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

06•01385 Electrical braking of large wind turbines Rajambal, K. et al. Renewable Energy, 2005, 30, (15), 2235 2245. This paper analyses the electrodynamic braking (EDB) performance of a grid connected wind energy conversion system, during a grid loss. A dual pole induction generator driven by a fixed speed wind turbine is considered for the present study. The modelling of the wind turbine- induction generator unit, with the excitation capacitor C and braking resistor R, at the generator terminals is presented. Through simulation, the steady state as well as the dynamic performance of the system is studied for different R C combinations. The experimental results on a 1.5 kW induction machine confirm the feasibility and effectiveness of the EDB.

06•01386 Experimental studies on effect of guide vane shape on performance of impulse turbine for wave energy conversion Thakker, A. et al. Renewable Energy, 2005, 30, (15), 2203 2219. This paper presents the experimental results of effect of guide vane shape on performance of an impulse turbine for wave energy conversion. Two types of guide vanes are considered in the present study: two-dimensional (2D) guide vanes and three-dimensional (3D) guide vanes. The previous investigations by the authors revealed that the 2D guide vanes cause large recirculation zones at leading edge of downstream guide vanes, which affect the performance of turbine considerably. In order to improve the performance of turbine, three- dimensional guide vanes are designed based on free-vortex theory. Detailed aerodynamic and performance tests have been conducted on impulse turbine with the two types of guide vanes. The experiments have been conducted under various inlet conditions such as steady, sinusoidal and random (real Sea) flows. From the results, it was proved that the efficiency of impulse turbine has been improved for 4.5% points due to 3D guide vanes. The hysteric characteristic has been noticed from the experimental results of impulse turbine with sinusoidal and random flow inlet conditions. Furthermore, it was investigated that the performance of turbine is considerably more during deceleration of inlet flow than the acceleration in a half cycle of sinusoidal wave.

06•01387 Numerical heat transfer studies of the fatty acids for different heat exchanger materials on the performance of a latent heat storage system Sharma, A. et al. Renewable Energy, 2005, 30, (14), 2179 2187. Theoretical investigations of fatty acids as a phase change material (PCM) for energy storage system have been conducted in this study. The selected fatty acids were capric acid, lauric acid, myristic acid, palmitic acid and stearic acid. For the two-dimensional simulation model based on the enthalpy approach, calculations have been made for the melt fraction with conduction only. Glass, stainless steel, tin, aluminium mixed, aluminium and copper were used as heat exchanger materials in the numerical calculations. Theoretical results show that capric acid was found good compatibility with latent heat storage system. The large value of thermal conductivity of heat exchanger materials did not make significant contribution on the melt fraction.

06•01388 Renewable energy technologies for irrigation water pumping in India: projected levels of dissemination, energy delivery and investment requirements using available diffusion models Purohit, P. and Kandpal, T. C. Renewable and Sustainable Energy Reviews, 2005, 9, (6), 592 607. Using the past diffusion trends of four renewable energy technologies for irrigation water pumping in India (SPV pumps, windmill pumps and biogas/producer gas driven dual fuel engine pumps), results of an attempt to project their future dissemination levels, have been presented in this study. The likely contribution of the renewable energy options considered in the study to the projected energy demand for irrigation water pumping in India has been estimated. Estimates of the associated investment requirements taking into account the learning effect have also been presented.

06•01389 User-led innovations and participation processes: lessons from sustainable energy technologies Ornetzeder, M. and Rohracher, H. Energy Policy, 2006, 34, (2), 138 150. This paper considers whether a higher level of user participation could be used as a strategy to improve the development and dissemination of sustainable energy technologies. It especially focuses on user-led innovation processes with a high involvement of individual end-users. Several case studies in the field of renewable energy technologies are drawn on in particular solar collectors and biomass heating systems and sustainable building technologies. Users in these case studies were involved in the design or planning processes, sometimes in a very selective way and with limited influence, sometimes very active and for quite a long period of time. Especially in the case of renewable energy technologies self-building groups were highly successful and resulted in

improved and widely disseminated technologies. Based on the empirical results of the authors' case studies, the paper considers the potential of user involvement (especially in self-building groups) for the development and promotion of sustainable energy technologies and outline technological and social pre-conditions for the success of such approaches.

14 FUEL SCIENCE A N D T E C H N O L O G Y

Fundamental science, analysis, instrumentation

06•01390 A new gas release model for a homogeneous liquid-gas mixture flow in pipelines Kessal, M. and Bennacer, R. International Journal of Pressure Vessels and Piping, 2005, 82, (9), 713 721. The gas release phenomenon, resulting from a rapid decompression in a homogeneous gas liquid flow is expressed by multiplying the mixture density by a degassing coefficient Gr. The effect of this coefficient is calculated by using the classical conservation equations of fluid mechanics and diffusion laws. These equations are solved by an improved new two time step finite difference scheme. The method of characteristics is used at the boundaries. The theoretical results obtained are in good agreement with experimental data and confirm the gas release effect on the flow parameters.

06•01391 A.R.T. (associated reversible transformations) as a basis for thermodynamic cycles analysis Reini, M. Energy, 2006, 31, (1), 126 137. This paper tries to give a general description of a thermodynamic cycle (whatever kind and number of transformations) as a function of a set of independent parameters characterizing thermodynamic transform- ations, as well as of constraints imposed on the cycle by plant physical nature, lay-out and controls. An 'Associated reversible transformation' (ART), defined in the paper, is used to describe each real thermodynamic transformation of working fluid, similarly to well- known description of ideal gas adiabatic compression by means of a polytropic transformation, so that ART may be regarded as polytropics generalized. A simple gas cycle is used to present an application of ART in the field of energy Diagnosis, underlining usefulness of a complete set of independent parameters for cycle description. Further application in the fields of second law analysis and thermo-economics are outlined in the concluding part of the paper.

06•01392 Application limits of finite element models for simulation of shock transfer processes in concrete structures Krutzik, N. J. and Eibl, J. Nuclear Engineering and Design, 2005, 235, (17 19), 1789 1798. Shocks on building structures due to impact loads (drop of wreckage and heavy masses from accidents, transport operations, explosions, etc.), especially in case of a postulated aircraft crash, may lead to feasibility problems due to high-induced vibrations and large expen- ditures at safety-related systems accommodated inside the building structures. A rational and cost-effective qualification of the function- ality of such systems requires the prediction of reliable information about the nature of structural responses induced by impact loading in the corresponding regions of the structure. The analytic derivation of realistic and reliable structural responses requires the application of adequate mathematical models and methods as well as a critical evaluation of all factors that influence the entire shock transmission path, from the area of impact to the site of installation of the affected component or system in the structure. Despite extensive studies and computational analyses of impact-induced shocks performed using finite element simulation method, limited and insufficient experimental results to date have precluded a complete investigation and clarifica- tion of several 'peculiarities' in the field of shock transmission in finite element models. This refers mainly to the divergence of results observed using FE models when not considering a the required FE element discretization ratio as well as to the attenuation and scatter behaviour of the dynamic response results obtained for large building structures and given large distances between the load impact application areas and the component anchoring locations. The cause

206 Fuel and Energy Abstracts May 2006