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Hydrodynamic and thermal characteristics of combined electroosmotic and pressure driven flow in a microannulus
, Article Journal of Heat Transfer ; Volume 134, Issue 10 , 2012 ; 00221481 (ISSN) ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
ASME
2012
Abstract
The present study considers both the hydrodynamic and thermal characteristics of combined electroosmotic and pressure driven flow in a microannulus. Analytical solutions are presented using the Debye-Hückel linearization along with the uniform Joule heating and negligible viscous dissipation assumptions, whereas exact results are achieved numerically. Here, the range of validity for the Debye-Hückel linearization is found to be about two times of that for a parallel plate microchannel. Accordingly, this linearization may successfully be used to evaluate the potential and velocity distributions up to the zeta potentials of 100 mV, provided that the dimensionless Debye-Hückel parameter is...
Influence of material ductility and crack surface roughness on fracture instability
, Article Journal of Physics D: Applied Physics ; Volume 44, Issue 39 , 2011 ; 00223727 (ISSN) ; Wnuk, M. P ; Yavari, A ; Sharif University of Technology
2011
Abstract
This paper presents a stability analysis for fractal cracks. First, the Westergaard stress functions are proposed for semi-infinite and finite smooth cracks embedded in the stress fields associated with the corresponding self-affine fractal cracks. These new stress functions satisfy all the required boundary conditions and according to Wnuk and Yavari's (2003 Eng. Fract. Mech. 70 1659-74) embedded crack model they are used to derive the stress and displacement fields generated around a fractal crack. These results are then used in conjunction with the final stretch criterion to study the quasi-static stable crack extension, which in ductile materials precedes the global failure. The material...
Temperature rise in electroosmotic flow of typical non-newtonian biofluids through rectangular microchannels
, Article Journal of Heat Transfer ; Volume 136, Issue 3 , March , 2014 ; ISSN: 00221481 ; Sadeghi, A ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
2014
Abstract
Electroosmosis is the main mechanism for flow generation in lab-on-a-chip (LOC) devices. The temperature rise due to the Joule heating phenomenon, associated with the electroosmosis, may be detrimental for samples being considered in LOCs. Hence, a complete understanding of the heat transfer physics associated with the electroosmotic flow is of high importance in design and active control of LOCs. The objective of the present study is to estimate the temperature rise and the thermal entry length in electroosmotic flow through rectangular microchannels, having potential applications in LOC devices. Along this line, the power-law rheological model is used to account for non-Newtonian behavior...
Combined influences of viscous dissipation, non-uniform Joule heating and variable thermophysical properties on convective heat transfer in microtubes
, Article International Journal of Heat and Mass Transfer ; Volume 55, Issue 4 , January , 2012 , Pages 762-772 ; 00179310 (ISSN) ; Sadeghi, A ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
2012
Abstract
This study presents a comprehensive investigation on hydrodynamic and thermal transport properties of mixed electroosmotically and pressure driven flow in microtubes. Particular emphasis is given to investigating the combined consequences of viscous dissipation, non-uniform Joule heating, and variable thermophysical properties. Analytical solutions are obtained using the Debye-Hückel linearization and constant fluid properties assumption, while a numerical solution is presented for variable fluid properties and non-uniform distribution of Joule heating. The results indicate that, viscous heating effect is pronounced significantly when a favorable pressure gradient exists and cannot be...
Shear-rate-dependent rheology effects on mass transport and surface reactions in biomicrofluidic devices
, Article AIChE Journal ; Volume 61, Issue 6 , 2015 , Pages 1912-1924 ; 00011541 (ISSN) ; Amini, Y ; Saidi, M. H ; Yavari, H ; Sharif University of Technology
John Wiley and Sons Inc
2015
Abstract
Consideration is given to shear-rate-dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power-law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear-thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed...
Experimental Study on Two-Phase Flow Characteristics in Micro-Channels
, M.Sc. Thesis Sharif University of Technology ; Nouri, Ali (Supervisor)
Abstract
The present study provids an experimental investigation on two-pase flow characteristics in microchannels. Experiment were conducted with a mixture of air and water in horizontal circular pyrex channel with 400µm inner diameter. The pressure drop and flow rates of the liquid and gas were measured using new method and images of the flow patterns recorded by high shutter speed camera. The gas and liquid superficial velocity ranges were 0.025-12.5m/s and 0.016-3.6m/s, respectively. The flow pattern map is developed from the observed flow patterns based on phases superficial velocity as wel as We numbers of liquid and gas phases. The flow pattern map is compared with those of larger channels....
Dynamic NMR Study of Ethyle-4-Morpholine-Carbotiate
, M.Sc. Thesis Sharif University of Technology ; Tafazzoli, Mohsen (Supervisor)
Abstract
In this project rotational barrier around the C-N bond in 4-ethyle-morpholine- carboxylate has been studied using DNMR spectroscopy. Spectra were taken at variable temperature, and then with simulation of bandshape broadening pattern at coalescence region, rate constants of exchange were obtained for all temperatures. For simulation of line-shape broadening Spinworks software was used, that with two interfaces made possible simulation with two bandshape simulator programs, DNMR and MEXICO. The rate constants obtained from simulations, were used for calculation of thermodynamic activation parameters (∆G#, ∆H#, ∆S# and Ea). ∆G# 298 value of 13.66 Kcal/mol for 4-ethyle-morpholine- carboxylate...
Model enrichment: Concept, measurement, and application
, Article Journal of Simulation ; Volume 6, Issue 2 , 2012 , Pages 125-140 ; 17477778 (ISSN) ; Roeder, T ; Sharif University of Technology
2012
Abstract
Simplicity and validity are recognized as important attributes of an effective simulation model. However, some disagreement exists both on the definitions of these concepts and on quantitative measures for them. This paper introduces Enrichment Level (EL) for (simulation) models. The EL is a quantitative measure to compare the effectiveness of alternative models when used in a particular project. While there is no conceptual restriction on expanding the EL, it currently captures the bias, speed, variance, and scope of a model as the main contributing enrichment factors. This paper explores these factors and suggests a utility-based method to combine them according to the relative importance...
Estimating terminal velocity of rough cracks in the framework of discrete fractal fracture mechanics
, Article Engineering Fracture Mechanics ; Volume 77, Issue 10 , 2010 , Pages 1516-1526 ; 00137944 (ISSN) ; Khezrzadeh, H ; Sharif University of Technology
2010
Abstract
In this paper we first obtain the order of stress singularity for a dynamically propagating self-affine fractal crack. We then show that there is always an upper bound to roughness, i.e. a propagating fractal crack reaches a terminal roughness. We then study the phenomenon of reaching a terminal velocity. Assuming that propagation of a fractal crack is discrete, we predict its terminal velocity using an asymptotic energy balance argument. In particular, we show that the limiting crack speed is a material-dependent fraction of the corresponding Rayleigh wave speed
Aero-thermal redesign of a high pressure turbine nozzle guide vane
, Article Propulsion and Power Research ; Volume 8, Issue 4 , 2019 , Pages 310-319 ; 2212540X (ISSN) ; Khavari, A ; Alizadeh, M ; Kashfi, B ; Khaledi, H ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typical high pressure turbine nozzle guide vane. Design targets are lower coolant consumption, reduced manufacturing costs and improved durability. These goals are sought by 25% reduction in vane count number and lower number of airfoils per segment. Design challenges such as higher airfoil loading, associate aerodynamic losses and higher thermal loads are discussed. In order to maximize coolant flow reduction and avoid higher aerodynamic losses, airfoil Mach distribution is carefully controlled. There has been an effort to limit design changes so that the proven design features of the original vane...
The Zerodivisor Graph of a Qoset
, M.Sc. Thesis Sharif University of Technology ; Pournaki, Mohammad Reza (Supervisor)
Abstract
We study colorings of quasiordered sets (qosets) with a least element 0. To any qoset Q with 0 we assign a graph (called a zerodivisor graph) whose vertices are labelled by the elements of Q with two vertices x; y adjacent if the only elements lying below x and y are those lying below 0. We prove that for such graphs, the chromatic number and the clique number coincide
Reducing surface recombination by a poly(4-vinylpyridine) interlayer in perovskite solar cells with high open-circuit voltage and efficiency
, Article ACS Omega ; Volume 3, Issue 5 , 2018 , Pages 5038-5043 ; 24701343 (ISSN) ; Mazloum Ardakani, M ; Gholipour, S ; Tavakoli, M. M ; Taghavinia, N ; Hagfeldt, A ; Tress, W ; Sharif University of Technology
American Chemical Society
2018
Abstract
Identifying and reducing the dominant recombination processes in perovskite solar cells is one of the major challenges for further device optimization. Here, we show that introducing a thin interlayer of poly(4-vinylpyridine) (PVP) between the perovskite film and the hole transport layer reduces nonradiative recombination. Employing such a PVP interlayer, we reach an open-circuit voltage of 1.20 V for the best devices and a stabilized efficiency of 20.7%. The beneficial effect of the PVP interlayer is proven by statistical analysis of various samples, many of those showing an open-circuit voltage larger than 1.17 V, and a 30 mV increase in average compared to unmodified samples. The reduced...
Ambient Vibrations Effect on Sensitive Equipment Using Passive and Active Control Method
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor)
Abstract
Today, with improvements in industries such as the sensitive equipment’ industries and the optics industries which need great precision for their optimum performance, the need for a vibration-free environment is felt more than ever. The main objective in this thesis is the effective reduction of the effects of ambient vibrations on points on an optical concrete table using active control. In this research, other than separating the table with the passive method, the reduction of vibrations with active control and the LQR algorithm is investigated. In order to study the dynamic characteristics of the table and to observe the active control process better and more carefully, finite element...
Impact of Practical Beam Shapes on the Performance of Free Space Optical
, M.Sc. Thesis Sharif University of Technology ; Marvasti, Farokh (Supervisor)
Abstract
Free-Space Optical (FSO) communication has received an increasing attention in recent years with its ability to achieve ultra-high data rates (at the order of multiple gigabits per second) over unlicensed optical spectrum. A major degrading factor, particulary in long links is the stmospheric turbulence induced fading. In this thesis, we use spatial diversity and use and make several contributions to the performance analysis of MIMO (Mutli Input-Multi Output) FSO systems. We use MRC(Maximum Ratio Combining),EGC(Equal Gain Combinig),SC(Selection Combinig) and yield significant performance improvments. Finally we import the charectristic of different beamshapes and yields performance...
A rigorous finite volume model to simulate subaerial and submarine landslide-generated waves
, Article Landslides ; 2015 , Pages 1-19 ; 1612510X (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Verlag
2015
Abstract
This paper presents a new landslide-generated wave (LGW) model based on incompressible Euler equations with Savage-Hutter assumptions. A two-layer model is developed including a layer of granular-type flow beneath a layer of an inviscid fluid. Landslide is modeled as a two-phase Coulomb mixture. A well-balanced second-order finite volume formulation is applied to solve the model equations. Wet/dry transitions are treated properly using a modified non-linear method. The numerical model is validated using two sets of experimental data on subaerial and submarine LGWs. Impulsive wave characteristics and landslide deformations are estimated with a computational error less than 5 %. Then, the...
Numerical modeling of subaerial and submarine landslide-generated tsunami waves—recent advances and future challenges
, Article Landslides ; Volume 13, Issue 6 , 2016 , Pages 1325-1368 ; 1612510X (ISSN) ; Ataie Ashtiani, B ; Sharif University of University
Springer Verlag
2016
Abstract
Landslide-generated waves (LGWs) are among natural hazards that have stimulated attentions and concerns of engineers and researchers during the past decades. At the same period, the application of numerical modeling has been progressively increased to assess, control, and manage the risks of such hazards. This paper represents an overview of numerical studies on LGWs to explore associated recent advances and future challenges. In this review, the main landslide events followed by an LGW hazard are scrutinized. The uncertainty regarding landslide characteristics and the lack of data concerning generated tsunami properties highlights the necessity of probabilistic analysis and numerical...
Simulation of wave generated by landslides in Maku dam reservoir
, Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009 ; 2009 , Pages 91-96 ; 9780415804820 (ISBN) ; Ataie Ashtiani, B ; Sharif University of Technology
2009
Abstract
In this work, impulsive wave generation and propagation generated by landslides are studied numerically for a real case. Maku dam reservoir, in the northwestern of Iran is considered as the case study. Generated wave heights, wave run-up, maximum wave height above the dam crest and the probable overtopping volume have been evaluated, using a two-dimensional numerical model (LS3D). This model is validated using available three-dimensional experimental data for simulating impulsive wave caused by sub-aerial landslides. Based on the results, the generated wave height for first and second scenarios are 12 m and 18 m respectively. The wave height of 8 m is observed close to dam body. Because of...
On the effects of landslide deformability and initial submergence on landslide-generated waves
, Article Landslides ; 2018 ; 1612510X (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Verlag
2018
Abstract
This paper represents a numerical study on the effects of landslide initial submergence and its geotechnical and rheological properties on the characteristics of landslide-generated waves (LGWs) and landslide deformation. A number of 117 numerical experiments are performed using a two-layer Coulomb Mixture Flow (2LCMFlow) model on a real-sized numerical flume as a simplified cross section of the Maku dam reservoir, located in the Northwest of Iran. Three different initial locations are considered for landslide representing a subaerial (SAL), a semi-submerged (SSL), and a submarine (SML) landslide. Based on the numerical results, the majority of SMLs and in some cases SSLs generate tsunami...
A rigorous finite volume model to simulate subaerial and submarine landslide-generated waves
, Article Landslides ; Volume 14, Issue 1 , 2017 , Pages 203-221 ; 1612510X (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Verlag
2017
Abstract
This paper presents a new landslide-generated wave (LGW) model based on incompressible Euler equations with Savage-Hutter assumptions. A two-layer model is developed including a layer of granular-type flow beneath a layer of an inviscid fluid. Landslide is modeled as a two-phase Coulomb mixture. A well-balanced second-order finite volume formulation is applied to solve the model equations. Wet/dry transitions are treated properly using a modified non-linear method. The numerical model is validated using two sets of experimental data on subaerial and submarine LGWs. Impulsive wave characteristics and landslide deformations are estimated with a computational error less than 5 %. Then, the...
On the effects of landslide deformability and initial submergence on landslide-generated waves
, Article Landslides ; Volume 16, Issue 1 , 2019 , Pages 37-53 ; 1612510X (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Verlag
2019
Abstract
This paper represents a numerical study on the effects of landslide initial submergence and its geotechnical and rheological properties on the characteristics of landslide-generated waves (LGWs) and landslide deformation. A number of 117 numerical experiments are performed using a two-layer Coulomb Mixture Flow (2LCMFlow) model on a real-sized numerical flume as a simplified cross section of the Maku dam reservoir, located in the Northwest of Iran. Three different initial locations are considered for landslide representing a subaerial (SAL), a semi-submerged (SSL), and a submarine (SML) landslide. Based on the numerical results, the majority of SMLs and in some cases SSLs generate tsunami...