy and exergy analyses of variations in dead-state properties, and involves two main tasks: (i) examination of the sensitivities of energy and exergy values to the choice of the dead-state properties and (ii) analysis of the sensitivities of the results of energy and exergy analyses of complex systems to the choice of dead-state properties. A case study of a coal- fired electrical generating station is considered to illustrate the actual influences. The results indicate that the sensitivities of energy and exergy values and the results of energy and exergy analyses to reasonable variations in dead-state properties are sufficiently small that the findings, conclusions and recommendations based on such analyses usually are not significantly affected by the property variations.

    0402608 Empirical modeling of polymer electrolyte membrane fuel cell performance using artificial neural networks Lee, W.-Y. et al. International Journal of Hydrogen Energy, 2004, 29, (9), 961-966. Using an artificial neural network (ANN), a technique for modelling a polymer electrolyte membrane fuel cell is proposed for providing a tool for the design and analysis of fuel cell total systems. The focus of this study is to derive a non-parametric empirical model including process variations to estimate the performance of fuel ceils without extensive calculations. ANN models are trained to fit experimental data obtained in a 300 cm- single cell in HJalr operatmn using Nation 115 and Nation 1135 membrane electrolytes. The models take into account not only the current density hut also the process variations, such as the gas pressure, temperature, humidity, and utilization to cover operating processes which are important factors in determining the real performance of fuel cells. All experimental data using Nation 115 and Nation 1135 membranes are fitted very well with the ANN models over a wide operating range. The ANN models can be used to investigate the influence of process variables for design optimization of fuel cells, stacks, and complete fuel cell power system.

    0402609 Experimental investigation of the effect of exhaust gas cooling on diesel particulate Ning, Z. et aL Journal of Aerosol Science, 2004, 35, (3), 333-345. Particulate emission from diesel engines is receiving a great deal of attention due to its probable carcinogenic property. In the exhaust pipe of a diesel engine, the change of the exhaust gas temperature can result in nucleation and condensation of volatile materials and coagulation of particulates. The objective of the present study is to investigate experimentally the transformation of diesel particulates within the exhaust pipe when the exhaust gas is being cooled. Using a water cooler to control and adjust the exhaust gas temperature, the influences of exhaust-gas cooling on mass concentration, composition, size distri- bution and number-averaged diameter of the particulates, under different engine operating conditions, were analysed. In addition, the effect of the flow rate of the exhaust gas in the cooler on the number- averaged diameter of the particulates was also discussed. The results showed that the transformation of the diesel particulates in the exhaust pipe depended mainly on the level of cooling, the concentration of the volatile materials, the initial concentration of the particulates in the exhaust, and the residence time of the exhaust gas within the exhaust pipe.