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

the flow field has a great effect on charge mixing. The charge mixing is satisfactorily close to the desirable mixing distribution when the fuel charge is prescribed properly.

04/02119 Analytical model for the thermal conductance of double-compound honeycomb transparent insulation, with validation Hum, J. E. Y. et al. Solar Energy, 2004, 76, (1-3), 85-91. Whereas early thermal models of honeycomb transparent insulation assumed the honeycomb to be bounded by opaque plates on both faces, more recent models have allowed for an air gap between the honeycomb and one of the plates: the 'compound honeycomb' configuration. This paper deals with a new configuration, one that is basically the compound honeycomb configuration, but the other bounding plate is diathermous (i.e. partly transparent to long-wave radiation) rather than opaque. This new configuration has arisen in the application of honeycombs in greenhouses. This paper extends the existing compound honeycomb model, by adding a new variable and a new equation. It was found that a 9 x 9 matrix needs to be inverted rather than the 8 x 8 required by the earlier formalism. To test the model, the overall conductance across a set of transparent honeycombs resting on one of two diathermous plastics was measured, using a guarded heater plate apparatus. The honeycombs were fabricated from UV-stabilized polypropylene, and had a cell size of about 10 mm. Although the model tended to slightly over-predict the measurements (by about 10%) it is considered to be accurate enough for design purposes.

04/02120 Analytical solution for the Feynman-AIpha formula for ADS with pulsed neutron sources Ceder, M. and P~izsit, I. Progress in Nuclear Energy, 2003, 43, (1-4), 429-436. The theory of Feynman-alpha measurements is elaborated for the case of a 'stochastically pulsed' subcritical system. The corresponding physical situation is when a pulsed neutron source is used, and no synchronization between the start of the measurement time gate and the pulsing is made. This is the case in the European Community supported research project MUSE. The solution to the Feynman-alpha formula was obtained for such a case through complex function techniques in an analytical form by Laplace transform and residue calculus. The final expression is a smoothly regular function with a simple periodic modulation. It consists of a Feynman-curve corre- sponding to a stationary source, plus an infinite sum of periodic sine functions squared. The series converges as 1/n 6 with the summation index n, thus in practice two or three terms are sufficient for a high accuracy quantitative result. This few-term representation amounts to a compact closed form analysis solution. Such a solution is well suitable for use in the determination of the subcritical reactivity from measurements, in contrast to the case of deterministic pulsing (measurement start synchronized with pulsing), where no simple solution is available, and where no explicit relationship between the continuous and pulsed forms of the Feynman-alpha exists.

04/02121 Application of global optimization to VVER-1000 reactor diagnostics Kinelev, V. G. et al. Progress in Nuclear Energy, 2003, 43, (1-4), 51-56. Problems of reactor equipment diagnostics are formulated as inverse eigenvalue problems. Numerical methods of solving the inverse problems are presented. Incompleteness of spectral data results in the error function being non-convex. As the function has numerous local minima, it is necessary to use global optimization methods. Two different strategies are discussed: the modified TRUST algorithm and the algorithm that reduces the original problem to a one-dimensional form. The outcome algorithm that combines the strategies is proposed. Results of computational experiments are presented to illustrate the efficiency of the approach.

04/02122 Beam optimization: improving methodology Quinteiro, G. F. Annals of Nuclear Energy, 2004, 31, (4), 399-411. Different optimization techniques commonly used in biology and food technology allow a systematic and complete analysis of response functions. In spite of the great interest in medical and nuclear physics in the problem of optimizing mixed beams, little attention has been given to sophisticate mathematical tools. Indeed, many techniques are perfectly suited to the typical problem of beam optimization. This article is intended as a guide to the use of two methods, namely Response Surface Methodology and Simplex, which are expected to fasten the optimization process and, meanwhile give more insight into the relationships among the dependent variables controlling the response.

04/02123 Calculation for physical and chemical exergy of flows in systems elaborating mixed-phase flows and a case study in an IRSOFC plant Xiang, J. Y. et al. International Journal of Energy Research, 2004, 28, (2), t01-115. The paper deals with the calculation of physical and chemical exergy of flows in systems elaborating mixed-phase flows, such as steam methane reforming and coal gasification systems. The flows involved are mixtures of gases, which can be treated as ideal gases, and steam. The mixtures in which the steam can be treated as ideal gas and those in which the steam cannot be treated as ideal gas are considered separately. As a case study, the calculation is used to evaluate the physical and chemical exergy content of the flows of a system composed by a pressurized internal reforming solid oxide fuel cell (IRSOFC) combined with a gas turbine. Finally, a thermo-economic analysis of the system is made.

04/02124 Collector test method under quasi-dynamic conditions according to the European Standard EN 12975-2 Fischer, S. et al. Solar Energy~ 2004, 76, (1-3), 117 123. In April 2001 the new European Standard EN 12975:2000: 'Thermal solar systems and components-Solar Collectors' was established. With the publication of this European standard all national standards, related to the same topic, have to be withdrawn by the nations of the European Community. Now only one standard for testing solar collectors is valid throughout Europe. This European Standard specifies test methods for validating the durability, reliability and safety requirements for liquid heating collectors. The standard also includes two alternative test methods for the thermal performance characterization for liquid heating collectors. Apart from the well- known test method under steady-state conditions according to ISO 9806-1, ISO 9806-3 and ASHRAE 93-77 the EN 12975 permits a quasi-dynamic test method for the thermal performance characteriz- ation of solar thermal collectors. This paper presents the improved approach to outdoor performance testing of solar thermal collectors under quasi-dynamic test conditions. The test requirements and collector theory are closely connected to those long agreed on for steady-state testing, as described in the ISO and ASHRAE standards mentioned above. The most important effects for the all day performance of the collector are taken into account. The test method covers most collector designs on the market today (except ICS type). Only some correction terms are added to the basic collector models of the present steady-state test methods. Still this limited change wiI1 allow test data to be collected and used from whole days. An important fact is that the collector model used for the parameter identification is written so that the error in collector output power is minimized. Therefore an accurate long-term prediction of the collector perform- ance can be an integral part of the test method, where the same collector model and parameters are dsed for both testing and prediction.

04/02125 Combustion of a substitution fuel made of cardboard and polyethylene: influence of the mix characteristics-experimental approach Salvador, S. et al. Fuel, 2004, 83, (4-5), 451 462. This article presents an experimental study of the combustion of substitution fuels elaborated from compressed mixes of cardboard and polyethylene (PE). These components are representative of two classical classes of waste materials: materials derived from wood and plastics. The combustion of these fuels has been experimentally characterized in terms of combustion rate, and quantity of PolyAro- matic Hydrocarbons (PAH) pollutants emitted. The temperature levels reached within the fuel sample are also reported and discussed. A parametric study has been performed with three characteristics of the fuel as the parameters: (i) the size of the elements before mixing; (ii) the proportion of PE in the mix; (iii) and the apparent density of the 'bricks' that were prepared. Experiments were conducted using a standard calorimeter cone. This device leads to a quasi- lD situation, and good repeatability has been observed. A special sample holder and a PAH sampling system were adapted to the system. The samples were irradiated with a flux of 50 kW m -z. No air was blown through the samples, and the ash layer formed at the surface was not removed. It was observed that combustion occurs with two different stages. During the first stage, the fuel is devolatilized, and a flame is formed at the surface. It was observed that the duration of this period was proportional to the fuel density. The mass loss rate (kg s -x m -z) appeared not to depend upon the brick characteristics. In second stage, the fuel is oxidized. The mass loss rate is again very similar from one brick to another. It is approximately 10 times smaller than during the devolatilization stage. An examination of the temperature levels at three locations inside the bricks indicates that there is not a thin combustion front propagating through the sample. As a consequence of this, despite the large quantity of energy released by the combustion, the temperature reached remains between 700 and 900°C, which is very close to the surface steady state temperature resulting from the surface

292 Fuel and Energy Abstracts July 2004