Danijela Nikolić

Maximizing performances of variable tilt flat-plate solar collectors for Belgrade (Serbia)

In Serbia, for heating of domestic hot water (DHW) it is customary to use electricity. As around 70% of electricity is produced by using low quality coal with high greenhouse emission, it is beneficial to environment to use solar energy by flat-plate solar collectors for heating of DHW in a solar DHW system (SDHWS). The SDHWS with variable tilt flat-plate solar collectors placed in north-south direction at roofs of houses are investigated for their optimal operation in Belgrade, Serbia. The investigated variable-tilt collectors annually take 2 tilts, 4 tilts, and 12 tilts. The used weather data are from the meteorological station. These investigations use three computer codes: EnergyPlus, GenOpt, and Hooke-Jeeves search algorithm. For different solar collectors, the investigations revile their optimum tilts that maximize the solar fraction by the SDHWS. Then, the solar fraction and avoided fossil energy by the SDHWS are maximized. In addition, the deficit in the solar fraction is estimated when the solar ...

Application of Computational Fluid Dynamics to flow next to high-rise buildings in Hong Kong due to air-conditioner heat rejection

This paper presents the results of several studies done for high-rise residential buildings in Hong Kong that involved Computational Fluid Dynamics (CFD) simulation. During summer, a number of Window Air-Conditioners (WACs) could be rejecting condenser heat into a recessed space of these high-rise residential buildings. FLUENT 5.0, a CFD code can be used to predict temperatures and flow field of a powerful rising hot air stream formed in the recessed space. In these cases, for simulations, we use κ-e turbulence model, and 2D and 3D model of the building. A CFD code can also be used to predict temperature and flow fields inside the recessed spaces that differ in heights and condenser-unit locations. The CFD code also employed to predict the airflow patterns. The papers study the worst-case scenario in summer when all the WAC units reject condenser heat into this space.

Optimization of photovoltaics panels area at Serbian zero-net energy building

In this study, the possibilities to decrease energy consumption of a residential building in Serbian conditions are analyzed. The building uses electricity for space heating system, heating of domestic hot water, lighting, and for other electric equipment. The electrical energy is generated by photovoltaics (PV) system and it may be consumed by the building or may be fed-in to the electricity grid. The major aim of the optimization of PV area is to determine the avoided electricity from the grid (avoided exergy), and to minimize the consumption of primary energy. The residential buildings with variable thermal insulation thickness, hot water consumption, life time, and PVs embodied energy are investigated, in order to achieve zero-net energy building or positive-net energy building. The buildings are presented by a mathematical model, in EnergyPlus environment. Open Studio plug-in in Google SketchUp was used for building virtual design, Hooke-Jeeves algorithm for optimization, and GENOPT software for sof...

An Investigation Into Hybrid Aluminium/Composite Cardan Shaft

It is a well-known fact that natural resources are becoming increasingly scarce. Consequently, whenever possible in the machine element manufacture, metallic materials should be replaced with new artificial materials. This paper studies the possibility of replacing two cardan shafts of a truck TURBO ZETA 85.14B with one shaft made of aluminium and a composite material, while the basic requirements concerning the given load transfer and fundamental natural frequencies remain satisfied.