Background and Objective: Vegetation that is commonly used in urban design has a significant impact on air quality in the urban canyons. Thus, planners should be aware of vegetation impacts. In Isfahan metropolis, though vegetation covers a considerable portion o More
Background and Objective: Vegetation that is commonly used in urban design has a significant impact on air quality in the urban canyons. Thus, planners should be aware of vegetation impacts. In Isfahan metropolis, though vegetation covers a considerable portion of the city, the streets are encountered with pollution problems. In this study, distribution of pollution in urban canyons is evaluated using an optimal model for pollution reduction. Method: A three-dimensional modeling software called ENVI-met along with local and sub-climatic air quality model based on CFD-computational fluid dynamics- is used to study the influence of vegetation on pollution level in urban canyons. In this study, first a sample of real field and next a simpler version of the selected area are simulated. Findings: Different parameters such as height to width ratio in urban canyons, density of trees, location of trees in the streets and gaps between the trees are evaluated. Conclusion: The obtained results show that the increase of wind velocity in the shallow valleys is at the the lower level and the absence of natural obstacles such as trees reduces the level of pollution due to the high velocity of wind at this condition. When trees are located in the center of urban canyons, pollution and tree distances are inversely correlated and pollution level reduces by increasing the distance between the trees. In the other words, the pollution that is caught by the tree canopies decreases with the reduction in tree canopies.
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Today, Solar stills have become a popular water purification facilities in desalination research areas. They use solar energy as a never ending, low cost and clean energy. They have no moving parts and without any noise. In this study, we investigate the effect of parti More
Today, Solar stills have become a popular water purification facilities in desalination research areas. They use solar energy as a never ending, low cost and clean energy. They have no moving parts and without any noise. In this study, we investigate the effect of partially cooling on the productivity of a tubular solar still. For this purpose, 2-D finite volume method was used to solve velocity, momentum, energy and mass transfer equations for humid air inside the enclosure. Moreover, the effect of using glass-cover partially-cooling on the stream lines, isotherms, mass fraction and water productivity was investigated. The results showed that numerical simulation has a good agreement with experimental results. Furthermore, we concluded that increasing the Rayleigh number and using partially cooling lead to enhance water productivity. Moreover, the maximum productivity was achieved in Ra=105 when using partially cooling on top of the glass cover.
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Along with the increasing development of countries, the daily need to transport various goods and equipment and travel in general for many reasons is increasing and for this reason, the number of different types of cars has significantly increased in recent years. In th More
Along with the increasing development of countries, the daily need to transport various goods and equipment and travel in general for many reasons is increasing and for this reason, the number of different types of cars has significantly increased in recent years. In this way, this issue has caused heavy traffic on highways and various roads in big cities. Various actions and approaches, including public transportation, have been taken into consideration to facilitate the traffic. However, in some cases the solution to facilitate traffic jams, especially in big cities, is to build urban tunnels. Therefore, in recent years, urban tunnels have been considered as a solution to facilitate traffic. In this regard, the study of safety in tunnels becomes very important. The aim of this article is to simulate a fire in a short tunnel with natural ventilation to consider the behavior of smoke in different scenarios of natural air flow in the tunnel. The results of CFD simulation showed that limited fire (usual small passenger cars) will not cause problems for people as well as rescue team, especially fire extinguishing.
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