Modelling the transport sector fuel demand for developng economies

This paper concentrates on the transport sector of six developing countries with similar common denominators, namely Turkey, Thailand, Pakistan, Morocco, Tunisia and Malaysia. By using standard econometric techniques, we analyse the evolution of oil demand for road transport in these countries in relation to independent variables such as income, population, price of gasoline and diesel etc. Unlike the treatment in the present literature on the subject, gasoline and diesel consumption are estimated separately due to the high share of diesel in the total transport sector consumption. On the basis of the estimation over the period 1970–1990, on a country by country basis, we forecast the demand for these six countries until 2010. The results of this study indicate that the transport sector will be the driving force for energy and oil demand as part of economic growth in these developing countries. Its share in the future energy market structure is expected to grow. Consequently, the (pricing) policies of oil products in this sector have a crucial role for shaping rational economic and energy strategies within the framework of rising environmental concern.     

The influence of drift fields in thin silicon solar cells

The influence of electric “drift” fields in the base of silicon solar cells on device performance is investigated. The drift fields are the result of a nonuniform dopant density in the base material. Numerical modelling is carried out for a range of representative cell structures and two different models for the dependence of the minority carrier lifetime on the dopant density. The cell design variables, in particular the dopant densities and the thicknesses of the device regions, are optimized with respect to the cell efficiency. Comparison of optimized cells incorporating a drift field with those not having a drift field, shows that a drift field can offer only small efficiency advantages for particular cell structures and recombination parameters, and only if large variations in dopant concentration can be achieved.     

Predictions of concentration in the pyrolysis of biomass materials—I

The present work involves the prediction of the concentration profiles in the case of pyrolysis of different lignocellulosic materials in isothermal and non-isothermal conditions. The operative temperature range is from 573 to 973 K for isothermal conditions, and for non-isothermal conditions, the heating rate ranges from 5 to 80 K/min (5, 20, 40, 60 and 80 K/min).

The concentration for the above mentioned conditions is predicted for various biomass components, viz. cellulose, hemicellulose and lignin. Based on the concentration profiles of different biomass materials, it is possible to predict the pyrolysis behavior over a wide range of temperatures under isothermal and non-isothermal conditions for a large number of biomass materials, provided the activation energy and the frequency factor for the various reaction steps are known. It is also possible to ascertain the degree of combustibility of different biomass materials.

The simulation model utilizes a 4th order Runge-Kutta Predictor-Corrector method to solve the coupled ordinary differential equations. Based on thermogravimetric analysis done elsewhere, it is considered that temperature and time have a linear relationship. The above technique enables us to predict concentration profiles of different biomass materials for the entire range of pyrolysis. The concentration vs time data is plotted graphically for both isothermal and non-isothermal conditions utilizing the Harvard Graphics package on a PC-A/T personal computer.     

A 3-D water/rock chemical interaction model for prediction of HDR/HWR geothermal reservoir performance

A three-dimensional (3-D) water/rock chemical interaction model has been developed to examine the effect of water/rock chemical interaction (WRCI) on the long-term performance of hot dry rock and hot wet rock (HDR/HWR) reservoirs. The model, which integrates many field observations and thus generates a fracture network very similar to the natural fracture distribution in the reservoir, can predict the influence of WRCI on the overall fractured reservoir. Factors affecting WRCI and the effect of WRCI on long-term performance of Hijiori deep reservoir (Japan) have been modelled. Simulated results show that fluid chemistry, initial rock temperature, magnitude of flow rate and well spacing have a major effect on WRCI, and for such a multi-well Hijiori geothermal system, WRCI seems to make the flow distribution tend towards uniformity. The model described deals solely with chemical interactions as a function of flow rate and temperature, and takes no account of aperture variation as a result of thermoelastic effects. It is only a partial model, though it could form an important module of a coupled model.     

Influence of intrinsic hydrogenation/dehydrogenation kinetics on the dynamic behaviour of metal hydrides: A semi-empirical model and its verification

Metal hydrides can store hydrogen at low pressures and with high volumetric capacity. For the possible application as storage medium in hydrogen stand-alone power systems, large metal hydride hydrogen storage units are usually required. A reliable and verified kinetic correlation is an important tool in the designing process of a larger storage unit. This paper describes kinetic investigation of a AB₅-type alloy and its corresponding hydride, with the purpose of finding a semi-empirical correlation suitable for use in heat and mass transfer modelling and engineering design of metal hydride storage units.     

Estimation of user's cost for a depletable resource such as oil

This paper presents an attempt to derive an empirically tractable definition of the user's cost for a depletable resource such as oil. It is shown that, in an intertemporal optimization framework, the user's cost can be measured by the marginal replacement cost (MRC) of the resource, defined as the cost of adding one unit to the stock of the resource. This definition is applied to data for the Middle East. Based on an econometric analysis of the proven reserves' ‘production’ process, the user's cost is estimated for that area for the period 1960-76. The empirical results show that the user's cost is but a small fraction of the market price of crude oil for the period under consideration.     

Microstructure simulation and ballistic behaviour of weld zones in friction stir welds in high strength aluminium 7xxx plate

The effect of friction stir welding (FSW) on the knockdown in properties and failure mechanisms of high strength aluminium plate (AA7010-T7651) under ballistic impact has been investigated by modelling and ballistic testing, simulated, and actual weld zone microstructures, in order to systematically study the link to weld microstructural variation. FSW of thick plate leads to an extremely wide heat affected zone (HAZ). The microstructures within the weld zones were successfully modelled and simulated. However, the maximum loss of hardness in the HAZ resulted in only a 20% reduction in the ballistic limit (V₅₀). The maximum V₅₀ was associated with the highest level of hardness reached prior to a change in failure mechanism, from ductile hole enlargement, using an armour piercing (AP) projectile, or plugging with a fragment simulation projectile (FSP) to excessive spalling and associated adiabatic shear banding at too high hardness levels. The behaviour of the nugget zone has also been examined. The trends in the ballistic data are discussed in the context of the weld zone microstructures and fracture mechanisms.     

Modelling of metal/dielectric composite films — From sphere to columnar inclusions

Composite films consisting of metal inclusions of various shapes embedded into a dielectric matrix were created by computer experiments using a brand-new model. Obtained structures were analyzed as concerns the correlation between morphological and transport properties (the percolation threshold). It was found that the inclusion shapes (ellipsoids) and inclusion arrangements (columnar structures) influence the percolation threshold in such a way that (i) the more different the shapes from spheres are, and (ii) the more random the structures is the lower value of the percolation threshold one can expect.     

Relationship between electrical and morphological properties of nanocomposites

This paper presents a computer study of electrical and morphological properties of composite and nanocomposite films by help of self-made analytical software tools. Main attention is devoted to a relationship between the electrical properties and the morphology of the films. Methods of mathematical morphology are used to obtain structural parameters. A Monte Carlo method and the theory of percolation are used for the study of electrical properties. Conductivity is supposed to be either ohmic or by tunnel effect, or both in parallel. Current paths inside the composite structure form so-called fuzzy clusters below and especially close to the percolation threshold. Their study produces valuable additional information. The results of the morphological and transport analyses are compared and discussed. From them, information is searched about the processes.     

Influence of the atmospheric pressure on the mass transfer rate of desiccant wheels

The performance of a desiccant wheel is evaluated by modelling a representative channel. The hypothesis of negligible resistances to heat and mass transfer in the cross-direction is assumed in the thin porous desiccant wall of the channels and the airflow is treated as a bulk flow. Parametric studies were conducted to investigate the influence of the atmospheric pressure decrease from 101,325 Pa to 60,000 Pa (0-4217 m of altitude) on the mass transfer rate of desiccant wheels considering distinct channel lengths and different inlet airflow rates, a large range of values of the rotation speed, as well as three alternative ways to specify the inlet conditions of the regeneration and of the process airflows. A procedure to derive correlations based on the numerical results is presented for the correction factor of the mass transfer rate when a desiccant wheel is operating at non-standard atmospheric conditions. Four parametric studies were performed, the derived correlations were tested and a good agreement was found between the estimated correction factor and the correction factor calculated after the numerical results.