Sharif Digital Repository

Hospital ventilation is defined as the providing of fresh and clean air stream in hospital wards or patients’ room to provide and establish a healthy environment for personnel’s and patient’s breath, reducing concentration of produced contaminations in hospital and removing them from clean spaces. Thus, it can prevent spread of airborne infections among patients, people who works around and more importantly, outside the hospital. Hospital infections have a huge influence on mortality of the patients in which respiratory tract infections and surgical wound infections plays a major role. Depending on the quality and the mass flow rate of the exploited air, cleanness of a surgery room can be... 

In this research, the airflow pattern and particle dispersion in a contaminated full-scale cleanroom are investigated numerically using both Eulerian and Lagrangian approaches. Three different supply diffuser configurations namely (1) central, (2) horizontal and (3) vertical and three different exhaust grille configurations namely (4) vertical symmetric, (5) asymmetric and (6) horizontal symmetric are selected for the analysis. The presented results reveal that the supply/exhaust openings arrangement has a significant influence on the particulate contaminant dispersion in the cleanrooms. The comparison of the above different supply diffuser configurations shows that the vertical and... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

Magnetorheological fluids (MRFs) are a category of functional materials that exhibit magneto-mechanical coupling. These materials exhibit a reversible and instantaneous change from a free-flowing Newtonian fluid to a semi-solid state upon application of a magnetic field. In contrast to ordinary fluids, MRFs can tolerate shear stresses up to a yield value in the presence of a magnetic field. The yield stress strongly depends on intensity of the applied magnetic field and volume fraction of magnetic particles. As the yield stress is the most important parameter of an MRF and must be considered in the design of MR devices, in this work, effects of magnetic field and volume fraction of particles... 

In this article, the induced airflow and the resultant particles resuspension due to a disk falling freely under the effect of gravity is studied using numerical and experimental approaches. The results showed that an axisymmetric vortex is generated on the disk tip as the disk falls and sheds after impacting the floor. While the effect of this ring vortex on the particles detachment from the floor is small, it has considerable influence on the dispersion of resuspended particles. The simulation results indicated that particles are mainly resuspended from an annular area beneath the disk tip where the generated wall shear is sufficiently high. As particles detachment is mainly controlled by... 

Cu-Sn composites incorporated with graphite and/or SiC particles were produced by electrodeposition technique. The effect of particle concentration in the plating bath and current density on tin content and volume percentage of particles in the coatings has been investigated. Structure, morphology, micro hardness and wear properties of the coatings have been studied. The results showed that particles cause an increase of tin content in the plated Cu-Sn. Graphite and silicon carbide particles had different effects on coating hardness; 7.8. vol.% graphite decreased the hardness of Cu-Sn layer from 231. Hv to 172. Hv whereas, 5.1. vol.% SiC raised the hardness to 316. Hv. Moreover, friction... 

Effect of using Al 2O 3-water nanofluids with different volume fractions and particle diameters on generated entropy, hydrodynamic performance and heat transfer characteristics of a tangential micro-heat sink (TMHS) was numerically investigated in this research. Results indicated that considerable heat transfer enhancement is possible when using Al 2O 3-water nanofluids as coolant and clearly the enhancement improves with increasing particles concentration and decreasing particles size. However, using nanofluid has also induced drastic effects on the pumping power that increases with particles volume fraction and Reynolds number. Finally, it was found that generated total entropy decreases... 

Nanofluid is the term applied to a suspension of solid, nanometer-sized particles in conventional fluids; the most prominent features of such fluids include enhanced heat characteristics, such as convective heat transfer coefficient, in comparison to the base fluid without considerable alterations in physical and chemical properties. In this study, nanofluids of aluminum oxide and copper oxide were prepared in ethylene glycol separately. The effect of forced convective heat transfer coefficient in turbulent flow was calculated using a double pipe and plate heat exchangers. Furthermore, we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical... 

Magnesium alloys are considered as potential biodegradable biomaterials in hard tissue implants. However, the fast degradation rate of these alloys in the biological environment causes failure of the implant just prior to the desirable time. In the present work, in order to decrease and curb the bio-corrosion rate of AZ91D Magnesium alloy, zirconia, which is classified as a biocompatible ceramic, was coated on the alloy surface through electrophoretic deposition (EPD) technique. The effects of alterations in the EPD parameters such as current density, duration time and ZrO2 particles concentration on coating properties including thickness, morphology and adhesion were then characterized.... 

The current study is allocated to experimental evaluation of the multiphase flow of fine solid particles (FSPs) as well as comprehensive numerical study in an annular space under static, laminar, and turbulent flow conditions with consideration of the inner pipe eccentricity and rotation. The experimental investigation was carried out using an annular pipe flow loop. The numerical modeling and simulation of the multiphase flow in the annular space have been performed using the Euler-Euler approach. The unsteady-state multiphase model based on the kinetic theory of granular flow (KTGF) is developed to investigate the particulate flow characteristics in the annular space. Moreover, Standard... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

Modeling the behavior of suspended particles in gaseous phase is important for diverse reasons; e.g. aerosol is usually the main subject of CFD simulations in clean rooms. Additionally, to determine the rate and sites of deposition of particles suspended in inhaled air, the motion of the particles should be predicted in lung airways. Meanwhile there are two basically different approaches to simulate the behavior of particles suspension, Lagrangian and Eulerian approaches. This study compares the results of these two approaches on simulating the same problem. An in-house particle tracking code was developed to simulate the motion of particles with Lagrangian approach. In order to simulate the... 

The novel idea of the Hydromagnetic Micropump and Flow Controller (HMFC) is used in this paper to construct a laboratory setup capable of bidirectional pumping and controlling the flow in microtubes. A laboratory setup, which contains no moving parts, is integrated with a pressure-driven flow setup to make the presented HMFC device. The device operation is based on controllable motion of magnetic particles, added to the carrier fluid, caused by the magnetic field, produced by solenoids located just next to the microtube. The magnitude of these forces is proportional to the strength and gradient of magnetic field which, in turn, is related to the electrical current and arrangement of the... 

Because of the recent frequent observations of major dust storms in southwestern cities in Iran such as Ahvaz, and the importance of the ionic composition of particulate matters regarding their health effects, source apportionment, etc., the present work was conducted aiming at characterizing the ionic composition of total suspended particles (TSP) and particles on the order of ∼10 μm or less (PM10) during dust storms in Ahvaz in April-September 2010. TSP and PM10 samples were collected and their ionic compositions were determined using an ion chromatography. Mean concentrations of TSP and PM10 were 1,481.5 and 1,072.9 μg/m 3, respectively. Particle concentrations during the Middle Eastern...