This paper deals with an analysis of a two-dimensional viscous fluid flow between the two parallel plates inclined with respect to the horizontal plane, where the lower plate is heated and the upper one is cooled. The temperature difference between the plates is gradually increased during a certain time period after which it is temporarily constant. The temperature distribution on the lower plate is not constant in x-direction, there is a longitudinal sinusoidal temperature variation imposed on the mean temperature. We have investigated the wave number and amplitude influence of this variation on the subcritical stability and the onset of the Rayleigh-Bénard convective cells, by direct numerical simulation of 2D Navier-Stokes and energy equation.

In this paper a new method for burned mass fraction - pressure relation, x-p relation, for two-zone model combustion calculation is developed. The main application of the two-zone model is obtaining laminar burning velocity, SL, by using a pressure history from a closed vessel combustion experiment. The linear x-p relation by Lewis and Von Elbe is still widely used. For linear x-p relation, the end pressure is necessary as input data for the description of the combustion process. In this paper a new x-p relation is presented on the basis of mass and energy conservation during the combustion. In order to correctly represent pressure evolution, the model proposed in this paper needs several input parameters. They were obtained from different sources, like the PREMIX software (with GRIMECH 3.0 mechanism) and GASEQ software, as well as thermodynamic tables. The error analysis is presented in regard to the input parameters. The proposed model is validated against the experiment by Dahoe and Goey, and compared with linear x-p relation from Lewis and Von Elbe. The proposed two zone model shows sufficient accuracy when describing the combustion process in a closed vessel without knowing the end pressure in advance, i.e. both peak pressure and combustion rates can be sufficiently correctly captured

Abstract. Obtaining all acceptable locations is one of the main tasks

The objective of this experiment was to design, build and evaluate a solar oven that was both economically viable and thermally efficient. In addition to the economic objective, I sought to determine the best reflector angle for the solar cooker, by measuring the following parameters: cooking power, efficiency, and effectiveness. Halogen lamps were used to simulate natural sunlight, as the outdoor condition was too variable in the UK to guarantee continued sunlight for 120 minutes in a controlled fashion. The most effective reflector angle i.e. the reflector angle with the greatest ability to convert the solar insolation into thermal energy is the 60°C. However, the data shows that the 70°C reflector angle produces the highest temperature consistently. Over the series of different methods for evaluating the best reflector and angle, it would seem that a 70°C angle is consistently highest in most of the test. With a reflector angle of 70°C, by 120 minutes, the solar oven was able to heat a pan of water to 78°. resumen El objetivo de esta investigación fue diseñar, construir y evaluar un horno solar que fuera económicamente viable y térmicamente eficiente. Los hornos solares son estructuras en forma de caja que concentran la luz solar natural utilizando reflectores para calentar el agua. Las cocinas solares son una alternativa útil al uso de combustible de carbono y sus efectos sobre la deforestación y el cambio climático. Además del objetivo económico, se buscó determinar el mejor ángulo de reflector para la cocina solar, midiendo los siguientes parámetros: potencia de cocción, eficiencia y efectividad. Se utilizaron lámparas de halógeno para simular la luz solar natural, ya que la condición al aire libre era demasiado variable en el Reino Unido para garantizar la continuidad de la luz solar durante 120 minutos de manera controlada. El ángulo del reflector que ofrece mayor capacidad para convertir la insolación solar en energía térmica es de 60 grados. Sin embargo, los datos muestran que el ángulo del reflector de 70 grados produce una temperatura mayor y a la vez constante. Con un ángulo de reflector de 70 grados, por 120 minutos, el horno solar fue capaz de calentar una cacerola con agua a 78 grados Celsius.

Altering the surface cover of an area causes the change in the environment. By erecting buildings change in the flow of energy and matter through the urban ecosystems occurs creating multiple environmental problems. Built areas exert considerable influence over their local climate, amplifying problems such as heat waves, air pollution, and flooding. Greening the building envelope these problems can be partially mitigated. By combining nature and built areas in their designs, architects and urban planners can respond to these serious human health and welfare issues and restore the environmental quality of dense urban areas. Green living systems are not the only solution for new designs. Retrofitting existing buildings by altering the buildings' surficial properties can reduce buildings' energy consumption in case of older buildings with poor existing insulation. Implementation of green living systems in the building envelope, greening horizontal surfaces with intensive and extensive green roofs or using vegetation in vertical greening systems for fa?ades, is a strategy that provides ecological, economic, and social benefits. This review paper presents collected evidence of effects and explores the important role that the green living systems can play in the dense urban areas. Benefits such as heat island amelioration, reduction of buildings energy consumption, air quality and indoor and outdoor comfort conditions improvement, stormwater management and improved water run-off quality, will be mainly considered. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III42008]

Wind power assessment in complex terrain is a very demanding task. Modeling wind conditions with standard linear models does not sufficiently reproduce wind conditions in complex terrain, especially on leeward sides of terrain slopes, primarily due to the vorticity. A more complex nolinear model, based on Reynolds averaged Navier-Stokes equations have been used. Turbulence was modeled by modified two-equations k- model for neutral atmospheric boundary layer conditios, written in general curvelinear nonorthogonal coordinate system. The full set of mass and momentum conservation equations as well as turbulence model equations are numerically solved, knowing as computational fluid dynamics (CFD) technique. A comparison of the application of linear model and nonlinear model is presented. Considerable discrepancies of estimated wind speed have been obtained using linear and nonlinear models. Statistics of annual electricity production vary up to 30% of the model site. Even anemometer measurements directly at a wind turbine's site do not necessarily deliver the results needed for prediction calculations, as extrapolations of wind speed to hub height is tricky. The results of the simulation are compared by means of the turbine type, quality and quantity of the wind data and load factor. Finally, the comparison to the results with the measured data at 10, 30 and 50m.

Integration of nature, live, organic materials, in the design of built areas and building structure is an architectural response to environmental problems of dense urban areas. At the site where green space is limited, greening the building envelope is the solution for the issues such as heat waves, flooding, and noise and air pollution. The benefits could be predicted only using accurate simulation model of this technology. The energy balance of green living roof was researched through models developed over the years by various authors. Most models have been developed and validated with data from extensive roofs and more than 50% of the models were validated using data from warm temperate climatic zones. Ability to determine the impact of green living roofs at different stages of their architectural design process is of most importance if the incorporation this technology is planned due to the impact on building and urban level.

The goal of this paper is to establish the optimal operating regime of the observed perforated plate air/water heat exchanger in a wide range of parameters. The experimental investigation was carried out in a package of three perforated plates which were placed in the experimental chamber and heated by hot water. A fan with the variable air volume flow was connected to the experimental chamber, so the air flow rates varied from 100 to 300 m 3 /h, while the water flow varied from 0.03 to 0.06 m 3 /h. The thermocouples were attached to the surface of the middle perforated plate in the package along its upwind and downwind sides, as well as at the inlet and outlet of the chamber and between the perforated plates. During each experiment, the readings of thermocouples were recorded alongside with the air and water volume flow and temperatures of water at the inlet and outlet of the chamber. In order to predict the performance of the observed perforated plate heat exchanger, NTU-Effectiveness analysis was performed on the basis of the experiment results and analytical relations. Experimental results showed that the effectiveness of the perforated plate heat exchanger can be calculated the same as for the concentric tube counter flow. At the end of the paper, the optimal operating point in the range of varied parameters was determined.