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air-entrainment
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The Effect of the Step Height on Energy Dissipation in Stepped Spillways Using Numerical Simulation
, Article Arabian Journal for Science and Engineering ; Vol. 39, issue. 4 , 2014 , p. 2587-2594 ; Hosseini, K ; Abdi, H ; Hosseini, M ; Sharif University of Technology
Abstract
From 1970s, studies have been conducted on the hydraulic design of stepped spillways and many empirical formulas were developed. Despite the simple geometry of these spillways, their hydraulic behavior is complicated. As a result, for many cases, the physical models are studied to verify the design. Numerical simulation is considered as a tool to reduce the laboratory tests, in order to save time and money. Furthermore, the parameters which are not investigated or measured in physical models could be evaluated. In this paper, the results of numerical simulations are compared with the results of physical models and empirical formulas for the spillway of Renwick dam studied in a 1/8 scale...
Movement of Entrapped Air-Pockets in the Bottom Outlet of Dams and Solutions to Related Problems
, M.Sc. Thesis Sharif University of Technology ; Shamsaei, Abolfazl (Supervisor) ; Ghaemian, Mohsen (Supervisor)
Abstract
The purpose of this study is to investigate the entrapment and movement of air pockets in the bottom outlet of dams and numerical simulation of the process of entrapment and entrainment of air pockets. One of the most common problems with bottom outlets is the air-water mixture flow. The main purpose of this study is to investigate the causes of air pockets in pressurized tunnels before service and emergency gates in the bottom outlets and to provide effective solutions to prevent the occurrence of unwanted air entrapment and many problems resulting from it. To do this, using FLOW-3D flow simulator, the way of entraping air pockets in the Bottom outlet of Darian Dam has been investigated and...
Design Optimization of Pouring basin in the Shape Casting Process
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Tavakoli, Rohollah (Supervisor)
Abstract
The pouring basin is a main part in the gating system. The formation of a vortical flow is a big problem occurs during the discharge of melt from the pouring basin. The vortex formation can enter the floating slag and inclusion into the mold. In the case that the vortex is more stronger, a fully air core to the sprue forms and leads to entraining of the air to the mold. These phenomena can decrease the casting quality significantly. Therefore preventing of the vortex is necessary to produce a sound cast. In this study the mechanism of vortex formation is investigated and several solutions are presented to avoid its detrimental effects. For this purpose discharge of a tank is simulated...
Effects of anti-vortex plates on air entrainment by free vortex
, Article Scientia Iranica ; Volume 20, Issue 2 , 2013 , Pages 251-258 ; 10263098 (ISSN) ; Borghei, S. M ; Sharif University of Technology
2013
Abstract
Free surface vortex and air entrainment are not favorable experiences in hydropower and pumping projects. While complete omission of vortex and air entrainment is not always cost effective, partially weakened free-surface vortex flow is more economical and practical. Hence, in this study, a comprehensive set of experiments were conducted to partially reduce vortex strength and air entrainment at vertical pipe intakes, using rectangular anti-vortex plates. This phenomenon results in increasing water discharge compared with a corresponding free-surface vortex for the same water depth, i.e. in cases of shaft spillway. The plates were used as singles and in pairs and placed symmetrically and...
Spray characteristics and atomization behavior of bio-diesel (Norouzak) and diesel fuel blends
, Article Particulate Science and Technology ; 2016 , Pages 1-12 ; 02726351 (ISSN) ; Jafari, M ; Ahari, M ; Saidi, M. H ; Hajinezhad, A ; Mozaffari, A. A ; Sharif University of Technology
Taylor and Francis Inc
2016
Abstract
Norouzak oil seeds that are the source of bio-diesel (Norouzak) fuel grow mostly in Gonabad and Kashmar located in Khorasan, north east of Iran. Spray characteristics of Norouzak bio-diesel have been experimentally and theoretically studied in this work. Norouzak fuel is added to the conventional diesel fuel, and mixture formations of several blends have been investigated and compared with each other. Moreover, by varying ambient and injection conditions, behaviors of spray of different blends have been explored. Microscopic and macroscopic properties of spray such as Sauter Mean Diameter (SMD), Ohnesorge number, spray tip penetration, spray cone angle, spray projected area and volume have...
Understanding the occurrence of the surface turbulence in a nonpressurized bottom gating system: numerical simulation of the melt flow pattern
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 232, Issue 3 , March , 2018 , Pages 230-241 ; 14644207 (ISSN) ; Baghani, A ; Bahmani, A ; Tamizifar, M ; Davami, P ; Ostad Shabani, M ; Mazahery, A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
Surface turbulence during the filling of the mold triggers the entrainment of oxide films, which appears to be detrimental to the soundness of the final casting. Nonpressurized and bottom-gating systems have been employed in order to avoid such casting defects by reducing the surface velocity of the liquid metal. However, recent studies have shown that the melt front velocity in the mold entrance may exceed the critical value in the nonpressurized and bottom-gating systems. Therefore, a study was conducted on numerical simulation melt flow pattern in nonpressurized and bottom-gating systems. It was noted that the liquid metal enters the gate and then mold cavity with a higher velocity by...
Effect of anti-vortex plates on critical submergence at a vertical intake
, Article Scientia Iranica ; Volume 17, Issue 2 A , 2010 , Pages 89-95 ; 10263098 (ISSN) ; Kabiri Samani, A. R ; Sharif University of Technology
2010
Abstract
One of the sources of disturbance at intakes is the occurrence of free-surface vortices with an air core. The most common solution for avoiding air-entrainment is the use of anti-vortex devices and, especially, plates for large pipe or shaft intakes. If plates are used, then, the geometry and position of them should be studied experimentally. Since only general guidance for use of plates is available, a study for the more precise placement of plates is needed. Hence, a comprehensive set of experiments have been carried out using rectangular plates with different dimensions and at various positions with respect to the vertical outlet pipe intakes and two different pipe diameters (D = 75 and...
Experimental investigation of spray characteristics of a modified bio-diesel in a direct injection combustion chamber
, Article Experimental Thermal and Fluid Science ; 2016 ; 08941777 (ISSN) ; Saidi, M. H ; Hajinezhad, A ; Mozafari, A. A ; Sharif University of Technology
Elsevier Inc
2016
Abstract
Macroscopic and microscopic characteristics of spray of a Modified Bio-diesel Fuel (MBF), applying direct injection system have been explored and compared with those of conventional diesel fuel. MBF is a new combination of bio-diesel, molasses bio-ethanol, and water, which has been kept as a single-phase bio-fuel, employing an emulsifier. Lower emissions and production costs, higher oxygen content and cetane number are the key advantages of the MBF to be replaced by conventional fossil fuels in internal combustion engines. Applying atomization model, the spray atomization properties such as Ohnesorge number and Sauter Mean Diameter (SMD) have been investigated. Air entrainment analysis has...
Experimental investigation of spray characteristics of a modified bio-diesel in a direct injection combustion chamber
, Article Experimental Thermal and Fluid Science ; Volume 81 , 2017 , Pages 445-453 ; 08941777 (ISSN) ; Saidi, M. H ; Hajinezhad, A ; Mozafari, A. A ; Sharif University of Technology
Elsevier Inc
2017
Abstract
Macroscopic and microscopic characteristics of spray of a Modified Bio-diesel Fuel (MBF), applying direct injection system have been explored and compared with those of conventional diesel fuel. MBF is a new combination of bio-diesel, molasses bio-ethanol, and water, which has been kept as a single-phase bio-fuel, employing an emulsifier. Lower emissions and production costs, higher oxygen content and cetane number are the key advantages of the MBF to be replaced by conventional fossil fuels in internal combustion engines. Applying atomization model, the spray atomization properties such as Ohnesorge number and Sauter Mean Diameter (SMD) have been investigated. Air entrainment analysis has...
Experimental and theoretical investigations on spray characteristics of bio-ethanol blends using a direct injection system
, Article Scientia Iranica ; Volume 24, Issue 1 , 2017 , Pages 237-248 ; 10263098 (ISSN) ; Jafari, M ; Ahari, M ; Saidi, M. H ; Hajinezhad, A ; Mozafari, A. A ; Sharif University of Technology
Sharif University of Technology
2017
Abstract
In the present work, the spray characteristics of bio-ethanol and its blends have been experimentally and theoretically investigated. To have a comprehensive study, the effects of ambient condition and injection pressure on the spray of different blends have been considered. Macroscopic and microscopic characteristics of spray such as tip penetration length, cone angle, projected area, volume, Sauter Mean Diameter (SMD), and Ohnesorge number are investigated precisely. Besides, air entrainment and atomization analyses have been carried out to improve mixture formation process. Using curve fitting and least squares method, theoretical correlations have been suggested in such a way to predict...
Spray characteristics and atomization behavior of bio-diesel (Norouzak) and diesel fuel blends
, Article Particulate Science and Technology ; Volume 36, Issue 3 , 2018 , Pages 270-281 ; 02726351 (ISSN) ; Jafari, M ; Ahari, M ; Saidi, M. H ; Hajinezhad, A ; Mozaffari, A. A ; Sharif University of Technology
Taylor and Francis Inc
2018
Abstract
Norouzak oil seeds that are the source of bio-diesel (Norouzak) fuel grow mostly in Gonabad and Kashmar located in Khorasan, north east of Iran. Spray characteristics of Norouzak bio-diesel have been experimentally and theoretically studied in this work. Norouzak fuel is added to the conventional diesel fuel, and mixture formations of several blends have been investigated and compared with each other. Moreover, by varying ambient and injection conditions, behaviors of spray of different blends have been explored. Microscopic and macroscopic properties of spray such as Sauter Mean Diameter (SMD), Ohnesorge number, spray tip penetration, spray cone angle, spray projected area and volume have...
Studying effect of entrainment on dynamics of debris flows using numerical simulation
, Article Computers and Geosciences ; Volume 134 , 2020 ; Manzari, M. T ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This paper studies entrainment phenomenon in debris flows using full flow (non-depth-averaged) equations and an Incompressible Smoothed Particle Hydrodynamics (ISPH) method. A viscoplastic constitutive relationship is adopted for both the overlying fluid and bed material. Collapse of a two-dimensional dry granular column on a horizontal bed consisting of entrainable dry granular material is considered as a benchmark problem. The adopted ISPH method for simulation of collapse over rigid and entrainable beds is validated using available numerical and experimental data. To quantify the effects of entrainment on dynamics of flow, the initial aspect ratio of granular column (a) is varied and the...
Experimental investigation on freeze-thaw durability of polymer concrete
, Article Frontiers of Structural and Civil Engineering ; Volume 15, Issue 4 , 2021 , Pages 1038-1046 ; 20952430 (ISSN) ; Heidarnezhad, F ; Moammer, O ; Jarrah, M ; Sharif University of Technology
Higher Education Press Limited Company
2021
Abstract
Assessing the durability of concrete is of prime importance to provide an adequate service life and reduce the repairing cost of structures. Freeze-thaw is one such test that indicates the ability of concrete to last a long time without a significant loss in its performance. In this study, the freeze-thaw resistance of polymer concrete containing different polymer contents was explored and compared to various conventional cement concretes. Concretes’ fresh and hardened properties were assessed for their workability, air content, and compressive strength. The mass loss, length change, dynamic modulus of elasticity, and residual compressive strength were determined for all types of concretes...