Sharif Digital Repository

Having an efficient and reliable system for oil-water separation is of crucial importance in oil and gas industry. Hydrocyclones have been used for more than a century to separate oil from water as well as sand from liquid or gas. The main objectives of this research are as follows: Determination the hydrocyclone principle of operation, based on computational fluid dynamic simulations. Hydrocyclones, in a spite of simple structure, are widely used in industry such as Petrochemical, Mining, Chemical Industries, Pharmacy, Food and Pulp Industries. The CALC BFC is one phase flow numerical code based on finite volume method and SIMPLEC algorithm. It was extended for simulating the two phase flow... 

Centrifugal Fans are widely used in industrial and commercial applications, from shop ventilation to material handling to boiler applications. They consume extremely high amount of energy each year. Because of this high consumption, even a small efficiency improvement could led to high amount of energy saving. Many projects have been done with this goal up to now, and present work is one of them, with aim to optimize a industrial centrifugal BI fan performance, with wheel diameter about 400 mm. The research has been done based on 3D numerical methods, done by commercial code Fluent 6.3, in steady state. MRF and k-E models have been used to simulate flow around blades, and turbulence... 

Development of cities as well as population growth causes to development of public transportation especially subway lines. Fire is the one of the most important issues that may occur in subways. The difference in flame size, emission heat, smoke and pollutants generation of subway fires attracts an especial attention of fire investigators. The emergency ventilation of subways in the case of fire should have the ability of discharging heat, smoke and pollutants from passenger escape route and preparing a safe place for a specific duration. The aim of this research is simulating fire in subway stations and defining proper regional fire scenarios to prepare a safe route for passengers escape.... 

Hydrocyclones are used for separating different materials from liquids in a variety of applications. Compactness, efficiency, reliability and low maintenance costs are their noteworthy characteristics. Dewatering and deoiling hydrocyclones used for refining crude oil or oily waste water in offshore platforms are examples of liquid-liquid hydrocyclones. Separation process in hydrocyclones is based on the fact that swirl flow induces a centrifugal force and leads to separation due to density difference. The density difference in liquid-liquid mixtures is smaller than solid-liquid types and trying to separate one liquid from another takes much more effort than the other type. Increase of... 

Fire phenomenon and its hazards through urbun transportation systems like subway is a major debate in management of these territories. Recently, varios factors, such as great deal of passengers whom travel by these systems, financial damages and psychological disorders due to fire accidents resulte in noticeable investigation to prevent and reduce these subjects. In this research, simulating of railcar fire has been conducted to estimate the amount of heat release rate (HRR) and parameters which affect on it by modelling behavior of combustible materials inside railcar. As regards to materials which are available inside railcar that participate in fire, their behavior face to heat flux has... 

Designing of an efficient emergency ventilation system is one of the main approaches to prevent the perilous fire in tunnel phenomenon. For this purpose, firstly, fire behavior and its heat release rate should be investigated. Knowing about temperature distribution and smoke movement is the second step. One of the most considerable factors in smoke control is critical velocity. It means the minimum velocity to prevent backlayering flow. If longitudinal ventilation velocity were less than this amount, smoke and hot gases originated from the fire can enter the upstream zone. This may cause lack of oxygen and decrease visibility for the passengers when they are escaping from the fire field. In... 

Due to growth of the number of passengers in subway transportation systemsthe capacity of the metro stations are on the rise.The generated heat loads in subway line shall be increased by thegrowth of the its capacity. As a result, current subway ventilation systems cannot provide comfort conditions for passengers. Nowadays, modern ventilation systems are designedto improve ventilation performance and to create suitable thermal conditions. Among of these, the under platform andover track exhaust systems and use of platform screen doors can be Cited. The aim of this study is three-dimensional simulation of air flow in modern ventilation systems of subway stations. Numerical simulations are in... 

Necessity of a public transport network, environmental protection and a highly land cost in urban areas have increased the desire for underground transportation systems. On the other hand, ventilation system design should be done precisely specially for longer tunnels, large undergrounds spaces and crowded places. Rate of energy reduction for vent systems operation is dependent on their proper implementation. Tunnel design efficiently is influenced by ventilation system. The tunnel mid shaft is complementary part of the underground railway systems that is required for exchange air between the tunnel and the railway station with ambient fresh air. An important application of the tunnel mid... 

Fire in enclosures is one of the most important disasters due to the presence of human and physical risks, so, investigation of the firefighting scenarios in this case has much importance. In the present study, novel enclosures fire suppression scenarios are simulated using computational fluid dynamics (CFD). The simulations have two major categories. In the first part, performance of different natural ventilation, positive pressure ventilation (PPV) and negative pressure ventilation (NPV) scenarios, which are new methods in firefighting, are evaluated and compared. In this part, the influence of different parameters like geometry, position of inlet and outlets and fire heat release rate... 

Air pollution is lateral and inappropriate product of industry and technology development that grows along them, unfortunately. Now its domain extended from local and national issues to global issues. For years like other branches of environmental sciences and other scientific fields, scientists apply formulas and mathematical equations. Nowadays, air pollution modeling is fundamental and powerful tool for air pollution studies, especially in prediction of air pollution conditions, pollutants emission and their concentration under different conditions and arbitrary locations. In this research, numerical modeling of urban air pollutants dispersion is discussed. After validation of results,... 

Fire events and the related toxicants such as CO are responsible for many fatalities inthe current century. These hazardous events are more dangerous when they occur in enclosedspaces. In the present study, a theoretical relation is developed for horizontal distribution of COin a large tunnel fire. Then, developed criterion is used to study the effect of rudimentaryparameters such as Heat Release Rate (HRR) of fire and tunnel Aspect Ratio (AR) on CO andtemperature stratification. Theoretical results of various heat release rates and aspect ratios forhorizontal distribution of CO are compared with numerical results using Fire DynamicsSimulator (FDS5.5). It is found that big fires have higher... 

Buses are among safe means of transportation; however, they have a risk of a fire catastrophe with high fatalities if fire occurs in a situation where escape is difficult. In this study, numerical simulation is used to investigate bus fire using Fire Dynamics Simulator of NIST. Five fire scenarios have been considered to investigate the impact of doors and ceiling windows on fire with the aim of protecting the lives of passengers and controlling fire. In the simulations, time of flashover, temperature distribution near the ceiling, heat release rate and smoke distribution are investigated. Results show that scenarios with open ceiling windows are appropriate for passenger safety as they have... 

In general, a combustible mixture can support two modes of combustion: deflagration and deto-nation. In the deflagration regime, in the limit it can burn as a laminar flame at a typical velocity of the order of about 0.5 m/s, or it may accelerate to a turbulent flame where velocity can be or-ders of magnitude higher. The other extreme is the detonation mode, in which a detonation wave propagates at about 2000 m/s amplifying the pressure by a factor of 20 across the wave. Detona-tion is defined as a combustion supported shock wave with significant pressure and density rise across the wave. The main characteristic of detonation waves is the coupled motion of the shock front and the reaction... 

One of the major concerns in the use of light flying objects is propulsion for cruise and take off from land. Creating propulsion force is important in such way that no excessive weight is introduced, especially in case of UAVs. A common trend for propulsion in light flying objects is using propellers. Propellers are commonly driven by an external motive force and due to this force and their geometry, they convert energy from this motive force into the momentum of fluid in which they are immersed as a result a lift force is generated.In the present work, trend of propeller design with optimum performance is introduced with use of vortex theory, optimum energy loss condition or Betz condition... 

Because of increase in use of cars in recent years, demands for parking spaces have also dramatically grown. To resolve this issue construction of multi-storey underground car parks has sharply increased. Due to the high level of contaminants emitted by cars in parking lots and also the continuous presence of humen within them, the control of pollution level and parking indoor air quality is a vital matter. Type of ventilation systems including modern and conventional used for ventilating parking lots and also exhaust and supply vents locations are the most important factors affecting contaminants distribution. Thus investigation the performance of the conventional and modern ventilation... 

Generally speaking, there are two types of self-propagating combustion waves: deflagrations and detonations. deflagrations waves propagate at relatively low subsonic velocities with respect to the reactants ahead of it. The propagation velocity in deflagration wave is of order of 1 to 10 meters per second depend on laminar or turbulent regime. On the other hand, the detonation wave is a supersonic combustion wave (of the order of 2000 m/s) across which the thermodynamic states (e.g., pressure and temperature) increase sharply. It can be considered as a reacting shock wave where reactants transform into products, accompanied by an energy release across it. Due to drastic changes that... 

Underground gas pipelines are one of the vital parts of each country which surface blasts can break them down, make destructive explosions and threaten the safety of neighborhood structures and people. In this paper, to enhance the safety of these lines, response of buried 56 inch high pressure gas pipeline to a surface blast is numerically investigated. Beside the main aim, parametric studies on the effects of: i) explosive mass, ii) pipeline thickness, iii) burial depth and iv) concrete protective layer, on pipeline deformation are performed. To simulate the problem according to actual explosion events, geometries are modeled in real scales, pipeline properties are predicted with... 

Based on thecnology development, humans are able to shorten the ways by using tunnels. But beside this big benefit, there are some limitations, both in digging and utilization stages. One of the most important challenges in utilization stage is ventilation. Beside the normal ventilation -which is done to reduce the pollutants like carbon monoxide- a special system must be designed to control the hot and high energy combustion products. This system is named emergency ventilation. In this research, emergency ventilation in long road tunnels, using water curtain is simulated numerically using FDS code, and different parameters are investigated. The fuel source in this research is a pool of... 

Based on thecnology development, humans are able to shorten the ways by using tunnels. But beside this big benefit, there are some limitations, both in digging and utilization stages. One of the most important challenges in utilization stage is ventilation. Beside the normal ventilation -which is done to reduce the pollutants like carbon monoxide- a special system must be designed to control the hot and high energy combustion products. This system is named emergency ventilation. In this research, emergency ventilation in long road tunnels, using water curtain is simulated numerically using FDS code, and different parameters are investigated. The fuel source in this research is a pool of... 

Coal has always been an unneglectable share of countries’ energy basket as the oldest known fuel. Concerning Iran’s rich coal mines, it plays a particular role in the country’s development programs. Mine Ventilation is one of the most vital issues in mining activities. While excavation activities might experience an overhaul phase, Ventilation must be operating nonstop. Since coal mines are gassy generally, mine ventilation design should include appropriate principles. U ventilation scheme is the most common ventilation scheme being used in longwall coal mines. While spontaneous combustion is less probable in the scheme in comparison by other schemes, methane accumulation in tailgate entries...