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Page 1: Parameter estimation in thermal hydraulic models using the multidirectional search method : Carlos, S. et al. Annals of Nuclear Energy, 2003, 30, (2), 133–158

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

when the bed's temperature was raised; this was accounted for by changes in the following physical properties: the density of the fluidizing gas, the diffusivity of 02, the viscosity, and minimum fluidizing velocity of the air. There was no clear trend of Sh with the actual superficial velocity of the fluidizing air. On the other hand, Sh was increased significantly by using larger sand particles, mainly as a consequence of increasing the gas velocity in the interstices between the sand particles.

03/00878 Modeling the impact of ethanol on the persistence of benzene in gasoline-contaminated groundwater Molson, J. W. et al. Water Resources Research, 2002, 38, (l), 4/1-4/12. The effect of ethanol on the persistence of benzene in gasoline- polluted aquifers was simulated using a multi-component reactive transport model. This conceptual model includes a residual gasoline source which is dissolving at the water table into an aquifer containing a limited amount of dissolved 02. Coupled processes include non- aqueous phase liquid (NAPL) source dissolution, dissolved component transport, and competitive aerobic biodegradation. Comparisons were made between dissolved benzene plumes from a gasoline spill and those from an otherwise equivalent spill containing 10% ethanol (gasohol). Simulations showed that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by _<150% relative to that from an equivalent ethanol- free gasoline spill. The increase occurs because ethanol preferentially consumes O2, which reduces the biodegradation rate of benzene; however, the impact is limited because sufficient Oz disperses behind the ethanol plume into the slightly retarded benzene plume. A sensitivity analysis for two common spill scenarios showed background Oz concentrations and benzene retardation have the most significant impact on ethanol-induced benzene persistence. Results are highly relevant in fight of the increasing use of ethanol-enhanced fuel throughout the world and the forthcoming ban of Me tert-Bu ether in California and its probable replacement by ethanol by the end of 2002.

03/00879 Monte Carlo transport and burnup calculation Li, D. et al. Annals of Nuclear Energy, 2003, 30, (1), 127 132. A 3-D multigroup P3 neutron transport Monte Carlo code MCMG- BURN is developed for coupling neutron transport with burnup. MCMG-BURN code is based on Monte Carlo code MCNP with the continuous energy cross-section and the reactor lattice code WIMS. It uses the up-front multigroup macroscopic cross-section library based on burnup for Monte Carlo calculations. Almost consistent results with the experiments have been achieved.

03•00880 Optimal unit sizing of cogeneration systems in consideration of uncertain energy demands as continuous random variables Gamou, S. et al. Energy Conversion and Management, 2002, 43, (9-12), 1349-1361. An optimal unit sizing method for cogeneration systems is proposed using energy demands as continuous random variables. In this method, design variables such as equipment capacities and maximum contract utility demands are determined together with the systems' operational strategies so as to minimize an expected value of the annual total cost subject to the satisfaction of all the possible energy demands. In evaluating the expected value, decision variables and the objective function are considered as piece-wise linear functions of energy demands by applying a sensitivity analysis in linear programming and an enumeration method in mixed-integer programming. This optimiz- ation problem is formulated and solved based on a hierarchical optimization algorithm. A numerical study is carried out on a fuel cell cogeneration system installed in an office building. Through the study, the influence of uncertainties in energy demands on a system's economics and optimal equipment capacities are clarified.

03/00881 Optimization of sensitivity in pulsed 13C NMR on coals • Botto, R. E. Energy & Fuels. 2002. 16, (4), 925 927. Pulsed 13C NMR analyses (SPE) were performed on Argonne Premium coals using a modified version of the ring-down elimination (RIDE) pulse sequence that included high-power proton decoupling. Employing RIDE in combination with the use of 02 as a relaxation agent and appropriate considerations of the Ernst-Anderson angle produced high-quality spectra devoid of baseline artifacts in reasonable measuring times. Employing this approach reduced the total acqui- sition time over the standard procedure of applying a 90 ° excitation pulse by as much as a factor of 1/17 in some instances. Carbon aromaticity values detected in this manner were similar to those obtained previously by SPE using a 90:' pulse and long recycle delay times. Values detected by both methods are generally found to be higher than those by cross polarization.

03/00882 Parameter estimation in thermal hydraulic models using the multidirectional search method Carlos, S. et al. Annals o f Nuclear Energy, 2003, 30, (2), 133-158. Some uncertainty is introduced in the simulation of the behaviour of a nuclear power plant because some of the parameters of the models used for the simulation are undefined or unknown. The values of these parameters are usually determined by the analyst using their own judgement and thus a user effect is introduced into the simulation process. The uncertainty caused by user effects may be mitigated by the utilization of an automatic and systematic search and optimization method to estimate parameters for the simulation model of a particular plant. The multidirectional search algorithm is proposed as an optimization technique. Two different applications have been studied which successfully show the applicability of the optimization method- ology. First, the methodology is applied using the RELAP5 code to determine the best boundary conditions to simulate an experiment performed at the facility of the Royal Institute of Technology. The second application consists of the development of a two loop reduced PWR reactor model and the determination of some of its effective parameters to adjust the reduced model behaviour to a given reference associated with particular operational transients.

03/00883 Physical and neural network models of a silica- gel desiccant wheel Cejudo, J. M. et al. Energy and Buildings, 2002, 34, (8), 837-844. Two methods for modelling the performance of a desiccant wheel are presented: a physical model, based on mass and energy balances of the process, and a neural network model, based on the training of a black box model with real data. The physical model consists of a set of non- linear differential equations solved by finite differences techniques. The neural network model consists of a four-input-four-output network that calculates the outlet conditions from inlet ones. Real data are used to validate the physical model and to train the neural network. The physical model shows discrepancies between calculated and measured values mainly due to the fact that the system is assumed to be adiabatic. The heat losses in the ducts and the wheel are not considered in the model, but in the experimental facility these losses occur. In the case of the neural network model, the temperature and humidity ratio calculated for the outlet air are in accordance with the experimental data.

03/00884 Prediction of the COP of existing rooftop units using artificial neural networks and minimum number of sensors Zmeureanu, R. Energy, 2002, 27, (9), 889-904. This paper proposes a new approach for evaluating the Coefficient of performance (COP) of existing rooftop units, using the General Regression Neural Networks. This approach reduces the installation cost of monitoring equipment since only a minimum number of sensors is needed, and it also reduces the costs for re-calibration or replacement of sensors during the operation. The new approach was developed and tested using measurements taken on two existing rooftop units in Montreal, Canada.

03/00885 Studies of the measurement of respirabie coal dusts and diesel particulate matter Litton, C. D. Measurement Science and Technology, 2002, 13, (3), 365- 374. Experiments were conducted to detect the optical scattering properties of respirable coal dusts and diesel particulate matter (DPM) at discrete angles in the forward direction and at light source wavelengths of 6328 and 635 nm. In addition to the scattering data, simultaneous measure- ments were made of the total mass concentration of dust, DPM or mixture of the two, and the responses of a unipolar ion chamber and a simpler, more common bipolar ion chamber typical of residential smoke detectors. The results of these experiments indicate, for respirable coal dusts, that the intensity per unit mass concentration at discrete angles in the range of 15-30 ° varies linearly with mass concentration independent of the volatility of the dust, but that at larger scattering angles, intensities per unit mass concentration are affected by dust volatility. For DPM, the intensities per unit mass concentration are significantly lower. The results also indicate that the ion chambers respond significantly to DPM while there is no response to respirab[e coal dust, and that when mixtures of the two are present, the ion chambers respond to the DPM mass fraction only. In addition, it was found that the angular intensity distribution for respirable dusts is adequately described by classical Mie scattering theory, while for DPM classical Mie scattering is inadequate, and treatment of the particles as fractal-like aggregates yields much better agreement with the experimental data. This paper describes the experiments and their results.

116 Fuel and Energy Abstracts March 2003

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